JP2006264075A - Driving method for droplet ejection head, and droplet ejector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enable the formation of a high-quality image by surely preventing the thickening of a liquid through the use of a simple constitution. <P>SOLUTION: In an inkjet recording head 20, voltages levels HV1 and HV2, which enable the drive of a piezoelectric element 36 so that a droplet can be ejected from a droplet ejector 34, are input into a driving IC which is provided on each ejector substrate 28, and the driving IC outputs driving waveforms at the voltage levels, so that the droplet can be ejected. Electric power at a voltage level HV0, enabling the piezoelectric element to be driven to the extent to which the droplet is not ejected from the droplet ejector, is input into the driving IC by being converted into electric power at the voltage level HV1. Microvibration is applied to the droplet ejector by applying the electric power to the piezoelectric element while making the electric power switch between an on-state and an off-state, so that the occurrence of the thickening in ink can be prevented. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a droplet discharge device that discharges ink droplets and the like, and more specifically, a method of driving a droplet discharge head that discharges droplets by a change in pressure generated by a change in voltage applied to a piezoelectric element, and The present invention relates to a droplet discharge device.

  In the droplet discharge device, a piezoelectric element or the like is used as an actuator to change the volume (volume) of the pressure generation chamber filled with ink by expanding and contracting, so that the internal pressure changes to the pressure generation chamber. There is an ink jet recording apparatus or the like in which an ink jet recording head that discharges ink droplets from the tip of a communicating nozzle is provided as a droplet discharging head.

  On the other hand, in an inkjet recording apparatus, it is desired to improve image quality with an increase in speed. From this, a plurality of drive waveforms are generated, and a piezoelectric drive waveform selected from the plurality of drive waveforms according to the size of the ink droplets to be ejected is used. An ink jet recording apparatus that drives an element has been proposed (for example, see Patent Document 1).

  By the way, for example, ink used in an ink jet recording apparatus is thickened due to moisture evaporation caused by being left unattended. In the ink jet recording apparatus, when the ink in the pressure generating chamber is thickened, the ejection efficiency of the ink is lowered, and thus a droplet having a normal size (desired size) or speed cannot be obtained. is there. In other words, when trying to eject ink droplets by driving the piezoelectric element using the same drive waveform, the landing position due to the size and speed difference between the ejected droplet just after purging and the ejected droplet after leaving unattended It can be very different.

  Such thickening of the ink greatly affects the quality of the finished product when an image is formed on the recording paper by the ink jet recording apparatus.

  As a method of preventing such deterioration in image quality due to thickening, if the increase in ink viscosity is predicted when the number of pulses in the driving waveform is changed according to the size of the ejected droplet, the pulse in the driving waveform Proposals have been made to change the number and pulse generation timing (see, for example, Patent Document 2).

  However, this method does not suppress the thickening of the ink, and thus the effect may vary depending on the standing time. In addition, the print data must be inspected in order to grasp the state before discharge, which increases the load on the controller and requires a plurality of drive waveforms for discharge.

  On the other hand, as a method for preventing the viscosity increase of the ink in the pressure generation chamber, there is known a method of applying vibration to the ink in the pressure generation chamber to such an extent that the droplet does not discharge. There has been proposed a method in which a fine vibration pulse for depressurizing / pressurizing the pressure generating chamber is generated and a piezoelectric element is driven by the fine vibration pulse (see, for example, Patent Document 3).

However, when the piezoelectric element is driven by a drive signal using a rectangular wave, it is necessary to separately provide a drive circuit that generates fine vibrations for preventing thickening.
JP 2001-26102 A JP 2001-26120 A JP 2001-121722 A

  The present invention has been made in view of the above-described facts, and provides a droplet ejection head driving method and a droplet ejection apparatus that can prevent the viscosity of the ejection liquid from increasing without using a dedicated signal generation circuit. For the purpose.

  In order to achieve the above object, the present invention provides a piezoelectric element and a droplet ejector provided in pairs, and a liquid ejecting liquid from a nozzle provided in the droplet ejector based on a voltage change of a driving waveform applied to the piezoelectric element. A method for driving a droplet discharge head for discharging a liquid in a droplet ejector, the driving power of a voltage enabling discharge of the droplet from the nozzle, and the droplet from the nozzle when applied to the piezoelectric element A preliminary driving power having a voltage set in a range equal to or lower than a minimum voltage necessary for discharging the liquid is generated, and the piezoelectric element is driven by a driving waveform generated using the preliminary driving power during the non-ejection of the droplet. It is characterized by being driven.

  According to the present invention, it is possible to generate a driving power of a voltage that can discharge a droplet from the nozzle and a preliminary driving power of a voltage that can drive the piezoelectric element to the extent that the droplet is not discharged from the nozzle. When discharging, driving power is used.

  When the droplet is not discharged, the piezoelectric element is driven with a predetermined drive waveform using the preliminary drive power.

  That is, the droplet ejector ejects droplets from the nozzles when the volume of the pressure generating chamber containing the liquid is expanded or contracted by a predetermined width or more by driving the piezoelectric element. In addition, when the expansion / contraction width of the pressure generating chamber is narrow, droplets are not ejected, only the liquid is stirred, and changes such as increase in liquid viscosity (thickening) over time due to evaporation of moisture can be suppressed. .

  From this, the voltage change width applied by the piezoelectric element is reduced, and the liquid ejector is finely vibrated to prevent the liquid from being thickened.

  At this time, preliminary driving power is generated separately from normal driving power, and switching between driving power and preliminary driving power makes it easy to switch between driving when droplets are ejected and applying fine vibration when not ejecting. With a simple structure, it is possible to reliably prevent the liquid from thickening.

  Such a droplet discharge device to which the present invention is applied includes a droplet discharge head in which a piezoelectric element and a droplet ejector are provided in pairs, and a voltage of a driving waveform applied to the piezoelectric element based on discharge data Is a droplet discharge device that discharges the liquid in the droplet ejector from the nozzle provided in the droplet ejector, the driving power of the voltage enabling the piezoelectric element to be driven, and the piezoelectric A power supply unit capable of generating a preliminary driving power having a voltage set in a range equal to or lower than a minimum voltage necessary for discharging the droplet from the nozzle when applied to the element; and the piezoelectric device based on the discharge data Drive waveform generation means for generating the drive waveform for driving the element, and driving the piezoelectric element based on the power input from the power supply unit and the drive waveform generated by the drive waveform generation unit And a switching means for switching the power output from the power supply means to the drive means from the drive power to the preliminary drive power when the droplets are not ejected from the nozzles of the droplet ejector. I need it.

  Further, in the droplet discharge device to which the present invention is applied, when the preliminary driving power is supplied to the driving unit by switching by the switching unit, the driving waveform generating unit generates a preset preliminary driving waveform. It is preferable to output.

  Furthermore, in the droplet discharge device to which the present invention is applied, the power supply unit can include a step-down means for stepping down the drive power to the preliminary drive power. As the step-down means at this time, for example, PWM control An inverter circuit to which is applied can be used, so that power of a desired voltage can be obtained easily and easily.

  On the other hand, the droplet discharge device to which the present invention is applied, the preliminary driving power is supplied via the driving means when the discharge data is not input until the discharge of the droplet based on the discharge data is started. And supplying to the piezoelectric element.

  In the present invention, for example, when an image is formed by ejected droplets, the image data becomes droplet ejection data. When this image data is not input, it is in a standby state where no droplet is ejected.

  In such a standby state, the piezoelectric element is driven using the pre-driving electric power to stir the liquid such as ink in the droplet ejector to prevent thickening. Thereby, when the discharge of a droplet is started based on the input discharge data, it is possible to appropriately control the droplet amount to be discharged.

  In addition, the droplet discharge device to which the present invention is applied, when the droplets are discharged at a series of timings based on the discharge data, the preliminary drive power is generated when the droplet non-discharge timing occurs. It supplies to the said piezoelectric element, It is characterized by the above-mentioned.

  According to the present invention, when the non-ejection timing is generated while the ink is continuously ejected while conveying the recording paper, only a slight vibration is applied to the piezoelectric element. As a result, the occurrence of thickening during non-ejection is suppressed, and the amount of ejected droplets before and after is appropriately controlled.

  Thereby, when an image is formed based on image data that is ejection data, high-quality image formation is possible.

  As described above, according to the present invention, when preliminary drive power having a voltage set in a range in which droplets are not ejected is generated and fine vibration is applied to the droplet ejector to prevent thickening, Use preliminary drive power. This makes it possible to accurately prevent thickening with a simple configuration, and enables high-quality image formation without blurring of pictures and characters even when ink is ejected to form an image. An excellent effect is obtained.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a schematic configuration of an inkjet recording apparatus 10 which is a droplet discharge recording apparatus applied as a droplet discharge apparatus to the present embodiment.

  The ink jet recording apparatus 10 includes a head unit 12 provided with a droplet discharge head, and a drive mechanism that is responsible for transport of recording paper for performing image formation (printing) with ink discharged from the droplet discharge head, ink replenishment, and the like. And a controller unit 16 that controls the operation of the head unit 12 and the drive mechanism unit 14.

  The inkjet recording apparatus 10 is connected to an image processing apparatus 18 such as a personal computer or a workstation, and executes a printing process based on image data input from the image processing apparatus 18 to the controller unit 16. To do. That is, image formation is performed (printing) according to image data by ejecting ink based on the image data using the image data as ink ejection data.

  FIG. 2 shows a schematic configuration of an ink jet recording head 20 provided in the head unit 12 as a droplet discharge head. The ink jet recording head 20 includes a head bar 22 set to a length corresponding to the maximum width of a recording sheet (not shown). A plurality of head units 24 are connected to the head bar 22 in a row, arranged two-dimensionally, and fixed individually.

  As shown in FIG. 3A, each head unit 24 includes, for example, extending portions 26A and 26B in which both end portions of a substantially parallelogram project linearly outwardly, and are extended as a substantially parallelogram portion. Between the portions 26A and 26B, two ejector bases 28A and 28B (hereinafter collectively referred to as an ejector substrate 28) made of a droplet ejector group are disposed. The ejector bases 28A and 28B have a substantially trapezoidal shape, and are disposed in the head unit 24 so that the oblique sides having the same length (here, the short oblique sides) face each other, and the extending portions 26A and 26B include the ejector bases 28A and 26B. 28B is provided with an ink supply port 30 for supplying ink which is a discharge liquid.

  A large number of droplet ejectors (not shown in FIGS. 3A and 3B) are two-dimensionally arranged on the ejector bases 28A and 28B, one for each droplet ejector. A nozzle 32 is formed on the surface of the head unit 24 corresponding to the ejector bases 28A and 28B. The ejector bases 28A and 28B are, for example, 512 droplet ejectors arranged two-dimensionally in 32 stages and are asymmetrical on the left and right sides. The inkjet recording head 20 drives all the droplet ejectors. The nozzles 32 are arranged so as not to overlap when one line is printed.

  As a result, the ink jet recording apparatus 10 can print on the entire width of the recording paper without scanning the ink jet recording head 20, and the recording paper only passes once under the ink jet recording head 20 (nozzle 32 side). The printing on the entire surface of the recording paper is completed. The configuration of the droplet discharge head to which the present invention is applied is not limited to this, and an arbitrary configuration can be applied.

  On the other hand, FIG. 4 shows an outline of a main part of the ink jet recording apparatus 10. In the inkjet recording apparatus 10, an inkjet recording head 20 is provided in the head portion 12. The inkjet recording head 20 is provided with piezoelectric elements (piezo elements) 36 corresponding to the respective droplet ejectors 34 provided on the ejector substrate 28.

  The droplet ejector 34 and the piezoelectric element 36 form an actuator that ejects ink droplets. The piezoelectric element 36 is deformed by an applied voltage, and a part of the wall surface of the pressure generating chamber of the droplet ejector 34 is deformed. The formed diaphragm is vibrated. The droplet ejector 34 expands and contracts the pressure generating chamber by the vibration of the diaphragm, so that the ink filled from the nozzle 32 (see FIGS. 3A and 3B) into the pressure generating chamber. It has a general configuration for discharging liquid droplets.

  The ink jet recording head 20 is provided with a drive IC (Integrated Circuit) 38 corresponding to each of the ejector substrates 28. Note that the inkjet recording apparatus 10 can form a color image using a plurality of colors such as Y (yellow), M (magenta), C (cyan), and K (black). In addition, the ink jet recording head 20 is provided for each color, but the basic configuration is the same for each color, and only one color will be described below.

  The controller unit 16 is provided with a controller 40 to which each drive IC 38 provided in the inkjet recording head 20 is connected.

  The controller 40 outputs to each of the driving ICs 38 a clock signal, print data, a latch signal, a waveform signal A, a waveform signal B, a waveform signal C, and the like, each of which is a pair of signals. That is, the operation of the inkjet recording head 20 is controlled.

  The controller unit 16 is provided with a power supply unit 42 for driving the inkjet recording head 20, and power is supplied from the power supply unit 42 to each of the drive ICs 38 of the inkjet recording head 20.

  FIG. 5 shows an example of a schematic configuration of the drive IC 38. In the drive IC 38, a shift register 44, a latch circuit 46, a selector 48, a level shifter 50, and a drive waveform generation circuit 52 are formed.

  The clock signal and print data output from the controller 40 are input to the shift register 44, and the latch signal is input to the latch circuit 46.

  The controller 40 selects, as print data, a selection signal (a selection signal of the waveform signal A, a selection signal of the waveform signal B, one of the waveform signal A, the waveform signal B, and the waveform signal C). Serial data consisting of a selection signal of the waveform signal C). Each selection signal can use 1-bit data that becomes “0” or “1”. For example, the selection signal of the waveform signal A becomes “1” when the waveform signal A is selected, and the waveform signal The signal is “0” when A is not selected, and the print data is “100” when the waveform signal A is selected, “010” when the waveform signal B is selected, and the waveform signal C is selected. In this case, the data is 3-bit serial data “001”.

  Such print data is obtained by adding the number of droplet ejectors 34 included in the corresponding ejector substrate 28 and the number of droplet ejectors 34 overlapping in the short side direction of the inkjet recording head 20 of the adjacently disposed ejector substrate 28. This number is continuously input to the shift register 44.

  In the following, a case where a drive waveform is supplied to one piezoelectric element 36 will be described, but the same applies to the other piezoelectric elements 36, and thus description thereof will be omitted.

  The shift register 44 converts the input print data, which is 3-bit serial data, into 3-bit parallel data and outputs the converted data to the latch circuit 46. The latch circuit 46 latches (self-holds) the parallel data input from the shift register 44 according to the input of the latch signal.

  The selector 48 receives the waveform signal A, the waveform signal B, and the waveform signal C from the controller 40 as selection target signals, and the parallel data of the print data latched by the latch circuit 46 is input to the select terminal. Therefore, the selector 48 selects and outputs the waveform signal A, the waveform signal B, and the waveform signal C that are instructed to be selected by the print data.

  The output terminal of the waveform signal of the selector 48 is connected to the level shifter 50, and the level shifter 50 performs level conversion on the waveform signal input from the selector 48 and outputs it.

  On the other hand, each of the drive ICs 38 is supplied with power at a predetermined voltage level from the power supply unit 42 (see FIG. 4). In the present embodiment, as an example, the voltage level HVDD is higher than 40V (for example, 40V), HV1 is a predetermined level within a range of 10V to 30V, and HV2 is a predetermined level within a range of 20V to 40V. . In the present embodiment, the voltage levels HVDD, HV1, and HV2 are set such that HVDD> HV2> HV1.

  As the level shifter 50, any configuration that converts the level of the waveform signal selected by the print data to a voltage level corresponding to the voltage level HVDD can be applied.

  As shown in FIG. 5, in the present embodiment, as an example, the drive waveform generation circuit 52 is formed by a first signal generation circuit 54 and a second signal generation circuit 54, and the first signal generation circuit 54 is The PMOSFET (hereinafter referred to as PMOS 58A) and the NMOSFET (hereinafter referred to as NMOS 58B) are connected in series. Similarly, the second signal generation circuit 56 is also an inverter circuit in which PMOS 58A and NMOS 58B are connected in series. It is configured as.

  Here, the power of the voltage level HV1 is supplied to the source of the PMOS 58A in the first signal generation circuit 54, and the source of the NMOS 58B is grounded (ground level). In the first signal generation circuit 54, one output terminal of the level shifter 48 is connected to the gates of the PMOS 58A and the NMOS 58B, and one of the pair of waveform signals selected by the selector 46 and the level shifter 48 set the level. The converted waveform signal S1 is input.

  Therefore, in the first signal generation circuit 54, when the signal level of the waveform signal S1 input from the level shifter 50 is high, the PMOS 58A is turned off and the NMOS 58B is turned on. Is at ground level. On the other hand, when the signal level of the waveform signal S1 input from the level shifter 50 is low, the PMOS 58A is on and the NMOS 58B is off, so that the voltage level of the output voltage is the voltage level HV1. .

  As a result, the voltage output from the first signal generation circuit 52 has the same waveform as the inverted waveform of the waveform signal S1 input from the level shifter 50, and has two voltage levels, the ground level and the voltage level HV1. It becomes.

  On the other hand, the power of the voltage level HV2 is supplied to the source of the PMOS 58A in the second signal generation circuit 58, and the connection point (drain) of the PMOS 52A and NMOS 52B in the first signal generation circuit 54 is connected to the source of the NMOS 58B. Has been. Therefore, the inverter output of the first signal generation circuit 52 is applied to the source of the NMOS 58B. Further, the other output terminal of the level shifter 50 is connected to the gates of the PMOS 58A and the NMOS 58B, and the waveform signal S2 which is the other of the pair of waveform signals selected by the selector 48 and whose level is converted by the level shifter 50 is input. Is done.

  Therefore, in the second signal generation circuit 56, when the signal level of the waveform signal S2 input from the level shifter 50 is high, the PMOS 58A is turned off and the NMOS 58B is turned on. The voltage level of the drive waveform is the same as the voltage output from the first signal generation circuit 52 (the waveform is the same as the inverted waveform of the waveform signal S1 input from the level shifter 50, and the voltage level is the ground level and voltage). Having two levels HV1).

  On the other hand, if the signal level of the waveform signal S2 input from the level shifter 50 is low, the PMOS 58A is on and the NMOS 58B is off, so that the voltage level of the output voltage (drive waveform) is the voltage level. It becomes HV2.

  As a result, the voltage (drive waveform) output from the second signal generation circuit 56 is output from the first signal generation circuit 52 and the second signal generation circuit 54 in accordance with the pair of waveform signals S1 and S2 input from the level shifter 50. The output voltage is a combination of three output voltages: a ground level, a voltage level HV1, and a voltage level HV2.

  On the other hand, in the ink jet recording apparatus 10, the ink droplets discharged from each nozzle 32 of the ink jet recording head 20 are divided into four stages of large droplets, medium droplets, small droplets, and no (no droplets). Thus, the output waveform of the drive waveform generation circuit 52 is set. An example is shown in FIGS. 6A, 6B, and 6C. 6A shows a driving waveform for large droplets, FIG. 6B shows a driving waveform for medium droplets, and FIG. 6C shows a driving waveform for small droplets. In FIGS. 6A to 6C, the horizontal axis is the time axis.

  A combination (selection signal) of the waveform signal A, the waveform signal B, and the waveform signal C is set in the controller 16 so that each drive waveform can be obtained.

  By the way, in the inkjet recording apparatus 10, the piezoelectric element 36 is driven at a predetermined timing during non-printing so that the ink droplets are not ejected from the nozzles 32 of the inkjet recording head 20, and the pressure generating chamber of the droplet ejector 34 is expanded or contracted. (Hereinafter referred to as preliminary driving).

  As shown in FIG. 4, in the inkjet recording apparatus 10 applied to the present embodiment, a switching unit 62 and a preliminary waveform generation circuit 64 are provided in the power supply unit 42 together with the main power supply circuit 60.

  The main power supply circuit 60 generates power of the voltage levels HVDD, HV2, and HV1 supplied to the drive IC 38, and outputs the generated power of each voltage level to the switching unit 62.

  Further, the preliminary waveform generation circuit 64 generates power of a predetermined voltage level using the power input from the main power supply circuit 60 and outputs the generated power to the switching unit 62.

  The switching unit 62 outputs the power of each voltage level input from the main power supply circuit 60 to the inkjet recording head 20 (drive IC 38), and also converts the power of a part of the voltage level based on the signal from the controller 40. The power is switched to the voltage level power input from the preliminary waveform generating circuit 64 and output to the ink jet recording head 20.

  FIG. 7 shows an example of the preliminary waveform generation circuit 64. The preliminary waveform generating circuit 64 includes an fV converter 66, a switching circuit 68 using a switching element (for example, PMOSFET) and a rectifier circuit 70.

  The switching circuit 68 receives power at a predetermined voltage level from the main power supply circuit 60. Further, the controller 40 (see FIG. 4) is configured to input a signal having a predetermined cycle (for example, a pulse signal, a sawtooth wave, etc.) to the fV converter 66, and the fV converter 66 is inputted. A voltage signal of a predetermined level is output to the switching circuit 68 with a period and an ON width according to the received signal. In the switching circuit 68, the switching element is driven on / off in accordance with the voltage signal input from the fV converter 66.

  As a result, the electric power input to the switching circuit 68 is output as a pulse signal having a predetermined width by turning on / off the switching element (PWM control), and is smoothed by the rectifier circuit 70. Electric power is output. In other words, in the preliminary waveform generation circuit 64, the power input from the main power supply circuit 60 is stepped down and output by the gate voltage control of the switching circuit 68.

  Here, as an example, the description will be made assuming that the power at the voltage level HV1 is converted to the voltage level HV0 (HV1> HV0).

  On the other hand, the piezoelectric element 36 vibrates the diaphragm provided in the droplet ejector 34 according to the voltage change width. Further, the droplet ejector 34 ejects an ink droplet when the amplitude of the vibration plate becomes a predetermined value or more.

  Here, the preliminary waveform generation circuit 64 outputs a voltage based on a voltage width at which ink droplets are not ejected. That is, the power of the voltage level HV0 output from the preliminary waveform generation circuit 64 vibrates the diaphragm of the droplet ejector 34, but the amplitude at that time is within a range in which droplets are not ejected from the nozzle 32.

  The controller 40 outputs a signal of a level and a period based on this to the fV converter 66.

  4 switches the power of voltage level HV1 output from main power supply circuit 60 to the voltage level HV0 input from preliminary waveform generation circuit 64 based on the signal from controller 40. The output is made to the ink jet recording head 20.

  The controller 40 operates the switching unit 62 at a preset timing and outputs a selection signal so as to output a drive signal of the voltage level HV0 to the piezoelectric element 36. FIG. 8 shows an example of the drive waveform (preliminary drive waveform) at this time, and the controller 40 outputs a selection signal set so as to obtain such a preliminary drive waveform. Yes.

  Thereby, in each droplet ejector 34 of the ink jet recording head 20, the pressure generating chamber is expanded and contracted so that the ink liquid is not discharged from the nozzle 32, and the ink filled in the pressure generating chamber is agitated. ing.

  In the inkjet recording apparatus 10 configured as described above, when image data to be printed is input from the image processing apparatus 18, the image data is two-dimensionally developed by performing, for example, RIP processing, and the recording paper 1. Generate print data for each page.

  Thereafter, the print data is divided for each ejector substrate 26 of the inkjet recording head 20 and serially output from the controller 40 to the drive IC 38 for each ejector substrate 26. As a result, the print data is input to the shift register 44 of the driving IC for writing.

  At the same time, the controller 40 inputs a latch signal at a predetermined timing, and inputs waveform signals A, B, and C, thereby generating a drive waveform of the piezoelectric element 36 corresponding to the print data, and the generated drive waveform. The piezoelectric element 36 of the droplet ejector 34 is supplied with electric power according to the above. At this time, by using the SWIC (not shown) to turn on / off the drive waveform for each piezoelectric element 36 according to the print data, the amount of droplets (large droplet, medium droplet, Small droplets or no droplets) are ejected.

  As a result, the inkjet recording apparatus 10 forms an image for each line on the recording paper.

  By the way, the inkjet recording apparatus 10 performs preliminary driving by generating a preliminary driving waveform during non-printing and supplying electric power corresponding to the preliminary waveform driving to the piezoelectric element 36 for each droplet ejector 34. By stirring the ink in the droplet ejector 34 (in the pressure generating chamber), the ink is prevented from thickening.

  Here, the preliminary drive executed in the inkjet recording apparatus 10 will be described. As a timing for performing the preliminary drive in the inkjet recording apparatus 10, it is possible to apply a print pause state (hereinafter referred to as a job interval) waiting for printing without inputting image data while the power switch is turned on. While printing is in progress, for example, it is possible to apply a page interval such as a recording paper switching timing or a line interval before the start of printing of the next line after printing of one line is completed. (Print interval including page interval and line interval) Here, the line interval is a printing timing (droplet discharge timing), but is a timing at which the droplet discharge is stopped because there is no pixel to be printed.

  Here, the preliminary drive will be described separately for the job interval and the print interval.

  FIG. 9 shows an outline of the preliminary drive processing in the job interval. This flowchart is executed at a predetermined time interval, for example, when the inkjet recording apparatus 10 is turned on and waiting for input of image data. In the first step 100, it is confirmed whether or not image data is input from the image processing device 18. Note that it is preferable to save the pre-driving process at the job interval when the ink jet recording apparatus 10 is in a so-called sleep mode in order to reduce power consumption.

  If no image data is input, a negative determination is made in step 100 and the process proceeds to step 102. When image data is input, an affirmative determination is made in step 100, the flowchart is terminated, and a printing process based on the input image data is executed.

  In this step 102, the preliminary waveform generating circuit 64 is controlled to generate power for the preliminary waveform (voltage level HV0), and the switching unit 62 is operated, so that this power is supplied to each inkjet recording head 20. Supplied to the drive IC 38.

  At the same time, in step 104, a selection signal for the drive waveform is output, and SWIC (not shown) for the piezoelectric element 36 of each droplet ejector 34 is controlled (ON).

  As a result, the power of the pre-driving waveform is generated by each driving IC 38, the pre-driving of the droplet ejector 34 is performed, and the pressure generating chamber of the droplet ejector 34 is expanded and contracted to such an extent that the droplet is not ejected, thereby stirring the ink. Is done.

  Thereafter, in step 106, it is confirmed whether or not image data has been input. When image data has been input, an affirmative determination is made in step 106 and the routine proceeds to step 108, where output of the selection signal for the preliminary waveform is stopped. At the same time, preliminary drive end processing such as switching of the switching unit 62 and stopping of the operation of the preliminary waveform generating circuit 64 is executed.

  As described above, by driving the piezoelectric element 36 while the inkjet recording apparatus 10 is on standby, the viscosity of the ink in the droplet ejector 34 increases, and a desired ejection droplet amount can be obtained when printing is attempted. It is possible to reliably prevent the image from being lost and to maintain a state in which high-quality image formation is possible when the printing process is started.

  Note that the preliminary drive during the job interval is not always executed during standby, but can take an arbitrary configuration such as being executed at predetermined time intervals at predetermined time intervals. For example, the preliminary drive may be performed at predetermined time intervals at predetermined time intervals.

  On the other hand, FIG. 10 shows an outline of preliminary driving during the printing interval. Note that this flowchart may be executed separately for each inkjet recording head 20, each ejector substrate 28, and the like when image data for performing a printing process is input. Further, when executing this flowchart, it is preferable that the preliminary waveform generating circuit 64 is activated in advance to generate power for the preliminary waveform.

  In this flowchart, in the first step 120, it is confirmed whether or not printing is in progress, that is, whether or not the piezoelectric element 36 is not driven to eject droplets. At this time, if it is driven to eject droplets, a negative determination is made in step 120 so that the preliminary drive process is not executed.

  Here, if not printing, an affirmative determination is made in step 120 and the routine proceeds to step 122. In step 122, the switching unit 62 is operated to supply the preliminary waveform to the drive IC 38 to which the droplet ejector 34 that performs the preliminary drive is connected. In step 124, the drive IC 38 and the SWIC (not shown) are controlled. The preliminary drive waveform is output to the piezoelectric element 36, and the piezoelectric element is driven by the power of the preliminary drive waveform.

  As a result, the non-operating (non-printing) droplet ejector 34 is expanded and contracted by the piezoelectric element 36, and the ink inside is agitated.

  On the other hand, when the preliminary driving is started, in step 126, it is confirmed whether or not the printing start timing is reached, that is, whether or not the timing for ejecting ink droplets from the nozzle 32 corresponding to the droplet ejector 34 is reached. The ink ejection timing can be a timing that is synchronized with the operation of the drive mechanism section 14 such as a recording paper conveyance timing and that does not cause a delay in the start of printing.

  Here, when the print timing is reached, an affirmative determination is made at step 126 and the routine proceeds to step 128 where the power output to the drive IC 38 is switched from the power at the voltage level HV0 for the preliminary waveform to the voltage level HV1 for the drive waveform. The preliminary drive process is terminated.

  In this way, by performing the preliminary driving prior to the discharge of the droplets, the viscosity of the ink in each droplet ejector 34 of the inkjet recording head 20 can be made substantially uniform. Since a desired drop amount of ink can be ejected, an image of a constant quality can be formed along the line direction on the entire surface of the recording paper.

  Therefore, in the inkjet recording apparatus 10, it is possible to prevent image quality deterioration such as blurring of the image due to ink thickening and the like, and to always form a high quality image with a constant quality.

  At this time, the ink jet recording apparatus 10 can reliably prevent ink thickening with a simple configuration that converts drive power. In addition, when pre-driving is performed, power consumption used for pre-driving can be suppressed by lowering the voltage level.

  In the present embodiment, the power supply unit 42 is provided with the preliminary drive waveform generation circuit 64 that generates power for the preliminary waveform together with the main power supply circuit 60. However, the preliminary waveform generation circuit 64 is not specially provided, The power supply circuit may be configured to switch the switching unit 62 when generating the power at the voltage level for the preliminary drive together with the power at the voltage level for the normal drive and outputting the power to the drive IC 38.

  On the other hand, in the present embodiment, the rectangular pulse shown in FIG. 8 is used as the preliminary drive waveform, but the drive waveform (preliminary drive waveform) when performing the preliminary drive is not limited to this, and at least the amplitude is Any waveform can be used as long as no droplet is ejected from the droplet ejector 34. Further, the individual waveforms may be different as long as the potential difference is in the above range, and the period of the drive waveform may be a variable period instead of a constant period.

  That is, as shown in FIG. 11A, the preliminary drive waveform may be trapezoidal, and the voltage level changes so as to gradually decrease and increase as shown in FIG. It may be a waveform. Although not shown, any waveform such as a half-wave rectified waveform, a full-wave rectified waveform, or a sawtooth wave can be applied.

  Furthermore, as shown in FIG. 11C, if the amplitude (potential difference) is in a range where no droplet is ejected from the droplet ejector 34 (in this embodiment, the voltage level HV0 is an example), the drive waveform The voltage peak may be higher than the voltage level HV0.

  That is, the droplet ejector 34 provided in the inkjet recording head 20 ejects droplets from the nozzle 32 by increasing the amplitude of the diaphragm in the pressure generating chamber. At this time, the amplitude of the diaphragm is in accordance with the potential difference of the power supplied to the piezoelectric element 36.

  From this point, by suppressing the potential difference within a predetermined range, it is possible to prevent thickening by stirring the ink without discharging the ink from the nozzle 32.

  Further, it is conceivable that the ink viscosity of the droplet ejector 34 changes according to the environmental temperature and the environmental humidity. From here, the amplitude and period of the pre-driving waveform and the pre-driving timing may be variable according to the environmental temperature, the environmental humidity, and the like.

  The ink jet recording apparatus 10 applied to the present embodiment can change the voltage level to be output by changing the cycle of the signal input to the fV converter 66. Further, in the inkjet recording apparatus 10, the width and interval of the preliminary drive waveform can be changed by switching the selection signal and the latch signal output from the controller 40 when performing the preliminary drive.

  From here, environmental temperature and humidity, at least environmental humidity, may be detected, and the voltage level, driving width (for example, pulse width), and driving interval (for example, pulse interval) may be set based on the detection result. This makes it possible to prevent the thickening more efficiently and accurately.

  In the present embodiment described above, the inkjet recording apparatus 10 which is a droplet discharge recording apparatus that forms an image on a recording sheet or the like by using discharged droplets is described as an example of the droplet discharge apparatus. The present invention is not limited to this, and the present invention can be applied to a droplet discharge recording apparatus such as an ink jet recording apparatus having an arbitrary configuration. The present invention can be applied not only to a droplet discharge recording apparatus but also to a droplet discharge apparatus having an arbitrary configuration including a droplet discharge head that discharges droplets.

It is a schematic block diagram of the inkjet recording device applied to this Embodiment. It is a schematic perspective view which shows an example of an inkjet recording head. (A) And (B) is the schematic which shows an example of the ejector board | substrate provided in an inkjet recording head. 1 is a block diagram illustrating a schematic configuration of a main part of an ink jet recording apparatus. It is a block diagram which shows schematic structure of the principal part of drive IC. (A) to (C) are schematic diagrams showing examples of drive waveforms when droplets are discharged, (A) for large droplets, (B) for medium droplets, and (C) for small droplets. For use. It is a schematic block diagram which shows an example of a preliminary waveform generation circuit. It is the schematic which shows an example of a preliminary drive waveform. It is a flowchart which shows the outline of the preliminary drive in a job interval. It is a flowchart which shows the outline of the preliminary drive in a printing interval. Each of (A), (B), and (C) is a schematic diagram showing another example of applicable preliminary drive waveforms.

Explanation of symbols

10 Inkjet recording device (droplet ejection device)
12 power supply unit 16 controller unit 18 image processing apparatus 20 inkjet recording head (droplet ejection head)
28 (28A, 28B) Ejector substrate 32 Nozzle 34 Droplet ejector 36 Piezoelectric element 38 Drive IC (drive means)
40 controller (drive control means, switching means)
42 Power supply unit 60 Main power supply circuit 62 Switching unit (switching means)
64 Preliminary waveform generator

Claims (6)

Droplet discharge in which a piezoelectric element and a droplet ejector are provided in pairs, and the liquid in the droplet ejector is discharged from a nozzle provided in the droplet ejector based on a voltage change of a drive waveform applied to the piezoelectric element. A driving method of the head,
A reserve of voltage that is set within a range that is equal to or lower than the minimum voltage required to eject the droplet from the nozzle when applied to the piezoelectric element, and the driving power of the voltage that enables the droplet to be ejected from the nozzle. Generate drive power,
A method of driving a droplet discharge head, wherein the piezoelectric element is driven by a drive waveform generated using the preliminary drive power during non-discharge of the droplet. A droplet discharge head provided with a pair of a piezoelectric element and a droplet ejector is provided, and the drive waveform voltage applied to the piezoelectric element is changed based on the discharge data, thereby being provided in the droplet ejector. A droplet discharge device that discharges liquid in a droplet ejector from a nozzle,
A driving power of a voltage enabling driving of the piezoelectric element, and a preliminary driving power of a voltage set in a range equal to or lower than a minimum voltage necessary for ejecting the droplet from the nozzle when applied to the piezoelectric element. A power supply unit that can be generated;
Drive waveform generation means for generating the drive waveform for driving the piezoelectric element based on the ejection data;
Driving means for driving the piezoelectric element based on the electric power input from the power supply unit and the driving waveform generated by the driving waveform generation unit;
Switching means for switching the power output from the power supply means to the drive means from the drive power to the preliminary drive power when the droplets from the nozzle of the droplet ejector are not ejected;
A droplet discharge apparatus comprising:   3. The liquid according to claim 2, wherein when the preliminary driving power is supplied to the driving unit by switching by the switching unit, the driving waveform generating unit outputs a preset preliminary driving waveform. 4. Drop ejection device.   4. The droplet discharge device according to claim 2, wherein the power supply unit includes step-down means for stepping down the drive power to the preliminary drive power. 5.   3. The preliminary driving power is supplied to the piezoelectric element through the driving means when the ejection data is not input until ejection of the droplet based on the ejection data is started. The droplet discharge device according to claim 1.   3. The preliminary drive power is supplied to the piezoelectric element when a non-ejection timing of the droplet occurs when the droplet is ejected at a series of timings based on the ejection data. The droplet discharge device according to claim 5.

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