Patent Grant
10639885
The entire disclosure of Japanese Patent Application No 2018-034418, filed Feb. 28, 2018 is expressly incorporated by reference herein.
The present invention relates to a liquid discharging apparatus which includes nozzles configured to discharge liquid and has a check function to check whether or not a discharge abnormality in that it is not possible to normally discharge liquid from the nozzles occurs.
In the related art, an ink jet type printer that prints a document, an image, or the like on a medium such as paper by discharging inks (as an example of liquid) from a plurality of nozzles provided in a discharge head is known as this type of liquid discharging apparatus. In such a printer, a discharge abnormality may occur. The discharge abnormality refers to a situation in which it is not possible to normally discharge droplets from nozzles by, for example, clogging in which the nozzles of a discharge head become clogged with the thickened or dried ink, or bubbles in an ink in a pressure chamber communicating with the nozzles. In a case where foreign substances such as paper dust adhere to the vicinity of the nozzle of the discharge head, a discharge abnormality such as flying curve in which droplets discharged from the nozzles are brought into contact with the foreign substances so as to bend the flying pathways of the droplets may also occur.
JP-A-2004-314457 discloses a liquid discharging apparatus including a discharge abnormality check unit capable of checking this type of discharge abnormality. In the liquid discharging apparatus, whether or not foreign substances such as paper dust are adhering is detected based on information of a residual vibration of liquid in a pressure chamber just after a piezoelectric element to which a drive signal has been applied drives. In the technology, a discharge abnormality caused by foreign substances such as paper dust adhere to the vicinity of the nozzle and a discharge abnormality caused by other factors for example clogging and mixing of bubbles are checked based on measurement results obtained in a manner as follows. That is, a drive signal having the same check waveform is applied to the piezoelectric element. While liquid in the nozzles is vibrated, the change of a residual vibration just after driving by this application is measured, and thereby the measurement results are obtained.
JP-A-2015-168146 discloses a technology of adjusting the meniscus position (liquid level position) of liquid in nozzles in consideration of the entrance of fuzz and the like of paper into nozzle openings. In the technology, the meniscus position of liquid in the nozzles is controlled so as to avoid an occurrence of problems such as discharge abnormalities which may occur by fuzz and the like of paper touching the liquid in the nozzles in a printing operation.
However, in the liquid discharging apparatus disclosed in JP-A-2004-314457 and JP-A-2015-168146, in a case where an adhering situation in which foreign substances such as paper dust adhere to a head surface (on which the nozzle of the discharge head opens) in the vicinity of the nozzle, and some of the adhering foreign substances floats from the head surface so as to be positioned with spaced from the nozzle in a discharge direction occurs, this situation may not be detected as a discharge abnormality. That is, there is a problem in that, even though the foreign substances as the cause of the occurrence of the discharge abnormality adhere, detecting this case as the discharge abnormality has difficulty because a difference of the change of the residual vibration is smaller than that in the normal time.
An advantage of some aspects of the invention is to provide a liquid discharging apparatus capable of improving check accuracy for checking whether or not a discharge abnormality of liquid by foreign substances adhering to a surface on which a nozzle opens occurs.
Hereinafter, means of the invention and operation effects thereof will be described.
According to an aspect of the invention, a liquid discharging apparatus includes a nozzle that discharges liquid by driving a piezoelectric element, a drive signal generation unit that generates a drive signal for driving the piezoelectric element, and a residual vibration detection unit that detects a change of an electromotive force of the piezoelectric element, which is caused by a residual vibration in a pressure chamber communicating with the nozzle after the drive signal is supplied. The drive signal generation unit generates a first drive signal for checking whether or not a first discharge abnormality caused by a foreign substance adhering to a surface on which the nozzle opens occurs and a second drive signal for checking whether or not a second discharge abnormality caused by a cause other than the foreign substance occurs. A potential of the first drive signal when the residual vibration detection unit performs checking is different from a potential of the second drive signal when the residual vibration detection unit performs checking.
According to this configuration, the potential of the first drive signal for checking whether or not the first discharge abnormality caused by the foreign substance (such as paper dust) adhering to the surface on which the nozzle opens occurs is different from the potential of the second drive signal for checking whether or not the second discharge abnormality caused by the cause other than the foreign substance occurs. Therefore, when the occurrence of the first discharge abnormality is checked, it is possible to draw liquid in the pressure chamber excited in a discharge direction of the nozzle by the piezoelectric element, toward an opposite side of the discharge direction with a force greater than that when the occurrence of the second discharge abnormality is checked. Thus, the amplitude of the liquid in the nozzle by the residual vibration in the pressure chamber when the first drive signal is supplied to the piezoelectric element is greater than the amplitude of the liquid in the nozzle by the residual vibration in the pressure chamber when the second drive signal is supplied to the piezoelectric element. Accordingly, an abnormal time being in a state where the foreign substance adhering to the surface on which the nozzle opens has been in contact with the liquid in the nozzle and a normal time in which the foreign substance is not provided have a significant difference of a liquid level position in the nozzle in a residual vibration period. The significant difference in the liquid level position is shown as a significant difference of the change of the residual vibration. Thus, the residual vibration detection unit detects the difference of the change of the residual vibration, and thereby it is possible to check whether or not the first discharge abnormality caused by adhering of the foreign substance occurs, with high accuracy.
In the liquid discharging apparatus, preferably, the first drive signal and the second drive signal have the same mode, the mode being for defining discharge or non-discharge.
According to this configuration, when checking is performed by discharging liquid in order to secure high check accuracy, both the first drive signal and the second drive signal are in a discharge mode in which the potential change allowing discharging of the liquid is provided. When checking is performed in a non-discharge state in which liquid is not discharged, for example, in order to save the consumption of the liquid or because of being in the process of printing, both the first drive signal and the second drive signal are in a non-discharge mode in which the potential change which does not cause discharge of the liquid is provided. It is possible to perform checking (first checking) of whether or not the first discharge abnormality caused by adhering of the foreign substance occurs and checking (second checking) of whether or not the second discharge abnormality caused by the cause other than the foreign substance occurs, even in any case of discharge and non-discharge depending on the situation or needs at time of checking.
In the liquid discharging apparatus, preferably, the first drive signal and the second drive signal have a first potential in a first period, a second potential in a second period, and a third potential in a third period, and the first drive signal and the second drive signal transition from the first potential to the second potential and transition from the second potential to the third potential.
According to this configuration, the potentials of the first drive signal and the second drive signal transition in an order of the first potential, the second potential, and the third potential. The liquid in the pressure chamber, which has been pressed in the discharge direction by the piezoelectric element deforming when the first drive signal transitions from the first potential to the second potential is drawn toward an opposite side of the discharge direction when the first drive signal transitions from the second potential to the third potential. The liquid in the pressure chamber, which has been pressed in the discharge direction by the piezoelectric element deforming when the second drive signal transitions from the first potential to the second potential is drawn toward the opposite side of the discharge direction when the second drive signal transitions from the second potential to the third potential. The potential including the first potential, the second potential, and the third potential in the first drive signal is different from the potential including the first potential, the second potential, and the third potential in the second drive signal. Thus, the amplitude of the residual vibration when the first drive signal is supplied to the piezoelectric element is greater than the amplitude of the residual vibration when the second drive signal is supplied to the piezoelectric element. Accordingly, it is possible to check whether or not the first discharge abnormality caused by adhering of the foreign substance occurs, with high accuracy.
In the liquid discharging apparatus, preferably, the third potential of the first drive signal is different from the third potential of the second drive signal.
According to this configuration, pressure at which the liquid in the pressure chamber, which has been pressed in the discharge direction is drawn toward the opposite side of the discharge direction before the first drive signal transitions from the second potential to the third potential can be set to pressure at which the liquid in the pressure chamber, which has been pressed in the discharge direction is drawn toward the opposite side of the discharge direction before the second drive signal transitions from the second potential to the third potential. Thus, the amplitude of the liquid in the nozzle by the residual vibration becomes great. Accordingly, a significant difference in a liquid level position in the nozzle in a residual vibration period after the liquid in the pressure chamber has been drawn occurs between an abnormal time being in a state where the adhering foreign substance is in contact with the liquid in the nozzle, a normal time in which the foreign substance does not adhere. The significant difference in the liquid level position is shown as a significant difference of the change of the residual vibration. Thus, the residual vibration detection unit detects the significant difference of the change of the residual vibration, and thereby it is possible to check whether or not the discharge abnormality caused by adhering of the foreign substance occurs, with high accuracy.
In the liquid discharging apparatus, preferably, a potential difference of the first drive signal between the second potential and the third potential is greater than a potential difference of the second drive signal between the second potential and the third potential.
According to this configuration, it is possible to increase a force causing the liquid in the pressure chamber, which has been pressed in the discharge direction to be drawn toward the opposite side of the discharge direction by the piezoelectric element deforming when the signal transitions from the second potential to the third potential. Thus, if the foreign substance adhering to the surface on which the nozzle opens is in a state of being in contact with the liquid in the nozzle, a significant difference in a liquid level position in the nozzle in the third period after the liquid in the pressure chamber has been drawn is provided from that in the normal time. Since the significant difference in the liquid level position is shown as the significant difference of the change of the residual vibration, the residual vibration detection unit detects the significant difference of the change of the residual vibration, and thereby it is possible to improve check accuracy for checking whether or not a discharge abnormality occurs by adhering of the foreign substance.
In the liquid discharging apparatus, preferably, in a normal time in which the discharge abnormality does not occur, a liquid level position in the nozzle closest to the pressure chamber when the first drive signal having the third potential is supplied to the piezoelectric element is closer to the pressure chamber than a liquid level position in the nozzle closest to the pressure chamber when the second drive signal having the third potential is supplied to the piezoelectric element.
According to this configuration, in the normal time in which the discharge abnormality does not occur, the liquid level position in the nozzle closest to the pressure chamber when the first drive signal is supplied to the piezoelectric element is closer to the pressure chamber than that when the second drive signal is supplied to the piezoelectric element. Thus, a significant difference is provided between the liquid level position in the nozzle when the foreign substance is in a state of being in contact with the liquid in the nozzle and the liquid level position in the nozzle in the normal time. Since the significant difference in the liquid level position is shown as the significant difference of the change of the residual vibration, the residual vibration detection unit detects the significant difference of the change of the residual vibration, and thereby it is possible to improve check accuracy of a discharge abnormality caused by adhering of the foreign substance.
In the liquid discharging apparatus, preferably, the first potential and the third potential in the first drive signal are equal to each other.
According to this configuration, since the first potential and the third potential in the first drive signal are equal to each other, the next operation can be simply started without changing the potential after the residual vibration is attenuated, that is, after the checking ends. For example, if the first potential is different from the third potential, the change of pressure of the liquid in the pressure chamber is caused by the change of the potential after the checking ends, and this may influence the next discharge of the liquid. However, since the first potential and the third potential in the first drive signal are equal to each other, there is no concern of this type.
In the liquid discharging apparatus, preferably, the first potential in the first drive signal is a potential between the second potential and the third potential.
According to this configuration, it is possible to increase the potential difference when the signal transitions from the second potential to the third potential, and to increase the force causing the liquid in the pressure chamber to be drawn toward the opposite side of the discharge direction. As a result, a significant difference of a liquid level position in the nozzle, which changes by the residual vibration when the foreign substance has adhered is provided from that in the normal time. Since the significant difference in the liquid level position is shown as the significant difference of the change of the residual vibration, the residual vibration detection unit detects the significant difference of the change of the residual vibration, and thereby it is possible to improve check accuracy of a discharge abnormality caused by adhering of the foreign substance.
In the liquid discharging apparatus, preferably, the second potential and the third potential in the first drive signal interpose an intermediate potential corresponding to a reference volume of the pressure chamber.
According to this configuration, when the first drive signal transitions from the second potential to the third potential, the piezoelectric element deforms from the state of having deformed in the discharge direction of the nozzle, toward the opposite side of the discharge direction beyond a neutral position at which the pressure chamber is set to have a reference volume. Thus, it is possible to increase the force causing the liquid in the pressure chamber to be drawn toward the opposite side of the discharge direction. Therefore, when the foreign substance has adhered, a significant difference of a liquid level position in the nozzle is provided from that in the normal time by the residual vibration. Since the significant difference in the liquid level position is shown as the significant difference of the change of the residual vibration, the residual vibration detection unit detects the significant difference of the change of the residual vibration, and thereby it is possible to improve check accuracy of a discharge abnormality caused by adhering of the foreign substance.
In the liquid discharging apparatus, preferably, the second potential of the first drive signal is equal to the second potential of the second drive signal.
According to this configuration, since the second potential of the first drive signal is equal to the second potential of the second drive signal, it is possible to reduce a risk of applying an inappropriate voltage such as an overvoltage or a reverse voltage to the piezoelectric element.
In the liquid discharging apparatus, preferably, the first potential of the first drive signal is equal to the first potential of the second drive signal.
According to this configuration, since the first potential of the first drive signal is equal to the first potential of the second drive signal, it is possible to reduce a risk of applying an inappropriate voltage such as an overvoltage or a reverse voltage to the piezoelectric element.
In the liquid discharging apparatus, preferably, the piezoelectric element includes a first electrode to which a reference potential is supplied and a second electrode to which the first drive signal and the second drive signal are supplied, and the first potential and the third potential in the first drive signal are in a range closer to an intermediate potential corresponding to a reference volume of the pressure chamber, than the reference potential.
According to this configuration, it is possible to avoid application of a reverse voltage to the piezoelectric element even though the first potential and the third potential of the first drive signal is supplied to the piezoelectric element.
In the liquid discharging apparatus, preferably, the first drive signal transitions from the first potential to the second potential via a first transitional potential, and the first potential is a potential between the second potential and the first transitional potential.
According to this configuration, since the first drive signal transitions from the first potential to the second potential via the first transitional potential, the piezoelectric element can be deformed once in a pull direction on an opposite side of a direction of pushing the piezoelectric elements in the discharge direction, and then be largely deformed in the direction of pushing the piezoelectric elements in the discharge direction. Thus, it is possible to largely vibrate the liquid in the pressure chamber by the large deformation of the piezoelectric element. As a result, it is possible to increase the amplitude of the liquid level in the nozzle. For example, even in the non-discharge mode in which liquid is not discharged, if the liquid in the nozzle is greatly amplified, the liquid temporarily protrudes from the opening, and thus may be brought into contact with the foreign substance adhering to the surface on which the nozzle opens. If the first drive signal transitions from the second potential to the third potential, the liquid in the pressure chamber is excited toward the opposite side of the discharge direction. For example, a vibration for the liquid in the pressure chamber is controlled, and the liquid moving in the nozzle in the discharge direction is cutout, and thereby it is possible to discharge a large droplet or to draw the liquid level in the nozzle after the discharge, toward the opposite side of the discharge direction. Even in any case, when discharge abnormality may occur by adhering of the foreign substance, a significant difference of the liquid level position in the nozzle is provided from that in the normal time because, for example, a force such as a capillary force, which attracts the liquid in the nozzle to the foreign substance acts on the liquid in the nozzle. Since the significant difference in the liquid level position is shown as the significant difference of the change of the residual vibration, the residual vibration detection unit detects the significant difference of the change of the residual vibration, and thereby it is possible to improve check accuracy of a discharge abnormality caused by adhering of the foreign substance.
In the liquid discharging apparatus, preferably, the first drive signal transitions from the third potential to the first potential via a second transitional potential, and the second transitional potential is a potential between the third potential and the first potential.
According to this configuration, since the signal transitions stepwise from the third potential via the second transitional potential and returns to the first potential, it is possible to suppress erroneous discharge or the like after the transition, without the rapid potential change.
In the liquid discharging apparatus, preferably, a first holding time at which the first drive signal is held to be the second potential is different from a second holding time at which the second drive signal is held to be the second potential.
According to this configuration, the first holding time at which the first drive signal is held to be the second potential is set to be an appropriate time which is different from the second holding time at which the second drive signal is held to be the second potential, and thereby it is possible to increase the difference of the change of the residual vibration between a foreign substance adhering time and the normal time. Accordingly, the residual vibration detection unit detects the difference of the change of the residual vibration, and thereby it is possible to check whether or not the first discharge abnormality caused by adhering of the foreign substance occurs, with high accuracy.
In the liquid discharging apparatus, preferably, when the first drive signal has been supplied, the residual vibration detection unit detects an amplitude of the residual vibration based on an electromotive force of the piezoelectric element and checks whether or not the first discharge abnormality occurs, based on the detected amplitude.
According to this configuration, when the first drive signal has been supplied, the residual vibration detection unit detects the amplitude of the residual vibration based on the change of the electromotive force of the piezoelectric element. In an abnormal time in which the foreign substance adheres and the normal time, a significant difference in a liquid level position in the nozzle is provided by the residual vibration, and the significant difference of the liquid level position is shown as the significant difference of the amplitude of the residual vibration. Therefore, it is possible to check whether or not the first discharge abnormality caused by adhering of the foreign substance occurs, with high accuracy by performing the checking based on the amplitude of the residual vibration, which has been detected by the residual vibration detection unit.
In the liquid discharging apparatus, preferably, when the first drive signal has been supplied, the residual vibration detection unit detects a phase of the residual vibration based on an electromotive force of the piezoelectric element and checks whether or not the first discharge abnormality occurs, based on the detected phase.
According to this configuration, the residual vibration detection unit detects the phase of the residual vibration based on the change of the electromotive force of the piezoelectric element when the first drive signal has been supplied. In an abnormal time in which the foreign substance adheres and the normal time, a significant difference in a liquid level position in the nozzle is provided by the residual vibration, and the significant difference of the liquid level position is shown as the significant difference of the phase of the residual vibration. Therefore, it is possible to check whether or not the first discharge abnormality caused by adhering of the foreign substance occurs, with high accuracy by performing the checking based on the phase of the residual vibration, which has been detected by the residual vibration detection unit.
To solve the above problems, a liquid discharging apparatus includes a nozzle that discharges liquid by driving a piezoelectric element, a drive signal generation unit that generates a drive signal for driving the piezoelectric element, and a residual vibration detection unit that detects a change of an electromotive force of the piezoelectric element, which is caused by a residual vibration in a pressure chamber communicating with the nozzle after the drive signal is supplied. The drive signal generation unit generates a first drive signal and a second drive signal. The first drive signal is used for performing first checking in which it is checked whether or not a first discharge abnormality caused by a foreign substance adhering to a surface on which the nozzle opens occurs and second checking in which it is checked whether or not a second discharge abnormality caused by a cause other than the foreign substance occurs, together. The second drive signal is used for performing printing by discharging the liquid from the nozzle to a medium. A potential of the first drive signal when the residual vibration detection unit performs checking is different from a potential of the second drive signal when the printing is performed.
According to this configuration, the potential of the first drive signal supplied to the piezoelectric element when the first checking and the second checking are performed together is different from the potential of the second drive signal supplied to the piezoelectric element when the liquid is discharged to the medium. Thus, it is possible to improve check accuracy of the first checking in which it is checked whether or not the first discharge abnormality caused by the foreign substance occurs. In addition, since the first checking and the second checking are performed by detecting the common residual vibration, it is possible to reduce time required for discharge abnormality checking. In a case where checking is performed in the discharge mode, it is possible to reduce the consumed amount of the liquid at the time of the discharge abnormality checking.
The invention will be described with reference to the accompanying drawings, wherein like numbers reference like elements.
Hereinafter, an embodiment will be described with reference to the drawings. In the drawings, the dimensions and the scales of the units are appropriately different from those in practice. Embodiments described below are preferred specific examples of the invention. Thus, various limitations which are technically preferable are given. However, the scope of the invention is not limited to the forms unless particular statements of limiting the invention are provided in the following descriptions.
An ink jet type printer as an example of a liquid discharging apparatus will be described below with reference to the drawings. An ink jet type line printer that forms an image on recording paper P (example of “a medium”) by discharging an ink (example of “liquid”) will be described as an example of an ink jet type printer 11.
As illustrated in
As illustrated in
As illustrated in
Regarding printing processing in the embodiment, as illustrated in
Next, a configuration of the discharging portion D that discharges ink droplets from the nozzles N of the head portion 30 will be described with reference to
As illustrated in
The cavity 264 is defined by a cavity plate 266, a nozzle plate 267 in which the nozzle N has been formed, and the diaphragm 265. The cavity plate 266 is formed into a predetermined shape having a recess portion. The cavity 264 communicates with a reservoir 272 through an ink supply port 271. The reservoir 272 communicates with one ink cartridge 31 through an ink supply flow path 273.
In the embodiment, a unimorph (monomorph) type as illustrated in
The lower electrode 201 of the piezoelectric element 200 is bonded to the diaphragm 265 provided in a state of closing an upper opening portion of the cavity plate 266. Therefore, if the piezoelectric element 200 vibrates by the drive signal Vin, the diaphragm 265 also vibrates. The volume of the cavity 264 changes by the diaphragm 265 vibrating, and pressure of the ink in the cavity 264 changes with the change of the volume of the cavity 264. Thus, a portion of the ink with which the cavity 264 is filled is discharged by the nozzle N.
The ink in the cavity 264 is reduced by discharging the ink, and the liquid amount of the reduced ink is replenished by supplying the ink from the reservoir 272 to the cavity 264. The ink is supplied from the ink cartridge 31 to the reservoir 272 through the ink supply flow path 273.
Next, an ink discharge operation of the discharging portion D will be described with reference to
A functional configuration of the printer 11 according to the embodiment will be described with reference to
The printer 11 includes a controller 60 that controls operations of the transport mechanism 40, the head driver 50, and the recovery mechanism 70 based on image data Img supplied from a host computer 100 such as a personal computer or a digital camera. The controller 60 controls performing of various kinds of processing such as printing processing of forming an image on recording paper P, discharge abnormality detection processing of detecting a discharge abnormality of the discharging portion D, and recovery processing of recovering the discharge state of the discharging portion D to be normal.
The controller 60 includes a central processing unit (CPU) 61 and a storage unit 62. The storage unit 62 includes an electrically erasable programmable read-only memory (EEPROM) which is one kind of non-volatile semiconductor memory and stores image data Img supplied from the host computer 100 through an interface unit (not illustrated), in a data storage area. The storage unit 62 includes a random access memory (RAM) that temporarily stores data required when printing processing of, for example, information on the shape of recording paper P and discharge-abnormality detection result data indicating a result obtained by discharge abnormality detection processing, or temporarily develops a control program for performing various kinds of processing such as printing processing. The storage unit 62 includes a PROM which is one kind of non-volatile semiconductor memory and stores a control program and the like for controlling the components of the printer 11.
The CPU 61 controls performing of various kinds of processing such as printing processing, discharge abnormality detection processing, and recovery processing. More specifically, the CPU 61 stores image data Img supplied from the host computer 100, in the storage unit 62. The CPU 61 generates various signals and various control signals for controlling driving of the recovery mechanism 70, based on various kinds of data such as image data Img. Examples of the various signals include a driver control signal Ctr for controlling driving of the transport motor 44, and a printing signal SI, a switching control signal Sw, and a drive waveform signal Com which are used for controlling driving of the head driver 50. The CPU 61 supplies the signals to the components of the printer 11. Thus, the CPU 61 controls operations of the transport motor 44, the head driver 50, and the recovery mechanism 70 and controls performing of various kinds of processing such as printing processing, discharge abnormality detection processing, and recovery processing. The constituent components of the controller 60 are electrically connected to each other via a bus (not illustrated).
The head driver 50 illustrated in
The drive signal generation unit 51 generates a drive signal Vin for driving the discharging portion D provided in the head portion 30, based on the printing signal SI and the drive waveform signal Com supplied from the controller 60. The printing signal SI and the drive waveform signal Com are collectively referred to as “a printing control signal”. That is, the drive signal generation unit 51 generates a drive signal Vin based on the printing control signal. Although the details thereof will be described later, the drive waveform signal Com in the embodiment includes three drive waveform signals Com-A, Com-B, and Com-C.
The discharge abnormality detection unit 52 detects the change of pressure in the discharging portion D, as a residual vibration signal Vout. The change of the pressure occurs after the discharging portion D has been driven by the drive signal Vin and is caused by a vibration and the like of the ink in the discharging portion D. Specifically, the discharge abnormality detection unit 52 detects a residual vibration of the diaphragm 265 vibrating with being attenuated in a vibration state depending on a state of liquid in the cavity 264 communicating with the nozzle N, after the drive signal Vin has been supplied to the piezoelectric element 200. The discharge abnormality detection unit performs the detection from the change of an electromotive force of the piezoelectric element 200. Then, the discharge abnormality detection unit acquires the change of the electromotive force, in a form of the residual vibration signal Vout. The discharge abnormality detection unit 52 determines whether or not a discharge abnormality occurs in the discharging portion D and determines a discharge state of the ink in the discharging portion D, based on the residual vibration signal Vout. Then, the discharge abnormality detection unit outputs a determination result in a form of a determination result signal Rs.
The switching unit 53 connects each of the discharging portions D to either the drive signal generation unit 51 or the discharge abnormality detection unit 52, based on the switching control signal Sw supplied from the controller 60. That is, the switching unit 53 performs switching between a first connection state and a second connection state. In the first connection state, the discharging portion D and the drive signal generation unit 51 are electrically connected to each other. In the second connection state, the discharging portion D and the discharge abnormality detection unit 52 are electrically connected to each other. The controller 60 outputs the switching control signal Sw for controlling the connection state of the switching unit 53, to the switching unit 53. Specifically, the controller 60 supplies the switching control signal Sw causing the switching unit 53 to maintain the first connection state, to the switching unit 53 in a unit operation period in which discharge processing is performed. Therefore, the drive signal Vin is supplied from the drive signal generation unit 51 to the discharging portion D in the unit operation period.
If it is a timing to end the unit operation period and start a unit checking period, the controller 60 changes the switching control signal Sw so as to switch the connection state from the first connection state to the second connection state. The switching unit 53 maintains the second connection state in a unit checking period (detection period Td which will be described later) in which checking the occurrence of a discharge abnormality in the discharging portion D of the head portion 30 is performed. In a unit period which is a sum of the unit operation period and the unit checking period, a discharge operation of ink droplets for one dot based on application of the drive signal Vin to the piezoelectric element 200 of the discharging portion D is performed, and the residual vibration signal Vout output by the piezoelectric element 200 receiving a residual vibration with performing the discharge operation of the ink droplets for the one dot is acquired. In a case where the discharge abnormality checking is performed in the process of printing, the checking is performed in a non-discharge state where the piezoelectric element 200 is vibrated as slight as an ink is not discharged, and thus an ink droplet is not discharged from the discharging portion D.
In a case where discharge abnormality checking is performed in non-printing in which printing is not performed, the controller 60 arranges the head portion 30 and the recovery mechanism 70 to have a position relationship for checking, and performs the discharge abnormality checking of the discharging portion D. In the unit period which is a sum of the unit operation period and the unit checking period, a discharge operation of ink droplets for checking based on application of the drive signal Vin to the piezoelectric element 200 of the discharging portion D is performed, and the residual vibration signal Vout output by the piezoelectric element 200 receiving a residual vibration with performing the discharge operation of the ink droplets for checking is acquired. The controller 60 switches the switching unit 53 to be in the second connection state, in the unit checking period. The discharge abnormality checking performed in the non-printing is performed by discharging ink droplets from the discharging portion D. The discharged ink droplets are collected in a waste liquid receiving portion (not illustrated) constituting the recovery mechanism 70.
The controller 60 is electrically connected to a motor driver 46 for driving the transport motor 44. The controller 60 supplies the driver control signal Ctr to the motor driver 46 so as to control driving of the transport motor 44. The transport mechanism 40 includes a feeding motor (not illustrated) for rotating the roll body PR.
A serial printer including a recording unit of a serial recording type may also be set as the printer 11, instead of the line printer. In this case, the head portion 30 is mounted in a carriage (not illustrated) and is configured to be movable in the X-axis direction. The serial recording type printer 11 includes a carriage motor for moving the carriage and a carriage motor driver for driving the carriage motor (none illustrated). While the controller 60 controls driving of the carriage motor with the carriage motor driver so as to perform reciprocating of the carriage in the X-axis direction as a scanning direction, ink droplets are discharged from each of the discharging portions D of the head portion 30, in the process of the moving. The controller 60 alternately repeats a printing operation and a conveyance operation so as to perform printing of an image and the like on the recording paper P. In the printing operation, an ink is discharged onto recording paper P from the nozzle N (see
In discharge abnormality checking, a residual vibration remains in the diaphragm 265 of each of the discharging portions D by vibrating, in a period from after a discharge operation for one ink droplet or one vibration operation for slighting vibrating the ink in the nozzle N ends, until the next vibration operation starts. The residual vibration occurring in the diaphragm 265 of the discharging portion D may be assumed to have a natural vibration frequency determined by acoustic resistance Res (depending on the shape of the nozzle N or the ink supply port 271, viscosity of the ink, and the like), inertance Int (depending on the weight of the ink in the flow path), and compliance Cm of the diaphragm 265 and the like.
Uv={Ps/(ω·Int)}e−ω
ω={1/(Int·Cm)−α2}1/2
α=Res/(2·Int)
The experiment on the residual vibration of the discharging portion D is performed. The experiment on the residual vibration is an experiment of detecting a residual vibration occurring in the diaphragm 265 of the discharging portion D after an ink has been discharged from the discharging portion D in which the discharge state of the ink has been normal.
Details of each of the causes of (a) to (c), which causes the discharge abnormality will be described with reference to
As illustrated in
As illustrated in
As illustrated in
From the above descriptions, it is possible to detect a discharge abnormality of the ink droplet in the discharging portion D and to specify the cause of the discharge abnormality, by the difference of the residual vibration of the diaphragm 265. Therefore, in this example, the discharge abnormality detection unit 52 in the head driver 50 illustrated in
Here, the discharge abnormality typically means a state where it is not possible to discharge an ink from the nozzle N. Thus, in this case, dot missing for pixels occurs in an image of which printing has been performed on the recording paper P. The discharge abnormality also includes an abnormal nozzle in which an ink has been discharged from the nozzle N, but the amount of the discharged ink is too small or in which the flight direction (ballistic trajectory) of the discharged ink droplet is deviated, and thus the ink droplet is not landed on an appropriate position and flight deflection inducing deviation of the landing position is obtained.
Next, a configuration and an operation of the head driver 50 will be described with reference to
As illustrated in
The shift register SR holds the printing signal SI for each of the three bits corresponding to each of the discharging portions D. Specifically, the M shift registers SR of a first stage, a second stage, . . . , and an M-th stage, which are in one-to-one correspondence with the M discharging portions D are consecutively connected to each other, and the printing signal SI is sequentially transferred to the subsequent stage in accordance with the clock signal CL. At a time point at which the printing signal SI has been transferred to all the M shift registers SR, the supply of the clock signal CL is stopped, and each of the M shift registers SR maintains a state of holding data of 3 bits in the printing signal SI, which correspond to the own shift register.
Each of the M latch circuits LT latches the printing signal SI of the three bits corresponding to the stage at a timing at which the latch signal LAT rises. The printing signals SI of the three bits have been held in the M shift registers SR, respectively. In
A printing operation period which is a period in which the printer 11 performs printing by forming an image on recording paper P includes a plurality of unit operation periods Tu. The controller 60 assigns the unit operation period Tu to printing processing for one dot, for each of the M discharging portions D. Discharge abnormality checking performed in the printing operation period is performed in non-discharge in which an ink droplet is not discharged. Discharge abnormality checking performed in a not-printing period is performed by discharging an ink droplet to the waste liquid receiving portion of the recovery mechanism 70. Discharge abnormality checking with discharging an ink droplet is performed in a state where the waste liquid receiving portion is disposed at a position facing the head portion 30. In a case where the printer 11 is a serial printer, the checking is performed in a state where the head portion 30 is disposed at a home position at which the recovery mechanism 70 is disposed.
The controller 60 controls the discharging portion D in three forms. In a first form, printing processing is assigned to some of the M discharging portions D, and discharge abnormality detection processing is assigned to other discharging portions D. In a second form, printing processing is assigned to all the M discharging portions D. In a third form, discharge abnormality detection processing is assigned to all the M discharging portions D. In the first form, the discharge abnormality detection processing is performed in a non-discharge state. In the third form, the discharge abnormality detection processing is performed in a discharge or the non-discharge state.
Each unit operation period Tu includes a control period Tc1 and a control period Tc2 subsequent to the control period Tc1. In the embodiment, the control periods Tc1 and Tc2 have time lengths which are equal to each other.
The controller 60 supplies the printing signal SI to the drive signal generation unit 51 for each unit operation period Tu. The latch circuit LT latches the printing signals SI[1], SI[2], . . . , and SI[M] for each unit operation period Tu.
The decoder DC decodes the printing signal SI of the three bits, which has been latched by the latch circuit LT, and outputs selection signals Sa, Sb, and Sc in each of the control periods Tc1 and Tc2.
In a case where the lower bit b3 is “1”, regardless of the values of the upper bit b1 and the middle bit b2, the m-th decoder DC sets the selection signals Sa and Sb to the low level L and sets the selection signal Sc to the high level H, in the control periods Tc1 and Tc2.
Descriptions will be made with reference to
The transmission gate TGa is in an ON state when the selection signal Sa is at the H level and is in an OFF state when the selection signal Sa is at the L level. The transmission gate TGb is in the ON state when the selection signal Sb is at the H level and is in the OFF state when the selection signal Sb is at the L level. The transmission gate TGc is in the ON state when the selection signal Sc is at the H level and is in the OFF state when the selection signal Sc is at the L level.
For example, at the m-th stage, in a case where the contents represented by the printing signal SI[m] is (b1, b2, b3)=(1, 0, 0), the transmission gate TGa is in the ON state and the transmission gates TGb and TGc are in the OFF state, in the control period Tc1. When the transmission gates TGa and TGc are in the OFF state in the control period Tc2, the transmission gate TGb is in the ON state.
The drive waveform signal Com-A is supplied to one end of the transmission gate TGa. The drive waveform signal Com-B is supplied to one end of the transmission gate TGb. The drive waveform signal Com-C is supplied to one end of the transmission gate TGc. Other ends of the transmission gates TGa, TGb, and TGc are connected to each other.
The transmission gates TGa, TGb, and TGc are exclusively in the ON state. The drive waveform signal Com-A, Com-B, or Com-C selected for each control period Tc1 and each control period Tc2 is supplied as a drive signal Vin[m]. The drive signal Vin[m] is supplied to the m-th discharging portion D via the switching unit 53.
As illustrated in
The drive waveform signal Com-B supplied from the controller 60 in the unit operation period Tu is a waveform in which the potential is held to the intermediate potential Vc during the control period Tc1 and the unit waveform PB is disposed in the control period Tc2. All potentials at timings when the unit waveform PB starts and ends are intermediate potentials Vc. A potential difference between a potential Vb of the unit waveform PB and the intermediate potential Vc is smaller than the potential difference between the potential Va21 and the potential Va22 of the unit waveform PA2. Even in a case where the piezoelectric element 200 provided in each of the discharging portions D is driven by the unit waveform PB, the ink is not discharged from the nozzle N provided in the corresponding discharging portion D. Even in a case where the intermediate potential Vc is supplied to the piezoelectric element 200, the ink is not discharged from the nozzle N.
The drive waveform signal Com-C supplied from the controller 60 in the unit operation period Tu is a waveform which has a unit waveform PT disposed in the control period Tc1 and has an intermediate potential Vc held in the control period Tc2. A first potential V1 which is a potential at a start timing of the unit waveform PT is the intermediate potential Vc in this example. A third potential V3 which is a potential at an end timing of the unit waveform PT is the intermediate potential Vc in this example.
The unit waveform PT transitions from the first potential V1 to a second potential V2, transitions from the second potential V2 to the third potential V3, and then holds the third potential V3. In this example, the unit waveform PT transitions from the first potential V1 to the second potential V2 via a first transitional potential V4. The drive waveform signal Com-C is selected when there is an attempt to check the discharge state of the ink. In this example, the first potential V1 and the third potential V3 are set to the intermediate potential Vc which is a potential to be held in the piezoelectric element 200 when the ink is not discharged.
As described above, the M latch circuits LT respectively output the printing signals SI[1], SI[2], . . . , and SI[M] at a rising timing of the latch signal LAT, that is, at a timing at which the unit operation period Tu (Tp or Tt) is started.
As described above, the m-th decoder DC outputs the selection signals Sa, Sb, and Sc based on the contents of the table illustrated in
As described above, the transmission gates TGa, TGb, and TGc at the m-th stage select any of the drive waveform signals Com-A, Com-B, and Com-C based on the selection signals Sa, Sb, and Sc and outputs the selected drive waveform signal Com as the drive signal Vin[m].
The waveform of the drive signal Vin output by the drive signal generation unit 51 in the unit operation period Tu will be described with reference to
As a result, in the m-th discharging portion D, in the unit operation period Tu, the ink of the substantially middle amount based on the unit waveform PA1 is discharged, and the ink of the substantially small amount based on the unit waveform PA2 is discharged. The inks discharged twice in this manner are combined on the recording paper P, and thus a large dot is formed on the recording paper P.
In a case where the contents of the printing signal SI[m] supplied in the unit operation period Tu is (b1, b2, b3)=(1, 0, 0), the selection signals Sa, Sb, and Sc are respectively at the H level, the L level, and the L level in the control period Tc1. Thus, the drive waveform signal Com-A is selected by the transmission gate TGa. As a result, the unit waveform PA1 is output as the drive signal Vin[m]. In the control period Tc2, the selection signals Sa, Sb, and Sc are respectively at the L level, the H level, and the L level. Thus, the drive waveform signal Com-B is selected by the transmission gate TGb, and the unit waveform PB is output as the drive signal Vin[m]. As a result, in the m-th discharging portion D, in the unit operation period Tu, the ink of the substantially middle amount based on the unit waveform PA1 is discharged, and thus a middle dot is formed on the recording paper P.
In a case where the contents of the printing signal SI[m] supplied in the unit operation period Tu is (b1, b2, b3)=(0, 1, 0), the selection signals Sa, Sb, and Sc are respectively at the L level, the H level, and the L level in the control period Tc1. Thus, the drive waveform signal Com-B is selected by the transmission gate TGb. Therefore, in the control period Tc1, a signal having a waveform of a predetermined potential Vc is output as the drive signal Vin[m]. In the control period Tc2, the selection signals Sa, Sb, and Sc are respectively at the H level, the L level, and the L level. Thus, the drive waveform signal Com-A is selected by the transmission gate TGa. Therefore, in the control period Tc2, the unit waveform PA2 is output as the drive signal Vin[m]. As a result, in the m-th discharging portion D, in the unit operation period Tu, the ink of the substantially small amount based on the unit waveform PA2 is discharged. Thus, a small dot is formed on the recording paper P.
In a case where the contents of the printing signal SI[m] supplied in the unit operation period Tu is (b1, b2, b3)=(0, 0, 0), the selection signals Sa, Sb, and Sc are respectively at the L level, the H level, and the L level in the control periods Tc1 and Tc2. Thus, the drive waveform signal Com-B is selected by the transmission gate TGb. Therefore, in the control periods Tc1 and Tc2, the unit waveform PB is output as the drive signal Vin[m]. As a result, in the unit operation period Tu, the ink is not discharged from the m-th discharging portion D, and a dot is not formed on the recording paper P.
In a case where the contents of the printing signal SI[m] supplied in the unit operation period Tu is (b1, b2, b3)=(0, 0, 1), the selection signals Sa, Sb, and Sc are respectively at the L level, the L level, and the H level in the control periods Tc1 and Tc2. Thus, the drive waveform signal Com-C is selected by the transmission gate TGc. Therefore, in the control periods Tc1 and Tc2, the unit waveform PT is output as the drive signal Vin[m]. As a result, in the unit operation period Tu, the ink for checking is discharged from the m-th discharging portion D, and the discharge state of the ink is checked.
Here, in a case where the drive signal Vin is supplied to the piezoelectric element 200, a mode in which a droplet is discharged from the nozzle N is defined as the discharge mode. In a case where the drive signal Vin is supplied to the piezoelectric element 200, a mode in which a droplet is not discharged from the nozzle N is defined as the non-discharge mode. That is, as a mode for defining discharge or non-discharge (also referred to as “a discharge/non-discharge mode), the discharge mode in which liquid is discharged and the non-discharge mode in which the liquid is not discharged are provided. In
In the embodiment, a checking drive signal Vin including a unit waveform PT for checking is used in at least paper dust checking in which it is checked whether or not paper dust Pe adheres. When the occurrence of a discharge abnormality caused by a cause such as bubbles B or dry other than the paper dust Pe is checked, a paper-dust checking drive signal Vin is commonly used or another drive signal Vin is used. In this example, a signal having the same discharge/non-discharge mode as that of the paper-dust checking drive signal Vin among printing drive signals Vin is used as this another drive signal Vin. For example, in
The drive signal Vin for paper dust checking will be described below with reference to
In the drive signal VinA illustrated in
In
The first drive signal VinA transitions from the first potential V1 to the second potential V2 via the first transitional potential V4. The first drive signal VinA has the first transitional potential V4 in a fourth period T4 from a time point t4s to a time point toe. That is, the first drive signal VinA transitions from the first potential V1 to the first transitional potential V4, transitions from the first transitional potential V4 to the second potential V2, and then transitions from the second potential V2 to the third potential V3. The first transitional potential V4 is a potential causing the first potential V1 to be interposed between the first transitional potential V4 and the intermediate potential Vc. The first transitional potential V4 is a potential causing the first potential V1 and the intermediate potential Vc to be interposed between the first transitional potential V4 and the second potential V2. Therefore, the potential difference |V2-V41 at time of Push driving when the first drive signal VinA transitions from the first transitional potential V4 to the second potential V2 is greater than the potential difference |V2-V11 of the drive signal transitioning from the first potential V1 to the second potential V2 without passing through the first transitional potential V4. Thus, the first drive signal VinA can cause liquid in the cavity 264 to be excited more largely at the time of Push driving than that of this type of drive signal. The potential difference |V2−V3| in the first drive signal VinA illustrated in
In this example, charges charged in the piezoelectric element 200 in a period from the time point tie to the time point t4s, in which transitions from the first potential V1 to the first transitional potential V4 is performed are discharged. As a result, the piezoelectric element 200 is excited so as to draw the meniscus in the nozzle N toward the cavity 264. Then, the first drive signal VinA holds the first transitional potential V4 in the fourth period T4, and transitions from the first transitional potential V4 to the second potential V2 in a period from the time point t4e to the time point t2s. Charges are charged in the piezoelectric element 200 in a period from the time point t4e to the time point t2s. As a result, the piezoelectric element 200 is excited so as to perform displacement in a direction in which the meniscus in the nozzle N is pushed out of the cavity 264. The second potential V2 is set to discharge a droplet from the nozzle N.
Then, the first drive signal VinA holds the second potential V2 in the second period T2 and transitions from the second potential V2 to the third potential V3 in a period from the time point t2e to the time point t3s. Charges are charged in the piezoelectric element 200 in a period from the time point t2e to the time point t3s. As a result, the piezoelectric element 200 is excited so as to draw the meniscus in the nozzle N toward the cavity 264. The vibration in the drawing direction is a vibration opposing a vibration in a pushout direction when the first drive signal VinA transitions from the first transitional potential V4 to the second potential. Thus, the vibration in the drawing direction functions as vibration damping of suppressing a vibration by vibrating the tip of the liquid in the cavity 264. In this specification, excitation in a direction in which the piezoelectric element 200 pushes the liquid in the cavity 264 toward the opening of the nozzle N is referred to as “Push”. Excitation in a direction in which the piezoelectric element 200 pulls the liquid toward an opposite side of the discharge direction of the nozzle N is referred to as “Pull”.
An excitation force at the time of Push driving when the first drive signal VinA is supplied to the piezoelectric element 200 and transitions from the first transitional potential V4 to the second potential V2 may be larger than an excitation force at the time of Push driving when the drive signal which does not include the waveform of the first transitional potential V4 is supplied to the piezoelectric element 200. As described above, since Pull driving is performed in a period from the time point tie to the time point t4s just before Push driving, a large potential difference at the time of Push driving, which is from the next time point toe to the time point t2s, is secured. In addition, an excitation force which is larger than that in a case where the signal does not pass through the first transitional potential V4 in the process of transitioning from the first potential V1 to the second potential V2 is obtained.
As described above, since the first drive signal VinA illustrated in
Here, the first drive signal VinA illustrated in
Similar to the first drive signal VinA illustrated in
In
The first drive signal VinA illustrated in
In
In the first drive signal VinA illustrated in
The amount of the first potential V1 and the third potential V3 shifted from the intermediate potential Vc toward the second potential V2 is smaller than the amount of the second potential V2 shifted from the second potential Va12. Therefore, the potential difference between the second potential V2 and the second potential Va12 is greater than the potential difference between the first potential V1 and the first potential Vc and the potential difference between the third potential V3 and the third potential Vc. Therefore, the potential difference |V2−V3| between the second potential V2 and the third potential V3 in the first drive signal VinA is greater than the potential difference |Va12−Vc| between the second potential Va12 and the third potential Vc in the second drive signal VinB. The first transitional potential V4 in the first drive signal VinA is equal to the first transitional potential V4 in the second drive signal VinB.
As described above, in the first drive signal VinA illustrated in
A timing at which the liquid in the cavity 264 is drawn in Pull driving next to Push driving is set to a timing at which a vibration of a pressure wave propagating to the liquid in the cavity 264 by excitation at time of Push driving is suppressed. The timing in Pull driving is defined by a first holding time Th which is a holding time of the second potential V2 of the first drive signal VinA, which is held in the second period T2. In this case, a force of drawing toward the opposite side of the discharge direction is applied to the diaphragm 265 at a timing in a predetermined period including a time point at which the phase of the pressure wave in the liquid in the cavity 264 turns from the discharge direction to the reverse discharge direction. Thus, the vibration of the liquid in the cavity 264 by excitation at the time of Push driving is damped. Therefore, the liquid in the nozzle N is cut out at a position of the back side toward the cavity 264 and is discharged in a form of a droplet. For example, in a case where the timing at which the liquid in the cavity 264 is drawn is before the phase of the pressure wave turns to the reverse discharge direction, the damping force of the liquid increases, and thus the amount of droplets discharged from the nozzle N increases. In a case where this timing is after the phase of the pressure wave turns to the reverse discharge direction, the force of drawing the liquid in the cavity 264 is accelerated. Even in any case, in the normal time, the liquid level position in the nozzle N just after discharge of a droplet can be more drawn to the back side of the nozzle N. Meanwhile, the droplet is set to have a discharge amount depending on a required dot size, or a separation of a droplet, which allows suppression of mist is performed, and then a second holding time Tho at which the second drive signal VinB is held to the second potential Va12 is set.
In the embodiment, the discharge abnormality checking is performed with a first checking method or a second checking method. The first checking method is a checking method in which first checking and second checking is performed with the common first drive signal VinA. In the first checking, it is checked whether or not a first discharge abnormality caused by foreign substances such as paper dust Pe, which have adhered to the head surface 261 on which the nozzle N opens, occurs. In the second checking, it is checked whether or not a second discharge abnormality caused by the cause other than the foreign substances such as paper dust Pe occurs. The second checking method is a checking method in which the first checking is performed with the first drive signal VinA and the second checking is performed with the second drive signal VinB.
In a case of the first checking method any one of the first drive signals VinA illustrated in
In a case of the first checking method, the common first drive signal VinA is used in the first checking and the second checking. In this case, the potential difference |V2−V3| between the second potential V2 and the third potential V3 of the first drive signal VinA for checking is greater than the potential difference |Va12−Vc| between the second potential Va12 and the third potential Vc of the second drive signal VinB for printing.
In a case of the second checking method, the first drive signal VinA is used in the first checking, and the second drive signal VinB is used in the second checking. In this case, the potential difference |V2−V3| between the second potential V2 and the third potential V3 of the first drive signal VinA for the first checking is greater than the potential difference |Va12−Vc| between the second potential Va12 and the third potential Vc of the second drive signal VinB for the second checking. In a case of the second checking method, the potential difference between the second potential and the third potential of the second drive signal VinB for the second checking may be different from the potential difference between the second potential and the third potential of the printing drive signal Vin[m].
A potential difference (voltage) between the reference potential VSS applied as a bias potential to the lower electrode 201 and the potential of the drive signal Vin supplied to the upper electrode 202 is applied to the piezoelectric element 200. The reference potential VSS is set to 0 Volts or a positive potential, for example. The intermediate potential Vc corresponding to the reference volume of the discharging portion D is equal to the reference potential VSS or is set to a potential between the reference potential VSS and the second potential V2. The reference potential VSS may be appropriately set in accordance with the characteristics of the piezoelectric element 200 and may be a negative potential, for example.
In a case of the first drive signal VinA illustrated in
In the embodiment, the first holding time Th held to the second potential V2 preferably has a value in a range satisfying a condition of Tc/2−Tc/4<Th≤Tc+α when the natural vibration period of the cavity 264 is set as Tc. α indicates a margin value and indicates a value satisfying 0<α≤Tc/10, for example. The reason that the first holding time Th is set to the value in the range satisfying the condition is as follows. Pressure in the cavity 264 excited by the piezoelectric element 200 at the time of Push driving increases or decreases in synchronization with the natural vibration period Tc. In this case, the pressure in the cavity 264 turns from an increase to a decrease at a timing at which the first holding time Th reaches Tc/2. Starting Pull driving at a timing in a predetermined period including a time point at which the pressure in the cavity 264 turns from an increase to a decrease is preferable because the liquid in the nozzle N is cut out at the position on the back side. The first holding time Th is set to have a value appropriate for improving check accuracy of the paper dust checking, in the range. The first holding time Th is different from the second holding time Tho in which the second drive signal VinB is held to the second potential Va12. Only in a case where check accuracy of the paper dust checking is improved, the first holding time Th may have a value out of the above range or have a value equal to the second holding time Tho.
In the printer 11, the discharging portion D is driven by the first drive signal Vin for checking, which is generated by the drive signal generation unit 51 and is illustrated in
Next, a configuration for the discharge abnormality detection processing will be described with reference to
The controller 60 supplies a switching control signal Sw[m] for controlling the connection state of the switching circuit U[m], to the m-th switching circuit U[m]. Specifically, the controller 60 outputs switching control signals Sw[1], Sw[2], . . . , and Sw[M] in the unit operation period Tu such that the switching circuit corresponding to the discharging portion D by which printing is performed is in the first connection state, and the switching circuit corresponding to the discharging portion D as a target of checking is in the second connection state. That is, in the unit operation period Tu, the switching control signals Sw for the first connection state and the second connection state may be mixed, all the switching control signals Sw may designate the first connection state, and all the switching control signals Sw may designate the second connection state.
The waveform shaping unit 57 includes a high pass filter or a low pass filter, for example. The high pass filter is used for outputting a signal obtained by attenuating a frequency component in a frequency band lower than a frequency band of the residual vibration signal Vout. The low pass filter is used for outputting a signal obtained by attenuating a frequency component in a frequency band higher than the frequency band of the residual vibration signal Vout. The waveform shaping unit 57 has a configuration capable of limiting a frequency range of the residual vibration signal Vout and outputting the shaped waveform signal Vd obtained by removing the noise component. The waveform shaping unit 57 may have a configuration in which a negative feedback type amplifier for regulating the amplitude of the residual vibration signal Vout, a voltage follower for converting the impedance of the residual vibration signal Vout and outputting a shaped waveform signal Vd having low impedance, and the like are provided.
The shaped waveform signal Vd from the waveform shaping unit 57, a mask signal Msk generated by the controller 60, a threshold potential Vth_c determined to be a potential at the center level of the amplitude of the shaped waveform signal Vd, a threshold potential Vth_o determined to be a potential higher than the threshold potential Vth_c, and a threshold potential Vth_u determined to be a potential lower than the threshold potential Vth_c are supplied to the measuring unit 58. The measuring unit 58 outputs a validity flag Flag based on the signals Vd and Msk and the threshold potentials Vth_c, Vth_o, and Vth_u which have been input. The validity flag Flag indicates whether or not the shaped waveform signal Vd is valid when discharge abnormality detection is performed.
As illustrated in
The measuring unit 58 compares the potential of the shaped waveform signal Vd to the threshold potential Vth_o. The measuring unit generates a comparison signal Cmp2 which has a high level in a case where the potential of the shaped waveform signal Vd is equal to or greater than the threshold potential Vth_o, and has a low level in a case where the potential of the shaped waveform signal Vd is smaller than the threshold potential Vth_o.
The measuring unit 58 compares the potential of the shaped waveform signal Vd to the threshold potential Vth_u. The measuring unit generates a comparison signal Cmp3 which has a high level in a case where the potential of the shaped waveform signal Vd is smaller than the threshold potential Vth_u, and has a low level in a case where the potential of the shaped waveform signal Vd is equal to or greater than the threshold potential Vth_u.
The mask signal Msk has a high level only during a predetermined period Tmsk from when a supply of the shaped waveform signal Vd from the waveform shaping unit 57 is started. In the embodiment, it is possible to obtain a measurement value in which a noise component superimposed just after the residual vibration starts has been removed, with high accuracy by measuring the period NTc, a phase time TF, and the amplitude Vmax with only the shaped waveform signal Vd after the elapse of the period Tmsk, in the shaped waveform signal Vd, as a target.
The period measuring unit 581 includes a first counter (not illustrated). The first counter starts counting of a clock signal (not illustrated) at a time point t1 which is a timing at which the potential of the shaped waveform signal Vd becomes equal to the threshold potential Vth_c for the first time after the mask signal Msk falls to the low level. That is, the first counter starts counting at the time point t1 which is the earlier timing among a timing at which the comparison signal Cmp1 rises to the high level for the first time or a timing at which the comparison signal Cmp1 falls to the low level for the first time, after the mask signal Msk falls to the low level.
After starting the counting, the first counter ends counting of the clock signal at a time point t2 which is a timing at which the potential of the shaped waveform signal Vd becomes the threshold potential Vth_c for the second time. The first counter outputs the obtained count value as the period NTc. That is, the first counter ends counting at the time point t2 which is the earlier timing among a timing at which the comparison signal Cmp1 rises to the high level for the second time or a timing at which the comparison signal Cmp1 falls to the low level for the second time, after the mask signal Msk falls to the low level. As described above, the measuring unit 58 acquires the period NTc by measuring a time length from the time point t1 to the time point t2 as the time length of one period of the shaped waveform signal Vd.
In a case where the amplitude of the shaped waveform signal Vd is small as indicated by a broken line in
The phase-difference measuring unit 582 includes a second counter (not illustrated). If the time enters into the detection period Td, the second counter starts counting of a clock signal (not illustrated). The second counter ends the counting of the clock signal at a timing which is the time point t1 in the example illustrated in
The amplitude measuring unit 583 acquires the maximum potential or the minimum potential in a period from the time point t1 (which is a timing at which the potential of the shaped waveform signal Vd becomes equal to the threshold potential Vth_c for the first time after the mask signal Msk falls to the low level) to a time point which is a timing at which the potential of the shaped waveform signal Vd becomes equal to the threshold potential Vth_c for the next time. That is, the time point t is the earlier timing among a timing at which the comparison signal Cmp1 rises to the high level for the first time or a timing at which the comparison signal Cmp1 falls to the low level for the first time, after the mask signal Msk falls to the low level. The amplitude measuring unit 583 acquire the maximum potential or the minimum potential in the period from the time point t1 to the time point which is a timing at which the comparison signal Cmp1 rises to the high level for the next time or a timing at which the comparison signal Cmp1 falls to the low level for the next time. That is, the amplitude measuring unit measures the maximum potential in the shown potential of the shaped waveform signal Vd if the period is a period in which the comparison signal Cmp1 is at the high level. The amplitude measuring unit measures the minimum potential in the shown potential of the shaped waveform signal Vd if the period is a period in which the comparison signal Cmp1 is at the low level. The amplitude measuring unit 583 acquires a potential difference between the maximum potential or the minimum potential which has been acquired, and the threshold potential Vth_c, as the amplitude Vmax.
The determination unit 56 determines the discharge state of the ink in the discharging portion D based on the period NTc, the phase difference NTF, the amplitude Vmax, and the validity flag Flag which have been input from the measuring unit 58. Then, the determination unit outputs a determination result as the determination result signal Rs.
The determination unit 56 is used for determining the period NTc. Three thresholds of NT×1, NT×2, and NT×3, which have a relation of NT×l<NT×2<NT×3 are set. The determination unit compares the period NTc to the thresholds NT×1, NT×2, and NT×3. Here, the threshold NT×1 is a threshold for determining whether or not bubbles are provided in the cavity 264. The threshold NT×2 is a threshold for determining whether or not paper dust adheres. The threshold NT×3 is a threshold for determining sticking or thickening of the ink. In a case where paper dust Pe floating in a state of being spaced from the nozzle N in the discharge direction adheres to the head surface 261, a condition of NT×2<NTc≤NT×3, which is set for detecting the paper dust Pe may not be satisfied. Therefore, in the embodiment, in order to reduce the omission of detection of this type of floating paper dust Pe, the first drive signal VinA illustrated in any one of
With the next Pull driving, pressure in the drawing direction which is opposite to the discharge direction is applied to the liquid Liq in the cavity 264. That is, a damping force in the drawing direction, which hinders movement in the discharge direction is applied to the liquid Liq in the cavity 264 in the process of moving in the nozzle N in the discharge direction. As a result, the liquid Liq in the nozzle N is cut out at a position close to the cavity 264. The separated liquid Liq is discharged from the nozzle N as a droplet Drp. Then, the meniscus Mnc of the liquid Liq cut out on the back side in the nozzle N converges at a predetermined position on the opening side of the nozzle N with an amplitude motion by a residual vibration. In the embodiment, the change of the residual vibration is detected in the detection period Td just after Pull driving, and whether or not discharge abnormality occurs is checked based on a result obtained by detecting the change of the residual vibration.
Next, a principle of detecting paper dust Pe adhering to the head surface 261 will be described with reference to
Push driving of the discharging portion D will be described with reference to
Next, discharge abnormality detection in the paper dust adhering time illustrated in
The liquid comes into contact with the paper dust Pe adhering to the head surface 261, in the process of being discharged from the nozzle N, and thus a force in a direction where the liquid is attracted to the paper dust Pe acts on the liquid Liq in the nozzle N by a capillary force. Therefore, the liquid level position illustrated in
Next, Pull driving of the discharging portion D will be described with reference to
Firstly, checking in the normal time, illustrated in
Next, checking in a case where paper dust Pe adheres to the head surface 261 will be described with reference to
In this discharge process, the liquid Liq comes into contact with the paper dust Pe. Thus, a force in a direction where the liquid is attracted to the paper dust Pe acts on the liquid Liq in contact with the paper dust Pe in the nozzle N by a capillary force or receive a resistance force from the paper dust Pe. In this state, a damping force in the direction in which the liquid Liq in the cavity 264 is drawn is applied by Pull driving. As a result, the position at which the liquid Liq in the nozzle N is cut out after the droplet Drp has been discharged varies from that in the normal time. In the example illustrated in
At this time, as illustrated in
Next, a principle of the paper dust checking will be described with reference to
NTc=2π(Mi·Cm)1/2 (1)
Here, Mi indicates inertance, and Cm indicates compliance. The compliance Cm is an integer determined by the liquid (ink in this example), the structural member of the discharging portion D, such as a flow path wall and the diaphragm 265, and the like.
A model of an ink discharge system in which an ink supply tube including the reservoir 272, the pressure chamber configured by the cavity 264, and a nozzle tube including the nozzle N are connected to each other is considered. The model is represented by an equivalent circuit illustrated in
Mi=(Mn·Ms)/(Mn+Ms) (2)
The inertance Mk on a path is represented by Mk=ρ·l/s with the sectional area s and the length l of the path and density ρ of the liquid. Thus, the inertance Ms on the path of the ink supply tube configured to supply an ink into the cavity 264 and the inertance Mn on the path of the nozzle tube configured to discharge the ink from the cavity 264 are given by the following expressions, respectively.
Ms=ρ·l1/s1Mn=ρ·l2/s2
Here, ρ indicates the density of the ink and is an integer which is slightly greater than 1. l1 indicates an ink length which is the length of a portion of the ink supply tube, which has been filled with the ink. s1 indicates the sectional area of the ink supply tube. l2 indicates an ink length which is the length of a portion of the nozzle N, which has been filled with the ink, to the liquid level. s2 indicates the sectional area of the nozzle N. The ink length l1 and the sectional area s1 of the ink supply tube which is normally filled with liquid are integers together. Thus, the inertance Ms on the supply side is an integer. The sectional area s2 of the nozzle tube is an integer. Therefore, the inertance Mi changes depending on the ink length l2 of the nozzle N. Thus, the period NTc of the residual vibration changes depending on the ink length l2 of the nozzle N, that is, on the liquid level position.
When the liquid level in the nozzle N is drawn to the cavity 264 side and is positioned on the back side, the ink length l2 becomes short, the inertance Mn on the nozzle side is reduced, and the inertance Mi of the discharging portion D is reduced. Thus, the period NTc of the residual vibration becomes short. On the contrary, when the liquid level in the nozzle N is positioned on the opening side of the nozzle, the ink length l2 of the nozzle N becomes long, the inertance Mn on the nozzle N increases, and the inertance Mi of the discharging portion D increases. Thus, the period NTc of the residual vibration becomes long.
In the embodiment, Pull driving illustrated in
The residual vibration signal Vout is measured when paper dust checking is performed with a checking method which is an example of Pull-Push-Pull driving. As a comparative example, a residual vibration signal Vout when a non-discharge type paper dust checking is performed is measured.
Two kinds of adhesion forms having different ways of adhering paper dust are prepared, and the residual vibration signal Vout is measured for each adhesion form. The first adhesion form is an adhesion form in which paper dust Pe adhering to the head surface 261 is near to the opening of the nozzle N, as illustrated in
As illustrated in the graph of
As illustrated in the graph of
As understood from
As understood from the graph in
As understood from the graph in
From both the graphs illustrated in
Thus, in the discharge abnormality checking in the embodiment, paper dust checking is performed with the phase difference NTF and the amplitude Vmax in addition to the period NTc of the residual vibration. Therefore, the measuring unit 58 measures the phase difference NTF and the amplitude Vmax in addition to the period NTc of the residual vibration, and outputs the period NTc, the phase difference NTF, and the amplitude Vmax which have been measured to the determination unit 56. The determination unit 56 determines whether or not a discharge abnormality occurs, based on the validity flag Flag, the period NTc, the phase difference NTF, and the amplitude Vmax.
The measuring unit 58 may determine whether or not a first discharge abnormality occurs, by using only one of the phase difference NTF and the amplitude Vmax instead of the configuration in which both the phase difference NTF and the amplitude Vmax are measured and used for determining the occurrence of the first discharge abnormality. For example, in a case where only the amplitude Vmax among the phase difference NTF and the amplitude Vmax is employed, the holding time variable amount Δt is set to a value in the range of −0.2≤Δt≤2.0, that is, a value in the range of −0.04·Tho≤Δt≤0.04·Tho. For example, in a case where only the phase difference NTF among the phase difference NTF and the amplitude Vmax is employed, the holding time variable amount Δt is set to a value in the range of −0.4≤Δt≤0, that is, a value in the range of −0.08·Tho≤Δt≤0. In the cases, preferably, the first holding time Th is set to be different from the second holding time Tho, and the holding time Th is adjusted to time proper for the paper dust checking.
Next, the action of the printer 11 will be described.
The controller 60 of the printer 11 performs discharge abnormality detection in a predetermined checking time before printing start, in the middle of printing, after the printing ends, and in the middle of not printing. In printing, the drive signal Vin generated by selecting the drive waveform signals Com-A and Com-B is applied to the piezoelectric element 200, and thus an image and the like is formed on recording paper P by droplets discharged from the nozzles N. In discharge abnormality detection, the drive signal Vin generated by selecting the drive waveform signal Com-C is supplied to the piezoelectric element 200, and thus whether or not a discharge abnormality occurs in the nozzle N is checked. At this time, before the time enters into the detection period Td, the switching unit 53 performs switching to the first connection state, and the drive signal VinA generated by the drive signal generation unit 51 is output to the discharging portion D.
The clock signal CL, the printing signal SI, the latch signal LAT, the change signal CH, and the drive waveform signal Com (Com-A, Com-B, and Com-C) are supplied from the controller 60 to the drive signal generation unit 51. At this time, the printing signal SI has a value for discharge abnormality detection, and specifically has a value of (b1, b2, b3)=(0, 0, 1). The drive signal generation unit 51 generates the drive signal Vin including the unit waveform PT for paper dust checking illustrated in
The potential difference between the second potential V2 and the third potential V3 in the first drive signal VinA illustrated in
The third potential V3 in the first drive signal VinA illustrated in
In the first drive signal VinA illustrated in
In the discharge abnormality detection, the first drive signal VinA illustrated in
The potential supplied to the piezoelectric element 200 transitions from the first potential V1 to the first transitional potential V4 of the first drive signal VinA, and the piezoelectric element 200 is subjected to Pull driving in the process of the potential transitioning. Then, the potential supplied to the piezoelectric element 200 transitions from the first transitional potential V4 to the second potential V2, and the piezoelectric element 200 is subjected to Push driving in the process of the potential transitioning. The potential supplied to the piezoelectric element 200 transitions from the second potential V2 to the third potential V3, and the piezoelectric element 200 is subjected to Pull driving in the process of the potential transitioning.
Since the first drive signal VinA for Pull-Push-Pull driving is supplied to the piezoelectric element 200, as illustrated in
In the normal time, as illustrated in
When the paper dust Pe adheres, as illustrated in
As described above, the excitation force for pushing the liquid Liq at the time of Push driving is set to be larger than those at other discharge times. In addition, the large damping force is applied to the liquid Liq by Pull driving at a timing at which the liquid Liq in the nozzle N is cut out when a droplet is discharged. Thus, the liquid level position in the nozzle N is largely different between the normal time and the paper dust adhering time. Thus, the difference ΔLpull between the position of the meniscus Mnc in the normal time indicated by the broken line in
After the discharge, the diaphragm 265 performs a residual vibration. If Pull-Push-Pull driving ends, the switching unit 53 performs switching from the first connection state to the second connection state. As a result, the residual vibration signal Vout from each of the discharging portions D is input to the discharge abnormality detection unit 52.
The residual vibration signal Vout input to the discharge abnormality detection unit 52 is input to each of the discharge abnormality detection circuits DT which respectively correspond to the discharging portions D. The waveform shaping unit 57 in the detection unit 55 constituting the discharge abnormality detection circuit DT removes noise from the residual vibration signal Vout, and the resultant is input to the measuring unit 58 as the shaped waveform signal Vd. The period measuring unit 581 measures the period of the residual vibration signal Vout by using the shaped waveform signal Vd. The phase-difference measuring unit 582 measures the elapsed time from when the detection period Td starts until the shaped waveform signal Vd after the mask period ends is greater than the threshold potential Vth_c for the first time, by using the counter (not illustrated), so as to measure the phase time TF of the residual vibration signal Vout. The phase-difference measuring unit 582 acquires the phase difference NTF by calculating the difference between the measured phase time TF of the residual vibration signal Vout and the phase time TFo in the normal time, which is stored in the storage unit 62. The amplitude measuring unit 583 measures the amplitude Vmax of the residual vibration signal Vout by using the shaped waveform signal Vd. The detection unit 55 outputs the validity flag Flag, the period NTc, the phase difference NTF, and the amplitude Vmax to the determination unit 56.
The determination unit 56 receives inputs of the validity flag Flag, the period NTc, the phase difference NTF, and the amplitude Vmax from the detection unit 55. In a case where the validity flag Flag is set to “1” which is a value indicating that the measurement value is valid, the determination unit 56 determines whether or not the discharge abnormality occurs, that is, determines whether or not an abnormal nozzle in which it is not possible to normally discharge a droplet is provided, based on the period NTc, the phase difference NTF, and the amplitude Vmax. The determination unit 56 determines the cause in a case where the abnormal nozzle is provided. In a case where at least paper dust checking is set as a target, the determination unit 56 determines whether or not the discharge abnormality occurs, based on the phase difference NTF and the amplitude Vmax in addition to the period NTc. Even though a determination result indicating being normal is obtained based on the period NTc, the determination unit 56 determines that the first discharge abnormality caused by paper dust occurs, if a determination result indicating paper dust abnormality is obtained from a comparison between the phase difference NTF and the phase difference threshold is obtained, or a determination result indicating paper dust abnormality is obtained from a comparison between the amplitude Vmax and the amplitude threshold is obtained.
Here, in the first checking method, the first checking of checking the occurrence of the first discharge abnormality caused by foreign substances such as paper dust Pe and the second checking of checking the occurrence of the second discharge abnormality caused by the cause other than the foreign substance are performed by commonly using the first drive signal VinA in the discharge mode. In this case, the second drive signal VinB having the same discharge mode as that when printing is performed on the recording paper P is used. In the second checking method, the first checking of checking the occurrence of the first discharge abnormality caused by foreign substances such as paper dust Pe is performed by using the residual vibration occurring after the droplet has been discharged, based on the first drive signal VinA in the discharge mode. The second checking of checking the occurrence of the second discharge abnormality caused by the cause other than the foreign substance is performed by using the residual vibration occurring after the droplet has been discharged, based on the second drive signal VinB in the discharge mode. In the cases, the second checking method is performed in the third form in which discharge abnormality detection processing is assigned to all the M discharging portions D. In a case of the discharge mode, in any of the first checking method and the second checking method, it is not possible to perform the discharge abnormality checking in the process of printing. Therefore, the discharge abnormality checking is performed by discharging droplets from the nozzle N to the waste liquid receiving portion in a not-printing period, for example, a flushing time or time before and after printing.
In a case where the discharge abnormality checking is performed in the process of printing, the checking is performed in the non-discharge mode in which droplets are not discharged from the nozzle N. In this case, if the first drive signal VinA for generating a fine vibration (not illustrated) for checking is supplied to the piezoelectric element 200, discharge abnormality detection processing is performed in the first form in which printing processing is assigned to some of the M discharging portions D, and discharge abnormality detection processing is assigned to others. In the first drive signal VinA in the non-discharge mode, the second potential V2 has a potential having a magnitude such that it is not possible to discharge droplets from the nozzle N. In the non-discharge mode, the first checking method and the second checking method are also provided. In the first checking method, the first checking and the second checking are performed with the common first drive signal VinA in the non-discharge mode. In the second checking method, the first checking is performed with the first drive signal VinA in the non-discharge mode, and the second checking is performed with the second drive signal VinB in the non-discharge mode. The discharge abnormality checking in the non-discharge mode may also be performed in the not-printing period in which the printing operation is not performed.
In a case where the discharge abnormality is detected, the controller 60 arranges the head portion 30 and the recovery mechanism 70 at positions facing each other and performs recovery processing on each of the discharging portions D of the head portion 30. As the recovery processing, cleaning in which the liquid is forcibly removed from the nozzle N is performed. As the recovery processing, weak recovery processing including flushing in which droplets are discharged from the nozzle N to the waste liquid receiving portion of the recovery mechanism 70, or flushing and the subsequent wiping of the head surface 261 by a wiping member such as a wiper may be performed. In a case where the weak recovery processing is performed, if the discharge abnormality checking is performed after the recovery processing ends, but the discharge abnormality is not solved, cleaning may be performed.
Hitherto, according to the embodiment described in detail, it is possible to obtain effects as follows.
(1) The printer 11 includes the nozzle N that discharges liquid by driving the piezoelectric element 200, the drive signal generation unit 51 that generates the drive signal for driving the piezoelectric element 200, and the discharge abnormality detection unit 52 that detects the change of the electromotive force of the piezoelectric element 200, which is caused by the residual vibration in the cavity 264 communicating with the nozzle N after the drive signal is supplied. The drive signal generation unit 51 generates the first drive signal VinA for checking whether or not the first discharge abnormality caused by foreign substances adhering to the head surface 261 occurs and the second drive signal VinB for checking whether or not the second discharge abnormality caused by the cause other than the foreign substances occurs. The potential of the first drive signal VinA when the discharge abnormality detection unit 52 performs checking is different from the potential of the second drive signal VinB when the discharge abnormality detection unit 52 performs checking. Therefore, when the occurrence of the first discharge abnormality is checked, it is possible to draw liquid in the cavity 264 excited in the discharge direction of the nozzle N by the piezoelectric element 200, toward the opposite side of the discharge direction with the force greater than that when the occurrence of the second discharge abnormality is checked. Accordingly, the abnormal time being in the state where the foreign substance adhering to the head surface 261 on which the nozzle N opens has been in contact with the liquid in the nozzle N and the normal time have a significant difference in the liquid level position in the nozzle N in the residual vibration period. Since the significant difference in the liquid level position is shown as the significant difference of the change of the residual vibration, the discharge abnormality detection unit 52 detects the significant difference of the change of the residual vibration, and thereby it is possible to check whether or not the first discharge abnormality caused by adhering of the paper dust Pe occurs, with high accuracy.
(2) The first drive signal VinA and the second drive signal VinB have the same mode for defining discharge or non-discharge. When checking is performed by discharging liquid in order to secure high check accuracy, both the first drive signal VinA and the second drive signal VinB are in the discharge mode in which the potential change allowing discharging of the liquid is provided. When checking is performed in a non-discharge state in which liquid is not discharged, for example, in order to save the consumption of the liquid or because of being in the process of printing, both the first drive signal VinA and the second drive signal VinB are in the non-discharge mode in which the potential change which does not cause discharge of the liquid is provided. It is possible to perform checking (first checking) of whether or not the first discharge abnormality caused by adhering of the foreign substance occurs and checking (second checking) of whether or not the second discharge abnormality caused by the cause other than the foreign substance occurs, with high accuracy even in a case where any type of checking of discharge and non-discharge is performed depending on the situation or needs at time of checking.
(3) The first drive signal VinA and the second drive signal VinB have the first potential V1 in the first period T1, have the second potential V2 in the second period T2, and have the third potential V3 in the third period T3. The first drive signal VinA and the second drive signal VinB transitions from the first potential V1 to the second potential V2 and transitions from the second potential V2 to the third potential V3. Thus, at least one (for example, V3) of the second potential V2 and the third potential V3 in the first drive signal VinA, which is used for determining a force causing the liquid in the cavity 264 excited in the discharge direction by deformation of the piezoelectric element 200 to be drawn to the opposite side of the discharge direction is different from at least the corresponding one (for example, Vc) of the second potential V2 and the third potential Vc of the second drive signal VinB. Accordingly, it is possible to check whether or not the first discharge abnormality caused by adhering of the foreign substance occurs, with high accuracy.
(4) The third potential V3 of the first drive signal VinA is different from the third potential Vc of the second drive signal VinB. Thus, when the first drive signal VinA transitions from the second potential V2 from the third potential V3, the pressure causing the liquid in the cavity 264 to be drawn toward the opposite side of the discharge direction can be set to be larger than that when the second drive signal VinB transitions from the second potential V2 to the third potential Vc. Accordingly, the significant difference in the liquid level position in the nozzle N in the third period T3 after the liquid in the cavity 264 has been drawn is provided between the abnormal time in which the foreign substance has adhered and the normal time. Since the significant difference in the liquid level position is shown as the significant difference of the change of the residual vibration, the discharge abnormality detection unit 52 detects the significant difference of the change of the residual vibration, and thereby it is possible to improve check accuracy for checking whether or not the first discharge abnormality caused by adhering of the paper dust Pe occurs.
(5) The potential difference between the second potential V2 and the third potential V3 in the first drive signal VinA is greater than that in the second drive signal VinB. Thus, it is possible to increase the force causing the liquid in the cavity 264, which has been pressed in the discharge direction to be drawn toward the opposite side of the discharge direction by the piezoelectric element 200 deforming when the signal transitions from the second potential V2 to the third potential V3. Thus, if the paper dust Pe adhering to the head surface 261 on which the nozzle N opens is in a state of being in contact with the liquid in the nozzle N, a significant difference of a liquid level position in the nozzle N in the third period T3 after the liquid in the cavity 264 has been drawn is provided from that in the normal time. Since the difference in the liquid level position is shown as the difference of the change of the residual vibration, the discharge abnormality detection unit 52 detects the difference of the change of the residual vibration, and thereby it is possible to improve check accuracy for checking whether or not the discharge abnormality caused by adhering of the paper dust Pe occurs.
(6) In the normal time in which a discharge abnormality does not occur, the liquid level position in the nozzle N, which is closest to the cavity 264 when the third potential V3 of the first drive signal VinA is supplied to the piezoelectric element 200 is closer to the cavity 264 than the liquid level position in the nozzle N, which is closest to the cavity 264 when the third potential Vc of the second drive signal VinB is supplied to the piezoelectric element 200. Thus, the significant difference is provided between the liquid level position in the nozzle N when the paper dust Pe is in a state of being in contact with the liquid in the nozzle N and the liquid level position in the nozzle N in the normal time. Accordingly, the discharge abnormality detection unit 52 detects the significant difference of the residual vibration, and thereby it is possible to improve check accuracy for checking whether or not the discharge abnormality caused by adhering of the paper dust Pe occurs.
(7) In the first drive signal VinA, the first potential V1 is equal to the third potential V3. Thus, the next operation can be simply started without changing the potential after the residual vibration is attenuated, that is, after the checking ends. For example, if the first potential V1 is different from the third potential V3, the change of pressure of the liquid in the cavity 264 is caused by the change of the potential after the checking ends, and this may influence the next discharge of the liquid. However, since the first potential V1 and the third potential V3 in the first drive signal VinA are equal to each other, there is no concern of this type.
(8) In the first drive signal VinA, the first potential V1 is a potential between the second potential V2 and the third potential V3. As a result, it is possible to increase the potential difference when the signal transitions from the second potential V2 to the third potential V3, and to increase the force causing the liquid in the cavity 264 to be drawn toward the opposite side of the discharge direction. As a result, the significant difference in the change of the residual vibration is provided when the paper dust Pe adheres, in comparison to the normal time. The discharge abnormality detection unit 52 detects the significant difference of the change of the residual vibration, and thereby it is possible to check whether or not the discharge abnormality caused by adhering of the paper dust Pe occurs, with high accuracy.
(9) The second potential V2 and the third potential V3 in the first drive signal VinA are potentials causing the intermediate potential Vc corresponding to the reference volume of the cavity 264 to be interposed between both the potentials V2 and V3. Thus, when the first drive signal VinA transitions from the second potential V2 to the third potential V3, the piezoelectric element 200 deforms from the state of having deformed in the discharge direction of the nozzle N, toward the opposite side of the discharge direction beyond the neutral position at which the cavity 264 is set to have the reference volume. Thus, it is possible to increase the force causing the liquid in the cavity 264 to be drawn toward the opposite side of the discharge direction. Therefore, when the paper dust Pe has adhered, the significant difference in the liquid level position in the nozzle N is provided from that in the normal time by the residual vibration. Since the significant difference in the liquid level position is shown as the significant difference of the change of the residual vibration, the residual vibration detection unit detects the significant difference of the change of the residual vibration, and thereby it is possible to improve check accuracy for checking whether or not the discharge abnormality caused by adhering of the foreign substance occurs.
(10) The second potential V2 in the first drive signal VinA is equal to the second potential V2 in the second drive signal VinB. Thus, it is possible to reduce the risk of applying an inappropriate voltage such as an overvoltage or a reverse voltage to the piezoelectric element 200. Even though the second potential V2 approaches the potential at which the overvoltage or the reverse voltage is applied, the third potential differs between the first drive signal VinA and the second drive signal VinB (V3≠Vc). Thus, it is possible to increase the potential difference in Push driving when the signal transitions from the second potential V2 to the third potential V3.
(11) The first potential V1 of the first drive signal VinA is equal to the first potential V1 of the second drive signal VinB. Thus, it is possible to reduce the risk of applying an inappropriate voltage such as an overvoltage or a reverse voltage to the piezoelectric element 200.
(12) The piezoelectric element 200 includes the lower electrode 201 to which the reference potential VSS is supplied, and the upper electrode 202 to which the first drive signal VinA and the second drive signal VinB are supplied. The first potential V1 and the third potential V3 in the first drive signal VinA are set to a potential in the range of the intermediate potential Vc side corresponding to the reference volume of the cavity 264, rather than the reference potential VSS. Thus, it is possible to avoid an occurrence of a situation in which the reverse voltage (reverse bias) is applied to the piezoelectric element 200 when the first potential V1 and the third potential V3 of the first drive signal VinA have been supplied to the upper electrode 202 of the piezoelectric element 200. For example, it is possible to avoid the induction of polarization collapse of the piezoelectric element 200, which is caused by applying the reverse bias to the piezoelectric element 200 or avoid the failure caused by cracks which occur by excessive stress distortion of the piezoelectric element 200, in the first period T1 and the third period T3 in which the first potential V1 and the third potential V3 are supplied to the piezoelectric element 200.
(13) The first drive signal VinA transitions from the first potential V1 to the second potential V2 via the first transitional potential V4. The first potential V1 is a potential between the second potential V2 and the first transitional potential V4. Thus, since the first drive signal VinA transitions from the first potential V1 to the first transitional potential V4, the piezoelectric element 200 can deform in the pull direction on the opposite side of the direction of pushing in the discharge direction, and then largely deform in the direction of pushing in the discharge direction. Thus, it is possible to largely excite the liquid in the cavity 264 by the large deformation of the piezoelectric element 200 in the push direction. As a result, it is possible to increase the amplitude of the liquid level in the nozzle N. The significant difference in the liquid level position in the nozzle N in the residual vibration period is provided between the abnormal time in which the paper dust Pe has adhered and the normal time in which the paper dust Pe does not adhere. The significant difference in the liquid level position is shown as the significant difference of the change of the residual vibration. The discharge abnormality detection unit 52 detects the significant difference of the change of the residual vibration, and thereby it is possible to check whether or not the first discharge abnormality caused by adhering of the paper dust Pe occurs, with high accuracy.
(14) The first holding time Th at which the first drive signal VinA is held to the second potential V2 is different from the second holding time Tho at which the second drive signal VinB is held to the second potential V2. Thus, it is possible to set the first holding time Th to an appropriate time which is different from the second holding time Tho. Accordingly, it is possible to increase the difference of the change of the residual vibration between the paper dust adhering time and the normal time. Thus, the discharge abnormality detection unit 52 detects the difference of change of the residual vibration, and thereby it is possible to improve check accuracy for checking whether or not the first discharge abnormality caused by adhering of the paper dust Pe occurs, with high accuracy.
(15) When the first drive signal VinA has been supplied, the discharge abnormality detection unit 52 detects the amplitude Vmax of the residual vibration based on the electromotive force of the piezoelectric element 200, and performs checking based on the amplitude Vmax. The significant difference in the liquid level position in the nozzle N in the residual vibration period is provided between the abnormal time in which the paper dust Pe adheres and the normal time, and the significant difference of the liquid level position is shown as the significant difference of the amplitude Vmax of the residual vibration. Therefore, the discharge abnormality detection unit 52 performs checking based on the amplitude Vmax, and thereby it is possible to check whether or not the first discharge abnormality caused by adhering of the paper dust Pe occurs, with high accuracy.
(16) When the first drive signal VinA has been supplied, the discharge abnormality detection unit 52 detects the phase of the residual vibration based on the electromotive force of the piezoelectric element 200, and checks whether or not the first discharge abnormality occurs, based on the phase. The significant difference in the liquid level position in the nozzle N is provided between the abnormal time in which the paper dust Pe adheres and the normal time, and the significant difference of the liquid level position is shown as the significant difference of the phase of the residual vibration. Therefore, the discharge abnormality detection unit 52 performs checking based on the phase, and thereby it is possible to check whether or not the first discharge abnormality caused by adhering of the paper dust Pe occurs, with high accuracy. Specifically, the discharge abnormality detection unit 52 measures the phase time TF indicating the phase of the residual vibration, based on the change of the electromotive force of the piezoelectric element 200, and performs checking by comparing the phase time TF to the phase time TFo indicating the phase of the residual vibration in the normal time. That is, the discharge abnormality detection unit 52 compares the phase time TF to the threshold (TFo-NTFo). If the phase time TF is smaller than the threshold (TFo-NTFo), that is, if the phase difference NTF indicated by the difference between the phase time TF and the phase time TFo in the normal time is greater than the phase difference threshold NTFo, the determination unit determines that the first discharge abnormality by adhering of the paper dust has occurred.
(17) The first drive signal VinA is supplied to the piezoelectric element 200 when first checking of checking whether or not the first discharge abnormality caused by paper dust Pe adhering to the head surface 261 occurs and the second checking of checking whether or not the second discharge abnormality caused by the cause other than the paper dust Pe occurs are performed together. The second drive signal VinB is supplied to the piezoelectric element 200 in the process of the printing operation in which the liquid is discharged from the nozzle N onto the recording paper P. Thus, the third potential V3 of the first drive signal VinA which is commonly supplied to the piezoelectric element 200 in the first checking and the second checking is different from the third potential Vc of the second drive signal VinB for discharging the liquid onto the recording paper P. For example, it is possible to set the potential difference between the second potential V2 and the third potential V3 in the first drive signal VinA to be larger than the corresponding potential difference in the second drive signal VinB. Thus, it is possible to improve check accuracy for the first checking of checking whether or not the first discharge abnormality caused by the paper dust Pe occurs. In addition, it is possible to perform the first checking and the second checking by using the common residual vibration after the liquid has been discharged. Therefore, it is possible to reduce the time required for the discharge abnormality checking and to reduce the consumed amount of the liquid in the discharge abnormality checking.
The embodiment may change like a modification example as follows. The components provided in the embodiment and components provided in the following modification example may be randomly combined, and the components provided in the following modification example may be randomly combined.
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