JP5115187B2 - Liquid ejector - Google Patents

Description

  The present invention relates to a liquid ejecting apparatus configured to print predetermined characters, images, and the like by ejecting minute liquid from a plurality of nozzles and forming fine particles (dots) on a print medium. .

Inkjet printers, which are one of such printing apparatuses, generally provide inexpensive and high-quality color prints, so that with the spread of personal computers and digital cameras, not only for offices but also for general users. It has become widespread.
A device that places a liquid ejecting head on which a liquid ejecting nozzle is formed on a moving body called a carriage and moves the liquid ejecting head in a direction intersecting with the conveyance direction of the printing medium is generally called a “multi-pass printing apparatus”. 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”.

By the way, in this type of liquid jet printing apparatus, a drive signal amplified by a power amplification circuit is applied to a nozzle actuator such as a piezoelectric element to eject liquid from the nozzle. When the drive signal is amplified by an analog power amplifier such as a transistor, loss is large and a large heat sink for heat dissipation is required. Therefore, in Patent Document 1 described below, the drive signal is amplified by a digital power amplifier, so-called class D amplifier, to reduce the loss and make the heat sink unnecessary.
JP 2005-329710 A

However, since the nozzle actuator such as a piezoelectric element is a capacitive load having an electrostatic capacity, when the drive signal is power amplified using a digital power amplifier as in Patent Document 1, the carrier of the modulation signal before the power amplification is performed. It is necessary to remove the component with a smoothing filter, and the filter is composed of a combination of the inductor and the capacitance of the nozzle actuator in the smoothing filter, and the filter characteristics change depending on the number of nozzle actuators, that is, the number of connections of the capacitance, As a result, the drive signal characteristic changes and changes to the liquid ejection characteristic. In order to solve this problem, dummy capacitance equivalent to the capacitance of the nozzle actuator is provided in each nozzle actuator, and dummy capacitance is connected to the nozzle actuator to which no drive signal is applied. However, if this is done, the total driving capacity increases, which causes a problem of increased power consumption.
The present invention has been developed by paying attention to these problems. When power amplification is performed using a digital power amplifier, the characteristic change of the drive signal can be suppressed and prevented without increasing power consumption. An object of the present invention is to provide a possible liquid ejecting apparatus.

In order to solve the above problems, a liquid ejection apparatus according to the present invention includes a drive waveform signal generation circuit that generates a drive waveform signal serving as a reference for driving a plurality of actuators for liquid ejection, and the drive waveform signal generation circuit A modulation circuit for pulse-modulating the drive waveform signal generated in step 1, a digital power amplifier for amplifying the modulation signal pulse-modulated by the modulation circuit by a pair of push-pull connected switching elements, and power amplification by the digital power amplifier A first smoothing filter for smoothing the generated power amplification modulation signal, and a second smoothing output provided to each of the plurality of actuators, further smoothing the output of the first smoothing filter, and outputting a drive signal to the actuator And a smoothing filter .

  As will be described later, the second smoothing filter of the present invention includes, for example, a case where a low-pass filter is configured in combination with the capacitance of the actuator. In such a case, the second smoothing filter is the second smoothing filter. Although it is considered appropriate to express as a smoothing filter function unit, for example, a low-pass filter composed of a combination of a resistance and a small capacitance may be interposed on the upstream side of the actuator. Since it is the second smoothing filter, these are collectively referred to as the second smoothing filter.

  Thus, according to the liquid ejecting apparatus of the present invention, by providing the second smoothing filter for each actuator, it is possible to suppress the fluctuation of the gain of the entire smoothing filter with respect to the capacitance fluctuation, thereby reducing the power consumption. Without increasing, it is possible to suppress and prevent a change in characteristics of the drive signal, and it is possible to simplify the circuit configuration by providing a common first smoothing filter on the digital power amplification side.

In the liquid ejecting apparatus according to the aspect of the invention, the first smoothing filter may be provided in association with characteristics of the digital power amplifier, and the second smoothing filter may be provided in association with characteristics of the plurality of actuators. It is a feature.
According to the liquid ejecting apparatus of the present invention, it is possible to efficiently remove the modulation period component of the power amplification modulation signal and to efficiently suppress and prevent the change in the characteristics of the drive signal.

In the liquid ejecting apparatus according to the aspect of the invention, the first smoothing filter may include a coil and a capacitor.
According to the liquid ejecting apparatus of the present invention, it is possible to efficiently remove the modulation period component of the power amplification modulation signal, and the number of coils and capacitors having a large volume is reduced, so that the circuit configuration is simplified and the circuit area is reduced. It becomes possible to do.

In the liquid ejecting apparatus according to the aspect of the invention, the second smoothing filter may be a low-pass filter including a capacitance of an actuator.
According to the liquid ejecting apparatus of the invention, each actuator is provided with a low-pass filter, and the capacitance of the low-pass filter configured with the first smoothing filter simply increases or decreases. Compared to the above, it is possible to efficiently suppress and prevent the change in characteristics of the drive signal.

In the liquid ejecting apparatus according to the aspect of the invention, the second smoothing filter may form a low-pass filter by a resistance provided in association with the capacitance of the actuator and the characteristics of each actuator. It is.
According to the liquid ejecting apparatus of the invention, the circuit configuration can be simplified and the circuit area can be reduced.

The liquid ejecting apparatus according to the aspect of the invention may include the inverse filter having filter characteristics opposite to the filter characteristics of the first smoothing filter, the second smoothing filter, and the actuator, and the number of actuators to which the driving signal is applied. And an inverse filter characteristic changing circuit for changing the filter characteristic of the inverse filter.
According to the liquid ejecting apparatus of the present invention, it is possible to further suppress and prevent the change in characteristics of the drive signal.

Next, a first embodiment of a liquid jet printing apparatus using the liquid jet apparatus of the present invention will be described.
FIG. 1 is a schematic configuration diagram of a printing apparatus according to the present embodiment, FIG. 1a is a plan view thereof, and FIG. 1b is a front view thereof. In FIG. 1, a print medium 1 is a line head type printing apparatus that is transported in the direction of an arrow from the right to the left in the figure and printed in a print area in the middle of the transport.

  In the figure, reference numeral 2 denotes a first liquid ejecting head provided on the upstream side in the transport direction of the print medium 1, and reference numeral 3 denotes a second liquid ejecting head also provided on the downstream side, and the first liquid ejecting head 2. A first transport unit 4 for transporting the print medium 1 is provided below the second liquid ejecting head 3, and a second transport unit 5 is provided below the second liquid ejecting head 3. The first transport unit 4 includes four first transport belts 6 arranged at predetermined intervals in a direction intersecting with the transport direction of the print medium 1 (hereinafter also referred to as nozzle row direction). Similarly, the second transport unit 5 includes four second transport belts 7 arranged at predetermined intervals in a direction (nozzle row direction) intersecting the transport direction of the print medium 1.

  The four second conveyor belts 7 as well as the four first conveyor belts 6 are arranged alternately adjacent to each other. In the present embodiment, among these conveyor belts 6, 7, two first conveyor belts 6 and 2 on the right side in the nozzle row direction and two first conveyor belts 6 and second on the left side in the nozzle row direction. The conveyor belt 7 is separated. That is, the right driving roller 8R is disposed in the overlapping portion of the two first conveyance belts 6 and the second conveyance belt 7 on the right side in the nozzle row direction, and the two first conveyance belts 6 and the second conveyance belts on the left side in the nozzle row direction. 7 is provided with a left driving roller 8L, a right first driven roller 9R and a left first driven roller 9L on the upstream side, and a right second driven roller 10R and a second left side on the downstream side. A driven roller 10L is provided. These rollers appear as a series, but are substantially divided at the central portion of FIG. 1a.

  The two first conveying belts 6 on the right side in the nozzle row direction are wound around the right driving roller 8R and the first driven roller 9R on the right side, and the two first conveying belts 6 on the left side in the nozzle row direction are connected to the left driving roller 8L and the left side. The two second conveying belts 7 on the right side in the nozzle row direction are wound around the first driven roller 9L, and the two second conveying belts on the left side in the nozzle row direction are wound on the right driving roller 8R and the second right driven roller 10R. 7 is wound around the left driving roller 8L and the second left driven roller 10L. The right electric motor 11R is connected to the right driving roller 8R, and the left electric motor 11L is connected to the left driving roller 8L.

  Accordingly, when the right driving roller 8R is rotationally driven by the right electric motor 11R, the first conveying unit 4 composed of the two first conveying belts 6 on the right side in the nozzle row direction and the two second conveying belts on the right side in the nozzle row direction. The second conveyance unit 5 configured by 7 moves in synchronization with each other at the same speed, and is configured by two first conveyance belts 6 on the left side in the nozzle row direction when the left driving roller 8L is rotationally driven by the left electric motor 11L. The second transport unit 5 including the first transport unit 4 and the two second transport belts 7 on the left side in the nozzle row direction are synchronized with each other and move at the same speed. However, if the rotation speeds of the right electric motor 11R and the left electric motor 11L are different, the conveyance speed in the left and right directions in the nozzle row can be changed. Specifically, the rotation speed of the right electric motor 11R is changed to that of the left electric motor 11L. When the rotation speed is higher than the rotation speed, the conveyance speed on the right side in the nozzle row direction can be made larger than that on the left side, and when the rotation speed of the left electric motor 11L is higher than the rotation speed of the right electric motor 11R, The speed can be greater than the right side. Then, by adjusting the transport speed in the nozzle row direction, that is, the direction intersecting the transport direction in this way, the transport posture of the print medium 1 can be controlled.

  The first liquid ejecting head 2 and the second liquid ejecting head 3 are arranged in the transport direction of the print medium 1 for each of four colors, for example, yellow (Y), magenta (M), cyan (C), and black (K). They are offset. Each of the liquid ejecting heads 2 and 3 is supplied with a liquid such as ink from a liquid tank of each color (not shown) via a liquid supply tube. Each of the liquid jet heads 2 and 3 has a plurality of nozzles formed in a direction intersecting with the transport direction of the print medium 1 (that is, the nozzle row direction), and a necessary amount of droplets are simultaneously applied to necessary positions from these nozzles. Are ejected to output minute dots on the print medium 1. By performing this for each color, it is possible to perform so-called one-pass printing by passing the print medium 1 conveyed by the first conveyance unit 4 and the second conveyance unit 5 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 an 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 an actuator made of a piezoelectric element is a capacitive load having a capacitance.

  The nozzles of the first liquid ejecting head 2 are formed only between the four first conveying belts 6 of the first conveying unit 4, and the nozzles of the second liquid ejecting head 3 are the four nozzles of the second conveying unit 5. It is formed only between the second conveyor belts 7. This is because the liquid ejecting heads 2 and 3 are cleaned by a cleaning unit, which will be described later. However, if one of the liquid ejecting heads is used in this way, the entire surface printing cannot be performed in one pass. Therefore, the first liquid ejecting head 2 and the second liquid ejecting head 3 are arranged so as to be shifted in the transport direction of the print medium 1 in order to compensate for the portions that cannot be printed with each other.

  Disposed below the first liquid ejecting head 2 is the first cleaning cap 12 for cleaning the first liquid ejecting head 2 and disposed below the second liquid ejecting head 3. 2 is a second cleaning cap 13 for cleaning the liquid jet head 3. Each of the cleaning caps 12 and 13 has such a size that it can pass between the four first conveying belts 6 of the first conveying unit 4 and between the four second conveying belts 7 of the second conveying unit 5. It is formed. These cleaning caps 12 and 13 are, for example, rectangular bottomed cap bodies that cover the nozzles formed on the lower surfaces of the liquid jet heads 2 and 3, that is, the nozzle surfaces and can be in close contact with the nozzle surfaces, and are arranged at the bottoms thereof. The liquid absorber is provided, a tube pump connected to the bottom of the cap body, and a lifting device that lifts and lowers the cap body. Therefore, the cap body is raised by the lifting device and is brought into close contact with the nozzle surfaces of the liquid jet heads 2 and 3. In this state, when a negative pressure is applied to the inside of the cap by the tube pump, liquid and bubbles are sucked out from the nozzles provided on the nozzle surfaces of the liquid jet heads 2 and 3, and the liquid jet heads 2 and 3 can be cleaned. it can. When the cleaning is completed, the cleaning caps 12 and 13 are lowered.

  On the upstream side of the first driven rollers 9R and 9L, there are two pairs of gate rollers 14 that adjust the paper feed timing of the printing medium 1 supplied from the paper feeding unit 15 and correct the skew of the printing medium 1. Is provided. The skew is a twist of the print medium 1 with respect to the transport direction. A pickup roller 16 for supplying the print medium 1 is provided above the paper supply unit 15. Reference numeral 17 in the drawing denotes a gate roller motor that drives the gate roller 14.

  A belt charging device 19 is disposed below the drive rollers 8R and 8L. The belt charging device 19 includes a charging roller 20 that is in contact with the first conveying belt 6 and the second conveying belt 7 with the driving rollers 8R and 8L interposed therebetween, and the charging roller 20 is connected to the first conveying belt 6 and the second conveying belt 7. It comprises a spring 21 to be pressed and a power source 18 for applying a charge to the charging roller 20, and charges the first conveying belt 6 and the second conveying belt 7 from the charging roller 20 to charge them. In general, these belts are composed of a medium / high resistance body or an insulator. Therefore, when charged by a belt charging device, the charge applied to the surface is also composed of a high resistance body or an insulator. The print medium 1 is caused to generate dielectric polarization, and the print medium 1 can be adsorbed to the belt by electrostatic force generated between the charge generated by the dielectric polarization and the charge on the belt surface. The charging means may be a so-called corotron that drops the charge.

  Therefore, according to this printing apparatus, the surfaces of the first conveyance belt 6 and the second conveyance belt 7 are charged by the belt charging device, and the printing medium 1 is fed from the gate roller 14 in this state, and a spur and a roller (not shown) are provided. When the printing medium 1 is pressed against the first conveying belt 6 by the paper pressing roller configured as follows, the printing medium 1 is attracted to the surface of the first conveying belt 6 by the action of the dielectric polarization described above. In this state, when the driving rollers 8R and 8L are rotationally driven by the electric motors 11R and 11L, the rotational driving force is transmitted to the first driven rollers 9R and 9L via the first conveying belt 6.

  In this manner, with the print medium 1 adsorbed, the first transport belt 6 is moved downstream in the transport direction, the print medium 1 is moved below the first liquid ejecting head 2, and the first liquid ejecting head 2 is moved to the first liquid ejecting head 2. Printing is performed by ejecting droplets from the nozzles formed. When printing by the first liquid ejecting head 2 is completed, the print medium 1 is moved downstream in the transport direction and transferred to the second transport belt 7 of the second transport unit 5. As described above, since the surface of the second conveyance belt 7 is also charged by the belt charging device, the print medium 1 is attracted to the surface of the second conveyance belt 7 by the action of the dielectric polarization described above.

  In this state, the second conveying belt 7 is moved downstream in the conveying direction to move the printing medium 1 below the second liquid ejecting head 3, and droplets are ejected from the nozzles formed in the second liquid ejecting head 3. Is printed. When the printing by the second liquid ejecting head 3 is completed, the printing medium 1 is further moved downstream in the conveying direction, and separated to the paper discharge unit while separating the printing medium 1 from the surface of the second conveying belt 7 by a separation device (not shown). Eject paper.

  When the first and second liquid jet heads 2 and 3 need to be cleaned, the first and second liquid jet heads 2 and 3 are lifted by raising the first and second cleaning caps 12 and 13 as described above. The cap body is brought into close contact with the nozzle surface, and in that state, the cap body is set to a negative pressure so that liquids and bubbles are sucked out from the nozzles of the first and second liquid ejecting heads 2 and 3 for cleaning. The second cleaning caps 12 and 13 are lowered.

  A control device for controlling itself is provided in the printing apparatus. For example, as shown in FIG. 2, the control device prints on a print medium by controlling a printing device, a paper feeding device, and the like based on print data input from a host computer 60 such as a personal computer or a digital camera. The processing is performed. An input interface 61 for receiving print data input from the host computer 60; a control unit 62 configured by, for example, a microcomputer that executes print processing based on the print data input from the input interface 61; A gate roller motor driver 63 for driving and controlling the gate roller motor 17, a pickup roller motor driver 64 for driving and controlling the pickup roller motor 51 for driving the pickup roller 16, and a head driver for driving and controlling the liquid ejecting heads 2 and 3. 65, a right electric motor driver 66R for driving and controlling the right electric motor 11R, a left electric motor driver 66L for driving and controlling the left electric motor 11L, the drivers 63 to 65, 66R and 66L, and the external gate roller motor 1 Composed pickup roller motor 51, the liquid jet heads 2 and 3, the right electric motor 11R, and an interface 67 for connecting the left side electric motor 11L.

  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 unit 61, the CPU 62a performs a predetermined process on the print data and ejects droplets from any nozzle. The nozzle selection data indicating how many droplets are to be ejected and the drive signal output data to the nozzle actuator are calculated, and each driver 63 is based on the print data, the drive signal output data, and the input data from various sensors. -65, 66R, 66L are output control signals. A drive signal for driving the actuator is output from each of the drivers 63 to 65, 66R, and 66L, the nozzle actuator corresponding to the plurality of nozzles of the liquid jet heads 2 and 3, the gate roller motor 17, the pickup roller motor 51, and the right side. The electric motor 11R and the left electric motor 11L are operated, respectively, to feed and convey the print medium 1, control the posture of the print medium 1, and print processing on the print medium 1. Each component in the control unit 62 is electrically connected through a bus (not shown).

  FIG. 3 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 apparatuses 2 and 3 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 to draw the liquid (which can be said to draw the meniscus when the liquid ejection surface is considered), and the falling portion of the drive pulse PCOM reduces the cavity volume to push 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 drive signal COM at the left end in FIG. 3 only draws liquid and does not push it out. This is called microvibration, and is used, for example, to suppress or prevent thickening of the nozzle without ejecting droplets.

  As a result, the liquid ejecting heads 2 and 3 select the nozzles to be ejected based on the drive signal COM output from the drive signal output circuit, which will be described later, and the print data, and the drive signals COM of the nozzle actuators such as piezoelectric elements. Drive signal selection data SI & SP for determining the connection timing of the nozzles, and after the nozzle selection data is inputted to all nozzles, the latch for connecting the drive signal COM and the nozzle actuators of the liquid jet heads 2 and 3 based on the drive signal selection data SI & SP A clock signal SCK for transmitting the signal LAT, the channel signal CH, and the drive signal selection data SI & SP as serial signals to the liquid jet heads 2 and 3 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.

  Next, a configuration for connecting a drive signal COM output from the drive circuit and a nozzle actuator such as a piezoelectric element will be described. FIG. 4 is a block diagram of a selection unit that connects the drive signal COM and an actuator such as a piezo element. This selection unit temporarily stores drive register selection data SI & SP for designating a nozzle actuator such as a piezoelectric element corresponding to a nozzle that should eject ink droplets, and data in the shift register 211 temporarily. The latch circuit 212 includes a level shifter 213 that converts the output of the latch circuit 212 and a selection switch 201 that connects the drive signal COM to the nozzle actuator 22 such as a piezo element in accordance with the output of the level shifter.

  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 SCK. 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. Further, 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 ink droplet ejection timing. To do. 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. 5 shows an example of a specific configuration of a drive signal output circuit in the head driver 65 that drives the nozzle actuator 22. A large number of nozzles are formed in the liquid jet heads 2 and 3 constituting the line head type printing apparatus, and the nozzle actuator 22 described above is provided for each of them. On the upstream side of these nozzle actuators 22, there are arranged selection switches 23 each composed of a transmission gate. Each selection switch 23 is turned on and off in accordance with print data by a nozzle selection control circuit (not shown). The drive signal COM (drive pulse PCOM) is applied only to the nozzle actuator 22 in which the switch 23 is turned on.

  On the other hand, the drive signal output circuit is based on the drive signal output data from the control unit 62, and is based on the drive signal COM (drive pulse PCOM), that is, the drive waveform signal WCOM that serves as a reference for the signal for controlling the drive of the nozzle actuator 22. Drive waveform signal generating circuit 25 for generating the signal, modulation circuit 26 for pulse-modulating the drive waveform signal WCOM generated by the drive waveform signal generating circuit 25, and digital power for amplifying the power of the modulation signal pulse-modulated by the modulation circuit 26 A first smoothing filter 29a and a second smoothing filter 29a that supply power to the nozzle actuator 22 as a drive signal COM (drive pulse PCOM) by smoothing the power amplification modulation signal amplified by the amplifier, so-called class D amplifier 28 and the digital power amplifier 28. And a smoothing filter 29b.

  The drive waveform signal generation circuit 25 outputs preset digital data in combination in time series, and analog-converts the digital data using a D / A converter and outputs it as a drive waveform signal WCOM. In the present embodiment, a general pulse width modulation (PWM) circuit is used as the modulation circuit 26 that performs pulse modulation on the drive waveform signal WCOM. Pulse width modulation is generated when a triangular wave signal having a predetermined frequency is generated by the triangular wave signal generation circuit 23, and this triangular wave signal and the drive waveform signal WCOM are compared by the comparator 24. For example, when the drive waveform signal WCOM is larger than the triangular wave signal, A pulse signal having a duty is output as a modulation signal. The digital power amplifier 28 is based on a half-bridge class D output stage 31 composed of a high-side switching element Q1 and a low-side switching element Q2 for substantially amplifying power, and a modulation signal from the modulation circuit 26. And the gate driver circuit 30 for adjusting the gate-source signals GH and GL of the switching elements Q1 and Q2. The first smoothing filter 29a is composed of a low-pass filter (low-pass filter) composed of a combination of a coil L and a capacitor C, and this low-pass filter modulates the modulation period component of the power amplification modulation signal, in this case, the frequency component of the triangular wave signal. Is removed. That is, the first smoothing filter 29 a is provided in correspondence with the output characteristics of the digital power amplifier 28. Further, the second smoothing filter 29b is configured to include a resistance R interposed between the nozzle actuators 22 by the number of the nozzle actuators 22 and a low-pass filter using the resistance R and the capacitance of the nozzle actuators 22. (Low-pass filter) is configured. That is, the low-pass filter is provided for the nozzle actuator 22 and the low-pass filter is connected to the drive signal output circuit each time the nozzle actuator 22 is turned on. Therefore, the second smoothing filter 29 b is provided in correspondence with the frequency characteristics of each nozzle actuator 22.

  In the digital power amplifier 28, 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 the supply power VDD. 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 zero.

  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 the digital power amplifier 28 is extremely small, a switching element such as a small MOSFET can be used, and cooling means such as a cooling heat sink is unnecessary. 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.

  FIG. 6 shows the frequency characteristics of the entire drive signal output circuit of this embodiment. The flat region of the gain in the figure is the frequency component of the drive waveform signal, and is the frequency component that should be reflected in the drive signal COM (drive pulse PCOM). Further, the gain reduction region in the figure is a frequency component corresponding to the modulation period of pulse modulation, that is, the period of the triangular wave signal generated from the triangular wave signal generation circuit 23, and is reflected in the drive signal COM (drive pulse PCOM). This should not be a frequency component. In the present embodiment, since the low-pass filter is configured by the capacitance of each nozzle actuator 22 and the resistance R of the second smoothing filter 29b connected to each nozzle actuator 22, when the nozzle actuator 22 is turned on, the low-pass filter is generated accordingly. Since the low-pass filter is connected to the drive signal output circuit, even when the number of nozzle actuators 22 that are turned on is large (the load in the figure is large), the number of nozzle actuators 22 that are turned on is small (in the figure). However, the frequency characteristics have not changed significantly. That is, regardless of the number of nozzle actuators 22 that are turned on, the frequency characteristics of the entire drive signal output circuit do not change much, and as a result, the power consumption as in the case where dummy capacitances are also provided for each nozzle actuator 22. It is possible to suppress and prevent a change in the characteristics of the drive signal COM (drive pulse PCOM) without increasing. In addition, by arranging only one first smoothing filter 29a composed of the coil L and the capacitor C on the digital power amplifier 28 side, the modulation period component of the power amplification modulation signal can be efficiently removed, Since the number of coils and capacitors having a large volume is small, the circuit configuration can be simplified and the circuit area can be reduced.

  In FIG. 7, the smoothing filter is a general primary low-pass filter composed of a coil L, a capacitor C, and a resistor R, and only one smoothing filter is interposed between the nozzle actuator 22 and a digital power amplifier (not shown). It is a block diagram of the output part of the drive signal output circuit. FIG. 8 shows the frequency characteristics of the entire conventional drive signal output circuit. In such a configuration, each time the nozzle actuator 22 is turned on, the capacitance of the nozzle actuator 22 is added to the smoothing filter, and the frequency characteristic of the low-pass filter changes. For example, in this comparative example, as the number of nozzle actuators 22 that are turned on increases (the load in the figure), the gain tends to increase, and as the number of nozzle actuators 22 that are turned on decreases (the load in the figure). Small), the gain tends to decrease. For example, when the gain increases, the frequency component of the pulse modulation to be removed remains and the drive signal COM (drive pulse PCOM) changes. When the gain decreases, the frequency component of the drive waveform signal WCOM to be reflected decreases. The drive signal COM (drive pulse PCOM) changes.

  As described above, according to the liquid ejecting apparatus of the present embodiment, the drive waveform signal WCOM serving as a reference for driving the nozzle actuator 22 is generated by the drive waveform signal generation circuit 25, and the drive waveform signal WCOM is generated by the modulation circuit 26. The pulse-modulated signal is amplified by the push-pull connected switching element pair of the digital power amplifier 28, and the power-amplified modulated signal is amplified by the first smoothing filter 29a and the second smoothing filter. In the smoothing by 29b and outputting to the nozzle actuator 22, by providing the second smoothing filter 29b for each actuator 22, it is possible to suppress the fluctuation of the gain of the entire smoothing filter with respect to the capacitance fluctuation. Without increasing the power consumption, the drive signal COM (drive pulse PCOM) It can together with the characteristic change can be prevented suppressed, to simplify the circuit configuration by providing a common first smoothing filter 29a to the digital power amplifier side.

Further, the first smoothing filter 29a is provided in correspondence with the characteristics of the digital power amplifier 28, and the second smoothing filter is provided in correspondence with the characteristics of the plurality of actuators. The components can be efficiently removed, and the characteristic change of the drive signal COM (drive pulse PCOM) can be efficiently suppressed and prevented.
In addition, since the first smoothing filter 29a is composed of the coil L and the capacitor C, the modulation period component of the power amplification modulation signal can be efficiently removed, and a large volume of the coil L and the capacitor C is small. Therefore, the circuit configuration can be simplified and the circuit area can be reduced.

Since the second smoothing filter 29b is a low-pass filter (low-pass filter) including the capacitance of the nozzle actuator 22, each nozzle actuator 22 is provided with a low-pass filter (low-pass filter). Therefore, the characteristic change of the drive signal COM (drive pulse PCOM) is changed as compared with the case where the capacitance of the low-pass filter (low-pass filter) constituted by the first smoothing filter 29a is simply increased or decreased. It is possible to prevent and prevent efficiently.
Further, since the second smoothing filter 29 is configured as a low-pass filter (low-pass filter) by the resistance R provided in correspondence with the capacitance of the nozzle actuator 22 and the characteristics of each actuator 22, the circuit configuration is It is possible to simplify and reduce the circuit area.

  Next, a second embodiment in which the liquid ejecting apparatus of the present invention is applied to a line head type printing apparatus will be described. FIG. 9 is a block diagram of the 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 shown in FIG. 5 and has many equivalent components. Therefore, equivalent constituent elements are denoted by the same reference numerals, and detailed description thereof is omitted. Specifically, the circuit configuration requirements of both are the same, and an inverse filter 32 is interposed between the modulation circuit 26 and the drive waveform signal generation circuit 25, and the filter characteristics of the inverse filter 32 are expressed as print data. An inverse filter characteristic changing circuit 33 that changes according to the above is added.

  The inverse filter 32 has a filter characteristic opposite to the filter characteristic of the low-pass filter (low-pass filter) composed of the first smoothing filter 29a, the second smoothing filter 29b, and the nozzle actuator 22, as described above. Since the filter characteristics of the low-pass filter (low-pass filter) vary depending on the number of nozzle actuators 22 that are turned on, some filter characteristics that are opposite to the filter characteristics of the low-pass filter corresponding to the number of nozzle actuators 22 that are turned on are several. I remember it. In the present embodiment, the filter characteristics are such that the frequency components of the drive waveform signal are output in a stable manner.

  The inverse filter characteristic changing circuit 33 calculates the number of nozzle actuators 22 that are turned on from the print data, and changes the filter characteristics of the inverse filter 32 according to the number of nozzle actuators 22 that are turned on. As in the embodiment, in the case of having several filter characteristics opposite to the filter characteristics of the low-pass filter corresponding to the number of nozzle actuators 22 for which the inverse filter 32 is turned on, the number of nozzle actuators 22 to be turned on A corresponding inverse filter characteristic is selected. In the present embodiment, the number of nozzle actuators 22 that are turned on changes for each drive pulse PCOM. Therefore, the selection of the inverse filter characteristic according to the number of nozzle actuators 22 that are turned on is performed between the drive pulses PCOM (connection). Eyes).

  The frequency characteristics of the entire drive signal output circuit are shown in FIGS. FIG. 10 shows the frequency characteristics when the number of nozzle actuators 22 that are turned on is small (low load in the figure), and FIG. 11 shows the frequency when the number of nozzle actuators 22 that are turned on is large (high load in the figure). Show properties. In the present embodiment, as described above, the filter characteristic stored in the inverse filter 32 is such that the frequency component of the drive waveform signal is stably output. For example, when the number of nozzle actuators 22 to be turned on is small The filter characteristic of the inverse filter 32 that reduces the frequency component of the drive waveform signal is stored, and the filter of the inverse filter 32 that increases the frequency component of the drive waveform signal when the number of nozzle actuators 22 to be turned on is large. Characteristics are stored. Therefore, in the drive signal output circuit in which these filter characteristics are selected, the frequency component of the drive waveform signal is stably output, and the characteristics of the drive signal COM (drive pulse PCOM) of the drive signal COM (drive pulse PCOM) are changed. Further suppression can be prevented.

  Thus, according to the liquid ejecting apparatus of the present embodiment, in addition to the effects of the first embodiment, the filter characteristics of the first smoothing filter 29a, the second smoothing filter 29b, and the nozzle actuator 22 are opposite to the filter characteristics. By including the inverse filter 32 and the inverse filter characteristic changing circuit 33 that changes the filter characteristic of the inverse filter 32 according to the number of nozzle actuators 22 to which the drive signal COM (drive pulse PCOM) is applied, the drive signal COM is provided. It is possible to further suppress and prevent the characteristic change of (driving pulse PCOM).

In the above-described embodiment, several filter characteristics stored in the inverse filter 32 are stored according to the number of nozzle actuators 22 that are turned on, but the number is not limited. Further, instead of storing several filter characteristics in the inverse filter 32, the inverse filter characteristic changing circuit 33 changes the parameter governing the filter characteristics of the inverse filter 32 according to the number of nozzle actuators 22 that are turned on. The filter characteristics of the inverse filter 32 may be continuously changed.
In the above-described embodiment, only the case where the liquid ejecting apparatus of the present invention is used in a line head type printing apparatus has been described in detail. However, the liquid ejecting apparatus of the present invention can be similarly applied to a multi-pass type printing apparatus. is there.

  In the above embodiment, the liquid ejecting apparatus of the present invention is embodied in an ink jet printing apparatus. However, the present invention is not limited to this, and liquids other than ink (functional material particles are dispersed in addition to liquids). It is also possible to embody the present invention in a liquid ejecting apparatus that ejects or ejects a fluid other than a liquid (including a fluid such as a liquid or gel) or a fluid other than a liquid (such as a solid that can be ejected by flowing as a fluid). 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. For example, 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 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.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic configuration diagram illustrating a first embodiment of a liquid jet printing apparatus using a liquid jet apparatus according to the present invention, where (a) is a plan view and (b) is a front view. FIG. 2 is a block diagram of a control device of the liquid jet printing apparatus of FIG. 1. It is explanatory drawing of the drive signal which drives a nozzle actuator. It is a block diagram of the selection part which connects a drive signal to an actuator. FIG. 3 is a block diagram of a drive signal output circuit constructed in the head driver of FIG. 2. FIG. 6 is a frequency characteristic diagram of the drive signal output circuit of FIG. 5. It is a block diagram of the output part of the conventional drive signal output circuit. FIG. 8 is a frequency characteristic diagram of the drive signal output circuit of FIG. 7. FIG. 6 is a block diagram illustrating a second embodiment of a drive signal output circuit of the liquid ejecting apparatus of the invention. FIG. 10 is a frequency characteristic diagram of the drive signal output circuit of FIG. 9. FIG. 10 is a frequency characteristic diagram of the drive signal output circuit of FIG. 9.

Explanation of symbols

  1 is a printing medium, 2 and 3 are liquid ejecting heads, 4 and 5 are conveyance units, 23 is a triangular wave signal generation circuit, 24 is a comparator, 25 is a drive waveform signal generation circuit, 26 is a modulation circuit, and 27 is a modulation cycle adjustment circuit. , 28 is a digital power amplifier, 29 is a smoothing filter, 30 is a gate driver circuit, 31 is a half-bridge output stage, 32 is an inverse filter, 33 is an inverse filter characteristic changing circuit, 62 is a control unit, and 65 is a head driver.

Claims (7)

A drive waveform signal generating circuit that generates a drive waveform signal that serves as a reference for driving a plurality of actuators for liquid ejection;
A modulation circuit for pulse-modulating the drive waveform signal generated by the drive waveform signal generation circuit;
A digital power amplifier that amplifies the power of a modulation signal pulse-modulated by the modulation circuit by a pair of push-pull connected switching elements;
A first smoothing filter for smoothing the power amplification modulated signal that has been power amplified by the digital power amplifier ;
A second smoothing filter that is provided in each of the plurality of actuators, further smoothes the output of the first smoothing filter, and outputs a drive signal toward the actuator;
A liquid ejecting apparatus comprising the.   2. The liquid according to claim 1, wherein the first smoothing filter is provided in correspondence with characteristics of the digital power amplifier, and the second smoothing filter is provided in correspondence with characteristics of the plurality of actuators. Injection device.   The liquid ejecting apparatus according to claim 2, wherein the first smoothing filter includes a coil and a capacitor.   The liquid ejecting apparatus according to claim 2, wherein the second smoothing filter is a low-pass filter including a capacitance of an actuator.   5. The liquid ejecting apparatus according to claim 4, wherein the second smoothing filter forms a low-pass filter by a resistance provided in association with a capacitance of the actuator and a characteristic of each actuator.   An inverse filter having a filter characteristic opposite to that of the first smoothing filter, the second smoothing filter, and the actuator, and an inverse filter that changes the filter characteristic of the inverse filter according to the number of actuators to which the drive signal is applied. The liquid ejecting apparatus according to claim 1, further comprising a characteristic changing circuit. A printing apparatus comprising the liquid ejecting apparatus according to claim 1.

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