JP6090508B2 - Liquid ejecting apparatus and liquid ejecting method - Google Patents

Description

  The present invention relates to a liquid ejection device and a liquid ejection method.

  2. Description of the Related Art Liquid ejecting apparatuses that record an image or the like by ejecting liquid from a head unit and landing droplets (dots) on a medium are widely used. As a method of ejecting liquid from the head unit, a method of ejecting liquid by applying a drive waveform signal to an element such as a piezoelectric element provided inside the head unit and vibrating the piezoelectric element is known. ing.

  In such a liquid ejecting apparatus, a voltage signal having a small amplitude is input to a head unit via a cable such as a flexible flat cable (FFC) from a control unit that generates a predetermined voltage signal. A method of generating a drive waveform signal by amplification is proposed. (For example, patent document 1).

JP 2000-343690 A

If a sufficiently large capacitor for power supply is provided on the head by the method of Patent Document 1, it is not necessary to flow a current having a large peak that flows instantaneously when driving the head through a cable such as an FFC. That is, since an average current flows through a cable such as an FFC, heat generation in the cable can be reduced, and the number of FFC cores can be reduced. However, when a voltage waveform signal having a small amplitude is transmitted from the control unit to the head unit, distortion or the like occurs in the voltage waveform signal due to the influence of disturbance such as noise in the transmission path (FFC). The drive waveform signal may not be generated. In such a case, the liquid ejection amount cannot be controlled with high accuracy.
An object of the present invention is to generate an accurate drive waveform signal that is resistant to disturbances in a liquid ejecting apparatus.

  A main invention for achieving the above object is (A) a digital signal generation unit that generates a digital signal that defines the waveform shape of a signal, and an analog voltage signal generation unit that generates an analog voltage signal based on the digital signal. A control unit having a current signal generation unit that generates a current signal having a magnitude corresponding to the waveform of the analog voltage signal, and (B) detecting a potential difference between two different points in the path through which the current signal flows, A head unit having a voltage signal generation unit that amplifies the potential difference and generates a voltage signal; an element that is driven by the voltage signal and that ejects liquid from a nozzle; and (C) the control unit A transmission unit having a path for transmitting from the control unit to the head unit, and the transmission unit transmits the current signal transmitted from the control unit to the head unit from the head unit. Further comprising a path back to the control unit, via the transmission unit performs the differential transmission in transmitting the current signal, it is a liquid ejecting apparatus according to claim.

  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 illustrating an overall configuration of a printer. FIG. 2A is a diagram illustrating the configuration of the printer according to the present embodiment. FIG. 2B is a side view illustrating the configuration of the printer according to the present embodiment. It is sectional drawing for demonstrating the structure of a head. It is a figure explaining the structure and operation | movement of the controller 60 and the head control part HC in embodiment. It is a figure explaining the flow until electric potential difference signal COM '' is produced | generated from a digital signal. It is a figure explaining the drive waveform signal COM. It is a figure explaining the structure and operation | movement of the controller 60 and the head control part HC in a comparative example.

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

(A) a digital signal generation unit that generates a digital signal that defines the waveform shape of the signal, an analog voltage signal generation unit that generates an analog voltage signal based on the digital signal, and a magnitude corresponding to the waveform of the analog voltage signal And (B) detecting a potential difference between two different points in the path through which the current signal flows and amplifying the potential difference to generate a voltage signal. A head unit having a voltage signal generation unit, an element driven by the voltage signal and ejecting liquid from a nozzle, and (C) a transmission unit that transmits the current signal from the control unit to the head unit; A liquid ejection device comprising:
According to such a liquid ejecting apparatus, it is possible to generate an accurate drive waveform signal that is resistant to disturbance.

In such a liquid ejecting apparatus, it is desirable that the potential at the low potential side of the two different points for detecting the potential difference is higher than the potential at GND.
According to such a liquid ejection device, it is possible to suppress malfunction of the voltage signal generation unit, and thus it becomes easier to generate a more accurate drive waveform signal.

In the liquid ejecting apparatus, it is preferable that the transmission unit has a path for returning the current signal transmitted from the control unit to the head unit from the head unit to the control unit.
According to such a liquid ejecting apparatus, when a current signal is transmitted, transfer without distortion is performed. It is also possible to perform differential transfer that reduces the influence of noise.

In the liquid ejecting apparatus, it is preferable that the control unit includes a chip in which the digital signal generation unit and the analog voltage signal generation unit are integrally formed.
According to such a liquid ejecting apparatus, since it is less likely to be affected by noise in the process of transmitting a digital signal (DAC value), it is easy to generate a drive waveform signal COM having an accurate waveform shape.

In the liquid ejecting apparatus, it is preferable that the control unit includes a chip in which the digital signal generation unit, the analog voltage signal generation unit, and the current signal generation unit are integrally formed.
According to such a liquid ejecting apparatus, since it is less likely to be affected by noise in the transmission process of a digital signal (DAC value) or an analog voltage signal (COM ′), the driving waveform signal COM having an accurate waveform shape is used. Is easier to generate. In addition, the number of parts of the control unit can be reduced and the cost can be reduced.

In such a liquid ejecting apparatus, it is preferable that a resistance is provided in a path through which the current signal flows, and that a potential difference generated at both ends of the resistance is detected when the current signal flows through the resistance.
According to such a liquid ejection device, the potential difference can be detected easily and accurately.

  Generating a digital signal that defines a waveform shape of the signal; generating an analog voltage signal based on the digital signal; and generating a current signal having a magnitude corresponding to the waveform of the analog voltage signal. And transmitting the generated current signal to the head unit, and detecting a potential difference between two points on the path where the current signal flows in the head unit, and amplifying the potential difference to generate a voltage signal. And a liquid ejection method including ejecting a liquid from the nozzle by driving the element with the voltage signal becomes clear.

=== Embodiment ===
An ink jet printer (printer 1) will be described as an example as a form of a liquid ejection device for carrying out the invention.

<Printer configuration>
FIG. 1 is a block diagram illustrating the overall configuration of the printer 1. The printer 1 is a liquid ejection device that records (prints) characters and images on a medium such as paper, cloth, and film, and is connected to a computer 110 that is an external device so as to be communicable.

  A printer driver is installed in the computer 110. The printer driver is a program for displaying a user interface on a display device (not shown) and converting image data output from an application program into print data. This printer driver is recorded on a recording medium (computer-readable recording medium) such as a flexible disk FD or a CD-ROM. Also, the printer driver can be downloaded to the computer 110 via the Internet. In addition, this program is comprised from the code | cord | chord for implement | achieving various functions.

  The computer 110 outputs print data corresponding to the image to be printed to the printer 1 in order to cause the printer 1 to print an image. The print data is data in a format that can be interpreted by the printer 1 and includes various command data and pixel data SI. The command data is data for instructing the printer 1 to execute a specific operation. The command data includes, for example, command data for instructing paper feed, command data for indicating the carry amount, and command data for instructing paper discharge. The pixel data SI is data related to the pixels of the image to be printed. Here, a pixel is a unit element constituting an image, and an image is formed by arranging these pixels two-dimensionally. The pixel data SI in the print data is data (for example, gradation values) related to dots formed on a medium (for example, paper S). The pixel data is composed of, for example, 2-bit data for each pixel. This 2-bit pixel data can represent one pixel in four gradations. That is, there is data [00] corresponding to no dot, data [01] corresponding to small dots, data [10] corresponding to formation of medium dots, and data [11] corresponding to large dots.

  The printer 1 includes a transport unit 20, a carriage unit 30, a head unit 40, a detector group 50, a controller 60, and a transmission unit 70. The controller 60 controls each unit such as the head unit 40 based on print data received from the computer 110 which is an external device, and prints an image on a medium. 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.

<Transport unit 20>
FIG. 2A is a bird's-eye view showing the configuration of the printer 1 of this embodiment, and FIG. 2B is a side view showing the configuration of the printer 1.

  The transport unit 20 is for transporting a medium (for example, paper S) in a predetermined direction (hereinafter referred to as a transport direction). Here, the transport direction is a direction that intersects the moving direction of the carriage. The transport unit 20 includes a paper feed roller 21, a transport motor 22, a transport roller 23, a platen 24, and a paper discharge roller 25 (FIGS. 2A and 2B).

  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 operation of the transport motor 22 is controlled by a controller 60 on the printer side. The platen 24 is a member that supports the paper S being printed from the back side of the paper S. 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.

<Carriage unit 30>
The carriage unit 30 is for moving (also referred to as “scanning”) the carriage 31 to which the head unit 40 is attached 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) (FIGS. 2A and 2B).

  The carriage 31 can reciprocate in the moving direction and is driven by a carriage motor 32. The operation of the carriage motor 32 is controlled by a controller 60 on the printer side. Further, the carriage 31 detachably holds an ink cartridge that stores ink.

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

  FIG. 3 is a cross-sectional view showing the structure of the head 41. The head 41 includes a case 411, a flow path unit 412, and a piezoelectric element group. The case 411 houses the piezoelectric element group, and the flow path unit 412 is joined to the lower surface of the case 411. The flow path unit 412 includes a flow path forming plate 412a, an elastic plate 412b, and a nozzle plate 412c. The flow path forming plate 412a is formed with a groove portion serving as a pressure chamber 412d, a through hole serving as a nozzle communication port 412e, a through port serving as a common ink chamber 412f, and a groove portion serving as an ink supply path 412g. The elastic plate 412b has an island portion 412h to which the tip of the piezo element PZT is joined. An elastic region is formed by an elastic film 412i around the island portion 412h. The ink stored in the ink cartridge is supplied to the pressure chamber 412d corresponding to each nozzle Nz via the common ink chamber 412f. The nozzle plate 412c is a plate on which the nozzles Nz are formed. On the nozzle surface, a yellow nozzle row Y for discharging yellow ink, a magenta nozzle row M for discharging magenta ink, a cyan nozzle row C for discharging cyan ink, and a black nozzle row K for discharging black ink are formed. Has been. Each nozzle row is configured by arranging a plurality of nozzles Nz at predetermined intervals in the transport direction.

  The piezo element group includes a plurality of comb-like piezo elements PZT (drive elements), and is provided in a number corresponding to the nozzles Nz. When a drive waveform signal COM, which is a voltage signal, is applied to the piezo element PZT by a wiring board (hereinafter, also referred to as a head board Base_H) on which the head control unit HC and the like are mounted, the piezo element PZT is changed according to the voltage signal. Extends (drives) vertically. When the piezo element PZT expands and contracts, the island portion 412h is pushed toward the pressure chamber 412d or pulled in the opposite direction. At this time, the elastic film 412i around the island portion 412h is deformed, and the pressure in the pressure chamber 412d rises and falls, thereby ejecting ink droplets from the nozzles.

  The head controller HC is a control IC for controlling the driving of the piezo element group PZT, and is provided on the head substrate Base_H fixed to the head 41. Details of the head controller HC will be described later.

<Detector group 50>
The detector group 50 is for monitoring the status of the printer 1. 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 (FIGS. 2A and 2B).

  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 medium (paper S) being fed. The optical sensor 54 detects the presence / absence of the medium at the opposing position by the light emitting unit and the light receiving unit attached to the carriage 31, for example, detects the position of the edge of the paper while moving, and detects the width of the paper can do. The optical sensor 54 also detects the front 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.

<Controller 60>
The controller 60 is a control unit (control unit) for controlling the printer 1. The controller 60 includes an interface unit 61, an SOC (System-on-a-chip), and a current signal generation unit 67, and is mounted on a main board Base_M fixed to the main body of the printer 1.

  The interface unit 61 transmits and receives data between the computer 110 that is an external device and the printer 1.

  The SOC is a chip in which a CPU 62, a memory 63, a unit control circuit 64, and an analog voltage signal generation circuit 65 are integrally formed (FIG. 1).

  The CPU 62 is an arithmetic processing device for performing overall control of the printer 1. The memory 63 is for securing an area for storing a program of the CPU 62, a work area, and the like, and includes a storage element such as a RAM or an EEPROM. The CPU 62 controls each unit such as the transport unit 20 and the carriage unit 30 via the unit control circuit 64 in accordance with a program stored in the memory 63.

  Further, the CPU 62 generates a digital signal that defines the waveform shape of a signal having a predetermined waveform, and outputs the digital signal to the analog voltage signal generation circuit 65 in the SOC. This digital signal is called a DAC value, and corresponds to waveform information for determining the waveform of the drive waveform signal COM that drives the piezo element PZT in this embodiment. That is, the CPU 62 corresponds to a digital signal generation unit that generates a digital signal (DAC value).

  Further, the CPU 62 generates various control signals such as a latch signal LAT, a change signal CH, and a transfer clock signal SCK, and outputs them to the head unit 40. These control signals are used when generating a SW signal for controlling application of the drive waveform signal COM to the piezo element PZT together with the pixel data SI described above in the head controller HC described later.

  The analog voltage signal generation circuit 65 is an analog waveform signal generation unit that generates an analog voltage signal COM ′, which is a voltage change pattern that is a basis of the drive waveform signal COM, based on a digital signal (DAC value) input from the CPU 62. is there. For example, for a digital signal (DAC value), an analog voltage signal having a waveform corresponding to the value of the digital signal is set so that the higher the value of the digital signal, the higher the voltage, and the lower the digital signal value, the lower the voltage. Generate. In the present embodiment, the analog voltage signal COM ′ is a voltage waveform signal having a voltage of about 3.3V.

  As described above, in this embodiment, since the CPU 62 and the analog voltage signal generation circuit 65 are integrally formed in the SOC, an accurate analog voltage signal COM ′ can be generated.

  When the CPU 62 and the analog voltage signal generation circuit 65 are installed at separate positions as separate units, the transmission path when the digital signal (DAC value) generated by the CPU 62 is transmitted to the analog voltage signal generation circuit 65. In this case, the DAC value may be distorted due to the influence of noise or the like. When distortion occurs in the DAC value, the distortion is also propagated to the analog voltage signal COM ′ generated from the DAC value in the analog voltage signal generation circuit 65, making it difficult to obtain an accurate waveform. Therefore, the finally generated drive waveform signal COM also becomes an inaccurate waveform, and the expansion / contraction operation of the piezo element PZT is disturbed, making it difficult to control the ink ejection amount.

  On the other hand, in the present embodiment, since the CPU 62 and the analog voltage signal generation circuit 65 are integrally configured as an SOC, the possibility of being affected by noise in the DAC value transmission process is very small. Therefore, the analog voltage signal COM ′ can be accurately generated, and the drive waveform signal COM having an accurate waveform shape can be easily generated.

  The current signal generation circuit 67 is a current signal generation unit that generates a current signal corresponding to the voltage signal. In other words, the current signal generation circuit 67 corresponds to a V / I converter that converts a voltage signal into a current signal. The current signal generation circuit 67 is a general V / I conversion circuit configured by combining an operational amplifier and a resistor.

  In the present embodiment, the current signal generation circuit 67 V / I converts the analog voltage signal COM ′ input from the analog voltage signal generation circuit 65 to generate a current signal corresponding to COM ′, and a transmission unit 70 described later. To the head unit 40. Specifically, by generating a current signal having a magnitude corresponding to the waveform (voltage) of the analog voltage signal COM ′, the voltage waveform information is transmitted to the head unit 40 as current value information. A method for generating the drive waveform signal COM from the transmitted current signal will be described later.

  Note that the current signal generation circuit 67 may be included in the SOC. In other words, the SOC is a chip in which the unit control circuit 64, the analog voltage signal generation circuit 65, and the current signal generation circuit 67 are integrally formed, and from the generation of the digital signal to the generation of the current signal within one chip. It is good also as performing in. Thereby, in the signal path between the analog voltage signal generation circuit 65 and the current signal generation circuit 67, the possibility of COM 'being affected by noise can be reduced. In addition, the number of parts in the controller 60 can be reduced.

<Transmitter 70>
The transmission unit 70 includes a plurality of transmission lines that connect the main board Base_M of the controller 60 and the head board Base_H of the head unit 40. Various control signals such as a current signal output from the controller 60, pixel data SI, latch signal LAT, change signal CH, and transfer clock signal SCK are transmitted to the head unit 40 side through each transmission line of the transmission unit 70. Is done. In this embodiment, a flexible flat cable (hereinafter also referred to as FFC) as shown in FIG. The FFC is a ribbon-shaped transmission member in which a plurality of flat transmission lines can be integrally moved while reducing the thickness of the cable itself by arranging a plurality of flat transmission lines in parallel.

  The FFC also includes a transmission line for supplying power to the head unit 40 from a power supply (for example, main power supply Vdd), a ground line for applying a ground (GND) voltage, and the like. In the present embodiment, the potential difference between the main power supply Vdd and the ground is about 42V.

<Printer operation>
The printing operation of the printer 1 will be briefly described. The controller 60 receives a print command from the computer 110 via the interface unit 61 and controls each unit to perform a paper feed process, a dot formation process, a transport process, and the like.

  The paper feed process is a process of supplying paper to be printed into the printer and positioning the paper at a print start position (also referred to as a cue position). The controller 60 rotates the paper feed roller 21 and sends the paper to be printed to the transport roller 23. Subsequently, the transport roller 23 is rotated, and the paper fed from the paper feed roller 21 is positioned at the print start position.

  The dot forming process is a process for forming dots on paper by ejecting ink intermittently from a head moving in the moving direction (scanning direction). The controller 60 moves the carriage 31 in the movement direction, and ejects ink from the head 41 based on the print data while the carriage 31 is moving. When the ejected ink droplets land on the paper, dots are formed on the paper, and a dot line composed of a plurality of dots along the moving direction is formed on the paper.

  The carrying process is a process of moving the paper relative to the head in the carrying direction. The controller 60 rotates the transport roller 23 to transport the paper in the transport direction. By this carrying process, the head 41 can form dots at positions different from the positions of the dots formed by the previous dot formation process.

  The controller 60 alternately repeats the dot formation process and the conveyance process until there is no more data to be printed, and gradually prints an image composed of dot lines on paper. When there is no more data to be printed, the paper discharge roller 25 is rotated to discharge the paper. The determination of whether or not to discharge paper may be based on a paper discharge command included in the print data.

  The same processing is repeated when printing on the next paper, and the printing operation is terminated when not printing.

=== Generation of Drive Waveform Signal COM ===
<Description of Head Control Unit HC>
First, the configuration and operation of the head controller HC will be described. FIG. 4 is a diagram illustrating the configuration and operation of the controller 60 and the head controller HC in the present embodiment.

  The head control unit HC includes a head control circuit 42, a potential difference detection unit 43, and a drive waveform signal generation circuit 44, and is provided on a head substrate Base_H fixed to the head 41 (FIG. 4). The drive waveform signal generation circuit 44 includes a voltage amplification unit 441, a switch 442, and a current amplification unit 443. Although only two piezo elements PZT are illustrated in FIG. 4, the printer 1 actually includes a large number of piezo elements. In the configuration shown in FIG. 4, the switch 442 and the current amplifying unit 443 are provided for each piezo element PZT.

  The head control circuit 42 outputs various control signals such as a transfer clock signal SCK, a latch signal LAT, and a change signal CH transmitted from the controller 60, and an SW signal for controlling the switch 442 according to the pixel data SI. To do.

  The potential difference detection unit 43 detects a potential difference between two different points in the transmission path of the current signal transmitted from the current signal generation circuit 67 of the controller 60 via the FFC, and outputs it as a potential difference signal COM ″. In the present embodiment, the potential difference is detected using a resistor having a predetermined resistance value. Specifically, a resistor is provided in a path through which a current signal flows, and a potential difference generated at both ends of the resistor when the current signal flows through the resistor is detected. This makes it possible to detect the potential difference easily and accurately. An element other than a resistor can be used as long as it can detect a potential difference between two different points in the current signal transmission path. For example, the potential difference may be detected using an element such as a transistor or a phototransistor.

  FIG. 5 is a diagram for explaining the flow until the potential difference signal COM ″ is generated from the digital signal. First, the CPU 62 generates a digital signal (DAC value) that defines the waveform shape of the drive waveform signal COM. Next, the analog voltage signal generation circuit 65 generates an analog voltage signal COM ′ based on the DAC value. It is assumed that the voltage value at a certain moment of COM ′ is represented by Vd. Subsequently, the current signal generation circuit 67 V / I converts COM ′ to generate a current signal. As described above, the current value of the current signal is a value corresponding to the voltage waveform of COM ′. For example, the current value at a certain moment is represented by Ia (= α · Vd). Thus, the current value is controlled by the current signal generation circuit 67 (current control), and is transmitted as a current signal to the potential difference detection unit 43 provided in the head unit 40 via the transmission unit 70 (FFC).

  Here, in the circuit through which current flows, the sum of currents flowing into arbitrary points is equal to the sum of currents flowing out (Kirchhoff's first law). Therefore, when the current value controlled by the current signal generation circuit 67 at a certain moment is Ia, the current value flowing at a certain moment at any point in the transmission path is Ia.

  In FIG. 5, when a resistor having a resistance value R is used as the potential difference detection unit 43, the potential difference of R · Ia between the terminals A (current input side terminal) and B (current output side terminal) of the resistor. Will occur. A potential difference signal COM ″ is generated by the potential difference detected between the terminals of AB. That is, the voltage value of the potential difference signal COM ″ is a value proportional to the current value of the current signal.

  In the present embodiment, it is possible to prevent malfunctions or the input itself from being sensed when a voltage lower than GND is input to each element of the drive waveform signal generation circuit 44 described later. For example, by providing an element such as a resistor between the low-potential side point (point B) and GND among the two points (points A and B in FIG. 5) for detecting the potential difference, the minimum potential at the point B can be reduced. It can be sufficiently higher than GND. As shown in FIG. 5, when a resistor having a resistance value r is provided between point B and GND, the potential at point B on the low potential side is r · Ia, which is more reliably determined from the potential of GND. Also have a high potential. This makes it easier to suppress malfunction of the drive waveform signal generation circuit 44. However, the drive waveform signal COM can be generated even when there is no resistance between the point B and GND.

  In FIG. 5, the transmission unit 70 has a path for returning to the main board Base_M after the current Ia flows out of the resistor R. That is, the transmission unit 70 has a path for transmitting (returning) the current signal from the head unit 40 to the controller 60. This path and the path from the main board Base_M to the head board Base_H are so-called differential. Therefore, transfer without distortion is performed by matching the resistance R and the characteristic impedance of the transmission unit 70. Further, if the path from the main board Base_M to the head board Base_H and the path in the opposite direction are close to each other, the two paths are equally affected by noise from the outside, so that the influence of noise can be reduced. It also has the feature of differential transfer.

  The drive waveform signal generation circuit 44 performs voltage amplification and current amplification on the potential difference signal COM ″ based on the potential difference detected from the current signal in the potential difference detection unit 43 to generate a drive waveform signal COM that is a voltage signal, and the piezo element PZT. To drive the piezo element PZT. That is, the drive waveform signal generation circuit 44 corresponds to a voltage signal generation unit (FIG. 4).

  The voltage amplifier 441 amplifies the voltage of the potential difference signal COM ″ to generate a potential difference signal COM ″ ″. For example, a voltage of about 3V is amplified to about 30V, which is a voltage necessary for driving each piezo element PZT. As the voltage amplifier 431, a general voltage amplifier circuit using an operational amplifier or the like can be used.

  The switch 442 inputs the potential difference signal COM ′ ″ voltage amplified by the voltage amplifier 441 to the current amplifier 443 in accordance with the SW signal input from the head control circuit 42. For example, when the SW signal is at the H level, the switch 442 is turned on, and the potential difference signal COM ′ ″ is input to the current amplification unit 443. On the other hand, when the SW signal is at the L level, the switch 442 is turned off, and the potential difference signal COM ′ ″ is not input to the current amplifier 443.

  The current amplifying unit 443 receives an input of the potential difference signal COM ′ ″, amplifies the current, generates a drive waveform signal COM, and applies it to the piezo element PZT. The current amplifying unit 443 is configured by complementarily connecting an NPN transistor and a PNP transistor. The collector of the NPN transistor is connected to the main power supply Vdd, and the collector of the PNP transistor is connected to the ground (GND). In addition, the current amplifying portion 443 can be configured using an element other than a transistor.

  The arrangement of the voltage amplification unit 441, the switch 442, and the current amplification unit 443 is not limited to the example illustrated in FIG. For example, the positions of the voltage amplification unit 441 and the switch 442 may be reversed, or the positions of the switch 442 and the current amplification unit 443 may be reversed. In this case, however, it should be noted that the number of voltage amplification units 441 and current amplification units 443 needs to be changed as appropriate.

  Further, the head substrate Base_H has a capacitor (not shown) having a sufficient capacity and is connected to Vdd. Even if a large current is simultaneously supplied to many piezoelectric elements PZT, a current is instantaneously supplied from the capacitor. Since no large current flows through the transmission unit 70, the current capacity of the transmission unit 70 can be reduced.

  FIG. 6 is a diagram for explaining the generated drive waveform signal COM. As shown in the figure, the drive waveform signal COM is generated using a period T with the rising timing of the latch signal LAT as a unit. The period T includes sections T1 to T4 divided by the rising timing of the latch signal LAT or the change signal CH. The sections T1 to T4 include drive pulses described later. A period T that is a repetition period corresponds to a period during which the nozzle moves by one pixel. For example, when the print resolution is 720 dpi, the period T corresponds to a period for the nozzle to move 1/720 inch. Then, based on the pixel data SI, by applying the drive pulses PS1 to PS4 of each section included in the period T to the piezo element PZT, the amount of ink ejected from the nozzles is adjusted, and an image having a plurality of gradations. Is possible.

The drive waveform signal COM includes a first waveform section SS1 generated in the section T1 in the repetition period, a second waveform section SS2 generated in the section T2, a third waveform section SS3 generated in the section T3, and a section T4. And a fourth waveform section SS4 generated in Here, the first waveform section SS1 has a drive pulse PS1. The second waveform section SS2 has a drive pulse PS2, the third waveform section SS3 has a drive pulse PS3, and the fourth waveform section SS4 has a drive pulse PS4.
Each drive pulse has a voltage waveform and is generated using a potential difference between the main power supply Vdd and the ground (GND).

  When the pixel data SI is [00], the first interval signal SS1 of the drive waveform signal COM is applied to the piezo element PZT, and the piezo element PZT is driven by the drive pulse PS1. When the piezo element PZT is driven in accordance with the drive pulse PS1, pressure fluctuations such that ink is not ejected occur in the ink, and the ink meniscus (the free surface of the ink exposed at the nozzle portion) vibrates slightly.

  When the pixel data SI is [01], the third interval signal SS3 of the drive waveform signal COM is applied to the piezo element PZT, and the piezo element PZT is driven by the drive pulse PS3. When the piezo element PZT is driven according to the drive pulse PS3, a small amount of ink is ejected, and a small dot is formed on the medium.

  When the pixel data SI is [10], the second interval signal SS2 of the drive waveform signal COM is applied to the piezo element PZT, and the piezo element PZT is driven by the drive pulse PS2. When the piezo element PZT is driven according to the drive pulse PS2, a medium amount of ink is ejected, and a medium dot is formed on the medium.

  When the pixel data SI is [11], the second interval signal SS2 and the fourth interval signal SS4 of the drive waveform signal COM are applied to the piezo element PZT, and the piezo element PZT is driven by the drive pulse PS2 and the drive pulse PS4. When the piezo element PZT is driven according to the drive pulse PS2 and the drive pulse PS4, a large dot is formed on the medium.

<Effect of transmitting current signal>
First, as a comparative example, when the analog voltage signal COM ′ generated by the analog voltage signal generation circuit 65 is not converted into a current signal but is transmitted to the head unit 40 as it is, the drive waveform signal COM is generated and printing is performed. Will be described.

  FIG. 7 is a diagram illustrating the configuration and operation of the controller 60 and the head controller HC in the comparative example. The printer of the comparative example does not include the current signal generation circuit 67 and the potential difference detection unit 43. Other configurations are basically the same as those of the printer 1 of the embodiment.

  In the comparative example, the analog voltage signal COM ′ is directly transmitted to the drive waveform signal generation circuit 44. At this time, the analog voltage signal COM ′ is transmitted over a relatively long distance in the FFC (transmission unit 70) that connects between the main board Base_M of the controller 60 and the head board Base_H of the head unit 40. There is a risk of receiving noise during transmission. Since COM ′ is an analog signal, distortion and disturbance are likely to occur in the shape of the voltage waveform when affected by noise. When disturbance or the like occurs in the waveform of COM ′, the waveform of the drive waveform signal COM generated based on COM ′ is also deformed, so that the amount and speed of ink droplets ejected from the piezo element PZT are accurately controlled. I can't do that.

  Therefore, in the case of the comparative example, the analog voltage signal COM ′ for generating the drive waveform signal COM cannot be generated accurately due to the influence of noise received when being transmitted through the FFC. Problems arise.

  On the other hand, in this embodiment, as shown in FIG. 4, the current signal generation circuit 67 V / I converts the analog voltage signal COM ′ to generate a current signal, and transmits the current signal in the FFC. ing. As described above, since the current value is equal at any point in a circuit, the current value itself is the same value. Since the current value of the current signal is controlled by the current signal generation circuit 67, if a predetermined current value is output at the exit of the current signal generation circuit 67, it is assumed that the current signal is affected by noise during FFC transmission. However, the current value is equal at any point in the circuit thereafter.

For example, in FIG. 5, when the current value at a certain moment of the current signal output from the current signal generation circuit 67 is represented by Ia, the input side terminal A of the potential difference detection unit 43 after transmitting the FFC is also used. The current value is Ia. The current value is also Ia at the output side terminal B of the potential difference detection unit 43. Therefore, even when the current signal is affected by noise during FFC transmission, the potential difference between the AB terminals detected by the potential difference detection unit 43 is R · Ia.
Further, since signals are sent differentially as shown in FIG. 5, there is an advantage of differential transfer.

  That is, in this embodiment, the voltage value detected as the inter-terminal voltage between AB is a value that does not depend on the influence of noise, and therefore the drive waveform signal COM generated by amplifying the inter-terminal voltage is also noise-induced. It can be said that the signal has a small influence. As a result, an accurate drive waveform signal COM resistant to disturbance is generated, and the driving of the piezo element PZT can be controlled with high accuracy.

<Summary>
In the present embodiment, the CPU 62 generates a DAC value that is a digital signal that defines the waveform shape of a predetermined signal, and the analog voltage signal generation circuit 65 generates an analog voltage signal COM ′ based on the DAC value. The generation circuit 67 generates a current signal having a magnitude corresponding to the waveform of the analog voltage signal COM ′. The generated current signal is transmitted from the control unit 60 to the head unit 40 via the FFC. In the transmitted current signal, a potential difference between two different points is detected in the current path in the potential difference detection unit 43, and the drive waveform signal COM is amplified by voltage amplification and current amplification of the potential difference by the drive waveform signal generation circuit 44. Generated. The drive waveform signal COM is applied to drive the piezo element PZT, thereby ejecting ink.

  Although the current signal may receive noise while being transmitted through the FFC, the current value of the current signal itself is equal at any point in the circuit, so the potential difference between two different points in the current path is It can be detected as a value proportional to the current value regardless of the influence of noise. Therefore, by amplifying the potential difference, it is possible to generate an accurate drive waveform signal COM that is resistant to disturbance.

=== 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 each of the above-described embodiments, the printer has been described as an example of the liquid ejection device, but the present invention is not limited to this. For example, color filter manufacturing apparatus, dyeing apparatus, fine processing apparatus, semiconductor manufacturing apparatus, surface processing apparatus, three-dimensional molding machine, liquid vaporizer, organic EL manufacturing apparatus (especially polymer EL manufacturing apparatus), display manufacturing apparatus, film formation You may apply the technique similar to this embodiment to the various liquid ejection apparatuses which applied inkjet technology, such as an apparatus and a DNA chip manufacturing apparatus.

<About piezo elements>
In each of the above-described embodiments, the piezo element PZT is exemplified as the element that performs the operation for ejecting the liquid. However, other elements may be used. For example, a heating element or an electrostatic actuator may be used.

<Regarding Transistor of Current Amplifier 443>
In each of the above-described embodiments, the NPN transistor and the PNP transistor are exemplified as the transistors included in the current amplifying unit 443. However, other types of transistors may be used as long as they can amplify current for the analog voltage signal COM ′.

<About other devices>
In each of the above-described embodiments, an ink jet printer (serial printer) of a type that moves the head 41 together with the carriage has been described as an example. However, the printer may be a so-called line printer having a fixed head.

  DESCRIPTION OF SYMBOLS 1 Printer, 20 Conveyance unit, 21 Feed roller, 22 Conveyance motor, 23 Conveyance roller, 24 Platen, 25 Discharge roller, 30 Carriage unit, 31 Carriage, 32 Carriage motor, 40 Head unit, 41 Head, 411 Case, 412 Flow path unit, 412a Flow path forming plate, 412b Elastic plate, 412c Nozzle plate, 412d Pressure chamber, 412e Nozzle communication port, 412f Common ink chamber, 412g Ink supply path, 412h Island portion, 412i Elastic film, 42 Head control circuit, 43 potential difference detection unit, 44 drive waveform signal generation circuit, 441 voltage amplification unit, 442 switch, 443 current amplification unit, 50 detector group, 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 analog voltage signal generation circuit, 67 current signal generation circuit, 70 transmission unit, 110 computer, SOC System-on-a -tip, PZT piezo element.

Claims (4)

(A) a control unit that generates a current signal ;
(B) a voltage signal generation unit that detects a potential difference between two different points in a path through which the current signal flows, amplifies the potential difference, and generates a voltage signal;
An element driven by the voltage signal to eject liquid from the nozzle;
A head portion having
(C) a transmission unit having a path for transmitting the current signal from the control unit to the head unit;
With
The transmission unit further includes a path for returning the current signal transmitted from the control unit to the head unit from the head unit to the control unit;
A liquid ejection apparatus, wherein differential transmission is performed when the current signal is transmitted through the transmission unit. The liquid ejection device according to claim 1,
Of the two different points for detecting the potential difference, the liquid jet device is characterized in that the potential at the low potential side is higher than the potential at GND. The liquid ejection device according to claim 1 or 2 ,
Having a resistance in the path through which the current signal flows;
A liquid ejecting apparatus that detects a difference in potential generated at both ends of a resistor when the current signal flows through the resistor. Generating a current signal;
Via the transmission unit having a path for transmitting the current signal from the control unit to the head unit, and a path for returning the current signal transmitted from the control unit to the head unit from the head unit to the control unit. Performing differential transmission when transmitting current signals;
Detecting a potential difference between two points on different paths through which the current signal flows in the head unit, amplifying the potential difference, and generating a voltage signal;
Driving the element with the voltage signal to eject liquid from the nozzle;
A liquid jetting method.

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