JP2011093231A - Liquid jetting device and liquid jetting type printer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid jetting device capable of securing the accuracy of a drive signal and a liquid jetting type printer using the liquid jetting device. <P>SOLUTION: A drive waveform signal WCOM is pulse-modulated, a modulated signal is power-amplified by using a digital power amplifier 28, the power-amplified modulated signal is smoothened by a smoothing filter 29 and the drive signal COM is output. In such a case, a state (mode B) in which currents output from the switching elements Q1 and Q2 of the digital power amplifier 28 based on the voltage change ratio dVact/dt of the drive waveform signal and the number of drive actuators Nact are always in one direction in one modulation period is detected. When the mode B is detected, the drive waveform signal WCOM is adjusted so that the pulse width of the power-amplified modulated signal is the same as when the currents output from the switching elements constituting the digital power amplifier are in a bi-direction in one modulation period or the modulation period T of a pulse modulation is adjusted not to generate the mode B. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a liquid ejecting apparatus that ejects liquid by applying a drive signal to an actuator, for example, by ejecting a minute liquid from a nozzle of a liquid ejecting head to form fine particles (dots) on a print medium, The present invention is suitable for a liquid jet printing apparatus that forms predetermined characters, images, and the like.

  In a liquid ejecting printing apparatus, a drive signal amplified by a power amplifying circuit is applied to an actuator such as a piezoelectric element to eject liquid from a nozzle. An analog power amplifier such as a push-pull connection type transistor that is linearly driven is used. When the drive signal is amplified, power loss is large and a large heat sink for heat dissipation is required. Therefore, in the following Patent Document 1, power loss is reduced by amplifying the drive signal with a digital power amplifier, and a heat sink is not required. The digital power amplifier controls on / off of switching elements such as MOSFETs, smooths the output power modulated signal with a smoothing filter as a drive signal, and inputs a modulation signal obtained by pulse-modulating the drive waveform signal. It is a signal.

JP 2005-329710 A

Liquid jet printers, particularly line head liquid jet printers, which enable high-speed printing in one pass, have demands for higher image quality, and drive signals for actuators have become higher in frequency. The accuracy of the drive signal is required. High frequency here means that the cycle of the drive signal is shortened. However, when accuracy is required for the drive signal thus increased in frequency, the pulse modulation cycle of the modulation signal input to the digital power amplifier is changed. As a result, the current output from the switching element of the digital power amplifier is always in one direction within one modulation period, and as a result, the pulse width of the power amplification modulation signal is generated. As a result, the accuracy of the drive signal decreases.
The present invention has been developed by paying attention to these problems, and provides a liquid ejecting apparatus capable of ensuring the accuracy of a drive signal and a liquid ejecting printing apparatus using the liquid ejecting apparatus. It is the purpose.

In order to solve the above problems, a liquid ejecting apparatus of the present invention is push-pull connected to a drive waveform signal generation circuit that generates a drive waveform signal, a modulation circuit that performs pulse modulation on the drive waveform signal, and generates a modulation signal. A digital power amplifier that amplifies the modulation signal by the switching element pair to obtain a power amplification modulation signal, a smoothing filter that smoothes the power amplification modulation signal to obtain a drive signal, and a switching element constituting the digital power amplifier And a pulse width correction circuit that adjusts the pulse width of the power amplification modulation signal when the current output from is always in one direction within one modulation period.
According to this liquid ejecting apparatus, it is possible to ensure the accuracy of the drive signal even when a state in which the current output from the switching element of the switching element of the digital power amplifier is always in one direction within one modulation period occurs.

Further, the pulse width correction circuit has a function of adjusting the pulse width of the power amplification modulation signal to be longer or shorter by the dead time.
Further, the pulse width correction circuit is configured to output digital power based on a voltage change state of the drive waveform signal, a load capacity of the actuator, a power supply voltage of the digital power amplifier, an inductance value of the smoothing filter, and an on-duty ratio of the modulation signal. The current flowing through the amplifier is determined, and the pulse width of the power amplification modulation signal is adjusted accordingly.

The pulse width correction circuit adds a predetermined voltage to the drive waveform signal during a period during which the voltage of the drive waveform signal is increased, and a predetermined period with respect to the drive waveform signal during a period during which the voltage is decreased. The voltage is subtracted.
The liquid ejecting apparatus of the present invention includes a drive waveform signal generation circuit that generates a drive waveform signal, a modulation circuit that modulates the drive waveform signal to generate a modulation signal, and amplifies the power by amplifying the modulation signal. A digital power amplifier as a modulation signal, a smoothing filter that smoothes the power amplification modulation signal as a drive signal, and a current output from a switching element constituting the digital power amplifier is always in one direction within one modulation period. And a modulation period adjusting unit that adjusts the modulation period of the pulse modulation so that a certain state does not occur.

According to this liquid ejecting apparatus, since the state in which the current output from the switching element of the digital power amplifier is always in one direction does not occur within one modulation period, the accuracy of the drive signal can be ensured.
Further, the modulation period adjustment unit performs modulation based on the voltage change state of the drive waveform signal, the load capacity of the actuator, the power supply voltage of the digital power amplifier, the inductance value of the smoothing filter, and the on-duty ratio of the modulation signal. It is characterized by lengthening the period.

1 is a schematic configuration front view illustrating a first embodiment of a liquid jet printing apparatus using a liquid jet apparatus according to the present invention. FIG. 2 is a plan view of the vicinity of a liquid jet head used in the liquid jet printing apparatus of FIG. 1. FIG. 2 is a block diagram of a control device of the liquid jet printing apparatus of FIG. 1. 6 is an explanatory diagram of a drive signal for driving an actuator in each liquid ejecting head. FIG. It is a block diagram of a switching controller. FIG. 2 is a block diagram of an actuator drive circuit of the liquid jet printing apparatus of FIG. 1. It is explanatory drawing of the state from which the electric current output from the switching element of a digital power amplifier is always one direction in one modulation period, and the state which is bidirectional | two-way. FIG. 4 is a detailed explanatory diagram of an output voltage and an output current in a state where the current output from the switching element of the digital power amplifier is always in one direction and in both directions within one modulation period. It is a flowchart which shows the arithmetic processing performed by the control part of FIG. It is a flowchart which shows the arithmetic processing performed by the control part of FIG. It is explanatory drawing of the drive waveform signal correct | amended by the arithmetic processing of FIG. 9, FIG. FIG. 6 is a block diagram of an actuator drive circuit showing a second embodiment of a liquid jet printing apparatus using the liquid jet apparatus of the present invention. It is explanatory drawing of a triangular wave signal. It is a flowchart which shows the arithmetic processing performed by the control part of FIG. It is explanatory drawing of the pulse modulation period adjusted by the arithmetic processing of FIG.

Next, the first embodiment of the liquid ejecting apparatus according to the invention will be described as applied to a liquid ejecting printing apparatus.
FIG. 1 is a schematic configuration diagram of the liquid jet printing apparatus according to the first embodiment. In FIG. 1, a print medium 1 is transported in the direction of an arrow from the left to the right in the figure, and a printing area in the middle of the transport Is a line head type printing apparatus (equivalent to a liquid jet type printing apparatus).

  Reference numeral 2 in FIG. 1 denotes a plurality of liquid ejecting heads (corresponding to a liquid ejecting apparatus) provided above the transport line of the print medium 1 so as to form two rows in the print medium transport direction and the print medium transport direction. Are arranged side by side in a direction intersecting with each other, and are respectively fixed to the head fixing plate 11. A large number of nozzles are formed on the lowermost surface of each liquid jet head 2, and this surface is called a nozzle surface. FIG. 2 is a top view of a plurality of liquid ejecting heads as viewed from above. As shown in FIG. 2, the nozzles are arranged in rows in the direction intersecting the print medium conveyance direction for each color of the liquid to be ejected. The rows are called nozzle rows, or the row directions are nozzles. Sometimes called the row direction. A line head that extends over the entire length in the direction intersecting the transport direction of the print medium 1 is formed by the nozzle rows of all the liquid jet heads 2 arranged in the direction intersecting the print medium transport direction. When the print medium 1 passes below the nozzle surfaces of these liquid ejecting heads 2, printing is performed by ejecting liquid from a large number of nozzles formed on the nozzle surfaces.

  For example, liquid such as yellow (Y), magenta (M), cyan (C), and black (K) ink is supplied to the liquid ejecting head 2 from a liquid tank (not shown) via a liquid supply tube. The Then, by ejecting a necessary amount of liquid from a nozzle formed in the liquid ejecting head 2 to a necessary location, minute dots are formed on the print medium 1. By performing this for each color, printing by one pass can be performed only by passing the print medium 1 conveyed by the conveyance unit 4 once.

  As a method for ejecting the liquid from the nozzle of the liquid ejecting head 2, there are an electrostatic method, a piezo method, a film boiling liquid ejecting method, and the like, and the piezo method is used in the first embodiment. In the piezo method, when a drive signal is given to a piezoelectric element that is an actuator, the diaphragm in the cavity is displaced to cause a pressure change in the cavity, and the liquid is ejected from the nozzle by the pressure change. The liquid ejection amount can be adjusted by adjusting the peak value of the drive signal and the voltage increase / decrease slope. Note that the present invention can be similarly applied to liquid ejection methods other than the piezo method.

  Below the liquid jet head 2, a transport unit 4 for transporting the print medium 1 in the transport direction is provided. The conveying unit 4 is configured by winding a conveying belt 6 around a driving roller 8 and a driven roller 9, and an electric motor (not shown) is connected to the driving roller 8. An adsorption device (not shown) for adsorbing the print medium 1 to the surface of the conveyance belt 6 is provided inside the conveyance belt 6. As this adsorption device, for example, an air suction device that adsorbs the print medium 1 to the conveyance belt 6 by negative pressure, an electrostatic adsorption device that adsorbs the print medium 1 to the conveyance belt 6 by electrostatic force, or the like is used. Accordingly, when only one sheet of the printing medium 1 is fed from the sheet feeding unit 3 to the conveying belt 6 by the sheet feeding roller 5 and the driving roller 8 is rotationally driven by the electric motor, the conveying belt 6 is rotated in the printing medium conveying direction. The print medium 1 is adsorbed to the conveyance belt 6 by the adsorption device and conveyed. While the printing medium 1 is being conveyed, printing is performed by ejecting liquid from the liquid ejecting head 2. The print medium 1 that has finished printing is discharged to the paper discharge unit 10 on the downstream side in the transport direction. The transport belt 6 is attached with a printing reference signal output device composed of, for example, a linear encoder. This printing reference signal output device pays attention to the fact that the transport belt 6 and the print medium 1 that is attracted and transported by the transport belt 6 are moved synchronously, and after the print medium 1 passes through a predetermined position in the transport path. A pulse signal corresponding to the printing resolution required in accordance with the movement of the conveying belt 6 is output, and a drive signal is output from the drive circuit described later to the actuator 22 in accordance with the pulse signal, whereby a predetermined signal on the print medium 1 is output. A liquid of a predetermined color is ejected to the position, and a predetermined image is drawn on the print medium 1 by the dots.

  A control device for controlling the liquid jet printing apparatus is provided in the liquid jet printing apparatus using the liquid jet apparatus according to the first embodiment. As shown in FIG. 3, the control device executes an input interface 61 for reading print data input from the host computer 60 and arithmetic processing such as print processing based on the print data input from the input interface 61. A control unit 62 composed of a microcomputer that performs the above operation, a paper feed roller motor driver 63 that drives and controls the paper feed roller motor 17 connected to the paper feed roller 5, and a head driver 65 that drives and controls the liquid ejecting head 2. An electric motor driver 66 for driving and controlling the electric motor 7 connected to the driving roller 8, a paper feed roller motor driver 63, a head driver 65, an electric motor driver 66 and a paper feed roller motor 17, and the liquid jet head 2. And an interface 67 for connecting the electric motor 7.

  The control unit 62 includes a CPU (Central Processing Unit) 62a that executes various processes such as a print process, and print data input via the input interface 61 or various data when executing the print process of the print data. ROM (Read-Only) comprising a RAM (Random Access Memory) 62c for temporarily storing or temporarily developing a program such as a printing process and a nonvolatile semiconductor memory for storing a control program executed by the CPU 62a Memory) 62d. When the control unit 62 obtains print data (image data) from the host computer 60 via the input interface 61, the CPU 62a executes a predetermined process on the print data, and from which nozzle the liquid is ejected. Alternatively, nozzle selection data (drive pulse selection data) indicating how much liquid is to be ejected is calculated, and based on the print data, drive pulse selection data, and input data from various sensors, the paper feed roller motor driver 63, the head A drive signal and a control signal are output to the driver 65 and the electric motor driver 66. By these drive signals and control signals, the paper feed roller motor 17, the electric motor 7, the actuator 22 in the liquid ejecting head 2, etc. are actuated to feed, convey and discharge the print medium 1, and the print medium 1. The printing process is executed. Each component in the control unit 62 is electrically connected through a bus (not shown).

  FIG. 4 shows an example of a drive signal COM that is supplied to the liquid ejecting head 2 from the control device of the liquid ejecting printing apparatus using the liquid ejecting apparatus according to the first embodiment and drives the actuator 22 made of a piezoelectric element. Show. In the first embodiment, a signal whose potential changes centering on the intermediate potential is used. This drive signal COM is a time series connection of drive pulses PCOM as unit drive signals for driving the actuator 22 to eject liquid, and a cavity (pressure chamber) in which the rising portion of the drive pulse PCOM communicates with the nozzle. ) Is expanded and the liquid is drawn in (it can be said that the meniscus is drawn in considering the liquid ejection surface), and the falling portion of the drive pulse PCOM reduces the volume of the cavity to push out the liquid (the liquid Considering the ejection surface, it can be said that the meniscus is extruded). As a result of the liquid being extruded, the liquid is ejected from the nozzle.

  By variously changing the voltage increase / decrease slope and peak value of the drive pulse PCOM consisting of this voltage trapezoidal wave, it is possible to change the amount of liquid drawn in, the speed of drawing in, the amount of liquid pushed out, and the speed of extrusion. Different sizes of dots can be obtained by changing the ejection amount. Therefore, even when a plurality of drive pulses PCOM are connected in time series, a single drive pulse PCOM is selected and supplied to the actuator 22 to eject liquid or select a plurality of drive pulses PCOM to select the actuator. It is possible to obtain dots of various sizes by supplying the liquid 22 and ejecting the liquid a plurality of times. That is, if a plurality of liquids are landed at the same position before the liquid is dried, it is substantially the same as ejecting a large liquid, and the size of the dots can be increased. By combining such techniques, it is possible to increase the number of gradations. Note that the driving pulse PCOM1 at the left end in FIG. This is called microvibration, and is used to suppress and prevent the increase in the viscosity of the nozzle without ejecting liquid.

  In addition to the drive signal COM, the liquid ejection head 2 selects a nozzle to be ejected based on print data as a control signal from the control device of FIG. 3 and connects to the drive signal COM of an actuator 22 such as a piezoelectric element. Drive pulse selection data SI & SP for determining timing, latch signal LAT and channel for connecting the drive signal COM and the actuator 22 of the liquid ejecting head 2 based on the drive pulse selection data SI & SP after nozzle selection data is input to all nozzles A clock signal SCK for transmitting the signal CH and the drive pulse selection data SI & SP to the liquid jet head 2 as a serial signal is input. Hereinafter, the minimum unit of the drive signal for driving the actuator 22 is referred to as a drive pulse PCOM, and the entire signal in which the drive pulses PCOM are connected in time series is referred to as a drive signal COM. That is, a series of drive signals COM starts to be output in response to the latch signal LAT, and a drive pulse PCOM is output for each channel signal CH.

  FIG. 5 shows a specific configuration of a switching controller built in the liquid ejecting head 2 in order to supply the drive signal COM (drive pulse PCOM) to the actuator 22. The switching controller includes a shift register 211 that stores drive pulse selection data SI & SP for designating an actuator 22 such as a piezoelectric element corresponding to a nozzle that ejects liquid, and a latch circuit that temporarily stores data of the shift register 211. 212 and a level shifter 213 for connecting the drive signal COM to the actuator 22 such as a piezo element by converting the level of the output of the latch circuit 212 and supplying the output to the selection switch 201.

  The drive pulse selection data signal SI & SP is sequentially input to the shift register 211, and the storage area is sequentially shifted from the first stage to the subsequent stage according to the input pulse of the clock signal SCK. The latch circuit 212 latches each output signal of the shift register 211 by the input latch signal LAT after the drive pulse selection data SI & SP 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, and the operating voltage range of the selection switch 201 is set higher accordingly. Therefore, the actuator 22 such as a piezoelectric element whose selection switch 201 is closed (switch-on) by the level shifter 213 is connected to the drive signal COM (drive pulse PCOM) at the connection timing of the drive pulse selection data SI & SP. In addition, after the drive pulse selection data SI & SP 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 liquid ejection timing. . In addition, the code | symbol HGND in a figure is a ground end of actuators 22, such as a piezoelectric element. In addition, even after the actuator 22 such as a piezoelectric element is disconnected from the drive signal COM (drive pulse PCOM) by the selection switch 201 (switch-off), the input voltage of the actuator 22 is maintained at the voltage just before the disconnection. . That is, the actuator 22 is a capacitive load.

  FIG. 6 shows a schematic configuration of the drive circuit of the actuator 22. This actuator drive circuit is constructed in the control unit 62 and the head driver 65 in the control circuit. Further, unlike the control unit 62 in FIG. 3, the control unit 23 in the figure is configured by an arithmetic processing program executed in the control unit 62, and corrects the drive waveform signal WCOM by a pulse width correction circuit 27 described later. To do. The pulse width correction circuit 27 is also configured by an arithmetic processing program executed in the control unit 62. The drive circuit according to the first embodiment is based on the drive waveform data DWCOM stored in advance in the waveform memory 24 and serves as a reference for a signal for controlling the drive of the actuator 22 based on the drive signal COM (drive pulse PCOM). A drive waveform signal generation circuit 25 that generates the drive waveform signal WCOM, a pulse width correction circuit 27 that corrects the drive waveform signal WCOM as necessary in response to a command from the control unit 23, and a drive waveform signal generation circuit 25 A modulation circuit 26 that performs pulse modulation on the drive waveform signal WCOM generated or corrected by the pulse width correction circuit 27, a digital power amplifier 28 that amplifies the modulation signal pulse-modulated by the modulation circuit 26, and a digital power amplifier 28 The power amplification modulated signal after power amplification is smoothed, and a liquid is ejected as a drive signal COM (drive pulse PCOM). Tsu is constituted by a smoothing filter 29 and supplies the de 2, the drive signal COM (the drive pulse PCOM) is applied to the actuator 22 from the selection switch 201.

  The drive waveform signal generation circuit 25 reads drive waveform data DWCOM composed of potential data and the like stored in the waveform memory 24 every predetermined clock period, converts the drive waveform data DWCOM into a voltage signal, and converts the drive waveform data DWCOM into a voltage signal. While holding the clock signal, the voltage signal is converted into an analog signal and output as a drive waveform signal WCOM. Further, the modulation circuit 26 performs pulse modulation using well-known pulse width modulation (PWM). Therefore, the modulation circuit 26 includes a triangular wave oscillator 34 that outputs a triangular wave signal serving as a reference signal at a predetermined clock timing, a driving waveform signal WCOM output from the driving waveform signal generating circuit 25, and a triangular wave output from the triangular wave oscillator 34. And a comparator 35 that compares the signal and outputs a pulse duty modulation signal that is on-duty when the drive waveform signal WCOM is greater than the triangular wave signal. The period of the triangular wave signal is defined as a modulation period, and the frequency of the triangular wave signal is defined as a modulation frequency (generally called a carrier frequency).

  The digital power amplifier 28 has a half-bridge output stage 21 composed of a high-side switching element Q1 and a low-side switching element Q2 for substantially amplifying power, and a high-side side based on a modulation signal from the modulation circuit 26. The switching element Q1 is configured to include a gate drive circuit 30 for adjusting gate voltages (more precisely, gate-source voltages) VH and VL on the low side Q2. In the digital power amplifier 28, when the modulation signal is at a high level, the gate voltage VH of the high-side switching element Q1 is at a high level and the gate voltage VL of the low-side switching element Q2 is at a low level. The element Q1 is turned on and the low-side switching element Q2 is turned off. As a result, the output voltage Va of the half bridge output stage 21 becomes the power supply voltage Vdd. On the other hand, when the modulation signal is at a low level, the gate voltage VH of the high-side switching element Q1 is at a low level and the gate voltage VL of the low-side switching element Q2 is at a high level, so the high-side switching element Q1 is off. Thus, the low-side switching element Q2 is turned on, and as a result, the output voltage Va of the half-bridge output stage 21 becomes zero.

  As the smoothing filter 29, a secondary filter composed of one capacitor C and a coil L was used. The smoothing filter 29 attenuates and removes the modulation frequency generated by the modulation circuit 26, that is, the frequency component of pulse modulation, and outputs the drive signal COM (drive pulse PCOM) having the waveform characteristics as described above. Although FIG. 6 is shown as a circuit for easy understanding, the drive waveform signal generation circuit 25 and the modulation circuit 26 are constructed by programming performed in the control unit 62 of FIG. Further, the smoothing filter 29 can be configured using parasitic inductance generated in circuit wiring, stray capacitance, or an actuator, and is not necessarily formed into a circuit. The waveform memory 24 is formed in the ROM 62d.

  FIG. 7 a shows the drive waveform signal WCOM and the normal output voltage Va and output current I of the digital power amplifier 28. Normally, the current I output from the switching element constituting the digital power amplifier crosses 0A (zero ampere) during one period of the modulation signal, and flows in both directions of the smoothing filter and the power supply or the ground (this The state will be referred to as mode A). FIG. 7b shows a state where the current I output from the switching element constituting the digital power amplifier is always in one direction within one modulation period (this state is referred to as mode B). .) Shows the output voltage Va and the output current I. Among these, when the output current I is always positive (referred to as mode B charging), as will be described later, the actuator 22 made of a piezoelectric element, which is a capacitive load, is always charged, and the output current I Is always negative (referred to as mode B discharge), the actuator 22 comprising a piezoelectric element, which is a capacitive load, always discharges.

  In the line head type printing apparatus, in addition to high-speed printing, higher image quality is required. Therefore, the drive signal COM (drive pulse PCOM) is increased in frequency, and the drive signal COM (drive pulse PCOM) is further increased. The waveform accuracy is also required. That is, the drive signal COM (drive pulse PCOM) having an accurate waveform must be generated in a very short cycle. To realize this, the modulation frequency f of the pulse modulation is expressed by several MHz and the modulation cycle T. nsec order. As will be described later, when the modulation period T of the pulse modulation is shortened, the mode B is easily generated in the digital power amplifier 28.

  FIG. 8 shows details of the gate voltage Vgs (VH, VL), output voltage Va, and output current I during mode A, mode B discharge, and mode B charge. As described above, the gate voltage Vgs is such that when the gate voltage VH of the high-side switching element Q1 is at a high level, the gate voltage VL of the low-side switching element Q2 is at a low level, and the gate voltage of the high-side switching element Q1. In principle, when VH is at a low level, the gate voltage VL of the low-side switching element Q2 is at a high level. However, the actual gate voltages VH and VL have a rising time when the voltage shifts from the low level to the high level and a time required for the falling when the voltage shifts from the high level to the low level. When the voltages VH and VL are both at a high level, a switching loss called shoot-through occurs in which the power supply voltage Vdd is directly grounded. Therefore, the transition period from the high level of the gate voltage VH of the high-side switching element Q1 to the high level of the gate voltage VL of the low-side switching element Q2, and the high-side from the high level of the gate voltage VL of the low-side switching element Q2 In the transition period of the gate voltage VH of the switching element Q1 to the high level, a dead time td is set in which both the gate voltage VH of the high side switching element Q1 and the gate voltage VL of the low side switching element Q2 are in the low level state. And avoid shoot-through.

  FIG. 8A shows the gate voltage Vgs, output voltage Va, and output current I in mode A, and the outputs of the high-side switching element Q1 and the low-side switching element Q2 are inverted during the dead time td. Therefore, the output voltage Va of the power amplification modulation signal rises at the fall of the gate voltage VL of the low side switching element Q2. Further, the output voltage Va of the power amplification modulation signal falls at the fall of the gate voltage VH of the high-side switching element Q1. On the other hand, during mode B discharge, as shown in FIG. 8b, current always flows through the body diode of the high-side switching element Q1 during the dead time td, so that the output voltage Va of the power amplification modulation signal is equal to the dead time td. Always high during the period. As a result, the output voltage Va of the power amplification modulation signal rises at the fall of the gate voltage VL of the low side switching element Q2. Further, the output voltage of the power amplification modulation signal falls at the rise of the gate voltage VL of the low-side switching element Q2. On the other hand, during mode B charging, as shown in FIG. 8c, current always flows through the body diode of the low-side switching element Q2 during the dead time td, so that the output voltage Va of the power amplification modulation signal is always during the dead time td. Become low level. As a result, the output voltage Va of the power amplification modulation signal rises at the rise of the gate voltage VH of the high side switching element Q1. The output voltage Va of the power amplification modulation signal falls at the fall of the gate voltage VH of the high side switching element Q1. In summary, the output voltage Va of the power amplification modulation signal in mode A is long for a high level by the dead time td during mode B discharge, and is high for the dead time td during mode B charging. short. In this case, the waveform accuracy of the drive signal COM (drive pulse PCOM) obtained by smoothing the power amplification modulation signal cannot be obtained.

Actually, as will be described later, in the digital power amplifier 28, the mode B does not occur in a portion where the voltage of the drive signal COM (drive pulse PCOM), that is, the voltage of the drive waveform signal WCOM does not change. Therefore, the presence / absence of the occurrence of mode B is detected from the voltage change state of the drive waveform signal WCOM, the number of actuators to be driven, the on-duty ratio of the modulation signal, etc., and when mode B occurs, power amplification for the dead time td is performed. The increase / decrease of the output voltage Va of the modulation signal is reduced in advance to the drive waveform signal WCOM so that the pulse width of the output voltage Va of the digital power amplifier 28 does not change from that in mode A, and the drive signal COM (drive pulse PCOM). Try to ensure accuracy. The principle of ensuring the accuracy of the drive signal COM (drive pulse PCOM) even when mode B occurs will be described below.
Assuming that the output current of the digital power amplifier 28 is Icom and the current flowing in the modulation period of pulse modulation is Ipwm, the condition for generating the mode B in the digital power amplifier 28 is expressed by the following equation (1).

  Since the actuator 22 made of a piezoelectric element is a capacitive load, the load capacity per actuator 22 is Cact, the number of actuators 22 to be driven is Nact, and the voltage change rate per unit time of the drive waveform signal WCOM (hereinafter referred to as “activate”). (Also simply referred to as voltage change rate) is dVact / dt, the output current Icom of the digital power amplifier 28 is expressed by the following two equations. The number of actuators 22 to be driven can be obtained from the drive pulse selection data SI & SP, that is, print data as described above. Further, the load capacity Cact per actuator 22 is a known number.

  Current Ipwm flowing in the modulation period of the pulse modulation when the voltage across the coil L of the smoothing filter 29 is Vcoil, the modulation period of the pulse modulation is T, the on-duty ratio of the modulation signal is D, and the inductance value of the coil L is L Is expressed by the following three formulas, and the modulation signal on-duty ratio D in the three formulas is expressed by the following four formulas.

  In the above two formulas, only the voltage change rate dVact / dt of the drive waveform signal WCOM changes to a positive value or a negative value. Therefore, the voltage change rate dVact / dt of the drive waveform signal WCOM is expressed as an absolute value. Substituting Formula 2 and Formula 3 into Formula 1, the following Formula 5 is obtained.

That is, when Formula 5 is satisfied, mode B occurs in digital power amplifier 28 (that is, mode B does not occur when the voltage of drive waveform signal WCOM does not change).
Next, the correction amount of the drive waveform signal WCOM is obtained. When the voltage of the regular drive signal COM (drive pulse PCOM) (in the mode A) is Vcom, the pulse width Tcom of the voltage amplification modulation signal is expressed by the following six equations.

  When mode B occurs in the digital power amplifier 28, if the voltage of the drive signal COM (drive pulse PCOM) changes to V'com, the pulse width becomes longer by the dead time td during mode B discharge, and mode B charge is performed. Since the pulse width is sometimes shortened by the dead time td, the following seven equations are established (the positive symbol is when discharging and the negative symbol is when charging).

  The following eight equations are obtained by solving these seven equations with respect to the voltage V'com of the drive signal COM (drive pulse PCOM) when the mode B is generated.

  Since the first term on the right side of the equation 8 is the voltage Vcom of the normal drive signal COM (drive pulse PCOM) (in mode A), the voltage V′com of the drive signal COM (drive pulse PCOM) in the occurrence of mode B Is increased or decreased with respect to the voltage Vcom by the amount of the second term on the right side of equation (8). Therefore, when mode B occurs, the drive waveform signal WCOM may be corrected to be increased or decreased by the amount corresponding to the second term on the right side of equation (8).

Here, when the mode B occurs, the drive waveform signal WCOM is corrected to be increased / decreased by the amount corresponding to the second term on the right side of the equation 8, thereby obtaining the voltage Vcom of the normal (mode A) drive signal COM (drive pulse PCOM). Prove that
First, the voltage Vcom of the normal drive signal COM (drive pulse PCOM) (in the mode A) is obtained by subtracting the second term on the right side of equation 8 from the voltage Vcom of the regular drive signal COM (drive pulse PCOM). The following nine formulas are assumed as' com.

  Assuming that the left side of the equation 7 is the pulse width T′com of the voltage amplification modulation signal when the mode B is generated, the following equation 10 is obtained by substituting the equation 9 into the equation 7.

  When the pulse width Tcom in the first term on the right side of the equation 8 is replaced with the pulse width T′com, and the equation 10 is substituted into the pulse width T′com, the normal (in mode A) ) The voltage Vcom of the drive signal COM (drive pulse PCOM) is obtained. As a result of correcting the drive waveform signal WCOM in this way, the voltage Vcom of the normal (mode A) drive signal COM (drive pulse PCOM) is obtained. This means that the pulse of the output voltage Va of the digital power amplifier 28 is obtained. This means that the width is the same as in mode A.

Next, calculation processing performed by the control unit 23 of the drive circuit in FIG. 6 in order to detect occurrence of mode B in the digital power amplifier 28 will be described with reference to the flowchart in FIG. 9. In this calculation process, first, in step S1, the number of drive actuators Nact is obtained from the print data, that is, the drive signal selection data SI & SP, and the voltage change rate dVact / dt of the drive waveform signal WCOM is read. Is satisfied, the process proceeds to step S2 if expression 5 is satisfied, otherwise the process proceeds to step S3.
In step S2, the mode B flag X indicating the occurrence of mode B of the digital power amplifier 28 is set to “1”, and then the process ends.
In step S3, it is determined that mode B does not occur in the digital power amplifier 28, the mode B flag X is reset to “0”, and then the process ends.

  Next, when the mode B occurs in the digital power amplifier 28, the arithmetic processing performed in the pulse width correction circuit 27 of the drive circuit of FIG. 6 to correct the drive waveform signal voltage Vwcom of the drive waveform signal WCOM is shown in FIG. It demonstrates using the flowchart of these. In this calculation process, first, in step S11, it is determined whether or not the mode B flag X is in the reset state, and if the mode B flag X is in the reset state, the process proceeds to step S12. If not, the process proceeds to step S13.

In step S12, the original drive waveform signal voltage Vwcom is output as it is, assuming that mode B of the digital power amplifier 28 does not occur, and then the process ends.
In step S13, it is determined whether or not the voltage change rate dVact / dt of the drive waveform signal WCOM is a positive value. If the voltage change rate dVact / dt of the drive waveform signal WCOM is a positive value, the process proceeds to step S14. If not, the process proceeds to step S15.

In step S14, the second term on the right side of Equation 8 (corresponding to β in the figure) is added to the original drive waveform signal voltage Vwcom, and the added value is output as a corrected drive waveform signal voltage Vwcom. finish.
In step S15, the second term on the right side of equation 8 (corresponding to β in the figure) is subtracted from the original drive waveform signal voltage Vwcom, and the subtracted value is output as a corrected drive waveform signal voltage Vwcom before processing. finish.

  According to these arithmetic processes, when the mode B is detected in the digital power amplifier 28 with respect to the original drive waveform signal voltage Vwcom shown by the broken line in FIG. The second term on the right side of the equation, that is, Vdd × td / T is added to the original drive waveform signal voltage Vwcom, and during discharge, the drive waveform signal is corrected by subtracting Vdd × td / dt from the original drive waveform signal voltage Vwcom. Since it is WCOM, even if mode B occurs in the digital power amplifier 28, the waveform accuracy of the drive signal COM (drive pulse PCOM) is ensured.

  As described above, in the liquid jet printing apparatus using the liquid jet apparatus according to the first embodiment, the voltage change rate dVact / dt of the drive waveform signal WCOM and the drive pulse selection data Si & SP, that is, the number of drive actuators Nact obtained from the print data are set. Based on this, mode B is detected in digital power amplifier 28, and when mode B is detected, drive waveform signal WCOM is adjusted so that the pulse width of the power amplification modulation signal from digital power amplifier 28 does not change from that in mode A. As a result, even if the mode B occurs in the digital power amplifier 28, the accuracy of the drive signal COM (drive pulse PCOM) can be ensured.

  Next, a second embodiment of a liquid jet printing apparatus using the liquid jet apparatus of the present invention will be described. The liquid jet printing apparatus according to the second embodiment is similar to the liquid jet printing apparatus according to the first embodiment. The schematic configuration, the vicinity of the liquid jet head, the control device, the drive signal, and the switching controller are the same as those in the first embodiment. This is the same as the embodiment. In the second embodiment, the actuator drive circuit is slightly different.

  FIG. 12 shows an actuator drive circuit according to the second embodiment. This actuator drive circuit is also similar to the actuator drive circuit of FIG. 6 of the first embodiment, and the same components are given the same reference numerals. In the actuator drive circuit of the second embodiment, the pulse width correction circuit of the first embodiment is omitted, and the control unit 23 is connected to the triangular wave oscillator 34. The triangular wave oscillator 34 outputs a triangular wave signal in response to a command from the control unit 23.

In the present embodiment, it is detected that mode B of the digital power amplifier 28 will occur, and if mode B is to occur in the digital power amplifier 28, the modulation period T of the pulse modulation is lengthened. Thus, the digital power amplifier 28 tries to avoid the occurrence of mode B itself.
When the mode B generation conditional expression expressed by the above equation 5 is solved for the modulation period T of the pulse modulation and the sign is reversed, the following 12 equations are obtained. By reversing the sign, Formula 12 is a conditional formula that does not cause Mode B. The modulation period T (or modulation frequency f) of the 12 types of pulse modulation is a modulation period (or modulation frequency) of pulse modulation that can avoid the occurrence of mode B in the digital power amplifier 28.

  Actually, when the left side of the equation (12) is α, α is multiplied by a margin coefficient γ larger than 1, and the multiplication value is set as a modulation period T of pulse modulation. In the present embodiment, as shown in FIG. 13, the triangular wave signal voltage Vsaw is increased by a predetermined increase voltage Vstep at a clock cycle Tck of the clock signal SCK to form a triangular wave signal. Here, consider a case where the modulation period T of pulse modulation is changed. When the peak value (arrival voltage) of the triangular wave signal is Vddsaw, the ratio of the clock period Tck to the modulation period T of the pulse modulation is equal to the ratio of the predetermined increase voltage Vstep to the peak value Vddsaw of the triangular wave signal (T: Tck = Vddsaw: Vstep). Here, the clock cycle Tck is a fixed value. Therefore, the predetermined increased voltage Vstep is obtained by multiplying the peak value Vddsaw of the triangular wave signal by the clock period Tck and dividing the value by the modulation period T (= α × γ) of the pulse modulation.

  FIG. 14 is a flowchart showing a calculation process for generating a triangular wave signal performed by the control unit 23. This calculation process is executed every time a drive waveform signal generation command is issued. First, in step S21, the drive actuator number Nact is obtained from the print data, that is, the drive pulse selection data SI & SP, and the drive waveform signal WCOM and its voltage change rate dVact / Read dt.

Next, the process proceeds to step S22, where it is determined whether or not the drive waveform signal WCOM read in step S21 is the end of the waveform. If it is the end of the waveform, the arithmetic processing is ended. The process proceeds to S23.
In step S23, it is determined whether or not the equation 12 is satisfied, that is, whether or not α <T is determined. If the equation 12 is satisfied, the process proceeds to step S24, and otherwise, the process proceeds to step S25. Migrate to
In step S24, the preset modulation period Tzvs for mode A is set to the modulation period T of pulse modulation, and the clock period Tck is multiplied by the triangular wave signal peak value Vddsaw, and the value is divided by the modulation period T to increase by a predetermined amount. After calculating the voltage Vstep, the process proceeds to step S26.

On the other hand, in step S25, the value obtained by multiplying the left side α of the equation (12) by the margin coefficient γ is set as the modulation period T of the pulse modulation, and the clock period Tck is multiplied by the triangular wave signal peak value Vddsaw. After dividing by (= α × γ) to calculate the predetermined increased voltage Vstep, the process proceeds to step S26.
In step S26, the timer counter Count is reset and the triangular wave signal voltage Vsaw is cleared to 0V.

Next, the process proceeds to step S27, where it is determined whether or not the timer counter Count is equal to the modulation period T of the pulse modulation. If the timer counter Count is equal to the modulation period T of the pulse modulation, the process proceeds to step S22. If not, the process proceeds to step S28.
In step S28, the timer counter Count is incremented by one corresponding to the clock cycle Tck, and a value obtained by adding the predetermined increased potential Vstep to the triangular wave signal voltage Vsaw is set as a new triangular wave signal voltage potential Vsaw, and then the process proceeds to step S27. .

  According to this arithmetic processing, when the modulation period T of the pulse modulation satisfies Equation 12, the modulation period Tzvs for mode A is set to the modulation period T of the pulse modulation, so that the drive waveform signal WCOM can be obtained with high accuracy. Pulse modulation can be performed. On the other hand, if the modulation period T of the pulse modulation does not satisfy the equation 12, the value obtained by multiplying the left side α of the equation 12 by the margin coefficient γ is set as the modulation cycle T of the pulse modulation. As shown in FIG. 15, the amplitude of the output current changes, and the occurrence of mode B itself is avoided in the digital power amplifier 28. As a result, the waveform accuracy of the drive signal COM (drive pulse PCOM) can be ensured.

  As described above, in the liquid jet printing apparatus using the liquid jet apparatus according to the second embodiment, the voltage change rate dVact / dt of the drive waveform signal WCOM and the drive pulse selection data SI & SP, that is, the number of drive actuators Nact obtained from the print data, Based on the power supply voltage Vdd of the digital power amplifier 28, the inductance value L of the smoothing filter 29, and the on-duty ratio D of the modulation signal, hard switching of the high-side switching element Q1 and the low-side switching element Q2 of the digital power amplifier 28 does not occur. By adjusting the modulation period T of the pulse modulation in this way, since the mode B itself does not occur in the digital power amplifier 28, the accuracy of the drive signal COM (drive pulse PCOM) can be ensured.

Further, since the region of mode B is the region that consumes the most power in the digital power amplifier 28, the power consumption may be reduced by avoiding mode B.
In the mode B region, the waveform quality of the switching elements Q1 and Q2 is deteriorated due to the reverse recovery current released at the time of switching from the capacitance components of the switching elements Q1 and Q2, and the occurrence of ringing in which the reverse recovery current oscillates with the inductance component. Problems occur. By avoiding mode B, effects such as improvement of waveform quality and reduction of radiated electromagnetic waves may be obtained.
In the first and second embodiments, only the case where the liquid ejecting apparatus of the present invention is used in a line head type liquid ejecting printing apparatus has been described in detail. However, the liquid ejecting apparatus of the present invention is a multi-pass type. The present invention can be similarly applied to the liquid jet printing apparatus.

  In addition, the liquid ejecting apparatus of the present invention may be a liquid other than ink (including a liquid material in which particles of functional material are dispersed and a fluid such as a gel) and a fluid other than a liquid (fluid) It is also possible to embody a liquid ejecting apparatus that ejects a solid that can be ejected as For example, a liquid material ejecting apparatus that ejects a liquid material that contains materials such as electrode materials and color materials used in the manufacture of liquid crystal displays, EL (electroluminescence) displays, surface-emitting displays, color filters, and the like in a dispersed or dissolved form. Further, it may be a liquid ejecting apparatus that ejects a bio-organic matter used for biochip manufacturing, or a liquid ejecting apparatus that ejects a liquid that is used as a precision pipette and serves as a sample. In addition, transparent resin liquids such as UV curable resins for forming liquid injection devices that inject lubricating oil onto precision machines such as watches and cameras, micro hemispherical lenses (optical lenses) used in optical communication elements, etc. Examples include a liquid ejecting apparatus that ejects a liquid onto a substrate, a liquid ejecting apparatus that ejects an etching solution such as acid or alkali to etch the substrate, a fluid ejecting apparatus that ejects a gel, and a powder such as toner. It may be a fluid ejection recording apparatus that ejects a solid. Furthermore, it may be a liquid ejecting apparatus as a surgical tool for incising or excising a living tissue by ejecting a liquid such as water or saline in pulses. The present invention can be applied to any one of these injection devices.

  1 is a print medium, 2 is a liquid ejecting head, 3 is a paper feed unit, 4 is a transport unit, 5 is a paper feed roller, 6 is a transport belt, 7 is an electric motor, 8 is a drive roller, 9 is a driven roller, 10 is A paper discharge unit, 11 is a head fixing plate, 21 is a half bridge output stage, 22 is an actuator, 23 is a control unit, 24 is a waveform memory, 25 is a drive waveform signal generation circuit, 26 is a modulation circuit, and 27 is a pulse width correction circuit. , 28 is a digital power amplifier, 29 is a smoothing filter, 30 is a gate drive circuit, 34 is a triangular wave oscillator, 35 is a comparison unit, and 65 is a head driver.

Claims (7)

A drive waveform signal generating circuit for generating a drive waveform signal;
A modulation circuit that modulates the drive waveform signal by pulse modulation;
A digital power amplifier that amplifies the modulated signal to obtain a power amplified modulated signal;
A smoothing filter that smoothes the power amplification modulation signal as a drive signal, and a pulse of the power amplification modulation signal when the current output from the switching element constituting the digital power amplifier is always in one direction within one modulation period. A liquid ejecting apparatus comprising: a pulse width correcting circuit for adjusting a width.   The liquid ejecting apparatus according to claim 1, wherein the pulse width correction circuit has a function of adjusting a pulse width of the power amplification modulation signal to be longer or shorter by a dead time. The pulse width correction circuit includes:
Determining a current flowing through the digital power amplifier based on a voltage change state of the drive waveform signal, a load capacity of the actuator, a power supply voltage of the digital power amplifier, an inductance value of the smoothing filter, and an on-duty ratio of the modulation signal; The liquid ejecting apparatus according to claim 1, wherein the pulse width of the power amplification modulation signal is adjusted accordingly. The pulse width correction circuit includes:
A predetermined voltage is added to the drive waveform signal during a period during which the voltage of the drive waveform signal is increased, and a predetermined voltage is subtracted from the drive waveform signal during a period during which the voltage is decreased. The liquid ejecting apparatus according to any one of claims 1 to 3. A drive waveform signal generating circuit for generating a drive waveform signal;
A modulation circuit that modulates the drive waveform signal by pulse modulation;
A digital power amplifier that amplifies the modulated signal to obtain a power amplified modulated signal;
A smoothing filter that smoothes the power amplification modulation signal to obtain a drive signal;
A modulation period adjusting unit that adjusts the modulation period of the pulse modulation so that the current output from the switching element constituting the digital power amplifier is not always in one direction within one modulation period. A liquid ejecting apparatus. The modulation period adjustment unit includes:
The modulation period is lengthened based on the voltage change state of the drive waveform signal, the load capacity of the actuator, the power supply voltage of the digital power amplifier, the inductance value of the smoothing filter, and the on-duty ratio of the modulation signal. The liquid ejecting apparatus according to claim 5.   A liquid ejecting printing apparatus comprising the liquid ejecting apparatus according to claim 1.

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