JP5973828B2 - Inkjet printer and printing method - Google Patents

Description

  The present invention relates to an inkjet printer and a printing method.

  2. Description of the Related Art Conventionally, a configuration for performing gradation printing (gradation printing) is known for an inkjet printer (see, for example, Patent Document 1). For example, in Patent Document 1, as background art, dots having different sizes can be ejected from a liquid ejection head (inkjet head) so that droplets having different sizes, for example, large droplets, medium droplets, and small droplets can be ejected. The structure which can be formed is described. In addition, for example, in paragraph [0080] of Patent Document 1, as a configuration for forming dots having different sizes, a drive waveform (drive signal) for controlling the discharge of droplets has a size of each size within one printing cycle. It is described that a signal including a pulse for forming a dot is used.

Japanese Patent No. 4347824

  The ink jet printer ejects ink droplets to dot positions that are positions of pixels constituting an image to be printed while moving (scanning) an ink jet head with respect to a medium. During this operation, the time interval (minimum ejection cycle) for ejecting ink droplets to adjacent dot positions in the inkjet scanning direction needs to be at least the cycle of the drive signal. Therefore, in order to print a high resolution image at high speed, it is necessary to shorten the cycle of the drive signal.

  However, for example, when gradation printing is performed by a method as described in Patent Document 1, a drive signal including a pulse corresponding to each size dot is used, so that the cycle of the drive signal becomes long. When the period of the drive signal becomes long, it is necessary to slow down the scanning speed of the inkjet head or reduce the printing resolution in accordance with the length of the drive signal.

  Therefore, when performing gradation printing by the conventional method, it is difficult to perform printing at high speed. On the other hand, when a drive signal with a shorter period is used, there is a risk that gradation expression will be insufficient with a conventionally known method. Accordingly, an object of the present invention is to provide an ink jet printer and a printing method that can solve the above-described problems.

  In order to perform printing at a higher speed than conventional gradation printing, it is conceivable to use a drive signal having a shorter cycle as described above. More specifically, for example, not a drive signal including a pulse corresponding to a plurality of size (diameter) dots (VD: Variable Dot), but only one type of size (diameter) dot (ND: Normal Dot) is supported. It is conceivable to use a drive signal including a pulse to be transmitted. Therefore, the inventors of the present application first conducted intensive research on a preferable configuration in the case of using such a drive signal.

  In general, an inkjet printer is required to be able to perform solid printing in which an area of an ink is filled by forming ink dots side by side. In order to enable high-speed solid printing, it is necessary to be able to form large-sized dots.

  That is, when the dots of ink to be formed are small, there is a possibility that the area cannot be filled only by printing at a normal printing resolution. In this case, in order to perform solid printing, it is necessary to increase the printing resolution at the time of solid printing than at the time of normal printing in order to arrange dots at a narrower interval. However, in this case, the time required for solid printing increases, and the printing speed decreases.

  On the other hand, when the formed ink dots are sufficiently large, the area can be filled only by printing at a normal printing resolution, so that solid printing can be performed at high speed. Therefore, when a drive signal including a pulse corresponding to only one type of dot is used, the size of the ink dot formed in accordance with this drive signal must be sufficiently large in order to perform printing at high speed. is necessary.

  Here, in order to increase the size of the ink dot formed in accordance with the drive signal, for example, a high voltage signal may be used. However, when the drive signal voltage is increased, the durability of the inkjet head may be affected. In addition, usable circuit elements are limited, which may increase the cost. Further, since the time required for the rise and fall of the pulse becomes long, the cycle of the drive signal becomes long. Therefore, it is desired to form larger size dots by a more appropriate method.

  In this regard, the inventor of the present application has further studied diligently and paid attention to the vibration of the meniscus generated at the nozzle position when ink droplets are ejected. Then, it has been found that large-sized dots can be appropriately formed by ejecting the next ink droplet at a timing that resonates with the vibration while the meniscus is vibrating. The present invention conceived by the inventors of the present application based on these findings has the following configuration.

(Configuration 1) An inkjet printer that performs printing by an inkjet method, including an inkjet head that ejects ink droplets from a nozzle to a medium, and an ejection control unit that controls ejection of ink droplets by the inkjet head. A drive signal output unit that outputs a drive signal that causes the ink jet head to eject ink droplets, and a control unit that controls the timing at which the drive signal output unit outputs the drive signal, and the period of vibration of the ink meniscus at the nozzle position inkjet head at the resonance timing at which ejects ink droplets, have a driving timing controller for outputting a drive signal to the driving signal output unit in a state in which resonates with, the timing control unit, other resonant timing In addition, the ink should not resonate with the meniscus vibration period. Even at the non-resonance timing when the jet head ejects ink droplets, it is possible to cause the drive signal output unit to output a drive signal, and select any timing from a plurality of timings including at least the resonance timing and the non-resonance timing, When the drive signal is output to the drive signal output unit at the selected timing and ink droplets are ejected in accordance with the drive signal output at the resonance timing, the ink jet head causes the first size dot to be ejected by the ejected ink droplets. And ejecting ink droplets according to the drive signal output at non-resonant timing, the inkjet head forms dots of a second size smaller than the first size by the ejected ink droplets, The drive timing control unit outputs the same drive signal as the resonance timing at the non-resonance timing. To be output to the radical 19.

  For example, the drive timing control unit causes the drive signal output unit to output a drive signal that causes ink droplets to be ejected at a timing at which the vibrating meniscus moves to the ejection side. The vibrating meniscus of ink is, for example, the meniscus of ink vibrating due to the previous ejection of ink droplets. The timing at which the ink meniscus moves to the ejection side is preferably the timing at which the meniscus first moves to the ejection side after the previous ink droplet ejection.

  When configured in this way, the drive signal is not a drive signal including pulses corresponding to dots of a plurality of sizes, for example, but a drive signal that causes the inkjet head to perform one ejection (for example, only one type of size dots) Drive signals including corresponding pulses). Therefore, with this configuration, for example, high-speed printing can be appropriately performed.

  Further, when configured in this manner, as a result of resonance with meniscus vibration, the ink jet head ejects ink droplets having a larger capacity than when not resonating. As a result, the dots of ink formed are also increased. Therefore, when configured in this way, solid printing can be performed at high speed and appropriately.

  (Configuration 2) In addition to the resonance timing, the timing control unit causes the drive signal output unit to output a drive signal at a non-resonance timing at which the ink jet head ejects ink droplets in a state where the ink jet head does not resonate with respect to the meniscus vibration period. It is possible to select any timing from a plurality of timings including at least resonance timing and non-resonance timing, and output a drive signal to the drive signal output unit at the selected timing and output at the resonance timing When ejecting ink droplets according to the drive signal, the inkjet head forms a first size dot with the ejected ink droplet and ejects the ink droplet according to the drive signal output at non-resonant timing The inkjet head has a second support smaller than the first size due to the ink droplets to be ejected. To form a view of the dot.

  When printing using only one type of dot size, if the dot size is set in consideration of ensuring the printing speed during solid printing, the dot size is fixed to a large dot (large ball). It will be. However, when printing is performed using only large dots, there is a case where sufficient gradation expression cannot be performed in a light portion (highlight portion or the like) which is a region with high brightness.

  In order to solve this problem, for example, it is conceivable to divide dots of a plurality of sizes such as large balls, medium balls, and small balls according to the brightness of the printing area. However, in this case, in the conventional method, as described above, it is necessary to use a drive signal including pulses corresponding to dots of a plurality of sizes, which causes a problem that the printing speed decreases.

  In contrast, the inventor of the present application conducts further research and uses the same drive signal as when forming ink dots at the resonance timing, and outputs the drive signal in a state that does not resonate with the meniscus vibration period. Thus, it has been found that dots having a smaller size than that at the time of ejection at the resonance timing can be formed. That is, instead of using a drive signal including a pulse corresponding to a plurality of size dots, a drive signal including a pulse corresponding only to a first size dot formed by the resonance timing is used as it is, and a non-resonance timing is used. It has been found that a dot having a second size smaller than the first size can be formed by outputting a drive signal.

  When configured in this way, it is not necessary to use a drive signal with a long cycle, and for example, printing can be performed at high speed. In addition to the first size, dots of the second size ink can be formed, so that a better gradation expression can be realized. Therefore, with this configuration, for example, high-speed printing and good gradation expression can be appropriately achieved.

  (Configuration 3) When printing is performed on a solid portion that is a region to be filled by forming ink dots side by side, the drive timing control unit causes the drive signal output unit to output a drive signal at a resonance timing and set in advance. When printing is performed on a highlight portion that is an area brighter than the lightness, the drive timing control unit causes the drive signal output unit to output a drive signal at a non-resonant timing.

  When configured in this manner, the solid portion can be printed at high speed and appropriately by using the large size ink dots of the first size. In addition, the gradation expression of the highlight portion can be improved by using dots of the second size ink having a small size. Therefore, with such a configuration, for example, high-speed printing and good gradation expression can both be appropriately achieved.

  (Configuration 4) When ink droplets are ejected in accordance with a drive signal output at a resonance timing, the inkjet head forms dots having a size in which at least a part of adjacent ink dots arranged in at least one direction are connected. . Adjacent dots may be integrated on the medium, for example. If comprised in this way, solid printing can be performed more appropriately, for example.

  (Configuration 5) The inkjet head ejects ink droplets from the nozzles while moving relative to the medium in a preset scanning direction to a dot position that is a position of each pixel constituting an image to be printed, When the ink jet head continuously ejects ink droplets to a plurality of dot positions continuously arranged in the scanning direction, the drive timing control unit at the resonance timing for at least the second and subsequent ink droplets A drive signal is output to the drive signal output unit. If comprised in this way, the output of the drive signal at a resonance timing can be performed more appropriately.

  (Configuration 6) When the ink jet head continuously ejects ink droplets to a plurality of dot positions continuously arranged in the scanning direction, the drive timing control unit In the meniscus vibration generated after the ejection of the ink droplet, a drive signal for causing the ink droplet to be ejected at the timing when the meniscus first moves to the ejection side is output to the drive signal output unit.

  When configured in this manner, the next ink droplet can be ejected in a state where the amplitude of the meniscus vibration generated by the previous ejection is large. Therefore, with this configuration, for example, it is possible to eject ink droplets with a large capacity more appropriately by ejecting ink droplets at the resonance timing.

  Further, in this case, the ink droplets are ejected at the minimum cycle in which the ink droplets can be ejected at the resonance timing. Therefore, if constituted in this way, it becomes possible to use a drive signal of a shorter cycle, for example. Thereby, the printing speed can be improved more appropriately.

  (Configuration 7) The inkjet head performs printing in a two-gradation operation of forming an ink dot or not forming an ink dot dot at the position of each pixel constituting an image to be printed 2 Value head. If constituted in this way, high-speed printing can be performed appropriately, for example.

  (Configuration 8) A printing method in which printing is performed by an inkjet method, using an inkjet head that ejects ink droplets from a nozzle to a medium, and performing ejection control that controls ejection of ink droplets by the inkjet head. Drive signal output control for outputting a drive signal for ejecting ink droplets to the head, and control of timing for outputting the drive signal, and the inkjet head is in a state of resonating with the oscillation cycle of the ink meniscus at the nozzle position. Drive timing control for outputting a drive signal is performed at a resonance timing that is a timing of ejecting ink droplets. In this way, for example, the same effect as that of Configuration 1 can be obtained.

  According to the present invention, for example, high-speed printing can be appropriately performed.

1 is a diagram illustrating an example of an inkjet printer 10 according to an embodiment of the present invention. FIG. 1A shows an example of the configuration of the inkjet printer 10. FIG. 1B shows an example of a detailed configuration of the control unit 104. It is a figure which shows an example of the timing of the ejection of a drive signal and an ink droplet. FIG. 2A shows an example of a drive signal used in this example. FIG. 2B is a diagram illustrating an example of ink droplet ejection timing. It is a figure which shows an example of the arrangement | sequence of the dot of the ink formed in this example. FIG. 3A shows an example of the arrangement of dots during continuous ejection. FIG. 3B shows an example of dot arrangement at the time of discrete ejection. FIG. 3C shows an example of the configuration of various collective dots. It is a figure explaining in more detail the effect acquired by this example. FIG. 4A is a diagram for explaining a case where printing is performed with a configuration different from the present example, and shows an example of a drive signal in the case of using dots of a plurality of types of sizes. FIG. 4B shows an example of ink dots formed in response to the drive signal.

  Hereinafter, embodiments according to the present invention will be described with reference to the drawings. FIG. 1 shows an example of an inkjet printer 10 according to an embodiment of the present invention. FIG. 1A shows an example of the configuration of the inkjet printer 10.

  In this example, the inkjet printer 10 is a printing apparatus that performs printing on a medium 50 by an inkjet method, and includes a head unit 102, a plurality of rollers 106, a main scanning drive unit 108, and a control unit 104.

  The head part 102 is a part having a plurality of inkjet heads. In this example, the head unit 102 includes inkjet heads 202m, 202c, 202y, and 202k for each color of M (magenta), C (cyan), Y (yellow), and K (black). Color printing is performed by the head.

  The plurality of rollers 106 are rollers that transport the medium 50 in a preset transport direction. In this example, the plurality of rollers 106 is an example of a sub-scanning drive unit, and the head unit 102 is moved in a predetermined sub-scanning direction relative to the medium 50 by conveying the medium 50 in the conveyance direction. Move. The main scanning driving unit 108 is a driving unit configured by a guide rail, a motor, and the like, and performs scanning in the main scanning direction orthogonal to the sub-scanning direction (main scanning, Scan) is performed by the head unit 102.

  The control unit 104 is a part that controls the printing operation by the inkjet printer 10. In this example, the control unit 104 moves the head unit 102 in the main scanning direction and the sub-scanning direction on the medium 50 by controlling the operations of the plurality of rollers 106 and the main scanning driving unit 108, for example. In this example, the control unit 104 controls the head unit 102 via the main scanning drive unit 108 to discharge ink droplets from each inkjet head of the head unit 102 that moves in the main scanning direction. Thus, during main scanning, each inkjet head in the head unit 102 ejects ink droplets at each position on the medium 50 according to the image to be printed while moving in a preset scanning direction.

  Here, the ink jet heads 202m, 202c, 202y, and 202k for each color used in this example will be described in detail. In this example, each of these inkjet heads has a plurality of nozzle rows arranged in the sub-scanning direction. In addition, the inkjet heads are arranged in the main scanning direction, and eject ink droplets from the nozzles constituting the nozzle row while moving at the same speed during the main scanning.

  In this example, the inkjet heads 202m, 202c, 202y, and 202k for each color are binary heads that perform printing in a two-gradation operation. A binary head is, for example, an inkjet that performs printing with a two-gradation operation of forming an ink dot or not forming an ink dot dot at the position of each pixel constituting an image to be printed. Head. The binary head may be an ink jet head (ND head) in which the size of ink dots formed on the medium 50 by ejecting ink droplets onto the medium 50 is one type (Normal Dot). In this case, one type of dot size of ink formed on the medium 50 by ejecting ink droplets corresponds to, for example, a plurality of dots as a drive signal (driving waveform) for ejecting ink droplets to the inkjet head. Instead of a signal including a pulse, a waveform signal for forming dots of one kind of size under a certain discharge condition is used. The relationship between the drive signal used in this example and ink droplet ejection will be described in more detail later.

  FIG. 1B shows an example of a detailed configuration of the control unit 104. In this example, the control unit 104 includes a print image processing unit 112, a scanning control unit 114, and an ejection control unit 116. In addition, each part or a part of function of the control part 104 may be implement | achieved by CPU etc. based on the firmware of the inkjet printer 10, for example. In addition, a part of the configuration of the control unit 104 (for example, a part of the ejection control unit 116) may be provided at a position closer to the head unit 102, for example, in the guide rail.

  The print image processing unit 112 is a processing unit that performs image processing corresponding to the configuration of the inkjet printer 10 on an image to be printed. For example, the print image processing unit 112 receives image data to be printed from an external host PC, and performs necessary image processing in accordance with, for example, a print condition set by the user. In this case, the print image processing unit 112 may further perform image forming processing such as RIP processing in accordance with the configuration of the inkjet heads 202m, 202c, 202y, and 202k in the head unit 102, for example. Alternatively, data after the image forming process may be received from the host PC, and only necessary image processing may be performed thereafter.

  In this example, the print image processing unit 112 performs a process of identifying a highlight portion that is an area brighter than a preset lightness for an image to be printed. For example, in the image forming process, the image process is performed so that the ink dots are not continuously formed in the main scanning direction in the highlight portion. The fact that ink dots are not continuously formed in the main scanning direction means, for example, that ink dots are not formed side by side at adjacent dot positions in the main scanning direction. The dot position is the position of each pixel constituting the image to be printed.

  Note that the print image processing unit 112 may receive data after performing such image processing from the host PC, for example. Further, the ejection of ink droplets to the highlight portion will be described in more detail later.

  The scanning control unit 114 performs scanning control for moving the head unit 102 relative to the medium 50. In this example, the control unit 104 moves the head unit 102 in the main scanning direction and the sub-scanning direction on the medium 50 by controlling the operations of the plurality of rollers 106 and the main scanning driving unit 108, for example.

  The ejection control unit 116 controls ejection of ink droplets by each inkjet head. In this example, the ejection control unit 116 includes a drive signal output unit 118 and a drive timing control unit 120. The drive signal output unit 118 is a signal output unit that outputs a drive signal that causes the inkjet head to eject ink droplets. In this example, the drive signal output unit 118 discharges ink droplets from the nozzles of each inkjet head by outputting a drive signal to each inkjet head of the head unit 102 during main scanning.

  The drive timing control unit 120 controls the output timing of the drive signal by the discharge control unit 116. In this example, the drive timing control unit 120 causes each inkjet head to output a drive signal to the drive signal output unit 118 in accordance with control by the scan control unit 114 during main scanning of the head unit 102. Ink droplets are ejected to each position above.

  At the time of main scanning, the drive timing control unit 120 selects a nozzle that should eject ink droplets from the nozzle row of each inkjet head based on data after image processing by the print image processing unit 112, for example. . Then, the selected nozzle receives the drive signal output from the drive signal output unit 118. Accordingly, the drive timing control unit 120 causes each inkjet head to eject ink droplets at a timing according to the image to be printed.

  Next, the relationship between the drive signal and ink droplet ejection will be described in more detail. FIG. 2 shows an example of the drive signal and ink droplet ejection timing. FIG. 2A shows an example of a drive signal used in this example.

  In the figure, a waveform VCOM indicates a waveform of a drive signal supplied to a nozzle that ejects ink droplets. The drive signal is supplied to the nozzle means, for example, that the drive signal is supplied to a drive element (such as a piezo element or a heating element) that ejects ink droplets from the nozzle. In this example, the waveform VCOM of the drive signal includes a state of a predetermined positive voltage (for example, about 14 to 16 V) and a state of a plurality of valleys 302, 304, and 306 in which the voltage is lower than the positive voltage. It is a signal that contains.

  A valley 302 is a voltage fluctuation portion for causing the ink jet head to eject ink droplets. In this example, in the valley 302, the control unit 104 first reduces the voltage to about 1V or less. As a result, the ink such as the meniscus at the nozzle position is temporarily drawn in the direction opposite to the ejection direction. Thereafter, by returning the voltage of the drive signal to a predetermined positive voltage, ink is pushed out in the ejection direction, and ink droplets are ejected from the nozzle to the medium.

  The valley 304 is a voltage fluctuation portion for preventing the meniscus from drying by adjusting the vibration of the ink. In this example, the control unit 104 temporarily decreases the voltage in the valley 304 by about 3 to 5V. A trough 306 is a voltage fluctuation portion for suppressing ink vibration. In this example, the control unit 104 temporarily reduces the voltage at the valley 306 by about 6 to 9V.

  According to this example, for example, ink droplets can be appropriately ejected by voltage fluctuations corresponding to the valleys 302. Further, by suppressing the vibration of the ink by the voltage fluctuation corresponding to the valley 306 thereafter, for example, the next ejection of the ink droplet can be performed more stably.

  In this example, the depth of the valley 306 does not completely suppress the vibration of the ink, and a constant vibration remains at the timing when the ink droplet is ejected to the position of the next pixel. Further, depending on the magnitude of ink vibration caused by ink droplet ejection, for example, as shown by a broken line in the figure, voltage fluctuation due to the valley 306 may be omitted.

  FIG. 2A shows waveforms of signals MN_LAT, D_LAT, and AN0 to AN3 in addition to the drive signal waveform VCOM. Among these, MN_LAT is a control signal for generating the waveform VCOM of the drive signal. D_LAT is a control signal indicating a period during which the drive signal is supplied.

  AN0 to AN3 are control signals for designating nozzles that should eject ink droplets in the nozzle row. In this example, the control unit 104 designates nozzles to be ejected with ink droplets by AN0 to AN1 according to the image to be printed. Then, by supplying a drive signal to designated nozzles, ink droplets are ejected from these nozzles. Also, ink droplets are not ejected by not supplying drive signals to nozzles that are not specified. In this way, for example, ink droplets can be appropriately ejected to each position on the medium in accordance with the image to be printed.

  FIG. 2B is a diagram illustrating an example of ink droplet ejection timing, and illustrates an example of the relationship between the ink ejection timing and the vibration cycle of the ink meniscus. In the figure, a curve indicated by a solid line shows an example of a state of meniscus vibration that occurs when an ink droplet is ejected once and the next ink droplet is not ejected. A broken line shows an example of a state of meniscus vibration that occurs when an ink droplet is ejected once and then ejected continuously to the positions of pixels that are continuously arranged in the main scanning direction.

  In the case indicated by the solid line, the ink meniscus is once drawn to the side opposite to the ejection direction at the timing when the voltage drops at the valley 302 of the waveform VCOM of the drive signal. Therefore, at this timing, the meniscus displacement greatly moves to the side opposite to the ejection direction. Thereafter, the meniscus moves greatly toward the ejection side at the timing when the voltage rises at the valley 302 of the waveform VCOM of the drive signal. Then, at the timing T1 that is most displaced to the ejection side, the inkjet head ejects ink droplets from the nozzles.

  Further, after the ink droplets are ejected, the meniscus vibrates at a constant cycle while gradually reducing the amplitude for a while. This cycle is a unique cycle determined by, for example, the structure of the nozzle and the ink chamber in the preceding stage of the nozzle. In the illustrated case, the meniscus vibration has a period in which the bottom peak comes at timings T2, T2, and T4.

  On the other hand, in this example, when ink droplets are continuously ejected to the positions of pixels continuously arranged in the main scanning direction, the next ink droplet is ejected while the meniscus vibrates due to the previous ink droplet ejection. It will be. For this reason, the relationship between the meniscus vibration period and the time interval at which ink is ejected becomes important.

  In this example, the drive timing control unit 120 causes the drive signal output unit 118 to output a drive signal at the resonance timing. The resonance timing is, for example, the timing at which the ink jet head ejects ink droplets in a state of resonating with respect to the oscillation cycle of the ink meniscus at the nozzle position. In addition, outputting the drive signal at the resonance timing means, for example, outputting the drive signal so that the ink jet head ejects ink droplets at the timing when the vibrating meniscus moves to the ejection side. Thereby, for example, when the ink jet head continuously ejects ink droplets to a plurality of dot positions continuously arranged in the main scanning direction (hereinafter referred to as continuous ejection), the drive signal for ejecting the second and subsequent ink droplets The drive timing control unit 120 causes the drive signal output unit 118 to output a drive signal at the resonance timing.

  Here, in this example, the timing at which the vibrating ink meniscus moves to the ejection side is the timing at which the meniscus first moves to the ejection side after the previous ink droplet ejection. With this configuration, for example, the next ink droplet can be ejected before the amplitude is reduced by repeating vibration. Thereby, the state of resonance can be realized more appropriately.

  In this case, each of the bottom peak timings T2, T3, and T4 of the vibration indicated by the solid line in the drawing is the second and subsequent ejection timings. Therefore, in the case of the vibration indicated by the broken line in the figure, immediately before these timings, the meniscus is once drawn to the side opposite to the ejection direction in accordance with the voltage fluctuation in the valley 302 of the drive signal. After that, it moves greatly in the discharge direction.

  Further, in this case, the meniscus vibration period generated by the previous ink droplet ejection and the meniscus movement generated by the drive signal valley 302 are in a resonant state, so that the amount of displacement when the meniscus is pulled in , And the amount of displacement at the time of discharge are larger than those at the time of the first discharge corresponding to the case of no resonance. As a result, the volume of the ejected ink droplet is larger than that during the first ejection. In addition, the dots of ink formed are also increased.

  As described above, according to this example, by synchronizing the meniscus vibration and the ink droplet ejection timing to a resonance state, the ink droplet can be ejected in a state where the amplitude of the meniscus vibration is large. In addition, this makes it possible to appropriately eject a large volume of ink droplets.

  Further, in this case, the ink droplets are ejected at the minimum period in which the ink droplets can be ejected at the resonance timing. Therefore, according to this example, it is possible to use a drive signal with a short cycle, for example. Thereby, the printing speed can be improved more appropriately.

  Here, as described above, during continuous ejection, the drive signal output unit 118 ejects the second and subsequent ink droplets in accordance with the drive signal at the resonance timing. However, since the meniscus does not vibrate before the first discharge, the drive signal at the first discharge does not become a drive signal at the resonance timing.

  Therefore, in this example, it can be said that the drive timing control unit 120 can cause the drive signal output unit 118 to output a drive signal at a non-resonant timing in addition to the resonance timing. In this case, the non-resonant timing is a timing at which the ink-jet head ejects ink droplets in a state where it does not resonate with the meniscus vibration period.

  In practice, the non-resonant timing may be a discharge timing in a case other than the second and subsequent discharges during continuous discharge. That is, when an ink droplet is ejected to the immediately preceding dot position during main scanning, the ejection of the ink droplet to the next dot position is automatically ejected at the resonance timing. Further, when an ink droplet is not ejected to the immediately preceding dot position, the ejection of the ink droplet to the next dot position is automatically ejected at a non-resonant timing.

  Therefore, in this example, the drive timing control unit 120 sets the resonance timing and the non-resonance timing for the ejection of the ink droplet to each dot position depending on whether or not the ink droplet is ejected to the immediately preceding dot position. Select either one automatically. In addition, this selection is performed according to the arrangement of dot positions for ejecting ink droplets based on, for example, data received from the print image processing unit 112.

  More specifically, for example, when ink droplets are not ejected to the previous dot position during main scanning, the drive timing control unit 120 selects non-resonant timing. As a result, the drive timing control unit 120 selects the non-resonant timing when performing the first discharge other than during continuous discharge or during continuous discharge. In the case of the second and subsequent discharges during continuous discharge, the drive timing control unit 120 selects the resonance timing. Then, the drive signal output unit 118 causes the drive signal output unit 118 to output a drive signal at the selected timing.

  In addition, as described above, in this example, the volume of the ink droplet ejected in response to the resonance timing drive signal is larger than the volume of the ink droplet ejected in response to the non-resonance timing drive signal. large. Thereby, for example, when ejecting ink droplets according to the drive signal at the resonance timing, the inkjet head forms the first size dots by the ejected ink droplets. Further, when ejecting ink droplets according to the drive signal at the non-resonant timing, the inkjet head forms dots of a second size smaller than the first size by the ejected ink droplets. Therefore, according to this example, it is possible to form a plurality of types of ink dots of the first size and the second size by using one type of drive signal, for example.

  As described above, in this example, the resonance timing and the non-resonance timing are distinguished for the drive signals output at the same timing in actual time according to the arrangement of the ink dots to be formed. However, in the modification of the present invention, for example, the resonance timing and the non-resonance timing may be distinguished by changing the output timing in the actual time. In this case, for example, the drive timing control unit 120 selects a resonance timing or a non-resonance timing for each dot position for ejecting ink droplets based on data received from the print image processing unit 112. Then, the output timing of the drive signal is varied according to the selection.

  Next, the state of the ink dots formed in this example will be described. FIG. 3 shows an example of the arrangement of the ink dots formed in this example. FIG. 3A shows an example of the arrangement of dots during continuous ejection. FIG. 3B shows an example of dot arrangement when ink droplets are not continuously ejected to adjacent dot positions in the main scanning direction (hereinafter referred to as discrete ejection).

  As described with reference to FIG. 2, during the continuous discharge, the first discharge is a discharge at a non-resonant timing. Therefore, in this case, a small size (second size) dot 406 is formed. On the other hand, the second and subsequent discharges are performed at the resonance timing. Therefore, in this case, a dot 402 having a size (first size) larger than the dot 406 at the non-resonant timing is formed. As a result, during continuous ejection, the arrangement of dots in the main scanning direction is configured such that large dots 402 are successively arranged after one small dot 406.

  On the other hand, at the time of discrete ejection, an ink droplet is not necessarily ejected to the immediately preceding dot position. Therefore, in this case, dots 406 having the same size as the first discharge during continuous discharge are formed. As a result, at the time of discrete ejection, the arrangement of dots in the main scanning direction is such that small dots 406 are arranged with a gap 408 of one dot or more.

  Here, in printing by an ink jet printer, high-speed and appropriate printing is performed on both a solid portion that is a region to be filled by forming ink dots side by side and a region highlight portion that is brighter than a preset brightness. It is desirable to do so. When printing on a solid portion, it is preferable to form dots of a larger size so that the necessary density can be secured and the region can be filled at high speed.

  On the other hand, in this example, a dot having a large size can be appropriately formed by using the dot 402 formed by the drive signal at the resonance timing. For example, the dot 402 may be a dot having a size connected to at least a part of the dots arranged adjacent to each other in the main scanning direction. Further, the adjacent dots 402 may be spread and integrated on the medium, for example. With such a configuration, according to this example, it is possible to perform printing of the solid portion at high speed and appropriately.

  On the other hand, when printing is performed on the highlight portion, it is preferable to form dots having a size smaller than at least a certain size in order to realize sufficient gradation expression. Therefore, when a large dot preferable for printing a solid part is used, there is a possibility that it is difficult to express a good gradation in a highlight part.

  On the other hand, in this example, a non-resonant dot 406 having a smaller size can be used as a dot used when printing a highlight portion. Therefore, according to the present example, it is possible to realize good gradation expression in the highlight portion. In addition, this makes it possible to perform high-speed and appropriate printing even for the highlight portion.

  As described above, according to the present example, high-speed and appropriate printing can be performed on both the solid part and the highlight part. Further, since dots 402 and 406 having different sizes can be used, high-speed and appropriate printing can be performed even in a halftone area other than the solid part and the highlight part. Therefore, according to this example, for example, high-speed printing and good gradation expression can be appropriately achieved.

  Further, in this example, for example, by using the dots 402 having a size that blurs and integrates with adjacent dots on the medium, it is possible to form collective dots of various sizes. FIG. 3C shows an example of the configuration of various collective dots.

  In the case of using the dot 402 of a size that bleeds and integrates with adjacent dots on the medium, according to this example, for example, as shown in the figure, one small dot 406, zero, one, Alternatively, by combining with a plurality of large dots 402, collective dots of various sizes can be formed. In addition, this makes it possible to express more various gradations. Therefore, with this configuration, for example, better gradation expression can be appropriately realized.

  FIG. 4 is a diagram for explaining the effect obtained by this example in more detail. FIG. 4A is a diagram for explaining a case where printing is performed with a configuration different from the present example, and shows an example of a drive signal in the case of using dots of a plurality of types of sizes. In FIG. 4 (a), a signal with the same label as in FIG. 2 (a) is a signal used for the same purpose as the signal with the same label in FIG. 2 (a). FIG. 4B shows an example of ink dots formed in response to the drive signal.

  In a configuration different from the example described with reference to FIGS. 1 to 3, for example, a plurality of dots 404S (small balls), 404M (medium balls), 404L (large balls) shown in FIG. When trying to divide the size dots according to the brightness of the print area, it is conceivable to use a drive signal (hereinafter referred to as a multi-valued drive signal) as shown in FIG. This multi-valued drive signal is a signal composed of a plurality of pulses respectively corresponding to dots of each size.

  More specifically, for example, the waveform VCOM of the multilevel drive signal is a signal including a predetermined positive voltage state and a plurality of valleys 308 to 322 in which the voltage is lower than the positive voltage. is there. Of these valleys, valleys 310, 314, and 320 are voltage fluctuations corresponding to the discharge of one ink droplet, and are the same as the valley 302 in the drive signal shown in FIG. Ink droplets are ejected from the nozzle to the medium. The other valleys 308, 312, 314, 316, and 322 are voltage fluctuations for controlling ink vibration, for example, similar to the valleys 304 and 306 in the drive signal shown in FIG.

  With the above configuration, when a multi-value drive signal is used, ink droplets can be ejected up to three times with respect to one cycle of the drive signal. In addition, by selecting the nozzles AN0 to AN1 that perform actual ejection for each ejection time, it is possible to form ink dots of various sizes by varying the number of ejection times of each nozzle. .

  For example, small dots 404 </ b> S are formed by causing each nozzle to perform only the first discharge corresponding to the valley 310. Further, by causing only the third discharge corresponding to the valley 320 to be performed, the medium-sized dots 404M are formed. Further, only the first and second discharges corresponding to the valley 310 and the valley 314 are performed to form a large-sized dot 404L.

  However, in order to perform printing at a predetermined resolution during the main scanning of the printing operation, it is necessary to eject ink droplets onto the medium at pixel intervals corresponding to the resolution. Therefore, it is necessary to move the inkjet head during main scanning at a speed that allows one cycle of the drive signal to be accommodated while moving the pixel interval according to the resolution.

  On the other hand, the cycle of the multi-value drive signal becomes longer than the cycle of the drive signal shown in FIG. 2A (hereinafter referred to as the drive signal in FIG. 2) as a result of corresponding to a plurality of ejections. . For example, the period of the drive signal in FIG. 2 is a period corresponding to a frequency of about 45 kHz, and is about 22 μs (for example, about 18 to 25 μs). The cycle of the multi-valued drive signal is a cycle corresponding to a frequency of about 15 kHz, about 67 μs (for example, about 60 to 75 μs), and about 3 times the cycle of the drive signal in FIG.

  Therefore, when printing at the same resolution, if a multi-valued drive signal is used, the moving speed of the inkjet head during main scanning is reduced to about 1/3 or less compared to the case of using the drive signal of FIG. There is a need. As a result, when the multi-valued drive signal is used, the printing speed is reduced as compared with the case of using the drive signal of FIG. As described above, when a multi-valued drive signal is used, good gradation expression can be realized, but the printing speed is lowered. Therefore, it is difficult to achieve both high-speed printing and good gradation expression.

  On the other hand, as described with reference to FIGS. 1 to 3, in this example, by ejecting ink droplets at the resonance timing and the non-resonance timing, the same drive signal causes a small dot. 406 and a large dot 402 (see FIG. 3) can be formed. In other words, according to this example, it is possible to perform ternary printing (no dots / small dots / large dots) by a drive signal with a short cycle that is originally a binary drive signal.

  In this case, since it is not necessary to use a drive signal with a long cycle, printing can be performed at high speed. Therefore, according to this example, for example, high-speed printing and good gradation expression can be appropriately achieved.

  Note that, in the case of printing with a configuration different from the present example, in order to realize good gradation expression, for example, it is conceivable to use dark ink and light ink (light ink) for the same color. However, in this case, there is a problem that the management and operation work of the ink jet printer becomes complicated due to an increase in types of ink. On the other hand, according to this example, it is possible to realize good gradation expression without using inks of the same color and different densities, for example. Therefore, according to this example, for example, high-speed printing and good gradation expression can be more appropriately achieved.

  As mentioned above, although this invention was demonstrated using embodiment, the technical scope of this invention is not limited to the range as described in the said embodiment. It will be apparent to those skilled in the art that various modifications or improvements can be added to the above embodiment. It is apparent from the description of the scope of claims that embodiments with such changes or improvements can be included in the technical scope of the present invention.

  The present invention can be suitably used for an inkjet printer, for example.

DESCRIPTION OF SYMBOLS 10 ... Inkjet printer, 50 ... Medium, 102 ... Head part, 104 ... Control part, 106 ... Roller, 108 ... Main scanning drive part, 112 ... Print image processing part , 114... Scanning control unit, 116... Ejection control unit, 118... Drive signal output unit, 120... Drive timing control unit, 202 m, 202 c, 202 y, 202 k. .. Valley, 304 ... Valley, 306 ... Valley, 308 ... Valley, 310 ... Valley, 312 ... Valley, 314 ... Valley, 316 ... Valley, 318 ... Valley, 320 ... Valley, 322 ... Valley, 402 ... Dot, 404S, 404M, 404L ... Dot, 406 ... Dot, 408 ... Gap

Claims (8)

An inkjet printer that performs printing by an inkjet method,
An inkjet head that ejects ink droplets from a nozzle to a medium;
An ejection controller that controls ejection of ink droplets by the inkjet head,
The discharge controller is
A drive signal output unit for outputting a drive signal for causing the inkjet head to eject ink droplets;
The control unit that controls the timing at which the drive signal output unit outputs the drive signal, and the timing at which the inkjet head ejects ink droplets in a state of resonating with respect to the oscillation cycle of the ink meniscus at the nozzle position. the resonance timing is, possess a drive timing control unit for outputting the driving signal to the driving signal output unit,
In addition to the resonance timing, the timing control unit outputs the drive signal to the drive signal output unit at a non-resonance timing at which the inkjet head ejects ink droplets in a state where the ink jet head does not resonate with respect to the meniscus vibration period. It is possible to output, by selecting any timing from a plurality of timings including at least the resonance timing and the non-resonance timing, at the selected timing, to output the drive signal to the drive signal output unit,
When ejecting ink droplets according to the drive signal output at the resonance timing, the inkjet head forms dots of a first size with the ejected ink droplets,
When ejecting ink droplets according to the drive signal output at the non-resonant timing, the inkjet head forms dots of a second size smaller than the first size by the ejected ink droplets,
The drive timing control unit causes the drive signal output unit to output the same drive signal as the resonance timing to the drive signal output unit at the non-resonance timing .   The inkjet head ejects ink droplets from the nozzles while moving relative to the medium in a preset scanning direction to a dot position that is a position of each pixel constituting an image to be printed,
  When the operation in which the inkjet head continuously ejects ink droplets to a plurality of dot positions continuously arranged in the scanning direction is defined as continuous ejection,
  The resonance timing is a discharge timing after the second time during the continuous discharge,
  The inkjet printer according to claim 1, wherein the non-resonant timing is an ejection timing in a case other than the second and subsequent ejections during the continuous ejection. When printing on a solid portion that is a region to be filled by forming ink dots side by side, the drive timing control unit causes the drive signal output unit to output the drive signal at the resonance timing,
When performing printing on a highlight portion that is brighter than a preset brightness, the drive timing control unit causes the drive signal output unit to output the drive signal at the non-resonant timing. An ink jet printer according to claim 1 or 2 . When ejecting ink droplets according to the drive signal output at the resonance timing, the inkjet head forms dots having a size in which at least a part of ink dots arranged adjacent to each other in at least one direction are connected. the ink jet printer according to claim 1, wherein the. The inkjet head ejects ink droplets from the nozzles while moving relative to the medium in a preset scanning direction to a dot position that is a position of each pixel constituting an image to be printed,
When the ink jet head continuously ejects ink droplets to a plurality of dot positions continuously arranged in the scanning direction, the drive timing control unit is configured to eject at least the second and subsequent ink droplets. 5. The inkjet printer according to claim 1, wherein the drive signal output unit outputs the drive signal at the resonance timing. 6.   When the inkjet head ejects ink droplets continuously to a plurality of dot positions lined up continuously in the scanning direction, the drive timing control unit performs the previous operation on the drive signal for ejecting ink droplets for the second and subsequent times. 6. The drive signal output unit outputs the drive signal that causes the ink droplets to be ejected at the timing when the meniscus first moves to the ejection side in the vibration of the meniscus that occurs after the ejection of the ink droplets. The inkjet printer as described. When printing on a solid portion that is a region to be filled by forming ink dots side by side, the drive timing control unit causes the drive signal output unit to output the drive signal at the resonance timing,
When performing printing on a highlight portion that is a brighter area than a preset brightness, the drive timing control unit causes the drive signal output unit to output the drive signal at the non-resonant timing,
The ink-jet head is a binary head that performs printing with a two-gradation operation of forming an ink dot or not forming an ink dot dot at the position of each pixel constituting an image to be printed. Oh it is,
The dot of the second size formed at the non-resonance timing is formed so as to be discrete from the dot of the first size formed at the resonance timing. The inkjet printer as described. A printing method for performing printing by an inkjet method,
Using an inkjet head that ejects ink droplets from the nozzle to the medium,
Perform discharge control to control the discharge of ink droplets by the inkjet head,
In the discharge control,
Drive signal output control for outputting a drive signal for causing the ink jet head to eject ink droplets;
The timing of outputting the drive signal is control of the drive signal at a resonance timing that is a timing at which the inkjet head ejects ink droplets in a state of resonating with a period of vibration of the ink meniscus at the nozzle position. There line and a drive timing control for outputting,
In the drive timing control, in addition to the resonance timing, it is possible to output the drive signal at a non-resonant timing at which the inkjet head ejects ink droplets in a state where the ink jet head does not resonate with respect to the meniscus vibration period. Yes, at least one of a plurality of timings including the resonance timing and the non-resonance timing is selected, and at the selected timing, the drive signal is output in the drive signal output control,
When ejecting ink droplets according to the drive signal output at the resonance timing, the inkjet head forms dots of a first size with the ejected ink droplets,
When ejecting ink droplets according to the drive signal output at the non-resonant timing, the inkjet head forms dots of a second size smaller than the first size by the ejected ink droplets,
In the driving timing control, the same driving signal as the resonance timing is output in the driving signal output control at the non-resonance timing .

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