JP2011156666A - Driving apparatus for actuator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a driving apparatus for an actuator capable of realizing the same actuation among a plurality of driving elements even when there exists performance variation among a plurality of the driving elements. <P>SOLUTION: A driver IC 47 for driving a piezoelectric actuator includes: a reference electric voltage setting circuit 55 for setting reference electric voltages respectively on a plurality of actuating parts 46 based on performance data of the actuating parts; and an outputting part 53 which adjusts individually the electric voltage levels of driving pulse signals respectively fed to a plurality of the actuating parts 46 in accordance with the reference electric voltages set by the reference electric voltage setting circuit 55 and outputs the adjusted driving pulse signals to a plurality of the actuating parts 46. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a drive device that drives an actuator including a plurality of drive elements.

  Conventionally, in various technical fields, there is an actuator including a plurality of driving elements that independently drive a plurality of driving objects. Usually, such an actuator is supplied with a drive pulse signal having a predetermined voltage level (crest value) from a drive device (driver IC) to a plurality of drive elements, whereby the plurality of drive elements are Configured to operate.

  For example, Japanese Patent Application Laid-Open No. 2004-151867, which is the same application as the present application, discloses a piezoelectric actuator that ejects droplets from a plurality of nozzles of an inkjet head. The piezoelectric actuator disclosed in Patent Document 1 is provided in a flow path unit including a plurality of pressure chambers that respectively communicate with a plurality of nozzles, and applies pressure to the ink in each pressure chamber so that the ink from the corresponding nozzle is supplied. A droplet is ejected. More specifically, the piezoelectric actuator of Patent Document 1 includes a piezoelectric layer disposed so as to cover a plurality of pressure chambers of a flow path unit, and two types of electrodes (a plurality of electrodes provided respectively on both surfaces of the piezoelectric layer). Individual electrode and common electrode). The plurality of individual electrodes are provided so as to face the plurality of pressure chambers, respectively, and the common electrode faces the plurality of individual electrodes in common with the piezoelectric layer interposed therebetween.

  When a driving pulse signal having a predetermined voltage level (pulse peak value) is supplied from the driving device (driver IC) to the plurality of individual electrodes of the piezoelectric actuator, a voltage is applied between the individual electrode and the common electrode. As a result, piezoelectric deformation occurs in a piezoelectric layer portion (hereinafter referred to as an active portion) sandwiched between the individual electrode and the common electrode, and pressure is applied to the ink in the pressure chamber. That is, in this piezoelectric actuator, each of the plurality of active portions sandwiched between the plurality of individual electrodes and the common electrode applies pressure to the ink in the pressure chamber when a drive pulse signal of a predetermined voltage level is applied. One drive element is configured.

JP 2008-2221464 A

  By the way, in an actuator having a plurality of drive elements as described above, a plurality of drive elements are used to supply a plurality of drive elements with the same voltage level and drive a plurality of drive targets to the same extent. Are assumed to have the same performance. However, in practice, it is inevitable that the actuators of any structure will vary in performance among a plurality of drive elements to some extent.

  For example, in the piezoelectric actuator described in Patent Document 1 described above, the active portion of the piezoelectric layer stores (charges) charge when a voltage is applied, and releases the stored charge when voltage application is released. Since it discharges, it can be regarded as a kind of capacitor, but the capacitance value often varies between a plurality of active portions. Factors that can be considered include variations in the electrode area, variations in the thickness of the active portion, variations in stress generated in the manufacturing process, variations in piezoelectric constants due to in-plane non-uniformity of the piezoelectric material, and the like. As described above, when the capacitance varies among the plurality of active portions, even when the drive pulse signals having the same voltage level are supplied and the same voltage is applied to the plurality of active portions, the deformation amount of the active portion is It varies depending on the capacitance. For example, the amount of deformation is large in the active portion having a small thickness (large capacitance), and the amount of deformation is small in the active portion having a large thickness (small capacitance).

  As described above, when there are performance variations among the plurality of drive elements, if the voltage levels of the supplied drive pulse signals are the same, the operations of the plurality of drive elements differ depending on the performance variations. This is not limited to the piezoelectric actuator described above, but may occur in common with various other actuators.

  An object of the present invention is to provide an actuator drive device capable of realizing the same operation between drive elements even when performance variations exist among a plurality of drive elements.

The actuator driving apparatus according to the first aspect of the present invention is an actuator driving apparatus that operates the plurality of driving elements by supplying driving pulse signals to the plurality of driving elements of the actuator, respectively.
A reference voltage setting unit that sets a reference voltage for each of the plurality of drive elements based on element performance data related to the performance of the drive elements input from the outside, and a reference set by the reference voltage setting unit An output unit that individually adjusts the voltage level of the drive pulse signal supplied to each of the plurality of drive elements according to a voltage and outputs the adjusted drive pulse signal to the plurality of drive elements; It is characterized by.

  In the present invention, based on element performance data related to the performance of the drive element, a reference voltage is set for each of the plurality of drive elements, and a drive pulse signal is supplied to each of the plurality of drive elements according to the reference voltage. Are individually adjusted. In other words, even when there are performance variations among the plurality of drive elements, the voltage levels of the drive pulse signals are individually set according to the performance, so that the operations of the plurality of drive elements can be made equal.

  The actuator driving apparatus according to a second aspect of the present invention is the actuator according to the first aspect, wherein the actuator is a piezoelectric actuator having a piezoelectric layer and a plurality of first electrodes and a plurality of second electrodes provided on the piezoelectric layer. The plurality of driving elements are a plurality of active portions including piezoelectric layer portions sandwiched between the plurality of first electrodes and the plurality of second electrodes.

  In the piezoelectric actuator, the capacitance may vary among a plurality of active portions of the piezoelectric layer sandwiched between the plurality of first electrodes and the plurality of second electrodes. If there is such a variation in capacitance among a plurality of active parts, even if a drive pulse signal of the same voltage level is applied, the operation (piezoelectric deformation) will vary, so the voltage level of the drive pulse signal for each active part Is preferably adjusted.

  According to a third aspect of the present invention, there is provided the actuator driving apparatus according to the first or second aspect, wherein the actuator is configured such that the plurality of driving elements respectively apply an ejection pressure to the plurality of nozzles of the droplet ejecting apparatus. Further, it is an actuator of a droplet ejecting apparatus.

  In the actuator of a droplet ejecting apparatus that ejects droplets from a plurality of nozzles, the operation between the plurality of drive elements is made equal so that the droplet ejection speed does not vary between the plurality of nozzles. It is desirable to make the jetting pressure applied to the liquid in the inside equal. Therefore, it is preferable that the voltage level of the drive pulse signal is adjusted for each drive element so that the operations can be made equal even if there are variations in performance among the plurality of drive elements.

  In the actuator drive device according to a fourth aspect of the present invention, in any of the first to third aspects of the invention, the reference voltage setting unit sets the reference voltage to a value equal to or lower than a predetermined power supply voltage. The output unit includes: a first switch that switches connection / cutoff of each drive element to / from a power source; a second switch that switches connection / cutoff of each drive element to / from ground; and the ON of the first switch and the second switch A switch control circuit that controls the supply of the drive pulse signal to each drive element by switching / OFF, the voltage level of the drive pulse signal supplied to each drive element is compared with the reference voltage, and the comparison signal is sent to the switch And a comparator for outputting to the control circuit.

  The output unit controls the first switch that switches connection / disconnection between each driving element and the power source and the second switch that switches connection / disconnection between each driving element and the ground by the switch control circuit, respectively. A voltage level drive pulse signal is output to the drive element. Here, in the reference voltage setting unit, the voltage level of the drive pulse signal of each drive element is set to a value equal to or lower than the power supply voltage according to the element performance. In the comparator, the voltage level of the drive pulse signal is compared with the reference voltage, and the comparison signal is output to the switch control circuit. The switch control circuit controls the first switch and the second switch based on the comparison signal from the comparator, and the voltage level of the drive pulse signal output to each drive element is set to a predetermined level set to be equal to or lower than the power supply voltage. Approach the reference voltage. According to the present invention, it is possible to generate drive pulse signals having different voltage levels with a simple circuit configuration.

  According to a fifth aspect of the present invention, there is provided the actuator drive device according to the fourth aspect, wherein the switch control circuit is configured such that the voltage level of the drive pulse signal is determined from the comparison signal of the comparator when the second switch is OFF. When it is determined that the voltage is higher than the reference voltage, the first switch is turned off. When it is determined from the comparison signal of the comparator that the voltage level of the drive pulse signal is lower than the reference voltage, the first switch is turned on. It is characterized by that.

  In the present invention, the voltage level of the drive pulse signal is brought close to the reference voltage by performing only the ON / OFF control of the first switch in the state where the second switch is turned off and the ground and the drive element are shut off. As described above, since the ON / OFF control of the second switch is not performed when a voltage is applied to the driving element, the switch control is simplified.

  According to a sixth aspect of the present invention, in the actuator of the fourth aspect, when the switch control circuit determines from the comparison signal of the comparator that the voltage level of the driving pulse signal is higher than the reference voltage. When the first switch is turned off and the second switch is turned on, and it is determined from the comparison signal of the comparator that the voltage level of the drive pulse signal is lower than the reference voltage, the first switch is turned on. The second switch is turned off while being turned on.

  In the present invention, in order to bring the voltage level of the drive pulse signal close to the reference voltage, not only the first switch between the drive element and the power supply but also the second switch between the drive element and the ground is turned on / off. Perform OFF control. That is, when the voltage level of the drive pulse signal exceeds the reference voltage, not only the first switch is turned off but also the second switch is turned on, so that the voltage level is actively lowered and quickly brought to the reference voltage. It becomes possible to approach.

According to a seventh aspect of the present invention, there is provided the actuator driving apparatus according to the fourth aspect, wherein the reference voltage setting unit includes a first reference voltage and a second higher than the first reference voltage for each of the plurality of driving elements. Two reference voltages of a reference voltage are set, and the output unit compares the voltage level of the drive pulse signal with the first reference voltage, the voltage level of the drive pulse signal, and the A second comparator for comparing with a second reference voltage;
The switch control circuit has a voltage level of the drive pulse signal between the first reference voltage and the second reference voltage based on the comparison signal of the first comparator and the comparison signal of the second comparator. When it is determined that the first switch and the second switch are both turned OFF, and when it is determined that the voltage level of the drive pulse signal is lower than the first reference voltage, the first switch is turned ON. When the second switch is turned off and it is determined that the voltage level of the drive pulse signal is higher than the second reference voltage, the first switch is turned off and the second switch is turned on. It is what.

  In the present invention, the first comparator for comparing the voltage level of the drive pulse signal with the first reference voltage and the second comparator for comparing with the second reference voltage higher than the first reference voltage are used. When the voltage level is between the first reference voltage and the second reference voltage, both the first switch and the second switch are turned OFF. When the voltage level is lower than the first reference voltage, the first switch connected to the power source is turned ON, When the voltage exceeds 2 reference voltage, the second switch connected to the ground is turned ON. According to this, normally, while the voltage level is adjusted so as to approach the first reference voltage, when the voltage level suddenly increases and exceeds the second reference voltage due to noise, the voltage level is adjusted. Since the second switch is turned on in order to immediately decrease the voltage, it is possible to prevent the voltage level from greatly deviating from the reference voltage when noise is mixed.

  In the actuator drive device according to an eighth aspect of the present invention, in any one of the first to seventh aspects, the output unit inputs drive data for driving each of the plurality of drive elements input from the outside, and Based on the reference voltage set by the reference voltage setting unit, it generates and outputs drive pulse signals to the plurality of drive elements, and the element performance data is input to the reference voltage setting unit first. The driving data is input after the setting of the reference voltage for each of the plurality of driving elements is completed in the reference voltage setting unit, and the driving pulse signal is generated in the output unit. To do.

  In the present invention, the setting of the reference voltage for all the driving elements is finished before the driving data for driving the driving elements is inputted, and the setting is already finished when the driving data is inputted. A drive pulse signal is generated using the reference voltage. In other words, since the reference voltage is not set every time drive data is input, the element performance data for setting the reference voltage is transmitted only once before the element is driven, which is used for data transfer time and drive pulse signal generation. This time is shortened.

  In the actuator drive device according to a ninth aspect of the present invention, in any one of the first to eighth aspects, the plurality of drive elements are divided into a plurality of drive element groups each including two or more drive elements. The reference voltage setting unit sets the same reference voltage for all the drive elements belonging to one drive element group.

  In the case where the element performance is the same among several drive elements among a plurality of drive elements, by setting the reference voltage to be the same for all the drive elements belonging to one drive element group, The amount of performance data can be reduced, or the circuit configuration can be simplified.

  According to the present invention, even when there is a performance variation among a plurality of drive elements of the actuator, the voltage levels of the drive pulse signals are individually set according to the performance, so that the operations of the plurality of drive elements are made equal. be able to.

1 is a plan view schematically showing an ink jet printer according to an embodiment. It is a top view of an inkjet head. FIG. 3 is a partially enlarged view of FIG. 2. FIG. 4 is a sectional view taken along line IV-IV in FIG. 3. It is a wave form diagram of the signal (a non-ejection signal and a drive pulse signal) supplied to a piezoelectric actuator from a driver IC. 2 is a block diagram schematically showing a circuit configuration of a driver IC. FIG. It is a circuit diagram which shows the circuit structure which outputs a drive pulse signal to one active part of an output part. FIG. 2 is a block diagram schematically illustrating an electrical configuration of a printer. It is a circuit diagram of the output part of a modification.

  Next, an embodiment of the present invention will be described. This embodiment is an example in which the present invention is applied to an inkjet printer including an inkjet head that ejects ink droplets onto a recording sheet.

  First, a schematic configuration of the inkjet printer 1 of the present embodiment will be described. FIG. 1 is a schematic plan view of the ink jet printer of the present embodiment. As shown in FIG. 1, a printer 1 includes a carriage 2 configured to be reciprocally movable along a predetermined scanning direction (left-right direction in FIG. 1), an inkjet head 3 mounted on the carriage 2, and a cover. A transport mechanism 4 for transporting the recording paper 100 as a print medium in a transport direction orthogonal to the scanning direction is provided.

  The carriage 2 is configured to be able to reciprocate along two guide shafts 17 extending in parallel with the scanning direction (left-right direction in FIG. 1). An endless belt 18 is connected to the carriage 2. When the endless belt 18 is driven to travel by the carriage drive motor 19, the carriage 2 moves in the scanning direction as the endless belt 18 travels. It has become. The printer 1 is provided with a linear encoder 10 having a large number of light transmitting portions (slits) arranged at intervals in the scanning direction. On the other hand, the carriage 2 is provided with a transmissive photosensor 11 having a light emitting element and a light receiving element. The printer 1 can recognize the current position in the scanning direction of the carriage 2 from the count value (number of detections) of the light transmitting portion of the linear encoder 10 detected by the photosensor 11 while the carriage 2 is moving. .

  An ink jet head 3 is mounted on the carriage 2. The ink-jet head 3 includes a large number of nozzles 30 (see FIGS. 2 to 4) on the lower surface (the surface on the opposite side of FIG. 1). The ink jet head 3 is configured to eject ink supplied from an ink cartridge (not shown) from a large number of nozzles 30 onto a recording paper 100 that is transported downward (conveying direction) in FIG. ing.

  The transport mechanism 4 includes a paper feed roller 12 disposed on the upstream side in the transport direction with respect to the ink jet head 3 and a paper discharge roller 13 disposed on the downstream side in the transport direction with respect to the ink jet head 3. The paper feed roller 12 and the paper discharge roller 13 are rotationally driven by a paper feed motor 14 and a paper discharge motor 15, respectively. The transport mechanism 4 transports the recording paper 100 from the upper side of FIG. 1 to the ink jet head 3 by the paper feed roller 12, and records the images, characters, etc. recorded by the ink jet head 3 by the paper discharge roller 13. The paper 100 is discharged downward in FIG.

  Next, the inkjet head 3 will be described. 2 is a plan view of the inkjet head, FIG. 3 is a partially enlarged view of FIG. 2, and FIG. 4 is a sectional view taken along line IV-IV of FIG. As shown in FIGS. 2 to 4, the inkjet head 3 includes a flow path unit 6 in which an ink flow path including a nozzle 30 and a pressure chamber 24 is formed, and a piezoelectric actuator 7 that applies pressure to the ink in the pressure chamber 24. And.

  First, the flow path unit 6 will be described. As shown in FIG. 4, the flow path unit 6 includes a cavity plate 20, a base plate 21, a manifold plate 22, and a nozzle plate 23, and these four plates 20 to 23 are joined in a laminated state. Among these, the cavity plate 20, the base plate 21, and the manifold plate 22 are substantially rectangular plates in plan view made of a metal material such as stainless steel. Therefore, ink flow paths such as a manifold 27 and a pressure chamber 24 described later can be easily formed on these three plates 20 to 22 by etching. Further, the nozzle plate 23 is formed of, for example, a polymer synthetic resin material such as polyimide, and is bonded to the lower surface of the manifold plate 22 with an adhesive. Or this nozzle plate 23 may be formed with metal materials, such as stainless steel, similarly to the other three plates 20-22.

  As shown in FIGS. 2 to 4, among the four plates 20 to 23, the uppermost cavity plate 20 has holes in which a plurality of pressure chambers 24 arranged along a plane penetrate the plate 20. It is formed by. The plurality of pressure chambers 24 are arranged in two rows in a staggered manner in the transport direction (the vertical direction in FIG. 2). Further, as shown in FIG. 4, the plurality of pressure chambers 24 are respectively covered with a diaphragm 40 and a base plate 21 described later from above and below. Furthermore, each pressure chamber 24 is formed in a substantially elliptical shape that is long in the scanning direction (left-right direction in FIG. 2) in plan view.

  As shown in FIGS. 3 and 4, communication holes 25 and 26 are respectively formed at positions where the base plate 21 overlaps both longitudinal ends of the pressure chamber 24 in plan view. The manifold plate 22 is formed with two manifolds 27 extending in the transport direction so as to overlap with the communication hole 25 side portions of the pressure chambers 24 arranged in two rows in a plan view. These two manifolds 27 communicate with an ink supply port 28 formed in a vibration plate 40 described later, and ink is supplied to the manifold 27 from an ink tank (not shown) via the ink supply port 28. Further, a plurality of communication holes 29 that are continuous with the plurality of communication holes 26 are formed at positions where the manifold plate 22 overlaps the ends of the plurality of pressure chambers 24 opposite to the manifolds 27 in plan view.

  Further, a plurality of nozzles 30 are formed at positions where the nozzle plate 23 overlaps the plurality of communication holes 29 in plan view. As shown in FIG. 2, the plurality of nozzles 30 are arranged so as to overlap with the end portions on the opposite side of the manifold 27 of the plurality of pressure chambers 24 arranged in two rows along the transport direction, respectively. A nozzle row is configured.

  As shown in FIG. 4, the manifold 27 communicates with the pressure chamber 24 through the communication hole 25, and the pressure chamber 24 communicates with the nozzle 30 through the communication holes 26 and 29. As described above, a plurality of individual ink flow paths 31 from the manifold 27 to the nozzles 30 through the pressure chambers 24 are formed in the flow path unit 6.

  In FIG. 2, only one type of flow path structure (manifold 27, pressure chamber 24, nozzle 30, etc.) connected to one ink supply port 28 is shown for simplicity of explanation, but the inkjet head 3 However, it has a configuration in which a plurality of flow path structures shown in FIG. 2 are arranged in the scanning direction and can eject a plurality of colors (for example, four colors of black, yellow, cyan, and magenta). An inkjet head may be used.

  Next, the piezoelectric actuator 7 will be described. As shown in FIGS. 2 to 4, the piezoelectric actuator 7 includes a vibration plate 40 disposed on the upper surface of the flow path unit 6 (cavity plate 20) so as to cover the plurality of pressure chambers 24, and an upper surface of the vibration plate 40. In addition, a piezoelectric layer 41 disposed to face the plurality of pressure chambers 24 and a plurality of individual electrodes 42 disposed on the upper surface of the piezoelectric layer 41 are provided.

  The diaphragm 40 is a substantially rectangular metal plate in plan view, and is made of, for example, an iron-based alloy such as stainless steel, a copper-based alloy, a nickel-based alloy, or a titanium-based alloy. The vibration plate 40 is joined to the cavity plate 20 in a state of being disposed on the upper surface of the cavity plate 20 so as to cover the plurality of pressure chambers 24. In addition, the upper surface of the conductive diaphragm 40 is disposed on the lower surface side of the piezoelectric layer 41, thereby generating an electric field in the thickness direction in the piezoelectric layer 41 with the plurality of individual electrodes 42 on the upper surface. Also serves as an electrode. The diaphragm 40 as the common electrode is connected to the ground wiring of the driver IC 47 that drives the piezoelectric actuator 7 and is always held at the ground potential.

  The piezoelectric layer 41 is made of a piezoelectric material mainly composed of lead zirconate titanate (PZT), which is a solid solution of lead titanate and lead zirconate and is a ferroelectric substance. As shown in FIG. 2, the piezoelectric layer 41 is continuously formed across the plurality of pressure chambers 24 on the upper surface of the vibration plate 40.

  A plurality of individual electrodes 42 are respectively disposed in regions on the upper surface of the piezoelectric layer 41 facing the plurality of pressure chambers 24. Each individual electrode 42 has a substantially oval planar shape that is slightly smaller than the pressure chamber 24, and faces the central portion of the pressure chamber 24. In addition, a plurality of contact portions 45 connected to a flexible wiring board (not shown) on which the driver IC 47 is mounted are drawn from the end portions of the plurality of individual electrodes 42 along the longitudinal direction of the individual electrodes 42. . Note that the plurality of individual electrodes 42 described above correspond to the plurality of first electrodes in the present application, and a plurality of diaphragms 40 as common electrodes that sandwich the piezoelectric layer 41 respectively facing the plurality of individual electrodes 42. This part corresponds to a plurality of second electrodes in the present application.

  A plurality of piezoelectric layer portions (active portions 46) sandwiched between the plurality of individual electrodes 42 and the diaphragm 40 as a common electrode are previously polarized in the thickness direction. When a potential difference (voltage) is generated between the individual electrode 42 and the diaphragm 40, piezoelectric deformation (piezoelectric strain) occurs in the active portion 46, and the pressure chamber facing the active portion 46 due to this deformation. Pressure is applied to the ink in 24. That is, one active portion 46 corresponds to one drive element in the present invention in which an ejection pressure is applied in one pressure chamber 24 and ink droplets are ejected from the nozzle 30.

  The piezoelectric actuator 7 is connected to a flexible wiring board (FPC) (not shown) on which a driver IC 47 (driving device) for driving the piezoelectric actuator 7 is mounted. The driver IC 47 and a plurality of individual ICs are connected to the piezoelectric actuator 7 via wiring on the FPC. The electrode 42 and the diaphragm 40 as a common electrode are electrically connected. Then, a drive pulse signal (see FIGS. 5B to 5D) having a predetermined pulse waveform and a voltage level (crest value) is supplied from the driver IC 47 to the individual electrode 42, whereby the active portion 46. Is switched between the voltage level of the drive pulse P and the ground.

  Next, the operation of each active part 46 of the piezoelectric actuator 7 when the drive pulse signal is supplied will be described. When a drive pulse signal is supplied from a driver IC 47 to a certain individual electrode 42, the individual electrode 42 is held at the ground potential at the timing at which the drive pulse P (see FIGS. 5B to 5D) is supplied. A voltage is applied to the active part 46 sandwiched between the diaphragm 40 as the common electrode, and an electric field in the thickness direction acts on the active part 46. Since the direction of the electric field is parallel to the polarization direction of the active portion 46, the piezoelectric layer 41 in the region (active region) facing the individual electrode 42 contracts in a plane direction perpendicular to the thickness direction. Here, since the lower vibration plate 40 of the piezoelectric layer 41 is fixed to the cavity plate 20, as the piezoelectric layer 41 positioned on the upper surface of the vibration plate 40 contracts in the surface direction, the vibration plate 40. The portion covering the pressure chamber 24 is deformed so as to protrude toward the pressure chamber 24 (unimorph deformation). At this time, since the volume in the pressure chamber 24 decreases, the ink pressure in the pressure chamber 24 rises, and ink is ejected from the nozzle 30 communicating with the pressure chamber 24.

  Next, the driver IC 47 that supplies a drive pulse signal to the piezoelectric actuator 7 will be described in detail. The driver IC 47 selects and supplies one type of signal from the four types of signals shown in FIG. 5 to each active unit 46 (individual electrode 42). Among these four types of signals, one type of signal (FIG. 5A) is a non-injection signal that does not have the drive pulse P (no voltage is applied to the active portion 46). Further, the remaining three types of signals (FIGS. 5B to 5D) are drive pulse signals having different pulse waveforms, and the size from one nozzle 30 is changed to enable multi-tone printing. It is a signal for ejecting three different types of liquid droplets (small balls, medium balls, large balls). More specifically, as shown in FIGS. 5B to 5D, the three types of driving pulse signals are the driving pulses P included in one printing cycle (a cycle for forming one dot on the recording paper 100). The number is different. Note that a pulse P ′ having a shorter pulse width than the drive pulse P, which is applied after the drive pulse P, is a stabilization pulse for stabilizing the ink pressure. Further, the driver IC 47 sends, to each active unit 46 based on the waveform selection data transmitted from the control device 8 (see FIG. 8) of the printer 1 described later, of the four types of signals shown in FIG. Select one.

  FIG. 6 is a block diagram schematically showing the circuit configuration of the driver IC 47. As illustrated in FIG. 6, the driver IC 47 includes a shift register 50, a latch circuit 51, a waveform selection circuit 52, and an output unit 53. Waveform selection data corresponding to each of the plurality of active units 46 is input to the shift register 50 from the control device 8 of the printer 1. The waveform selection data corresponding to one active unit 46 is a combination of 2-bit bit data (in order that the waveform selection circuit 52 described later can select one type of signal from the four types of signals shown in FIG. (4 types in total). In addition, the total number of bits of the waveform selection data corresponding to each of the plurality of active portions 46 in one printing cycle is (2 bits) × (total number of active portions 46). Serial input to the IC 47. The waveform selection data described above corresponds to “driving data for driving the driving element” in the present invention.

  The shift register 50 converts the number of serially input bit data to parallel conversion and sequentially outputs it to the latch circuit 51. The latch circuit 51 holds a large number of bit data (waveform selection data) output in parallel from the shift register 50 until input of all data is completed. When the input of all waveform selection data is completed, the held waveform selection data is output in parallel to the waveform selection circuit 52.

  The waveform selection circuit 52 receives four types of pulse waveform data shown in FIGS. 5A to 5D from the control device 8. Then, the waveform selection circuit 52 selects one type from among the four types of signals based on the 2-bit waveform selection data corresponding to each of the plurality of active units 46 input from the latch circuit 51, and The waveform signal is output to the output unit 53.

  The waveform signal output from the waveform selection circuit 52 is a signal of a control voltage level (for example, 3.3 V) of logic circuits such as the shift register 50, the latch circuit 51, and the waveform selection circuit 52. Then, the output unit 53 amplifies the waveform signal input from the waveform selection circuit 52 to a predetermined voltage level close to a power supply voltage (for example, 28 V) for actually driving the active unit 46, and drives the drive signal. A signal is generated and a drive pulse signal is output to the active part 46 (individual electrode 42).

  By the way, when there is a difference in performance among the plurality of active portions 46, if the voltage levels of the drive pulse signals supplied to the plurality of active portions 46 are the same, the operation (piezoelectric deformation) varies due to the difference in performance. End up. If the operation is different between the plurality of active portions 46 as described above, the droplet ejection speed varies among the plurality of nozzles 30. As a result, the landing position is deviated and the print quality is deteriorated. Connected. Therefore, the driver IC 47 of the present embodiment is supplied to the plurality of active units 46 at the output unit 53 in order to suppress variation in operation (piezoelectric deformation) due to a difference in performance between the plurality of active units 46. The voltage level of the drive pulse signal (the peak value of the drive pulse P) is individually adjusted. In order to enable individual adjustment of the voltage level in the output unit 53, the driver IC 47 further includes a latch circuit 54, a reference voltage setting circuit 55, and a voltage generation unit 56, as shown in FIG.

  In addition to the waveform selection data, active part performance data (element performance data) is input from the control device 8 to the shift register 50 described above. The active portion performance data is data relating to the performance of each of the plurality of active portions 46, and is used to adjust the voltage level of the drive pulse signal in multiple stages. For example, when the voltage level is adjusted in four stages according to the performance of the active part 46, the active part performance data is composed of 2-bit bit data in order to express the four voltage levels.

  Various performance parameters can be adopted for the active part 46. For example, the capacitance value of the active portion 46 of the piezoelectric layer 41 often varies due to factors such as thickness variation. If the capacitance values are different, the piezoelectric deformation of the active portion 46 is not affected even when the same voltage is applied. Will be different. Therefore, the active part performance data may be set according to the capacitance value of each active part 46 measured in advance. Alternatively, active part performance data may be set according to the thickness of the active part 46.

  The active unit performance data corresponding to each of the plurality of active units 46 is serially input from the control device 8 to the driver IC 47, and the shift register 50 converts the serially input active unit performance data into parallel data to the latch circuit 54. Output.

  The latch circuit 54 holds the active portion performance data output in parallel from the shift register 50 until all data input is completed. When the input of all active part performance data is completed, the held data is output in parallel to the reference voltage setting circuit 55.

  The reference voltage setting circuit 55 (reference voltage setting unit) is a reference for adjusting the voltage level at the output unit 53 for each of the plurality of active units 46 based on the active unit performance data input from the latch circuit 54. Set the reference voltage. Specifically, first, the voltage generator 56 generates a plurality of types of voltage levels equal to or lower than the power supply voltage (VDD). The circuit configuration of the voltage generator 56 is not particularly limited. For example, by dividing the power supply voltage into a plurality of stages by a plurality of resistors arranged in series between the power supply and the ground, A circuit configuration for obtaining a plurality of types of voltage levels below the voltage can be employed. Then, the reference voltage setting circuit 55 selects one type as a reference voltage from among a plurality of types of voltage levels generated by the voltage generation unit 56 according to the active unit performance data, and each of the plurality of active units 46 is selected. The selected reference voltage is output to the output unit 53. Here, the high performance of the active part 46 means that a large piezoelectric deformation can be obtained even when the applied voltage is low. Therefore, the reference voltage setting circuit 55 is indicated by the active part performance data. The higher the performance of the active part 46, the lower the reference voltage.

  Further, the reference voltage setting circuit 55 uses a first reference voltage and a second reference higher than the first reference voltage as a reference voltage for adjusting the voltage level of the drive pulse signal for each of the plurality of active units 46. Two reference voltages, high and low, are set. The reason for using these two reference voltages will be described later.

  The output unit 53 individually sets the voltage level of the drive pulse signal according to the two reference voltages (first reference voltage and second reference voltage) set by the reference voltage setting circuit 55 for each of the plurality of active units 46. adjust. FIG. 7 is a circuit diagram showing a circuit configuration for outputting a drive pulse signal to one active unit 46 of the output unit 53. The active portion 46 of the piezoelectric layer 41 can be regarded as a capacitor (capacitance component) that accumulates electric charge by applying a voltage between two types of electrodes (the individual electrode 42 and the diaphragm 40 as a common electrode). Portion 46 is indicated by a capacitor symbol.

  As shown in FIG. 7, the output unit 53 includes a first switch SW <b> 1 that switches connection / disconnection with the power supply (VDD) of each active unit 46, and a second switch that switches connection / disconnection between each active unit 46 and the ground. SW2 and a switch control circuit 60 that controls ON / OFF of the first switch SW1 and the second switch SW2 to control the supply of the drive pulse signal to each active unit 46.

  The first switch SW1 and the second switch SW2 are both configured by MOSFET type transistors, and are arranged in series between the power supply (VDD) and the ground. The connection point between the source of the first switch SW1 and the drain of the second switch SW2 is connected to the active part 46 (individual electrode 42) via the output resistor R.

  The switch control circuit 60 switches ON / OFF of these by applying gate voltages to the gates of the first switch SW1 and the second switch SW2. Further, the switch control circuit 60 receives the waveform signal output from the waveform selection circuit 52 for each active unit 46 and turns on / off the first switch SW1 and the second switch SW2 corresponding to each active unit 46. By switching each, the waveform signal is amplified to a predetermined voltage level to generate a drive pulse signal and supplied to each active unit 46.

  Further, the output unit 53 compares the voltage level of the drive pulse signal supplied to each active unit 46 (the voltage at the point A when the drive pulse P is applied) with the reference voltage set by the reference voltage setting circuit 55. Two comparators (a first comparator 61 and a second comparator 62). The first comparator 61 compares the voltage level of the drive pulse signal with the first reference voltage, which is the lower reference voltage set by the reference voltage setting circuit 55, and outputs the comparison signal to the switch control circuit 60. To do. The second comparator 62 compares the voltage level of the drive pulse signal with the second reference voltage, which is the higher reference voltage, and outputs the comparison signal to the switch control circuit 60.

  Based on the comparison signals input from the first comparator 61 and the second comparator 62, the switch control circuit 60 performs ON / OFF control of the first switch SW1 and the second switch SW2 as follows.

  At the timing of applying the drive pulse P (when the active unit 46 is charged), the voltage at the point A is initially ground and lower than the first reference voltage. The switch SW1 is turned on and the second switch SW2 is turned off. Then, the voltage at the point A increases, but when the first reference voltage is exceeded, the first switch SW1 is turned off.

  When the voltage level (the voltage at point A) is between the first reference voltage and the second reference voltage, both the first switch SW1 and the second switch SW2 are OFF. In this state, the voltage level gradually decreases. Then, it becomes lower than the first reference voltage again. Therefore, the switch control circuit 60 keeps the second switch SW2 in the OFF state, turns on the first switch SW1, connects the power source and the active unit 46, and increases the voltage level again. As described above, normally, the voltage level of the drive pulse signal is controlled to approach the first reference voltage by switching only the ON / OFF of the first switch SW1 while the second switch SW2 is OFF. The

  However, when noise is mixed from the outside, the voltage level rises instantaneously, and the voltage level rises due to noise mixing only by control using the comparison signal of the first comparator 61 that compares the voltage level with the first reference voltage. It is difficult to suppress and converge in a short time. Therefore, in the present embodiment, in order to prevent large fluctuations in the voltage level due to noise, a second comparator 62 that compares the voltage level with a second reference voltage higher than the first reference voltage is provided. .

  When noise is mixed in the drive pulse signal and the voltage level becomes higher than the second reference voltage, the switch control circuit 60 keeps the first switch OFF and turns on the second switch SW2 to turn on the ground and the active part. 46 is connected to lower the voltage level. When the voltage level becomes lower than the second reference voltage, the second switch SW2 is turned off again. Thereafter, if no noise is mixed in, the voltage level decreases and approaches the first reference voltage.

  The above-described control is switch control at the timing when the drive pulse P is applied (when the active portion 46 is charged), but at the timing when the drive pulse P is not applied (when the active portion 46 is discharged), the switch control circuit 60 turns off the first switch SW1 and turns on the second switch SW2 to connect the individual electrode 42 and the ground. In this state, no voltage is applied to the active portion 46.

  As described above, in the driver IC 47 of this embodiment, the reference voltage is set for each of the plurality of active portions 46 in the reference voltage setting circuit 55 based on the active portion performance data related to the performance of the active portion 46. The output unit 53 individually adjusts the voltage levels of the drive pulse signals respectively supplied to the plurality of active units 46 according to the reference voltage. In other words, even when there are performance variations among the plurality of active portions 46, the voltage levels of the drive pulse signals are individually set according to the performance, so that the operations of the plurality of active portions 46 can be made equal.

  The output unit 53 that outputs the drive pulse signal to the active unit 46 has a simple circuit configuration including the first switch SW1, the second switch SW2, the comparators 61 and 62, and the switch control circuit 60 as shown in FIG. Thus, drive pulse signals having different voltage levels can be generated.

  Further, the output unit 53 compares the two reference voltages (first reference voltage and second reference voltage) set by the reference voltage setting circuit 55 with the voltage levels of the drive pulse signals, respectively, and two comparators 61. , 62. Normally, the voltage level is adjusted so as to approach the first reference voltage, but when the voltage level suddenly increases and exceeds the second reference voltage due to noise, the voltage level is immediately decreased. Therefore, the second switch SW2 is switched to ON, so that it is possible to prevent the voltage level from greatly deviating from the reference voltage when noise is mixed.

  Next, the electrical configuration of the printer 1 will be described with reference to the block diagram of FIG. As shown in FIG. 8, the control device 8 includes a central processing unit (CPU) 70, a read only memory (ROM) 71, a random access memory (RAM) 72, and a bus 73 connecting them. Having a microcomputer. The bus 73 also has an ASIC (Application Specific Integrated Circuit) 74 that controls a driver IC 47 of the inkjet head 3, a carriage drive motor 19 that drives the carriage 2, a paper feed motor 14 and a paper discharge motor 15 of the transport mechanism 4. Is connected. The ASIC 74 is connected to an external device PC (personal computer) 79 via an input / output interface (I / F) 78 so that data communication is possible.

  The ASIC 74 also has a head control circuit 81 for controlling the driver IC 47 of the inkjet head 3 and the carriage drive motor 19 based on the image data input from the PC 79, and the paper feed of the transport mechanism 4 based on the image data. A conveyance control circuit 82 and the like for controlling the motor 14 and the paper discharge motor 15 are incorporated.

  Next, the head control circuit 81 will be specifically described. As shown in FIG. 8, the head control circuit 81 includes a waveform data storage unit 85, a waveform selection data generation unit 86, and a performance data storage unit 87. The waveform data storage unit 85 stores data (pulse waveform data) related to four types of pulse waveforms shown in FIGS. The waveform selection data generation unit 86 selects a 2-bit waveform for selecting one of the four types of pulse waveforms shown in FIG. 5 for each of the plurality of active units 46 based on the image data input from the PC 79. Generate data. The performance data storage unit 87 stores active unit performance data for each of the plurality of active units 46.

  The head control circuit 81 includes the pulse waveform data stored in the waveform data storage unit 85, the waveform selection data generated by the waveform selection data generation unit 86, and the active unit performance data stored in the performance data storage unit 87. Is transmitted to the driver IC 47. In response to this, the driver IC 47 individually adjusts the voltage level of the drive pulse signal for each of the plurality of active units 46 and then supplies the drive pulse signal to each of the plurality of active units 46.

  The transmission of the active part performance data from the control device 8 to the driver IC 47 (that is, the setting of the reference voltage based on the active part performance data in the driver IC 47) is performed by the waveform selection data (“driving element of the present invention”). May be performed prior to transmission of drive data for driving “). That is, first, only the active part performance data for each of the plurality of active units 46 is transmitted from the control device 8 to the driver IC 47, and the reference voltage for each of the plurality of active units 46 in the reference voltage setting circuit 55 of FIG. Is set. Thereafter, for each of the plurality of active portions 46, waveform selection data for a plurality of printing cycles generated from the image data is sequentially transmitted. In this case, since the setting of the reference voltage for all the active portions 46 is completed before printing (before the transmission of the waveform selection data), it is not necessary to set the reference voltage every time waveform selection data is input thereafter. . That is, since the active part performance data for setting the reference voltage is transmitted only once before printing, the time required for data transfer time and drive pulse signal generation is shortened.

  Alternatively, each time the waveform selection data of one printing cycle is transmitted, the active part performance data may be transmitted to the driver IC 47 together with the waveform selection data. That is, the waveform selection data (for example, 2 bits) and the active portion performance data (for example, 2 bits) are input to the driver IC 47 as a set. In this case, the reference voltage setting in the reference voltage setting circuit 55 is performed in parallel with the waveform selection in the waveform selection circuit 52.

  Next, modified embodiments in which various modifications are made to the embodiment will be described. However, components having the same configuration as in the above embodiment are given the same reference numerals and description thereof is omitted as appropriate.

1] After the reference voltage setting circuit 55 of the driver IC 47 is configured to set only one reference voltage for each of the plurality of active portions 46, the output portion 53A receives a drive pulse signal as shown in FIG. A configuration having only one comparator (only the first comparator 61) that compares the voltage level with the reference voltage may be used. In this case, compared to the configuration of the embodiment, it can be said that the influence of noise is likely to occur on the drive pulse signal by the amount that the second reference voltage that suppresses an instantaneous increase in voltage level due to noise mixing is not set. Since there is only one comparator, there is an advantage that the circuit configuration is simplified and the switch control based on the comparison signal of the comparator is simplified. In addition, when the circuit configuration with one comparator as shown in FIG. 9 is adopted, the switch control by the switch control circuit 60 based on the comparison signal of the comparator 61 can adopt any of the following two types. it can.

(1) When the drive pulse P is applied (when the active unit 46 is charged), the voltage of the drive pulse signal is switched by switching on / off only the first switch SW1 with the second switch SW2 turned off. The level may be close to the reference voltage. That is, the switch control circuit 60 turns off the first switch SW1 when determining that the voltage level of the drive pulse signal is higher than the reference voltage. When it is determined that the voltage level of the drive pulse signal is lower than the reference voltage, the first switch SW1 is turned on. In this case, since the ON / OFF control of the second switch SW2 is not performed when the drive pulse P is applied (the ON state of the second switch SW2 is only when the active part 46 is connected to the ground at the time of discharge), the switch control is simple. Become.

(2) When the drive pulse P is applied (when the active unit 46 is charged), the ON / OFF of both the first switch SW1 and the second switch SW2 is controlled to set the voltage level of the drive pulse signal to the reference voltage. It may be close. That is, when the switch control circuit 60 determines that the voltage level of the drive pulse signal is higher than the reference voltage, the switch control circuit 60 turns off the first switch SW1 and turns on the second switch SW2. When it is determined that the voltage level of the drive pulse signal is lower than the reference voltage, the first switch SW1 is turned on and the second switch SW2 is turned off. In this case, unlike the method (1) above, when the voltage level of the drive pulse signal exceeds the reference voltage, not only the first switch SW1 is turned off but also the second switch SW2 is turned on. Since the voltage level is lowered, it is possible to quickly approach the reference voltage.

2] When the performance is the same among several active parts 46 among the plurality of active parts 46, the reference voltage may be set to be the same between the groups of the active parts 46. That is, the plurality of active portions 46 are divided into a plurality of active portion groups each composed of two or more active portions 46 (active portions 46 having the same performance), and the reference voltage setting circuit is 1 The same reference voltage may be set for all the active portions 46 belonging to the group of one active portion. As described above, for all active parts 46 belonging to one active part group and having the same performance, by setting the same reference voltage, the data amount of the active part performance data can be reduced or the circuit configuration can be reduced. Can be simplified.

  Depending on the method of manufacturing the piezoelectric layer, for example, when the performances of the plurality of active portions 46 corresponding to one nozzle row (the row of pressure chambers 24) arranged in one direction are substantially equal. The reference voltage of the active portion 46 can be made the same for each nozzle row. Alternatively, the reference voltage of the active portion 46 can be made the same for each of a plurality of nozzle groups that eject ink of the same color.

3] The above embodiment is an example in which the present invention is applied to a piezoelectric actuator provided with a plurality of active portions 46 each composed of a piezoelectric layer sandwiched between two types of electrodes. It is not limited to such a piezoelectric actuator. Those skilled in the art will understand that the same problems as those of the piezoelectric actuator described above will occur even if actuators other than piezoelectric actuators are supplied with drive pulse signals at the same voltage level when performance varies among a plurality of drive elements. I can imagine it easily.

4] The actuator to which the present invention is applied is not limited to an actuator of a liquid droplet ejecting apparatus such as an ink jet head that applies a spray pressure to the liquid in the nozzle and ejects liquid droplets from the nozzle. For example, the present invention is not limited to applying pressure to a liquid, and the present invention can also be applied to an actuator that drives a solid drive target.

7 Piezoelectric actuator 30 Nozzle 40 Diaphragm 41 Piezoelectric layer 42 Individual electrode 46 Active part 47 Driver IC
53, 53A, 53B Output 55 Reference voltage setting circuit 60 Switch control circuit 61 First comparator 62 Second comparator SW1 First switch SW2 Second switch

Claims (9)

A drive device for an actuator for supplying a drive pulse signal to each of a plurality of drive elements of the actuator to operate the plurality of drive elements,
A reference voltage setting unit that sets a reference voltage for each of the plurality of drive elements based on element performance data related to the performance of the drive elements input from the outside;
According to the reference voltage set by the reference voltage setting unit, the voltage level of the drive pulse signal supplied to each of the plurality of drive elements is individually adjusted, and the adjusted drive pulse signal is supplied to the plurality of drive elements. And an output section for outputting to the actuator. The actuator is a piezoelectric actuator having a piezoelectric layer and a plurality of first electrodes and a plurality of second electrodes provided on the piezoelectric layer,
2. The actuator drive according to claim 1, wherein the plurality of drive elements are a plurality of active portions including piezoelectric layer portions sandwiched between the plurality of first electrodes and the plurality of second electrodes. apparatus. The actuator is
3. The actuator according to claim 1, wherein the plurality of driving elements are actuators of a droplet ejecting apparatus configured to apply an ejection pressure to the plurality of nozzles of the droplet ejecting apparatus, respectively. Drive device. The reference voltage setting unit is configured to set the reference voltage to a value equal to or lower than a predetermined power supply voltage;
The output unit is
A first switch for switching connection / disconnection of the power source of each drive element;
A second switch for switching connection / disconnection between each drive element and the ground;
A switch control circuit that controls ON / OFF of the first switch and the second switch to control supply of a drive pulse signal to each drive element;
4. A comparator that compares a voltage level of a drive pulse signal supplied to each drive element with the reference voltage and outputs a comparison signal to the switch control circuit. A drive device for an actuator according to 1. The switch control circuit is in a state where the second switch is OFF,
When it is determined from the comparison signal of the comparator that the voltage level of the drive pulse signal is higher than the reference voltage, the first switch is turned OFF,
5. The actuator driving device according to claim 4, wherein when the voltage level of the driving pulse signal is determined to be lower than the reference voltage from the comparison signal of the comparator, the first switch is turned on. 6. The switch control circuit includes:
When it is determined from the comparison signal of the comparator that the voltage level of the drive pulse signal is higher than the reference voltage, the first switch is turned off and the second switch is turned on,
The first switch is turned on and the second switch is turned off when it is determined from the comparison signal of the comparator that the voltage level of the drive pulse signal is lower than the reference voltage. Item 5. The actuator drive device according to Item 4. The reference voltage setting unit sets two reference voltages, a first reference voltage and a second reference voltage higher than the first reference voltage, for each of the plurality of drive elements,
The output unit includes: a first comparator that compares the voltage level of the drive pulse signal with the first reference voltage; a second comparator that compares the voltage level of the drive pulse signal with the second reference voltage; Have
The switch control circuit is based on a comparison signal of the first comparator and a comparison signal of the second comparator,
When it is determined that the voltage level of the drive pulse signal is between the first reference voltage and the second reference voltage, both the first switch and the second switch are turned OFF,
When it is determined that the voltage level of the drive pulse signal is lower than the first reference voltage, the first switch is turned on and the second switch is turned off,
5. The method according to claim 4, wherein when the voltage level of the drive pulse signal is determined to be higher than the second reference voltage, the first switch is turned off and the second switch is turned on. 6. Actuator drive. The output unit outputs drive pulse signals to the plurality of driving elements based on driving data input from outside and driving data for driving the plurality of driving elements, respectively, and a reference voltage set by the reference voltage setting unit. Is generated and output,
The element performance data is first input to the reference voltage setting unit, and after the reference voltage setting for each of the plurality of drive elements is completed in the reference voltage setting unit, the drive data is input, 8. The actuator driving apparatus according to claim 1, wherein the driving pulse signal is generated in an output unit. The plurality of driving elements are divided into a plurality of driving element groups each including two or more driving elements,
The reference voltage setting unit includes:
9. The actuator driving apparatus according to claim 1, wherein the same reference voltage is set for all the driving elements belonging to one driving element group.

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