JP4385843B2 - Electrostatic inkjet head driving method and inkjet printer - Google Patents

Description

  In the present invention, an ink pressure fluctuation is generated by applying a driving voltage pulse between the diaphragm electrode and the fixed electrode to vibrate the diaphragm electrode, and ink droplets are ejected from ink nozzles using the ink pressure fluctuation. The present invention relates to a method for driving an electrostatic inkjet head to be ejected and an inkjet printer. More specifically, an electrostatic ink jet head driving method and ink jet capable of performing multi-shot / pixel printing in which one pixel printing is performed by discharging ink droplets a plurality of times at high speed while maintaining excellent print quality. It relates to printers.

  As an inkjet head of an inkjet printer, a static actuator provided with an electrostatic actuator that discharges ink droplets from ink nozzles communicating with an ink chamber by changing the volume of an ink chamber that stores ink using electrostatic force. An electric inkjet head is known. The electrostatic actuator includes a diaphragm electrode that forms a part of the ink chamber and a fixed electrode that is disposed opposite to the diaphragm electrode. When a drive voltage pulse is applied between these electrodes, the diaphragm electrode is fixed to the fixed electrode. When the application of the drive voltage pulse is released, the diaphragm electrode is released from the fixed electrode and elastically returns. The ink pressure in the ink chamber fluctuates due to the vibration of the diaphragm electrode, and ink droplets are ejected from the ink nozzles communicating with the ink chamber in the process where the diaphragm electrode is released from the fixed electrode and elastically returns.

  Here, in the case of multi-shot / pixel printing in which one-pixel printing is performed by continuously ejecting ink droplets, particularly when such multi-shot / pixel printing is performed at a high drive frequency (high speed), the ink pressure The ink ejection characteristics at the time of each ejection change when ink droplets are ejected continuously under the influence of the residual vibration. That is, the pressure vibration that ejects ink droplets is the superposition of the pressure vibration caused by driving the diaphragm electrode and the residual vibration after ink droplet ejection, and the diaphragm electrode is attracted to the fixed electrode due to the residual vibration. The displacement state of the diaphragm electrode at the time when the operation to start is changed. As a result, the ink ejection characteristics vary greatly. Such fluctuations become more prominent as the amplitude of the residual vibration is larger, and the print quality may be greatly deteriorated.

  The residual vibration form of the ink pressure mainly depends on the natural vibration when the diaphragm electrode is opened from the fixed electrode. This natural vibration has a predetermined variation for each electrostatic ink jet head due to a manufacturing error of the electrostatic ink jet head.

Therefore, in the prior art, when printing for one pixel is performed by continuous ink droplet ejection, the driving interval from when the second driving voltage pulse is applied until the next driving voltage pulse is applied. Is proposed based on the natural vibration period of the electrostatic inkjet head. Further, a method for determining the pulse width of the drive voltage pulse based on the natural vibration period has been proposed. For example, it is disclosed in the following patent document.
JP 2002-67358 A

  Here, while an improvement in the printing speed of an ink jet printer is required, an even higher driving frequency is required for driving an electrostatic ink jet head. In order to increase the driving frequency, it is necessary to increase the natural frequency of the pressure fluctuation in the ink chamber of the electrostatic ink jet head. However, when the natural frequency is increased, the vibration waveform becomes steep, so that a range of driving conditions such as applying a driving voltage pulse at an appropriate timing according to the ink pressure fluctuation is narrowed. In this case, if there are variations in the natural frequency for each electrostatic ink jet head, it becomes more difficult to set appropriate driving conditions.

  If the driving conditions are not appropriate, when one-pixel printing is performed by ejecting a plurality of ink droplets, the ejection speed of the subsequent ink droplets is reduced and the ejection mass is reduced. As a result, the landing positions of the ink droplets on the recording paper are shifted, and a sufficient ink discharge amount necessary for one-pixel printing cannot be secured, so that the printing quality is greatly deteriorated.

  In view of these points, an object of the present invention is to increase the speed of multi-shot / pixel printing while maintaining the ejection characteristics of each ink droplet well without being affected by residual ink vibration. An electrostatic ink jet head driving method that can be performed, and an ink jet printer that drives the electrostatic ink jet head by the method are proposed.

  In order to solve the above-described problems, the driving method of the electrostatic ink jet head of the present invention includes: applying a driving voltage pulse between the diaphragm electrode and the fixed electrode opposed to each other at regular intervals, and between them Ink pressure fluctuation is generated by vibrating the diaphragm electrode by the generated electrostatic force, and ink droplets are ejected from the ink nozzle using the ink pressure fluctuation; one pixel printing is performed at most n times (n is (Integer of 2 or more) is performed by ejecting continuous ink droplets; each pulse interval of the first to nth drive voltage pulses applied for ejecting each ink droplet is determined by ink droplet ejection. It is characterized by being set individually based on the residual vibration waveform of the diaphragm electrode later.

  In the present invention, each pulse interval of each drive voltage pulse is individually set based on the residual vibration waveform of the diaphragm electrode. Therefore, the diaphragm electrode in which the residual vibration remains can be driven at an appropriate timing by each of the second to nth drive voltage pulses. As a result, it is possible to satisfactorily maintain the vibration state of the diaphragm electrode by the second to nth drive voltage pulses without being adversely affected by the residual vibration. In this way, each of the second to nth ink droplets is ejected with a sufficient ejection mass and ejection speed, so that it is possible to maintain good print quality even in high-speed printing.

  In order to realize such a printing operation, the diaphragm electrode at the application start time (rising time) of each of the second to n-th drive voltage pulses, that is, the drive start timing at which the diaphragm electrode suction operation starts. The pulse intervals of the first to n-th drive voltage pulses may be set so that the displacement positions are the same.

  In particular, the displacement position of the diaphragm electrode at the start of application of each of the second to nth drive voltage pulses is the same as the displacement position of the diaphragm electrode at the start of application of the first drive voltage pulse. Thus, it is desirable to set each pulse interval of the first to nth drive voltage pulses.

  That is, the displacement position due to the residual vibration of the diaphragm electrode at the start of application of the drive voltage pulse is set to be a neutral position of zero displacement immediately before the diaphragm electrode starts displacement toward the fixed electrode. It is desirable to do.

  Further, in this way, when the application of the drive voltage pulse is started when the diaphragm electrode is in the neutral position, the residual vibration of the diaphragm electrode included between the first to nth drive voltage pulses. When the number of peaks of the waveform is N (N is a positive integer), from the last nth drive voltage pulse in one pixel printing to the first drive voltage pulse for the next one pixel printing In addition, it is desirable to set the pulse interval of the nth to first driving voltage pulses so that (N + α) peaks of the residual vibration waveform of the diaphragm electrode are included (α is a positive integer). .

  Here, the residual vibration waveform of the diaphragm electrode of the electrostatic ink-jet head has a solid difference due to a manufacturing error or the like. Therefore, at the time before shipment, etc., the residual vibration waveform of the diaphragm electrode of each electrostatic ink-jet head, generally the residual frequency or the residual vibration frequency, is measured or calculated, and the static value is calculated based on the measured value or the calculated value. It is desirable to determine each pulse interval of the first to nth drive voltage pulses of the electric ink jet head.

  Further, the residual frequency or residual vibration period is divided into a plurality of groups for each predetermined range, and a pulse interval of the drive voltage pulse is assigned in advance to each group, and the measured or calculated residual frequency or residual vibration period is determined. The pulse intervals of the drive voltage pulses assigned to the included group may be adopted as the pulse intervals of the first to nth drive voltage pulses in the electrostatic ink jet head.

  Next, the present invention relates to an ink jet printer provided with an electrostatic ink jet head, and is characterized in that the electrostatic ink jet head is driven by the above driving method.

  As described above, according to the driving method of the electrostatic ink jet head of the present invention, the pulse intervals of the first to nth driving voltage pulses applied for one-pixel printing are determined after ink droplet discharge. Each is set individually based on the residual vibration waveform of the diaphragm electrode. Therefore, the diaphragm electrode that is oscillating residually can be driven at an appropriate timing by each of the second to nth driving voltage pulses. As a result, it is possible to satisfactorily maintain the vibration state of the diaphragm electrode by the second to nth drive voltage pulses without being adversely affected by the residual vibration. Therefore, according to the present invention, each of the second to nth ink droplets can be ejected with a sufficient ejection mass and ejection speed, and in particular, the print quality can be maintained well even in high-speed printing. Is possible.

  Therefore, according to the inkjet printer of the present invention, multi-shot / pixel printing can be performed with high quality and high speed.

  Hereinafter, an embodiment of an inkjet printer including an electrostatic inkjet head to which the present invention is applied will be described with reference to the drawings.

(Overall configuration of inkjet printer)
FIG. 1 is a schematic configuration diagram showing an ink jet printer provided with an electrostatic ink jet head according to the present embodiment.

  The ink jet printer 100 according to the present embodiment includes a platen 103 that conveys the recording paper 102 in the main scanning direction Y, an ink jet head 110 that faces the ink nozzle surface of the platen 103, and the ink jet head 110. A carriage 105 for reciprocating in the sub-scanning direction X and an ink tank 106 for supplying ink to each ink nozzle of the inkjet head 110 are provided. A nozzle cap 107 is disposed at a position away from the platen 103 in the sub-scanning direction X, and the nozzle cap 107 communicates with the waste ink collection unit 109 via the ink pump 108.

(Electrostatic inkjet head)
FIG. 2 is a schematic configuration diagram showing the electrostatic inkjet head 110. The electrostatic ink jet head 110 is configured by laminating a cavity substrate 112 made of a semiconductor, a nozzle substrate 113 also made of a semiconductor, and an electrode substrate 114 made of glass. A plurality of ink nozzles 115 are formed on the nozzle substrate 113. An independent ink chamber 116 communicating with each ink nozzle 115 is defined between the nozzle substrate 113 and the cavity substrate 112, and each ink chamber 116 has a single common ink chamber 118 via a thin ink orifice 117. Communicating with Ink is supplied to the common ink chamber 118 from the outside via an ink supply path (not shown).

  A diaphragm electrode 119 that can vibrate in the out-of-plane direction is formed on the bottom wall portion of each ink chamber 116, and each diaphragm electrode 119 functions as a common electrode. Concave portions 120 are respectively formed on the surface portions of the electrode substrate 114 facing the respective diaphragm electrodes 119, and individual electrodes 121 (facing the diaphragm electrodes 119 at predetermined intervals on the bottom surface of the respective concave portions 120. (Fixed electrode) is formed. Each diaphragm electrode 119 and the individual electrode 121 facing each other constitute an electrostatic actuator.

  The diaphragm electrode 119 is vibrated using an electrostatic force generated by applying a driving voltage pulse to the electrostatic actuator. Due to the vibration of the diaphragm electrode 119, the volume of the ink chamber 116 is increased or decreased. As a result, the ink droplet 122 is discharged from the ink nozzle 115 communicating with the ink chamber 116 based on the fluctuation of the ink pressure generated in the ink chamber 116. Discharge.

  The electrostatic ink jet head 110 of this example includes, for example, 64 ink nozzles 115 formed in a row on a nozzle substrate 113, and ink droplets are selectively ejected from these 64 ink nozzles 115. Thus, it is possible to print a desired character or image.

  The illustrated electrostatic inkjet head 110 is a face eject type that ejects ink droplets from the ink nozzles provided on the upper surface of the nozzle substrate 113. However, the electrostatic inkjet head to be controlled in the present invention is An edge eject type in which ink droplets are ejected from an ink nozzle provided at an end of the substrate may be used.

(Inkjet printer control system)
FIG. 3 is a schematic block diagram illustrating a control system of the inkjet printer 100. With reference to this figure, the control system of the inkjet printer 100 provided with the electrostatic inkjet head 110 is demonstrated. The ink jet printer 100 according to the present embodiment has an ink jet head drive control device 1 for driving and controlling the electrostatic ink jet head 110, and this ink jet head drive control device 1 is configured around a CPU 2a. Inkjet head controller 2 is provided. Print information is supplied to the CPU 2a from the external device 3 via the bus 3a, and a ROM 4a, a RAM 4b and a character generator 4c are connected via the internal bus 2b.

  The inkjet head control unit 2 executes a control program stored in the ROM 4a using the storage area in the RAM 4b as a work area, and based on the character information generated from the character generator 4c, a control signal for driving the inkjet head Is generated. The control signal becomes a drive control signal corresponding to the print information via the logic gate array 5 and the drive pulse generation circuit 6 and is supplied to the head driver IC 9 formed on the head substrate 8 via the connector 7. . The head driver IC 9 is also supplied with a drive voltage pulse signal V3 for printing, a control signal LP, a polarity inversion control signal REV, and the like.

  In the head driver IC 9, based on the supplied signals and the drive voltage Vp supplied from the power supply circuit 10, drive voltage pulses to be applied to the diaphragm electrodes 119 of the electrostatic ink jet head 110, that is, the common electrode, are applied. Drive voltage pulses output from the common output terminal COM and to be applied to the individual electrodes 121 corresponding to the ink nozzles 115 are output from the number of individual output terminals SEG corresponding to the individual electrodes 121. A potential difference between the output of the common output terminal COM and the output of the individual output terminal SEG is applied between each diaphragm electrode 119 corresponding to each ink nozzle 115 and the individual electrode 121 facing each other. A driving potential difference waveform in a designated direction is given during driving (when ink droplets are ejected), and no driving potential difference is given when not driving.

  FIG. 4 is a schematic block diagram showing an example of the internal configuration of the head driver IC 9. The head driver IC 9 is a CMOS 64-bit output high withstand voltage driver which operates by being supplied with a high voltage drive voltage Vp and a logic circuit drive voltage Vcc from the power supply circuit 10. The head driver IC 9 applies one of the drive voltage pulse and the GND potential between the counter electrodes corresponding to each ink nozzle 115 of the inkjet head 110 in accordance with the supplied drive control signal.

  Number 91 in the head driver IC 9 indicates a 64-bit shift register. The shift register 91 shifts up the data of the 64-bit length DI signal input transmitted from the logic gate array 5 as serial data by the XSCL pulse signal input, which is a basic clock pulse synchronized with the DI signal. This is a static shift register stored in this register. The DI signal is a control signal indicating selection information for selecting each of the 64 ink nozzles by ON / OFF, and this signal is transmitted as serial data.

  A 64-bit latch circuit 92 latches 64-bit data stored in the shift register 91 with a latch pulse LP, stores the data, and outputs the stored data to the 64-bit inversion circuit 93 as a signal. It is a tea clutch. In the latch circuit 92, the DI signal of the serial data is converted into a 64-bit parallel signal for outputting 64 segments for driving each ink nozzle.

  The inverting circuit 93 outputs an exclusive OR of the signal input from the latch circuit 92 and the REV signal to the level shifter 94. The level shifter 94 is a level interface circuit that converts the voltage level of the signal from the inverting circuit 93 from a logic system voltage level (5 V level or 3.3 V level) to a head drive system voltage level (0 V to 45 V level).

  The SEG driver 95 is a 64 channel transmission gate output, and outputs either a drive voltage pulse input or a GND input to the segment outputs SEG1 to SEG64 according to the input of the level shifter 94. The COM driver outputs either a driving voltage pulse input or a GND input to the COM in response to the REV input.

  The XSCL, DI, LP, and REV signals are logic system voltage level signals that are transmitted from the logic gate array 5 to the head driver IC 9.

  By configuring the head driver IC 9 in this manner, even when the number of segments to be driven (number of nozzles) increases, the drive voltage pulse to be driven by each ink nozzle of the head and the GND are easily switched, and a positive polarity described later. Reverse alternating driving can be easily realized.

(Printing operation)
In the ink jet head drive control apparatus 1 configured as described above, the electrostatic ink jet head 110 can be driven and controlled so that one print pixel is formed by discharging a plurality of continuous ink droplets. . For example, control is performed so that one pixel is printed by ejecting ink droplets up to three times. It is also possible to control the gradation of each pixel by changing the number of ink droplet ejections in one pixel printing period.

  FIG. 5 shows a timing chart when a print mode (3 shots / pixel mode) in which one pixel is formed by discharging ink droplets up to three times by a print mode command signal from the external device 3 is designated. is there. In the figure, V3 is a drive voltage pulse signal for printing supplied from the drive pulse generation circuit 6 of the inkjet head controller 2 to the head driver IC 9. LP and REV are control signals (latch pulses) and polarity inversion control signals supplied from the logic gate array 5 of the inkjet head control unit 2 to the head driver IC 9 as described above. The driver COM output is the output of the common terminal COM, and the driver SEG output is the output of each individual terminal SEG. The COM-SEG potential difference is a potential difference (nozzle drive voltage waveform) generated between the common electrode (diaphragm electrode 119) and the individual electrode 121. Note that a one-pixel printing period is defined by the control signal LP, and control is performed so that one pixel is formed in three shots.

  The driver COM output includes the second of the first to third printing drive voltage pulses Pw (1), Pw (2), and Pw (3) that appear in each one-pixel printing period T. The drive voltage pulse Pw (2) appears, and the others are held at GND. On the other hand, the driver SEG output includes the first and third drive voltage pulses Pw (1) in the case of printing by three shots / pixel in which one pixel is formed by discharging ink droplets three times. In the case of printing by two shots / pixel in which one pixel is formed by discharging ink droplets twice, only the first drive voltage pulse Pw (1) appears and one pixel is displayed once. In the case of printing by one shot / pixel formed by discharging the ink droplets, the first and second drive voltage pulses Pw (1) and Pw (2) appear.

  As described above, in this example, when one-pixel printing is performed by ejecting a plurality of ink droplets, a plurality of timings for one-pixel printing, of the three consecutive ejection timings in the example of FIG. The gradation expression is performed on the basis of the discharge timing (by the head reference).

  Further, the nozzle drive waveform applied between the diaphragm electrode 119 and the individual electrode 121, that is, the COM-SEG potential difference is switched in the reverse direction, the forward direction, and the reverse direction. Therefore, in the case of printing by 3 shots / pixel (the first one-pixel printing period T in FIG. 5), the ink droplet ejection operation is performed three times by reverse driving, normal driving, and reverse driving. In the case of printing by pixels (second one-pixel printing period T in FIG. 5), ink droplet ejection operations are performed in the reverse drive and forward drive order at the time of ejection of the first and second ink droplets. In the case of printing by one shot / pixel (the third one-pixel printing period T in FIG. 5), the ink droplet ejection operation is performed by reverse driving at the time of ejection of the first ink droplet.

  In addition, when the ink droplets are continuously ejected by the polarity reversal signal REV, the inkjet head 110 is alternately driven in the forward and reverse directions in the reverse drive and forward drive order or in the reverse order. Thus, by performing forward and reverse alternating energization, it is possible to suppress or avoid the generation of residual charges between the diaphragm electrode 119 and the individual electrode 121.

(Setting method of pulse interval of drive voltage pulse)
FIG. 6 shows a voltage waveform of the drive voltage pulse Pw in the drive voltage pulse signal V3. As shown in this figure, each drive voltage pulse Pw has a trapezoidal waveform, and has a pulse width for one cycle, that is, the rise time (application start time) of the drive voltage pulse Pw to the rise time (application) of the next drive voltage pulse Pw. The interval until the start point) is the pulse interval Pwi. In the voltage waveform of each drive voltage pulse Pw, the width of the charged portion rising at a constant gradient is Pwcp, the width of the hold portion held at a constant voltage after the rising is Pwhp, and thereafter the discharge falling at a constant gradient The width of the part is Pwdp. The width from the rising start point to the falling start point of the drive voltage pulse Pw, that is, the pulse width is Pwb.

  In this example, the pulse intervals Pwi1, Pwi2, and Pwi3 of the first to third drive voltage pulses Pw (1) to PW (3) for one-pixel printing are vibrations after ink droplet ejection. Each is determined individually based on the residual vibration waveform of the plate electrode 119.

  FIG. 7 shows the drive voltage pulse signal waveform and the behavior (residual vibration waveform) of the diaphragm electrode 119. In this figure, in order to facilitate understanding, the pulse intervals Pwi1 to Pwi3 of the drive voltage pulse waveform are shown widened.

  As shown in this figure, when the first drive voltage pulse Pw (1) is applied between the electrodes (time point T11), the diaphragm electrode 119 at the neutral position of zero displacement is the individual electrode (fixed electrode) 121. Is attracted to the negative electrode side (negative side in the figure) and contacts the individual electrode 121. With the displacement of the diaphragm electrode 119, the ink pressure in the ink chamber 116 changes to the negative pressure side, and the ink meniscus of the ink nozzle 115 is greatly drawn. When the drive voltage pulse Pw (1) falls, the diaphragm electrode 119 is released from the individual electrode 121 and starts elastic displacement toward its neutral position (time point T12). The diaphragm electrode 119 passes through the neutral position and is displaced to the positive side, whereby the ink pressure in the ink chamber 116 is rapidly increased, and the ink droplet 122 is ejected from the ink nozzle 115 (time T13). The diaphragm electrode 119 performs residual vibration with the ink pressure that vibrates in the natural period of the electrostatic inkjet head 110.

  In this example, the pulse interval Pwi1 between the first drive voltage pulse Pw (1) and the second drive voltage pulse Pw (2) is based on the residual vibration waveform of the diaphragm electrode 119 after ink droplet ejection. It has established. Specifically, the rising time T21 (application start time) of the second drive voltage pulse Pw (2) coincides with the time when the diaphragm electrode 119 is at the neutral position where the vibration is switched from the positive side to the negative side. The pulse interval Pwi1 is determined. Accordingly, the pulse interval Pwi1 includes N peaks (N is a positive integer) of the residual vibration waveform. In the illustrated example, two peaks are included, and the zero cross point (neutral position) of the second peak is the rising time T21 of the second drive voltage pulse Pw (2).

  As described above, when the diaphragm electrode 119 that vibrates in the natural period starts the application of the second drive voltage pulse Pw (2) at the neutral position where the positive electrode switches to the negative electrode, the diaphragm due to residual vibration. The displacement direction of the electrode 119 coincides with the displacement direction of the diaphragm electrode 119 caused by the drive voltage pulse. Therefore, the displacement of the diaphragm electrode 119 due to the drive voltage pulse Pw (2) is not inhibited or suppressed by the residual vibration. Therefore, the second ink droplet can be discharged (time T23) with a sufficient discharge mass and discharge speed. Further, when the driving voltage pulse Pw (2) is applied when the diaphragm electrode 119 is at the neutral position, the first ink is applied by applying the driving voltage pulse Pw (1) while the diaphragm electrode 119 is at the neutral position. Since the same behavior as that when the droplets are ejected is reproduced, the ejection characteristics of the second ink droplet can be kept substantially the same as the ejection characteristics of the first ink droplet.

  Similarly, the pulse interval Pwi2 between the second drive voltage pulse Pw (2) and the third drive voltage pulse Pw (3) is also determined. That is, the third drive voltage pulse Pw (3) is at the zero cross point (neutral position of zero displacement) at which the residual vibration waveform of the diaphragm electrode 119 after the second ink droplet discharge is switched from the positive side to the negative side. The pulse interval Pwi2 is determined so that the rising time T31 (application start time) coincides. In the example shown in the figure, the pulse interval Pwi2 includes two peaks in the residual vibration waveform, and the zero cross point (neutral position) of the second peak is the rise time T31 of the third drive voltage pulse Pw (3). It has become.

  Next, the pulse interval Pwi3 between the third drive voltage pulse Pw (3) and the first drive voltage pulse Pw (4) for the next one-pixel printing is also determined after the third ink droplet is ejected. The rise time T41 (application start time) of the first drive voltage pulse Pw (4) coincides with the zero cross point (neutral position of zero displacement) at which the residual vibration waveform of the diaphragm electrode 119 in FIG. As described above, the pulse interval Pwi3 is determined.

  Here, the number of peaks of the residual vibration waveform of the diaphragm electrode included in the first and second pulse intervals Pwi1 and Pwi2 is “2”, but the residual vibration included in the third pulse interval Pwi3. The pulse interval Pwi3 is determined so that the number of peaks in the waveform is “3”, which is one more. The pulse interval Pwi3 may be determined so that the number of peaks is two or more. That is, when the number of peaks of the residual vibration waveform included in the pulse intervals Pwi1 and Pwi2 is N (N is a positive integer), the number of peaks of the residual vibration waveform included in the last third pulse interval Pwi3 is ( The pulse interval Pwi3 may be determined so that N + α) (α is a positive integer).

  Next, in order to determine the pulse intervals Pwi1 to Pwi3 of the drive voltage pulse Pw as described above, in this example, sampling is performed for each production lot at a stage before shipment of the electrostatic ink jet head 110, etc. The residual vibration frequency or residual vibration period of the diaphragm electrode 119 after droplet discharge is measured or calculated. The optimum first to third pulse intervals Pwi1, Pwi2 and Pwi3 are determined individually for each electrostatic ink jet head based on the measured or calculated natural period or natural frequency.

  Further, as shown in FIG. 3, a pulse interval rank identification circuit 11 of the electrostatic inkjet head 110 is mounted on the head substrate 8 of this example. The ink jet head control unit 2 is equipped with a pulse interval discriminating circuit 12 that discriminates the rank designated by the pulse interval rank discriminating circuit 11. Each pulse for forming one pixel in the drive voltage pulse signal V3 by operating the pulse interval rank identification circuit 11 from the outside based on the natural period measured or calculated in a stage before shipment of the electrostatic ink jet head 110 or the like. The interval rank is set.

  For example, as shown in FIG. 8, a table 13 in which a pulse interval is assigned in advance for each natural period of equal width is prepared, and rank numbers 201 to 324 corresponding to the measured or calculated natural periods are shown. The pulse interval rank discriminating circuit 11 is set in a form associated with the first to third pulse intervals. The inkjet head drive control device 1 reads the three kinds of ranks set in the pulse interval rank discriminating circuit 11 by the pulse interval rank discriminating circuit 12, and based on this, the first to third pulse intervals Pwi1 to Pwi1. Pwi3 is set.

  Further, as shown in FIG. 9, the assigned pulse interval rank is printed on a portion such as the main body side surface 110 a of the electrostatic inkjet head 110. The leftmost number “238” is the rank of the first pulse interval Pwi1, the next number “236” is the second pulse interval Pwi2, and the leftmost number “311” is the third pulse. The interval pwi3. In addition, a production lot number “AB-040226” is printed below these numbers. When the rank is printed or displayed in this way, the pulse interval rank discriminating circuit 12 and the pulse interval rank identifying circuit 11 are omitted, and the rank is printed on the inkjet head drive control device 1 by a dip switch or the like. Each rank may be set.

  As shown in FIG. 10A, in this example, in the case of multi-shot / pixel printing, gradation expression is performed with reference to the leading ejection timing. Therefore, regardless of the number of ink droplet ejections, the first ink droplet ejection in one-pixel printing is performed at the first ejection timing, and the second ink droplet ejection is performed at the second ejection timing. The third ink droplet ejection is performed at the third ejection timing. Therefore, the pulse widths Pwb (1) to Pwb (3) of the drive voltage pulse at each ejection timing can be set to appropriate values separately.

  On the other hand, as shown in FIG. 10B, when multi-shot / pixel printing is used to express gradation with reference to the last ejection timing, the number of ink droplets ejected at each ejection timing. What is performed is different for each gradation. In this case, the pulse width Pwb of the drive voltage pulse at each ejection timing cannot be defined uniformly. Further, since the diaphragm electrode 119 is used as a common electrode in the electrostatic ink jet head, it is impossible to apply drive voltage pulses having different pulse widths for each ink nozzle at the same ejection timing. Therefore, when the discharge timing at the rear end is used as a reference, it is impossible to appropriately set the pulse width of each drive voltage pulse.

  Next, in this example, as shown in FIG. 5, the drive voltage pulse is applied by forward and reverse alternating energization. In the case of forward / reverse alternating energization, the pulse width characteristic varies depending on the energization direction (electric field direction). That is, the ink discharge speed and the pulse width that maximizes the ink discharge mass may be different. In this case, it is desirable to change the pulse width Pwb of the drive voltage pulse Pw according to the electric field direction. In this example, since the drive voltage pulses are applied in the reverse, forward and reverse directions, the pulse widths of the first and third drive voltage pulses are the same, and the pulse widths of the second drive voltage pulse are different. You can do it.

  Of course, in the case of multi-shot / pixel printing, if the pulse widths of the first, second, and third drive voltage pulses are different, each pulse width is set in consideration of the pulse width characteristics depending on the energization direction. Just decide.

As a method for measuring or calculating the natural period in the stage before shipment of the electrostatic ink jet head, the following method can be employed.
(1) A method of measuring a current waveform that fluctuates due to a change in capacitance between the diaphragm electrode 119 and the fixed-side electrode 121, and calculating based on this.
(2) A method of measuring the relationship between the pulse interval Pwi of the drive voltage pulse Pw and the mass of ink ejected from the ink nozzles, and calculating based on this relationship.
(3) A method of measuring the relationship between the pulse interval Pwi of the drive voltage pulse Pw and the ejection speed of the ink ejected from the ink nozzles, and calculating based on this relationship.
(4) A method of measuring a voltage waveform that fluctuates due to a change in capacitance between the diaphragm electrode 119 and the fixed-side electrode 121 and calculating based on this.

(Other embodiments)
Although the above embodiment is an example in the case of performing 3 shots / pixel printing, the present invention can be similarly applied to setting of each pulse interval when performing 1 pixel printing with a number of shots other than 3 shots.

  Further, when the driving period T for n shot / pixel printing is determined on the ink jet printer side, the interval between the driving voltage pulse for the last shot and the first driving voltage pulse for the next one pixel printing. The pulse interval Pwi (n) may be a value obtained by subtracting the sum of the pulse intervals Pwi1 to Pwi (n−1) determined based on the residual vibration waveform from the driving cycle T.

1 is a schematic configuration diagram illustrating an inkjet printer to which the present invention is applied. It is a schematic sectional drawing which shows the structural example of the electrostatic inkjet head of the inkjet printer of FIG. FIG. 2 is a schematic block diagram mainly showing a control system of the ink jet printer of FIG. 1. FIG. 4 is a schematic block diagram showing an internal configuration of the head driver IC in FIG. 3. 2 is a timing chart illustrating signal waveforms of respective units during a printing operation with 1 to 3 shots / pixel in the inkjet printer of FIG. 1. It is a wave form diagram which shows the voltage waveform of the drive voltage pulse in the inkjet printer of FIG. FIG. 2 is an explanatory diagram showing a relationship between a pulse interval of driving voltage pulses and a behavior (residual displacement) of a diaphragm electrode in the ink jet printer of FIG. 1. FIG. 3 is an explanatory diagram illustrating an example of a correspondence table between pulse intervals and rank numbers in the case of 3-shot / pixel printing in the inkjet printer of FIG. 1. It is explanatory drawing which shows the example of the side part of the electrostatic inkjet head on which the rank number of the pulse interval was printed. It is explanatory drawing for demonstrating that the drive by the head reference | standard in the case of multi-shot / pixel printing is advantageous.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 inkjet head drive control apparatus, 2 inkjet head control part, 6 drive pulse generation circuit, 8 head board | substrate, 9 head driver IC, 11 pulse interval rank identification circuit, 12 pulse interval rank discrimination circuit, 100 inkjet printer, 105 carriage, 110 Inkjet head, 115 ink nozzle, 116 ink chamber, 117 ink orifice, 118 common ink chamber, 119 diaphragm electrode, 121 individual electrode (fixed side electrode), V3 drive voltage pulse signal for printing, Pw drive voltage pulse, Pwi, PWi1, Pwi2, Pwi3 Pulse interval (cycle) of drive voltage pulse Pw, pulse width of Pwb drive voltage pulse Pw, LP control signal, REV polarity inversion control signal

Claims (3)

A drive voltage pulse is applied between the diaphragm electrode and the fixed electrode that are arranged to face each other at a constant interval, and the diaphragm electrode is vibrated by the electrostatic force generated between them, thereby generating ink pressure fluctuations. Ink droplets are ejected from ink nozzles using ink pressure fluctuations,
1-pixel printing is performed by discharging continuous ink droplets up to n times (n is an integer of 2 or more),
Each pulse interval of each of the first to nth driving voltage pulses applied to eject each ink droplet is expressed as follows:
The displacement position due to the residual vibration of the diaphragm electrode at the start of application of each of the second to n-th drive voltage pulses is a neutral position of zero displacement immediately before the diaphragm electrode starts to move toward the fixed electrode. A driving method for an electrostatic ink jet head.
In claim 1,
When the number of peaks of the residual vibration waveform of the diaphragm electrode included in each pulse interval of the first to nth drive voltage pulses is N (N is a positive integer),
There are (N + α) peaks of the residual vibration waveform of the diaphragm electrode in the pulse interval from the last nth drive voltage pulse in one pixel printing to the first drive voltage pulse for the next one pixel printing. (Α is a positive integer) A driving method of the electrostatic ink jet head for setting the pulse interval so as to be included. In claim 1 or 2,
Measuring or calculating a residual frequency or a residual vibration period of the diaphragm electrode of the electrostatic inkjet head;
The residual frequency or the residual vibration period is divided into a plurality of groups for each predetermined range, and a pulse interval of the drive voltage pulse is pre-assigned to each group,
The pulse interval of the drive voltage pulse assigned to the group including the measured or calculated residual frequency or residual vibration period is set to the first to nth drive voltage pulses in the electrostatic inkjet head. A method of driving an electrostatic ink jet head that is employed as each pulse interval.

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