Patent Grant
11117370
The present application is based on and claims priority under 35 U.S.C. § 119 to Japanese Patent Application No. 2018-182693, filed on Sep. 27, 2018, the contents of which are incorporated herein by reference in their entirety.
The present invention relates to a liquid discharging apparatus and an image forming system.
A recording head of an inkjet recording apparatus used as an image forming apparatus such as a printer, a facsimile machine, a copier, or a plotter, etc., includes a nozzle, a pressure generating chamber (a pressurizing liquid chamber) in communication with the nozzle, and a pressure generating element such as a piezoelectric element, etc., for discharging ink.
For example, Patent Document 1 describes that the through-down timing of the reference voltage applied to the piezoelectric element is changed according to the number of times of discharging ink by the recording head, after the scanning of the recording head, thereby reducing the variation in the polarization of the piezoelectric element, and reducing the variation of the discharging performance.
Patent Document 2 describes that a portion of the waveform of the discharge pulse applied to the piezoelectric element for discharging ink, is used to generate a non-discharge pulse by which ink is not discharged, thereby shortening the waveform length of the driving waveform generated commonly for a plurality of piezoelectric elements and increasing the efficiency of printing.
Patent Document 3 describes that in order to inhibit the heat generation of a print head caused by continuously discharging ink, a liquid droplet non-discharge period, which is longer than a liquid droplet discharge period in which pulses for discharging liquid droplets from the nozzle are generated, is provided in the driving cycle.
Patent Document 1: Japanese Unexamined Patent Application Publication No. 2013-014121
Patent Document 2: Japanese Unexamined Patent Application Publication No. 2015-174401
Patent Document 3: Japanese Unexamined Patent Application Publication No. 2014-028450
According to one aspect of the present invention, there is provided a liquid discharging apparatus including a nozzle hole (a hole of a nozzle) configured to discharge liquid; a liquid chamber provided so as to communicate with the nozzle hole; a piezoelectric element configured to change a pressure applied to the liquid in the liquid chamber to discharge the liquid from the nozzle hole; a driving waveform generation circuit configured to generate a driving waveform signal during a discharge control period having a predetermined cycle, to apply a driving waveform voltage to the piezoelectric element; a switch configured to selectively supply, to the piezoelectric element, at least one of a plurality of waveforms included in the driving waveform signal; and a controller configured to perform voltage setting control for applying a predetermined voltage to the piezoelectric element, in a case where a non-discharge control period, having a predetermined cycle, causes the piezoelectric element to change by a voltage that is greater than or equal to an allowable voltage, the non-discharge control period being a period during which the liquid is not discharged after the discharge control period.
When the application of a voltage to the electrode of a piezoelectric element is stopped during a non-discharge control period, during which liquid is not discharged within the driving cycle, the voltage of the electrode of the piezoelectric element gradually decreases with respect to the reference voltage that is the starting voltage of the driving pulses, due to the leakage current. When the difference between the voltage of the electrode of the piezoelectric element and the reference voltage becomes greater than or equal to a predetermined value, at the time of generating the driving pulses in the next driving cycle, there is a possibility that the voltage of the electrode of the piezoelectric element rises sharply to the reference voltage, causing liquid to be erroneously discharged from the nozzle. Further, when the voltage changes sharply during the driving operation, an excessive current may be caused to flow to the control circuit, etc., that controls the recording head, and a failure may occur in the control circuit.
In order to prevent erroneous discharges or failures, it is considered to drive the gate circuit that controls the voltage applied to the piezoelectric element during the non-discharge control period, to maintain the voltage of the electrode of the piezoelectric element at the reference voltage during the non-discharge control period. However, when the heat generated by the driving of the gate circuit is transmitted to the recording head and the temperature of the recording head rises, the temperature of the liquid rises and the viscosity of the liquid decreases, making it difficult to control the discharging of the liquid. In particular, the shorter the driving cycle, the higher the number of times the gate circuit is driven per time unit, and thus the temperature of the recording head is likely to rise.
A problem to be addressed by an embodiment of the present invention is to prevent the heat generation of the recording head while inhibiting a decrease in the voltage of the electrode of the piezoelectric element, during a non-discharge control period.
Hereinafter, embodiments will be described with reference to the drawings.
The image forming system 1 includes an image forming apparatus 40 including a liquid discharging apparatus for forming an image on the surface of a roll paper Md, a posttreating unit 50 for performing posttreating on the roll paper Md on which an image is formed, and a carry-out unit 60 for carrying out the post-processed roll paper Md. Further, the image forming system 1 includes a control unit (not illustrated) for controlling the operation of the image forming system 1.
The image forming system 1 carries in the roll paper Md by the carry-in unit 10 and performs pretreating and drying on the surface of the roll paper Md by the pretreating unit 20 and the drying unit 30. The image forming system 1 forms an image on the surface of the roll paper Md, which has been subjected to pretreating and drying, by the image forming apparatus 40. Further, the image forming system 1 performs posttreating on the roll paper Md, on which the image is formed, by the posttreating unit 50. Thereafter, the image forming system 1 winds up the roll paper Md and ejects or carries out the roll paper Md by the carry-out unit 60.
The image forming system 1 may be configured such that any one or more of the units such as the pretreating unit 20 or the like, are not included, except for the image forming apparatus 40, depending on the type of the medium on which images are formed.
The roll paper Md is not limited to roll paper. For example, the roll paper Md may be cut paper. Further, the roll paper Md may be a medium on which information can be recorded. For example, the roll paper Md may be plain paper, quality paper, thin paper, cardboard, recording paper, Overhead Projector (OHP) sheets, synthetic resin films, and metal films.
For example, the image forming system 1 includes a liquid discharging apparatus including dischargers corresponding to four colors that are black (K), cyan (C), magenta (M), and yellow (Y). However, the image forming system 1 may include a liquid discharging apparatus including dischargers corresponding to other colors such as green (G), red (R), and light cyan (LC), and may include a liquid discharging apparatus including a discharger corresponding to only black (K).
The image forming apparatus 40 including the liquid discharging apparatus is not limited to the form of being mounted in the image forming system 1 illustrated in
Further, embodiments according to the present invention may be applied to a device for forming, printing, copying, or recording an image or characters on the surface of the roll paper Md.
The carry-in unit 10 is a means for conveying the roll paper Md to the pretreating unit 20 or the like. In the present embodiment, the carry-in unit 10 includes a sheet feeding unit 11 and a plurality of conveying rollers 12. The carry-in unit 10 carries and moves the roll paper Md held by being wound around a paper feed roll of the sheet feeding unit 11, by using the conveying rollers 12 or the like, and conveys the roll paper Md to the pretreating unit 20 (a platen) or the like.
The pretreating unit 20 is a means for treating the roll paper Md before the image is formed. In the present embodiment, the pretreating unit 20 performs pretreatment on the surface of the roll paper Md, carried in by the carry-in unit 10, with a pretreatment liquid. The pretreatment is a process in which a pretreatment liquid having the function of agglomerating the ink is uniformly applied to the surface of the roll paper Md. The pretreatment liquid is, for example, a treatment liquid containing water-soluble aliphatic organic acid.
The drying unit 30 is a means for drying the roll paper Md by heating or the like. The drying unit 30 includes a pretreating drying unit 31 for drying the roll paper Md pretreated by the pretreating unit 20 and a posttreating drying unit 32 for drying the roll paper Md posttreated by the posttreating unit 50.
The pretreating drying unit 31 includes, for example, a heat roller 31h. The pretreating drying unit 31 heats the heat roller 31h, for example, to 50° C. to 100° C., and brings the surface of the roll paper Md coated with the pretreatment liquid into contact with the heat roller 31h. The pretreating drying unit 31 can heat the surface of the roll paper Md coated with the pretreatment liquid by the heat roller 31h, evaporate the water content of the pretreatment liquid, and dry the roll paper Md. The posttreating drying unit 32 has the same configuration as the pretreating drying unit 31.
The image forming apparatus 40 includes a liquid discharging apparatus and is a means for forming an image on the roll paper Md. The image forming apparatus 40 controls the liquid discharging apparatus to discharge liquid droplets (hereinafter referred to as ink) onto the roll paper Md dried by the drying unit 30 to form an image on the surface of the roll paper Md. Details of the liquid discharging apparatus are described below.
The posttreating unit 50 is a means for treating the roll paper Md after the image is formed on the roll paper Md. The posttreating unit 50 performs posttreatment on the surface of the roll paper Md on which an image is formed by the image forming apparatus 40, with a posttreatment liquid. The posttreatment is a process in which the posttreatment liquid is discharged in spot shapes on the roll paper Md.
The main control substrate 100 includes a Central Processing Unit (CPU) 101, a Field-Programmable Gate Array (FPGA) 102, a Random Access Memory (RAM) 103, a Read-Only Memory (ROM) 104, a Non-Volatile Random Access Memory (NVRAM) 105, a motor driver 106, and a driving waveform generation circuit 107 (driving waveform generator), etc.
The CPU 101 controls the entire image forming apparatus 40. For example, the CPU 101 uses the RAM 103 as a working area to execute various control programs stored in the ROM 104, and outputs control commands for controlling various operations in the image forming apparatus 40. In this case, the CPU 101 cooperates with the FPGA 102 to perform various kinds of operation control in the image forming apparatus 40, while communicating with the FPGA 102.
The FPGA 102 includes a CPU control unit 111, a memory control unit 112, an Inter-Integrated Circuit (I2C) control unit 113, a sensor processing unit 114, a motor control unit 115, and a recording head control unit 116 (voltage controller).
The CPU control unit 111 has a function for communicating with the CPU 101. The memory control unit 112 has a function for accessing the RAM 103 or the ROM 104. The I2C control unit 113 has a function for communicating with the NVRAM 105.
The sensor processing unit 114 processes the sensor signals of various sensors 130. The various sensors 130 are a collective term for referring to sensors that sense various states of the image forming apparatus 40. The various sensors 130 include an encoder sensor, a paper sensor for detecting the passage of a recording sheet, a cover sensor for detecting the opening of a cover member, a temperature and humidity sensor for detecting the ambient temperature and humidity, a paper fixing lever sensor for detecting the operation state of a lever for fixing the recording sheet, and a remaining amount detecting sensor for detecting the remaining ink amount in a cartridge. The analog sensor signal output from the temperature and humidity sensor is converted to a digital signal by an AD converter mounted, for example, on the main control substrate 100, and is input to the FPGA 102.
The motor control unit 115 controls various motors 140. The various motors 140 are a collective term for referring to motors provided in the image forming apparatus 40. The various motors 140 include a main scanning motor for operating a carriage, a sub-scanning motor for conveying a recording sheet in the sub-scanning direction, a paper feed motor for feeding a recording sheet, and a maintenance motor for operating a maintenance mechanism.
Here, an example of the operation control of the main scanning motor will be described, as a specific example of the control by cooperation between the CPU 101 and the motor control unit 115 of the FPGA 102. First, the CPU 101 reports, to the motor control unit 115, the movement speed and the travel distance of a carriage along with an instruction to start the operation of the main scanning motor. The motor control unit 115 that has received this instruction generates a driving profile based on the information of the movement speed and the travel distance reported from the CPU 101, and calculates a Pulse Width Modulation (PWM) command value and outputs the value to the motor driver 106 while making a comparison with an encoder value supplied from the sensor processing unit 114 (a value obtained by processing the sensor signal of the encoder sensor). When a predetermined operation is completed, the motor control unit 115 reports, to the CPU 101, the completion of the operation. Although an example in which the motor control unit 115 generates a driving profile is described above, the image forming apparatus 40 may have a configuration in which the CPU 101 generates a driving profile and gives an instruction to the motor control unit 115. The CPU 101 also counts the number of printed sheets and the number of scans of the main scanning motor.
The recording head control unit 116 transfers head driving data, a discharge synchronization signal LINE, and a discharge timing signal CHANGE stored in the ROM 104, to the driving waveform generation circuit 107, to cause the driving waveform generation circuit 107 to generate a common driving waveform signal Vcom. The common driving waveform signal Vcom generated by the driving waveform generation circuit 107 is input to a recording head driver 210, as described below, mounted on the head relay substrate 200.
The image processing unit 310 performs gradation processing, image conversion processing, or the like on received image data, and converts the image data into a format that can be processed by the recording head control unit 116. The image processing unit 310 outputs the converted image data to the recording head control unit 116.
Specifically, the image processing unit 310 includes an interface 41, a gradation processing unit 42, an image converting unit 43, and an image processing unit RAM 44.
The interface 41 is an input unit for inputting image data and is a communication interface with respect to the CPU 101 and the FPGA 102. The gradation processing unit 42 performs gradation processing on received multi-value image data and converts the image data to small value image data. The small value image data is image data having a gradation number corresponding to the type of liquid droplets (a large droplet, a medium droplet, or a small droplet) discharged by a recording head 6 mounted on the head relay substrate 200 as illustrated in
The image converting unit 43 converts the image data corresponding to one band in the image processing unit RAM 44, in units of images output by one scanning operation (one scan) in the main scanning direction X. This conversion is performed in line with the configuration of the recording head 6, according to the information of the printing order and the printing width (sub-scanning width of image recording per scan) accepted from the CPU 101 through the interface 41.
The printing order and the printing width may correspond to one-pass printing, in which an image is formed by one main scanning operation with respect to the recording medium, or may correspond to multi-pass printing, in which an image is formed by two or more main scanning operations by the same nozzle group or different nozzle groups with respect to the same area of the recording medium. Further, the heads may be arranged in the main scanning direction, and ink may be ejected to the same area by different nozzles. These recording methods may be appropriately combined.
The printing width is the width in the sub-scanning direction Y of an image recorded by one scanning operation (one scan) by the recording head 6 (see
The image converting unit 43 outputs the converted image data SD′ to the FPGA 102 via the interface 41.
The functions of the image processing unit 310 may be executed as hardware functions such as FPGA or Application Specific Integrated Circuit (ASIC), or may be implemented by image processing programs stored in a storage device inside the image processing unit 310.
The functions of the image processing unit 310 may be executed by software installed in a computer, and not within the image forming apparatus 40.
The recording head control unit 116 receives a trigger signal Trig that triggers the discharge timing, and then outputs a discharge synchronization signal LINE that triggers the generation of a driving waveform, to the driving waveform generation circuit 107. Further, the recording head control unit 116 outputs a discharge timing signal CHANGE, corresponding to the delay amount from the discharge synchronization signal LINE, to the driving waveform generation circuit 107 (see
Further, the recording head control unit 116 receives the image data SD′ that has undergone the image processing from the image processing unit 310 provided in the image processing substrate 300, and based on the image data SD′, the recording head control unit 116 generates a mask control signal MN for selecting a predetermined waveform of the common driving waveform signal Vcom according to the size of the ink droplets to be discharged from each nozzle hole 62 (a hole of each nozzle) (see
The recording head driver 210 includes a shift register 211, a latch circuit 212, a gradation decoder 213, a level shifter 214, and an analog switch 215 as illustrated in
The shift register 211 inputs the image data SD′ and the synchronization clock signal SCK transferred from the recording head control unit 116. The latch circuit 212 latches each register value of the shift register 211 by a latch signal LT transferred from the recording head control unit 116.
The gradation decoder 213 decodes the value latched by the latch circuit 212 (the image data SD′) and the mask control signal MN and outputs the result of the decoding. The level shifter 214 converts the logic level voltage signal of the gradation decoder 213 to a level at which the analog switch 215 is operable.
The analog switch 215 is a switch that is turned on/off by the output of the gradation decoder 213 provided via the level shifter 214. The analog switch 215 is provided for each nozzle hole 62 provided in the recording head 6, and is connected to an individual electrode 83 of a piezoelectric element 70 corresponding to each nozzle hole 62 (see
The discharge timing signal CHANGE illustrated in
For example, each piezoelectric element 70 is in contact with a wall surface adjacent to the pressurizing liquid chamber 61, that is, a wall surface facing a wall surface in which the nozzle hole 62 is provided, and the piezoelectric element 70 deforms as a result of receiving a driving waveform voltage from the analog switch 215 of
First, the operation until the mask control signal MN is output to the analog switch 215 of
For example, the recording head control unit 116 receives the image data SD′ having a number of pixels corresponding to the number of the nozzle holes 62 of the recording head 6, and outputs the received image data SD′ as serial data to the shift register 211 in synchronization with the synchronization clock signals SCK. The shift register 211 sequentially receives pieces of the serial image data SD′ in synchronization with the synchronization clock signals SCK, and shifts the pieces of the serial image data SD′ in the shift register 211 while sequentially receiving the pieces of the serial image data SD′, and holds the serial image data SD′ in the shift register 211. Then, the shift register 211 outputs the held image data SD′ to the latch circuit 212 as parallel data.
The latch circuit 212 latches the parallel image data SD′ in synchronization with the latch signal LT output from the recording head control unit 116, for each piece of the image data SD′ having a number of pixels corresponding to the number of nozzle holes 62, and outputs the latched image data SD′ to the gradation decoder 213.
The gradation decoder 213 decodes the gradation of the pixel data corresponding to each nozzle hole 62 of the recording head 6 included in the image data SD′. The gradation decoder 213 outputs the mask control signal MN (any of MN0 to MN3) corresponding to the decoded gradation, to the level shifter 214 for each pixel data. That is, the number of mask control signals MN output to the level shifter 214 is equal to the number of nozzle holes 62. The level shifter 214 converts the voltage level of the received mask control signal MN and outputs the mask control signal MN to the analog switch 215.
The analog switch 215 has a gate circuit for the piezoelectric element 70 corresponding to each of the plurality of nozzle holes 62 in the recording head 6. Each gate circuit applies a waveform of the common driving waveform signal Vcom to the individual electrode 83 of the piezoelectric element 70 according to the corresponding mask control signal MN. For example, each gate circuit is turned on in synchronization with a rectangular pulse of the mask control signal MN received at the gate input terminal VIN and selectively outputs a portion of the waveform of the common driving waveform signal Vcom as a driving waveform voltage to the individual electrode 83. Thus, the mask control signals MN0 to MN3 are a plurality of selection patterns for selecting at least one of a plurality of waveforms W1, W2, W3, and W4 included in the common driving waveform signal Vcom.
Accordingly, any one of the four voltage waveforms is applied to the individual electrode 83 in accordance with the gradation of the image data SD′ for each pixel. Each gate circuit of the analog switch 215 functions as a switch that selectively supplies at least one of a plurality of waveforms included in the common driving waveform signal Vcom, to the individual electrode 83 of the piezoelectric element 70.
The waveform W3 applied to the individual electrode 83 based on the mask control signal MN0 is used to vibrate the meniscus surface of the nozzle hole 62 without discharging ink from the nozzle hole 62 to prevent drying ((b) in
The waveforms W2 and W4 applied to the individual electrode 83 based on the mask control signal MN2, are used to discharge a second amount (medium droplet) of ink from nozzle hole 62 ((d) of
The dashed line in the waveform of the individual electrode 83 indicates the period during which the gate circuit does not apply a waveform to the individual electrode 83, and the individual electrode 83 is set to the reference voltage of the floating state during the period indicated by the dashed line. During the floating state, the voltage of the individual electrode 83 gradually decreases due to a leakage current flowing through a leakage path. The voltage drop of the individual electrode 83 due to the leakage current will be described in
In
Although
As illustrated in
By setting the mask control signal MN to a low level in the non-discharge control period, the number of times the gate circuit is driven per time unit can be prevented from increasing, and the temperature of the gate circuit can be prevented from rising excessively. Accordingly, the temperature of the recording head 6 can be prevented from rising, and the temperature of the ink in the pressurizing liquid chamber 61 can be prevented from exceeding the upper limit temperature, and the ink discharge control can be performed properly.
On the other hand, as illustrated in
For example, each mask control signal MN changes to a high level after a predetermined time from the start of the non-discharge control period (i.e., the end of the discharge control period). The on-timing of the gate circuit during the non-discharge control period does not depend on the driving cycle but is determined based on the waveform data for generating the waveform of the mask control signal MN. For example, the non-discharge control period of
The operations illustrated in
By applying a reference voltage to the individual electrode 83 during the non-discharge control period, it is possible to prevent the voltage of the individual electrode 83 from decreasing due to a leakage current. Thus, for example, even when a rectangular pulse of the mask control signal MN is applied to the gate circuit during the discharge control period of the driving cycle of the n+1 time (n being an integer of one or more), it is possible to prevent the voltage of the individual electrode 83 from sharply rising to the reference voltage. As a result, it is possible to prevent an abnormal voltage (abnormal pulse) from being applied to the individual electrode 83, and it is possible to prevent ink from being erroneously discharged from the nozzle holes 62 due to an abnormal pulse. That is, it is possible to prevent a malfunction of the liquid discharging apparatus 400, and it is possible to prevent a decrease in the quality of printing on paper or the like by the image forming apparatus 40.
For example, the recording head control unit 116 illustrated in
In order to make the explanation easier to understand, the timing at which the voltage of the individual electrode 83 falls below the allowable limit voltage (allowable voltage) when the gate circuit of the analog switch 215 continues to be turned off is, for example, 18 time units after the beginning of the discharge control period. However, the timing at which the voltage of the individual electrode 83 falls below the allowable limit voltage is not limited to after 18 time units. Here, the allowable limit voltage is a voltage at which there is a possibility that at the beginning of a subsequent discharge control period, the voltage of the individual electrode 83 rises sharply to the reference voltage, thereby generating an abnormal pulse that may cause ink to be erroneously discharged from the nozzle hole 62.
In the example illustrated in
The waveform data for generating the mask control signal MN is common to all driving cycles and is used in all driving cycles. That is, each of the mask control signals MN0 to MN3 (selection patterns) has a pattern length corresponding to the longest driving cycle with inclusion of an on-timing ON in the pattern corresponding to the non-discharge control period.
Thus, when the driving cycle is set to 20 time units or 23 time units, the voltage of the individual electrode 83 can be returned to the reference voltage before reaching the allowable limit voltage, thereby preventing erroneous discharging of ink from the nozzle hole 62 due to an abnormal pulse.
Note that the on-timing ON is set so as to occur a first time period or longer before the start of the discharge control period, in all driving cycles for which the on-timing ON can be set. That is, the recording head control unit 116 sets the timing of applying a reference voltage to the individual electrode 83 of the piezoelectric element 70 when the voltage setting control is performed, to occur a first time period or longer before the start timing of the discharge control period of any of the plurality of driving cycles. In other words, the end timing of the first cycle is set so as to be before the timing when the voltage of the individual electrode 83 would drop below the allowable limit voltage, and to occur a first time period or longer before the start of the discharge control period of a driving cycle that is longer than the first cycle.
For example, the first time period is set to a minimum time interval of transition edges adjacent to each other in two consecutive pulse waveforms generated during the discharge control period. That is, the first time period is the minimum time interval of two consecutive pulse waveforms generated during the discharge control period. In the example illustrated in
The time interval of the two consecutive pulse waveforms generated during the discharge control period is the time margin for allowing ink to be stably discharged from the nozzle hole 62. Accordingly, by allowing the time interval between the on-timing ON and the discharge control period to be longer than or equal to the first time period, it is possible to prevent the ink discharging by the first pulse of the discharge control period from becoming unstable, and it is possible to prevent the quality of printing onto paper or the like by the image forming apparatus 40 from decreasing. Note that if the discharging of ink by a first pulse becomes unstable, the unstable discharging may affect the ink discharging by subsequent pulses, and, therefore, it is important to stabilize the ink discharging by the first pulse.
At the on-timing ON illustrated in
In
The operation waveforms when the driving cycle is longer than the first cycle are similar to those in
On the other hand, by turning on the gate circuit in each non-discharge control period, the number of times the gate circuit is driven per time unit is increased. If the temperature of the recording head rises due to an increase in the number of times the gate circuit is driven, the ink viscosity may decrease and it may be difficult to perform the ink discharge control properly.
In
The operation waveforms when the driving cycle is shorter than the first cycle, are similar to those in
If the gate circuit is not turned on during the non-discharge control period, the voltage of the individual electrode 83 of the piezoelectric element 70 is set to a reference voltage in a floating state, and, therefore, the voltage of the individual electrode 83 gradually decreases due to a leakage current. In this case, when a rectangular pulse of the mask control signal MN is applied to the gate circuit during the next discharge control period, the voltage of the individual electrodes 83 rises sharply to the reference voltage, which may cause an abnormal pulse to be generated. If an abnormal pulse is generated, ink may be erroneously discharged from the nozzle hole 62.
As described in
When a printing operation, in which the number of times the gate circuit is turned on per time unit exceeds the predetermined number of times, continues for a long time, the temperature of the recording head control unit 116 may exceed the upper limit temperature. On the other hand, in the present embodiment, the number of times the gate circuit is turned on per time unit can be reduced compared to
Further, in the present embodiment, when the driving cycle is longer than the first cycle, the gate circuit of the analog switch 215 is turned on during the non-discharge control period, so that the number of times the gate circuit is turned on in one driving cycle is, for example, five times ((c) in
On the other hand, when the driving cycle is longer than the first cycle and the gate circuit of the analog switch 215 is not turned on during the non-discharge control period, the number of times the gate circuit is turned on in one driving cycle is, for example, four times ((d) in
Thus, in the embodiments described above, if the driving cycle is shorter than the first cycle, the gate circuit of the analog switch 215 is not turned on in the non-discharge control period, and, therefore, it is possible to prevent an increase in the number of times the gate circuit is turned on per time unit. Accordingly, it is possible to prevent the temperature of the gate circuit from rising excessively, and it is possible to prevent the temperature of the recording head 6 from rising. Accordingly, it is possible to prevent the temperature of the ink in the pressurizing liquid chamber 61 from exceeding the allowable temperature and to prevent the viscosity from falling below a predetermined value, and therefore the ink discharge control can be performed properly.
Further, if the driving cycle is longer than the first cycle, the gate circuit of the analog switch 215 is turned on in the non-discharge control period, and, therefore, it is possible to prevent the voltage of the individual electrode 83 of the piezoelectric element 70 from decreasing due to a leakage current. Accordingly, even when a rectangular pulse of the mask control signal MN is applied to the gate circuit during the discharge control period after the non-discharge control period, it is possible to prevent the voltage of the individual electrode 83 from sharply rising to the reference voltage. Accordingly, it is possible to prevent an abnormal voltage from being applied to the individual electrode 83, and it is possible to prevent ink from being erroneously discharged from the nozzle hole 62 due to an abnormal voltage.
As a result, it is possible to achieve both the inhibiting of voltage drop of the individual electrode 83 of the piezoelectric element 70 in the non-discharge control period and the preventing of the heat generation of the recording head 6. Further, a malfunction of the liquid discharging apparatus 400 can be prevented, and a decrease in the quality of printing on paper or the like by the image forming apparatus 40 can be prevented.
The waveform of the mask control signal MN (MN0 to MN3) output by the recording head control unit 116 is the same as the embodiment described in
When the driving cycle is shorter than the first cycle, the next discharge control period approaches before the waveform W3 of the non-discharge control period would appear, and, therefore, the operation waveform becomes the same as in
As described above, in the embodiment illustrated in
By shifting the on-periods of the mask control signals MN0 to MN3 in the non-discharge control period from each other, it is possible to prevent multiple gate circuits of the analog switch 215 from being turned on simultaneously, and to reduce the switching noise (power supply noise, etc.) generated by turning on the gate circuit. As a result, the malfunction of the liquid discharging apparatus 400 can be prevented, and the reliability of the image forming apparatus 40 and the image forming system 1 can be prevented from being decreased. By shifting the on-period in units of the mask control signals MN0 to MN3, the switching noise can be reduced without increasing the amount of waveform data held by the recording head control unit 116.
Note that the on-period of the non-discharge control period may be such that at least one mask control signal MN is shifted with respect to other mask control signals MN. For example, the on-period of the non-discharge control period may be shifted for each of two mask control signals MN. Further, the timing of turning off the mask control signal MN may not be shifted during the non-discharge control period.
As described above, in the embodiment illustrated in
For example, for each of the mask control signals MN0 to MN3, the recording head control unit 116 holds a waveform data group including data of four waveforms in which the on-periods in the non-discharge control period are shifted from each other; i.e., there are four waveform data groups respectively corresponding to the mask control signals MN0 to MN3. For example, in the analog switch 215, the gate circuits are divided into four gate circuit groups, each including a predetermined number of gate circuits, and the four waveform data groups respectively correspond to the four gate circuit groups. The recording head control unit 116 outputs a waveform data group corresponding to one of the gate circuit groups, as a mask control signal MN.
In
In other words, the on-periods of the mask control signals MN1 applied to the gate circuits arranged adjacent to each other in the analog switch 215, are sequentially shifted. Accordingly, it is possible to reduce the possibility that mask control signals MN having the same on-timings will be supplied to gate circuits that are adjacent to each other, and this contributes to the reduction of switching noise in the gate circuits.
For example, the on-periods of the other mask control signals MN0, MN2, and MN3 may be the same as the on-periods of the mask control signal MN1, or the on-periods of all of the mask control signals MN0 to MN3 may be slightly shifted from each other. That is, with respect to the on-period of the non-discharge control period, it will suffice if the mask control signal MN corresponding to at least one piezoelectric element 70 is shifted with respect to the other mask control signals MN.
As described above, in the embodiment illustrated in
Further, in the embodiment illustrated in
According to one embodiment of the present invention, the heat generation of the recording head can be prevented while inhibiting a decrease in the voltage of the electrode of the piezoelectric element, during a non-discharge control period.
The liquid discharging apparatus and the image forming system are not limited to the specific embodiments described in the detailed description, and variations and modifications may be made without departing from the spirit and scope of the present invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| JP2018-182693 | Sep 2018 | JP | national |
| Number | Name | Date | Kind |
|---|---|---|---|
| 8845052 | Tamura et al. | Sep 2014 | B2 |
| 20090289975 | Yoshida | Nov 2009 | A1 |
| 20150251414 | Araki | Sep 2015 | A1 |
| 20190202201 | Chikamoto | Jul 2019 | A1 |
| Number | Date | Country |
|---|---|---|
| 2013-014121 | Jan 2013 | JP |
| 2014-028450 | Feb 2014 | JP |
| 2015-174401 | Oct 2015 | JP |
| Entry |
|---|
| U.S. Appl. No. 16/299,267, filed Mar. 12, 2019. |
| Number | Date | Country | |
|---|---|---|---|
| 20200101726 A1 | Apr 2020 | US |
