The present invention relates to a technology for detecting an ejecting condition of ink droplets ejected from a printing head of a printing apparatus.
In the market of inkjet printing apparatuses that can print large-sized printed matters, applications of output matters are diverse, including CAD line drawings, posters, and art works. For this reason, the printing media suitable for the applications also vary from cost-sensitive to performance-sensitive. Furthermore, the amount of ejected ink and the ejection speed may change depending on various factors such as individual differences in the printing apparatus and the printing head, physical properties for each ink color, use situations, environmental influences, and the like.
In particular, when the ink ejection speed changes, the configuration that enables reciprocal printing of the printing head has a difference occurring between the adhesion position of the ink droplets ejected in the forward direction of the printing head and the adhesion position of the ink droplets ejected in the backward direction of the printing head. As a result, the definition of formed images and the reproducibility of thin lines deteriorate, and the overall image quality deteriorates.
Japanese Patent Laid-Open No. 2007-152853 discloses a registration adjusting method including a measurement unit that measures an ejection speed of ink, and appropriately sets ejection timing from a moving speed and an ejection speed of reciprocal printing based on a measurement result.
If the ejection speed of ink can be accurately measured, a registration adjusting method can be provided.
However, in the inkjet type printing apparatus, in addition to the change in ejection speed, there is a case where the flying state of the ink droplets ejected from the head becomes unstable, and the landing on a paper surface is not accurately performed. The known type has a problem of failing to detect image degradation due to an unstable flying state.
The present invention has been made in view of the above-described problems, and provides a printing apparatus that can more accurately land ink on a printing medium.
According to a first aspect of the present invention, there is provided a printing apparatus comprising: a detection unit that is arranged to face an ejecting surface on which a plurality of nozzles of a printing head that ejects liquid droplets are arrayed, and detects an ejecting condition of the liquid droplets; a recovery unit that recovers an ejecting condition of nozzles of the printing head; and a control unit that determines whether to perform or skip inspection of the ejecting condition by the detection unit based on a state of each of the nozzles of the printing head, and controls a nozzle for which the inspection of the ejecting condition is determined to be skipped so as to perform the inspection of the ejecting condition by the detection unit after the recovery unit recovers the ejecting condition of the nozzle.
According to a second aspect of the present invention, there is provided a method for controlling a printing apparatus including a detection unit that is arranged to face an ejecting surface on which a plurality of nozzles of a printing head that ejects liquid droplets are arrayed, and detects an ejecting condition of the liquid droplets, and a recovery unit that recovers an ejecting condition of nozzles of the printing head, the method comprising: determining whether to perform or skip inspection of the ejecting condition by the detection unit based on a state of each of the nozzles of the printing head, and controlling a nozzle for which the inspection of the ejecting condition is determined to be skipped so as to perform the inspection of the ejecting condition by the detection unit after the recovery unit recovers the ejecting condition of the nozzle.
Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.
Hereinafter, embodiments will be described in detail with reference to the attached drawings. Note, the following embodiments are not intended to limit the scope of the claimed invention. Multiple features are described in the embodiments, but limitation is not made to an invention that requires all such features, and multiple such features may be combined as appropriate. Furthermore, in the attached drawings, the same reference numerals are given to the same or similar configurations, and redundant description thereof is omitted.
The printing apparatus 100 illustrated in
The carriage 202 is driven by a carriage motor 208 via a carriage conveyance belt 207. The carriage 202 is caused to perform reciprocal scan in a direction orthogonal to the conveyance direction of the printing paper 203 while acquiring position information by detecting a linear scale 209 provided in a scan direction by an encoder sensor 210 mounted on the carriage 202. Furthermore, by including a lift motor 211 for changing the height of the carriage 202 in stages, it is possible to make the distance between the printing head 201 and the printing paper 203 close to or away from each other. The printing paper 203 is supported by a platen 212 and is conveyed in the conveyance direction by a paper conveyance roller 213. Here, the printing paper 203 will be described with an example of roll paper, but is not limited to this, and for example, cut paper may be used. The width of the printing paper 203 may be configured to correspond to a plurality of paper widths.
The CPU 301 includes a driver unit 306, a sequence control unit 307, an image processing unit 308, a timing control unit 309, and a head control unit 310. The sequence control unit 307 performs overall printing control, more specifically, start and stop of each functional block, conveyance control of printing paper, scan control of the carriage 202, and the like. Each functional block is implemented, for example, by the CPU 301 reading and executing various programs from the memory 303 or the like.
The driver unit 306 outputs each control signal based on a command from the sequence control unit 307, and transmits an input signal from each unit to the sequence control unit 307. The image processing unit 308 performs image processing of performing color separation/conversion on input image data from the host apparatus. The timing control unit 309 transfers the printing data converted and generated by the image processing unit 308 to the head control unit 310 in conjunction with the position of the carriage 202. The timing control unit 309 also controls ejection timing of the printing data based on the distance between the printing head 201 and the printing paper 203 detected by the distance detection sensor 204. Furthermore, the timing control unit 309 also controls output timing of the printing data based on ejection speed information of each ink droplet ejected from the printing head 201 detected by the ejection speed detection sensor 205. The head control unit 310 converts the printing data input from the timing control unit 309 into a head control signal and outputs the head control signal, and also controls the temperature of the printing head 201 based on a command from the sequence control unit 307.
Next, a detection method (inspection method) of an ejecting condition of ink droplets ejected from the printing head 201 in the present embodiment will be described with reference to
The ejection speed detection sensor 205 includes a light-emitting element 401, a light-receiving element 402, and a control circuit board 403. The light-emitting element 401 emits a light flux 404, and the light-receiving element 402 receives the light flux 404 emitted by the light-emitting element 401. The control circuit board 403 detects the amount of the light received by the light-receiving element 402. The control circuit board 403 is provided thereon with a current/voltage conversion circuit that converts a flowing current into a voltage signal, by the amount of light received by the light-receiving element 402, and outputs the voltage signal, and an amplification circuit for the level of the detection signal of ink droplets. Furthermore, in order to remove the influence of saturation of the output and a decrease in S/N due to variation of the detection signal level of ejection of ink droplets due to the influence of disturbance, the control circuit board 403 includes a clamp circuit for holding the level of the signal output from the amplification circuit to a predetermined value (clamp voltage) until immediately before ejection is observed.
These circuits ensure the level of the detection signal for detecting minute changes such as ink droplet ejection. In this configuration, since the amount of light received by the light-receiving element 402 changes when an ink droplet passes through the light flux 404 of the ejection speed detection sensor 205, the ejecting condition of the nozzle that is a detection target can be determined by comparing the level of the output detection signal (output signal) with a predetermined reference voltage.
The ejection speed detection sensor 205 is installed such that the optical axis of the light flux 404 is at the same position in the Z direction as the surface of the platen 212 on the side supporting the printing medium 203. A slit is provided in the vicinity of each of the light-emitting element 401 and the light-receiving element 402 to narrow the incident light flux 404 and improve the S/N ratio. The position of the printing head 201 in the X direction where the ink droplet can be ejected so that the ink droplet passes through the light flux 404 is set as a detectable position.
When the ink droplet is detected in order to detect the ejecting condition of the ink droplet, the sensor/motor control unit 302 controls the carriage motor 208 by a command of the sequence control unit 307 to move the printing head 201 to the detectable position. The cross-sectional area of the light flux 404 in the present embodiment is about 2 mm×2 mm. The parallel light projection area of the ink droplet when the ink droplet passes through the light flux 404 is about 2-3 (mm2).
An ejection orifice array and the light flux 404 are arranged in parallel to each other, and the creepage distance in the height direction (Z direction) is set to from 2 to 10 mm. When the creepage distance between each ejection orifice and the light flux 404 is made close, the passage of the ink droplet can be detected at a position where the light flux 404 is close to the flying distance of the ejected ink droplet, and thus the ejecting condition can also be stably detected. However, when the ejection orifice array and the light flux 404 are close to each other, a diffuse light component emitted from the light-emitting element 401 is reflected by the ejection orifice surface 201a of the printing head 201, and a light amount component received by the light-receiving element 402 is generated. As a result, this light amount component is superimposed on the detection signal as noise with respect to the detection of the ejecting condition, and there is a possibility that good detection can no longer be performed. Therefore, regarding the creepage distance between the light flux 404 of the ejection speed detection sensor 205 and the ejection orifice array of the printing head 201, it is desirable to detect the ejecting condition with more suitable arrangement in consideration of the correlation of them. It is necessary to match the condition for detecting the ejecting condition of the ink droplet by the ejection speed detection sensor 205 with the ejecting condition of the ink droplet onto the printing medium 203 at the time of image formation Therefore, it is desirable that the light flux 404 of the ejection speed detection sensor 205 and the platen 212 supporting the printing medium 203 are arranged at substantially the same height (Z direction).
Next, the configuration for detecting the ejecting condition and non-ejection of ink droplets to be ejected will be described.
Ejection of the ink droplets is started, and the operation by the clamp circuit is released immediately before the ink droplets ejected toward the light flux 404 shield the light flux 404. Thereafter, the detection signal level of the ejection speed detection sensor 205 decreases due to a decrease in the amount of light generated when the ejected ink droplets pass through the light flux 404 of the ejection speed detection sensor 205. The normal ejecting condition is determined by comparing the decrease in the signal level with a reference voltage value defined by the amount of change when the ink droplets shield the light flux 404. As a result, the N-th nozzle that is the detection target is determined to have normally ejected. Here, in order to further increase the reliability of the detection result of the ejecting condition by the ejection speed detection sensor 205, a result of performing the ejection from the N-th nozzle that is the detection target a plurality of times is illustrated.
Next,
In
Similarly to the case of
From
V1=(H2−H1)/(T2−T1)
Similarly to the cases of
From
V2=(H3−H2)/(T3−T2)
Similarly to the cases of
From
V3=(H4−H3)/(T4−T3)
As described above, ejection speed V of the ink droplets corresponding to each distance is calculated based on each distance in which the printing head 201 and the ejection speed detection sensor 205 are separated. The plurality of calculated ejection speeds of the ink droplets are stored as an average value thereof or as a speed corresponding to the distance between the printing head 201 and the printing sheet.
The distance between the printing head 201 and the ejection speed detection sensor 205 can be further separated by the lift motor 211. This makes it possible to measure more separated distances and detection times of the respective ink droplets, and possible to calculate the ejection speed of the ink droplets more accurately. On the other hand, it is possible to reduce the distance in which the printing head 201 and the ejection speed detection sensor 205 are separated by the lift motor 211 and the number of times of changing the distance, and shorten the time required for detection of the ejection speed of ink droplets.
As described above, by providing a lifting and lowering unit for changing the distance from the printing head 201 to the printing paper in a plurality of stages and detecting the ink ejection speed variation in each stage, it becomes possible to detect the ink ejection speed with high accuracy.
Next, monitoring of variation in the ejecting condition of ink droplets will be described. The ejecting condition of ink droplets may change when the ink droplets are ejected from the printing head. On the other hand, since there is no change with ejection of several ink droplets, the ejecting condition may be monitored about once in several pages as a guide. Note that, specifically, by performing the monitoring in a page interval or in a scan interval during printing, it is possible to hardly affect productivity. However, the monitoring performance timing is not limited to this.
First, in step S61, the CPU 301 causes the carriage 202 to scan under the same conditions as in image formation, and causes the carriage to pass over the ejection speed detection sensor 205. The same conditions as in image formation means that the drive of the main body of the printing apparatus 100 and the head drive have the same conditions. The driving of the main body includes a height of the carriage, the driving speed of the carriage, and control. The carriage driving speed includes an acceleration region and a constant speed region. However, most printing is performed in the constant speed region, and therefore it is desirable that ejection monitoring is also performed in the constant speed region. The head drive includes block drive and an ejection pulse width. In order to monitor the change in the landing state of the ejection ink droplets formed on the paper surface, the carriage 202 is driven under the same conditions as the image formation conditions, specifically, under the same conditions as the image formation conditions in terms of the carriage and the paper height and the scanning speed.
The ink droplets ejected from the printing head 201 are separately ejected into main droplets and small ink droplets (hereinafter referred to as satellites) other than the main droplets depending on the ejection conditions. At the time of ejection, the main droplets and the satellites are ejected from the same position, but the landing position on the paper surface may vary depending on a difference in ejection speed. In order to detect a change in the landing position and the landing dot shape on the paper surface, ejection monitoring is performed under the same conditions as those in image formation. The ejection conditions are preferably identical, but do not necessarily need to be the same in order to detect a change.
The ink droplets ejected from the nozzles are different in ejection size and ejection speed between main droplets and satellites. When performing the ejection detection while driving the carriage 202, it becomes possible to separate and detect the main droplets and the satellites. Therefore, by performing the detection while driving the carriage 202, it is possible to detect a change in the ejection size of the main droplets, a change in the ejection speed, a change in the ejection size of the satellites, and a change in the ejection speed.
In step S62, the CPU 301 causes the ink droplets to be ejected so that the ink droplets cross the light flux 404 of the ejection speed detection sensor 205 while causing the carriage 202 to scan under the same conditions as those in image formation.
In step S63, the CPU 301 calculates the ejection speeds of the main droplets and the satellites, and the ink droplet sizes of the main droplets and the satellites from the detection waveforms of the ejection speed detection sensor 205.
When the ink droplets pass through the ejection speed detection sensor 205, the signal at the time of passing changes as described with reference to
This function approximation is not necessarily performed with a normal distribution, and may be a polynomial approximation. Since the main droplets always have a speed equal to or higher than that of the satellites, the waveform at the head on the time axis of the two normal distribution results is the waveform of the main droplets, and the other is the waveform of the satellites.
In step S64, by comparing an initial or predetermined ejecting condition with the current ejecting condition, the CPU 301 determines whether or not the change amount of the ejection speed and the ejection amount is equal to or less than a reference value.
The ejection monitoring is performed with the time of printer adjustment as a start point, specifically, at the time point when registration adjustment (also referred to as landing position adjustment) or density adjustment (referred to as color calibration) is performed. The ejection speed and the ejection amount when the adjustment is performed are detected and recorded in the memory in the printer. Thereafter, the ejection speed and the ejection amount at the start point are compared at the timing detected as the ejection monitoring. The start point is updated at the timing when the registration adjustment or the density adjustment is performed.
In step S64, each of the ejection speed and the ejection amount of the main droplets or the satellites is compared, and when even any one of them changes by a certain amount or more, there is a possibility that the image quality is affected. A reference value at which an image defect is likely to occur is set in advance. When the change amount of the ejection speed and the ejection amount of the main droplets or the satellites is larger than the reference value, the process proceeds to step S65, a detection unallowable flag is turned on and the ejection speed and the ejection amount are stored in the memory in the printer, and the process ends. When it is determined that the change amount is equal to or less than the reference value, the process ends.
When the detection unallowable flag is on after the process of
Supplementary description will be given regarding the operation of causing the carriage 202 to scan under the same conditions as those of the image formation in step S61 of
The ejection speed detection sensor 205 differs from an ink droplet detection sensor that detects non-ejection in terms of the optical system configuration, purpose of implementation, and function, but is preferably used also as the ink droplet detection sensor from the viewpoint of the number of hardware components. Therefore, as one embodiment, the ejection speed detection sensor 205 is used also as the ink droplet detection sensor arranged outside the printing scan region.
On the other hand, the ejection monitoring can be performed during printing operation. In this case, movement to the ink droplet detection sensor arranged outside the printing scan region causes a decrease in the printing throughput. Therefore, a method of using the ejection speed detection sensor 205 also as a preliminary ejection means arranged closest to the printing region may be selected. By arranging the ejection speed detection sensor 205 in a region where the ink passes also at the time of printing, it is possible to perform ejection monitoring without decreasing the print throughput.
Supplementary description will be added regarding the determination of whether or not the change amount is equal to or less than the reference value in step S64 of
The ejection monitoring is intended to detect a change from a state determined to be correct. Start points determined to be correct include a state of initial installation of the printing apparatus 100. Other start points include a state immediately after the head is replaced and a state after the ejection landing position is adjusted. In each state, the ejecting condition is detected, and this value is stored as a predetermined ejecting condition. When the change amount from this predetermined ejecting condition becomes equal to or greater than a certain value, it is determined to be ejecting condition failure.
Next, a method of monitoring the ejecting condition (flying state) of ink droplets at the timing when each nozzle is brought into a state where the ink droplets can be stably ejected will be described.
First, in step S1001, the CPU 301 compares the time since the last ejection with a threshold in an ejecting condition monitoring target nozzle for which the ejecting condition monitoring is executed during printing. If a time exceeding the threshold has not elapsed since the last ejection, the ejecting condition monitoring sequence described with reference to
In S1004, the CPU 301 selects the next ejecting condition monitoring target nozzle.
At this time, in a preset ejecting condition monitoring target nozzle, selection may be started from the head nozzle, or the selection may be performed in descending order of the total number of dots of the nozzle. The threshold to be compared with the time since the last ejection is arbitrarily set depending on the state of the ink, the head, and the like. The preset ejecting condition monitoring target nozzles are set for nozzles of an identical color, but it is arbitrarily performed whether to set all nozzles of the identical color or to set some nozzles.
In step S1005, the CPU 301 confirms that the process of all the nozzles has ended, and further confirms that the page interval has come in step S1006. Here, “page interval” indicates a page interval in a print job, but may be timing when printing ends.
In step S1007, the CPU 301 confirms that recovery processing has been performed in a page interval, and if the recovery processing has not been performed, performs the recovery processing in step S1008.
At this time, the recovery processing performs optimum processing for the configuration of the main body of the printing apparatus 100 such as the ink and the head. Specifically, at least one of a wipe operation of wiping the face surface of the head, a preliminary ejection operation of ejecting a prescribed amount of ink from each nozzle, and a suction operation of sucking the ink (liquid) of the head with a pump is performed.
After the recovery processing is performed, the CPU 301 sequentially determines in step S1009 whether a skip flag is set for the ejecting condition monitoring target nozzle. Then, in step S1010, the ejecting condition monitoring sequence described with reference to
In step S1011, the CPU 301 releases the skip flag for the ejecting condition monitoring target nozzle for which the ejecting condition monitoring sequence has been executed, and selects the ejecting condition monitoring target nozzle for which the next skip flag has been set.
In step S1009, the CPU 301 confirms that the skip flags of all the ejecting condition monitoring target nozzles are released, and the process ends.
As described above, in the present embodiment, the ejecting condition (flying state) of ink droplets is detected at the timing when each nozzle is brought into a state where the ink droplets can be stably ejected. This makes it possible to highly accurately detect that the ejection speed and the ejection amount of the ink droplets have varied.
By monitoring the ejecting condition, it is possible to suppress image failure from occurring due to aging or an unintended change in ejection. As a result, it is possible to perform suitable printing with suppressed image failure.
In the ejecting condition detection during printing, the ejecting condition detection is performed in accordance with the state of the nozzle. Specifically, when there is a nozzle that requires the recovery operation, the ejecting condition is monitored after the recovery operation is performed. This enables detection in a state where the ejecting condition is appropriate. As a result, the ejecting condition can be monitored with high accuracy. When there is a nozzle that requires the recovery operation, the ejecting condition detection can be performed collectively after the recovery, and thus the detection time of the ejecting condition detection can be shortened.
Embodiment(s) of the present invention can also be realized by a computer of a system or apparatus that reads out and executes computer executable instructions (e.g., one or more programs) recorded on a storage medium (which may also be referred to more fully as a ‘non-transitory computer-readable storage medium’) to perform the functions of one or more of the above-described embodiment(s) and/or that includes one or more circuits (e.g., application specific integrated circuit (ASIC)) for performing the functions of one or more of the above-described embodiment(s), and by a method performed by the computer of the system or apparatus by, for example, reading out and executing the computer executable instructions from the storage medium to perform the functions of one or more of the above-described embodiment(s) and/or controlling the one or more circuits to perform the functions of one or more of the above-described embodiment(s). The computer may comprise one or more processors (e.g., central processing unit (CPU), micro processing unit (MPU)) and may include a network of separate computers or separate processors to read out and execute the computer executable instructions. The computer executable instructions may be provided to the computer, for example, from a network or the storage medium. The storage medium may include, for example, one or more of a hard disk, a random-access memory (RAM), a read only memory (ROM), a storage of distributed computing systems, an optical disk (such as a compact disc (CD), digital versatile disc (DVD), or Blu-ray Disc (BD)™), a flash memory device, a memory card, and the like.
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
This application claims the benefit of Japanese Patent Application No. 2022-195013, filed Dec. 6, 2022, which is hereby incorporated by reference herein in its entirety.
Number | Date | Country | Kind |
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2022-195013 | Dec 2022 | JP | national |