JP2007030343A - Head driving device of inkjet printer and head driving method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To exactly detect a state of nozzles by securing residual oscillation after driving of a piezoelectric actuator of an inkjet printer. <P>SOLUTION: When the piezoelectric actuator is driven by supplying a drive signal, the volume of a cavity is enlarged at a rise (first stage) of the drive signal to bring in ink. While the enlarged volume of the cavity is retained, the residual oscillation generated in the cavity is detected (second stage). The enlarged volume of the cavity is slowly reduced after the detection of the residual oscillation is completed (third stage). A meniscus is drawn in when the volume of the cavity is enlarged, so that the ink droplet is prevented from being ejected. The residual oscillation is enlarged by increasing an amount of the enlargement of the cavity volume or increasing its power enough. The residual oscillation can be made as large as possible by setting a rise time of the drive signal at the first stage so as to excite free oscillation of the cavity. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  In the present invention, for example, minute characters of liquid inks of a plurality of colors are ejected from a plurality of nozzles to form fine particles (ink dots) on a print medium, thereby drawing a predetermined character or image. The present invention relates to a head driving device and a head driving method for an ink jet printer.

Such inkjet printers are generally inexpensive and can easily obtain high-quality color prints, and therefore have become widespread not only in offices but also in general users with the spread of personal computers and digital cameras.
In general, such an ink jet printer has a moving body called a carriage in which an ink cartridge and a print head are integrally provided, reciprocating on a print medium in a direction intersecting the transport direction. By ejecting (jetting) liquid ink droplets from the nozzles to form minute ink dots on the printing medium, a desired printed matter is created by drawing predetermined characters or images on the printing medium. Yes. The carriage is equipped with four color (yellow, magenta, cyan) ink cartridges including black (black) and a print head for each color, so that not only monochrome printing but also full-color printing combining each color is easy. (Furthermore, 6 colors, 7 colors, or 8 colors in which light cyan, light magenta, etc. are added to these colors are also put into practical use).

  By the way, this type of ink jet printer employs ink or ink components that are easy to dry in order to prevent bleeding of ink on the print medium. As a result, when printing is not performed, the ink solvent component (water, solvent, oil, etc.) evaporates from the nozzles of the ink jet head and the ink viscosity at the nozzles increases, which may hinder the ejection of ink droplets. . In addition, ejection of ink droplets may be hindered when air bubbles are mixed into the cavity (ink storage portion) of the ink jet head or dust or paper dust adheres to the nozzle surface. In this way, when the so-called nozzles are clogged and ink droplets cannot be ejected, so-called dot omission occurs in the image on the print medium, causing deterioration in image quality.

Therefore, in Patent Document 1 below, in a device that ejects ink droplets from a pressure chamber by driving a piezoelectric element as an actuator with an electrical signal, the piezoelectric element is driven to expand the volume of the pressure chamber, and then the piezoelectric element The volume of the pressure chamber is reduced to such an extent that no ink droplets are ejected, the excess voltage (electromotive voltage) of the piezoelectric element generated at that time is detected, the ink is dried from the vibration state, and the bubbles in the ink chamber It detects the presence or absence of dust and adhesion of dust and paper dust to the nozzle surface to prevent malfunctions such as printing mistakes due to nozzle failures.
JP 2004-284189 A

  By the way, in order to increase the number of nozzles in order to increase the printing speed, so-called multiple nozzles and the miniaturization of the nozzle head have been promoted. Accordingly, the piezoelectric element as a print actuator has also been miniaturized. The electromotive voltage (electromotive force) of the element is small. Therefore, it is difficult to detect a vibration component (hereinafter also referred to as residual vibration) due to a change in load impedance of the piezoelectric element. This missing dot detection using residual vibration does not directly detect ink dots on the print medium like an optical sensor, but estimates the state of the nozzle flow path and pressure chamber in the nozzle head based on the residual vibration. Therefore, if it is difficult to detect the residual vibration, it leads to a problem of erroneous detection of missing dots.

  The present invention has been made paying attention to the above problems, and is a head drive for an ink jet printer capable of reliably detecting residual vibration in a pressure chamber when a piezoelectric element constituting an actuator is driven. An object is to provide an apparatus and a head driving method.

  [Invention 1] In order to solve the above problem, an ink jet printer head driving device according to Invention 1 corresponds to a plurality of nozzles for ejecting ink droplets, a pressure chamber communicating with each nozzle, and each pressure chamber. Drive means for outputting a drive signal to the actuator for a nozzle head of an ink jet printer provided with an actuator configured to eject ink droplets and including a piezoelectric element, and pressure change in the pressure chamber by the drive signal Residual vibration detection means for detecting residual vibration after the occurrence as a change in electromotive force of a piezoelectric element constituting the actuator, and the drive means expands the volume of the pressure chamber in the drive signal to apply ink. A first stage for drawing in, and a second stage for maintaining the volume of the pressure chamber following the first stage, wherein the residual vibration detecting means is configured to In the second step of the signal, it is characterized in detecting the residual vibration after the pressure change generated in the pressure chamber.

  According to the head drive device of the ink jet printer according to the first aspect of the present invention, the drive means for outputting a drive signal to the actuator, and the residual vibration after the pressure change is generated in the pressure chamber by the drive signal, the electromotive force of the piezoelectric element constituting the actuator And a residual vibration detecting means for detecting the change of the pressure chamber, wherein the driving means expands the volume of the pressure chamber and draws ink into the driving signal, and holds the volume of the pressure chamber following the first stage. And the residual vibration detecting means detects the residual vibration after the pressure change in the pressure chamber at the second stage of the drive signal, so that the pressure at the first stage of the drive signal is detected. By increasing the size and speed of the volume expansion of the chamber, it becomes possible to increase the residual vibration after the pressure change occurs in the pressure chamber without discharging ink droplets. It is possible to detect the residual vibration of certainty.

[Invention 2] The head drive device for an ink jet printer according to Invention 2 is the head drive device for an ink jet printer according to Invention 1. The drive means drives the drive signal so as to excite the natural vibration of the pressure chamber in the first stage. Is set.
According to the head drive device of the ink jet printer according to the second aspect of the invention, since the natural vibration of the pressure chamber is vibrated at the first stage of the drive signal, the residual vibration after the pressure change in the pressure chamber at the second stage is generated. The residual vibration can be reliably detected.

[Invention 3] The head drive device for an ink jet printer according to invention 3 is the head drive device for an ink jet printer according to invention 1 or 2, wherein the drive means does not eject ink droplets following the second stage of the drive signal. A third stage for reducing the volume of the pressure chamber is set.
According to the head driving device of the ink jet printer according to the third aspect of the present invention, following the second stage, the third stage for reducing the volume of the pressure chamber without ejecting ink droplets is set as the drive signal. The piezoelectric element can be gradually returned to the no-load state.

  [Invention 4] A head driving method for an ink jet printer according to Invention 4 is provided for ejecting ink droplets corresponding to each pressure chamber, a plurality of nozzles ejecting ink droplets, a pressure chamber communicating with each nozzle. The actuator is configured to output a drive signal to the nozzle head of an ink jet printer provided with an actuator composed of a piezoelectric element and to generate residual vibration after pressure change in the pressure chamber due to the drive signal. In detecting the change in the electromotive force of the piezoelectric element, the volume of the pressure chamber is expanded at the first stage of the drive signal, the volume of the pressure chamber is maintained at the second stage of the drive signal following the first stage, and the pressure is increased. It is characterized by detecting residual vibration after occurrence of a pressure change in the room.

  According to the head driving method of the ink jet printer according to the fourth aspect of the present invention, the plurality of nozzles for ejecting ink droplets, the pressure chambers communicating with the nozzles, and the ink droplets corresponding to the pressure chambers are provided. A drive signal is output to the actuator for the nozzle head of an ink jet printer provided with an actuator composed of a piezoelectric element, and the residual vibration after the pressure change in the pressure chamber is generated by the drive signal. In detecting the change in the electromotive force of the element, the volume of the pressure chamber is expanded in the first stage of the drive signal, the volume of the pressure chamber is maintained in the second stage of the drive signal following the first stage, and Since the residual vibration after the pressure change is detected, the size and speed of the volume expansion of the pressure chamber in the first stage of the drive signal is increased. Accordingly, without discharging ink droplets, it is possible to increase the residual vibration after the pressure change generated in the pressure chamber, it is possible to reliably detect the residual vibration.

Next, an embodiment of a head driving device for an inkjet printer according to the present invention will be described with reference to the drawings.
FIG. 1 is a plan view showing a schematic configuration of the ink jet printer 1 of the present embodiment. As shown in FIG. 1, the ink jet printer 1 includes a carriage 4 on which a head unit 2 and an ink cartridge 3 are mounted. The carriage 4 is guided by a set of carriage shafts 5 and can move in the main scanning direction. It has become. A part of the carriage 4 is fixed to a toothed belt 9, and the toothed belt 9 is stretched between a driving pulley 7 and a driven pulley 8 fixed to a rotating shaft of the motor 6.

  Further, an encoder 10 is attached to the carriage 4, and a linear scale 11 is provided along the moving direction of the carriage 4. Thereby, the position of the head unit 2 on the carriage 4 is detected by the encoder 10. In FIG. 1, reference numeral 12 denotes a cable for electrically connecting the head unit 2 and the system controller, reference numeral 13 denotes a wiper for cleaning the surface of an ink jet head described later, and reference numeral 14 denotes the ink jet. It is a cap for capping the nozzle substrate (see FIG. 3) of the head.

  In the ink jet printer 1 having such a configuration, when the detection signal of the encoder 10 is input to a motor control circuit (not shown), the motor control circuit causes the rotational operation of the motor 6 to be accelerated, constant speed, decelerated, Inversion, acceleration, constant speed, deceleration, inversion, etc. are controlled. Along with the operation of the motor 6, the carriage 4 repeats reciprocating movement in the main scanning direction, and the constant speed section corresponds to the printing area. Therefore, the head unit 2 mounted on the carriage 4 at the constant speed. Ink droplets are ejected from the nozzles onto the print medium a. As a result, predetermined characters and images are recorded (printed) on the printing medium a by the ink dots formed by the ink droplets.

  Next, a specific configuration of the head unit 2 shown in FIG. 1 will be described with reference to FIGS. 2A and 3. The head unit 2 includes a plurality of inkjet heads (nozzle heads) 20 as shown in FIG. 2a, and each inkjet head 20 uses a piezoelectric actuator. As shown in FIG. 2 a, the inkjet head 20 includes a vibration plate 21, a piezoelectric actuator 22 that displaces the vibration plate 21, an ink that is liquid inside, and an internal pressure caused by the displacement of the vibration plate 21. A cavity (pressure chamber) 23 that is increased or decreased, and a nozzle 24 that communicates with the cavity 23 and ejects ink as droplets by increasing or decreasing the pressure in the cavity 23 are provided.

  More specifically, the inkjet head 20 includes a nozzle substrate 25 on which nozzles 24 are formed, a cavity substrate 26, a vibration plate 21, and a laminated piezoelectric actuator 22 in which a plurality of piezoelectric elements 27 are laminated. Yes. The cavity substrate 26 is formed in a predetermined shape as shown in the figure, whereby a cavity 23 and a reservoir 28 communicating with the cavity 23 are formed. The reservoir 28 is connected to the ink cartridge 3 via the ink supply tube 29. The piezoelectric actuator 22 includes comb-shaped electrodes 31 and 32 arranged opposite to each other, and piezoelectric elements 27 arranged alternately with the comb teeth of the electrodes 31 and 32. The piezoelectric actuator 22 is joined to the diaphragm 21 through an intermediate layer 30 at one end side thereof as shown in FIG.

  In the piezoelectric actuator 22 having such a configuration, the drive signal from the drive signal source applied between the first electrode 31 and the second electrode 32 expands and contracts in the vertical direction as indicated by an arrow in FIG. The mode to use is used. Therefore, in the piezoelectric actuator 22, for example, when a drive signal as shown in FIG. 2A is applied, the vibration plate 21 is displaced, the pressure in the cavity 23 changes, and an ink droplet is ejected from the nozzle 24. It has become. Specifically, as will be described in detail later, the volume of the cavity 23 is enlarged to draw ink, and then the volume of the cavity 23 is reduced to eject ink droplets. The nozzles 24 for each inkjet head 20 formed on the nozzle substrate 26 shown in FIG. 2a are arranged as shown in FIG. 3, for example. The example of FIG. 3 shows an arrangement pattern of the nozzles 24 when applied to four colors of ink (Y: yellow, M: magenta, C: cyan, K: black). Full color printing is possible.

  In the ink jet printer 1 provided with such an ink jet head 20, ink that does not eject ink droplets from the nozzle 24 due to causes such as out of ink, generation of bubbles, clogging (drying), paper dust adhesion, and the like. Drop ejection abnormality (non-ejection), so-called dot dropout phenomenon may occur. Here, the paper dust is easily generated when a printing medium made of wood pulp as a raw material is brought into frictional contact with a recording roller or the like, and is composed of a part of the printing medium and is fibrous or an aggregate thereof.

  Here, another example of the piezoelectric actuator 22 is shown in FIG. The reference numerals in the figure are the same as those in FIG. 2a. This piezoelectric actuator is generally called a unimorph actuator and has a simple structure in which the piezoelectric element 27 is sandwiched between two electrodes 31 and 32. By applying a drive signal, the piezoelectric actuator is similar to the stacked actuator of FIG. 2a. Then, the ink expands and contracts in the vertical direction in the figure, expands the volume of the cavity 23 and draws ink, and then reduces the volume of the cavity 23 and discharges ink droplets from the nozzles 24.

  The inkjet printer 1 is provided with a control device for controlling itself. For example, as shown in FIG. 4, the control device prints on a print medium by controlling a printing device, a paper feeding device, and the like based on print data input from a host computer 60 such as a personal computer or a digital camera. The processing is performed. An input interface unit 61 that receives print data input from the host computer 60, and a control unit 62 configured by, for example, a microcomputer that executes print processing based on the check data input from the input interface unit 61; The carriage motor driver 63 for driving and controlling the carriage motor 41, the paper feeding motor driver 64 for driving and controlling the paper feeding motor 51, the head driver 65 for driving and controlling the inkjet head 20, and the outputs of the drivers 63, 64 and 65 The signal is converted into a control signal used by the external carriage motor 41, paper feed motor 51, and inkjet head 20, and output, and the residual vibration of the cavity detected by the residual vibration detection circuit 15 is input to the control unit 62. And an output interface 67. That.

  Here, the control unit 62 executes various processing such as printing processing, a CPU (Central Processing Unit) 62a, and print data input via the input interface 61 or various types when executing the printing data printing processing. ROM (Random Access Memory) 62c that temporarily stores data or temporarily develops application programs such as print processing, and ROM (non-volatile semiconductor memory that stores control programs executed by the CPU 62a) Read-Only Memory) 62d. When the control unit 62 obtains print data from the host computer 60 via the input interface unit 61, the CPU 62a executes predetermined processing on the print data, and based on the processing data and input data from various sensors. Thus, a control signal is output to each of the drivers 63 to 65. When the control signals are output from the drivers 63 to 65, these are converted into drive signals by the input / output interface unit 67, and the piezoelectric actuators 22, carriage motors 41, paper feeds corresponding to the plurality of nozzles 24 of the inkjet head 20 are performed. Each of the motors 51 operates to execute a printing process on the print medium. Each component in the control unit 62 is electrically connected through a bus (not shown).

  Further, the control unit 62 writes the write enable signal DEN, the write clock signal WCLK, and the write address data A0 to A0 in order to write the waveform forming data DATA for forming the drive signal described later into the waveform memory 701 described later. A3 is output to write, for example, 16-bit waveform forming data DATA into the waveform memory 701, and read address data A0 to A3 for reading out the waveform forming data DATA stored in the waveform memory 701. The first clock signal ACLK that sets the timing for latching the waveform forming data DATA read from the waveform memory 701, the second clock signal BCLK that sets the timing for adding the latched waveform data, and the latch data are cleared. Outputs clear signal CLER to head driver 65 That.

  The head driver 65 includes a drive signal generation circuit 70 that generates a drive signal COM and an oscillation circuit 71 that outputs a clock signal SCK. As shown in FIG. 5, the drive signal generation circuit 70 includes a waveform memory 701 for storing waveform formation data DATA for generating a drive signal input from the control unit 62 in a storage element corresponding to a predetermined address, A latch circuit 702 that latches the waveform forming data DATA read from the waveform memory 701 by the first clock signal ACLK described above, an output of the latch circuit 702, and waveform generation data WDATA output from a latch circuit 704 described later. An adder 703 for adding, a latch circuit 704 for latching the addition output of the adder 703 by the above-described second clock signal BCLK, and D for converting the waveform generation data WDATA output from the latch circuit 704 into an analog signal / A converter 705 and the analog output from this D / A converter 705 A voltage amplifier 706 amplifies the voltage signal, and a current amplifier 707 for outputting a drive signal COM output signal of the voltage amplifier 706 current amplification to. Here, the clear signal CLER output from the control unit 62 is input to the latch circuits 702 and 704, and the latch data is cleared when the clear signal CLER is turned off.

  As shown in FIG. 6, in the waveform memory 701, memory elements each having several bits are arranged at the designated address, and waveform data DATA is stored together with the addresses A0 to A3. Specifically, the waveform data DATA is input together with the clock signal WCLK to the addresses A0 to A3 instructed from the control unit 62, and the waveform data DATA is stored in the memory element by the input of the write enable signal DEN.

  The inkjet head 20 has a drive signal COM generated by the drive signal generation circuit 70, a data signal SI for selecting nozzles to be ejected based on print data, and nozzle selection data for all nozzles via the input / output interface 67. After the input, a latch signal LAT for connecting the drive signal COM and the piezoelectric actuator 22 of the inkjet head 20 by these data, and a clock signal SCK for transmitting these selection data signals SI to the inkjet head 20 as serial signals. Is entered.

  Next, a configuration for connecting the drive signal COM output from the drive signal generation circuit 70 and the piezoelectric actuator 22 will be described. FIG. 7 is a block diagram of a selection unit that connects the drive signal COM and the piezoelectric actuator 22. The selection unit includes a shift register 211 that stores data specifying the piezoelectric actuator 22 corresponding to the nozzle that should eject ink droplets, a latch circuit 212 that temporarily stores data in the shift register 211, and a latch circuit 212. The level shifter 213 converts the level of the output of the output signal and the selection switch 201 connects the drive signal COM to the piezoelectric actuator 22 in accordance with the level shifter output.

  A data signal SI is sequentially input to the shift register 211 as print data, and the storage area is sequentially shifted from the first stage to the subsequent stage in response to an input pulse of the clock signal CLK. The latch circuit 212 latches each output signal of the shift register 211 by the input latch signal LAT after print data for the number of nozzles is stored in the shift register 211. The signal stored in the latch circuit 212 is converted by the level shifter 213 to a voltage level at which the selection switch 201 at the next stage can be turned on / off. This is because the drive signal COM is higher than the output voltage of the latch circuit 212, so that the operating voltage range of the selection switch 201 is also set high. The selection switch 201 is composed of an analog switch having a transmission gate in which a P-channel FET and an N-channel FET are combined, and the gate voltage is level-converted to a high value in order to sufficiently operate the analog switch. The piezoelectric actuator 22 of the nozzle to which the gate voltage of the selection switch 201 is applied by the level shifter 213 is connected to the drive signal COM. Further, after the print data signal SI of the shift register 211 is stored in the latch circuit 212, the next print information is input to the shift register 211, and the stored data of the latch circuit 212 is sequentially updated in accordance with the ink droplet ejection timing. . Reference numeral HGND in the figure is the ground end of the piezoelectric actuator 22.

  Next, the principle of drive signal generation will be described. First, waveform data that is 0 as a voltage change amount per unit time is written in the address A0. Similarly, waveform data of + ΔV1 is written in the address A1, −ΔV2 is written in the address A2, and + ΔV3 is written in the address A3. In addition, the data stored in the latch circuits 702 and 704 is cleared by the clear signal CLER. The drive signal COM is raised to an intermediate potential (offset) according to desired waveform data.

  From this state, for example, as shown in FIG. 8, when the waveform data at the address A1 is read and the first clock signal ACLK is input, the digital data of + ΔV1 is stored in the latch circuit 702. The stored digital data of + ΔV1 is input to the latch circuit 704 via the adder 703, and the latch circuit 704 stores the output of the adder 703 in synchronization with the rise of the second clock signal BCLK. Since the output of the latch circuit 704 is also input to the adder 703, the output (COM) of the latch circuit 704 is added by + ΔV1 at the rising timing of the second clock signal BCLK. In this example, the waveform data at the address A1 is read during the time width T1, and as a result, the digital data of + ΔV1 is added until it is tripled.

  Next, when the waveform data at the address A0 is read and the first clock signal ACLK is input, the digital data stored in the latch circuit 702 is switched to zero. The digital data of 0 is added at the rising timing of the second clock signal BCLK through the adder 703 as described above, but since the digital data is 0, the value before that is substantially the same. Is retained. In this example, the drive signal COM is held at a constant value during the time width T0.

  Next, when the waveform data at the address A2 is read and the first clock signal ACLK is input, the digital data stored in the latch circuit 702 is switched to -ΔV2. The digital data of −ΔV2 passes through the adder 703 and is added at the rising timing of the second clock signal BCLK as described above. However, since the digital data is −ΔV2, the second clock is practically set. The drive signal COM is subtracted by −ΔV2 in accordance with the signal. In this example, during the time width T2, the drive signal COM is subtracted until the digital data of −ΔV2 becomes six times.

  The drive signal COM thus generated and output after being subjected to analog conversion and voltage-current amplification is a waveform signal as shown in FIG. Of these, the rising portion of the drive signal COM is a stage in which the volume of the cavity 23 is enlarged and ink is drawn in (it can be said that the meniscus is drawn in consideration of the ink discharge surface), and the falling portion of the drive signal COM is the volume of the cavity 23. Is reduced and the ink droplets are ejected (it can be said that the meniscus is extruded if the ink ejection surface is considered). Incidentally, the waveform of the drive signal depends on the waveform data 0, + ΔV1, −ΔV2, + ΔV3, the first clock signal ACLK, and the second clock signal BCLK written to the addresses A0 to A3, as can be easily guessed from the above. It can be adjusted.

  Now, when the drive signal COM is applied to the piezoelectric actuators 22 corresponding to the nozzles 24 in this way, after the pressure fluctuation at that time, residual vibrations (to be precise, free vibration of the diaphragm 21 in FIG. 2). Vibration). The state of each nozzle 24 (including the state in the cavity 23) can be detected from this residual vibration state. For example, as shown in FIG. 9, compared to when the nozzle is normal, when bubbles are mixed into the ink flow path or the nozzle tip (corresponding to “bubble mixing” in the figure), the ink weight (= Inertance is reduced, and it is equivalent to a state in which the nozzle diameter is increased by bubbles, resulting in a reduction in acoustic resistance and an increase in vibration frequency. In addition, when the ink in the nozzle portion is dried (corresponding to “drying” in the figure), the acoustic resistance increases due to the increase in the viscosity of the ink, resulting in overdamping. Also, when paper dust or dust adheres to the nozzle surface (corresponding to “paper dust” in the figure), the ink oozes from the nozzle with paper dust, increasing the ink weight viewed from the diaphragm and causing inertance. And the acoustic resistance is increased by the paper dust fibers adhering to the nozzle, and the period is increased (frequency is decreased).

  Therefore, for example, a circuit shown in FIG. 10 is provided as the residual vibration detection circuit 15 for detecting such residual vibration. The residual vibration detection circuit 15 detects the change in pressure in the cavity 23 by being transmitted to the piezoelectric actuator 22. Specifically, the residual vibration detection circuit 15 is caused by mechanical displacement of the piezoelectric actuator 22. A change in electric power (electromotive voltage) is detected. The residual vibration detection circuit 15 includes a switch (transistor Q) that grounds or opens the ground end HGND of the piezoelectric actuator 22 and a ground signal HGND that is grounded or opened after the drive signal COM is applied to the piezoelectric actuator 22. An AC amplifier 16 that amplifies the AC component of the generated residual vibration, a comparator 17 that converts the amplified residual vibration VaOUT into a pulse POUT with a reference voltage Vref1, a pulse POUT of the comparator 17 and a gate signal DSEL of the transistor Q are And an input OR circuit OR. Among these, the AC amplifier 16 includes a capacitor C that removes a DC component, and an arithmetic unit AMP that inverts and amplifies at a gain determined by the resistors R1 and R2 with reference to the potential of the reference voltage Vref1.

Next, the inkjet heads 20 shown in FIGS. 2a and 2b will be considered. FIG. 11 is an equivalent circuit of an inkjet head, particularly a portion where residual vibration occurs. The symbols in the figure are as follows.
Ca: Actuator compliance (volume change per unit pressure)
Ma: Inertance of actuator (mass)
Cn: Compliance due to meniscus surface tension Mn: Inertance of nozzle flow path Rn: Resistance of nozzle flow path Ms: Inertance of ink supply path Rs: Resistance of ink supply path Cc: Compliance of ink chamber = Ci + Cv
Ci: Compliance due to compressibility of ink Cv: Compliance of diaphragm The vibration mode of the cavity (pressure chamber) is expressed by the following formulas 1 and 2.

Tc = 2π√ (M × Cc) (1)
fc = 1 / (2π√ (M × Cc)) (2)

Tc is the natural frequency of the cavity (ink-filled state), and fc is the natural frequency (frequency) of the cavity. M is the inertance of the ink flow path as viewed from the cavity, and is a parallel synthesis inertance of the inertance Mn of the nozzle flow path and the inertance Ms of the ink supply path, and is expressed by the following three equations.
M = Mn × Ms / (Mn + Ms) (3)

On the other hand, the natural vibration period fa of the actuator and the natural frequency (frequency) of the actuator are expressed by the following equations 4 and 5, respectively, similarly to those of the cavity.
Ta = 2π√ (Ma × Ca) (4)
fa = 1 / (2π√ (Ma × Ca)) (5)

  For example, in the case of the laminated piezoelectric actuator 22 shown in FIG. 2 a, the piezoelectric element 27 having a small thickness is laminated and used in the longitudinal vibration mode, so that the compliance of the piezoelectric actuator 22 is the compliance of the diaphragm 21. Compared to a smaller value (hard). In addition, since the vertical dimension of the piezoelectric actuator 22 is large and the inertance Ma cannot be ignored, a component that vibrates at the natural vibration period Ta exists as a natural vibration mode of the piezoelectric actuator 22, which is the ink of the cavity 23. It is generated by the operation of the piezoelectric actuator 22 regardless of the presence or absence. The natural vibration period Tc of the cavity is set larger than the natural vibration period Ta of the actuator. On the other hand, in the case of the unimorph type piezoelectric actuator 22 of FIG. 2b, since the piezoelectric element 27 is thin and small, the inertance Ma of the piezoelectric actuator 22 can be ignored, and the natural vibration period Ta of the piezoelectric actuator 22 is approximately the ink. It can be considered as the natural vibration period Tc of the cavity 23 in the full state.

  2a includes the natural vibration mode of the piezoelectric actuator 22 in addition to the natural vibration mode of the cavity 23. The natural vibration mode of the piezoelectric actuator 22 is the cavity vibration mode. Since the vibration is unnecessary when detecting the residual vibration 23, it is necessary to set the drive signal COM that does not cause the natural vibration of the piezoelectric actuator 22 as much as possible and can ensure stable residual vibration. On the other hand, in the case of the unimorph type piezoelectric actuator 22 shown in FIG. 2B, the natural vibration mode of the piezoelectric actuator 22 can be ignored, so that the drive vibration COM that can secure stable residual vibration is set.

  FIG. 12 is a flowchart showing a calculation process for residual vibration detection according to the present embodiment. Since the residual vibration is for detecting an ink droplet ejection defect of the nozzle, it is performed, for example, every predetermined time, at power-on, or at power-off. In this arithmetic processing, first, in step S 1, the gate voltage DSEL of the transistor Q of the residual vibration detection circuit 15 is set to a high level, and the piezoelectric actuator 22 is connected to the drive signal generation circuit 70.

Next, the process proceeds to step S2, and a cavity volume expansion drive signal COMpull for expanding the volume of the cavity 23 is output.
Next, the process proceeds to step S3, where it is determined whether or not the output of the cavity volume expansion drive signal COMpull output in step S2 is completed. If the output of the cavity volume expansion drive signal COMpull is completed, step S4 is performed. If not, the process proceeds to step S2.

In step S 4, the gate voltage DSEL of the transistor Q of the residual vibration detection circuit 15 is set to a low level, and the piezoelectric actuator 22 is connected to the residual vibration detection circuit 15.
Next, the process proceeds to step S5, and residual vibration detection processing by the residual vibration detection circuit 15 is performed while maintaining the volume of the cavity expanded in step S2.
Next, the process proceeds to step S6, where it is determined whether or not the residual vibration detection process performed in step S5 is completed. If the residual vibration detection process is completed, the process proceeds to step S7. Goes to step S4.

In step S 7, the gate voltage DSEL of the transistor Q of the residual vibration detection circuit 15 is set to a high level, and the piezoelectric actuator 22 is connected to the drive signal generation circuit 70.
In step S8, a cavity volume reduction drive signal COMpush for reducing the volume of the cavity 23 is output.
Next, the process proceeds to step S9, where it is determined whether or not the output of the cavity volume reduction drive signal COMpush output in step S8 has been completed, and when the output of the cavity volume reduction drive signal COMpush is completed, the main program If not, the process proceeds to step S8.

  According to this calculation process, for example, as shown in FIG. 13, the drive signal is generated in a state where the gate voltage DSEL of the transistor Q of the residual vibration detection circuit 15 is set to the high level and the piezoelectric actuator 22 is connected to the drive signal generation circuit 70. A cavity volume expansion drive signal COMpull that increases the voltage of COM is output. If this state is maintained for a predetermined time T01 and the voltage of the drive signal increases to the predetermined potential VH, for example, the volume of the cavity 23 is expanded and pressure fluctuation occurs, so that the gate of the transistor Q of the residual vibration detection circuit 15 The voltage DSEL is set to a low level, the piezoelectric actuator 22 is connected to the residual vibration detection circuit 15, and the state, that is, the volume of the enlarged cavity 23 is maintained and the pressure fluctuation generated in the cavity 23, that is, the piezoelectric actuator 22 is generated. The remaining residual vibration is detected. The detected residual vibration becomes the residual vibration VaOUT amplified by the AC amplifier 16 of the residual vibration detection circuit 15, and the pulse POUT is output from the comparator 17. Therefore, as described above, the pulse POUT is stored in advance. The state of the nozzle is detected by comparison with the set reference value. Since this residual vibration detection ends at a predetermined time T02, when the residual vibration detection ends, the gate voltage DSEL of the transistor Q of the residual vibration detection circuit 15 is set to the high level again, and the piezoelectric actuator 22 is set to the drive signal generation circuit 70. For example, a cavity volume reduction drive signal COMpush that gradually decreases the voltage of the drive signal COM after a predetermined time T03 is output. In this case, it is possible to prevent ink droplets from being ejected from the nozzles by slowly decreasing the drive signal COM over a relatively long predetermined time T04. Then, after the predetermined time T04, when the potential of the drive signal COM becomes the initial state, the calculation process for residual vibration detection is completed. The reason why the drive signal generation circuit 70 is disconnected from the piezoelectric actuator 22 during the residual vibration detection is to prevent the residual vibration in the cavity 23 from being canceled by the feedback function of the drive signal generation circuit 70.

  FIG. 14 shows the state of the meniscus of the ink in the nozzle when this residual vibration is detected. In FIG. 14 a showing the initial state, the ink meniscus is at a position slightly retracted from the nozzle surface 25 (upper side in the figure). When the cavity volume expansion drive signal COMpull is output from this state and the volume of the cavity 23 is increased, the meniscus is drawn into the nozzle 24 as shown in FIG. 14B, and at the same time, a pressure fluctuation on the negative pressure side is generated in the cavity 23. When the pressure fluctuation is sufficiently generated, the volume of the enlarged cavity 23 is maintained, and the vibration of the meniscus as shown in FIG. 14c, that is, the vibration of the cavity 23 is detected as the residual vibration of the piezoelectric actuator 22. This residual vibration detection detects the meniscus by drawing it in, so there is no risk of ink droplets being ejected from the nozzles at that time. Therefore, in principle, there is no limit to the volume expansion of the cavity 23, the generated residual vibration can be increased, and the residual vibration can be reliably detected.

  On the other hand, in the conventional residual vibration detection, from the initial state shown in FIG. 15a, as in this embodiment, as shown in FIG. 15b, the volume of the cavity 23 is once expanded to draw the meniscus, and then FIG. 15c. As shown in FIG. 15, the volume of the cavity 23 is reduced to push out the meniscus, and in this state, the vibration of the meniscus as shown in FIG. 15d, that is, the vibration of the cavity 23 is detected as the residual vibration of the piezoelectric actuator 22. Therefore, if the amount and momentum of pushing out the meniscus are increased too much, ink droplets are ejected, so that there is a limit to the volume reduction of the cavity 23 and there is a problem that the residual vibration to be detected is reduced.

  The cavity volume reduction drive signal COMpush-p in FIG. 16a is a conventional residual vibration detection method in which the volume of the cavity 23 is reduced to push out the meniscus and the residual vibration is detected in this state following the cavity volume enlargement drive signal COMpull1. Residual vibration was detected in the subsequent detection period (predetermined time) T02. On the other hand, the cavity volume reduction drive signal COMpush1 is an example of the residual vibration detection method of the present embodiment in which the volume of the cavity 23 is enlarged by the cavity volume enlargement drive signal COMpull1 to draw the meniscus and the residual vibration is detected in this state. After residual vibration was detected in the detection period T02, the volume of the cavity 23 was slowly reduced to the initial state. The cavity volume expansion drive signal COMpull2 increases the voltage of the drive signal COM to a potential twice that of the cavity volume expansion drive signal COMpull1 at the same time (predetermined time T01) as the cavity volume expansion drive signal COMpull1, and in the detection period T02. After detecting the residual vibration, the volume of the cavity 23 was slowly reduced to the initial state. The respective residual vibration detection methods are shown as COM push-p, COM pull 1 and COM pull 2, and the ratio of the amplitudes of the detected residual vibrations is shown in FIG. 16b as a ratio when the conventional residual vibration detection method COM push-p is 1. Compared to the conventional residual vibration detection method that can vibrate the vibration of the cavity 23 by the cavity volume reduction drive signal COMpush-p, the residual vibration detection method of the present embodiment by the cavity volume expansion drive signal COMpull1 The amplitude ratio is slightly small. However, as described above, in the residual vibration detection method of the present embodiment that does not cause the ink droplets to be ejected, the voltage of the drive signal COM can be increased like the cavity volume expansion drive signal COMpull2, and thus, for example, the cavity 23 Can be amplified up to 1.7 times the conventional amplitude ratio. Therefore, in the residual vibration detection method of the present embodiment, the residual vibration of the cavity 23 can be reliably detected, and thereby the state of the nozzle can be reliably detected.

  Further, in order to increase the residual vibration of the cavity 23 as much as possible, the natural vibration period Tc of the cavity 23 may be excited by the cavity volume expansion drive signal COMpull. However, as described above, in the case of the stacked piezoelectric actuator 22 of FIG. 2 a, the natural vibration mode of the piezoelectric actuator 22 is included in addition to the natural vibration mode of the cavity 23. Since the vibration mode is unnecessary when detecting the residual vibration of the cavity 23, for example, as shown in FIG. 17, the natural vibration of the piezoelectric actuator 22 does not appear as much as possible, and the natural vibration of the cavity 23. It is necessary to set the drive signal COM that can secure the residual vibration that can be stably obtained only by the period Tc.

  Using this stacked piezoelectric actuator 22, the residual vibration waveform when the rise time (predetermined time) T01 is varied while the potential (crest value) of the cavity volume expansion drive signal COMpull is constant is subjected to fast Fourier transform and the cavity natural vibration is obtained. The power spectrum of the frequency fc and the actuator natural vibration frequency fa was measured. The measurement results are shown in FIG. The actuator natural vibration period Ta of the multilayer piezoelectric actuator 22 is about 0.4 times the cavity natural vibration period Tc of the cavity 23. When the rising time T01 of the cavity volume expansion drive signal COMpull is set to 0.4 times the cavity natural vibration period Tc, the cavity natural vibration frequency fc increases and the actuator natural vibration frequency fa is suppressed. This is because the cavity 23 is vibrated by natural vibration by stopping the cavity volume expansion drive signal COMpull at the rising time T01, and vibration generated up to that time and actuator natural vibration generated thereafter are generated. This is because they cancel each other by interfering in a state shifted from each other by a half cycle. Therefore, in this embodiment, by setting the rise time T01 of the cavity volume expansion drive signal COMpul to 0.4 times the cavity natural vibration period Tc, the natural vibration of the cavity 23 can be excited and the actuator natural vibration can be canceled out. .

  As described above, according to the head driving device and the head driving method of the ink jet printer of the present embodiment, the plurality of nozzles 24 that eject ink droplets, the cavities 23 that communicate with the nozzles 24, and the cavities 23 correspond to each other. A drive signal COM is output to the piezoelectric actuator 22 to the inkjet head 20 of the inkjet printer provided with the piezoelectric actuator 22 configured to eject ink droplets and configured by the piezoelectric element 27. In detecting the residual vibration after the pressure change in the cavity 23 due to COM as the change in electromotive force of the piezoelectric element 27 constituting the piezoelectric actuator 22, the first stage of the drive signal COM, that is, the cavity volume expansion drive signal COMpull. To increase the volume of the cavity 23, the first stage Since the volume of the cavity 23 is maintained in the second stage of the subsequent drive signal COM and the residual vibration after the pressure change in the cavity 23 is detected, the first stage of the drive signal COM, that is, the cavity volume expansion drive signal COMpull. By increasing the size and speed of the volume expansion of the cavity 23, the residual vibration after the pressure change in the cavity 23 can be increased without ejecting ink droplets. Can be detected.

Further, the residual vibration after the pressure change in the cavity 23 in the second stage is increased by exciting the natural vibration of the cavity 23 by the first stage of the drive signal COM, that is, the cavity volume expansion drive signal COMpull. And the residual vibration can be reliably detected.
In addition, following the second stage, the piezoelectric actuator 22 is a piezoelectric actuator 22 by setting the third stage in which the volume of the cavity 23 is reduced without ejecting ink drops, that is, by setting the cavity volume reduction drive signal COMpush as the drive signal COM. The element 27 can be gradually returned to the no-load state.

  In each of the above-described embodiments, only the example in which the head driving device of the ink jet printer of the present invention is applied to a so-called multi-pass ink jet printer is described in detail. However, the head driving device of the ink jet printer of the present invention is a line head. The present invention can be applied to any type of ink jet printer including a type printer.

1 is a plan view of an ink jet printer showing an embodiment of a head driving device of an ink jet printer of the present invention. It is a schematic block diagram of the inkjet head of the inkjet printer of FIG. It is explanatory drawing of the nozzle of the inkjet head of FIG. It is a block diagram of the control apparatus provided in the inkjet printer of FIG. FIG. 5 is a block diagram of the drive signal generation circuit of FIG. 4. It is explanatory drawing of the waveform memory of FIG. It is a block diagram of the selection part which connects a drive signal to a piezoelectric actuator. It is explanatory drawing of drive signal generation. It is explanatory drawing of a residual vibration. It is a block diagram of a residual vibration detection circuit. It is an equivalent circuit of an inkjet head. It is a flowchart which shows the arithmetic processing for a residual vibration detection. It is explanatory drawing of the drive signal for a residual vibration detection. It is explanatory drawing of the meniscus by the arithmetic processing of FIG. It is explanatory drawing of the meniscus in the conventional residual vibration detection. It is explanatory drawing of the amplitude ratio of the drive signal for residual vibration detection, and the detected residual vibration. It is explanatory drawing of a residual vibration. It is explanatory drawing of the power spectrum of a pressure chamber natural vibration and an actuator natural vibration when the rise time of the drive signal which expands a pressure chamber is changed.

Explanation of symbols

  1 is an inkjet printer, 15 is a residual vibration detection circuit, 16 is an AC amplifier, 17 is a comparator, 20 is an inkjet head, 21 is a diaphragm, 22 is a piezoelectric actuator, 23 is a cavity, 24 is a nozzle, 62 is a control unit , 70 is a drive signal generation circuit, a is a print medium

Claims (4)

  Inkjet printer comprising a plurality of nozzles for ejecting ink droplets, a pressure chamber communicating with each nozzle, and an actuator configured to eject ink droplets corresponding to each pressure chamber and configured with a piezoelectric element Drive means for outputting a drive signal to the actuator, and residual vibration after pressure change in the pressure chamber caused by the drive signal is detected as a change in electromotive force of the piezoelectric element constituting the actuator. Vibration detection means, and the drive means expands the volume of the pressure chamber and draws ink into the drive signal, and the second stage holds the volume of the pressure chamber following the first stage. The residual vibration detecting means detects the residual vibration after occurrence of a pressure change in the pressure chamber in the second stage of the drive signal. Head driving device of click-jet printer.   2. The head driving device of an ink jet printer according to claim 1, wherein the driving unit sets a driving signal so as to excite the natural vibration of the pressure chamber in the first stage.   3. The inkjet printer according to claim 1, wherein the driving unit sets a third stage in which the volume of the pressure chamber is reduced without ejecting ink droplets, following the second stage of the driving signal. Head drive device. Inkjet printer comprising a plurality of nozzles for ejecting ink droplets, a pressure chamber communicating with each nozzle, and an actuator configured to eject ink droplets corresponding to each pressure chamber and configured with a piezoelectric element When a drive signal is output to the nozzle head and a residual vibration after a pressure change in the pressure chamber due to the drive signal is detected as a change in electromotive force of a piezoelectric element constituting the actuator, the drive signal The volume of the pressure chamber is enlarged in the first stage of the first, the volume of the pressure chamber is held in the second stage of the drive signal following the first stage, and the residual vibration after the occurrence of the pressure change in the pressure chamber is detected. A head driving method for an inkjet printer.

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