JP2006076047A - Droplet ejector and droplet ejection control method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce power consumption by simplifying the constitution of a drive circuit for ejecting a droplet, and to easily adjust the gradation of each nozzle by using low electric power. <P>SOLUTION: This droplet ejector is equipped with a droplet ejection head which comprises an actuator 122 for ejecting the droplet from a nozzle by changing pressure of a pressure chamber by the input of a driving signal, and a drive control means for driving and controlling the actuator. The drive control means comprises a reference driving signal generating part which outputs a reference driving signal for the generation of the droplet to the actuator, a gradation signal generating part which generates a plurality of gradation signals for controlling the amount of the ejected droplet, and a gradation signal selecting part which selects the gradation signal, corresponding to specified gradation data, from among the plurality of gradation signals generated by the gradation signal generating part. The reference driving signal, which is output from the reference signal generating part, and the gradation signal, which is selected by the gradation signal selecting part, are supplied to different input ends of the actuator. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a droplet discharge device such as an ink jet printer and a droplet discharge control method.

An ink jet printer, which is one of droplet discharge devices, forms an image on a predetermined recording medium by discharging ink droplets (droplets) from a plurality of nozzles formed on a recording head. As this recording head, there is known a recording head in which pressure fluctuation is generated in a pressure chamber communicating with a nozzle by an actuator, and ink droplets are ejected from a nozzle opening.
Various systems have been proposed as such a recording head. These methods are roughly classified into a piezo method and a film boiling ink jet method.

In the piezo method, a driving signal is given to a piezo element which is an actuator, so that a vibration plate in the cavity serving as a pressure chamber is displaced to cause a pressure change in the cavity, and the ink change is ejected from the nozzle by the pressure change. I have to.
On the other hand, in the film boiling ink jet system, a micro heater is provided in the cavity, and the ink in the cavity is instantaneously heated to 300 ° C. or more by the micro heater to generate bubbles in a film boiling state. The ink droplets are ejected from the nozzles by the change.

In such a recording head, printing is performed by forming dots by ink droplets ejected from each nozzle landing on the recording medium. However, in this state, only the presence / absence of dots is controlled, and an intermediate gradation such as gray cannot be printed. Therefore, a method of expressing an intermediate gradation by expressing one image with a plurality of dots of 4 × 4, 8 × 8, or the like is used.
If one pixel is expressed by a 4 × 4 dot matrix, it is possible to express 17 gray levels. If the pixel resolution is increased, higher gradation can be obtained. However, if the gradation is increased without changing the dot diameter, the area constituting one pixel increases and the substantial resolution decreases.

Further, when the dot diameter is increased, the graininess becomes conspicuous when the number of dots per pixel is reduced at a low density.
Therefore, it is necessary to reduce the dot diameter by reducing the ink droplets.
For this purpose, conventionally, for example, a method is known in which the ink droplets that are contracted after the pressure chamber filled with ink is expanded and then contracted are discharged (see, for example, Patent Document 1).

According to this method, the dot diameter can be reduced and the granularity at a low density can be improved, but there is an unsolved problem that the printing time becomes longer because the ink ejection speed is lowered.
In order to solve this unsolved problem, a plurality of drive signals are input into the actuator to form one ink droplet, and a plurality of drives are set to set the desired ink weight before landing on the recording medium. A method is known in which a signal is applied to an actuator, a desired ink weight is generated before landing on a recording medium, and ink droplets having different weights are ejected from the same nozzle (for example, see Patent Document 2).

In the invention of Patent Document 2, it is difficult to combine a plurality of ink droplets into one ink droplet during ejection.
Therefore, a plurality of drive voltage waveforms corresponding to the ink discharge amount are generated for one nozzle, and one of these is selected by the gradation data signal, so that the size of the dot can be freely changed. A method for improving gradation expression has also been proposed (see, for example, Patent Document 3).
JP-A-55-175589 (first page, FIG. 3) US Pat. No. 5,285,215 (column 4, FIGS. 6-10) JP-A-9-11457 (first page, FIG. 4)

  However, in the conventional example described in Patent Document 3, since a plurality of driving voltage waveforms are generated for one nozzle, the power consumption is several tens of watts depending on the number of nozzles driven simultaneously. Therefore, it is necessary to design the drive circuit with a power transistor or the like that can drive all the nozzles, and to take heat dissipation into consideration. Further, in a configuration in which a plurality of drive voltage waveforms corresponding to the dot diameter are set, it is necessary to make power system drive signals as easy as the required number of gradations. Two power transistors are required for one drive circuit, and if 8 gradations are configured, 16 power transistors are required, which causes an unsolved problem that the circuit configuration becomes very large. is there.

Furthermore, there is an unsolved problem that correction of a change in ink viscosity caused by a change in ambient temperature must be performed for each drive signal in order to stably discharge the dot diameter expressing each gradation. .
Therefore, the present invention has been made paying attention to the unsolved problems of the above-described conventional example, simplifying the configuration of the drive circuit for discharging droplets, reducing power consumption, and for each nozzle. An object of the present invention is to provide a droplet discharge device and a droplet discharge control method capable of easily adjusting gradation with low power.

  According to a first aspect of the present invention, a plurality of pressure chambers filled with a liquid therein, a plurality of nozzles that individually communicate with the pressure chamber and discharge the liquid as droplets, and a pressure signal input to the pressure chamber. In a droplet discharge apparatus including a droplet discharge head having an actuator that changes the pressure to discharge a droplet from the nozzle and a drive control unit that drives and controls the actuator, the drive control unit includes the droplet A reference drive signal generating unit that outputs a reference drive signal for generating a signal to the actuator, a gradation signal generating unit that generates a plurality of gradation signals for controlling the ejection amount of the droplets, and the gradation signal generating unit A gradation signal selection unit that selects a gradation signal corresponding to the designated gradation data from the plurality of gradation signals generated by the reference signal, the reference drive signal output from the reference signal generation unit, and the floor Adjustment signal Gradation signal selected by the selecting section is characterized by being configured to provide a different input terminal of said actuator.

  According to the first aspect of the present invention, the gradation signal selecting unit selects the reference driving signal for generating the droplet formed by the reference driving signal generating unit and the plurality of gradation signals generated by the gradation signal generating unit according to the gradation data. One gradation signal is supplied to a different input terminal of the actuator, and the actuator is driven by the difference between the reference drive signal and the gradation signal, so that the gradation signal becomes a voltage value corresponding to the gradation change. In addition, a large breakdown voltage is not required on the drive circuit side, a plurality of gradation signal generation circuits can be arranged in a small size, and the overall configuration of the drive circuit can be miniaturized and power can be saved. .

According to a second aspect, in the first aspect, the gradation signal generation unit is configured to generate a plurality of gradation signals that control an amplitude amount of the reference drive signal in synchronization with the reference drive signal. It is characterized by having.
In the second aspect of the invention, since the gradation signal generator generates a plurality of gradation signals for controlling the amplitude of the reference drive signal, the gradation signal can be set to the voltage value corresponding to the gradation change, and the drive A large breakdown voltage is not required on the circuit side, and a plurality of gradation signal generation circuits can be arranged in a small size.

  According to a third aspect, in the first or second aspect, the gradation signal generation unit is configured to change the amplitude of the reference drive signal from the offset unit from the waveform data of one gradation signal serving as a reference of the gradation signal. A waveform data selection unit that separates the waveform unit that controls the waveform, and an adder that adds a gradation value that provides a desired gradation amount to each of the waveform units separated by the waveform data selection unit. It is characterized by being.

In the third aspect of the invention, the waveform data of one gradation signal serving as a reference of the gradation signal is separated into an offset part and a waveform part for controlling the amplitude change of the reference drive signal by the waveform data selection part, A plurality of gradation signals can be easily formed by adding desired gradation values to the separated waveform portions with an adder.
In a fourth aspect based on the third aspect, the waveform data selection unit stores the waveform formation data of the gradation signal in a storage element corresponding to a predetermined address, and reads out from the waveform memory And a coincidence comparator for detecting a coincidence between the address of the waveform forming data and the address of the necessary waveform forming data, and is necessary among the offset part and the waveform part based on the comparison result of the coincidence comparator. It is characterized by being configured to select whichever one.

In the fourth aspect of the invention, the coincidence comparator detects the coincidence between the address of the waveform forming data read from the waveform memory and the address of the necessary waveform forming data, and when the two do not coincide, the offset portion is selected. When the waveform portions are selected when they match, a plurality of different gradation signals synchronized with the reference gradation signal can be accurately formed.
According to a fifth aspect of the invention, in any one of the first to fourth aspects of the invention, the reference drive signal generator includes a temperature detection unit that detects an ambient temperature, and a temperature detected by the temperature detection unit. And a reference drive signal correcting means for correcting the reference drive signal waveform based on the above.

In the fifth aspect of the invention, the ambient temperature is detected by the temperature detecting means, and the reference drive signal waveform is corrected by the reference signal correcting means based on the detected temperature, so that it responds to changes in the ejection characteristics of the droplets due to changes in the ambient temperature. The optimum reference drive signal waveform can be formed.
According to a sixth aspect of the present invention, a plurality of pressure chambers filled with a liquid therein, a plurality of nozzles individually communicating with the pressure chamber and ejecting the liquid as droplets, and a pressure signal input to the pressure chamber. An actuator that discharges droplets from the nozzles by changing the pressure; and a drive control unit that drives and controls the actuators, and the actuators are driven and controlled by the drive control unit, whereby droplets are ejected from the plurality of nozzles. In a droplet discharge control method for discharging,
A reference drive signal generating step for generating a reference drive signal for generating the droplet for the actuator; a gradation signal generating step for generating a plurality of gradation signals for controlling the discharge amount of the droplet; and the gradation signal generation A gradation signal selection step for selecting a gradation signal corresponding to the specified gradation data from the plurality of gradation signals generated in the step; and the gradation signal selected in the reference drive signal and the gradation signal selection step Are supplied to different input terminals of the actuator, and the amplitude of the drive signal applied to the actuator is controlled by throwing it into the gradation data.

  In the sixth invention, as in the first invention described above, the reference drive signal for generating a droplet and one gradation signal selected from a plurality of gradation signals by gradation data are input differently from the actuator. By driving the actuator with the difference between the reference drive signal and the gradation signal, the gradation signal can be set to the voltage value corresponding to the gradation change, and a large withstand voltage is required on the drive circuit side. Accordingly, a plurality of gradation signal generation circuits can be arranged in a small size, and the overall configuration of the drive circuit can be reduced in size and power can be saved.

Hereinafter, embodiments of a droplet discharge apparatus and a droplet discharge control method of the present invention will be described with reference to the drawings.
FIG. 1 is a perspective view showing a schematic configuration when the liquid droplet ejection apparatus according to the first embodiment of the present invention is applied to an ink jet printer.
In the drawing, reference numeral 1 denotes an ink jet printer. The ink jet printer 1 includes an apparatus main body 2, and a tray 21 on which a recording paper P as a recording medium is placed on the upper rear side, and the recording paper P is ejected on the lower front side. A discharge port 22 is provided, and an operation panel 7 is provided on the upper surface.

The operation panel 7 is composed of, for example, a liquid crystal display, an organic EL display, an LED lamp, etc., and a display unit (not shown) for displaying a liquid crystal message and the like, and an operation unit (not shown) composed of various switches and the like. And.
Further, inside the apparatus main body 2, mainly, a printing apparatus 4 including a reciprocating printing unit 3, a paper feeding apparatus 5 that feeds recording paper P one by one to the printing apparatus 4, the printing apparatus 4, and paper feeding And a control device 6 for controlling the device 5.

  Under control of the control device 6, the paper feeding device 5 intermittently feeds the recording paper P one by one. The recording paper P passes near the lower part of the printing unit 3. At this time, the printing unit 3 reciprocates in a direction substantially orthogonal to the feeding direction of the recording paper P, and printing on the recording paper P is performed. That is, the reciprocation of the printing unit 3 and the intermittent feeding of the recording paper P become the main operation direction and the sub operation direction in printing, and ink jet printing is performed.

The printing apparatus 4 includes a printing unit 3, a carriage motor 41 that serves as a driving mechanism for moving the printing unit 3 in the main scanning direction, and a reciprocating mechanism 42 that reciprocates the printing unit 3 in response to the rotation of the carriage motor 41. It has.
The printing unit 3 includes a plurality of head units 35 corresponding to the type of ink having a plurality of nozzles 110 at a lower portion thereof, a plurality of ink cartridges 31 that supply ink to each head unit 35, and each head unit 35 and ink. And a carriage 32 on which the cartridge 31 is mounted.

Further, the head unit 35 includes a large number of ink jet recording heads (droplet discharge heads) 100 as shown in FIG.
As shown in FIG. 2, the inkjet head 100 includes a vibration plate 121, a piezoelectric actuator 122 that displaces the vibration plate 121, and a liquid ink inside, and the internal pressure is reduced by the displacement of the vibration plate 121. A cavity (pressure chamber) 123 that is increased or decreased, and a nozzle 124 that communicates with the cavity 123 and discharges ink as droplets by increasing or decreasing the pressure in the cavity 123 are provided.

More specifically, the inkjet head 100 includes a nozzle substrate 125 on which nozzles 124 are formed, a cavity substrate 126, a vibration plate 121, and a stacked piezoelectric actuator 122 in which a plurality of piezoelectric elements 127 are stacked. Yes.
The cavity substrate 126 is formed in a predetermined shape as shown in the figure, whereby a cavity 123 and a reservoir 128 communicating with the cavity 123 are formed. The reservoir 128 is connected to the ink cartridge 31 via the ink supply tube 129.

The piezoelectric actuator 122 includes comb-shaped electrodes 131 and 132 arranged opposite to each other, and piezoelectric elements 127 arranged alternately with the comb teeth of the electrodes 131 and 132. Further, one end of the piezoelectric actuator 122 is joined to the diaphragm 121 via the intermediate layer 130 as shown in FIG.
In the piezoelectric actuator 122 having such a configuration, a mode in which the actuator is extended or contracted in the vertical direction as shown in FIG. 2 by a drive signal from a drive signal source applied between the first electrode 131 and the second electrode 132. Is used. The piezoelectric actuator 122 is characterized in that a large driving force can be obtained because the piezoelectric elements 127 are laminated.

Therefore, in the piezoelectric actuator 122, when a drive signal as shown in FIG. 2 is applied, the diaphragm 121 is displaced, the pressure in the cavity 123 changes, and an ink droplet is ejected from the nozzle 124. .
The nozzles 124 for each inkjet head 100 formed on the nozzle substrate 126 shown in FIG. 2 are arranged, for example, as shown in FIG. In the example of FIG. 3, the arrangement pattern of the nozzles 124 when applied to four colors of ink (yellow Y, magenta M, cyan C, black K) is shown.

  The head unit 35 is shown in FIG. 1 as including the ink cartridge 31, but is not limited to such a configuration. For example, the ink cartridge 31 may be separately fixed and supplied to the head unit 35 by a tube or the like. Accordingly, in the following description, a unit provided with a plurality of inkjet heads 100 each including a diaphragm 121, an electrostatic actuator 122, a cavity 123, a nozzle 124, and the like separately from the printing unit 3 will be referred to as a head unit. .

  Note that full-color printing can be performed by using an ink cartridge 31 filled with ink of four colors, yellow, magenta, cyan, and black. In this case, the print unit 3 is provided with a head unit 35 corresponding to each color. Here, FIG. 1 shows four cartridges 31 corresponding to four colors of ink, but the printing unit 3 is further provided with ink cartridges 31 of other colors such as light cyan, light magenta, and dark yellow. It may be configured.

The reciprocating mechanism 42 includes a carriage guide shaft 422 supported at both ends by a frame (not shown), and a timing belt 421 extending in parallel with the carriage guide shaft 422.
The carriage 32 is supported by the carriage guide shaft 422 of the reciprocating mechanism 42 so as to be reciprocally movable, and is fixed to a part of the timing belt 421.

  When the timing belt 421 travels forward and backward via a pulley by the operation of the carriage motor 41, the printing unit 3 is reciprocated by being guided by the carriage guide shaft 422. During this reciprocation, ink is appropriately discharged from the nozzles 124 of the plurality of inkjet heads 100 in the head unit 35 corresponding to the image data to be printed (print data, droplet discharge control information), and recording is performed. Printing on the paper P is performed.

The sheet feeding device 5 includes a sheet feeding motor 51 serving as a driving source thereof, and a sheet feeding roller 52 that is rotated by the operation of the sheet feeding motor 51.
The paper feed roller 52 includes a driven roller 52 a and a drive roller 52 b that are vertically opposed to each other with the recording paper P sandwiched by the recording paper P feed path. The drive roller 52 b is connected to the paper feed motor 51. As a result, the paper feed roller 52 can feed a large number of recording sheets P set on the tray 21 one by one toward the printing apparatus 4. Instead of the tray 21, a configuration may be adopted in which a paper feed cassette that stores the recording paper P can be detachably mounted.

The control device 6 performs a printing process on the recording paper P by controlling the printing device 4, the paper feeding device 5, and the like based on print data input from a host computer 60 such as a personal computer or a digital camera. It is.
As shown in FIG. 4, the control device 6 receives the print data input from the host computer 60 and executes print processing based on the print data input from the input interface unit 61. For example, a control unit 62 configured by a microcomputer, 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, and a head driver 65 that drives and controls the head unit 35. The output signals of the drivers 63, 64 and 65 are converted into control signals used by the external carriage motor 41, the paper feed motor 51 and the head unit 35 and output, and the temperature at which the ambient temperature of the printing unit 3 is detected. Controls the temperature detection value detected by the temperature sensor 66 as detection means. Output interface unit 67 to be input to 62, and a temperature correction amount storage unit 68 composed of, for example, non-volatile memory for storing a temperature correction amount will be described later.

  Here, the control unit 62 includes a CPU (Central Processing Unit) 62a that executes various processes such as a printing process, and a data storage area (not shown) for print data input from the host computer 8 via the input interface unit 61. EEPROM (Electrically Erasable Programmable Read-Only Memory) 62b which is a kind of non-volatile semiconductor memory stored in the memory and various data temporarily when executing print data print processing or the like, or an application program such as print processing At least a RAM (Random Access Memory) 62c and a ROM (Read-Only Memory) 62d composed of a nonvolatile semiconductor memory for storing a control program executed by the CPU 62a.

Although not shown, the control unit 62 is electrically connected to various sensors capable of detecting, for example, the remaining amount of ink in the ink cartridge 31, the position of the printing unit 3, the printing environment such as humidity, and the like.
When the control unit 62 obtains print data from the host computer 60 via the input interface unit 61, the control unit 62 stores the print data in the EEPROM 62b. The CPU 62a executes predetermined processing on the print data, and outputs control signals to the drivers 63 to 65 based on the processing data and input data from various sensors. When control signals are output from the drivers 63, 64, and 65, these are converted into drive signals by the output interface unit 67, and the piezoelectric actuators 122 corresponding to the plurality of inkjet heads 100 of the head unit 35 and the printing device 4. The carriage motor 41 and the paper feeding device 5 are operated to execute printing processing on the recording paper P.

  Further, the control unit 62 writes write enable signals DENb and DENt to write waveform forming data DATAb and DATAt for forming a reference drive signal and a gradation signal, which will be described later, into waveform memories 701 and 811 which will be described later. The write clock signals WCLKb and WCLKt and the write address data A0 to A3 and B0 to B3 of the waveform memories 701 and 811 are output to write, for example, 16-bit waveform forming data DATAb and DATAt to the waveform memories 701 and 811. In addition, read address data A0 to A3 and B0 to B3 for reading the waveform forming data DATAb and DATAt stored in the waveform memories 701 and 811 and the waveform forming data read from the waveform memories 701 and 811 are read. The first clock that sets the latch timing To output clock signal ACLK and BCLK, the clear signal CLER to clear the second clock signal CLK and the latch data for setting the timing for adding the latched waveform data to the head driver 65.

  The head driver 65 includes a reference drive signal generation circuit 70 as a reference drive signal generation unit that forms a reference drive signal COM, and a plurality of, for example, four gradation signals VS0 to VS3 based on one reference gradation signal. A gradation signal generation circuit 80 as a gradation signal generation unit to be generated, and an oscillation circuit 90 that outputs a clock signal SCK for selecting the reference drive signal COM and the gradation signals VS0 to VS3 are provided.

  As shown in FIG. 5, the reference drive signal generation circuit 70 stores waveform forming data DATAb for generating a reference drive signal 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 read from the waveform memory 701 by the first clock signal ACLK described above, and an output of the latch circuit 702 and waveform generation data WDATA output from a latch circuit 704 described later. , A latch circuit 704 that latches the addition output of the adder 703 by the second clock signal CLK described above, and converts the waveform generation data WDATA output from the latch circuit 704 into an analog signal D / A converter 705 to be output and the output from the D / A converter 705 A voltage amplifier 706 amplifies the voltage log signal, and a current amplifier 707 for outputting the voltage reference driving signal COM output signal by the current amplification of the amplifier portion 706. 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. 6, the gradation signal generation circuit 80 receives waveform forming data DATAt for generating gradation signals input from the control unit 62 in a configuration similar to that of the reference drive signal generation circuit 70 at a predetermined address. A reference gradation signal generation unit 81 having a waveform memory 811 for storing in a storage element corresponding to the reference element, and generating a reference gradation signal, and a waveform read from the waveform memory 811 of the reference gradation signal generation unit 81 A waveform data selection unit 82 that separates the formation data WD into an offset part and a waveform part, and an offset signal that generates a grayscale signal VS0 consisting of only the offset signal based on the offset part separated by the waveform data selection part 82 A gradation signal VS similar to the reference gradation signal VS1 generated by the reference gradation signal generation section 81 based on the waveform section separated by the generation section 83 and the waveform data selection section 82. And it is composed of a gray scale signal generator 84 and 85 to form the VS3.

The reference gradation signal generation unit 81 stores waveform forming data DATAt for generating a gradation signal input from the control unit 62 in a storage element corresponding to a predetermined address B0 to B3, and this waveform memory 811 The latch circuit 812 that latches the waveform forming data read from the waveform memory 811 by the first clock signal BCLK described above, and the output of the latch circuit 812 and the waveform generation data WDATA output from the latch circuit 814 described later are added. An adder 813 for latching, a latch circuit 814 for latching the addition output of the adder 813 with the second clock signal CLK described above, and a D / D for converting the waveform generation data WDATA output from the latch circuit 814 into an analog signal. A converter 815 and the analog signal output from D / A converter 815 are A voltage amplifier 816 that amplifies, and a current amplifier 817 for outputting the voltage reference driving signal COM output signal by the current amplification of the amplifier portion 816. Here, the clear signal CLER output from the control unit 62 is input to the latch circuits 812 and 814, and the latch data is cleared when the clear signal CLER is turned off. The reference gradation signal VS1 that is finally output from the current amplification unit 817 is adjusted in advance so as to output the predetermined offset voltage V _OFF by adding the data in the waveform memory 811, and the drive waveform is not output. During the period, the offset voltage V _OFF is output.

Further, as shown in FIG. 7, the waveform data selection unit 82 reads out the read address numbers B0 to B3 from the waveform memory 811 of the reference gradation signal generation unit 81 and the desired address numbers B0 to B3 set by the control unit 62. Match comparators 821a to 821d that output, for example, a comparison signal of logical value “1” when both match, and OR gates to which comparison signals output from these match comparators 821a to 821d are input 822, the output signal of the OR gate 822 is input to one input side, the first clock signal BCLK is inverted by the inverter 823 and input to the other input side, and the output signal of the OR gate 822 is input An OR gate 825 in which the output signal of the inverter 823 is input to one input side and the OR gate 82 to the other input side. And the output signal of the AND gate 826 is input to the clock input terminal CK, and the output signal of the AND gate 826 is reset. A latch circuit 827 composed of a D-type flip-flop input to the terminal, and waveform data WD0 to WD3 of each address B0 to B3 read from the waveform memory 811 are latched on one input side and on the other input side And AND gates 828a to 828d to which an output signal output from the NOTQ output terminal 827 is input. Then, the selection data signal Ds indicating whether the state is the offset portion or the waveform portion is output from the output terminal Q of the latch circuit 827 to the gradation signal generation portions 84 and 85, and is output from the AND gates 828a to 828d. The offset waveform data WD _OFF is output to the offset signal generator 83.

Further, the offset signal generation unit 83 receives the offset waveform data WD _OFF output from the waveform data selection unit 82, latches it with the first clock signal BCLK described above, the output of the latch circuit 832 and the later-described latch circuit 832. An adder 833 for adding the waveform generation data WDATA output from the latch circuit 834, a latch circuit 834 for latching the addition output of the adder 833 by the second clock signal CLK, and the latch circuit 834. A D / A converter 835 that converts the output waveform generation data WDATA into an analog signal, a voltage amplifying unit 836 that amplifies the analog signal output from the D / A converter 835, and a voltage amplifying unit 836 A current amplifying unit 837 that amplifies the output signal and outputs a gradation signal VS0; I have. Here, the clear signal CLER output from the control unit 62 is input to the latch circuits 832 and 834, and the latch data is cleared when the clear signal CLER is turned off.

Further, the gradation signal generation unit 84 receives the selection data signal Ds output from the waveform data selection unit 82 at one input terminal and the gradation value + ΔVH from the gradation value setting unit 840 at the other input terminal. AND gate 841, a sign adjustment circuit 852 for adjusting the sign of the output of the AND gate 841, the output of the sign adjustment circuit 852, and the waveform data input from the waveform memory 811 of the reference gradation signal generation unit 81 described above. An adder 843 that adds WD, a latch circuit 844 that latches the addition output of the adder 843 by the first clock signal BCLK, and a waveform that is output from the latch circuit 844 and a latch circuit 846 described later. An adder 845 that adds the generated data WDATA, and the addition output of the adder 845 is based on the second clock signal CLK described above. Latch circuit 846 for latching, D / A converter 847 for converting waveform generation data WDATA output from latch circuit 846 into an analog signal, and voltage amplification for the analog signal output from D / A converter 847 And a current amplification unit 849 that amplifies the output signal of the voltage amplification unit 848 and outputs a gradation signal VS2. Here, the sign adjustment circuit 842 includes a switch 842a that switches the output of the AND gate 841, and a code converter 842b that multiplies the output value of the AND gate 841 connected to one output terminal of the switch 842a by -1. A switch 842c to which the output of the code converter 842b and the output from the other output terminal of the switch 842a are input, and a switch when the sign of the waveform data input from the waveform memory 811 is positive. And a digital comparator 842d that outputs a selection signal for switching the switches 842a and 842c to the encoder 842b side when the waveform data has a negative sign. Yes. The clear signal CLER output from the control unit 62 is input to the latch circuits 844 and 846. When the clear signal CLER is turned off, the latch data is cleared. Note that the gradation signal VS2 that is finally output from the current amplifier 849 is adjusted in advance so as to output a predetermined offset V _OFF by adding the data in the waveform memory 811, and in a section in which the drive waveform is not output. Offset V _OFF is output.

Further, the gradation signal generation unit 85 is the gradation signal except that the gradation value set by the gradation value setting unit 850 is set to + 2ΔVH and the gradation signal VS3 is output from the current amplification unit 859. The components having the same configuration as that of the generation unit 84 and corresponding parts to the gradation signal generation unit 84 are denoted by reference numerals obtained by adding 10 to the respective reference numerals, and detailed description thereof is omitted.
The input / output interface unit 67 outputs a reference drive signal COM output from the reference drive signal generation circuit 70, a plurality of gradation signals VS0 to VS3 output from the gradation signal generation circuit 80, and the oscillation circuit 90. The clock signal SCLK is output to the head unit 35 as it is, and the drive signal selection signal SLb for each nozzle and the plurality of gradation signals VS0 to VS3 for the reference drive signal COM output from the control unit 62 according to the print data are selected. The gradation signal selection signal SLt for latching and the latch signals LATc and LATt for latching the selection signals SLb and SLt are output to the head unit 35.

  Further, as shown in FIG. 8, the head unit 35 selects whether or not to supply the reference drive signal COM to the first electrode 131 of the piezoelectric actuator 122 corresponding to each nozzle 124 in units of a predetermined number of nozzles. The first selection switch 201 and the second selection switch 202 that selects and supplies any one of the correction signals VS0 to VS3 to the second electrode 132 are provided, and the selection switches 201 and 202 are selectively controlled. A driving signal selection control circuit 210 and a gradation signal selection control circuit 220 as a gradation signal selection unit are included.

  As shown in FIG. 8, the drive signal selection control circuit 210 is supplied with the drive signal selection signal SLb for the predetermined number of piezoelectric actuators 122 from the input / output interface unit 67 as serial data, and sequentially shifts in accordance with the clock signal SCK. A latch circuit 212 that latches the drive signal selection signal SLb stored in the shift register 211 as a parallel signal by the latch signal LATb, and the latch output of the latch circuit 212 is set to a voltage required by the first selection switch 201. And a level shifter 213 for conversion.

  As shown in FIG. 8, the gradation signal selection control circuit 220 is supplied with the gradation selection signal SLt for each piezoelectric actuator 122 output from the input / output interface section 67 as serial data, and shifts sequentially by the clock signal SCK. A register 221, a latch circuit 222 that latches the gradation selection signal SLt stored in the shift register 221 as a parallel signal by the latch signal LATt, and a latch output of the latch circuit 222 is converted to a voltage required by the decoder 224. The level shifter 223 and a decoder 224 that receives the output signal of the level shift 223 and decodes the gradation selection signal SLt for each piezoelectric actuator 122 as the selection signal of the second selection switch 202 are provided.

  Here, for the sake of simplicity, assuming that there are four gradation signals VS0 to VS3 output from the gradation signal generation circuit 80, the second selection switch 202 is shown in FIG. Since there are four switch parts SW1 to SW4, and the gradation selection signal SLt only needs 2 bit data, the decoder 224 selects the binary number data of the gradation selection signal SLt and selects the switch parts SW1 to SW4. Is converted to a quaternary number, and a selection signal that is turned on is output from the corresponding output terminals t1 to t4 to the switch sections SW1 to SW4, thereby making a desired gradation from a plurality of gradation signals VS0 to VS3. A signal can be selected.

  As shown in Table 1 below, the input / output relationship of the decoder 224 is a selection signal for turning on the switch section SW1 when the first bit B1 and the second bit B2 are both “0”. When the first bit B1 is “1” and the second bit B2 is “0”, a selection signal for turning on the switch section SW2 is output, and the first bit B1 is “ When the second bit B2 is "1" and the second bit B2 is "1", a selection signal for turning on the switch unit SW3 is output, and both the first and second bits B1 and B2 are "1". Sometimes a selection signal for turning on the switch section SW4 is output.

  Further, the temperature correction amount storage unit 68 is set with a reference drive signal waveform using as a parameter a temperature for correcting a change in ejection characteristics due to the ambient temperature of each nozzle 124 in each droplet ejection head 100 of the head unit 35. Data is stored. In the data for setting the reference drive signal waveform, the viscosity of the ink generally decreases as the ink temperature increases, and increases as the ink temperature decreases. Therefore, since the ink viscosity decreases as the ambient temperature increases, the flow path resistance in the head unit 35 decreases. For example, in the case of the same discharge pressure in the pressure chamber, the droplet is discharged with a larger amount of droplets when the ambient temperature is 40 ° C. than when the ambient temperature is 25 ° C. On the contrary, when the ambient temperature is lowered, the ink viscosity increases, so that the flow path resistance in the head unit 35 increases. In this case, with the same discharge pressure in the pressure chamber, the droplet is discharged with a smaller droplet amount when the ambient temperature is 10 ° C. than the ambient temperature is 25 ° C. In order to compensate for this, as shown in FIG. 10, the amplitude of the reference drive signal COM is decreased when the ambient temperature increases, and is increased when the ambient temperature decreases, and the discharge pressure is controlled to be appropriate. At this time, the waveform data ΔV 1 to ΔV 3 for each temperature and the output timing of the first clock signal ACLK are stored in the temperature correction amount storage unit 68.

  Then, when the power of the ink jet printer 1 is turned on, the control unit 62 executes the print control process of FIG. 11. First, in step S 1, the temperature detection value detected by the temperature sensor 66 is read, and then in step S 2. Based on the read temperature detection value, the reference drive signal waveform data at the corresponding temperature stored in the temperature correction amount storage unit 68 is selected, and then the process proceeds to step S3 to the waveform memories 701 and 811. The waveform data is written, and then the process proceeds to step S4 to determine whether or not the print data input from the host computer 8 exists. If the print data does not exist, the process jumps to step S17 to be described later and the print data exists. If so, the process proceeds to step S5.

In this step S5, it is determined whether or not one recording sheet P is in the middle of printing. If it is in the middle of printing, the process jumps to step S8 described later, and if it is not in the middle of printing, a new printing sheet P needs to be fed. The process proceeds to step S6, and a paper feed command for the recording paper P is output to the paper feed motor driver 64, and then the process proceeds to step S7.
In this step S7, it is determined whether or not the print start area of the recording paper P has reached the nozzle position of the head unit 35. If the print start area has not reached the nozzle position, the process waits until it reaches, and printing starts. When the region reaches the nozzle position, the process proceeds to step S8, and a 1-bit selection signal is supplied so as to supply the reference drive signal COM to the actuator 122 of the droplet discharge head 100 that discharges ink droplets based on the print data. SLb is output as serial data to the drive signal selection control circuit 210 and the clock signal SCK is output to the drive signal selection circuit 210, and then the process proceeds to step S9.

In step S9, it is determined whether or not the output of the selection signal SLb is completed. If the output of the selection signal SLb is not completed, the process waits until the output is completed, and when the output of the selection signal SLb is completed, the process proceeds to step S10. Then, the latch signal LATb is output to the latch circuit 212 of the reference drive signal selection circuit 210, and then the process proceeds to step S11.
In this step S11, the gradation data for each actuator 122 of the droplet discharge head 100 included in the print data is read, and the read gradation data is converted into 2-bit serial data as the gradation selection signal SLt, and then the nozzle. The serial data is sequentially output to the gradation signal selection circuit 220 in numerical order, and the clock signal SCK is output to the gradation signal selection circuit 220, and then the process proceeds to step S12.

  In step S12, it is determined whether or not the output of the gradation selection signal SLt has been completed. If the output of the gradation selection signal SLt has not been completed, the process waits until this is completed, and the output of the gradation selection signal SLt has been completed. When completed, the process proceeds to step S13, the latch signal LATt is output to the latch circuit 222 of the gradation signal selection circuit 220, and then the process proceeds to step S14.

  In this step S14, a command signal for causing the head driver 65 to output the reference drive signal COM from the reference drive signal forming circuit 70 and to output the gradation signals VS0 to VS3 from the gradation signal forming circuit 80, that is, the waveform memory 701 and The read address 811, the first clock signals ACLK and BCLK, the second clock signal CLK, and the clear signal CLER are output in a predetermined order.

  Next, the process proceeds to step S15, the temperature detection value detected by the temperature sensor 66 is read, and then the process proceeds to step S16 to determine whether or not there is a temperature change that needs to change the reference drive waveform data. If there is no temperature change that requires changing the reference drive waveform data, the process returns to step S4. If there is a temperature change that requires changing the reference drive waveform data, the process returns to step S1.

  On the other hand, if the determination result in step S4 is that there is no print data, the process proceeds to step S17 to determine whether or not it is after starting printing, and if it is after starting printing, the process proceeds to step S18. Thus, serial data for setting all the drive signal selection signals SLb to “0” is output to the drive signal selection control circuit 210, the first selection switches 201 in all the nozzles are turned off, and all the gradations are output. Serial data with the selection signal SLt set to “0” is output to the gradation signal selection control circuit 220, and the second selection switches 202 for all the nozzles are turned off, and then the process proceeds to step S19 to start printing. If not, the process proceeds directly to step S19.

In step S19, it is determined whether or not the printer power supply is cut off. If the printer power supply is on, the process proceeds to step S1. If the printer power supply is off, the printing process is terminated. .
Next, the operation of the first embodiment will be described.
Now, when the power of the inkjet printer 1 is turned on, first, the CPU 62a of the control unit 62 starts execution of the print control process of FIG. At this time, a temperature detection value around the head unit 35 detected by the temperature sensor 66 is read (step S1), and a reference corresponding to the temperature stored in the temperature correction amount storage unit 68 based on the read temperature detection value. The reference drive signal waveform data at the corresponding temperature is selected from the drive signal waveform data (step S2).

Then, the selected reference drive signal waveform data and preset gradation signal waveform data are converted into the waveform of the waveform memory 701 of the reference drive signal generation circuit 70 and the reference gradation signal generation unit 80A of the gradation signal generation circuit 80. Writing into the memory 811 (step S3).
At this time, writing of the reference drive signal waveform data to the waveform memory 701 of the reference drive signal generation circuit 70 outputs 16-bit waveform data DATAb in a state where an address is designated as shown in FIG. The write clock signal WCLKb is output, and the waveform data is stored in the memory elements corresponding to the addresses A0 to A3 of the waveform memory 701 by the generation of the enable signal DENb. At this time, the most significant bit MSB of the waveform data is used as a sign bit representing a positive / negative sign. In this embodiment, the waveform data of “0” is stored in the address A0 of the waveform memory 701, + ΔV1 that sets the initial increase amount of the reference drive signal is set in the address A1, and the initial value of the reference drive signal is set in the address A2. -ΔV2 is set to set the amount of decrease after the increase is finished, and + ΔV3 is set to the address A3 to set the amount of increase in the initial state return after the decrease of the reference drive signal. These are | ΔV1 | = | ΔV2 | , + ΔV1> + ΔV3.

  In the gradation signal generation circuit 80, the waveform memory 811 of the reference gradation signal generation unit 81 designates addresses B0 to B3 and outputs 16-bit waveform data DATAt at the same time as the reference drive signal generation circuit 70. The built-in clock signal WCLKt is output, and then the enable signal DENt is generated, whereby the waveform data is stored in the memory elements corresponding to the addresses B0 to B3 of the waveform memory 811. At this time, the most significant bit MSB of the waveform data is used as a sign bit representing a positive / negative sign. In this embodiment, the waveform data of “0” is stored in the address B0 of the waveform memory 811, + ΔV4 that sets the initial increase amount of the gradation signal is set in the address B1, and the initial value of the gradation signal is set in the address B2. -ΔV5 is set to set the decrease amount after the increase is finished, and + ΔV6 is set to the address B3 to set the initial state return increase amount after the decrease of the gradation signal, and these are | ΔV4 | = | ΔV5 | , + ΔV4> + ΔV6.

  If no print data is input from the external host computer 8 at this time, the process proceeds from step S4 to step S7, and printing is not started. Therefore, the process proceeds to step S19 and the printer power is turned on. Since the process continues, the process returns to step S1 to select the reference drive signal waveform data based on the detected temperature value and write the data into the waveform memory 701 of the reference drive signal generation circuit 70.

In this state, when print data including gradation data is input from the host computer 8 to the control unit 62 via the input inkjet circuit 61, the print data is stored in the EEPROM 62b.
As described above, when the print data is stored in the EEPROM 62b, in the print control process of FIG. 11, the process proceeds from step S4 to step S5, printing of the recording paper P is not started, and the recording paper P is fed. In step S6, a paper feed command is output to the paper feed motor driver 64.

  As a result, the paper feed motor 51 is driven to rotate to start feeding only one sheet of the recording paper P placed on the tray 21 to the printing unit 3. When the print start area of the recording paper P reaches the nozzle position of the head unit 35, the process proceeds to step S8, and a 1-bit reference is sent to the actuator 122 that ejects ink droplets based on the print data. The drive signal selection signal SLb is sequentially output as serial data to the reference drive signal selection control circuit 210 for each nozzle, and the clock signal SCK is output to the reference drive signal selection control circuit 210.

  Therefore, when the reference drive signal selection signal SLb is sequentially stored in the shift register 211 of the reference drive signal selection control circuit 210 and the reference drive signal selection signals SLb of all the nozzles 124 are stored, the latch signal LATb is output. The reference drive signal selection signal SLb is latched in the latch circuit 212, and the latched reference drive signal selection signal SLb is converted to a voltage required for operating the first selection switch 201 by the level shifter, and the first Since the data is supplied to the selection switch 201, the first selection switch 201 corresponding to the nozzle 124 that ejects ink droplets is controlled to be in an ON state based on the print data.

Next, the gradation selection signal for selecting the gradation signal corresponding to each nozzle is sequentially read based on the gradation data included in the print data, converted into a 2-bit gradation selection signal SLt, and sequentially converted into serial data. Are output to the gradation signal selection control circuit 220, and the clock signal SCK is output to the gradation signal selection control circuit 220 (step S11).
When the serial data gradation selection signal SLt and the clock signal SCK are input to the gradation signal selection control circuit 220, the serial data is sequentially stored in the shift register 221 in accordance with the clock signal SCK, and the gradation selection signals of all the nozzles. When SLt is stored in the shift register 221, a latch signal LATt is output, and 2-bit gradation signal selection data corresponding to each nozzle stored in the shift register 221 is latched and latched in the latch circuit 222, respectively. The gradation signal selection data is supplied to the level shifter 223, converted into a voltage that can be handled by the decoder 224, and supplied to the decoder 224.

For this reason, if the decoder 224 has, for example, four gradation correction signals VS0 to VS3, one of the switch units SW1 to SW4 corresponding to the gradation selection signal SLt is selected and is controlled to be turned on. Is done.
In this manner, when the setting of the reference drive signal selection signal SLb for the reference drive signal selection control circuit 210 is completed and the setting of the gradation selection signal SLt for the gradation signal selection control circuit 220 is completed, the process proceeds to step S14. A signal output command for outputting the reference drive signal COM and the gradation signals VS0 to VS3 is output to the head driver 65.

  When this signal output command is input to the head driver 65, the reference drive signal forming circuit 70 performs reading processing of the waveform data stored in the waveform memory 701. In this embodiment, the case where the reference drive signal selection signal SLb is composed of 1 bit and the gradation selection signal SLt is composed of 2 bits has been described. However, the present invention is not limited to this. A plurality of waveforms may be provided in time series and may be selected from each other by a selection signal of several bits.

In the waveform data reading process, first, as shown in FIG. 13A, the clear signal CLER is output from the control unit 62 to the reference drive signal generation circuit 70 at time t1, and the reference drive signal generation circuit 70 After the latch data of the latch circuits 702 and 704 are cleared, predetermined addressing is performed and the desired offset voltage V _{0FF (COM)} of the reference drive signal COM is set. Next, at time t2, as shown in FIG. 13D, the second clock signal CLK is supplied to the latch circuit 704 of the reference drive signal generation circuit 70. At this time, new addressing is performed. Therefore, the reference drive signal COM output from the current amplifier 707 maintains the offset voltage V _{OFF (COM)} as shown in FIG.

Next, when the address A1 is designated by the control unit 62 at time t3 and then the first clock signal ACLK rises as shown in FIG. 13C at time t4, the address A1 read from the waveform memory 701 is read. The waveform data + ΔV1 is latched by the latch circuit 702, which is supplied to the adder 703. Since the latch output of the latch circuit 704 to which the adder 703 is input maintains the offset voltage V _{OFF (COM)} , the addition is performed. The added value of the unit 703 is a value obtained by adding + ΔV1 to the offset voltage V _{OFF (COM)} , and this added value is latched by the latch circuit 704 at the time t5 when the second clock signal CLK rises, and the V _{OFF is} output from the latch circuit 704. _(COM) Reference drive signal waveform data WDATA of + ΔV1 is output.

For this reason, the reference drive signal waveform data WDATA is converted into an analog signal by the D / A converter 705, voltage amplified by the voltage amplifier 706, current amplified by the current amplifier 707, and output as the reference drive signal COM. , And supplied to the first electrode 131 as one input end of the actuator 122.
Thereafter, at time t6, the address of the waveform memory 701 is changed to A0. However, since the first clock signal ACLK does not rise, the latch circuit 702 maintains the previous latch signal, so that the above-described time t5 is reached. When the reference drive signal waveform data becomes V _{OFF (COM)} + ΔV1 at the time of latching of the latch circuit 704, the addition value of the adder 702 is V _{OFF (COM)} + 2ΔV1, which is the second clock signal CLK. Is latched by the latch circuit 704 at the time t7 when the signal rises, and the reference drive signal waveform data WDATA of + 2ΔV1 is output from the latch circuit 704 as shown in FIG.

Thereafter, the latch circuit 704 latches at t8 when the second clock signal CLK rises, so that the reference drive signal waveform data WDATA becomes V _{OFF (COM)} + 3ΔV1 as shown in FIG. 13E, and then at time t9. When the first clock signal ACLK rises, the waveform data “0” at the address A0 is latched by the latch circuit 702. However, since the waveform data is “0”, the addition value of the adder 703 is not changed. This state continues until time t13.

In the meantime, address data A2 is output at time t11, waveform data of -ΔV2 is read from the waveform memory 701, and this is latched in the latch circuit 702 when the first clock signal ACLK rises at time t14.
For this reason, the output of the adder 703 becomes V _{OFF (COM)} + 3ΔV1−ΔV2, which is latched by the latch circuit 704 at the time t15 when the second clock signal CLK rises, so that the reference drive signal waveform data WDATA is shown in FIG. The reduction starts as shown in (e).

Thereafter, the reference drive signal waveform data WDATA and the reference drive signal COM continue to decrease until time t19, and the waveform data “0” at address A0 is latched by the latch circuit 702 at time t20, so that the reference drive signal waveform data The decrease stops from the decrease state of WDATA and the reference drive signal COM.
Thereafter, the address data A3 is output at time t22, and the waveform data of + ΔV3 is read from the waveform memory 701, and this is latched in the latch circuit 702 when the first clock signal ACLK rises at time t24.

For this reason, the output of the adder 703 becomes V _{OFF (COM)} + 3ΔV1−4ΔV2 + ΔV3, which is latched by the latch circuit 704 at the time tt25 when the second clock signal CLK rises, whereby the reference drive signal waveform data WDATA is shown in FIG. As shown in (e), the increase starts, and + ΔV3 is further added at time t27.
At time t26 during this period, address data A0 is output, and waveform data “0” is read from the waveform memory 701. This is latched in the latch circuit 702 by the rise of the first clock signal ACLK at time t28.

For this reason, the output of the adder becomes V _{OFF (COM)} + 3ΔV1−4ΔV2 + 2ΔV3, and returns to the same offset voltage V _{OFF (COM)} between the time points t1 and t4.
On the other hand, in the gradation signal generation circuit 80, the time points t3, t6, t11, t16, t22 when the address data A1, A0, A2, A0, A3, and A0 are output in synchronization with the generation of the reference drive signal COM described above. Address data B1, B0, B2, B3, and B0 are output at t26 and t26, and the first clock signal BCLK is synchronized with the first clock signal ACLK at times t4, t9, t14, t20, t24, and t28. As a result, the reference gradation signal generator 81 and the gradation signal generators 84 and 85 output gradation signals VS1 to VS3 similar to the reference drive signal COM and the gradation signal VS0 that maintains the offset value. The

Here, the gradation signal VS1 output from the reference gradation signal generation unit 81 outputs the clear signal CLER from the control unit 62 to the gradation signal generation circuit 80 at time t1, as shown in FIG. 13 (j). Then, after the latch data of the latch circuits 812 and 814 of the reference gradation signal generation unit 81 is cleared, predetermined addressing is performed and the desired offset voltage V _0FF of the gradation signal VS1 is set. Next, at time t2, as shown in FIG. 13D, the second clock signal CLK is supplied to the latch circuit 814 of the reference gradation signal generation unit 81. At this time, new addressing is performed. Therefore, the gradation signal VS1 output from the current amplifying unit 817 maintains the offset voltage V _OFF as shown in FIG.

Next, at time point t3, the address B1 is designated by the control unit 62. After that, when the first clock signal BCLK rises as shown in FIG. 13G at time point t4, the address B1 read from the waveform memory 811 is read. The waveform data + ΔV4 is latched by the latch circuit 812, which is supplied to the adder 813. Since the latch output of the latch circuit 814 input to the adder 813 maintains the offset voltage V _OFF , The added value becomes a value V _OFF + ΔV4 obtained by adding the waveform data + ΔV4 of the address B1 to the offset voltage V _{OFF (COM)} , and this added value is latched by the latch circuit 814 at time t5 when the second clock signal CLK rises.

Further, at time t7, the waveform data + ΔV4 is added to obtain V _OFF + 2ΔV4, and at time t8, the waveform data + ΔV4 is added to obtain V _OFF + 3ΔV4. This state continues until time t14, and then the waveform at address B2 at time t15. By subtracting data −ΔV5 to obtain V _OFF + 3ΔV4−ΔV5, and subsequently subtracting waveform data −ΔV5 at time t17, time t18 and time t19, V _OFF + 3ΔV4−4ΔV5 becomes the minimum value at time t19. After this state is continued until time t24, the waveform data + ΔV6 of address B3 is added at time t25 to become V _OFF + 3ΔV4-4ΔV5 + ΔV6, and then waveform data + ΔV6 is added at time t27 to become V _OFF + 3ΔV4-4ΔV5 + 2ΔV6. It returns to the same offset value V _OFF as in t4.

The gradation signal generation unit 84 (or 85) is the same as the reference gradation signal generation unit 81 except that the gradation value + ΔVH (or + 2ΔVH) is added to the waveform data + ΔV5 read from the waveform memory 811. The gradation signal VS2 (or VS3) shown in FIG. 13 (i) (or (h)) is generated by performing the gradation signal generation process.
At this time, the gradation signal generators 84 and 85 add the gradation values + ΔVH and + 2ΔVH to the waveform data WD read from the waveform memory 811 by the adders 843 and 853, so that the waveform data is −ΔV5. Thus, when the sign is negative, the sign adjustment circuits 842 and 852 cause the gradation values + ΔVH and + 2ΔVH to be inverted and input to the adders 843 and 853 via the encoders 842b and 852b. The gradation signals VS2 and VS3 having the amplitude corresponding to the gradation values + ΔVH and + 2ΔVH can be generated.

As described above, when the reference drive signal COM and the gradation signals VS0 to VS3 synchronized with each other are output from the reference drive signal generation circuit 70 and the gradation signal generation circuit 80, these are the actuators of the recording heads 100 of the head unit 35. 122 is applied to the first selection switch 201 and the second selection switch 202.
For this reason, in the actuator 122 of the recording head 100 that ejects ink droplets based on print data, the first selection switch 201 is controlled to be in the ON state, and the switch in the second selection switch 202 is set according to the gradation data. Any of the units SW1 to SW4 is controlled to be in an on state.

  Therefore, the reference drive signal COM is supplied to the first electrode 131 of the actuator 122, and any one of the grayscale signals VS0 to VS3 is supplied to the second electrode 132. Therefore, as shown in FIG. 14, the drive signal applied to the actuator 122 is a pull-push-pull drive waveform provided with an intermediate potential assuming an inkjet head 100 using a piezoelectric element, as shown by a thin solid line. , Represented by the difference between the reference drive signal COM shown in bold lines and the grayscale signals VS0 to VS3 shown in broken lines, and when the grayscale signal VS0 is selected, the drive signal waveform has the maximum amplitude, whereas the grayscale signal VS1 , VS2 and VS3 in the order of the drive signal waveform.

The relationship between the voltage of the drive signal of the actuator 122 and the weight of the ink droplet ejected from the nozzle 124 is that, as shown in FIG. 15, the ink droplet weight increases as the drive voltage increases. As described above, by selecting the four kinds of gradation signals VS0 to VS3, dot printing of four gradations can be performed.
In this way, by setting the drive signal supplied to the actuator 122 as the difference between the reference drive signal COM and the gradation signals VS0 to VS3, an accurate drive signal corresponding to the gradation data can be supplied to the actuator 122. .

  In addition, since the actuator 122 is configured to apply a voltage difference between the reference drive signal (large voltage) and the gradation signal (small voltage), an active element having a large withstand voltage is used to generate a plurality of gradation signals. The gradation signal generating circuit 80 can be set compactly without being used. In addition, common gradation signals VS0 to VS3 are generated for the actuators 122 of the ink jet heads 100, and one gradation signal VSi (i = 0 to 3) is individually generated by the second selection switch 202 from each of the actuators. ) Is selected, the circuit configuration can be greatly reduced as compared with the case where a gradation signal is individually generated for each actuator.

Furthermore, in the above embodiment, the temperature in the vicinity of the head unit 35 is detected by the temperature sensor 66, and the reference drive signal waveform data is selected based on the detected ambient temperature of the head unit 35. An optimum reference drive signal can be generated in accordance with a change in ink droplet ejection performance due to the change.
In the above embodiment, the case where the gradation signal generation circuit 80 generates the gradation signals VS0 to VS3 corresponding to four gradations has been described. However, the present invention is not limited to this. The gradation signal generation unit that has the same configuration as the units 84 and 85 and generates a gradation value represented by (j−1) × ΔVH when the number of gradations is j in the gradation value setting circuit. By adding an arbitrary number, it is possible to generate a gradation signal having an arbitrary number of gradations, and according to this, the number of switch sections in the second selection switch 202 of the actuator 122 and the gradation signal selection control circuit 220 The number of output terminals of the decoder 224 may be set.

  In the above embodiment, the case where the reference drive signal selection signal SLb and the gradation signal selection signal SLt are supplied as serial data to the reference drive signal selection control circuit 210 and the gradation signal selection control circuit 220 has been described. However, the present invention is not limited to this, and parallel transmission may be performed. In this case, a shift register for serial-parallel conversion can be omitted.

  Furthermore, in the above embodiment, the case where the ambient temperature of the head unit 35 is detected by the temperature sensor 66 and the waveform data of the reference drive signal is selected based on this is described. However, the present invention is not limited to this. When the temperature change at the installation position of the inkjet printer 1 is small, the selection of the waveform data of the reference drive signal based on the temperature change is omitted, and the reference drive signal is formed based on one reference drive signal waveform data. May be.

  In the above-described embodiment, the case where the inkjet head 100 having the piezoelectric actuator 127 is applied is described. However, the present invention is not limited to this, and the piezoelectric material 301 is made up of the upper and lower electrodes 302 as shown in FIG. , 303 is used to vibrate the diaphragm 121 using a simple structure actuator, and a piezoelectric unimorph actuator 304 using a mode in which it is bent in the vertical direction in FIG. 16 is applied as a vibration mode, as shown in FIG. Thus, electrodes 312 are formed at both ends of the piezoelectric material 311 and pressure chambers 313 are formed. The actuator drives every other nozzle, and when a drive signal is given, the pressure chambers are shown in FIG. Piezo-type having a configuration in which the pressure inside 313 changes and ink liquid is ejected from nozzle 314 When the air mode 1 actuator 315 is applied or as shown in FIG. 18, electrodes 322 and 323 are alternately provided on the surface of the piezoelectric material 321 and when a drive signal is given, the pressure chamber is deformed as shown by the broken line in FIG. For example, a 4-piezo type air mode 2 actuator in which an ink droplet is ejected from the nozzle 325 by changing the pressure in the 324 can be applied.

  In addition to the piezo method, as shown in FIGS. 19 and 20, a heating element 332 and a connection line 334 to the driver 333, an anti-cavitation film 335, a partition wall 336, and a nozzle wall 337 are usually used on a substrate 331. Then, the top plate 338 is joined, the ink is introduced into the reservoir 341 from the ink inlet 340 formed in the top plate 338, this ink is supplied to the pressure chamber 342 surrounded by the nozzle wall 337, and the When the driving signal is transmitted to each heating element 332 disposed in the pressure chamber 340 of the head unit, the heating element 332 instantaneously generates heat at a temperature of 300 ° C. or more, and bubbles are generated on the anti-cavitation film 335 due to film boiling. Ink droplets are ejected from the nozzle holes 339 due to the pressure change, and bubbles are generated immediately after the ink droplets are ejected. Click droplets are ejected, immediately after the ink droplets have been ejected, the bubble can also be applied film boiling ink jet method which is adapted to return to the original state rapidly shrink. In this film boiling ink jet system, a heating element 332 such as a heater is applied as an actuator. A reference drive signal COM is input to one input end of the heating element 332 and a second selection switch 201 is connected to the other input end. By inputting the selected correction signal, the calorific value can be controlled by the differential voltage between the two signals, and gradation setting can be performed for each nozzle.

1 is a perspective view illustrating a schematic configuration of an inkjet printer according to a first embodiment of the present invention. It is sectional drawing which shows the structure of the inkjet head of the inkjet printer shown in FIG. It is a top view which shows the structure of the nozzle substrate of the head shown in FIG. It is a block which shows an example of the control apparatus which can be applied to 1st Embodiment. It is a block diagram which shows an example of a drive signal generation circuit. It is a block diagram which shows an example of a gradation signal generation circuit. It is a block diagram which shows an example of a waveform data selection part. It is a block diagram which shows a reference | standard drive signal selection control circuit and a gradation signal selection control circuit. It is a block diagram which shows the reference drive signal selection control circuit and gradation signal selection control circuit of a nozzle unit. It is a characteristic diagram which shows the reference drive signal waveform which used temperature as a parameter. 6 is a flowchart illustrating an example of a print control processing procedure executed by a control unit of the control device. It is a time chart with which it uses for description of the data writing procedure to the waveform memory. 5 is a time chart for explaining a reference drive signal and a gradation signal. It is explanatory drawing which shows the drive signal applied to the actuator by a reference drive signal and a correction signal. FIG. 6 is a characteristic diagram showing a relationship between a drive voltage of a reference drive signal and an ink discharge weight. It is sectional drawing which shows the unimorph actuator in a piezo type. It is sectional drawing which shows the shear mode 1 actuator in a piezo type. It is sectional drawing which shows the share mode 2 actuator in a piezo system. It is the perspective view which removed the top plate which shows a film boiling ink jet type head unit. It is sectional drawing of FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Inkjet printer, 3 ... Printing part, 4 ... Printing apparatus, 5 ... Paper feeding apparatus, 6 ... Control apparatus, 31 ... Ink cartridge, 32 ... Carriage, 35 ... Head unit, 62 ... Control part, 65 ... Head driver, DESCRIPTION OF SYMBOLS 66 ... Temperature sensor, 68 ... Temperature correction amount memory | storage part, 70 ... Reference | standard drive signal generation circuit, 701 ... Waveform memory, 702, 704 ... Latch circuit, 703 ... Adder, 705 ... D / A changer, 706 ... Voltage amplification 707 ... Current amplifier, 80 ... Gradation signal generation and generation circuit, 81 ... Reference gradation signal generation unit, 811 ... Waveform memory, 812,814 ... Latch circuit, 815 ... D / A converter, 816 ... Voltage amplification , 817 ... current amplifying part, 82 ... waveform data selection part, 821a to 821d ... coincidence comparator, 822, 825 ... OR gate, 823 ... inverter, 824, 826, 8 8a to 828d ... AND gate, 827 ... D-type flip-flop, 83 ... offset signal generation unit, 84, 84 ... gradation signal generation unit, 90 ... oscillation circuit, 100 ... inkjet head, 120 ... electrostatic actuator, 121 ... vibration Plate 122: Piezoelectric actuator 123 ... Cavity (pressure chamber) 124 ... Nozzle 201 ... First selection switch 202 ... Second selection switch 210 ... Reference drive signal selection control circuit 220 ... Correction signal selection Control circuit

Claims (6)

A plurality of pressure chambers filled with liquid therein, a plurality of nozzles individually communicating with the pressure chambers to discharge the liquid as droplets, and a pressure of the pressure chamber being changed by input of a drive signal; In a droplet discharge apparatus including a droplet discharge head having an actuator that discharges a droplet from a nozzle and a drive control unit that drives and controls the actuator.
The drive control means generates a reference drive signal generation unit that outputs a reference drive signal for generating the droplet to the actuator, and a gradation signal generation that generates a plurality of gradation signals for controlling the discharge amount of the droplet And a gradation signal selection unit that selects a gradation signal corresponding to gradation data designated from a plurality of gradation signals generated by the gradation signal generation unit, from the reference signal generation unit A liquid droplet ejection apparatus configured to supply a reference drive signal to be output and a gradation signal selected by the gradation signal selection unit to different input ends of the actuator.   2. The gradation signal generation unit is configured to generate a plurality of gradation signals that control an amplitude amount of the reference drive signal in synchronization with the reference drive signal. Droplet discharge device.   The gradation signal generation unit separates an offset unit and a waveform unit that controls the amplitude change of the reference drive signal from the waveform data of one gradation signal serving as a reference of the gradation signal; 3. The liquid according to claim 1, further comprising: an adder that adds gradation values each having a desired gradation amount to the waveform parts separated by the waveform data selection part. Drop ejection device.   The waveform data selection unit includes: a waveform memory that stores waveform formation data of the gradation signal in a storage element corresponding to a predetermined address; an address of waveform formation data read from the waveform memory; A coincidence comparator that detects coincidence with the address of the waveform forming data, and is configured to select a necessary one of the offset portion and the waveform portion based on the comparison result of the coincidence comparator. The droplet discharge device according to claim 3.   The reference drive signal generation unit includes temperature detection means for detecting an ambient temperature and reference drive signal correction means for correcting a reference drive signal waveform based on the temperature detected by the temperature detection means. The droplet discharge device according to claim 1. A plurality of pressure chambers filled with liquid therein, a plurality of nozzles individually communicating with the pressure chambers to discharge the liquid as droplets, and a pressure of the pressure chamber being changed by input of a drive signal; A liquid that includes an actuator that discharges droplets from the nozzles, and a drive control unit that drives and controls the actuators, and the actuator is driven and controlled by the drive control unit to discharge droplets from the plurality of nozzles. In the droplet discharge control method,
A reference drive signal generating step for generating a reference drive signal for generating the droplet for the actuator; a gradation signal generating step for generating a plurality of gradation signals for controlling the discharge amount of the droplet; and the gradation signal generation A gradation signal selection step for selecting a gradation signal corresponding to the specified gradation data from the plurality of gradation signals generated in the step; and the gradation signal selected in the reference drive signal and the gradation signal selection step Is supplied to different input terminals of the actuator, and the amplitude of the drive signal applied to the actuator is controlled by being applied to the gradation data.

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