JP2006341391A - Drive circuit of liquid droplet jet head and liquid droplet jet device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To detect the capacitance of a piezoelectric element with high accuracy without degrading a characteristic of ejecting a liquid droplet of a liquid droplet jet head. <P>SOLUTION: This drive circuit has a bridge circuit wherein a first circuit 150 having a piezoelectric element 42 and a resistor Rd serially connected with each other and a second circuit 152 having a reference capacitance capacitor 119 with a predetermined capacitance and a resistor Rdd with a resistance equal to that of the resistor Rd serially connected with each other, are connected with each other in parallel and a voltage indicative of a potential difference between a first connection line of the piezoelectric element 42 and the resistor Rd in the first circuit 150 and a second connection line of the capacitor 119 and the resistor Rdd in the second circuit 152 can be output as an output voltage. A CPU 40 computes a difference in the capacitance between the capacitor 119 and the piezoelectric element 42 on the basis of the potential difference between the first connection line and the second connection line indicated by the output voltage from the bridge circuit to calculate the capacitance of the piezoelectric element 42 by adding the value based on the difference to the predetermined capacitance of the capacitor 119. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  According to the present invention, a predetermined voltage is applied to a piezoelectric element based on image data indicating an image to be recorded, and the piezoelectric element is vibrated to generate a vibration wave in the pressure chamber, so that the liquid filled in the pressure chamber is ejected from the nozzle. The present invention relates to a droplet discharge head drive circuit that discharges from a droplet discharge device and a droplet discharge device that includes the droplet discharge head drive circuit.

  2. Description of the Related Art In recent years, ink jet recording apparatuses (so-called ink jet printers) that eject ink from nozzles of a recording head have been used as many image forming processing engines because of their small size and low cost. Among these ink jet recording apparatuses, there are many piezoelectric ink jet systems that provide a piezoelectric element for each nozzle of the recording head and eject ink from each nozzle by using deformation of each piezoelectric element from the viewpoint of high resolution and high speed printability. It's being used.

  An ink jet recording apparatus that uses vibration energy of a piezoelectric element such as a piezoelectric element applies a voltage to a piezoelectric element provided in an ink flow path according to image data to vibrate, and forms ink droplets by distortion of the piezoelectric element. To do.

  By the way, the piezoelectric element is deformed according to the amount of charge stored by applying a voltage, and the capacitance can be obtained from the applied voltage and the amount of stored charge. However, since the capacitance of the piezoelectric element varies in the recording head manufacturing process, even if the same voltage is applied, there is a difference in the amount of stored charge, resulting in a difference in the degree of deformation. Variations in the amount of ink ejected may result in a reduction in image quality of the formed (printed) image.

Therefore, Patent Document 1 discloses a technique in which a circuit for measuring capacitance is provided in a drive circuit that drives a piezoelectric element, and an applied voltage is changed according to the obtained capacitance. According to the technique of Patent Document 1, a resistor is inserted in series with a power supply line to a piezoelectric element, a test signal is applied to a drive circuit, a potential difference between both ends of the inserted resistor is measured, and a flowing current is obtained. Is measuring the capacitance.
JP-A-9-207325

  However, in the technique described in Patent Document 1, unless a resistor having a large resistance value is inserted, the capacitance of the piezoelectric element can be measured only with a low S / N ratio, and the capacitance of the piezoelectric element can be accurately detected. In addition, when a resistor having a large resistance value is inserted, the capacitance of the piezoelectric element can be detected with high accuracy, but the voltage drop due to the inserted resistor increases when a voltage is applied, resulting in a voltage applied to the piezoelectric element. There is a problem in that the ink ejection characteristics are deteriorated because the piezoelectric element cannot be sufficiently deformed due to the reduction in size.

  The present invention has been made to solve the above-described problems, and is a droplet discharge capable of accurately detecting the capacitance of the piezoelectric element without deteriorating the droplet discharge characteristics of the droplet discharge head. It is an object of the present invention to provide a head discharge circuit and a droplet discharge device including the droplet discharge head drive circuit.

  In order to achieve the above object, the invention described in claim 1 applies a predetermined voltage to a piezoelectric element based on image data indicating an image to be recorded and vibrates the piezoelectric element to generate a vibration wave in the pressure chamber. A liquid droplet ejection head driving circuit for ejecting liquid filled in the pressure chamber from a nozzle, wherein the piezoelectric element and a first resistor are connected in series, and a predetermined static electricity is connected. A second wiring in which a capacitor having a capacitance and a second resistor having a resistance value equivalent to the first resistor are connected in series is connected in parallel, and the piezoelectric element and the first wiring in the first wiring are connected. A bridge circuit using as an output voltage a voltage indicating a potential difference between the capacitor and the second connection line of the second resistor in the second wiring; Output voltage from the circuit Based on the potential difference between the first connection line and the second connection line shown, a difference in capacitance between the capacitor and the piezoelectric element is obtained, and a value based on the difference is determined in advance for the capacitor. Calculating means for calculating the capacitance of the piezoelectric element by adding to the calculated capacitance.

  According to the first aspect of the present invention, a first wiring in which a piezoelectric element and a first resistor are connected in series, a capacitor having a predetermined capacitance, and a resistance value equivalent to the first resistor are set. A second wiring connected in series with the second resistor, connected in parallel, the piezoelectric element in the first wiring and the first connection line of the first resistance, and the capacitor in the second wiring and the second wiring A bridge circuit having an output voltage as a voltage indicating a potential difference between the second connection line of the resistor and a second connection indicated by the output voltage from the bridge circuit by the calculating means Based on the potential difference between the lines, the capacitance difference between the capacitor and the piezoelectric element is obtained, and the capacitance based on the difference is added to the predetermined capacitance of the capacitor to calculate the capacitance of the piezoelectric element. The

  As described above, according to the first aspect of the present invention, the first wiring in which the piezoelectric element and the first resistor are connected in series, the capacitor having a predetermined capacitance, and the first resistor are equivalent. A second wiring in which a second resistance having a resistance value is connected in series is connected in parallel, and the piezoelectric element in the first wiring, the first connection line of the first resistance, and the second wiring A bridge circuit having an output voltage that is a voltage indicating a potential difference between the capacitor and the second connection line of the second resistor is provided between the first connection line and the second connection line indicated by the output voltage. Based on the potential difference, the difference between the capacitance of the capacitor and the piezoelectric element is obtained, and the value based on the difference is added to the predetermined capacitance of the capacitor to calculate the capacitance of the piezoelectric element. Piezoelectric without reducing the droplet discharge characteristics of the droplet discharge head The capacitance of the child can be accurately detected.

  According to the first aspect of the present invention, as in the second aspect of the present invention, drive signal generating means for generating a drive signal indicating the timing of applying the predetermined voltage to the piezoelectric element based on the image data; Pulse signal output means for outputting a plurality of pulse signals that have been subjected to any of the pulse modulations and different modulation states, and a pulse signal to be applied from the plurality of pulse signals according to the capacitance of the piezoelectric element Storage means for preliminarily storing the determined application information; and specifying means for specifying a pulse signal to be applied from the application information stored in the storage means based on the capacitance of the piezoelectric element calculated by the calculation means; Selection means for selectively outputting the pulse signal specified by the specifying means from the plurality of pulse signals output from the pulse signal output means; and An AND circuit that calculates a logical product of the pulse signal selectively output by the means and the drive signal generated by the drive signal generation means, and outputs the logical product as a signal indicating the timing of applying the predetermined voltage; It may be a thing.

  According to a second aspect of the present invention, it is preferable that the pulse signal output means outputs a plurality of pulse width modulation signals having different duty ratios, as in the third aspect of the present invention. The pulse signal output means may output a pulse signal that has been subjected to pulse modulation such as pulse amplitude modulation (PAM), delta modulation, or sigma delta modulation.

  According to a fourth aspect of the present invention, there is provided a switch for switching at least one of the first resistor and the second resistor between applying and not applying the predetermined voltage to the piezoelectric element. It is preferable to have an on-resistance.

  On the other hand, in order to achieve the above object, a droplet discharge device according to a fifth aspect includes the droplet discharge head according to any one of the first to fourth aspects.

  Therefore, the invention according to claim 5 operates in the same manner as the invention according to any one of claims 1 to 4, so that the droplet discharge characteristics of the droplet discharge head are not deteriorated. The capacitance of the piezoelectric element can be detected with high accuracy.

  As described above, according to the present invention, the first wiring in which the piezoelectric element and the first resistor are connected in series, the capacitor having a predetermined capacitance, and the resistance equivalent to the first resistance. A second wiring in which a second resistor having a value is connected in series is connected in parallel, and the piezoelectric element in the first wiring, the first connection line of the first resistance, and the capacitor in the second wiring And a second connection line of the second resistor are provided with a bridge circuit having an output voltage as a voltage indicating a potential difference between the first connection line and the second connection line indicated by the output voltage. Based on the potential difference, the difference between the capacitance of the capacitor and the piezoelectric element is obtained, and the capacitance based on the difference is added to the predetermined capacitance of the capacitor to calculate the capacitance of the piezoelectric element. Piezoelectric element without degrading the droplet ejection characteristics of the droplet ejection head Can be detected with the electrostatic capacitance accuracy, it has an excellent effect that.

  FIG. 1 shows a schematic configuration of an inkjet recording apparatus 10 according to the present embodiment.

  In the present embodiment, the conveyance direction of the recording paper P as a recording medium is the sub-scanning direction (see arrow S in FIG. 1), and the direction orthogonal to the sub-scanning direction is the main scanning direction (arrow M in FIG. 1). Reference).

  The ink jet recording apparatus 10 includes a carriage 14 on which black (K), yellow (Y), magenta (M), and cyan (C) ink jet recording units 12 are mounted.

  A pair of brackets 16 protrude from the carriage 14 on the upstream side in the conveyance direction of the recording paper P, and the bracket 16 has a circular opening 16A. A shaft 18 (see FIG. 1) installed in the main scanning direction is inserted through the opening 16A.

  As shown in FIG. 1, a driving pulley 22 and a driven pulley 24 constituting the main scanning mechanism 20 are disposed at both ends in the main scanning direction, respectively. A timing belt 26 is wound around the driving pulley 22 and the driven pulley 24, and the carriage 14 is fixed to a part of the timing belt 26. As a result, the carriage 14 can reciprocate in the main scanning direction.

  The ink jet recording apparatus 10 is provided with a sub-scanning mechanism 32 including a transport roller 28 and a discharge roller 30. The sub-scanning mechanism 32 sub-records the recording paper P fed one by one from the paper feed tray 34 that stores the recording paper P before printing (printing) in a bundle at a predetermined pitch or continuously at a constant speed. Transport in the scanning direction.

  A cleaning device 33 is disposed at one end of the shaft 18 so that the lower surface of the carriage 14 is opposed to the ink jet recording unit 12 when the carriage 14 is positioned immediately above the cleaning device. On the other hand, maintenance such as capping and suction is performed. For example, it is possible to suck ink from the nozzle 40 shown in FIG.

  As shown in FIG. 2, each color ink jet recording unit 12 includes a recording head 36 and an ink cartridge 38 that supplies ink to the recording head 36, and is formed on the lower surface of the recording head 36. A plurality of formed nozzles 40 (see FIG. 3) are mounted on the carriage 14 so as to face the recording paper P.

  Accordingly, the recording head 36 selectively ejects ink droplets from the nozzles 40 on the recording paper P based on the image data while moving in the main scanning direction by the main scanning mechanism 20 (see FIG. 1). An image is formed (printed) on a predetermined band area BE.

  When one movement in the main scanning direction is completed, the recording paper P is conveyed at a predetermined pitch in the sub scanning direction by the sub scanning mechanism 32 (see FIG. 1), and the inkjet recording unit 12 moves again in the main scanning direction. An image is formed (printed) on the next band area. By repeating this, an entire image based on the image data is formed on the recording paper P.

  As shown in FIG. 3, the recording head 36 includes an ink tank 41, a supply path 44, a pressure chamber 46, a nozzle 40, and a piezoelectric element 42.

  The ink tank 41 stores ink from the above-described ink cartridge 38 (see FIG. 2). The ink tank 41 communicates with the pressure chamber 46 through the supply path 44, and the pressure chamber 46 further passes through the nozzle 40. Communicate with the outside.

  A part of the wall surface (the lower surface in FIG. 3) of the pressure chamber 46 is made of a vibration plate 46A, and the piezoelectric element 42 is attached to the vibration plate 46A. A pressure wave is generated in the ink in the chamber 46. That is, the ink stored in the ink tank 41 is ejected from the nozzle 40 through the supply path 44 and the pressure chamber 46 by the pressure wave generated by the vibration of the piezoelectric element 42.

  FIG. 4 shows a schematic configuration of the electrical system of the inkjet recording apparatus 10 according to the present embodiment.

  The inkjet recording apparatus 10 stores in advance a CPU (Central Processing Unit) 50 that controls the entire operation, various programs including a control program for controlling the entire apparatus, an applied pulse voltage setting processing program described later, various parameters, various tables, and the like. ROM 52, RAM 54 for temporarily storing image data and various data received via a communication medium such as a network (not shown), and driving of a motor (not shown) for rotating the drive pulley 22 described above are controlled. Is used to control the movement of the carriage 14 in the main scanning direction and to control the conveyance of the recording paper P in the sub-scanning direction by controlling the driving of other motors (not shown) that rotate the conveyance roller 28 and the discharge roller 30. Used for the conveyance control unit 56 and the piezoelectric element 42 corresponding to each nozzle 40 A non-volatile memory 58 for storing a use signal storage table 70 (see FIG. 5) in which information indicating a pulse width modulation signal (hereinafter referred to as a PWM signal) (to be described in detail later) is stored, and a carriage controlled by the transport control unit 56. And a head drive circuit 100 that reads the image data stored in the RAM 54 in synchronization with the movement of 14 and vibrates each piezoelectric element 42 of the recording head 36 to eject ink from each nozzle 40.

  The head drive circuit 100 includes a capacitance detection circuit 101 (details will be described later), and can detect the capacitance Cd of each piezoelectric element 42 corresponding to each nozzle 40.

  In addition, the ROM 52 stores an applied pulse signal setting table 80 (see FIG. 6) in which PWM signals to be applied are determined according to the capacitance Cd of the piezoelectric element 42.

As shown in FIG. 6, the CPU 50, ROM 52, RAM 54, transport control unit 56,
The nonvolatile memory 58 and the head drive circuit 100 are connected to each other via a system bus BUS. Therefore, the CPU 50 accesses the ROM 52, RAM 54, and nonvolatile memory 58, controls the conveyance of the recording paper P by controlling the conveyance control unit 56 and the movement of the carriage 14 in the main scanning direction, and the head driving circuit 100. Control of the printing process on the recording paper P by controlling the control, and control of the detection process of the electrostatic capacitance Cd of each piezoelectric element 42 by outputting various signals such as a pulse voltage selection signal and a detection nozzle selection signal described later, Can be performed respectively.

  In the inkjet recording apparatus 10 according to the present embodiment, the electrostatic capacity Cd of each piezoelectric element 42 attached to each nozzle 40 is detected by an applied pulse voltage setting process to be described later, and an applied pulse signal setting table 80 (FIG. 6). And a nozzle use signal storage table 70 (see FIG. 5) in which a PWM signal corresponding to the capacitance Cd of each piezoelectric element 42 is specified, and information indicating the specified PWM signal is stored in the nonvolatile memory 58. ) Of the nozzle 40 to which the piezoelectric element 42 is attached.

  FIG. 7 shows a detailed configuration of the head drive circuit 100 according to the present embodiment.

  In addition to the original function of selectively driving each piezoelectric element 42 of the recording head 36, the head drive circuit 100 includes a capacitance detection circuit that measures the capacitance Cd of each piezoelectric element 42 as described above. 101 is incorporated.

  The head drive circuit 100 is provided with a voltage amplification circuit 102 at a ratio of 1: 1 with respect to each piezoelectric element 42.

  On the other hand, a dedicated selector 104 is connected to one input terminal of the voltage amplifier circuit 102. Each of the selectors 104 is connected to m PWM (1) 106 to PWM (m) 106 that output pulse width modulation (PWM) signals having different duty ratios. The select terminal of the selector 104 receives a pulse voltage selection signal from the CPU 50, and selects a PWM signal to be output to the voltage amplification circuit 102 by this voltage selection signal.

  The drive signal generation unit 105 is connected to the other input terminal of the voltage amplification circuit 102. The drive signal generation unit 105 outputs a drive signal for driving each piezoelectric element 42 based on the image data.

  Further, the voltage amplifier circuit 102 is connected to a power line connected to a driving power source (not shown), and power is supplied from the driving power source.

  FIG. 8 shows a detailed configuration of the voltage amplifier circuit 102.

  The voltage amplifier circuit 102 is provided with an AND circuit 130. The PWM signal output from the selector 104 is input to one input terminal of the AND circuit 130, and the drive signal output from the drive signal generation unit 105 is input to the other input terminal of the AND circuit 130. The AND circuit 130 outputs a timing signal for driving the piezoelectric element 42 at a timing when both the input PWM signal and the drive signal are ON.

  The output terminal of the AND circuit 130 is connected to the gate of an N-channel MOSFET (field effect transistor) 132. The drain of the MOSFET 132 is connected to a drive power supply (not shown), and the source of the MOSFET 132 is connected to the piezoelectric element 42 via a resistor Rd. In the present embodiment, the resistor Rd is an internal resistance (on-resistance) of the voltage amplifier circuit 102 itself, and the actual circuit does not include a resistor corresponding to the resistor Rd. As shown in FIG. 9, a voltage is applied to the piezoelectric element 42 from the drive power supply when both the drive signal and the PWM signal are on.

  The drive voltage applied to the piezoelectric element 42 is repeatedly turned on and off in synchronization with the pulse signal. However, since the piezoelectric element 42 has a capacitance Cd, Since the resistor Rd forms a low-pass filter and the voltage waveform is smoothed, the voltage value applied to the piezoelectric element 42 changes according to the duty ratio of the PWM signal. That is, as shown in FIG. 9, when the duty ratio of the PWM signal is high, the smoothed voltage value is high, and when the duty ratio is low, the smoothed voltage value is low.

  Here, the recording head 36 may have a variation of about ± 10%, for example, with respect to the design value in the capacitance Cd of the piezoelectric element 42 in the manufacturing process. Therefore, each of PWM (1) 106 to PWM (m) of the head drive circuit 100 is within a predetermined range based on a duty ratio that is a suitable voltage in the piezoelectric element 42 having the capacitance Cd as designed. A PWM signal having a slightly different duty ratio is output. Therefore, in the head drive circuit 100 according to the present embodiment, the selector 104 selects the PWA signal to be output from the PWM (1) 106 to PWM (m) to the voltage amplification circuit 102 and is applied to the piezoelectric element 42. The voltage value of the voltage is controlled.

  On the other hand, a gate of a P-channel MOSFET 134 is connected between the drive signal generator 105 and the AND circuit 130 via an inverter 136. The drain of the MOSFET 134 is connected between the source of the MOSFET 132 and the resistor Rd, and the source of the MOSFET 134 is grounded. The MOSFET 134 is supplied with a signal that is turned on and off by the inverter 136, turns on the MOSFET 134 when the drive signal is turned off, and releases the charge accumulated in the piezoelectric element 42.

  As shown in FIG. 7, one end of a switch 112 is connected between the resistor Rd and the piezoelectric element 42. The other end of the switch 112 is short-circuited by the output signal line 114, and the output signal line 114 is connected to the negative side input terminal 118 </ b> A of the differential amplifier 118 via the resistor 116.

  On the other hand, a drive signal is directly input from one drive signal generation unit 105 without passing through the selector 104 to one of the voltage amplification circuits 102 (the lowest stage of the voltage amplification circuit 102 arranged in FIG. 7). This voltage amplifier circuit 102 is for energizing the resistor Rdd for detecting capacitance and the reference capacitor 119. Since the voltage amplification circuit 102 does not receive the PWM signal, the AND circuit 130 shown in FIG. 8 is not provided, and the drive signal is directly input to the MOSFET 132.

  The output signal line 122 having one end connected between the resistor Rdd and the reference capacitor 119 has the other end connected to the positive input end 118B of the differential amplifier 118 via the resistor 124.

  The resistor Rdd has an equivalent resistance value that is substantially the same as the resistor Rd of the switching element 108. Note that the internal resistance (on-resistance) of the switching element 108 may be used as long as the resistance value is substantially the same as the resistance Rd. The capacitance Co of the reference capacitance capacitor 119 is the capacitance of the design value of the piezoelectric element 42, and the capacitance Cd of the piezoelectric element 42 is detected based on the capacitance Co of the reference capacitance capacitor 119. The

  With the above configuration, during normal printing, each selector 104 selects the PWM signal to be output based on the pulse voltage selection signal, and all the switches 112 are turned off by the detection nozzle selection signal, and based on the image data. Printing is executed by controlling the output of the drive signal by the drive signal generation unit 105.

  The above is the basic circuit system showing the original function of the head drive circuit 100. In the present embodiment, the following capacitance detection circuit 101 is incorporated in the basic circuit system.

  That is, at the time of electrostatic capacitance detection, the selector 104 connected to the piezoelectric element 42 to be detected selects a predetermined PWM signal based on the pulse voltage selection signal, and from the drive signal generation unit 105 for the electrostatic capacitance test. A drive signal is output. As a result, the voltage amplification circuit 102 applies the drive voltage to the piezoelectric element 42 at the timing when both the PWM signal and the drive signal for the capacitance test are on, and the capacitance test is also applied to the reference capacitor 119. The drive voltage is applied at the timing when the drive signal for turning on is turned on.

  Further, at the time of electrostatic capacitance detection, only the switch 112 connected to the piezoelectric element 42 to be detected is turned on by the detection nozzle selection signal.

  As a result, the differential amplifier 118 outputs a voltage indicating a potential difference between the voltage of the piezoelectric element 42 to be detected and the voltage of the reference capacitor 119.

  The potential difference between the voltage applied to the piezoelectric element 42 to be detected and the voltage applied to the reference capacitor 119 corresponds to the difference in capacitance between the reference capacitor 119 and the piezoelectric element 42 to be detected. Yes.

  Note that resistors 126 and 128 for adjusting the voltage to be divided and input to the differential amplifier 118 are interposed between the output signal lines 114 and 122 and the ground, respectively.

  The output terminal of the differential amplifier 118 is connected to the synchronous rectification unit 122 via the low-pass filter 120. Since the voltage output from the differential amplifier 118 may include a high-frequency component that is likely to cause noise, the low-frequency filter 120 cuts off the high-frequency component of the voltage fluctuation and synchronously rectifies only the low-frequency component. The data is output to 122.

  On the other hand, the synchronous rectification unit 122 is also connected to a wiring branched from the drive signal generation unit 105 and the voltage amplification circuit 102, and is output as it is when the drive signal is on with respect to the voltage output from the low-pass filter 120. When it is off, rectification that inverts the voltage value is performed and output to the AD converter 124. The AD conversion unit 124 performs digital conversion on the input voltage and outputs a digital voltage signal to the CPU 50.

  The CPU 50 calculates the electrostatic capacity Cd of the piezoelectric element 42 based on the voltage signal, and according to the electrostatic capacity Cd of the piezoelectric element 42 based on the applied pulse signal setting table 80 (see FIG. 6) stored in the ROM 52. The PWM signal to be applied is specified, and information indicating the specified PWM signal is stored in the nozzle number corresponding to the piezoelectric element 42 in the nozzle use signal storage table 70 (see FIG. 5).

  Next, the operation of the inkjet recording apparatus 10 when measuring the electrostatic capacitance Cd of the piezoelectric element 42 for each nozzle 40 will be described with reference to FIG. FIG. 10 is a flowchart showing the flow of the applied pulse voltage setting process program executed by the CPU 50 at this time, and the program is stored in a predetermined area of the ROM 52 in advance.

  In step 200 of the figure, any one of the piezoelectric elements 42 of the plurality of nozzles 40 provided in the recording head 36 is set as the detection target piezoelectric element 42, and the switch is connected to the detection target piezoelectric element 42. A detection nozzle selection signal is output to each switch 112 of the head drive circuit 100 so that only 112 is turned on and the other switches 112 are turned off.

  As a result, as shown in FIG. 11, the first wiring 150 in which the piezoelectric element 42 to be detected and the resistance Rd of the switching element 108 (see FIG. 4) are connected in series, the reference capacitance capacitor 119, and the resistance Rd A bridge circuit is configured by the second wiring 152 in which a resistor Rdd having an equivalent resistance value is connected in series. Since the other ends of the piezoelectric element 42 and the reference capacitor 119 are both grounded, in FIG. 11, the other ends of the piezoelectric element 42 and the reference capacitor 119 are short-circuited and grounded.

  In the next step 202, a pulse voltage selection signal is output to the selector 104 connected to the piezoelectric element 42 to be processed, and a predetermined PWM signal is output to the voltage amplification circuit 102. In this embodiment, the PWM signal (1) 106 is selected by the selector 104.

  In the next step 204, the drive signal generator 105 is controlled to output a test rectangular wave drive signal to the voltage amplification circuit 102 connected to the piezoelectric element 42 to be detected.

  As a result, a drive voltage is applied to the piezoelectric element 42 at a timing when both the PWM signal and the drive signal are on. As described above, since the low-pass filter is configured by the piezoelectric element 42 and the resistor Rd and smoothed, a voltage having a voltage value corresponding to the duty ratio of the PWM signal is applied to the piezoelectric element 42. The In addition, a driving voltage is applied to the reference capacitor 119 when the driving signal is turned on.

  As a result, the differential amplifier 118 outputs a voltage indicating a potential difference between the voltage of the piezoelectric element 42 to be detected and the voltage of the reference capacitor 119.

  12A and 13A show the voltage at the output terminal of the differential amplifier 118. FIG. The amplitude of the voltage waveform decreases as the electrostatic capacitance Cd and the electrostatic capacitance Co of the reference capacitance capacitor 119 are closer to the piezoelectric element 42 to be detected, and when Cd> Co (see FIG. 12A). ) Has a positive value, and when Cd <Co (see FIG. 13A), the voltage has a negative value. In FIGS. 12 and 13, voltage waveforms are shown when Co is changed with Cd = 575 [pF].

  The voltage output from the differential amplifier 118 is a high-frequency component cut off by the low-pass filter 120, rectified by the synchronous rectification unit 122 according to on / off of the drive signal, and digitally converted by the AD conversion unit 124. A signal is output to the CPU 50.

  FIG. 12B shows the result of rectifying the voltage waveform shown in FIG. 12A by the synchronous rectifier 122, and FIG. 13B shows the result shown in FIG. The result of rectifying the voltage waveform by the synchronous rectification unit 122 is shown.

  The synchronous rectification unit 122 outputs the drive voltage as it is with respect to the input voltage, and inverts the plus and minus during the off period, so that the waveform is on the plus side in FIG. In B), the waveform is on the negative side.

  In the next step 206, the CPU 50 detects the waveform of the potential difference between the negative input end 118A and the positive input end 118B of the differential amplifier 118 indicated as a voltage signal for a predetermined period. The potential difference V0 of the peak (maximum value) on the side is measured. If the waveform is on the minus side, the potential difference V0 of the peak (minimum value) on the minus side is measured.

  In the next step 208, the capacitance Cd of the piezoelectric element 42 to be detected is calculated based on the measured potential difference V0.

  That is, in the circuit configuration as shown in FIG. 11, the potential between the resistors Rd is input to the negative side input terminal 118A of the differential amplifier 118 (input voltage V1), and the potential between the resistors Rdd is set to the positive side of the differential amplifier 118. When wiring is performed so as to input (input voltage V2) to the input terminal 118B, the potential difference V0 output from the differential amplifier 118 can be expressed as V1-V2. This potential difference V0 is proportional to a value obtained by subtracting the electrostatic capacitance Co of the reference capacitance capacitor 119 from the electrostatic capacitance Cd of the piezoelectric element 42 to be detected, as shown in the following equation (1).

V0 = V1-V2∝Cd-Co (1)
Since the proportional constant K between V0 and Cd-Co can be determined in advance according to the circuit configuration of the head drive circuit 100, the capacitance Cd of the piezoelectric element 42 to be detected is obtained from the following equation (2). be able to.

Cd = Co + V0 / K (2)
In the next step 210, the PWM signal corresponding to the calculated electrostatic capacitance Cd of the piezoelectric element 42 to be detected is specified based on the applied pulse signal setting table 80 (see FIG. 6) stored in the ROM 52.

  In the next step 212, information indicating the PWM signal specified in step 210 is added to the nozzle number corresponding to the piezoelectric element 42 to be detected in the nozzle use signal storage table 70 (see FIG. 5) stored in the nonvolatile memory 58. Remember.

  In the next step 214, it is determined whether or not the setting process has been completed for all the piezoelectric elements 42. If the determination is affirmative, the process ends. If not, the process is not processed. The process proceeds to step 200 again using the piezoelectric element 42 as the detection target piezoelectric element 42.

  As described above, according to the applied pulse voltage setting process, the information indicating the PWM signal used according to the capacitance Cd for each piezoelectric element 42 of each nozzle 40 is stored in the use signal storage table 70 (see FIG. 5). The

  In the ink jet recording apparatus 10 according to the present embodiment, when printing is performed on the recording paper P, each nozzle number of the use signal storage table 70 is connected to the selector 104 connected to the piezoelectric element 42 attached to each nozzle 40. A pulse voltage selection signal is output based on the information stored in, and the selector 104 selects the PWM signal. As a result, a PWM signal corresponding to the capacitance of each piezoelectric element 42 is input to the voltage amplification circuit 102 connected to each piezoelectric element 42, and the piezoelectric element 42 is driven when both the drive signal and the PWM signal are on. A voltage from the power source is applied.

  That is, the voltage value of the voltage applied to the piezoelectric element 42 is controlled by changing the duty ratio of the PWM signal in accordance with the capacitance of the piezoelectric element 42. Thereby, even if there is variation in the capacitance of each piezoelectric element 42, the amount of stored charge can be made substantially the same. As a result, the degree of deformation of each piezoelectric element 42 is substantially the same, so that the amount of ink ejected from each nozzle 40 of the recording head 36 is reduced, and the image quality of the image formed (printed) on the recording paper P is reduced. Can be suppressed.

  In this embodiment, as described above, a signal having a high SN ratio can be obtained by using the output voltage V0 of the differential amplifier 118. That is, as shown in FIG. 10, the mechanical admittance of the recording head 36 can be detected with a high S / N ratio. Accordingly, it is possible to detect a non-ejection nozzle from the fluctuations in the normal ejection frequency and the non-ejection frequency shown in FIG.

  As described above, according to the present embodiment, the first wiring in which the piezoelectric element and the first resistor (here, the resistor Rd) are connected in series, and the capacitor having a predetermined capacitance (here Then, a second wiring in which a reference capacitor (119) and a second resistor (here, resistor Rdd) having a resistance value equivalent to the first resistor are connected in series is connected in parallel. A voltage indicating a potential difference between the piezoelectric element and the first connection line of the first resistor in one wiring and the capacitor and the second connection line of the second resistance in the second wiring; A bridge circuit serving as an output voltage is provided, and the calculation means (here, the CPU 40) is based on a potential difference between the first connection line and the second connection line indicated by the output voltage from the bridge circuit. The capacitor and the pressure Since the capacitance of the piezoelectric element is calculated by calculating the difference in capacitance of the elements and adding a value based on the difference to the predetermined capacitance of the capacitor, The capacitance of the piezoelectric element can be accurately detected without deteriorating the droplet ejection characteristics.

  In addition, a drive signal generation unit (here, drive signal generation unit 105) that generates a drive signal indicating the timing of applying the predetermined voltage to the piezoelectric element based on image data, and any pulse modulation is performed. Pulse signal output means (here, PWM (1) 106 to PWM (m) 106) for outputting a plurality of pulse signals in different modulation states, and the plurality of pulses according to the capacitance of the piezoelectric element Storage means for preliminarily storing application information (here, the application pulse signal setting table 80) that defines a pulse signal to be applied from the signal, and the specifying means (here, the CPU 40) is the calculation unit Based on the capacitance of the piezoelectric element, a pulse signal to be applied is identified from the application information stored in the storage unit, and a selection unit (here, a selector 1) is specified. 4) selectively outputs the pulse signal specified by the specifying means from the plurality of pulse signals output from the pulse signal output means, and the AND circuit selectively outputs the pulses selectively output by the selecting means. Since the logical product of the signal and the drive signal generated by the drive signal generation means is taken and output as a signal indicating the timing of applying the predetermined voltage, the liquid discharged from each nozzle of the droplet discharge head It is possible to reduce the variation in the amount of droplets and suppress the deterioration of the image quality of the formed image.

  Further, since the pulse signal output means outputs a plurality of pulse width modulation signals having different duty ratios, the voltage value applied to the piezoelectric element can be easily adjusted by changing the duty ratio of the pulse signals. it can.

  Furthermore, at least one of the first resistor and the second resistor is an on-resistance of a switch (here, the voltage amplification circuit 102) that switches application / non-application of the predetermined voltage to the piezoelectric element. In addition, since it is not necessary to add a resistor on the wiring connected to the piezoelectric element, the droplet discharge characteristics of the droplet discharge head are not deteriorated.

  In the present embodiment, the case where information indicating the PWM signal used for each nozzle 40 is stored in the nozzle use signal storage table 70 (see FIG. 5) has been described, but the present invention is not limited to this. For example, when the electrostatic capacity of the piezoelectric element 42 corresponding to the nozzle number is stored in the nozzle use signal storage table 70 and an image is formed, the electrostatic capacity for each nozzle stored in the nozzle use signal storage table 70 is used. Accordingly, the configuration may be such that the PWM signal to be applied is specified from the applied pulse signal setting table 80. Also in this case, the same effects as in the present embodiment can be obtained.

  In the present embodiment, the case of the inkjet recording apparatus 10 that forms an image on the recording paper P while the recording head 36 (see FIG. 1) is reciprocated in the main scanning direction by the main scanning mechanism 20 will be described. However, the present invention is not limited to this. For example, as a long head in which the recording head is wider than the width of the recording paper P, a large number of nozzles are arranged along the width direction of the recording paper P. The present invention is applied to an ink jet recording apparatus 10 that records the entire width of the recording paper P at a time by ejecting ink from each nozzle of the recording head, while the recording paper P is not moved relatively in the sub-scanning direction. May be applied. Also in this case, the same effects as in the present embodiment can be obtained.

In addition, the configuration of the inkjet recording apparatus 10 described in the present embodiment (FIGS. 1 to 4,
See FIG. 7 and FIG. ) And applied pulse voltage setting processing (see FIG. 10) are merely examples, and it goes without saying that they can be changed as appropriate without departing from the spirit of the present invention.

  The data structure of the nozzle use signal storage table (FIG. 5) and the applicable pulse signal setting table (FIG. 6) is also an example, and it goes without saying that it can be changed as appropriate without departing from the gist of the present invention.

  Furthermore, although the inkjet recording apparatus 10 described in the present embodiment forms an image (including characters) on a recording medium, the inkjet recording apparatus 10 of the present invention is not limited to this. . That is, the recording medium is not limited to recording paper, and the liquid to be ejected is not limited to ink. For example, the present invention can also be applied to other liquid droplet ejection recording apparatuses such as a pattern forming apparatus that ejects liquid droplets onto a sheet-like substrate for pattern formation of a semiconductor or a liquid crystal display.

1 is a perspective view illustrating an appearance of an ink jet recording apparatus according to an embodiment. 2 is a perspective view of a carriage provided in the ink jet recording apparatus according to the present embodiment. FIG. 2 is a cross-sectional view showing an internal structure of a recording head according to the present embodiment. FIG. 1 is a block diagram illustrating a configuration of an electric system of an ink jet recording apparatus according to an embodiment. It is a schematic diagram which shows an example of the data structure of the nozzle use signal storage table memorize | stored in the non-volatile memory. It is a schematic diagram which shows an example of the data structure of the applicable pulse signal setting table memorize | stored in ROM. FIG. 3 is a circuit diagram showing a detailed configuration of a head drive circuit according to the present embodiment. It is a circuit diagram which the detailed structure of the voltage amplifier circuit which concerns on this Embodiment shows. It is a wave form diagram which shows the waveform of the various signals which concern on this Embodiment. It is a flowchart which shows the flow of a process of the applied pulse voltage setting process program which concerns on this Embodiment. It is an equivalent circuit diagram when detecting the electrostatic capacitance of the piezoelectric element to be detected according to the present embodiment. It is a wave form diagram which shows the waveform of the voltage in the output terminal of a differential amplifier in the case of Cd> Co based on this Embodiment. It is a wave form diagram which shows the waveform of a voltage in the output terminal of a differential amplifier in the case of Cd <Co concerning this Embodiment.

Explanation of symbols

10 Inkjet recording device 40 CPU
52 ROM
80 Applied Pulse Signal Setting Table 100 Head Drive Circuit 102 Voltage Amplifier Circuit 104 Selector 105 Drive Signal Generation Unit 106 PWM (1) to PWM (m)
130 AND circuit 150 1st wiring 152 2nd wiring Rd resistance Rdd resistance

Claims (5)

A liquid that applies a predetermined voltage to the piezoelectric element based on image data indicating an image to be recorded, and vibrates the piezoelectric element to generate a vibration wave in the pressure chamber, thereby discharging the liquid filled in the pressure chamber from the nozzle. A droplet discharge head drive circuit comprising:
A first wire in which the piezoelectric element and the first resistor are connected in series, a capacitor having a predetermined capacitance, and a second resistor having a resistance value equivalent to the first resistor are connected in series. The connected second wiring is connected in parallel, and the piezoelectric element and the first connection line of the first resistance in the first wiring, and the capacitor and the second resistance in the second wiring A bridge circuit having a voltage indicating a potential difference between the second connection lines as an output voltage;
Based on the potential difference between the first connection line and the second connection line indicated by the output voltage from the bridge circuit, a difference in capacitance between the capacitor and the piezoelectric element is obtained, and a value based on the difference. Calculating means for calculating the capacitance of the piezoelectric element by adding to the predetermined capacitance of the capacitor;
A drive circuit for a droplet discharge head comprising: Drive signal generating means for generating a drive signal indicating timing of applying the predetermined voltage to the piezoelectric element based on the image data;
Pulse signal output means for outputting a plurality of pulse signals that have been subjected to any of the pulse modulations and in different modulation states;
Storage means for preliminarily storing application information defining a pulse signal to be applied from the plurality of pulse signals according to the capacitance of the piezoelectric element;
Specifying means for specifying a pulse signal to be applied from the application information stored in the storage means based on the capacitance of the piezoelectric element calculated by the calculation means;
Selecting means for selectively outputting the pulse signal specified by the specifying means from the plurality of pulse signals output from the pulse signal output means;
An AND circuit that takes a logical product of the pulse signal selectively output by the selection unit and the drive signal generated by the drive signal generation unit, and outputs the logical product as a signal indicating the timing of applying the predetermined voltage;
The droplet discharge head drive circuit according to claim 1, further comprising: The droplet discharge head drive circuit according to claim 2, wherein the pulse signal output means outputs a plurality of pulse width modulation signals having different duty ratios. 4. The switch according to claim 1, wherein at least one of the first resistor and the second resistor is an on-resistance of a switch that switches application / non-application of the predetermined voltage to the piezoelectric element. 5. A drive circuit of the described droplet discharge head. A droplet discharge apparatus comprising the droplet discharge head drive circuit according to claim 1.

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