JP2010124040A - Power amplifying device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid injection device reducing the stages of a smoothing filter and reducing switching loss, when carrying out power amplification using a digital power amplifier. <P>SOLUTION: A drive wave signal WCOM is pulse modulated in a modulation circuit 26. The modulated signal is power amplified in a digital power amplifying circuit 28. The power-amplified modulated signal, for which power amplification is carried out, is smoothed at a smoothing filter 29 and outputted to a nozzle actuator in a liquid injection head 2. The digital power amplifying circuit 28 includes two steps of digital power amplifiers 27a and 27b having a push-pull connected switching device pair. The second digital power amplifier 27b is biased with the output of the first digital power amplifier 27a. While the number of steps for attainment voltage potential of the power-amplified modulated signal is made into a signal of multiple values, a supply potential VHV is adopted as an intermediate potential of a driving signal. That is, the supply potential VHV is adopted as a voltage maintenance voltage potential. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a power amplifying apparatus that pulse-modulates a drive waveform signal that becomes a reference of a drive signal for driving an actuator, for example, and amplifies the modulated signal to output it as a drive signal.

Compared to analog power amplifiers that linearly drive push-pull connected transistor pairs, digital power amplifiers that switch-pull connected switching elements, that is, digitally drive and amplify power, so-called class D amplifiers, are more efficient Has been used in a wide range. When power amplifying a drive signal with a digital power amplifier, the drive waveform signal that is the basis of the drive signal is pulse-modulated, and after the modulated signal is power amplified with a digital power amplifier, the frequency component of the modulated signal is removed with a smoothing filter. . For example, in Patent Document 1 below, this digital power amplifier is used in a liquid jet printing apparatus, and a drive signal to the nozzle actuator is amplified by the digital power amplifier, thereby reducing loss and making a heat sink unnecessary.
JP 2005-329710 A

By the way, when the drive signal is power amplified using a digital power amplifier as in Patent Document 1, it is necessary to remove the frequency component of the modulation signal before power amplification with a smoothing filter, and the modulation signal frequency component is sufficiently In order to eliminate the noise, a smooth filter with a steep frequency characteristic that stably passes the drive waveform signal component and sufficiently removes the modulation signal frequency component, in other words, a higher-order smoothing filter is required. In this case, the potential difference between terminals of the coil used for the smoothing filter increases, and the loss due to hysteresis increases.
The present invention has been developed by paying attention to these problems. When power amplification is performed using a digital power amplifier, the order of the smoothing filter can be reduced and the switching loss can be reduced. The object is to provide an amplifying device.

In order to solve the above problems, a power amplification device according to the present invention includes a modulation circuit that modulates a drive waveform signal that is a basis of a drive signal, and a digital power amplification that power-amplifies the modulation signal pulse-modulated by the modulation circuit. And a smoothing filter for smoothing the power amplification modulation signal amplified by the digital power amplification circuit and outputting it as a drive signal, the digital power amplification circuit comprising a plurality of push-pull connected switching element pairs. And a power supply circuit in which a power supply potential to at least one digital power amplifier is a voltage holding potential in the drive signal.
In this power amplifying device, the modulated signal that has been pulse-modulated is power-amplified by a plurality of stages of digital power amplifiers, and their outputs are combined into a power-amplified modulated signal. Become. In addition, the number of steps and the number of steps reached by the pulsed or stepped power amplification modulation signal are multivalued.

  Thus, according to this power amplifying device, since the output of a plurality of stages of digital power amplifiers is combined into a power amplification modulation signal, the potential difference between steps of the potential reached by the power amplification modulation signal is reduced. It is possible to reduce the order of the smoothing filter for removing the frequency component of the modulation signal from the power amplification modulation signal, and to obtain a highly accurate drive signal by making the power amplification modulation signal a multilevel signal. Become. Further, by reducing the order of the smoothing filter, the circuit configuration can be simplified and miniaturized. In addition, since the potential difference between the steps of the arrival potential of the power amplification modulation signal is small, the withstand voltage of the switching element of the digital power amplifier can be lowered, and the circuit can be downsized. Then, by setting the power supply potential to the digital power amplifier as the voltage holding potential in the drive signal, it is not necessary to switch the digital power amplifier when outputting the potential, and switching loss can be reduced. Become.

In the power amplifying device of the present invention, the power supply circuit is a variable power supply circuit having a variable power supply potential, and includes a control circuit for controlling the power supply potential of the power supply circuit.
According to this power amplifying apparatus, since the power supply potential of the power supply circuit is controlled according to the environment, a highly accurate drive signal can be output.
In the power amplifying apparatus of the present invention, the plurality of stages of digital power amplifiers are connected to the same power supply circuit.

According to this power amplifying apparatus, it is possible to reduce the size of the circuit by sharing the power supply circuit of a plurality of stages of digital power amplifiers.
The power amplifying device of the present invention is characterized in that the plurality of stages of digital power amplifiers are connected to power supply circuits having different potentials.
According to this power amplifying device, the drive signal waveform flexibility is increased by making the power supply potentials of the digital power amplifiers of a plurality of stages different.

Next, an embodiment used in a liquid jet printing apparatus will be described as an embodiment of the power amplification apparatus of the present invention.
FIG. 1 is a schematic configuration diagram of a printing apparatus according to the present embodiment. In the drawing, a print medium 1 is conveyed in the direction of an arrow from the left to the right in the figure, and is printed in a printing area in the middle of the conveyance. It is a line head type printing apparatus.
Among liquid ejecting printing apparatuses, a liquid ejecting head on which a liquid ejecting nozzle is formed is placed on a moving body called a carriage and moved in a direction crossing the transport direction of the print medium, and generally called a “multi-pass printing apparatus”. I'm calling. On the other hand, what is capable of printing in a so-called one pass by arranging a long liquid jet head in a direction crossing the conveyance direction of the printing medium is generally called a “line head type printing apparatus”.

  Reference numeral 2 in FIG. 1 denotes a plurality of liquid ejecting heads provided above the conveyance line of the print medium 1, arranged in two rows in the print medium conveyance direction and in a direction intersecting the print medium conveyance direction. And fixed to the head fixing plate 11, respectively. 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. 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, liquids such as yellow (Y), magenta (M), cyan (C), and black (K) inks are supplied to the liquid ejecting head 2 from liquid tanks of respective colors (not shown) through liquid supply tubes. Supplied. Then, a small amount of liquid is output onto the print medium 1 by ejecting a necessary amount of liquid from a nozzle formed in each liquid ejecting head 2 to a necessary portion at the same time. By performing this for each color, it is possible to perform printing by so-called one-pass only by passing the print medium 1 conveyed by the conveyance unit 4 once.
As a method of ejecting liquid from each nozzle of the liquid ejecting head, there are an electrostatic method, a piezo method, a film boiling liquid ejecting method, and the like. In this embodiment, the piezo method is used. In the piezo method, when a drive signal is given to a piezoelectric element that is a nozzle actuator, the diaphragm in the cavity is displaced to cause a pressure change in the cavity, and a droplet is ejected from the nozzle by the pressure change. . The droplet 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, for example, the transport belt 6 and the print medium 1 that is attracted and transported are synchronously moved, and after the print medium 1 has passed a predetermined position in the transport path. Outputs a pulse signal corresponding to the printing resolution required in accordance with the movement of the conveyor belt 6, and outputs a drive signal from a drive circuit, which will be described later, to the nozzle actuator in response to the pulse signal. A liquid of a predetermined color is ejected to a predetermined position, and a predetermined image is drawn on the print medium 1 by the dots.

  A control device for controlling itself is provided in the printing apparatus. For example, as shown in FIG. 3, 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. Then, an input interface 61 for reading print data input from the host computer 60 and a control unit 62 configured by, for example, a microcomputer that executes arithmetic processing such as print processing based on the print data input from the input interface 61. A paper feed roller motor driver 63 for driving and controlling the paper feed roller motor 17 connected to the paper feed roller 5, a head driver 65 for driving and controlling each liquid ejecting head 2, and the drive roller 8. An electric motor driver 66 for driving and controlling the electric motor 7, and an interface 67 for connecting the drivers 63, 65, 66 to the external paper feed roller motor 17, the liquid ejecting head 2, and the electric motor 7. Is done.

  The control unit 62 temporarily stores a CPU (Central Processing Unit) 62a that executes various processes such as a print process, and print data input through the input interface 61 or various data when the print data print process is executed. A random access memory (RAM) 62c that temporarily stores a program such as a print process or a nonvolatile semiconductor memory that stores a control program executed by the CPU 62a. ) 62d. When the control unit 62 obtains print data (image data) from the host computer 60 via the interface 61, the CPU 62a executes a predetermined process on the print data to determine which nozzle of any liquid ejecting head 2. Nozzle selection data (driving signal selection data) indicating how much liquid is to be ejected or how much liquid is to be ejected, and based on this print data, driving signal selection data, and input data from various sensors, each driver Control signals are output to 63, 65, 66. A drive signal for driving the actuator is output from each of the drivers 63, 65, and 66, and the paper feed roller motor 17, the electric motor 7, the nozzle actuator in the liquid ejecting head 2, and the like are operated, respectively. Paper feed, conveyance, paper discharge, and print processing on the print medium 1 are 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 from the control device of the printing apparatus of the present embodiment to the liquid ejecting head 2 and drives a nozzle actuator made of a piezoelectric element. In the present embodiment, a signal whose potential changes around an intermediate potential is used. This drive signal COM is a time series connection of drive pulses PCOM as unit drive signals for driving the nozzle actuator to eject liquid, and the rising portion of each drive pulse PCOM communicates with the nozzle (pressure). The volume of the chamber 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 cavity volume and pushes out the liquid (liquid In this stage, it can be said that the meniscus is extruded), and as a result of extruding the liquid, droplets are ejected from the nozzle.

  By variously changing the voltage increase / decrease slope and peak value of the driving pulse PCOM composed of this voltage trapezoidal wave, the liquid drawing amount and drawing speed, the liquid pushing amount and the pushing speed can be changed. It is possible to obtain dots of different sizes by changing the amount of injection. 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, and droplets are ejected or a plurality of drive pulses PCOM are selected and the actuator is selected. In this way, dots of various sizes can be obtained by ejecting droplets a plurality of times. That is, if a plurality of droplets land on the same position before the liquid dries, it is substantially the same as ejecting a large droplet, and the size of the dot 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, for example, to suppress or prevent thickening of the nozzle without ejecting droplets.

  In addition to the drive signal COM, each liquid ejecting head 2 selects a nozzle to be ejected based on print data as a control signal from the control device in FIG. 3 and outputs it to a drive signal COM for a nozzle actuator such as a piezoelectric element. The drive signal selection data SI & SP for determining the connection timing, the latch signal LAT for connecting the drive signal COM and the nozzle actuator of the liquid ejecting head 2 based on the drive signal selection data SI & SP after the nozzle selection data is inputted to all the nozzles, and A clock signal CLK for transmitting the channel signal CH and the drive signal 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 nozzle actuator 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 the switching controller constructed in each liquid jet head 2 in order to supply the drive signal COM (drive pulse PCOM) to the nozzle actuator 22. This switching controller temporarily stores the shift register 211 that stores drive signal selection data SI & SP for designating the nozzle actuator 22 such as a piezoelectric element corresponding to the nozzle that should eject liquid, and the data of the shift register 211. The level shifter 213 is configured to connect the drive signal COM to the nozzle actuator 22 such as a piezo element by converting the level of the output of the latch circuit 212 and the output of the latch circuit 212 to the selection switch 201.

  The drive signal 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 in accordance with the 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 the drive signal 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. Accordingly, a nozzle actuator such as a piezoelectric element whose selection switch 201 is closed by the level shifter 213 is connected to the drive signal COM (drive pulse PCOM) at the connection timing of the drive signal selection data SI & SP. In addition, after the drive signal 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 in 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 nozzle actuators, such as a piezoelectric element. Further, according to the selection switch 201, even after the nozzle actuator such as a piezoelectric element is disconnected from the drive signal COM (drive pulse PCOM), the input voltage of the nozzle actuator 22 is maintained at the voltage just before the disconnection.

  FIG. 6 shows a specific configuration of the drive circuit of the nozzle actuator. The drive circuit according to the present embodiment includes a waveform memory 23 in which drive waveform data DWCOM of a drive waveform signal WCOM serving as a reference of a drive signal COM, that is, a signal for controlling the drive of the nozzle actuator 22, is stored in advance, and the waveform memory 23 The drive waveform data DWCOM stored in the control circuit 24, the power supply potential of the variable power supply circuit 33 to be described later is controlled, and the drive waveform signal based on the drive waveform data DWCOM read by the control circuit 24 A drive waveform signal generation circuit 25 for generating WCOM, a modulation circuit 26 for pulse-modulating the drive waveform signal WCOM generated by the drive waveform signal generation circuit 25, and a digital for amplifying power of the modulation signal pulse-modulated by the modulation circuit 26 Power amplification circuit 28 and power amplification modulation signal amplified by digital power amplification circuit 28 By smoothing, and includes a supply smoothing filter 29 as the drive signal COM (the drive pulse PCOM) to the liquid jet head 2.

  In the liquid ejecting head 2, as shown in FIG. 7, a nozzle actuator 22 is provided for each of the aforementioned many nozzles, and a selection switch 201 is connected to each of the nozzle actuators 22, and all the selection switches A drive signal COM common to 201 is supplied. Therefore, the selection switch 201 for the nozzle to be ejected with liquid is selected based on the drive signal selection data SI & SP, and the selection switch 201 is controlled to be turned on / off by the switching controller to eject a necessary amount of liquid from the necessary nozzle.

  The drive waveform signal generation circuit 25 converts the drive waveform data DWCOM output from the control circuit 24 into a voltage signal, holds it for a predetermined sampling period, and converts it into an analog signal by a D / A converter, thereby converting the drive waveform signal WCOM. Output as. In the present embodiment, a pulse width modulation (PWM) circuit is used as the modulation circuit 26 that performs pulse modulation on the drive waveform signal WCOM. As shown in FIG. 8, in the pulse width modulation, a triangular wave signal having a predetermined frequency is generated by a triangular wave signal generating circuit 203, and this triangular wave signal and the drive waveform signal WCOM are compared by a comparator 204, and driven by, for example, a triangular wave signal. A pulse signal that is on-duty when the waveform signal WCOM is large is output as a modulation signal. However, the triangular wave signal of the present embodiment has only a potential about half the peak value of the drive waveform signal WCOM, and outputs a comparison pulse between the triangular wave signal and the drive waveform signal WCOM as the first modulation signal PWM1. A comparison pulse between a signal obtained by biasing a triangular wave signal with a potential corresponding to the peak value of the triangular wave signal and the drive waveform signal WCOM is output as the second modulation signal PWM2. In this embodiment, since the digital power amplifier circuit 28 is provided with two stages of digital power amplifiers, the modulation circuit 26 outputs modulation signals corresponding to the number of digital power amplifiers.

  As described above, the digital power amplifier circuit 28 includes the first digital power amplifier 27a that amplifies the power of the first modulation signal PWM1, and the second digital power amplifier 27b that amplifies the power of the second modulation signal PWM2. The high side of the first digital power amplifier 27a is connected to the power supply potential VHV of the variable power supply circuit 33, and the low side is grounded. A bootstrap circuit 32 is interposed between the second digital power amplifier 27b and the first digital power amplifier 27a, and the high side of the second digital power amplifier 27b is connected to a variable power source via the commutator D of the bootstrap circuit 32. The circuit 33 is connected to the power supply potential VHV, and the low side is connected to the output terminal of the first digital power amplifier 27a. That is, the low side of the second digital power amplifier 27b corresponding to the subsequent stage is biased by the output of the first digital power amplifier 27a corresponding to the previous stage. The bootstrap circuit 32 includes a commutator D that regulates a current from the high side of the second digital power amplifier 27b, and a capacitor CB that is charged with a potential difference between the power supply VHV and the output of the first digital power amplifier 27a. . The capacity of the capacitor CB is sufficient to drive the nozzle actuator 22 which is a capacitive load made of a piezoelectric element as described above. Specifically, when the first digital power amplifier 27a at the front stage is turned on and the second digital power amplifier 27b at the rear stage is turned on / off, the capacitance is set to secure a bootstrap potential.

  As shown in FIG. 9, the first and second digital power amplifiers 27a and 27b include a half-bridge class D output stage 31 including a high-side switching element Q1 and a low-side switching element Q2 for substantially amplifying power. And a gate driver circuit 30 for adjusting the gate-source signals GH and GL of the switching elements Q1 and Q2 based on the modulation signal from the modulation circuit 26. The gate-source signals GH and GL of the two switching elements Q1 and Q2 are inverted signals. In the digital power amplifiers 27a and 27b, when the modulation signal is at the Hi level, the gate-source signal GH of the high-side switching element Q1 is at the Hi level, and the gate-source signal GL of the low-side switching element Q2 is at the Lo level. Therefore, the high-side switching element Q1 is turned on, and the low-side switching element Q2 is turned off. As a result, the output of the half-bridge class D output stage 31 becomes a high-side potential. On the other hand, when the modulation signal is at the Lo level, the gate-source signal GH of the high-side switching element Q1 is at the Lo level, and the gate-source signal GL of the low-side switching element Q2 is at the Hi level. The side switching element Q1 is turned off and the low side switching element Q2 is turned on. As a result, the output of the half-bridge output stage 31 is at a low side potential.

  In this way, when the high-side and low-side switching elements are digitally driven, a current flows through the ON-state switching elements, but the resistance value between the drain and source is very small and almost no loss occurs. In addition, since no current flows through the switching element in the OFF state, no loss occurs. Therefore, the loss of these digital power amplifiers 27a and 27b is extremely small, a switching element such as a small MOSFET can be used, and cooling means such as a cooling heat sink is not necessary. Incidentally, the efficiency when the transistor is linearly driven is about 30%, whereas the efficiency of the digital power amplifier is 90% or more. In addition, since the cooling heat dissipation plate of the transistor needs to be about 60 mm square with respect to one transistor, if such a cooling heat dissipation plate is unnecessary, it is overwhelmingly advantageous in terms of actual layout.

As shown in FIG. 10, the smoothing filter 29 is composed of a low-pass filter (low-pass filter) composed of a combination of a coil L and a capacitor C, and the low-pass filter modulates the modulation frequency component of the power amplification modulation signal APWM. In this case, the frequency component of the triangular wave signal is removed.
In the present embodiment, a second digital power amplifier 27b is disposed at the rear stage of the first digital power amplifier 27a of the preceding stage whose high side is connected to the power supply potential VHV of the variable power supply circuit 33, and the second digital power amplifier 27b Since the low side is bootstrapped to the power supply potential VHV by the bootstrap circuit 32, when the second digital power amplifier 27b is off, the output of the first digital power amplifier 27a is directly subjected to power amplification modulation from the second digital power amplifier 27b. Although output as the signal APWM, when the second digital power amplifier 27b is on, the sum of the output of the first digital power amplifier 27a and the output of the second digital power amplifier 27b is the power from the second digital power amplifier 27b. It is output as an amplified modulation signal APWM.

  FIG. 11 shows an example of temporal changes of the first and second modulation signals PWM1, PWM2, the power amplification modulation signal APWM, and the drive signal COM of the present embodiment. In the present embodiment, the peak value potential of the triangular wave signal is set to about half the peak value of the drive waveform signal WCOM, a comparison pulse between the triangular wave signal and the drive waveform signal WCOM is output as the first modulation signal PWM1, and the triangular wave signal In addition, since the comparison pulse between the signal biased with the potential corresponding to the peak value of the triangular wave signal and the drive waveform signal WCOM is output as the second modulation signal PWM2, the drive signal COM and the drive waveform signal WCOM shown in FIG. Then, the triangular wave signal changes from the potential 0 to the power supply potential VHV, and a signal obtained by biasing the triangular wave signal with a potential corresponding to the peak value of the triangular wave signal changes between the power supply potential VHV and its double value VHV × 2. Accordingly, in the region where the drive waveform signal WCOM (drive signal COM in the figure) is equal to or higher than the power supply potential VHV, the first modulation signal PWM1 maintains the Hi level.

  The power amplification modulation signal APWM is a value obtained by adding the first modulation signal PWM1 and the second modulation signal PWM2, and the power amplification modulation signal APWM of the first modulation signal PWM1 amplified by the first digital power amplifier 27a is the power supply potential VHV. The power amplification modulation signal APWM of the second modulation signal PWM2 amplified by the second digital power amplifier 27b added to this is a pulse between the power supply potential VHV and its double value VHV × 2. Become. Therefore, since the power amplification modulation signal APWM composed of the sum of the two power amplification modulation signals has the potential 0, the power supply potential VHV, and the double value VHV × 2 of the power supply potential as the arrival potential, the number of steps of the arrival potential is “3”. ", Which is larger than the number of stages" 2 "of the digital power amplifiers 27a and 27b. As the number of steps of the potential reached of the power amplification modulation signal APWM before smoothing by the smoothing filter 29 increases, the waveform accuracy of the drive signal COM after smoothing improves.

  Further, since the power supply potential VHV may be about half the peak value of the drive signal COM, that is, the power amplification modulation signal APWM, even if the frequency characteristic of the smoothing filter 29 is a relatively gradual frequency characteristic, the modulation frequency is sufficiently high. Can be removed. In other words, the order of the smoothing filter 29 can be lowered, the circuit configuration can be simplified and downsized, and the potential difference between the terminals of the coil L is also reduced, so that the loss due to hysteresis is also small. Further, even if the total current flowing through the two-stage digital power amplifiers 27a and 27b is the same, the power supply potential VHV may be about half the peak value of the drive signal COM, that is, the power amplification modulation signal APWM, so that power saving can be achieved. At the same time, the withstand voltages of the switching elements Q1 and Q2 of the digital power amplifiers 27a and 27b can be lowered, and the circuit can be downsized. Further, when the first digital power amplifier 27a at the front stage is turned on and the second digital power amplifier 27b at the rear stage is turned off by the bootstrap circuit 32, the charge of the capacitor CB of the nozzle actuator 22 and the bootstrap circuit 32 which are capacitive loads Regeneration that flows to the power supply VHV side occurs, so that further power saving can be achieved.

  The drive signal COM in FIG. 11 is for explaining the operation of the modulation circuit 26, the digital power amplifier circuit 28, and the smoothing filter 29. The actual drive signal COM (drive pulse PCOM) is the same as that in FIG. It is a waveform like this. That is, the drive signal COM (drive pulse PCOM) rises from the intermediate potential, then falls to a potential smaller than the intermediate potential, rises again, and returns to the intermediate potential. In the present embodiment, the intermediate potential, that is, the voltage holding potential of the drive signal COM (drive pulse PCOM) is set to the power supply potential VHV of the variable power supply circuit 33 as shown in FIG. When the drive signal COM (drive pulse PCOM) is the power supply potential VHV, the first modulation signal PWM1 is always high level with a duty ratio of 100%, for example, and the second modulation signal PWM2 is always low level with a duty ratio of 0%, for example. The first digital power amplifier 27a is always on, and the second digital power amplifier 27b is always off. Therefore, when the voltage holding potential of the drive signal COM (drive pulse PCOM) is set to the power supply potential VHV of the variable power supply circuit 33, the number of switching times of the switching elements Q1 and Q2 of the digital power amplifiers 27a and 27b can be reduced. Thus, switching loss can be reduced. Further, when the switching elements Q1 and Q2 of the digital power amplifiers 27a and 27b are switched by the modulation signals PWM1 and PWM2, the modulation frequency components of the modulation signals PWM1 and PWM2 are added to the power amplification modulation signal APWM, and the modulation frequency components are converted into the modulation frequency components. The included power amplification modulation signal APWM is attenuated by the smoothing filter 29. On the other hand, since the power amplification modulation signal APWM is not attenuated during the period when the switching elements Q1 and Q2 of the digital power amplifiers 27a and 27b need not be switched, the accuracy of the drive signal COM (drive pulse PCOM) can be ensured. it can.

  In the present embodiment, the control circuit 24 variably controls the power supply potential VHV of the variable power supply circuit 33. The control parameter of the power supply potential VHV includes, for example, individual differences of the liquid ejecting heads, characteristics of the ejected liquid, and the liquid characteristics include viscosity that varies with temperature. By controlling the power supply potential VHV corresponding to the voltage holding potential in this way, the accuracy of the drive signal COM (drive pulse PCOM) can be further ensured.

  As described above, according to the power amplifying apparatus of the present embodiment, the drive waveform signal WCOM that is a basis for driving the nozzle actuator 22 is pulse-modulated by the modulation circuit 26, and the modulation signal is amplified by the digital power amplification circuit 28. Then, when the power amplified modulated signal APWM amplified by the power is smoothed by the smoothing filter 29 and outputted to the nozzle actuator 22, the digital power amplifying circuit 28 includes a pair of switching elements Q1 and Q2 that are push-pull connected. Since the digital power amplifiers 27a and 27b are provided in two stages and the power amplification modulation signal APWM is a multi-value signal, the outputs of the two stages of digital power amplifiers 27a and 27b are combined into the power amplification modulation signal APWM. The potential difference between the steps of the arrival potential of the power amplification modulation signal APWM becomes small, The order of the smoothing filter 29 for removing the frequency component of the modulation signal from the force amplification modulation signal APWM can be lowered, and a highly accurate drive signal COM is obtained by using the power amplification modulation signal APWM as a multilevel signal. It becomes possible. Further, by reducing the order of the smoothing filter 29, the circuit configuration can be simplified and reduced in size. In addition, since the potential difference between the steps of the potential reached of the power amplification modulation signal APWM is small, the withstand voltage of the switching elements Q1 and Q2 of the digital power amplifiers 27a and 27b can be lowered, thereby making it possible to reduce the size of the circuit. . Then, by setting the power supply potential VHV to the digital power amplifiers 27a and 27b as the voltage holding potential in the drive signal COM (drive pulse PCOM), the digital power amplifiers 27a and 27b are switched when the potential is being output. This eliminates the need for switching loss.

The power supply circuit 33 is composed of a variable power supply circuit having a variable power supply potential VHV, and the control circuit 24 controls the power supply potential VHV of the power supply circuit 33 according to the environment. Pulse PCOM) can be output.
Further, by connecting a plurality of stages of digital power amplifiers 27a and 27b to the same power supply circuit 33, the circuit can be reduced in size.

Next, a second embodiment in which the power amplifying device of the present invention is applied to a liquid jet printing apparatus will be described. The schematic configuration of the liquid jet printing apparatus to which this embodiment is applied is the same as that of the first embodiment, and the configurations and operations of the control device and the switching controller are also the same as those of the first embodiment. FIG. 13 shows a drive signal output circuit of this embodiment. The drive signal output circuit according to the present embodiment is similar to the drive signal output circuit according to the first embodiment. The same components are denoted by the same reference numerals, and detailed description thereof is omitted.
In the present embodiment, the high side of the second digital power amplifier 27b is connected to the power supply potential VHV of the first variable power supply circuit 33, as in the first embodiment, whereas the first digital power amplifier 27a. The high side of the second variable power supply circuit 34 is connected to the power supply potential VHV ′ of the second variable power supply circuit 34. The power supply potentials VHV and VHV ′ of the variable power supply circuits 33 and 34 can be independently controlled by the control circuit 25, respectively.

  In this embodiment, since the output of the second digital power amplifier 27b is bootstrapped with the power supply potential VHV ′ of the second variable power supply circuit 34, in this embodiment, as shown in FIG. 14, the second variable power supply circuit The power supply potential VHV ′ of 34 is set to an intermediate potential of the drive signal COM (drive pulse PCOM), that is, a voltage holding potential. Accordingly, as in the first embodiment, when the drive signal COM (drive pulse PCOM) is at the intermediate potential, that is, the voltage holding potential, the first digital power amplifier 27a is always on and the second digital power amplifier 27b is always off. Thus, the number of switching operations of the switching elements Q1 and Q2 of the digital power amplifiers 27a and 27b can be reduced, whereby the switching loss can be reduced. In the present embodiment, the power supply potentials VHV and VHV ′ of the variable power supply circuits 33 and 34 are variably controlled according to the environment.

For example, the first embodiment cannot cope with the case where the total peak value of the drive signal COM (drive pulse PCOM) exceeds twice the power supply potential VHV, which is an intermediate potential. In the present embodiment, the maximum output potential VHV ′ + VHV of the drive signal COM (drive pulse PCOM) can be freely set with respect to the power supply potential VHV ′ that is an intermediate potential. be able to.
Thus, according to the power amplifying apparatus of the present embodiment, in addition to the effects of the first embodiment, the plurality of stages of digital power amplifiers 27a and 27b are connected to the power supply circuits 33 and 34 having different power supply potentials VHV and VHV ′, respectively. By connecting to, the degree of freedom of the drive signal COM (drive pulse PCOM) is increased.
In the above-described embodiment, only the case where the power amplifying apparatus of the present invention is used in a line head type liquid jet printing apparatus has been described in detail. However, the power amplifying apparatus of the present invention is a multi-pass type liquid jet printing apparatus. The same applies to the apparatus.

  In the above embodiment, the power amplifying device of the present invention is embodied in the drive circuit of the digital power amplifier of the liquid jet printing apparatus. However, the present invention is not limited to this. The present invention is embodied in a liquid ejecting apparatus that ejects or ejects a fluid other than a liquid (including a liquid material in which particles of material are dispersed, a fluid such as a gel), or a fluid other than a liquid (such as a solid that can be ejected as a fluid). You can also. 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 to become 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. The present invention can be applied to any one of these injection devices.

1 is a schematic configuration front view showing an embodiment of a liquid jet printing apparatus using a power amplification device of 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. FIG. 6 is an explanatory diagram of a drive signal for driving a nozzle actuator in each liquid ejecting head. It is a block diagram of a switching controller. 1 is a block diagram illustrating a first embodiment of a drive signal output circuit. FIG. FIG. 7 is a block diagram of the liquid jet head in FIG. 6. It is a block diagram of the modulation circuit of FIG. FIG. 7 is a block diagram of the digital power amplifier of FIG. 6. It is a block diagram of the smoothing filter of FIG. It is explanatory drawing of the power amplification modulation signal and drive signal by the drive signal output circuit of FIG. It is explanatory drawing of the drive signal by the drive signal output circuit of FIG. It is a block diagram which shows 2nd Embodiment of a drive signal output circuit. It is explanatory drawing of the drive signal by the drive signal output circuit of FIG.

Explanation of symbols

  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 fixed plate, 22 is a nozzle actuator, 23 is a waveform memory, 24 is a control circuit, 25 is a drive waveform signal generation circuit, 26 is a modulation circuit, 27a and 27b are digital power amplifiers, and 28 is digital power amplification. Circuit, 29 is a smoothing filter, 30 is a gate drive circuit, 31 is a half-bridge class D output stage, 32 is a bootstrap circuit, 33 and 34 are variable power supply circuits

Claims (4)

  A modulation circuit that performs pulse modulation on a drive waveform signal that is a basis of the drive signal, a digital power amplification circuit that amplifies the power of the modulation signal that has been pulse-modulated by the modulation circuit, and power amplification modulation that is power amplified by the digital power amplification circuit And a smoothing filter for smoothing a signal and outputting it as a drive signal, wherein the digital power amplifier circuit comprises a plurality of stages of digital power amplifiers composed of a pair of push-pull connected switching elements, and a power source for at least one digital power amplifier And a power supply circuit having a voltage holding potential in the driving signal.   The power amplifying apparatus according to claim 1, wherein the power supply circuit is a variable power supply circuit having a variable power supply potential, and includes a control circuit that controls the power supply potential of the power supply circuit.   The power amplifier according to claim 1, wherein the plurality of stages of digital power amplifiers are connected to the same power supply circuit.   3. The power amplifying apparatus according to claim 1, wherein the plurality of stages of digital power amplifiers are connected to power supply circuits having different potentials.

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