JP2006256149A - Driving device of piezoelectric element, method of driving, and liquid droplet jet device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a driving device of a piezoelectric element capable of improving energy efficiency by recycling an electric charge accumulated on the piezoelectric element by using the fact that the piezoelectric element is of a capacity to reuse the charge and of producing two kinds of vibration energies by driving the piezoelectric element by one system of a power source, and to provide a method of driving the piezoelectric element and a liquid droplet jet device. <P>SOLUTION: By paying attention to the fact that a piezoelectric element 42 has capacitor properties, an electric charge accumulated on the piezoelectric element 42 when applying the electricity thereto and discharged to be thrown away heretofore is made to establish a potential difference by switching between serial connection and parallel connection of two capacitors 118, 124, and then charging and discharging is repeated. A drive voltage with a prescribed pulse width having an amplitude equal to a difference between a peak voltage and a base voltage is applied to the piezoelectric element 42. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a driving device and driving method for a piezoelectric element that vibrates a piezoelectric element by repeatedly applying a driving voltage having a predetermined pulse width, and a droplet discharge device.

  2. Description of the Related Art In recent years, so-called inkjet printers that eject ink from ink ejection ports have been used as many image forming processing engines because of their small size and low cost. Among these ink jet printers, a piezo ink jet method that ejects ink by using deformation of a piezoelectric element is widely used from the viewpoint of high resolution and high speed printability.

  An ink jet printer that uses vibration energy of a piezoelectric element such as a piezoelectric element vibrates a piezoelectric element provided in an ink flow path in accordance with image information, and forms ink droplets by distortion of the piezoelectric element. By controlling the waveform of the voltage applied to the piezoelectric element, it is possible to control the meniscus of the ink ejection port and the re-supply of the ink after ejection. Gradation recording with varying amounts becomes possible.

  As a drive circuit for applying vibration energy to the piezoelectric element, driving by an analog amplifier or driving by a digital rectangular wave can be considered.

  In the case of driving with an analog amplifier, a voltage with a highly accurate waveform can be applied, but the circuit configuration is complicated and energy efficiency is poor. On the other hand, in the digital rectangular wave drive, the circuit configuration is simple, but the waveform accuracy is poor and the energy efficiency is not as high as that of the analog amplifier, but it is wasteful.

  This waste means that the accumulated charge is conventionally discarded by discharge on the assumption that the piezoelectric element is capacitive and can accumulate charge.

  This discarding of the charge causes a decrease in energy efficiency. In other words, using this discarded charge as regenerative energy leads to an increase in efficiency.

In addition, as a prior art regarding the regeneration of energy, the technique which receives a discharge current with a transformer and regenerates by making DC-DC high voltage (refer to patent documents 1), and the technique which receives and regenerates the discharge current with a transformer by bridge composition (patent) Reference 2) is disclosed.
JP-A-11-314364 Japanese Patent Laid-Open No. 2001-026109

  However, it is difficult to directly introduce the regenerative techniques described in Patent Document 1 and Patent Document 2 into the drive circuit of the piezoelectric element, and the current situation is that it has not been established.

  In addition, when the vibration energy generated by the piezoelectric element is specialized for the ink ejection described above, shuffle driving may be performed to adjust the viscosity of the ink separately from the printing driving. However, generation of different signals (pulse width modulation, etc.) is necessary.

  In consideration of the above facts, the present invention utilizes the fact that a piezoelectric element is capacitive, regenerates and reuses the charge accumulated in the piezoelectric element, and can improve energy efficiency. It is an object to obtain an element driving apparatus and a driving method.

  In addition to the above object, another object is to obtain a piezoelectric element driving apparatus and driving method, and a droplet discharge apparatus capable of generating two types of vibration energy by driving a piezoelectric element with a single power source. .

  A first aspect of the present invention is a piezoelectric element driving apparatus that vibrates a piezoelectric element by repeatedly applying a driving voltage having a predetermined pulse width, and includes a plurality of capacitors, and these capacitors are connected in series. Or a switching means that can be switched to a second position that is in a parallel connection state, and a first switch that is turned on while being switched to the first position by the switching means. An initial charging means for initially charging each capacitor, and a second switch that is turned on for a predetermined time after the initial charging by turning off the first switch, and based on the charge charged in each capacitor A peak voltage applying means for applying a peak voltage to the piezoelectric element, and the switching means is moved to a second position after the second switch is turned off after the predetermined time has elapsed. Switching and turning on the second switch again discharges the charge accumulated in the piezoelectric element to a base voltage and recharges each capacitor based on the charge released by the discharge Means, and alternately repeating the application of a predetermined voltage to the piezoelectric element by the peak voltage applying means and the recharging of the charge accumulated in the piezoelectric element by the recharging means, A drive voltage having the predetermined pulse width having an amplitude that is the difference between the peak voltage and the base voltage is applied to the piezoelectric element.

  According to the first invention, the plurality of capacitors are directly connected by setting the switching means to the first position. In this state, the initial charging means turns on the first switch, whereby the initial charge is performed on each capacitor by the power from the power source.

  After the initial charging is completed, the first switch is turned off, while the peak voltage applying means turns on the second switch. Thereby, a peak voltage is applied to the piezoelectric element by the electric charge accumulated in the capacitor.

  In the recharging unit, when a predetermined time elapses, the second switch is turned off and the switching unit is set to the second position, so that the plurality of capacitors are connected in parallel. Thereafter, by turning on the second switch again, the electric charge accumulated in the piezoelectric element is discharged and used as the base voltage. Each capacitor is recharged based on the electric charge released by this discharge (correlated with the potential difference between the direct connection and the parallel connection).

  By alternately repeating the application of a predetermined voltage to the piezoelectric element by the peak voltage applying unit and the recharging of the charge accumulated in the piezoelectric element by the recharging unit, the piezoelectric element The driving voltage having the predetermined pulse width having the amplitude of the difference between the peak voltage and the base voltage can be applied.

  In the first invention, the plurality of capacitors are two capacitors having the same capacitance, and the base voltage is set to be ½ of the peak voltage.

  By connecting two capacitors directly or in parallel, the base voltage becomes 1/2 of the peak voltage, and it is most efficient to repeat charging and discharging.

  In the first invention, the initial charging by the initial charging means is periodically performed to compensate for the loss of charge accumulation in the piezoelectric element and the loss in recharging the capacitor. It is characterized by.

  Theoretically, after one initial charge, the drive voltage having the amplitude of the potential difference between the peak voltage and the base voltage can be applied semipermanently by repeatedly charging and discharging the capacitor. Since there is a loss on the circuit, it is sufficient to compensate for the loss by periodically performing initial charging.

  Furthermore, in the first invention, the piezoelectric element is applied to apply a vibration wave to a pressure chamber filled with a liquid and vibrate the liquid in the pressure chamber.

  When a vibration wave is applied to the liquid in the pressure chamber, for example, the liquid can be discharged according to the vibration energy from a nozzle provided in a part of the pressure chamber. Further, although there is not enough energy to be ejected from the nozzle as vibration energy, the viscosity or the like may be adjusted by shuffling the liquid in the pressure chamber.

  In particular, the first invention can maximize the improvement in energy efficiency by using it as the drive voltage of the latter (that is, shuffle).

  A second invention is a method of driving a piezoelectric element that vibrates a piezoelectric element by repeatedly applying a driving voltage having a predetermined pulse width, in a state where two capacitors having the same capacitance are connected in series. , The battery is initially charged with power from the power source, the piezoelectric element is applied with the voltage across the two capacitors initially charged as a peak voltage, and the charge accumulated in the piezoelectric element by the application of the peak voltage is By recharging the capacitors in a parallel connection state, the piezoelectric element is used as a base voltage, the two recharged capacitors are connected in series again, and the piezoelectric element is applied repeatedly at a peak voltage. Yes.

  According to the second invention, attention is paid to the fact that the piezoelectric element is capacitive, and in the past, the charge accumulated in the piezoelectric element was discharged and discarded, and the discharge from the piezoelectric element was accumulated in the capacitor. In addition, a plurality of capacitors can be switched in synchronization with the driving of the piezoelectric element so that a plurality of capacitors can be directly connected (at the time of initial charge and reuse) and connected in parallel (at the time of recharge) so that they can be reused.

  This makes it possible to effectively use (regenerate) the charge accumulated in the piezoelectric element that has been simply discarded.

  In the second invention, the initial charging by the initial charging means is periodically executed to compensate for the loss of charge accumulation in the piezoelectric element and the loss during recharging of the capacitor. It is characterized by.

  Theoretically, after one initial charge, the drive voltage having the amplitude of the potential difference between the peak voltage and the base voltage can be applied semipermanently by repeatedly charging and discharging the capacitor. Since there is a loss on the circuit, it is sufficient to compensate for the loss by periodically performing initial charging.

  According to a third aspect of the invention, there is provided a recording head that discharges droplets from the nozzles by applying a drive signal to the piezoelectric element based on the image data, and the liquid discharge surface of the recording head with respect to the conveyance path of the recording paper A liquid droplet ejection apparatus for forming an image on the recording paper by ejecting liquid droplets at a predetermined ejection timing and facing each other at a predetermined interval, wherein the piezoelectric element of the recording head is the above-described piezoelectric element. The drive control is performed by the drive device according to claim 4.

  According to the third invention, the piezoelectric element driving device shown in the first invention can be applied as a piezoelectric element driving device mounted on a recording head of a droplet discharge device.

  That is, by setting the switching means to the first position, the plurality of capacitors are directly connected. In this state, the initial charging means turns on the first switch, whereby the initial charge is performed on each capacitor by the power from the power source.

  After the initial charging is completed, the first switch is turned off, while the peak voltage applying means turns on the second switch. Thereby, a peak voltage is applied to the piezoelectric element by the electric charge accumulated in the capacitor.

  In the recharging unit, when a predetermined time elapses, the second switch is turned off and the switching unit is set to the second position, so that the plurality of capacitors are connected in parallel. Thereafter, by turning on the second switch again, the electric charge accumulated in the piezoelectric element is discharged and used as the base voltage. Each capacitor is recharged based on the electric charge released by this discharge (correlated with the potential difference between the direct connection and the parallel connection).

  By alternately repeating the application of a predetermined voltage to the piezoelectric element by the peak voltage applying unit and the recharging of the charge accumulated in the piezoelectric element by the recharging unit, the piezoelectric element The driving voltage having the predetermined pulse width having the amplitude of the difference between the peak voltage and the base voltage can be applied.

  It is most efficient to repeat charge and discharge by connecting two capacitors directly or in parallel.

  Theoretically, after one initial charge, the drive voltage having the amplitude of the potential difference between the peak voltage and the base voltage can be applied semipermanently by repeatedly charging and discharging the capacitor. Since there is a loss on the circuit, it is sufficient to compensate for the loss by periodically performing initial charging.

  When a vibration wave is applied to the liquid in the pressure chamber, for example, the liquid can be discharged according to the vibration energy from a nozzle provided in a part of the pressure chamber. Further, although there is not enough energy to be ejected from the nozzle as vibration energy, the viscosity or the like may be adjusted by shuffling the liquid in the pressure chamber. In particular, the energy efficiency can be maximized by using the latter (ie, shuffle) drive voltage.

  As described above, in the present invention, it is possible to improve the energy efficiency by regenerating and reusing the charge accumulated in the piezoelectric element by utilizing the capacitive property of the piezoelectric element. It has the effect.

  In addition to the above effect, there is an effect that two types of vibration energy can be generated by driving the piezoelectric element with a single power source.

  FIG. 1 shows a schematic configuration of a PWA (Partial Width Array) type ink jet printer 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 printer 10 includes a carriage 14 on which black, yellow, magenta, and cyan 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 inkjet printer 10 is provided with a sub-scanning mechanism 32 including a conveyance 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.

  As shown in FIG. 2, each color inkjet 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. The plurality of 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.

  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 connects the nozzle 40. It communicates with the outside through.

  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 drive circuit 100 for the piezoelectric element 42 according to the present embodiment.

  The drive circuit 100 is provided with a selector 102 at a ratio of 1: 1 for each piezoelectric element 42, and the viscosity adjustment signal from the viscosity adjustment signal output unit 104 selected by the selector 102 or the print drive signal output unit 106. Any one of the print drive signals is input. The selection of the viscosity adjustment signal and the print drive signal is made based on the print nozzle selection signal input to the selector 102.

  Accordingly, the drive power is supplied to the piezoelectric element 42 by either the viscosity adjustment signal or the print drive signal, and the piezoelectric element 42 can be driven.

  Here, the print drive signal output unit 106 outputs a voltage having such an energy (amplitude) that ink can actually be ejected from the pressure chamber 46 through the nozzle 40, whereas the viscosity adjustment signal output unit 104. From the above, a predetermined vibration is applied to the pressure chamber 46, but a voltage having an energy (amplitude) that does not eject ink from the nozzle 40 is output. That is, the viscosity adjustment signal is applied outside the printing period in order to stabilize the viscosity of the ink in the pressure chamber 46.

  In the present embodiment, the circuit for generating the viscosity adjustment signal in the viscosity adjustment signal output unit 104 has an energy regeneration function.

  As shown in FIG. 5, in the power supply circuit in the viscosity adjustment signal output unit 104, the first switch 110 and the second switch 112 are connected in series between the power supply 108 and the piezoelectric element 42.

  One end of each of the two branch lines 114 and 116 is connected between the first switch 110 and the second switch 112.

  A branch line 114 near the first switch 110 is connected to one end of the first capacitor 118. The other end of the first capacitor 118 is connected to the common terminal 120C of the third switch 120 that forms part of the switching means.

  Further, the branch line 116 near the second switch 112 is connected to the first contact 122A of the fourth switch 122 that constitutes a part of the switching means. The common terminal 122C of the fourth switch 122 is grounded via the second capacitor 124.

  In the present embodiment, the first capacitor 118 and the second capacitor 124 have the same capacitance.

  Further, the first contact 120A of the third switch 120 is grounded, and the second contact 120B is electrically connected to the second contact 122B of the fourth switch 122.

  Here, the third switch 120 and the fourth switch 122 are interlocked and simultaneously switched to the first contacts 120A and 122A (hereinafter referred to as the second position), or the second contacts 120B and 122B (hereinafter referred to as the second contacts). , Referred to as the first position).

  That is, when the third switch 120 and the fourth switch 122 are in the first position, the two capacitors (the first capacitor 118 and the second capacitor 124) are connected in series with each other, When the first switch 110 is on and the second switch 112 is off, charging is performed with power from the power source (initial charging).

  In addition, when the first switch 110 is off and the second switch 112 is on, a predetermined voltage (peak voltage) is applied to the piezoelectric element 42 by the charges charged in the two capacitors 118 and 124. (Reuse)

  On the other hand, when the third switch 120 and the fourth switch 122 are in the second position, the two capacitors are connected in parallel with each other (1/2 potential (base voltage) when connected in series). When the first switch 110 is off and the second switch 112 is on, charging is performed by discharging electric charges accumulated in the piezoelectric element 42.

  That is, in the present embodiment, the two capacitors 118 and 124 that are initially charged with the power from the power source 108 are discharged to the piezoelectric element 42 in a serial connection state, and the charge from the piezoelectric element 42 is regenerated in a parallel connection state. Will have a role to play.

  The operation of this embodiment will be described below.

  When printing is instructed, the recording paper P fed one by one from the paper feed tray 34 is conveyed in the sub-scanning direction at a predetermined pitch or continuously at a constant speed.

  When the recording sheet P is positioned at a predetermined position, the recording head 36 is selectively moved from the nozzle 40 to the recording sheet P based on the image data while moving in the main scanning direction by the main scanning mechanism 20. Discharge drops. As a result, an image is formed (printed) on the predetermined band area BE.

  When one movement in the main scanning direction is completed, the recording paper P is conveyed by a predetermined pitch in the sub scanning direction by the sub scanning mechanism 32. In the present embodiment, the intermittent transport is performed at predetermined pitches, but the sub-scan may always be performed at a constant speed even during the one main scan.

  After transporting the predetermined pitch, the inkjet recording unit 12 forms (prints) an image on the next band area while moving in the main scanning direction again.

  By repeating this, the entire image based on the image data can be formed on the recording paper P.

  In the repeated main scanning movement, the carriage 12 always decelerates, stops, and accelerates. This is outside the printing period and is also an indispensable time.

  The recording paper P on which the image is formed is discharged by the discharge roller 30 and one printing is completed. In addition, when printing a plurality of pages continuously, the next recording paper P is fed from the paper feed tray 34 at the same time as or after the discharge of the recording paper P by the discharge roller 30.

  At the time of printing, the drive circuit 100 outputs a print drive signal based on a signal from the print drive signal output unit 106.

  The image data is converted into a print nozzle selection signal, a current flows through the piezoelectric element 42, and vibration starts.

  This vibration is transmitted to the vibration plate 46A of the pressure chamber 46, and the vibration plate 46A vibrates to generate a pressure wave in the ink in the pressure chamber 46. By this pressure wave, the ink stored in the ink tank 41 is ejected from the nozzle 40 through the supply path 44 and the pressure chamber 46.

  On the other hand, when adjusting the viscosity of the ink in the pressure chamber 46, a viscosity adjustment drive signal is output based on the signal from the viscosity adjustment signal output unit 104. Thereby, although the ink in the pressure chamber 46 is not ejected from the nozzle 40, it can maintain an appropriate viscosity by being stirred (shuffled).

  Here, since the voltage (amplitude) of the viscosity adjustment waveform is ½ that of the print drive signal, conventionally, the voltage adjustment is performed using two power sources. Further, since the electric charge accumulated in the piezoelectric element 42 by being applied to the piezoelectric element 42 was discharged and discarded each time, the loss of energy was large.

  Therefore, in the present embodiment, when a voltage based on the viscosity adjustment signal is applied, the electric charge accumulated in the piezoelectric element 42 is regenerated.

  Hereinafter, an operation procedure of the power supply circuit in the viscosity adjustment signal output unit 104 in the drive circuit will be described. Note that the numbers in parentheses correspond to the numbers indicated by arrows in the operating characteristics of FIG.

  When not driven, both the first switch 110 and the second switch 112 are in the OFF state, and the third switch 120 and the fourth switch 122 are set to the second contacts 120B and 122B (first position), respectively. (Capacitor connected in series).

  (1) When driving is started, the first switch 110 is turned on, and as a result, the first capacitor 118 and the second capacitor 124 are initially charged by the power from the power source 108 (the charging voltage is a peak voltage).

  (2) After the initial charging, the first switch 110 is turned off and the second switch 112 is turned on, so that the piezoelectric element 42 is based on the charges charged in the first capacitor 118 and the second capacitor 124. Is applied.

  (3) When the second switch 112 is turned off, the piezoelectric element 42 is maintained in a peak voltage state (charge is accumulated in the piezoelectric element 42).

  (4) In this state, the third switch 120 and the fourth switch 122 are switched to the first contacts 120A and 122A, respectively (second position). As a result, the first capacitor 118 and the second capacitor 124 are connected in parallel.

  (5) When the second switch 112 is turned on again, the potential of the piezoelectric element 42 is ½ of the peak voltage (base voltage) with respect to the first capacitor 118 and the second capacitor 124 in the parallel connection state. The first capacitor 118 and the second capacitor 124 are recharged with the base voltage charge (regeneration).

  (6) In this state, the third switch 120 and the fourth switch 122 are switched to the second contacts 120B and 122B, respectively (first position). As a result, the first capacitor 118 and the second capacitor 124 are connected in series.

  As a result, the potentials of the first capacitor 118 and the second capacitor 124 are doubled (peak voltage), and the peak voltage is applied to the piezoelectric element 42 again.

  Theoretically, by repeating the following (2) to (6), the application of the peak voltage-base voltage is repeated to the piezoelectric element 42, so that a minute vibration is realized without supplying external power. be able to.

  In reality, since there is an energy loss in the circuit, in order to compensate for the loss, the steps (1) to (6) are repeated. As a result, energy efficiency can be improved.

(Modification)
FIG. 7 shows a circuit configuration using a switching element such as a transistor for the first switch 110, the second switch 112, the third switch 120, and the fourth switch 122 in the above embodiment. It can be controlled by a binary signal of “L” or “H” from a controller (not shown).

  In particular, the third switch 120 and the fourth switch 122 are configured by two transistors 150154 and the third switching element 152 and one inverter 156, so that the switching timing can be synchronized.

  As shown in FIG. 7, the power source 108 is connected to the drain (D) of the first transistor 158, and when the “H” signal is input to the gate (G), the drain (D) -source (S). It becomes a conduction state. The source (S) of the first transistor 158 is connected to the input / output terminal A of the second switching element 160.

  When the “H” signal is input to the control terminal of the second switching element 160, the switching elements are brought into conduction.

  The input / output terminal B of the second switching element 160 is connected to one end of the piezoelectric element 42. The other end of the piezoelectric element 42 is grounded.

  The first capacitor 118 interposed in the branch line 114 near the first transistor 158 includes a drain (D) of the pair of third transistors 150 functioning as a third switch and an input / output of the third switching element 152. Each is connected to a terminal A.

  The source (S) of one third transistor 150 is grounded, and the other third switching element 152 is connected to the source (S) of the fourth transistor 154 functioning as a fourth switch.

  The drain (D) of the fourth transistor 154 is connected to the branch line 116 near the second switching element 160.

  Here, the signal line 164 from the signal output unit 162 that controls on / off of the third transistor 150, the third switching element 152, and the fourth transistor 154 is connected to the third transistor 150 and the fourth transistor 154. Directly input to each gate (G), the third switching element 152 is connected to a control terminal via an inverter 156.

  That is, when the “L” signal is output from the signal output unit 162, the third transistor 150 and the fourth transistor 154 are nonconductive between the drain (D) and the source (S) (off state), In the switching element 152 of No. 3, the input / output is conducted (ON state). In this state, the first capacitor 118 and the second capacitor 124 are connected in series.

  On the other hand, when the “H” signal is output from the signal output unit 162, the third transistor 150 and the fourth transistor 154 are electrically connected between the drain (D) and the source (S) (ON state), In the switching element 152, the input and output become non-conductive (off state). In this state, the first capacitor 118 and the second capacitor 124 are connected in parallel.

  Hereinafter, the operation procedure of the power supply circuit in the viscosity adjustment signal output 104 in the drive circuit according to this modification will be described. Note that the numbers in parentheses correspond to the numbers indicated by arrows in the operating characteristics of FIG.

  At the time of non-driving, both the first transistor 158 and the second switching element 160 are in an off state, and an “L” signal is output from the signal output unit 162, and the third transistor 150 and the fourth transistor 154 are respectively The source (S) and the drain (D) are non-conducting (off state), and the input / output of the third switching element 152 is conducting (on state) (capacitor series connection state).

  (1) When driving is started, the first transistor 158 is turned on, and as a result, the first capacitor 118 and the second capacitor 124 are initially charged by the power from the power supply 108 (the charging voltage is a peak voltage).

  (2) After the initial charging, the first transistor 158 is turned off and the second switching element 160 is turned on, so that the piezoelectric element is based on the charges charged in the first capacitor 118 and the second capacitor 124. 42 is applied.

  (3) When the second switching element 160 is turned off, the piezoelectric element 42 is maintained in a peak voltage state (a state where electric charges are accumulated in the piezoelectric element 42).

  (4) In this state, by outputting the “H” signal from the signal output unit 162, the third transistor 150 and the fourth switch 154 are turned on, and the third switching element 152 is turned off. As a result, the first capacitor 118 and the second capacitor 124 are connected in parallel.

  (5) When the second switching element 160 is turned on again, the potential of the piezoelectric element 42 is ½ of the peak voltage (base voltage) with respect to the first capacitor 118 and the second capacitor 124 in the parallel connection state. The first capacitor 118 and the second capacitor 124 are recharged with the base voltage charge (regeneration).

  (6) In this state, the signal output unit 162 outputs an “L” signal. As a result, the first capacitor 118 and the second capacitor 124 are connected in series.

  As a result, the potentials of the first capacitor 118 and the second capacitor 124 are doubled (peak voltage), and the peak voltage is applied to the piezoelectric element 42 again.

  Theoretically, by repeating the following (2) to (6), the application of the peak voltage-base voltage is repeated to the piezoelectric element 42, so that a minute vibration is realized without supplying external power. be able to.

  In reality, since there is an energy loss in the circuit, in order to compensate for the loss, the steps (1) to (6) are repeated. As a result, energy efficiency can be improved.

  As described above, in the present embodiment, attention is paid to the fact that the piezoelectric element 42 is capacitive. Conventionally, the charge accumulated when applied to the piezoelectric element 42 is discharged and discarded. By switching the capacitors 118 and 124 to series connection or parallel connection so as to have a potential difference and repeat charging and discharging, energy can be used effectively. In particular, the piezoelectric element 42 can be used as a vibration energy source for adjusting the viscosity of ink in the pressure chamber 46 when the piezoelectric element 42 is applied as a recording head for discharging ink.

  In this embodiment, two capacitors having the same capacitance are connected in series and connected in parallel to perform charging / discharging. However, three or more capacitors having different capacitances are used. You may do it.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view showing an external appearance of a PWA type ink jet printer according to an embodiment. FIG. 4 is a perspective view of a carriage provided in the inkjet printer according to the present embodiment. 2 is a cross-sectional view showing an internal structure of a recording head according to the present embodiment. FIG. It is a drive circuit diagram for driving the piezoelectric element according to the present embodiment. It is a circuit diagram which shows the detail of the viscosity adjustment output part in the drive circuit which concerns on this Embodiment. It is a voltage characteristic figure with the piezoelectric element based on the viscosity adjustment signal from the viscosity adjustment output part which concerns on this Embodiment. It is a circuit diagram which shows the detail of the viscosity adjustment output part in the drive circuit which concerns on a modification. It is a voltage characteristic figure with the piezoelectric element based on the viscosity adjustment signal from the viscosity adjustment output part which concerns on a modification.

Explanation of symbols

P Recording paper 10 Inkjet printer (PWA)
DESCRIPTION OF SYMBOLS 12 Inkjet recording unit 14 Carriage 20 Main scanning mechanism 32 Sub scanning mechanism 34 Paper feed tray 36 Recording head 40 Nozzle 41 Ink tank 42 Piezoelectric element 44 Supply path 46 Pressure chamber 46A Diaphragm 100 Drive circuit 102 Selector 104 Viscosity adjustment signal output part 106 Print drive signal output unit 108 Power supply 110 First switch (initial charging means)
112 Second switch (peak voltage applying means, recharging means)
114, 116 Branch line 118 First capacitor 120 Third switch (switching means)
120A First contact 120B Second contact 120C Common terminal 122 Fourth switch (switching means)
122A First contact 122B Second contact 122C Common terminal 124 Second capacitor

Claims (7)

A driving device for a piezoelectric element that vibrates a piezoelectric element by repeatedly applying a driving voltage having a predetermined pulse width,
A switching means comprising a plurality of capacitors and capable of switching to a first position where these capacitors are connected in series or a second position where they are connected in parallel;
An initial charging means that includes a first switch that is turned on in a state of being switched to the first position by the switching means, and that initially charges each capacitor with power from a power source;
A peak voltage for applying a peak voltage to the piezoelectric element based on the charges charged in the respective capacitors, the second switch being turned on for a predetermined time after the first switch is turned off after the initial charging; Applying means;
After the second switch is turned off after the lapse of the predetermined time, the switching means is switched to the second position, and the second switch is turned on again, whereby the charge accumulated in the piezoelectric element is discharged. And recharging means for recharging each capacitor based on the electric charge released by the discharge,
By alternately repeating the application of a predetermined voltage to the piezoelectric element by the peak voltage applying unit and the recharging of the charge accumulated in the piezoelectric element by the recharging unit, the piezoelectric element A drive device for a piezoelectric element, wherein a drive voltage having a predetermined pulse width having an amplitude that is a difference between a peak voltage and a base voltage is applied.   2. The driving of a piezoelectric element according to claim 1, wherein the plurality of capacitors are two capacitors having the same capacitance, and the base voltage is set to be ½ of the peak voltage. apparatus.   The initial charge by the initial charge means is periodically executed to compensate for a charge accumulation loss in the piezoelectric element and a loss in recharging the capacitor. The drive device for a piezoelectric element according to claim 2.   2. The piezoelectric element according to claim 1, wherein the piezoelectric element is applied to apply a vibration wave to a pressure chamber filled with a liquid to vibrate the liquid in the pressure chamber. 4. The driving device for a piezoelectric element according to any one of 3 above. A driving device for a piezoelectric element that vibrates a piezoelectric element by repeatedly applying a driving voltage having a predetermined pulse width,
In the state where two capacitors of the same capacitance are connected in series, the initial charge is made with the power from the power source,
Apply the piezoelectric element with the voltage across the two capacitors that were initially charged as the peak voltage,
By recharging the charge accumulated in the piezoelectric element by applying this peak voltage with the two capacitors connected in parallel, the piezoelectric element becomes the base voltage,
A method of driving a piezoelectric element, characterized in that two recharged capacitors are connected again in series and a piezoelectric element is applied at a peak voltage repeatedly.   6. The driving of a piezoelectric element according to claim 5, wherein the initial charge is periodically performed to compensate for a charge accumulation loss in the piezoelectric element and a loss in recharging the capacitor. Method. By providing a drive signal to the piezoelectric element based on the image data, a recording head for discharging droplets from the nozzles is provided, and the liquid discharge surface of the recording head is opposed to the recording paper conveyance path at a predetermined interval. A droplet discharge device that forms an image on the recording paper by discharging droplets at a predetermined discharge timing,
5. A liquid droplet ejection apparatus, wherein the piezoelectric element of the recording head is driven and controlled by the driving apparatus according to any one of claims 1 to 4.

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