JP4899592B2 - Ink jet printer and ink jet printer driving method - Google Patents

Description

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

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

  In such an ink jet printer, each of a plurality of nozzles is provided with a pressure chamber and an actuator, and the actuator is driven by a drive pulse to change the pressure in the pressure chamber, and the ink in the pressure chamber is transferred to the pressure chamber by the pressure change. The ink is ejected as ink droplets from the communicating nozzle. There are also several types of actuators. For example, in a piezoelectric inkjet printer, when a power signal corresponding to a drive pulse is applied to a piezoelectric element that is an actuator, the diaphragm in contact with the pressure chamber is displaced. The pressure in the pressure chamber changes and ink droplets are ejected. The drive pulse is formed into a trapezoidal wave shape as a whole by adding or subtracting waveform data defining the voltage value in units of clock operation to increase or decrease the voltage value in a stepwise manner. Then, this trapezoidal wave is combined in the opposite direction to make a drive pulse, the pressure chamber is expanded at the front stage to draw ink, and the pressure chamber is contracted at the rear stage to eject the ink, thereby ejecting ink droplets from the nozzles. To do. Therefore, the slope and peak value of the trapezoidal wave of the drive pulse become an element that controls ink drawing and extrusion, and adjusting them enables changing the volume of ejected ink droplets to enable, for example, multiple gradations. .

As a drive circuit for driving the actuator, for example, a current amplification circuit in which two transistors are push-pull connected is used. By supplying the drive pulse described above to the gate (base) of one transistor, the output, that is, the drive pulse is amplified. The power signal is supplied from the power source to the actuator to charge the actuator as the capacitive load, and is discharged from the actuator as the capacitive load via the other transistor. This actuator driving method has a problem that the heat generation of the transistor is large because the actuator charge / discharge state is controlled to have a predetermined inclination using a so-called unsaturated region of two transistors connected in a push-pull manner. Therefore, in the ink jet printer described in Patent Document 1 below, for example, a plurality of drive pulses having different voltage rise and fall timings are generated, and the drive timings of the actuators to which the respective drive pulses are supplied are shifted. The total peak current is reduced.
JP 7-125195 A

  However, a drive pulse generation circuit is required for the generated drive pulses, and the drive circuit is large and complicated. Also, since the rise and fall timings of multiple drive pulses are shifted, the ink droplet discharge timing is shifted at the nozzle of the actuator to which each drive pulse is supplied, and the accuracy of the landing position of the ink droplet at the target position is improved. There is also a problem that it falls.

  The present invention has been made paying attention to the above-mentioned problems, and avoids various problems by using a single drive pulse, and simultaneously reduces the heat generation of two transistors that are push-pull connected. It is an object of the present invention to provide an inkjet printer and an inkjet printer driving method capable of performing the above.

[Invention 1] In order to solve the above problems, an ink jet printer of the invention 1 comprises an actuator in response to Roh nozzle supplies a driving waveform signal to a push-pull-connected two transistors, the output from the transistor by applying to the actuator as a drive pulse, an inkjet printer for ejecting ink droplets from the nozzles corresponding, stepwise voltage waveform data defining the voltage values by adding or subtracting the operating units of the clock There the drive pulse generating means for causing generation of the driving pulses to increase or decrease, a selection switch for intermittently the actuator to the drive pulse provided to the actuator, within a time in which the voltage value is maintained of the drive pulses, with respect to the selection switch, the election in the filter timing different from the other selection switch It is characterized in that a selection switch control means for controlling the intermittent switch.

According to the ink jet printer according to the present invention 1, supplies a driving waveform signal to a push-pull-connected two transistors, by applying to the actuators by the output drive pulse, ejects an ink droplet from the corresponding nozzle In doing so, waveform data that defines the voltage value is added or subtracted in units of clock operation to generate a drive pulse whose voltage value increases or decreases stepwise, and the voltage value of the drive pulse is retained for this single drive pulse. within the time being, to select switch, due to a configuration which controls the intermittence of select switch filter timing different from the other selection switch, extremely short actuator is a capacitive load is charged and discharged to a predetermined potential The application timing of the drive pulse, that is, the drive timing of the actuator can be shifted by the time difference. While avoiding the problem of 置精 degree decreases, it is possible to reduce heat generation of the transistors in a single drive pulse.

[Invention 2] invention 2 of the ink jet printer is an ink jet printer of the invention 1, the disengage start timing of the selection switch by the selection switch control means, the charge potential of the actuator is set to a timing after reaching a predetermined value It is characterized by.
According to the ink jet printer according to the present invention 2, by setting the cutoff start timing of the selection switches, to the timing after the charge potential of the least A also actuator from the start selection switch connection reaches a predetermined value, the state of charge of the actuators Can be made to correspond to the original voltage state of the drive pulse, whereby the actuator can be driven to the original state of the drive pulse.

[Invention 3] invention 3 of the ink jet printer, in the first or second aspect of the inkjet printer, the Intermittent timing so that the connection time of the selection switch by the selection switch control means does not polymerize and connection time of the other selection switch It is characterized by setting. According to the ink jet printer according to the present invention 3, by connecting time of the selected switch to set the Intermittent timing so as not to polymerization and connection time of the other selection switch, the heating of the two transistors push-pull connected It can be surely reduced.

[Invention 4] invention 4 of the inkjet printer driving method, generating an actuator in response to Roh nozzle, the drive pulse whose voltage value increases or decreases by subtracting the waveform data defining a voltage value at the operating unit of the clock stepwise A drive pulse generating means for selecting, and a selection switch arranged for the actuator to intermittently connect the actuator to the drive pulse, and supplying a drive waveform signal to two push-pull connected transistors to output from the transistor by applying to the actuator as the driving pulse, in an inkjet printer for ejecting ink droplets from said corresponding nozzle, within the time the voltage value of the drive pulse is maintained, with respect to the selection switch, the selection of other the intermittence of the selection switch filter timing different from the switch It is characterized in that Gosuru.

According to the inkjet printer driving method according to the present invention 4, it supplies a driving waveform signal to a push-pull-connected two transistors, by applying to the actuators by the output drive pulse, the ink from the corresponding nozzle drops In order to discharge, the waveform data that defines the voltage value is added or subtracted in clock operation units to generate a drive pulse whose voltage value increases or decreases stepwise, and for this single drive pulse, the voltage value of the drive pulse within the time but is held against select switch, due to a configuration which controls the intermittence of select switch filter timing different from the other selection switch, in a very short time difference actuators is charged and discharged to a predetermined potential The drive pulse application timing, that is, the drive timing of the actuator can be shifted. While avoiding the problem below, it is possible to reduce heat generation of the transistors in a single drive pulse.

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

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

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

  Methods for ejecting and outputting ink from each nozzle of the inkjet head include an electrostatic method and a piezo method. In the piezo method, when a drive pulse is applied to a piezo element that is an actuator, the diaphragm in the cavity is displaced to cause a pressure change in the cavity, and an ink droplet is ejected from the nozzle by the pressure change. In the electrostatic method, when a drive pulse is applied to the electrostatic gap, which is an actuator, the diaphragm in the cavity is displaced, causing a pressure change in the cavity, and an ink droplet is ejected from the nozzle by the pressure change. is there. Any ink output method can be applied to the present invention as long as it has an actuator composed of a capacitive load.

  A specific configuration of the ink jet head according to the present embodiment will be described with reference to FIGS. The ink jet head 20 uses a piezoelectric actuator. As shown in FIG. 2a, the vibration plate 21, a piezoelectric actuator 22 for displacing the vibration plate 21, and a liquid ink are filled therein. At least a cavity (pressure chamber) 23 in which the internal pressure is increased or decreased by the displacement of the vibration plate 21 and a nozzle 24 that communicates with the cavity 23 and discharges ink as droplets by increasing or decreasing the pressure in the cavity 23 are provided. ing.

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

  In the piezoelectric actuator 22 having such a configuration, the drive pulse from the drive pulse source applied between the first electrode 31 and the second electrode 32 expands and contracts in the vertical direction as indicated by an arrow in FIG. The mode to use is used. Therefore, in the piezoelectric actuator 22, for example, when a driving pulse as shown in FIG. 2A is applied, the diaphragm 21 is displaced, the pressure in the cavity 23 changes, and an ink droplet is ejected from the nozzle 24. It has become. Specifically, as will be described in detail later, the volume of the cavity 23 is enlarged to draw ink, and then the volume of the cavity 23 is reduced to eject ink droplets. In addition, the nozzles 24 for each inkjet head 20 formed on the nozzle substrate 26 shown in FIG. 2A are arranged as shown in FIG. 4, for example. The example of FIG. 3 shows an arrangement pattern of the nozzles 24 when applied to four colors of ink (Y: yellow, M: magenta, C: cyan, K: black). Full color printing is possible.

  FIG. 2 b shows another example of the piezoelectric actuator 22. The reference numerals in the figure are the same as those in FIG. 2a. This piezoelectric actuator is generally called a unimorph actuator and has a simple structure in which the piezoelectric element 27 is sandwiched between two electrodes 31 and 32. By applying a driving pulse, the piezoelectric actuator is similar to the stacked actuator of FIG. 2a. Then, the ink expands and contracts in the vertical direction in the figure, expands the volume of the cavity 23 and draws ink, and then reduces the volume of the cavity 23 and discharges ink droplets from the nozzles 24. The ink jet head 20 is also connected to the ink cartridge via an ink supply tube (not shown).

  FIG. 3 shows an example of an ink jet head using the electrostatic actuator 22. Among the reference numerals in the figure, the same functions and the same names as those in FIGS. The ink in the ink tank 3 flows into the reservoir 28 and is introduced into the cavity 23 through the narrow channel 101. A conductive diaphragm 21 that is electrically connected to the common electrode 102 is in contact with the flow path 101 and the cavity 23. In addition, an individual electrode 104 is disposed on the diaphragm 21 via a gap 103. As a result, the gap 103 is interposed between the common electric curve 102 and the individual electrode 104, and the electrostatic actuator 22 is configured using the capacitance of the gap 103. Therefore, when a driving pulse is applied to the electrostatic actuator 22, the diaphragm 21 is attracted to the individual electrode 104 side by the electrostatic attraction force of the gap 103 to store elastic energy, and the diaphragm is released by releasing the elastic energy. 21 bends to the side opposite to the individual electrode 104, the pressure in the cavity 23 increases, and ink droplets are ejected from the nozzle 24.

  The inkjet printer 1 is provided with a control device for controlling itself. For example, as shown in FIG. 5, the control device prints on a print medium by controlling a printing device, a paper feeding device, and the like based on print data input from a host computer 60 such as a personal computer or a digital camera. The processing is performed. An input interface unit 61 that receives print data input from the host computer 60, a control unit 62 configured by, for example, a microcomputer that executes print processing based on the print data input from the input interface unit 61, A carriage motor driver 63 that drives and controls the carriage motor 41, a paper feed motor driver 64 that drives and controls the paper feed motor 51, a head driver 65 that drives and controls the inkjet head 20, and output signals of the drivers 63, 64, and 65 And an interface 67 that converts the output signal into a control signal used by the inkjet head 20 and outputs the control signal.

  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 ROM (Read-Only ROM) comprising a RAM (Random Access Memory) 62c that temporarily stores an application program such as print processing or the like, and a non-volatile semiconductor memory that stores a control program executed by the CPU 62a Memory) 62d. When the control unit 62 obtains print data (image data) from the host computer 60 via the interface unit 61, the CPU 62a performs a predetermined process on the print data and ejects ink droplets from any nozzle. Alternatively, print data indicating how many ink droplets are to be ejected is output, and control signals are output to the drivers 63 to 65 based on the print data and input data from various sensors. When the control signals are output from the drivers 63 to 65, these are converted into drive signals by the interface unit 67, and the actuator 22, the carriage motor 41, and the paper feed motor 51 corresponding to the plurality of nozzles 24 of the inkjet head 20 are respectively provided. In operation, a printing process is performed on the print medium. Each component in the control unit 62 is electrically connected through a bus (not shown).

  The control unit 62 also writes a write enable signal DEN, a write clock signal WCLK, and write address data A0 to A0 in order to write waveform forming data DATA for forming drive pulses described later into a waveform memory 701 described later. A3 is output to write, for example, 16-bit waveform forming data DATA into the waveform memory 701, and read address data A0 to A3 for reading out the waveform forming data DATA stored in the waveform memory 701. The first clock signal ACLK that sets the timing for latching the waveform forming data DATA read from the waveform memory 701, the second clock signal BCLK that sets the timing for adding the latched waveform data, and the latch data are cleared. Outputs clear signal CLER to head driver 65 That. In addition, the control unit 62 sends the first switch signal SS1 and the second switch signal SS2 forcibly switching the selection switch 201 for switching the drive pulse COM and the actuator 22 to the inkjet head 20 via the interface unit 67. Output.

  The head driver 65 includes a drive pulse generation circuit 70 that generates a drive pulse COM and an oscillation circuit 71 that outputs a clock signal SCK. As shown in FIG. 6, the drive pulse generating circuit 70 includes a waveform memory 701 for storing waveform forming data DATA for generating a drive pulse input from the control unit 62 in a storage element corresponding to a predetermined address, A latch circuit 702 that latches the waveform forming data DATA read from the waveform memory 701 by the first clock signal ACLK described above, an output of the latch circuit 702, and waveform generation data WDATA output from a latch circuit 704 described later. An adder 703 for adding, a latch circuit 704 for latching the addition output of the adder 703 by the above-described second clock signal BCLK, and D for converting the waveform generation data WDATA output from the latch circuit 704 into an analog signal / A converter 705 and the output from this D / A converter 705 A voltage amplifier 706 amplifies the voltage log signal, and a current amplifier 707 for outputting a driving pulse COM output signal of the voltage amplifier 706 current amplification to. Here, the clear signal CLER output from the control unit 62 is input to the latch circuits 702 and 704, and the latch data is cleared when the clear signal CLER is turned off.

  As shown in FIG. 7, in the waveform memory 701, memory elements each having several bits are arranged at the designated address, and waveform data DATA is stored together with the addresses A0 to A3. Specifically, the waveform data DATA is input together with the clock signal WCLK to the addresses A0 to A3 instructed from the control unit 62, and the waveform data DATA is stored in the memory element by the input of the write enable signal DEN.

  In the ink jet head 20, printing is performed by selecting nozzles to be ejected based on the drive pulse COM generated by the drive pulse generation circuit 70 and print data via the interface 67 and setting how much ink droplets are to be ejected. After data SI and nozzle selection data are input to all nozzles, a latch signal LAT and a channel signal CH for connecting the drive pulse COM and the actuator 22 of the inkjet head 20 based on these data, and these print data SI as serial signals The clock signal SCK for transmitting to the inkjet head 20 and the first switch signal SS1 and the second switch signal SS2 for forcibly switching the selection switch 201 for switching the drive pulse COM and the actuator 22 are input. . The first switch signal SS1 and the second switch signal SS2 are clock signals synchronized with the second clock signal BCLK, but the ON / OFF timing is slightly different as will be described in detail later. The first switch signal SS1 and the second switch signal SS2 are 180 ° out of phase.

  Next, a configuration for connecting the drive pulse COM output from the drive pulse generation circuit 70 and the actuator 22 will be described. FIG. 8 is a block diagram of a selection unit that connects the drive pulse COM and the actuator 22. The selection unit designates the actuator 22 corresponding to the nozzle 24 that should eject ink droplets, and stores the print data SI that also designates the piezoelectric actuator 22 corresponding to the nozzle 24 that does not eject ink droplets; A latch circuit 212 that temporarily stores data of the shift register 211, a first AND gate 214 and a second AND gate 215 that receive the output of the latch circuit 212 and the switch signal SS, and a first AND gate 214 and a second AND gate 214 The level shifter 213 converts the output of the 2-AND gate 215 and the selection switch 201 connects the drive pulse COM to the actuator 22 in accordance with the output of the level shifter 213. Note that half the number of data output from the latch circuit 212 is input to the first AND gate 214, and the remaining half of the data output from the latch circuit 212 is input to the second AND gate 215. . Further, the output of the first AND gate 214 and the output of the second AND gate 215 are all input to the level shifter 213.

  The print data SI is sequentially input to the shift register 211, and the storage area is sequentially shifted from the first stage to the subsequent stage according to the input pulse of the clock signal SCK. After the print data SI for the number of nozzles is stored in the shift register 211, the latch circuit 212 latches each output signal of the shift register 211 with the input latch signal LAT and channel signal CH. That is, the data output from the latch circuit 212 is ON / OFF signals for all the nozzles, half of which is input to the first AND gate 214, and the remaining half of the data is the first. 2 is input to the AND gate 215.

  The data corresponding to the total number of nozzles output from the first AND gate 214 and the second AND gate 215 is converted to a voltage level at which the next stage selection switch 201 can be turned on / off by the level shifter 213. This is because the drive pulse COM is higher than the output voltage of the latch circuit 212 and the AND gate 214, and the operating voltage range of the selection switch 201 is set higher accordingly. The selection switch 201 is composed of an analog switch having a transmission gate in which a P-channel FET and an N-channel FET are combined, and the gate voltage is level-converted to a high value in order to sufficiently operate the analog switch. The nozzle actuator 22 to which the gate voltage of the selection switch 201 is applied by the level shifter 213 is connected to the drive pulse COM. Further, after the print data SI of the shift register 211 is stored in the latch circuit 212, the next print data 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. Reference numeral HGND in the figure is the ground end of the piezoelectric actuator 22.

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

  From this state, for example, as shown in FIG. 9, when the waveform data at the address A1 is read and the first clock signal ACLK is input, the digital data of + ΔV1 is stored in the latch circuit 702. The stored digital data of + ΔV1 is input to the latch circuit 704 via the adder 703, and the latch circuit 704 stores the output of the adder 703 in synchronization with the rise of the second clock signal BCLK. Since the output of the latch circuit 704 is also input to the adder 703, the output (COM) of the latch circuit 704 is added by + ΔV1 at a timing when the second clock signal BCLK becomes equal to or higher than the threshold LV0. In this example, the waveform data at the address A1 is read during the time width T1, and as a result, the digital data of + ΔV1 is added until it is tripled.

  Next, when the waveform data at the address A0 is read and the first clock signal ACLK is input, the digital data stored in the latch circuit 702 is switched to zero. Similarly to the above, this 0 digital data is added through the adder 703 at the timing when the second clock signal BCLK becomes equal to or higher than the threshold value LV0. The previous value is retained. In this example, the drive pulse COM is held at a constant value during the time width T0.

  Next, when the waveform data at the address A2 is read and the first clock signal ACLK is input, the digital data stored in the latch circuit 702 is switched to -ΔV2. Similarly to the above, the digital data of -ΔV2 passes through the adder 703 and is added at the timing when the second clock signal BCLK becomes equal to or higher than the threshold LV0. However, since the digital data is -ΔV2, the digital data is substantially The drive pulse COM is subtracted by −ΔV2 in accordance with the second clock signal. In this example, during the time width T2, the drive pulse COM is subtracted until the digital data of −ΔV2 becomes six times.

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

  10 shows the configuration of the voltage amplification unit 706, the current amplification unit 707, the selection switch 201, the actuator 22, the level shifter 213, and the first AND gate 214, and FIG. 11 shows the voltage amplification unit 706, the current amplification unit 707, and the selection. A configuration of the switch 201, the actuator 22, the level shifter 213, and the second AND gate 215 is shown. As described above, the current amplifying unit 707 is configured by connecting the two transistors Tr1 and Tr2 by push-pull connection, and the collector of one of the NPN transistors Tr1 is connected to a constant voltage power supply Vcc composed of, for example, a + 42V DC power supply. The emitter is connected to the input side of the selection switch 201, and the base is connected to one output Q1 of the voltage amplifier 706. The emitter of the other PNP transistor Tr2 is connected to the input side of the selection switch 201, the collector is grounded, and the base is connected to the other output Q2 of the voltage amplifier 706. In the current amplifying unit 707, one transistor Tr1 supplies electric charge to the actuator 22 that is a capacitive load from the constant voltage power supply Vcc through the selection switch 201 with a voltage waveform corresponding to the drive pulse COM. The other transistor Tr2 discharges the electric charge of the actuator 22, which is a capacitive load, with a voltage waveform corresponding to the drive pulse COM via the selection switch 201. Accordingly, when the output of the voltage amplification unit 706 is defined as a drive waveform signal, the drive waveform signal obtained by current amplification of the drive waveform signal is applied to the actuator 22 from the selection switch 201 by supplying the drive waveform signal to the two transistors Tr1 and Tr2. be able to.

  Incidentally, in this embodiment, the output voltage of the current amplifying unit 707 is fed back to the voltage amplifying unit 706. As described above, since the actuator 22 has a capacitance as described above, for example, a low-pass filter is constructed in the drive circuit by a combination with the parasitic impedance of the wiring, and the characteristic of the low-pass filter is the number of the actuators 22 to be connected. This is due to the change. As described above, when the low-pass filter is constructed in the drive circuit, the drive pulse COM actually applied to the actuator 22 is different from the drive pulse COM corresponding to the drive waveform signal, and the actuator 22 to be further connected is connected. When the characteristics of the low-pass filter change depending on the number, the drive pulse COM itself also changes depending on the number of connected actuators. The drive pulse COM is fed back to the voltage amplification unit 706 in order to feedback-correct such a change in the drive pulse COM to the actuator 22.

  With such a configuration, when the selection switch 201 of the nozzle to eject ink droplets is turned ON and a drive pulse COM as shown in FIG. 9 is output in this state, the drive pulse COM is applied to the corresponding actuator 22. Should be. However, simply doing so would cause the transistors Tr1 and Tr2 to generate a large amount of heat and increase the power consumption as described above. Therefore, in the present embodiment, the plurality of actuators are not simply left with the selection switch 201 of the nozzle that should eject ink droplets turned on, but according to the logic of FIG. 12 (actually achieved by hardware). 22 is divided into two systems, and while the voltage value of the drive pulse COM is held, the selection switch 201 of any one system is turned on to supply the drive pulse COM, and the actuators 22, That is, when the charging potential of the capacitive load reaches a predetermined value corresponding to the drive pulse COM, the selection switch 201 is turned off, and then the selection switch 201 of the other system is turned on to supply the drive pulse COM. When the charging potential of the capacitive load reaches a predetermined value corresponding to the drive pulse COM, the selection switch 201 is turned off. , Or to reduce the heat generation of the transistors Tr1, Tr2, or reduce power consumption.

In this logic, first, in step S1, all the selection switches 201 are turned off.
Next, the process proceeds to step S2, and the waveform data DATA is read from the waveform memory 701.
Next, the process proceeds to step S 3, where the waveform data DATA is stored in the latch circuit 702.
Next, the process proceeds to step S 4, and the output of the adder 703 is stored in the latch circuit 704.
In step S5, the corresponding selection switch 201 of the first AND gate 214, that is, the selection switch 201 of one system is turned OFF.

Next, the process proceeds to step S6, where it is determined whether or not the first switch signal SS1 is greater than or equal to the threshold value LV1, and when the first switch signal SS1 is greater than or equal to the threshold value LV1, the process proceeds to step S7. To step S5.
In step S7, the corresponding selection switch 201 of the first AND gate 214, that is, the selection switch 201 of one system is turned ON.

Next, the process proceeds to step S8, where it is determined whether or not the first switch signal SS1 is less than or equal to the threshold value LV1, and when the first switch signal SS1 is less than or equal to the threshold value LV1, the process proceeds to step S9. To step S7.
In step S9, the corresponding selection switch 201 of the first AND gate 214, that is, the selection switch 201 of one system is turned OFF.

In step S10, the corresponding selection switch 201 of the second AND gate 215, that is, the selection switch 201 of the other system is turned off.
Next, the process proceeds to step S11, where it is determined whether or not the second switch signal SS2 is greater than or equal to the threshold value LV2. If the second switch signal SS2 is greater than or equal to the threshold value LV2, the process proceeds to step S12. To step S10.

In step S12, the corresponding selection switch 201 of the second AND gate 215, that is, the selection switch 201 of the other system is turned ON.
Next, the process proceeds to step S13, where it is determined whether or not the second switch signal SS2 is less than or equal to the threshold value LV2. If the second switch signal SS2 is less than or equal to the threshold value LV2, the process proceeds to step S14. Then, the process proceeds to step S12.

In step S14, the corresponding selection switch 201 of the second AND gate 215, that is, the selection switch 201 of the other system is turned OFF.
Next, the process proceeds to step S15 to determine whether or not the drive pulse COM has reached the target value. If the drive pulse COM has reached the target value, the process proceeds to step S16. Otherwise, the process proceeds to step S4. Migrate to
In step S16, it is determined whether or not the output of the drive pulse COM has been completed. If the output of the drive pulse COM has been completed, the process ends. If not, the process proceeds to step S2.

  The drive pulse COM by this logic, the ON / OFF signal of the selection switch 201, that is, the first switch signal SS1 and the second switch signal SS2, the charging potential Va1 of the actuator 22 of one system connected to the first AND gate 214, the first FIG. 13 shows changes with time of the charging potential Va2 of the actuator 22 of the other system connected to the 2-and gate 215. The second clock signal BCLK, the first switch signal SS1, and the second switch signal SS2 are all clock signals and are so-called trapezoidal waves that are not completely rectangular waves. Further, the pulse widths of the first switch signal SS1 and the second switch signal SS2 are both narrower than the pulse width of the second clock signal BCLK. Further, the first switch signal SS1 and the second switch signal SS2 have the same waveform, but are 180 degrees out of phase. Specifically, the first switch signal SS1 rises when the rising second clock signal BCLK becomes equal to or higher than the threshold LV0, and the first switch signal SS1 rises before the second clock signal BCLK becomes equal to or lower than the threshold LV0. The second switch signal SS2 rises when the second clock signal BCLK that is falling and then falling falls below the threshold LV0, and the second switch signal SS2 falls before the second clock signal BCLK becomes greater than or equal to the threshold LV0. . Incidentally, the time during which the first switch signal SS1 is greater than or equal to the threshold LV2 and the time during which the second switch signal SS2 is greater than or equal to the threshold LV3 are times when the actuator 201 can be charged and discharged to a predetermined potential.

  On the other hand, even if the drive pulse COM is continuously output as shown in FIG. 13, in the selection circuit of FIG. 10, the first switch signal SS1 becomes equal to or higher than the threshold LV2, and the output of the first AND gate 214 becomes Hi level. Otherwise, the selection switch 201 is not turned ON. In the selection circuit of FIG. 11, the selection switch 201 is not turned on unless the second switch signal SS2 is equal to or higher than the threshold LV3 and the output of the second AND gate 215 becomes Hi level.

  Therefore, for example, when the voltage value of the drive pulse COM increases stepwise by + ΔV1 for each period ΔT of the second clock signal BCLK in the time width T1 shown in FIG. 13, the second clock signal BCLK is greater than or equal to the threshold LV1. Then, the voltage value of the drive pulse COM is increased by + ΔV1, and then, while the voltage value of the drive pulse COM is being held, the first switch signal SS1 becomes the threshold LV2 or more first, and the selection switch of one system 201 is turned on, whereby the actuator 22 of one system is connected to the drive pulse COM, and the electric charge corresponding to the drive pulse COM is supplied to the actuator 22 of one system, which is a capacitive load, and charged. Therefore, if the charging potential Va1 of the actuator 22 of one system is charged to a predetermined potential, even if the first switch signal SS1 is equal to or lower than the threshold LV2 and the selection switch 201 is turned off, the self-discharge is performed. As long as it does not occur, the charging potential Va1 of the actuator 22 of one system is maintained.

  When the charging of the actuator 22 of one system is completed in this way, the second switch signal SS2 becomes equal to or higher than the threshold LV3 while the voltage value of the drive pulse COM is held, and the selection of the other system is performed. The switch 201 is turned on, whereby the actuator 22 of the other system is connected to the drive pulse COM, and the electric charge according to the drive pulse COM is supplied to the actuator 22 of the other system that is a capacitive load and charged. Accordingly, if the charging potential Va2 of the actuator 22 of the other system is charged to a predetermined potential, even if the second switch signal SS2 is equal to or lower than the threshold LV3 and the selection switch 201 is turned off, the self-discharge is performed. As long as it does not occur, the charging potential Va2 of the actuator 22 of the other system is maintained.

  For example, when the voltage value of the drive pulse COM decreases stepwise by −ΔV2 for each period ΔT of the second clock signal BCLK in the time width T3 shown in FIG. 13, the second clock signal BCLK is equal to or higher than the threshold LV1. Then, the voltage value of the drive pulse COM is decreased by −ΔV2, and after that, while the voltage value of the drive pulse COM is held, the first switch signal SS1 becomes equal to or higher than the threshold LV2 first. The selection switch 201 is turned on, whereby the actuator 22 of one system is connected to the drive pulse COM, and the electric charge corresponding to the drive pulse COM is discharged from the actuator 22 of the one system. When the discharge of the actuator 22 of one system is completed, while the voltage value of the drive pulse COM is also held, the second switch signal SS2 becomes the threshold value LV3 or more and the selection switch 201 of the other system is turned ON. Thereby, the actuator 22 of the other system is connected to the drive pulse COM, and the electric charge corresponding to the drive pulse COM is discharged from the actuator 22 of the other system.

  Incidentally, also during the time width T0 in FIG. 13, the actuator 22 generates the drive pulse COM during the time when the first switch signal SS1 is greater than or equal to the threshold LV2 and the time when the second switch signal SS2 is greater than or equal to the threshold LV3. Since they are connected, they do not self-discharge.

  As described above, according to the ink jet printer of this embodiment, the drive waveform signal is supplied to the two transistors Tr1 and Tr2 that are push-pull connected, and the output is applied as the drive pulse COM to each actuator 22 including the capacitive load. Thus, when ink droplets are ejected from the corresponding nozzles 24, the waveform data DATA defining the voltage value is added or subtracted in the operation unit of the second clock signal BCLK to generate a drive pulse COM in which the voltage value increases or decreases stepwise. A configuration in which the selection switch 201 is controlled to be intermittently controlled at a plurality of different intermittent timings with respect to the plurality of selection switches 201 within a time during which the voltage value of the drive pulse COM is held with respect to the single drive pulse COM Therefore, the actuator 22 composed of a capacitive load is extremely short to charge / discharge to a predetermined potential. The application timing of the drive pulse COM, that is, the drive timing of the actuator 22 can be shifted by the time difference, thereby reducing the heat generation of the transistor with a single drive pulse COM, while avoiding the problem of ink droplet landing position accuracy degradation. Can do.

  In addition, by setting the cutoff start timing of the selection switch 201 at least after the timing when the charging potential of the actuator 22 consisting of the capacitive load reaches a predetermined value from the start of connection of the selection switch, the charging state of the actuator 22 consisting of the capacitive load In accordance with the original voltage state of the drive pulse COM, whereby the actuator 22 can be driven to the original state of the drive pulse COM.

In addition, by setting a plurality of different intermittent timings so that the connection times of the selection switches 201 do not overlap, heat generation of the two transistors Tr1 and Tr2 that are push-pull connected can be reliably reduced.
In the above embodiment, the selection switch intermittent pattern is divided into two systems. However, the selection switch intermittent pattern divided by the inkjet printer of the present invention may be three or more systems. In short, as long as the actuator to be charged / discharged can be charged / discharged to a predetermined potential while the voltage value of the drive pulse is being held, any number of intermittent patterns of the selection switch may be used.

  In the above embodiment, only an example in which the head drive device of the inkjet printer of the present invention is applied to a so-called multi-pass inkjet printer has been described in detail. However, the inkjet printer of the present invention includes a line head printer. Any type of ink jet printer can be applied.

It is a top view which shows one Embodiment of the inkjet printer of this invention. It is a schematic block diagram of the inkjet head of the inkjet printer of FIG. It is a schematic block diagram which shows the other example of the inkjet head of the inkjet printer of FIG. It is explanatory drawing of the nozzle of the inkjet head of FIG. It is a block diagram of the control apparatus provided in the inkjet printer of FIG. FIG. 6 is a block diagram of the drive pulse generation circuit of FIG. 5. It is explanatory drawing of the waveform memory of FIG. It is a block diagram of the selection part which connects a drive pulse to an actuator. It is explanatory drawing of a drive pulse production | generation. It is a block diagram of one system | strain of the current amplification part of FIG. It is a block diagram of the other system | strain of the current amplification part of FIG. It is a flowchart which shows the logic of a drive pulse production | generation and selection switch control. 4 is a timing chart of drive pulses and actuator charging potential according to an embodiment of the inkjet printer of the present invention.

Explanation of symbols

  1 is an inkjet printer, 20 is an inkjet head, 21 is a diaphragm, 22 is an actuator, 23 is a cavity, 24 is a nozzle, 60 is a host computer, 62 is a control unit, 70 is a drive pulse generation circuit, 707 is a current amplification unit, a is a print medium, Tr1 and Tr2 are transistors

Claims (4)

An actuator corresponding to the nozzle is provided, a drive waveform signal is supplied to two transistors connected in a push-pull manner, and an output from the transistor is applied to the actuator as a drive pulse. An ink jet printer for discharging,
Drive pulse generating means for generating the drive pulse in which the voltage value is increased or decreased stepwise by adding / subtracting in units of operation of the clock signal for setting the timing for adding / subtracting the waveform data defining the voltage value;
A selection switch arranged for the actuator, the actuator being intermittently connected to the drive pulse;
Selection switch control means for controlling the on / off of the selection switch at a timing different from that of other selection switches with respect to the selection switch within one cycle of the clock signal ;
An ink jet printer comprising:   2. The ink jet printer according to claim 1, wherein the selection switch control means sets the cutoff start timing of the selection switch after the timing when the charging potential of the actuator reaches a predetermined value.   3. The ink jet printer according to claim 1, wherein the intermittent timing is set so that a connection time of the selection switch by the selection switch control means does not overlap with a connection time of other selection switches. Drive pulse generation means for generating drive pulses that increase or decrease in voltage stepwise by adding and subtracting in units of clock signals that set the timing for adding and subtracting waveform data that defines voltage values to actuators corresponding to nozzles And a selection switch that is arranged with respect to the actuator and intermittently switches the actuator to the drive pulse, and supplies a drive waveform signal to two transistors that are push-pull connected, and outputs from the transistor as the drive pulse. In an inkjet printer that ejects ink droplets from the corresponding nozzles by applying to the actuator,
An ink jet printer driving method comprising: controlling the selection switch on / off at a timing different from that of another selection switch within one cycle of the clock signal .

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