JP2011207114A - Liquid ejecting device and liquid ejection control method - Google Patents

Abstract

[PROBLEMS] To reduce costs while maintaining good discharge characteristics.
A drive element that performs an operation for discharging liquid from a nozzle, a drive signal generation unit that generates a drive signal applied to one end of the drive element, and an input electrode connected to the other end of the drive element An N-channel transistor that is turned on or off for each liquid discharge section, and the drive signal generation unit starts with a ground potential in a certain discharge section, and A drive signal that sequentially changes to a non-ejection intermediate potential V0 higher than the ground potential, a potential V1 higher than the intermediate potential V0, a potential V2 lower than the intermediate potential V0, and a potential V3 higher than the potential V2 is generated.
[Selection] Figure 12

Description

  The present invention relates to a liquid ejection apparatus and a liquid ejection control method.

  As a liquid ejecting apparatus having a drive element for ejecting liquid (for example, ink), for example, an inkjet printer is known. In such an ink jet printer, a drive signal for driving the drive element is generated, and a desired waveform of the drive signal is applied to the drive element by control by an analog switch (for example, a transmission gate) (for example, Patent Documents). 1). Then, ink is ejected from the nozzles by driving the drive element with the drive signal.

Japanese Patent Laid-Open No. 10-250061

In the printer as described above, a transmission gate is provided for each drive element in order to selectively drive a plurality of drive elements. Thus, it is necessary to provide as many transmission gates as the number of nozzles, and there is a problem that costs increase. Note that an analog switch can be configured with only one polarity (for example, N channel type) transistor instead of a transmission gate. However, in this case, as will be described later, the liquid ejection characteristics may be deteriorated.
Accordingly, an object of the present invention is to reduce costs while maintaining good discharge characteristics.

A main invention for achieving the above object includes a drive element that performs an operation for discharging liquid from a nozzle, a drive signal generation unit that generates a drive signal applied to one end of the drive element, and an input electrode that includes the input electrode An N-channel transistor connected to the other end of the drive element and controlled to be turned on or off for each liquid ejection section, and the drive signal generation unit includes a certain ejection In the section, the non-ejection intermediate potential V0 that starts with the ground potential and is higher than the ground potential, the potential V1 that is higher than the intermediate potential V0, the potential V2 that is lower than the intermediate potential V0, and the potential V2 In the liquid ejecting apparatus, the driving signal that sequentially changes to a high potential V3 is generated.
Other features of the present invention will become apparent from the description of the present specification and the accompanying drawings.

1 is a block diagram of an overall configuration of a printer. FIG. 2A is a perspective view of the printer. FIG. 2B is a cross-sectional view of the printer. FIG. 8 is an explanatory diagram of processing by a printer driver. It is a block diagram which shows the structure of a drive signal generation circuit. It is explanatory drawing which shows the arrangement | sequence of the nozzle in the lower surface of a head. It is sectional drawing of the periphery of the nozzle of a head. It is explanatory drawing of the head control part HC. 6 is a diagram illustrating a configuration of a switch unit of Comparative Example 1. FIG. FIG. 6 is a diagram illustrating a drive signal COM ′ of Comparative Example 1. 10 is a diagram illustrating a configuration of a switch unit of Comparative Example 2. FIG. FIG. 10 is a diagram illustrating a drive signal COM ″ of Comparative Example 2. It is explanatory drawing of the drive signal COM of 1st Embodiment. FIG. 6 is a diagram illustrating a waveform of a drive signal COM in a repetition period T. It is a figure which shows the structure of the switch part of 2nd Embodiment. It is explanatory drawing of the drive signal COM of 2nd Embodiment.

  At least the following matters will become clear from the description of the present specification and the accompanying drawings.

A drive element that performs an operation for discharging liquid from the nozzle, a drive signal generation unit that generates a drive signal applied to one end of the drive element, and an N channel in which an input electrode is connected to the other end of the drive element An N-channel transistor that is controlled to be turned on or off for each liquid discharge section, and the drive signal generation unit starts with a ground potential in a certain discharge section, and The drive signal that sequentially changes to a non-ejection intermediate potential V0 higher than the ground potential, a potential V1 higher than the intermediate potential V0, a potential V2 lower than the intermediate potential V0, and a potential V3 higher than the potential V2. A liquid ejection device that is characterized in that it produces will be apparent.
According to such a liquid ejecting apparatus, it is possible to reduce the cost because the switch is composed of only an N-channel transistor while maintaining good ejection characteristics.

In this liquid discharge apparatus, it is preferable that the drive signal starts at the ground potential in each discharge section.
According to such a liquid ejection apparatus, it is possible to prevent malfunction of the drive element.

In this liquid discharge apparatus, it is preferable that the voltage of the output electrode of the N-channel transistor is changed according to the voltage of the one end of the driving element.
According to such a liquid ejection apparatus, it is possible to cope with a case where the voltage at one end of the drive element is boosted.

In such a liquid ejection apparatus, it is preferable that a signal based on pixel data is applied to the control electrode of the N-channel transistor.
According to such a liquid ejection apparatus, it is possible to eject liquid according to pixel data.

In addition, a drive element that performs an operation for discharging liquid from the nozzle, a drive signal generation unit that generates a drive signal applied to one end of the drive element, and an output electrode are connected to the other end of the drive element A P-channel transistor that is controlled to be turned on or off for each liquid discharge section, and the drive signal generation unit starts with a power supply potential in a certain discharge section. Further, the non-ejection intermediate potential V0 lower than the power supply potential, the potential V1 lower than the intermediate potential V0, the potential V2 higher than the intermediate potential V0, and the potential V3 lower than the potential V2 are sequentially changed. A liquid ejection device characterized by generating a signal becomes clear.
According to such a liquid ejecting apparatus, it is possible to reduce the cost because the switch is composed of only the P-channel transistor while maintaining good ejection characteristics.

  In addition, a liquid discharge method using a liquid discharge apparatus including a drive element that performs an operation for discharging liquid from a nozzle, which starts at a ground potential in a certain discharge section and is higher than the ground potential. Generating an ejection intermediate potential V0, a potential V1 higher than the intermediate potential V0, a potential V2 lower than the intermediate potential V0, and a drive signal that sequentially changes to a potential V3 higher than the potential V2, and the drive element Applying the drive signal to one end of the liquid crystal display, and controlling an N-channel transistor having an input electrode connected to the other end of the drive element to be turned on or off for each liquid discharge section. The liquid discharge method is clarified.

  In addition, a liquid discharge method using a liquid discharge apparatus including a drive element that performs an operation for discharging liquid from a nozzle, which starts with a power supply potential in a certain discharge section and is lower than the power supply potential. Generating a drive signal that sequentially changes to an ejection intermediate potential V0, a potential V1 that is lower than the intermediate potential V0, a potential V2 that is higher than the intermediate potential V0, and a potential V3 that is lower than the potential V2, and the drive element And applying a drive signal to one end of the P-channel transistor, and controlling a P-channel transistor having an output electrode connected to the other end of the drive element to be turned on or off for each liquid discharge section. The liquid discharge method is clarified.

  In the following embodiments, an ink jet printer (hereinafter also referred to as printer 1) will be described as an example.

=== Printer configuration ===
FIG. 1 is a block diagram of the overall configuration of the printer 1 of the present embodiment. 2A is a perspective view of the printer 1, and FIG. 2B is a cross-sectional view of the printer 1. Hereinafter, a basic configuration of the printer 1 of the present embodiment will be described.

  The printer 1 of this embodiment includes a transport unit 20, a carriage unit 30, a head unit 40, a detector group 50, and a controller 60. The printer 1 that has received print data from the computer 110 that is an external device controls each unit (the conveyance unit 20, the carriage unit 30, and the head unit 40) by the controller 60. The controller 60 controls each unit based on the print data received from the computer 110 and prints an image on paper. The situation in the printer 1 is monitored by the detector group 50, and the detector group 50 outputs the detection result to the controller 60. The controller 60 controls each unit based on the detection result output from the detector group 50.

  The transport unit 20 is for transporting a medium (for example, paper S) in a predetermined direction (hereinafter referred to as a transport direction). The transport unit 20 includes a paper feed roller 21, a transport motor 22 (also referred to as a PF motor), a transport roller 23, a platen 24, and a paper discharge roller 25. The paper feed roller 21 is a roller for feeding the paper inserted into the paper insertion slot into the printer. The transport roller 23 is a roller that transports the paper S fed by the paper feed roller 21 to a printable region, and is driven by the transport motor 22. The platen 24 supports the paper S being printed. The paper discharge roller 25 is a roller for discharging the paper S to the outside of the printer, and is provided on the downstream side in the transport direction with respect to the printable area.

  The carriage unit 30 is for moving (also referred to as “scanning”) the head in a predetermined direction (hereinafter referred to as a moving direction). The carriage unit 30 includes a carriage 31 and a carriage motor 32 (also referred to as a CR motor). The carriage 31 can reciprocate in the moving direction and is driven by a carriage motor 32. Further, the carriage 31 detachably holds an ink cartridge that stores ink.

  The head unit 40 is for ejecting ink onto paper. The head unit 40 includes a head 41 having a plurality of nozzles and a head controller HC. Since the head 41 is provided on the carriage 31, when the carriage 31 moves in the movement direction, the head 41 also moves in the movement direction. Then, by intermittently ejecting ink while the head 41 is moving in the moving direction, dot lines (raster lines) along the moving direction are formed on the paper.

The head controller HC is a control IC for controlling the driving of the piezo element PZT and is provided in the head 41. The head controller HC selectively drives the piezo elements PZT corresponding to the nozzles of the head 41 in accordance with the head control signal from the controller 60. As a result, ink is ejected from the nozzles of the head 41.
Details of the head unit 40 will be described later.

  The detector group 50 includes a linear encoder 51, a rotary encoder 52, a paper detection sensor 53, an optical sensor 54, and the like. The linear encoder 51 detects the position of the carriage 31 in the moving direction. The rotary encoder 52 detects the rotation amount of the transport roller 23. The paper detection sensor 53 detects the position of the leading edge of the paper being fed. The optical sensor 54 detects the presence or absence of paper by a light emitting unit and a light receiving unit attached to the carriage 31. The optical sensor 54 can detect the position of the edge of the paper while being moved by the carriage 31, and can detect the width of the paper. The optical sensor 54 also detects the leading end (the end on the downstream side in the transport direction, also referred to as the upper end) and the rear end (the end on the upstream side in the transport direction, also referred to as the lower end) depending on the situation. it can.

  The controller 60 is a control unit for controlling the printer. The controller 60 includes an interface unit 61, a CPU 62, a memory 63, a unit control circuit 64, and a drive signal generation circuit 65. The interface unit 61 transmits and receives data between the computer 110 that is an external device and the printer 1. The CPU 62 is an arithmetic processing unit for controlling the entire printer. The memory 63 is for securing an area for storing a program of the CPU 62, a work area, and the like, and includes storage elements such as a RAM and an EEPROM. The CPU 62 controls each unit via the unit control circuit 64 in accordance with a program stored in the memory 63.

  The drive signal generation circuit 65 generates a drive signal COM that drives the piezo element PZT of the head 41. The details of the drive signal generation circuit 65 will be described later.

<Printing procedure>
When receiving a print command and print data from the computer 110, the controller 60 analyzes the contents of various commands included in the print data, and performs the following processing using each unit.

  First, the controller 60 rotates the paper feed roller 21 to send the paper S to be printed to the conveyance roller 23. Next, the controller 60 rotates the transport roller 23 by driving the transport motor 22. When the transport roller 23 rotates with a predetermined rotation amount, the paper S is transported with a predetermined transport amount.

  When the paper S is conveyed to the lower part of the head unit 40, the controller 60 rotates the carriage motor 32 based on the print command. In response to the rotation of the carriage motor 32, the carriage 31 moves in the movement direction. Further, as the carriage 31 moves, the head unit 40 provided on the carriage 31 also moves in the moving direction at the same time. Further, while the head unit 40 is moving in the movement direction, the controller 60 causes the drive signal generation circuit 65 to generate the drive signal COM and applies the drive signal COM to the piezo elements of the head 41. Thus, ink droplets are intermittently ejected from the head 41 while the head unit 40 is moving in the moving direction. When the ink droplets land on the paper S, a dot row in which a plurality of dots are arranged in the moving direction is formed. A dot forming operation by ejecting ink from the moving head 41 is called a pass.

  Further, the controller 60 drives the transport motor 22 while the head unit 40 reciprocates. The transport motor 22 generates a driving force in the rotation direction according to the commanded driving amount from the controller 60. And the conveyance motor 22 rotates the conveyance roller 23 using this driving force. When the transport roller 23 rotates with a predetermined rotation amount, the paper S is transported with a predetermined transport amount. That is, the transport amount of the paper S is determined according to the rotation amount of the transport roller 23. In this way, the pass and the transport operation are alternately repeated to form dots on each pixel of the paper S. Thus, an image is printed on the paper S.

  Finally, the controller 60 discharges the paper S on which printing has been completed by the paper discharge roller 25 that rotates in synchronization with the transport roller 23.

<Outline of processing by printer driver>
As described above, the printing process is started when print data is transmitted from the computer 110 connected to the printer 1. The print data is generated by processing by the printer driver. Hereinafter, processing by the printer driver will be described with reference to FIG. FIG. 3 is an explanatory diagram of processing by the printer driver.

The printer driver receives image data from the application program, converts it into print data in a format that can be interpreted by the printer 1, and outputs the print data to the printer. When converting image data from an application program into print data, the printer driver performs resolution conversion processing, color conversion processing, halftone processing, rasterization processing, command addition processing, and the like.
The resolution conversion process is a process for converting image data (text data, image data, etc.) output from an application program into a resolution (print resolution) for printing on paper. For example, when the print resolution is specified as 720 × 720 dpi, the vector format image data received from the application program is converted into bitmap format image data with a resolution of 720 × 720 dpi. Note that each pixel data of the image data after the resolution conversion process is multi-gradation (for example, 256 gradations) RGB data represented by an RGB color space. This gradation value is determined based on RGB image data, and is hereinafter also referred to as a command gradation value.

  The color conversion process is a process for converting RGB data into data in the CMYK color space. The image data in the CMYK color space is data corresponding to the ink color of the printer. In other words, the printer driver generates CMYK plane image data based on the RGB data.

  This color conversion processing is performed based on a table (color conversion lookup table LUT) in which gradation values of RGB data and gradation values of CMYK data are associated with each other. Note that the pixel data after the color conversion processing is CMYK data of 256 gradations represented by a CMYK color space.

  The halftone process is a process for converting high gradation number data into gradation number data that can be formed by a printer. By this halftone processing, data indicating 256 gradations is converted into 1-bit data indicating 2 gradations or 2-bit data indicating 4 gradations. In the image data after halftone processing, 1-bit or 2-bit pixel data corresponds to each pixel, and this pixel data indicates the dot formation status (the presence / absence of dots, the size of dots) in each pixel. Become data. For example, in the case of 2 bits (4 gradations), no dot corresponding to the dot gradation value [00], formation of a small dot corresponding to the dot gradation value [01], and medium corresponding to the dot gradation value [10] It is converted into four stages like dot formation and large dot formation corresponding to the dot gradation value [11]. Thereafter, the dot generation rate is determined for each dot size, and pixel data is created so that the printer 1 forms the dots in a dispersed manner by using a dither method, γ correction, error diffusion method, or the like. .

  The rasterizing process is a process of rearranging pixel data arranged in a matrix according to the dot formation order at the time of printing. For example, when the dot formation process is performed several times during printing, pixel data corresponding to each dot formation process is extracted and rearranged according to the order of the dot formation process. In addition, since the dot formation order at the time of printing differs if the printing method is different, rasterization processing is performed according to the printing method.

  The command addition process is a process for adding command data corresponding to the printing method to the rasterized data. The command data includes, for example, conveyance data indicating the medium conveyance speed.

  The print data generated through these processes is transmitted to the printer 1 by the printer driver.

=== Drive Signal Generation Circuit ===
FIG. 4 is a block diagram illustrating an example of the configuration of the drive signal generation circuit 65.
A drive signal generation circuit 65 (corresponding to a drive signal generation unit) generates a drive signal COM based on the DAC data from the CPU 62. As illustrated in FIG. 4, the drive signal generation circuit 65 includes a DAC circuit 651, a voltage amplification circuit 652, and a current amplification circuit 653. The DAC circuit 651 converts digital DAC data into an analog signal. The voltage amplification circuit 652 amplifies the voltage of the analog signal converted by the DAC circuit 651 to a level at which the piezo element PZT can be driven. In this printer 1, the maximum analog signal output from the DAC circuit 651 is 3.3V, while the amplified analog signal output from the voltage amplification circuit 652 is 42V at maximum. The current amplifying circuit 653 amplifies the current of the analog signal from the voltage amplifying circuit 652 and outputs the amplified signal as a drive signal COM. Note that the current amplifier circuit 653 is configured by, for example, a push-pull connected transistor pair (not shown).

=== Head unit ===
<About the head>
FIG. 5 is an explanatory diagram showing the arrangement of nozzles on the lower surface of the head 41. As shown in FIG. 5, on the lower surface of the head 41, a black ink nozzle row K, a cyan ink nozzle row C, a magenta ink nozzle row M, and a yellow ink nozzle row Y are formed side by side in the movement direction. . Each nozzle row includes a plurality of nozzles (180 in this embodiment) that are ejection openings for ejecting ink of each color.

  The plurality of nozzles in each nozzle row are aligned and arranged at regular intervals (nozzle pitch: k · D) along the transport direction. Here, D is a minimum dot pitch in the transport direction (that is, an interval at the highest resolution of dots formed on the paper S). K is an integer of 1 or more. For example, when the nozzle pitch is 180 dpi (1/180 inch) and the dot pitch in the transport direction is 720 dpi (1/720), k = 4.

  The nozzles in each nozzle row are assigned a lower number in the downstream nozzle (# 1 to # 180). That is, the nozzle # 1 is located downstream of the nozzle # 180 in the transport direction. Each nozzle is provided with a piezo element (not shown) as a drive element for driving each nozzle to eject ink droplets. Further, the optical sensor 54 is located at substantially the same position as the nozzle # 180 on the most upstream side with respect to the position in the transport direction.

  FIG. 6 is a cross-sectional view around the nozzles of the head 41. The head 41 includes a drive unit 42, a case 43 for housing the drive unit 42, and a flow path unit 44 attached to the case 43.

  The drive unit 42 includes a piezo element group composed of a plurality of piezo elements PZT, a fixed plate 423 to which the piezo element group is fixed, and a flexible cable 424 for supplying power to each piezo element PZT. . Each piezo element PZT is attached to the fixed plate 423 in a so-called cantilever state. The fixed plate 423 is a plate-like member having rigidity capable of receiving a reaction force from the piezo element PZT. The flexible cable 424 is a flexible sheet-like wiring board, and is electrically connected to the piezo element PZT on the side surface of the fixed end opposite to the fixed plate 423. On the surface of the flexible cable 424, a head controller HC, which is a control IC for controlling the driving of the piezo element PZT, is mounted.

  The case 43 has a rectangular parallelepiped block-like outer shape having a storage empty portion 431 in which the drive unit 42 can be stored. The flow path unit 44 is joined to the front end surface of the case 43. The housing empty portion 431 has a size that allows the drive unit 42 to be fitted exactly. The case 43 is also formed with an ink supply path 432. The ink supply path 432 is a supply path for supplying the ink stored in the ink cartridge to the reservoir 453.

  The flow path unit 44 includes a flow path forming substrate 45, a nozzle plate 46, and an elastic plate 47. The flow path forming substrate 45 is laminated and integrated so that the flow path forming substrate 45 is sandwiched between the nozzle plate 46 and the elastic plate 47. Constructed. The nozzle plate 46 is a thin plate made of stainless steel on which nozzles are formed.

  In the flow path forming substrate 45, a plurality of vacant portions serving as pressure chambers 451 and ink supply ports 452 are formed corresponding to the respective nozzles. The reservoir 453 is a liquid storage chamber for supplying the ink stored in the ink cartridge to each pressure chamber 451, and communicates with the other end of the corresponding pressure chamber 451 through the ink supply port 452. The ink from the ink cartridge is introduced into the reservoir 453 through the ink supply path 432.

  The drive unit 42 is inserted into the housing empty portion 431 with the free end of the piezo element PZT directed toward the flow path unit 44, and the distal end surface of this free end is bonded to the corresponding island portion 473. Further, the back surface of the fixing plate 423 is bonded to the inner wall surface of the case 43 that partitions the housing empty portion 431. When a drive signal is supplied to the piezo element PZT via the flexible cable 424 in this stored state, the piezo element PZT expands and contracts to expand and contract the volume of the pressure chamber 451. Due to such a change in the volume of the pressure chamber 451, pressure fluctuation occurs in the ink in the pressure chamber 451. Then, ink droplets can be ejected from the nozzles by utilizing the variation in the ink pressure.

<About the head controller HC>
FIG. 7 is an explanatory diagram of the head controller HC.
7 includes a first shift register 81A, a second shift register 81B, a first latch circuit 82A, a second latch circuit 82B, a decoder 83, a control logic 85, and a switch unit. 86. The first shift register 81A, the second shift register 81B, the first latch circuit 82A, the second latch circuit 82B, and the decoder 83 are provided for each nozzle (for each piezo element PZT).

  A latch signal LAT, a change signal CH, pixel data SI, and a clock signal CLK are input to the head controller HC. Hereinafter, each of these signals will be described. Note that the drive signal COM is also input to the head controller HC, which will be described later.

  The latch signal LAT is a signal indicating a repetition period T (a period in which the head 41 moves in a section of one pixel). The latch signal LAT is generated by the controller 60 based on the signal of the linear encoder 51, and is input to the control logic 85 and the latch circuit (first latch circuit 82A, second latch circuit 82B).

  In the present embodiment, the change signal CH is a signal indicating a period (hereinafter also referred to as a discharge section) obtained by dividing the repetition period T into three equal parts. The change signal CH is generated by the controller 60 based on the signal from the linear encoder 51 and input to the control logic 85.

  The pixel data SI is a signal indicating the gradation (no dot, small dot, medium dot, large dot) for each pixel. This pixel data is composed of 2 bits for each nozzle. For example, when the number of nozzles is 180, pixel data SI of 2 bits × 180 is transmitted wirelessly from the apparatus main body side every repetition cycle T. The pixel data SI is input to the first shift register 81A and the second shift register 81B.

  The clock signal CLK is a signal used when the pixel data SI sent from the controller 60 is set in each shift register (first shift register 81A, second shift register 81B).

  Next, signals generated by the head controller HC will be described. In the head controller HC, selection signals q0 to q3 and a switch control signal SW are generated.

  The selection signals q0 to q3 are generated by the control logic 85 based on the latch signal LAT and the change signal CH. Then, the generated selection signals q0 to q3 are input to the decoders 83 provided for the respective piezo elements PZT.

  As for the switch control signal SW, one of the selection signals q0 to q3 is selected by the decoder 83 based on the pixel data (2 bits) latched in each latch circuit (the first latch circuit 82A and the second latch circuit 82B). It is a thing. The switch control signal SW generated by each decoder 83 is input to the switch unit 86.

  The switch unit 86 has a switch corresponding to each piezo element PZT, and operates the corresponding switch based on the switch control signal SW output from each decoder 83 to thereby send the drive signal COM to the piezo element. Apply to PZT.

<Operation of the head controller HC>
The head controller HC controls driving (operation for ejecting ink) of each piezo element PZT based on the pixel data SI. In the present embodiment, the pixel data SI is composed of 2 bits. The pixel data SI is sent to the head 41 in synchronization with the transfer clock CLK. Further, the upper bit group of the pixel data SI is set in each first shift register 81A, and the lower bit group is set in each second shift register 81B. A first latch circuit 82A is electrically connected to the first shift register 81A, and a second latch circuit 82B is electrically connected to the second shift register 81B. When the latch signal LAT from the controller 60 becomes H level, each first latch circuit 82A latches the upper bit of the corresponding pixel data SI, and each second latch circuit 82B latches the lower bit of the pixel data SI. . Pixel data SI (a set of upper bits and lower bits) latched by the first latch circuit 82A and the second latch circuit 82B is input to the decoder 83, respectively. The decoder 83 selects one of the selection signals q0 to q3 output from the control logic 85 (for example, the selection signal q1) in accordance with the pixel data SI latched by the first latch circuit 82A and the second latch circuit 82B. ) And the selected selection signal is output to the switch unit 86 as the switch control signal SW.

=== Comparative Example 1 ===
<Switch part of Comparative Example 1>
FIG. 8 is a diagram illustrating a configuration of the switch unit 86 of the first comparative example. The switch unit 86 of the first comparative example includes a transmission gate 49 including a P-channel type MOSFET (hereinafter also referred to as PMOS) T1 and an N-channel type MOSFET (hereinafter also referred to as NMOS) T2. The parts other than the piezo element PZT are integrated (IC).

  The transmission gate 49 functions as an analog switch that controls application of the drive signal COM to the piezo element PZT. The transmission gate 49 is provided for each nozzle (for each piezo element PZT). In the figure, only a portion corresponding to one piezo element PZT is shown.

  A drive signal COM is applied to the input side of the transmission gate 49, and the output side is connected to one end of the piezo element PZT. The conduction between the input and output is controlled by applying a voltage to the gates of PMOST1 and NMOST2. The on / off of the PMOST1 is controlled by the output of the inverter PA composed of the PMOST11 and NOST12, and the on / off of the NMOST2 is controlled by the output of the inverter PB composed of the PMOST21 and NOST22. Further, the output of each inverter changes according to the switch control signal SW output from the corresponding decoder 83. That is, on / off of the transmission gate 49 is controlled based on the switch control signal SW (in other words, the pixel data SI).

  With the above configuration, the piezoelectric element PZT can be charged and discharged in both directions. Specifically, the piezo element PZT can be charged by the PMOST1 during charging. Further, at the time of discharging, the charge of the piezo element PZT can be discharged by the NMOST1.

<Drive signal of Comparative Example 1>
Next, the relationship between the drive signal COM ′ used in Comparative Example 1 and ink ejection will be described with reference to FIGS. FIG. 9 is a diagram illustrating the drive signal COM ′ of the first comparative example. In the figure, the waveform of one discharge section is shown.

In this example, the drive signal generation circuit 65 outputs the intermediate potential Vc (GND <Vc <VDD) until time T0, and the intermediate potential Vc is applied to one end of the piezo element PZT. The volume of the pressure chamber 451 at this time is set as a reference volume. Thereafter, between time T0 and time T1, the drive signal generation circuit 65 raises the potential from the intermediate potential Vc to the maximum potential Vh. Due to this potential increase, the piezo element PZT contracts in the longitudinal direction and expands the volume of the pressure chamber 451. As a result, the pressure in the pressure chamber 451 is reduced.
Then, after maintaining the maximum potential Vh until time T2, the drive signal generation circuit 65 lowers the potential from the maximum potential Vh to the minimum potential Vl between time T2 and time T3, and expands the piezo element PZT. Then, the volume of the pressure chamber 451 contracts, the pressure in the pressure chamber 451 is pressurized at once, and ink is ejected from the nozzle.
Thereafter, the drive signal generation circuit 65 maintains the lowest potential Vl until time T4, and increases the potential from the lowest potential Vl to the intermediate potential Vc between time T4 and time T5. As a result, the volume of the contracted pressure chamber 451 expands, and the volume in the pressure chamber 451 is returned to the reference volume.

=== Comparative Example 2 ===
<Switch part of comparative example 2>
FIG. 10 is a diagram illustrating a configuration of the switch unit 86 of the second comparative example.
Each switch of the switch part 86 of this comparative example 2 is comprised only by NMOS instead of the transmission gate. Also in FIG. 10, only a portion corresponding to one piezo element PZT is shown. In the figure, parts other than the piezo element PZT are integrated (integrated with IC).
The switch unit 86 of the comparative example 2 includes an inverter PT, an NMOS T3, diodes D1 to D4, and a resistor R1. The drive signal COM is applied to one end of the piezo element PZT as shown in the figure.

  The inverter PT is composed of PMOST31 and NMMOST32. The output of the inverter PT is applied to the gate (control electrode) of the NMOS T3. The output of the inverter PT changes according to the switch control signal SW output from the corresponding decoder 83. That is, a signal based on the pixel data SI is applied to the gate of the NMOS T3.

  The drain (input electrode) of the NMOS T3 is connected to the other end of the piezo element PZT via the output terminal DOn of the IC. The source of the NMOS T3 is connected to the ground terminal GND2. The NMOST3 is turned on when the output of the inverter PT is at the H level, and turned off when the output of the inverter PT is at the L level.

The diode D1 is a parasitic diode of the PMOST31, and the diode D2 is a parasitic diode of the NMOST32.
The diode D3 and the diode D4 are backflow prevention diodes.

  The resistor R2 is a voltage drop resistor. One end of the resistor R2 is connected to the anode side of the diode D4. The other end is connected to the ground terminal GND2.

<Drive signal of Comparative Example 2>
11 is a diagram showing the drive signal COM ″ of Comparative Example 2. In Comparative Example 2, it is not possible to make the intermediate potential at the start of the discharge section as in Comparative Example 1. This is because if at the start of the discharge section, piezo is assumed. If the one end side of the element PZT is at an intermediate potential, a current flows through the piezo element PZT and the piezo element PZT may malfunction when the NMOS T3 switches from off to on.

  As described above, since the intermediate potential cannot be set at the start of the discharge period, the drive signal COM ″ starts from the ground potential in Comparative Example 2. The potential of the drive signal COM ″ increases from the ground potential and reaches the maximum potential. Then, it descends and returns to the ground potential. As described above, the waveform of the drive signal COM ″ in the comparative example 2 is a pulse waveform. Then, ink is ejected from the nozzles by the vibration of the piezo element PZT according to the potential change.

  In Comparative Example 2, the number of transistors can be reduced compared to Comparative Example 1 using a transmission gate as a switch for applying the drive signal COM to the piezo element PZT, thus realizing cost reduction and IC miniaturization. can do. However, in the waveform (pulse waveform) of the comparative example 2, the stroke (the volume of the pressure chamber 451 is expanded from the reference volume and returned to the reference volume) or pushed (the volume of the pressure chamber 451 is reduced from the reference volume to the reference volume). (Return to capacity).

  Thus, in Comparative Example 2, the amount of displacement of the pressure chamber 451 and the amount of ink ejected from the nozzles are smaller than those in Comparative Example 1. Therefore, the ink ejection characteristics are worse than those in the first comparative example.

=== First Embodiment ===
Hereinafter, a first embodiment will be described with reference to the drawings. In addition, the structure of the switch part 86 of 1st Embodiment is the same as the comparative example 2 (FIG. 9) mentioned above. That is, each switch of the switch part 86 of this embodiment is comprised only by NMOST3 instead of a transmission gate. However, the waveform of the drive signal COM of the present embodiment is different from that of Comparative Example 2. Hereinafter, the drive signal COM of the first embodiment will be described.

<Drive Signal of First Embodiment>
FIG. 12 is an explanatory diagram of the drive signal COM of the first embodiment.
In the present embodiment, the ground potential is started at the start of the discharge period in which the NMOST 3 is turned on. For this reason, even if the NMOS T3 is turned on at the start of the ejection section, no current flows suddenly through the piezo element PZT. The volume of the pressure chamber 451 at this time is set as a reference volume. Thereafter, between time Ta and time Tb, the drive signal generation circuit 65 raises the potential from the ground potential GND to the intermediate potential V0. Due to the potential increase, the piezo element PZT contracts in the longitudinal direction and expands the volume of the pressure chamber 451. Then, after maintaining the intermediate potential V0 until time Tc, the drive signal generation circuit 65 raises the potential from the intermediate potential V0 to the maximum potential V1 between time Tc and time Td. Due to this potential increase, the piezo element PZT further contracts in the longitudinal direction, further expanding the volume of the pressure chamber 451.

  Then, after maintaining the maximum potential V1 until time Te, the drive signal generation circuit 65 decreases the potential from the maximum potential V1 to the minimum potential V2 (here, the ground potential GND) between the time Te and the time Tf. Extend the piezo element PZT. At this time, the volume of the pressure chamber 451 contracts, the pressure in the pressure chamber 451 is pressurized at once, and ink is ejected from the nozzles.

  Thereafter, the drive signal generation circuit 65 maintains the minimum potential V2 until the time Tg, and increases the potential from the minimum potential V2 to the potential V3 between the time Tg and the time Th. As a result, the volume of the contracted pressure chamber 451 expands. Then, after maintaining the potential V3 until the time Ti, the potential is lowered from the potential V3 to the ground potential GND between the time Ti and the time Tj. Due to this potential drop, the volume of the pressure chamber 451 returns to the reference volume.

It should be noted that potential changes at times Ta to Tb and Ti to Tj are set so as not to eject ink from the nozzles.
By doing so, the waveform from time Tb to time Th in the figure becomes the same waveform (discharge waveform) as the discharge waveform in FIG. 9 (Comparative Example 1). That is, the same ejection characteristics as those of the comparative example 1 can be realized by the configuration of the comparative example 2.

  FIG. 13 is a diagram illustrating an example of the waveform of the drive signal COM in the repetition period T. In FIG.

  The drive signal COM is generated in the period T11 in the repetition period T (period in which the head 41 moves in one pixel section), the drive pulse PS2 generated in the period T12, and the period T13. Drive pulse PS3. The drive pulse PS1, the drive pulse PS2, and the drive pulse PS3 are applied to the piezo element PZT when a large dot, which will be described in detail later, is formed, and have the same waveform. In addition, the drive pulse PS1 and the drive pulse PS2 are applied to the piezo element PZT also during the formation of medium dots, which will be described in detail later. The drive pulse PS1 is also applied to the piezo element PZT when forming small dots, which will be described in detail later. Note that when no drive pulse is applied to the piezo element PZT, ink is not ejected (dots are not formed).

(Relationship between pixel data and dots)
First, a case where dots are not formed (when pixel data SI is data [00]) will be described. When the pixel data [00] is latched, the selection signal q0 is output as the switch control signal SW. In this case, the NMOS T3 is turned off in the period T. As a result, the piezo element PZT is not driven by the drive signal COM, and no ink droplet is ejected from the nozzle.

  Next, a case where small dots are formed (when pixel data SI is data [01]) will be described. When the pixel data [01] is latched, the selection signal q1 is output as the switch control signal SW. In this case, the NMOS T3 is turned on in the period T11, and the NMOS T3 is turned off in the periods T12 and T13. As a result, the piezo element PZT is driven by the drive pulse PS1 of the drive signal COM, and an ink droplet corresponding to a small dot is ejected from the nozzle.

  Next, the case of forming a medium dot (when the pixel data SI is data [10]) will be described. When the pixel data [10] is latched, the selection signal q2 is output as the switch control signal SW. In this case, the NMOS T3 is turned on in the periods T11 and T12, and the NMOS T3 is turned off in the period T13. As a result, the piezo element PZT is driven by the drive pulse PS1 and the drive pulse PS2 of the drive signal COM, and an ink droplet (medium ink droplet) corresponding to the medium dot is ejected from the nozzle.

  Next, a case where large dots are formed (when pixel data SI is data [11]) will be described. When the pixel data [11] is latched, the selection signal q3 is output as the switch control signal SW. In this case, the NMOS T3 is turned on in the period T11, the period T12, and the period T13. As a result, the piezo element PZT is driven by the driving pulse PS1, the driving pulse PS2, and the driving pulse PS3 of the driving signal COM, and an ink droplet (large ink droplet) corresponding to a large dot is ejected from the nozzle.

  As described above, the drive signal generation circuit 65 of the present embodiment starts with the ground potential in each ejection section, and is the non-ejection intermediate potential V0 higher than the ground potential and the highest potential higher than the intermediate potential V0. The drive signal COM that sequentially changes to V1, the lowest potential V2 lower than the intermediate potential V0, and the potential V3 higher than the lowest potential V2 is generated. As a result, the driving of the piezo element PZT by the ejection waveform (FIG. 9) having the intermediate potential of the comparative example 1 can be realized using the configuration of the comparative example 2 (FIG. 10). Therefore, it is possible to reduce the cost while maintaining the discharge characteristics.

  Furthermore, in the present embodiment, the ink in the pressure chamber 451 is given vibration (fine vibration) to the extent that ink is not ejected due to an increase in potential between time Ta and time Tb (until the intermediate potential V0 is reached). Can do. Thereby, since the effect of micro vibration is obtained, ink can be ejected more stably.

  In the present embodiment, the discharge waveform of FIG. 12 is included in each discharge section of the repetition period T, but the present invention is not limited to this. For example, one ejection section may include a waveform that slightly vibrates the piezo element PZT. In the present embodiment, there are three discharge sections in the repetition period T, but the present invention is not limited to this. For example, four may be sufficient. Further, the repetition period T may be one discharge section.

  Further, in the drive signal COM of the present embodiment, after rising from the ground potential to the intermediate potential V0, the potential further rises to the maximum potential V1, but between the intermediate potential V0 and the maximum potential V1. May include other waveforms. For example, the potential may once decrease from the intermediate potential V0, increase again, return to the intermediate potential, and then reach the maximum potential V1.

  In short, it is the ground potential at the start of each discharge section (latch signal LAT and change signal CH pulse timing), and if the discharge waveform as shown in FIG. 12 is included in at least one discharge section. Good.

  The voltage on the side (one end side) to which the drive signal COM of the piezo element PZT is applied may be boosted. In this case, the voltage of the ground terminal GND2 (the source voltage of the NMOST3) may be adjusted to the boosted voltage. Thus, it is possible to cope with the case where the voltage on one end side of the piezo element PZT is boosted.

=== Second Embodiment ===
In the embodiment described above, the switch of the switch unit 86 is formed of only NMOS. On the other hand, in the second embodiment, the switch is composed only of PMOS.

<Switch Unit 86 of Second Embodiment>
FIG. 14 is a diagram illustrating a configuration of the switch unit 86 according to the second embodiment. In FIG. 14, parts having the same configuration as in FIG.
The switch unit 86 of the comparative example 2 includes a PMOST4. Also in the second embodiment, the drive signal COM is applied to one end of the piezo element PZT as shown in the figure.
The drain (output electrode) of the PMOS T4 is connected to the other end of the piezo element PZT via the output terminal DOn. A power supply voltage VHV is applied to the source of the PMOST4. The output of the inverter PT is applied to the gate of the PMOST4. The PMOST4 is turned on when the output of the inverter PT is at L level, and turned off when the output of the inverter PT is at H level.

<Drive Signal of Second Embodiment>
FIG. 15 is an explanatory diagram of the drive signal COM of the second embodiment.
The drive signal COM generated by the drive signal generation circuit 65 of the second embodiment starts from the power supply potential VHV at the start of the ejection section. This is because a malfunction may occur if there is a potential difference between both ends of the piezo element PZT when the PMOST 4 is switched from OFF to ON.
The drive signal generation circuit 65 includes a non-ejection intermediate potential V0 lower than the power supply potential VHV, a minimum potential V1 lower than the intermediate potential V0, and a potential V2 higher than the intermediate potential V0 (power supply potential VHV in the present embodiment). The drive signal COM that sequentially changes to the potential V3 lower than the potential V2 is generated.

  Also in the second embodiment, a switch can be configured only by the PMOST 4 and the piezo element PZT can be driven by an ejection waveform having an intermediate potential. Therefore, cost can be reduced while maintaining good discharge characteristics.

=== Other Embodiments ===
Although a printer or the like as one embodiment has been described, the above embodiment is for facilitating the understanding of the present invention, and is not intended to limit the present invention. The present invention can be changed and improved without departing from the gist thereof, and it is needless to say that the present invention includes equivalents thereof. In particular, the embodiments described below are also included in the present invention.

<About liquid ejection device>
In the above-described embodiment, an ink jet printer is described as an example of the liquid ejecting apparatus. However, the liquid ejecting apparatus is not limited to the ink jet printer, and liquids other than ink (including liquids in which functional material particles are dispersed and liquids such as gels other than liquids) and liquids are also used. The present invention is also applicable to a fluid discharge device that discharges fluid (a solid that can be discharged as a fluid, such as powder). For example, a discharge device that discharges a liquid colorant or an electrode material used for manufacturing a liquid crystal display, an EL display, or a surface-emitting display, or a discharge device that discharges a liquid bioorganic material used for biochip manufacturing is described above. The embodiment may be applied.

<About the printer>
The printer of the above-described embodiment is a printer (so-called serial printer) that alternately repeats a dot forming operation (pass) in which the head moves in the movement direction and a conveyance operation in which the paper is conveyed in the conveyance direction. However, the type of printer is not limited to this. For example, a printer (so-called line printer) that performs printing by fixing the head and discharging the ink from the head while conveying the paper while facing the head may be used.

<About ink>
Since the above-described embodiment is an embodiment of a printer, ink is ejected from the nozzles, but this ink may be water-based or oil-based. The fluid ejected from the nozzle is not limited to ink. For example, liquids (including water) including metal materials, organic materials (especially polymer materials), magnetic materials, conductive materials, wiring materials, film-forming materials, electronic inks, processing liquids, gene solutions, etc. are ejected from nozzles. May be.

1 printer, 20 transport unit, 21 paper feed roller,
22 transport motor (PF motor), 23 transport roller,
24 platen, 25 paper discharge roller, 30 carriage unit,
31 carriage, 32 carriage motor (CR motor),
40 head units, 41 heads, 42 drive units,
423 fixing plate, 424 flexible cable, 43 case,
431 Storage empty part, 432 Ink supply path, 44 Flow path unit,
45 flow path forming substrate, 451 pressure chamber, 452 ink supply port, 453 reservoir,
46 Nozzle plate, 47 Elastic plate, 49 Transmission gate,
50 detector groups, 51 linear encoder, 52 rotary encoder,
53 Paper detection sensor, 54 Optical sensor, 60 Controller,
61 interface unit, 62 CPU, 63 memory,
64 unit control circuit, 65 drive signal generation circuit,
110 Computer, HC head controller, PZT piezo element

Claims (7)

A driving element that performs an operation for discharging liquid from the nozzle;
A drive signal generator for generating a drive signal applied to one end of the drive element;
An N-channel transistor having an input electrode connected to the other end of the driving element, the N-channel transistor being controlled to be turned on or off for each liquid discharge section;
Have
The drive signal generation unit starts with a ground potential in a certain discharge section and is a non-discharge intermediate potential V0 higher than the ground potential, a potential V1 higher than the intermediate potential V0, and the intermediate potential V0. A liquid ejection apparatus that generates the drive signal that sequentially changes to a lower potential V2 and a potential V3 that is higher than the potential V2. The liquid ejection device according to claim 1,
The drive signal starts at the ground potential in each discharge section.
A liquid discharge apparatus characterized by that. The liquid ejection device according to claim 1 or 2,
The voltage of the output electrode of the N-channel transistor is changed according to the voltage of the one end of the driving element.
A liquid discharge apparatus characterized by that. The liquid ejection device according to any one of claims 1 to 3,
A signal based on pixel data is applied to the control electrode of the N-channel transistor.
A liquid discharge apparatus characterized by that. A driving element that performs an operation for discharging liquid from the nozzle;
A drive signal generator for generating a drive signal applied to one end of the drive element;
A P-channel transistor having an output electrode connected to the other end of the driving element, the P-channel transistor being controlled to be turned on or off for each liquid discharge section;
Have
The drive signal generation unit starts with a power supply potential in a certain discharge section, and is a non-discharge intermediate potential V0 lower than the power supply potential, a potential V1 lower than the intermediate potential V0, and the intermediate potential V0. A liquid ejection apparatus that generates the drive signal that sequentially changes to a higher potential V2 and a potential V3 that is lower than the potential V2. A liquid discharge method by a liquid discharge apparatus including a drive element that performs an operation for discharging liquid from a nozzle,
In a certain discharge section, a non-discharge intermediate potential V0 that starts with a ground potential and is higher than the ground potential, a potential V1 that is higher than the intermediate potential V0, a potential V2 that is lower than the intermediate potential V0, and the potential Generating a drive signal that sequentially changes to a potential V3 higher than V2,
Applying the drive signal to one end of the drive element;
Controlling an N-channel transistor having an input electrode connected to the other end of the driving element to be turned on or off for each liquid discharge section;
A liquid discharge method comprising: A liquid discharge method by a liquid discharge apparatus including a drive element that performs an operation for discharging liquid from a nozzle,
In a certain discharge section, a non-ejection intermediate potential V0 lower than the power supply potential, a potential V1 lower than the intermediate potential V0, a potential V2 higher than the intermediate potential V0, and the potential starting from the power supply potential Generating a drive signal that sequentially changes to a potential V3 lower than V2,
Applying the drive signal to one end of the drive element;
Controlling the P-channel transistor, whose output electrode is connected to the other end of the driving element, to be turned on or off for each liquid discharge section;
A liquid discharge method comprising:

Images