JP5024145B2 - 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. .

A liquid jet printing apparatus, which is one of such liquid jet apparatuses, is generally inexpensive and can easily obtain high-quality color prints. Therefore, along with the widespread use of personal computers and digital cameras, not only offices. It is also widely used by general users.
Among such liquid ejecting printing apparatuses, those that place a liquid ejecting head in which liquid ejecting nozzles are formed on a moving body called a carriage and move in a direction crossing the transport direction of the print medium are generally referred to as “multi-pass printing”. Called "device". 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”. When configuring a line head type liquid ejecting head, a plurality of block-shaped liquid ejecting heads each having a plurality of nozzles arranged in a row are arranged in a direction intersecting the print medium conveying direction to form a line head type liquid. An ejection head may be configured.

By the way, in this type of liquid ejecting type printing apparatus, a plurality of nozzles for ejecting liquid are formed on the liquid ejecting head, and a nozzle actuator such as a piezoelectric element is disposed on each nozzle, and driven by the nozzle actuator of the liquid ejecting head. By applying the signal, the liquid is ejected toward the print medium conveyed from the corresponding nozzle. Since a relatively large voltage or current is required to drive a nozzle actuator such as a piezoelectric element, in order to amplify the power of the drive signal, the liquid ejecting apparatus described in Patent Document 1 below drives the nozzle actuator. A drive waveform signal serving as a reference of a signal for controlling the signal is analog-converted by an analog conversion circuit, and the analog drive waveform signal is power-amplified by an analog power amplifier circuit. In the liquid ejecting apparatus described in Patent Document 2 below, the drive waveform signal is converted into an analog signal by an analog conversion circuit, the analog drive waveform signal is pulse-modulated, and the modulated signal is amplified by a digital power amplifier circuit. I am doing so.
Japanese Patent Laid-Open No. 2001-80069 JP-A-11-204850

However, since the nozzle actuator such as a piezoelectric element is a charge / discharge actuator, for example, when the drive signal is a voltage trapezoidal waveform signal, the drive signal is amplified by linearly driving the push-pull connected transistor pair of the analog power amplifier circuit. In this case, the voltage difference between the charging source voltage and the driving signal and the voltage difference between the discharging destination voltage and the driving signal are lost, most of which must be discarded as heat, and a transistor with a large capacity or a heat sink with a large heat dissipation amount. Is required. On the other hand, when the drive signal is amplified by the digital power amplifier circuit, the switching element is simply turned on and off, so that the amount of heat radiation can be reduced, but the modulation period of pulse modulation, for example, the sampling period or more However, there is a problem that the waveform accuracy of the drive signal cannot be increased.
The present invention has been developed by paying attention to these problems, and an object thereof is to provide a liquid ejecting apparatus capable of reducing loss while ensuring the waveform accuracy of a drive signal. is there.

  In order to solve the above problems, the liquid ejecting apparatus of the present invention has a plurality of nozzles for ejecting liquid on the liquid ejecting head, and a nozzle actuator is disposed on each nozzle. A liquid ejecting apparatus that ejects liquid from a corresponding nozzle toward a print medium by being driven by a drive signal, wherein a drive waveform signal serving as a reference for driving the nozzle actuator is digitally amplified by a digital power amplifier circuit. A digital drive circuit for outputting a drive signal; an analog drive circuit for outputting an analog drive signal by amplifying a drive waveform signal serving as a reference for driving the nozzle actuator by an analog power amplifier circuit; and the digital drive signal and the analog drive A selection circuit that selects one of the signals and applies it to the nozzle actuator A driving signal including a driving pulse used for ejecting the smallest amount of liquid droplets out of the ejected liquid droplets is output from the analog driving circuit and includes a driving pulse used for ejecting the largest amount of liquid droplets. Is output from the digital drive circuit.

Thus, according to the liquid ejecting apparatus of the present invention, a driving signal that does not require high waveform accuracy, such as a driving pulse used for ejecting the largest amount of liquid droplets, is output from the digital driving circuit, and the smallest amount of liquid is output. If a drive signal that requires high waveform accuracy, such as a drive pulse used for droplet ejection, is output from an analog drive circuit, it is possible to reduce loss while ensuring the waveform accuracy of the drive signal. .
The liquid ejecting apparatus of the present invention is characterized in that a drive signal including a drive pulse used when the liquid droplet is not ejected is output from the digital drive circuit.
According to the liquid ejecting apparatus of the present invention, the drive pulse used when the liquid droplet is not ejected does not require high waveform accuracy, so that the drive signal including the drive pulse is output from the digital drive circuit. Loss can be further reduced.

In the liquid ejecting apparatus according to the aspect of the invention, the digital drive circuit may include a drive waveform signal generation circuit that generates the drive waveform signal, and a modulation circuit that performs pulse modulation on the drive waveform signal generated by the drive waveform signal generation circuit. A digital power amplifier circuit that amplifies the power of the modulation signal pulse-modulated by the modulation circuit, the digital power amplifier circuit comprising a half-bridge class D output stage comprising a pair of switching elements for amplifying power, And a gate driving circuit configured to adjust a gate-source signal of the switching element of the half-bridge class D output stage based on a modulation signal from the modulation circuit.
According to the liquid ejecting apparatus of the invention, the digital drive circuit can be easily implemented.

In the liquid ejecting apparatus according to the aspect of the invention, the analog drive circuit may include a drive waveform signal generation circuit that generates the drive waveform signal, and an analog conversion circuit that converts the drive waveform signal generated by the drive waveform signal generation circuit into an analog signal. And an analog power amplifier circuit that amplifies the analog drive waveform signal analog-converted by the analog converter circuit, the analog power amplifier circuit includes a push-pull connected transistor pair for charging and discharging a nozzle actuator, and the analog And a pre-driver circuit that adjusts a base voltage of the transistor pair based on an analog drive waveform signal analog-converted by the conversion circuit.
According to the liquid ejecting apparatus of the invention, the analog drive circuit can be easily implemented.

Next, an embodiment of the liquid ejecting apparatus of the present invention will be described using a liquid ejecting printing apparatus.
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.

  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 piezoelectric element used in the piezo method is a capacitive load. Further, the present invention can be similarly applied to a liquid ejecting method 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.

  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 jet heads 2, 3, and the electric motor 7. Configured.

  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. 5 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 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. The mechanism for selecting the drive signal by the drive signal selection data SI & SP can be realized in the form described in, for example, Japanese Patent Application Laid-Open No. 2003-1824. In this embodiment, for example, when a small dot is formed in the corresponding pixel by the drive signal selection data SI & SP, the second drive pulse PCOM2 from the left in the drawing is applied to the nozzle actuator as a small dot drive signal, and the corresponding pixel In the case of forming a large dot, the second drive pulse PCOM3 from the right in the figure is applied to the nozzle actuator as a large dot drive signal. Further, when a dot having an intermediate size is formed, the rightmost drive pulse PCOM4 in the figure is applied to the nozzle actuator as a medium dot drive signal. 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 the present embodiment, a unit drive signal for driving the nozzle actuator is defined as a drive pulse PCOM, and a signal obtained by connecting a predetermined number of these is defined as a drive signal COM. However, there is no difference that the drive pulse PCOM is also a drive signal.

  As described above, the drive signal COM (drive pulse PCOM) applied to the nozzle actuator is common, but in this embodiment, two types of drive signal generation circuits, that is, drive circuits are provided in the head driver 65 of the control device. Provided. FIG. 5 shows a specific configuration of the drive circuit. Reference numeral 23 in the figure denotes a digital drive circuit, and reference numeral 24 denotes an analog drive circuit. Based on the digital drive drive waveform data DWCOMd output from the control unit 62 to generate and output a drive signal, the digital drive circuit 23 generates a drive signal source, that is, a reference of a signal for controlling the drive of the nozzle actuator 22. A drive waveform signal generation circuit 25 for generating a digital drive drive waveform signal WCOMd, a modulation circuit 26 for pulse-modulating the digital drive drive waveform signal WCOMd generated by the drive waveform signal generation circuit 25, and a pulse by the modulation circuit 26 A digital power amplifying circuit that amplifies the modulated modulation signal, that is, a so-called class D amplifier 28, and a power amplification modulated signal that has been amplified by the digital power amplifying circuit 28 are smoothed to obtain a digital drive signal COMd from a selection switch described later. A smoothing filter 29 for supplying the nozzle actuator 22 It is.

  The drive waveform signal generating circuit 25 converts the digital drive drive waveform data DWCOMd output from the control unit 62 into a voltage signal, holds it for a predetermined sampling period, and converts it into analog by a D / A converter and converts it to digital. A drive waveform signal for driving WCOMd is output. In the present embodiment, a general pulse width modulation (PWM) circuit is used as the modulation circuit 26 that performs pulse modulation on the digital drive waveform signal WCOMd. As is well known, in the pulse width modulation, a triangular wave signal having a predetermined frequency is generated by a triangular wave signal generating circuit, and this triangular wave signal and the digital driving driving waveform signal WCOMd are compared by a comparator. A pulse signal that is on-duty when the drive waveform signal WCOMd is large is output as a modulation signal. The digital power amplification circuit 28 is based on a half-bridge class D output stage 21 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 a gate driving circuit 30 for adjusting the gate-source signals GH and GL of the switching elements Q1 and Q2. Further, the smoothing filter 29 is constituted by, for example, a low-pass filter (low-pass filter) comprising a combination of a coil and a capacitor, and this low-pass filter removes the modulation period component of the power amplification modulation signal, in this case, the frequency component of the triangular wave signal. The

  In the digital power amplifier circuit 28, when the modulation signal is at a high level, the gate-source signal GH of the high-side switching element Q1 is at a high level, and the gate-source signal GL of the low-side switching element Q2 is at a low 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 21 is the supply voltage VDD. On the other hand, when the modulation signal is at a low level, the gate-source signal GH of the high-side switching element Q1 is at a low level, and the gate-source signal GL of the low-side switching element Q2 is at a high 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 21 becomes 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. Further, since no current flows through the switching element in the off state, no loss occurs. Accordingly, the loss itself of the digital power amplifier circuit 28 is extremely small, and a switching element such as a small MOSFET can be used.

  On the other hand, the analog drive circuit 24 generates a drive signal based on the analog drive waveform data DWCOMa output from the control unit 62 to generate and output a drive signal, that is, a signal for controlling the drive of the nozzle actuator 22. A drive waveform signal generation circuit 31 that generates a reference analog drive waveform signal WCOMa, and a D / A conversion circuit that converts the analog drive waveform signal WCOMa generated by the drive waveform signal generation circuit 31 (analog conversion) Circuit) 32 and an analog power amplifier circuit 33 that amplifies the power of the analog drive waveform signal AWCOM analog-converted by the D / A converter circuit 24. The power amplifier circuit 33 includes a push-pull connected transistor pair 35 and a pre-driver circuit 34 for driving the transistors Tr1 and Tr2 of the transistor pair 35.

  The drive waveform signal generation circuit 31 reads the analog drive drive waveform data DWCOMa output from the control unit 62, converts it into a voltage signal, and holds it for a predetermined sampling period, thereby holding the analog data drive waveform for the digital data. The signal WCOMa is output. The D / A conversion circuit 32 uses a general digital-analog conversion circuit, which converts the analog data drive waveform signal WCOMa of digital data into an analog drive waveform signal AWCOM. The pre-driver circuit 34 controls the base voltage of each of the transistors Tr1 and Tr2 of the push-pull connected transistor pair 35. For example, the base current of the charging transistor rises when the number of connected nozzle actuators changes. Suppress. As this pre-driver circuit 34, for example, the one described in Japanese Patent Application Laid-Open No. 2004-306434 previously proposed by the present applicant is applicable. The transistor pair 35 is configured by push-pull connection of a charging transistor Tr1 and a discharging transistor Tr2. The collector of one NPN-type charging transistor Tr1 is supplied with a power supply voltage VDD, and an emitter is connected via a selection switch described later. The base is connected to one output of the pre-driver circuit 34. The emitter of the other PNP type discharge transistor Tr2 is connected to the nozzle actuator via a selection switch described later, the collector is grounded, and the base is connected to the other output of the pre-driver circuit 25. In this transistor pair 33, one charging transistor Tr1 supplies a charge from the power supply voltage VDD to the nozzle actuator 22 that is a capacitive load, with a voltage waveform corresponding to the analog drive signal COMa, via a selection switch described later. In other words, the other discharging transistor Tr2 discharges the electric charge of the nozzle actuator 22 which is a capacitive load with a voltage waveform corresponding to the analog driving signal COMa via a selection switch described later.

  In this embodiment, as shown in FIG. 6, the digital drive signal COMd output from the digital drive circuit 23 does not generate the drive pulse PCOM2 corresponding to the small dot, but outputs it from the analog drive circuit 24. Only with the analog drive signal COMa, the drive pulse PCOM2 corresponding to the small dot is generated. The drive pulse PCOM4 corresponding to the medium dot is also generated by the analog drive signal COMa output from the analog drive circuit 24. The contents of the drive signal selection data SI & SP defining the relationship between the drive pulses PCOM1 to PCOM4, the analog drive signal COMa, and the digital drive signal COMd are as shown in Table 1 below. In the figure, symbol CH is a channel signal for setting the generation timing of each drive pulse PCOM, and symbol LAT is a latch signal for setting the generation timing of the drive signal COM formed by connecting the drive pulses PCOM in time series. is there. The effect of the distribution of the drive pulse PCOM to the digital drive signal COMd and the analog drive signal COMa will be described in detail later.

  For each liquid ejecting head 2, as a control signal from the control device of FIG. 3, a nozzle to be ejected is selected based on the print data, and a drive signal selection for determining a connection timing to a drive signal COM of a nozzle actuator such as a piezoelectric element After data SI & SP and nozzle selection data are input to all nozzles, a latch signal LAT, a channel signal CH, and drive signal selection data for connecting the drive signal COM and the nozzle actuator of the liquid jet head 2 based on the drive signal selection data SI & SP A clock signal SCK for transmitting SI & SP as a serial signal to the liquid jet head 2 is input. That is, a series of drive signals COMd and COMa starts to be output in response to the latch signal LAT, and a drive pulse PCOM is output for each channel signal CH.

  FIG. 7 shows a configuration of the selection circuit 36 constructed in each liquid ejecting head 2 in order to supply the drive signals COMd and COMa (drive pulse PCOM) to the nozzle actuator 22. This selection circuit 36 schematically shows a selection circuit described in Japanese Patent Application Laid-Open No. 2006-56101 previously proposed by the present applicant, and includes one nozzle actuator 22 consisting of two transmission gates. A switch 201 is connected, one of them is closed, and either the digital drive signal COMd or the analog drive signal COMa (the drive pulse PCOM) is applied to the nozzle actuator 22. The selection circuit 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 the liquid, and the data of the shift register 211. A latch circuit 212; a decoder 213 that decodes the output of the latch circuit 212; and an output decoded by the decoder 213, which is level-converted and supplied to the selection switch 201, and either one of the two selection switches 201 is closed, The level shifter 214 is configured to connect the drive signals COMd and COMa to the nozzle actuator 22 such as a piezo element.

  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 decoded by the decoder 213 and then converted to a voltage level by which the next-stage selection switch 201 can be turned on / off by the level shifter 214. This is because the drive signals COMd and COMa are higher in voltage than the output voltage of the latch circuit 212, and the operating voltage range of the selection switch 201 is set higher accordingly. Accordingly, the nozzle actuator 22 such as a piezoelectric element whose selection switch 201 is closed by the level shifter 214 is connected to the drive signals COMd and COMa (drive pulse PCOM thereof) 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. 8 shows the relationship between the analog drive signal COMa generated and output by the analog drive circuit 24, the power supply voltage VDD, and the ground voltage. In FIG. 8a, since the voltage of the analog drive signal COMa is increased, charges are stored in the nozzle actuator 22 made of a piezoelectric element, that is, charged, and in FIG. 8b, the voltage of the analog drive signal COMa is decreased. Therefore, the electric charge of the nozzle actuator 22 made of a piezoelectric element is released, that is, discharged. When the nozzle actuator 22 is charged, the shaded portion in FIG. 8a, that is, the difference between the analog drive signal COMa and the power supply voltage VDD, that is, the charging source voltage is lost, and when the nozzle actuator 22 is discharged, FIG. The shaded portion, that is, the difference between the analog drive signal COMa and the ground voltage, that is, 0 V, is a loss. Since most of the loss is heat, a large heat sink for releasing this heat is required, or a transistor with a large capacity is required. These are disadvantageous not only in terms of configuration and cost, but also in terms of layout.

  On the other hand, since the digital drive signal COMd generated and output by the digital drive circuit 23 only turns on and off the switching elements Q1 and Q2 as described above, the loss is small and the heat generation amount is also small. However, the digital drive signal COMd has a limit in improving its waveform accuracy. FIG. 9 shows the relationship between the digital drive signal COMd generated and output by the digital drive circuit 23 and the modulation signal, and in this embodiment, the pulse width modulation signal PWM. For example, when the pulse modulation is pulse width modulation, the accuracy of the pulse width modulation signal PWM does not exceed the sampling period of the triangular wave signal, that is, the modulation period.

  For example, the drive pulse PCOM2 corresponding to the small dot is a complicated voltage trapezoidal waveform signal, and there is a limit to the generation and output of the digital drive signal COMd by the digital drive circuit 23. On the other hand, the analog drive circuit 24 can generate and output a highly accurate voltage trapezoidal waveform signal. Therefore, in the present embodiment, the drive pulse PCOM2 corresponding to a small dot is generated and output only by the analog drive circuit 24. Of course, the analog drive circuit 24 can also generate and output a drive pulse PCOM1 corresponding to micro-vibration and a drive pulse PCOM3 corresponding to a large dot whose waveform accuracy is not so high. As shown in FIG. 4, these drive pulses are also generated and output by the analog drive circuit 24. Of course, it is possible to reduce the loss by generating and outputting the drive pulse with not so high waveform accuracy by the digital drive circuit 23. Incidentally, in this embodiment, the analog drive circuit 24 generates and outputs the drive pulse PCOM4 corresponding to the medium dot. However, the drive pulse PCOM4 corresponding to the medium dot is about the same as the drive pulse PCOM2 corresponding to the small dot. Since the waveform accuracy is not required, the digital drive circuit 23 may generate and output as necessary.

  As described above, according to the liquid ejecting apparatus of the present embodiment, a plurality of nozzles for ejecting liquid to the liquid ejecting head 2 are formed, and the nozzle actuators 22 are disposed in the respective nozzles. Is driven by the drive signal COM, and when the liquid is ejected from the corresponding nozzle toward the print medium 1, the digital drive drive waveform signal WCOMd, which is the reference for driving the nozzle actuator 22, is amplified by the digital power amplifier circuit 28. The digital drive circuit 23 that outputs the digital drive signal COMd and the analog drive drive waveform signal WCOMa that serves as a reference for driving the nozzle actuator 22 are amplified by the analog power amplifier circuit 33 and the analog drive signal COMa is output. Drive circuit 24 and digital drive signal COMd And a selection circuit 36 that selects any one of the analog drive signals COMa and applies them to the nozzle actuator 22, and includes a drive pulse PCOM2 used for ejecting the smallest amount of liquid droplets to be ejected. Since COMa is output from the analog drive circuit 24 and the drive signal COMd including the drive pulse PCOM3 used for ejecting the largest amount of liquid droplets is outputted from the digital drive circuit 23, it is used for ejecting the largest amount of liquid droplets. A drive signal that does not require high waveform accuracy such as the drive pulse PCOM3 is output from the digital drive circuit 23, and a drive signal COMa that requires high waveform accuracy such as the drive pulse PCOM2 used to eject the smallest amount of liquid droplets is Since it can be output from the analog drive circuit 24, the wave of the drive signal COMa While maintaining the accuracy, it is possible to reduce the loss.

  Further, since the drive signal COMd including the drive pulse PCOM1 used when the liquid droplet is not ejected is output from the digital drive circuit 23, the drive pulse PCOM1 used when the liquid droplet is not ejected requires high waveform accuracy. Therefore, the loss can be further reduced by outputting the drive signal COMd including the drive pulse PCOM1 from the digital drive circuit 23.

  The digital drive circuit 23 includes a drive waveform signal generation circuit 25 that generates a digital drive drive waveform signal WCOMd, and a modulation circuit 26 that performs pulse modulation on the digital drive drive waveform signal WCOMd generated by the drive waveform signal generation circuit 25. And a digital power amplifier circuit 28 for amplifying the power of the modulation signal pulse-modulated by the modulation circuit 26. The digital power amplifier circuit 28 is a half-bridge class D output stage 21 comprising a pair of switching elements for amplifying power. And a gate drive circuit 30 for adjusting the gate-source signals of the switching elements Q1 and Q2 of the half-bridge class D output stage 21 based on the modulation signal from the modulation circuit 26, thereby providing digital drive. Implementation of the circuit 23 is facilitated.

The analog drive circuit 24 includes a drive waveform signal generation circuit 31 that generates an analog drive drive waveform signal WCOMa, and an analog conversion circuit that converts the analog drive drive waveform signal WCOMa generated by the drive waveform signal generation circuit 31 into an analog signal. 32 and an analog power amplifier circuit 33 that amplifies the analog drive waveform signal AWCOM converted by the analog converter circuit 32. The analog power amplifier circuit 33 is a push-pull connected transistor that charges and discharges the nozzle actuator 22. Implementation of the analog drive circuit 24 by comprising the pair 35 and a pre-driver circuit 34 that adjusts the base voltage of the transistor pair based on the analog drive waveform signal AWCOM analog-converted by the analog conversion circuit 32 Becomes easier.
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 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 front view of a schematic configuration showing an embodiment of a printing apparatus using a liquid ejecting apparatus of the present invention. FIG. 2 is a plan view of the vicinity of a liquid ejecting head used in the liquid ejecting 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. FIG. 4 is a block diagram of a digital drive circuit and an analog drive circuit in the head driver of FIG. 3. It is explanatory drawing of the digital drive signal and analog drive signal which are output from the drive circuit of FIG. FIG. 7 is a block diagram of a selection circuit that selects the digital drive signal and the analog drive signal of FIG. 6 and applies them to the nozzle actuator. It is explanatory drawing of the loss of an analog drive signal. It is explanatory drawing of the waveform precision of a digital drive signal.

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 11 is a fixed plate, 21 is a half bridge class D output stage, 22 is a nozzle actuator, 23 is a digital drive circuit, 24 is an analog drive circuit, 25 is a drive waveform signal generation circuit, 26 is a modulation circuit, and 28 is Digital power amplifier, 29 is a smoothing filter, 30 is a gate drive circuit, 31 is a drive waveform signal generation circuit, 32 is a D / A conversion circuit (analog conversion circuit), 33 is an analog power amplification circuit, 34 is a pre-driver circuit, 35 Is a transistor pair, 62 is a control unit, and 65 is a head driver.

Claims (4)

  A plurality of nozzles for ejecting liquid to the liquid ejecting head are formed, and nozzle actuators are provided for each nozzle, and each nozzle actuator of the liquid ejecting head is driven by a drive signal so that the corresponding nozzle is directed to the print medium. A liquid ejecting apparatus that ejects liquid, wherein a digital drive circuit that outputs a digital drive signal by power-amplifying a drive waveform signal serving as a reference for driving the nozzle actuator by a digital power amplifier circuit; and driving of the nozzle actuator An analog drive circuit that amplifies a drive waveform signal serving as a reference by an analog power amplifier circuit and outputs an analog drive signal; a selection circuit that selects one of the digital drive signal and the analog drive signal and applies the selected signal to the nozzle actuator; The smallest amount of liquid droplets to be ejected A liquid ejection characterized in that a drive signal including a drive pulse used for ejection is output from the analog drive circuit, and a drive signal including a drive pulse used for ejecting the largest amount of liquid droplet is output from the digital drive circuit. apparatus.   The liquid ejecting apparatus according to claim 1, wherein a driving signal including a driving pulse to be used when the liquid droplet is not ejected is output from the digital driving circuit.   The digital drive circuit includes a drive waveform signal generation circuit that generates the drive waveform signal, a modulation circuit that performs pulse modulation on the drive waveform signal generated by the drive waveform signal generation circuit, and modulation that is pulse modulated by the modulation circuit A digital power amplifier circuit that amplifies the signal, and the digital power amplifier circuit is based on a half-bridge class D output stage composed of a pair of switching elements for amplifying power, and a modulation signal from the modulation circuit, The liquid ejecting apparatus according to claim 1, further comprising a gate driving circuit configured to adjust a gate-source signal of the switching element of the half-bridge class D output stage.   The analog drive circuit is analog-converted by a drive waveform signal generation circuit for generating the drive waveform signal, an analog conversion circuit for analog conversion of the drive waveform signal generated by the drive waveform signal generation circuit, and an analog conversion circuit An analog power amplifier circuit that amplifies an analog drive waveform signal, and the analog power amplifier circuit includes a push-pull connected transistor pair that charges and discharges a nozzle actuator, and an analog drive waveform analog-converted by the analog converter circuit. The liquid ejecting apparatus according to claim 1, further comprising: a pre-driver circuit that adjusts a base voltage of the transistor pair based on a signal.

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