JP2007030180A - Inkjet printer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inkjet printer which can surely suppress irregularities in size of ink dots on a printing medium formed by ink droplets ejected from inkjet nozzles. <P>SOLUTION: An image of the ink dots is photographed by an image sensor which uses an optical lens. A dot area S of the ink dot is measured from the image. Driving waveforms are arranged in a drive signal which drives an actuator, in time series so that the ink dots of a larger number of gradations than that of a required gradient can be formed. For example, the preliminarily set driving waveform is selected to eject the ink droplets. If the dot area S of the ink dot is too large, the driving waveform is renewed to the driving waveform which forms ink dots smaller by one level, and is stored. If the dot area S of the ink dot is too small, the driving waveform is renewed to the driving waveform which forms ink dots larger by one level, and is stored. A quantity of the ink droplets is thus adjusted while reflecting the size of the ink dot. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an ink jet printer that prints predetermined characters and images by ejecting fine particles (ink droplets) of a plurality of liquid inks from nozzles and forming minute dots on a print medium, for example. is there.

Such inkjet printers are generally inexpensive and can easily obtain high-quality color prints, and therefore have become widespread not only in offices but also in general users with the spread of personal computers and digital cameras.
In general, such an ink jet printer reciprocates in a direction intersecting with the conveyance direction of a print medium by a moving body called a carriage integrally provided with an ink cartridge and an ink discharge head (generally called an ink jet head). However, by discharging (jetting) and outputting fine particles of liquid ink from the nozzles of the inkjet head, minute ink dots are formed on the print medium, and predetermined characters and images are drawn to create a desired printed matter. It has become. The carriage is equipped with four color (yellow, magenta, cyan) ink cartridges including black (black) and an inkjet head for each color, so that not only monochrome printing but also full-color printing combining each color is easy. (Furthermore, 6 colors, 7 colors, or 8 colors in which light cyan, light magenta, etc. are added to these colors are also put into practical use).

  Further, in this type of ink jet printer in which printing is executed while reciprocating the ink jet head on the carriage in a direction intersecting with the conveyance direction of the print medium, the ink jet head is set to 10 to cleanly print the entire page. Since it is necessary to reciprocate from several times to several tens of times, there is a disadvantage that it takes much printing time compared with other types of printing apparatuses such as laser printers and copying machines using electrophotographic technology.

  In contrast, in an inkjet printer of a type in which a long inkjet head (not necessarily integrated) having the same dimensions as the width of the print medium is disposed and the carriage is not used, the inkjet head is moved in the width direction of the print medium. This is not necessary, and so-called one-pass printing is possible, so that high-speed printing similar to the laser printer is possible. The former inkjet printer is generally referred to as a “multi-pass (serial) inkjet printer”, and the latter inkjet printer is generally referred to as a “line head inkjet printer”.

Incidentally, ink droplets ejected from a plurality of ink jet nozzles or ink dots formed on a print medium vary. For example, the inkjet nozzles between the inkjet heads arranged side by side also vary between the inkjet nozzles formed in one inkjet head. Therefore, in the inkjet printer described in Patent Document 1 below, density unevenness is detected for each of the divided density areas, and the ink jet nozzle is corrected based on the density unevenness, for example, by applying correction to the read image signal. Density unevenness due to the variation between them is suppressed.
Japanese Patent Laid-Open No. 5-220977

  However, in the ink jet printer described in Patent Document 1, density unevenness is detected for each divided density region, so that variations in ink droplets ejected from ink jet nozzles or ink dots formed on a print medium are suppressed. There is a limit to doing it. In other words, the so-called optical density in a predetermined region is related to the so-called flying curvature of ink droplets, in which ink dots are not formed at predetermined positions, in addition to the variation of ink dots due to the variation of ink droplets. This is because the upper optical density changes.

  The present invention has been made paying attention to the above problems, and an ink jet capable of suppressing variations in ink droplets ejected from an ink jet nozzle or ink dots formed on a print medium. The object is to provide a printer.

  [Invention 1] In order to solve the above problems, an inkjet printer according to Invention 1 is an inkjet printer that performs printing by ejecting ink droplets from inkjet nozzles to form ink dots on the printing medium. An ink dot detecting unit for detecting the size of the ink dot, and an ink droplet for adjusting an amount of the ink droplet ejected from the ink jet nozzle based on the size of the ink dot on the print medium detected by the ink dot detecting unit. And adjusting means.

  The ink jet nozzle referred to in the present invention refers to an ink output nozzle used in, for example, an ink jet printer, and ejects fine ink droplets onto a print medium by a known electrostatic method, piezo method, film boiling ink jet method, or the like. Treated as a generic term for what forms round ink dots. Further, the size of the ink dot can be evaluated based on the area and diameter of the ink dot.

  According to the ink jet printer according to the first aspect of the invention, the size of the ink dots on the print medium is detected, and the amount of ink droplets ejected from the ink jet nozzle is determined based on the detected size of the ink dots on the print medium. Since the adjustment is made, variations in ink droplets ejected from the inkjet nozzles or variations in ink dots formed on the print medium can be reliably suppressed.

  [Invention 2] The ink jet printer of Invention 2 is the ink jet printer of Invention 1, wherein the amount of ink droplets ejected from the ink jet nozzles is changed by changing the drive signal to the actuator, and the ink on the print medium is changed. A multi-gradation output unit that forms a dot size with two or more gradations, and the ink dot detection unit includes an image processing unit that detects an area of an ink dot on a print medium, and the ink droplet adjustment unit Comprises drive signal setting means for setting a drive signal for the multi-tone output means based on the area of the ink dots on the print medium detected by the image processing means.

  According to the ink jet printer according to the second aspect of the invention, by changing the drive signal to the actuator, the amount of ink droplets ejected from the ink jet nozzle is changed, and the size of the ink dots on the print medium is set to two or more. Since it is possible to form with gradation, and the drive signal to the actuator is set based on the area of the ink dot on the printing medium detected by the image processing means, the ink jet nozzle is ejected at each gradation degree of two or more. It is possible to reliably suppress variations in ink droplets or variations in ink dots formed on the print medium.

  [Invention 3] The inkjet printer according to Invention 3 is the inkjet printer according to Invention 2, in which the multi-gradation output means selects a combination of one or more drive waveforms from the drive waveform selection table corresponding to the gradation, and is requested. A drive signal corresponding to the tone is created, and the drive signal setting unit selects the drive waveform corresponding to the tone level of the multi-tone output unit based on the area of the ink dots on the print medium detected by the image processing unit. The table is updated.

  According to the ink jet printer according to the third aspect of the present invention, when a combination of one or more drive waveforms is selected from the drive waveform selection table corresponding to the gray scale and a drive signal corresponding to the required gray scale is created, the image processing means Since the gradation-corresponding drive waveform selection table is updated based on the detected area of the ink dots on the print medium, variations in the ink droplets ejected from the inkjet nozzles or ink dots formed on the print medium are determined. It is possible to suppress the storage capacity of the drive signal when the variation is to be suppressed.

[Invention 4] The inkjet printer of Invention 4 is characterized in that, in the inkjet printer of Invention 3, the number of combinations of drive waveforms that can be selected is larger than the required number of gradations.
According to the ink jet printer according to the fourth aspect of the invention, the number of combinations of drive waveforms that can be selected is larger than the required number of gradation levels, so that the number of drive waveform selection patterns increases and ink droplets ejected from the ink jet nozzles. Or variations in ink dots formed on the print medium can be reliably suppressed.

[Invention 5] The inkjet printer according to Invention 5 is the inkjet printer according to any one of Inventions 1 to 4, wherein the ink droplet adjusting means is configured to supply ink droplets ejected from the inkjet nozzles after power-on and before printing. It is characterized by adjusting the amount.
In the ink jet printer according to the fifth aspect of the present invention, the amount of ink droplets ejected from the ink jet nozzles is adjusted after the power is turned on and before printing is performed. It is possible to suppress the variation of the ink dots formed above at an appropriate timing.

[Invention 6] The inkjet printer according to Invention 6 is the inkjet printer according to any one of Inventions 1 to 5, wherein the ink droplet adjusting means discharges from the inkjet nozzle when the temperature change amount exceeds a predetermined value. The amount of ink droplets is adjusted.
According to the ink jet printer according to the sixth aspect of the invention, since the amount of ink droplets ejected from the ink jet nozzles is adjusted when the temperature change amount exceeds a predetermined value, variations in ink droplets ejected from the ink jet nozzles are achieved. Alternatively, it is possible to suppress variations in ink dots formed on the print medium at an appropriate timing.

[Invention 7] The ink-jet printer according to Invention 7 is the ink-jet printer according to any one of Inventions 1 to 6, wherein the ink droplet adjusting means is an amount of ink droplets ejected from the ink-jet nozzle when the type of printing medium is changed. It is characterized by adjusting.
According to the ink jet printer according to the seventh aspect of the invention, since the amount of ink droplets ejected from the ink jet nozzles is adjusted when the type of the print medium is changed, variations in the ink droplets ejected from the ink jet nozzles or on the print medium It is possible to suppress the variation of the ink dots formed at the appropriate timing.

[Invention 8] The inkjet printer according to Invention 8 is the inkjet printer according to any one of Inventions 1 to 7, wherein the ink droplet adjusting means discharges from the inkjet nozzle when the ink cartridge filled with ink is replaced. The amount of ink droplets is adjusted.
According to the ink jet printer according to the eighth aspect of the invention, since the amount of ink droplets ejected from the ink jet nozzles is adjusted when the ink cartridge filled with ink is replaced, variations in the ink droplets ejected from the ink jet nozzles are achieved. Alternatively, it is possible to suppress variations in ink dots formed on the print medium at an appropriate timing.

[Invention 9] The inkjet printer according to Invention 9 is the inkjet printer according to any one of Inventions 1 to 8, wherein the ink droplet adjusting means adjusts the amount of ink droplets ejected from the inkjet nozzle before the power is turned off. It is a feature.
In the ink jet printer according to the ninth aspect of the invention, since the amount of ink droplets ejected from the ink jet nozzles is adjusted before the power is turned off, ink droplets ejected from the ink jet nozzles or ink formed on the print medium It becomes possible to suppress dot variation at an appropriate timing.

Next, a first embodiment of the inkjet printer of the present invention will be described with reference to the drawings.
FIG. 1 a is a schematic configuration diagram of the ink jet printer of the present embodiment. Reference numeral 101 in the drawing is an endless conveyance belt for conveying the print medium 102. As described above, the print medium 102 is a sheet-like member such as print paper or an OHP sheet. Further, the conveying belt 101 includes a driving roller 103 disposed at the left end portion in the drawing, a driven roller 104 disposed at the right end portion in the drawing, and a tension roller 105 disposed below the central portion thereof. It is wound. The driving roller 103 is driven to rotate in the direction of the arrow in the figure by a driving source (not shown), and the printing medium 102 is moved from the right side of the figure in a state where the printing medium 102 is adsorbed to the conveyance belt 101 by negative pressure or electrostatic attraction force. Transport to the left, that is, in the direction of the arrow. A paper pressing roller 109 is in contact with the driven roller 104, and the printing medium 102 is pressed against the conveying belt 101 by the two rollers, and the printing medium 102 is brought into close contact with and adsorbed to the conveying belt 101. The tension roller 105 is urged downward by a spring (not shown), thereby applying tension to the conveyor belt 101.

  When the print medium 102 is attracted to the conveyance belt 101 by negative pressure, for example, a plurality of holes are formed in the conveyance belt 101 and the negative pressure is generated in the holes to cause the print medium 102 to adhere to the conveyance belt 101. Adsorbed. When the print medium 102 is attracted to the conveyance belt 101 by electrostatic attraction force, for example, a medium-resistance charging roller is brought into close contact with the dielectric conveyance belt 101, and a high voltage is applied to the charging roller to apply the conveyance belt. 101 is charged, dielectric charge is generated in the print medium 102 by the charge, and the print medium 102 is applied to the surface of the transport belt 101 by electrostatic force due to the charge of the print medium 102 due to the dielectric polarization and the charge of the surface of the transport belt 101. Adsorbed.

  A gate roller (not shown) is disposed on the upstream side of the paper pressing roller 109 in the conveyance direction of the printing medium 102. This gate roller adjusts the timing at which the print medium 102 fed from the paper feed unit 114 is fed onto the transport belt 101, and also bends the print medium 102 in the transport direction and corrects so-called skew. Further, a backup roller 112 is provided below an ink jet head 34 (to be described later) constituting the print area so as to face the ink jet head 34. By restricting the position of the conveyor belt 101 by the backup roller 112 and by regulating the tension of the conveyor belt 101 by the tension roller 105, speed fluctuation and position fluctuation of the conveyor belt 101, that is, the printing medium 102 in the printing region are suppressed. be able to. Note that reference numeral 115 in the drawing denotes a paper discharge unit that discharges the print medium 2.

  Reference numeral 34 in FIG. 1 denotes an inkjet head. The ink-jet head 34 is arranged so as to be shifted in the transport direction of the printing medium 102 for each of the four colors of yellow (Y), magenta (M), cyan (C), and black (K). Ink is supplied to each inkjet head 34 from the corresponding ink tank 111 of each color via the ink supply tube 110. Each inkjet head 34 is formed with a plurality of nozzles in a direction intersecting with the transport direction of the print medium 102, and by ejecting a necessary amount of ink droplets from these nozzles to a required location at the same time, the print medium 102. A minute ink dot is formed and output on the top. By performing this for each color, it is possible to perform so-called one-pass printing by passing the print medium 102 adsorbed on the conveyor belt 101 once.

  As a method for discharging and outputting ink from each nozzle of the ink jet head, there are an electrostatic method, a piezo method, a film boiling ink jet method, and the like. In the electrostatic system, when a drive signal is given to the electrostatic gap, which is an actuator, the diaphragm in the cavity is displaced, causing a pressure change in the cavity, and ink drops are ejected from the nozzle by the pressure change. It is. In the piezo method, when a drive signal is given to a piezo element that is an actuator, the diaphragm in the cavity is displaced to cause a pressure change in the cavity, and ink droplets are ejected from the nozzle by the pressure change. . In the film boiling ink jet method, there is a minute heater in the cavity, the ink is instantaneously heated to 300 ° C. or more, the ink becomes a film boiling state, bubbles are generated, and ink droplets are ejected from the nozzle by the pressure change. That's it. Any ink output method can be applied to the present invention.

  FIG. 2 shows two examples of the inkjet head 34 of the present embodiment. 2A is an example of an ink jet head using a multilayer piezoelectric element, and FIG. 2B is an example of an ink jet head using a single layer piezoelectric element. In the laminated piezoelectric element of FIG. 2 a, a plurality of single-layer piezoelectric elements 71 are laminated and supported by a support 73. In any case, a diaphragm 72 is provided at the upper end of the inkjet head 34, and a laminated or single-layer piezoelectric element 71 is disposed above the diaphragm 72. A plurality of nozzles 5 are provided on the nozzle surface 4 corresponding to the lower surface of the inkjet head 34, and cavities (pressure chambers) 75 communicating with the nozzles 5 communicate with the common ink unit 76. Ink is supplied directly from the main tank or the ink cartridge or via the sub tank. Therefore, when a drive signal COM is input from the drive signal generation circuit 70 described later to the stacked or single-layer piezoelectric element 71, each piezoelectric element 71 is bent, and the vibration of the vibration plate 72 is generated. Then, the volume of the cavity 75 is enlarged to draw ink, and then the volume of the cavity 75 is reduced to eject ink droplets. The laminated piezoelectric element has a feature that a large driving force can be obtained because the piezoelectric element 71 is laminated.

  By the way, in this type of inkjet head, if bubbles are generated in the cavity (pressure chamber), floating paper powder or dust adheres to the vicinity of the nozzle, or the nozzle (inner ink) dries, Ink droplets may not be ejected and dots may not be formed on the print medium. Ink droplet ejection failure is generally called “dot missing”. When a dot missing phenomenon occurs, recovery is performed by a cleaning device. For example, when a dot drop phenomenon occurs due to the generation of bubbles, the ink in the nozzle is sucked with a pump to discharge the bubbles inside the cavity, and then the ink attached to the nozzle surface is removed with a wiping member called a wiper. Wiping off and discharging the ink droplets called non-printing, called flushing, to discharge the mixed ink. This series of cleaning steps recovers the dot drop phenomenon due to bubbles.

  Returning to FIG. 1 a, in the present embodiment, the size of the ink dots formed on the print medium 102 on the downstream side in the print medium 102 transport direction of the ink jet 34 arranged shifted in the transport direction of the print medium 102. More precisely, an ink dot detection device 3 for detecting the area is provided. FIG. 1 b shows details of the ink dot detection device 3. A symbol id on the print medium 102 indicates an ink dot. The ink dot detection device 3 includes a carriage shaft 60 that is long in a direction that intersects the conveyance direction of the print medium 102, a drive pulley 61 that is provided at the right end of the carriage shaft 60, and the carriage shaft 60. A driven pulley 62 provided at the left end, a toothed belt 63 wound around the driving pulley 61 and the driven pulley 62, a carriage motor 22 for rotationally driving the driving pulley 61, and a driven pulley 62 are provided. A tensioner 65 for adjusting the tension of the toothed belt 63 by force, a carriage 8 fixed to the toothed belt 63 and slidably attached to the carriage shaft 60, and a carriage moved parallel to the carriage shaft 60 An encoder 66, a carriage encoder sensor 28 that is attached to the carriage 8 and reads the carriage encoder 66, and a carrier The image sensor 6 is attached to the printer 8 and reads the ink dot id on the print medium 102, and the illumination 7 that irradiates the surface of the print medium 102 to read the ink dot id by the image sensor 6. The According to the ink dot detection device 3, when the carriage motor 22 is driven and the drive motor 61 is rotated, the carriage 8 intersects the conveyance direction of the print medium 102 along the carriage shaft 60 as the toothed belt 63 moves. It is moved in the direction, that is, in the direction of the arrow. At this time, the ink dot id is read by the image sensor 6 while illuminating the surface of the print medium 102 with the illumination 7.

  The size of the ink dots formed on the print medium 102 by the ink droplets ejected from the inkjet nozzle 5 is approximately 20 to 100 μm in diameter. In order to measure the area, it is difficult with a linear type image sensor having a resolution several times to 10 times the recording resolution (for example, 720 dpi) of an ink jet printer, and it is necessary to enlarge it with an optical lens and read it with the image sensor. is there. For example, consider the resolution when a round ink dot id indicated by a solid line in FIG. 3 is read by the image sensor 6 in which square pixels are arranged in a square shape. For example, when the number of pixels of the image sensor 6 is 1 million pixels, the number of pixels on one side of the square shape is 1000 pixels. When the effective window size of the pixel sensor is 0.5 mm square, the size of one pixel is 0.5 μm. For example, if the magnification of the optical lens is 8 times, an image having a size of 0.06 μm can be read by one pixel of the image sensor 6 substantially.

  In the present embodiment, for example, the number of pixels in the round circle of ink dots id (the dark hatched portion in FIG. 3a) and the pixel corresponding to the outline of the round circle (the thin hatched portion in FIG. 3a) are counted. And measure the area of the ink dots. FIG. 3b shows details of the contour portion. For example, in FIG. 3b, the upper row is m, the lower row is m-1, the rightmost column is n, the middle column is n-1, and the leftmost column is n-2. The brightness of a pixel, for example, pixel (m−1, n−2) is expressed as D (m−1, n−2). The maximum value of the lightness of the ink dot id is, for example, the lightness D (m, n) of the pixel (m, n), and the minimum value of the lightness of the ink dot id is, for example, the pixel (m-1, n-2). ) Brightness D (m−1, n−2). For example, when half the values of the lightness values D (m, n) and D (m−1, n−2) are set as the threshold value Ds and the lightness values of the respective pixels are plotted, the result is as shown in FIG. Therefore, the lightness values D (m, n-1) and D (m-1, n) of the pixels (m, n-1) and (m-1, n) having a lightness value greater than the threshold value Ds are counted. The brightness of the lightness D (m, n-2) and D (m-1, n-1) of the pixels (m, n-2) and (m-1, n-1) whose brightness is smaller than the threshold value Ds is counted. do not do.

  FIG. 4 shows the inkjet printer 2 of the present embodiment and the host computer 1 for driving it. The host computer 1 can be any computer system including a personal computer. A device driver 30 for driving itself is built in the inkjet printer 2, and the device driver 30 is driven by an appropriate program to drive the inkjet printer 2, that is, perform printing.

  The device driver 30 is configured by hardware and a program. In order to operate the device driver 30, a computer system as an arithmetic processing unit is built in the control unit 31 of the inkjet printer 2. Therefore, the control unit 31 includes a CPU 32 that is a central processing unit that performs various types of control and arithmetic processing, and a memory 33 such as a RAM that constitutes a main storage device and a ROM that is a read-only storage device. The device driver 30 detects the position of the carriage 8 or the image sensor 6 from the values of the inkjet head driver 35 that drives the inkjet head 34, the carriage driver 36 that drives the carriage motor 22, and the carriage encoder 66 detected by the carriage encoder sensor 28. A carriage position detecting circuit 37 for moving, a conveying motor 101 for moving a conveying belt 101, that is, a conveying motor 38 provided for a driving roller 103 for conveying a printing medium 102, and a belt encoder provided for the conveying belt 101. Is detected by the belt encoder sensor 40, the position of the conveyor belt 101 is detected from the signal from the belt encoder sensor 40, and the image information of the ink dot id read by the image sensor 6. The image processing circuit 9 that detects the area of the ink dot id as the size of the ink dot id, and the print medium that detects that the print medium 102 has been changed from the signal of the print medium sensor 10 provided in the paper feed unit 114 Change detection circuit 11, ink remaining amount detection circuit 13 for detecting that the ink cartridge 111 has been replaced from the signal of the ink remaining amount sensor 12 provided in the vicinity of the ink cartridge 111, and temperature provided in the vicinity of the inkjet head 34 A temperature detection circuit 15 that detects the temperature from the signal of the sensor 14 is provided. The control unit 31 is connected to the host computer 1 via the interface 42, and performs printing according to the operation state of the operation panel 43 and the command of the program processed by the host computer 1. Various information associated with printing and cleaning is displayed on the display panel 44. The program for driving the device driver may also be executed in a printer control unit provided in the ink jet printer, or may be executed in a completely separate computer system. Further, functions equivalent to device drivers and programs may be configured by hardware.

  When the control unit 31 obtains print data from the host computer 1 via the interface 42, the CPU 32 executes predetermined processing on the print data, and based on the processing data and input data from various sensors, the device A control signal is output to the driver 30. The device driver 30 outputs a drive signal for each device, and for example, the piezoelectric elements 71 corresponding to the plurality of nozzles 5 of the inkjet head 34 and the transport motor 38 are operated to execute a printing process on the print medium 102. Each component in the control unit 31 is electrically connected through a bus (not shown).

  Further, the control unit 31 outputs drive waveform data DATA, write address data A0 to A3, a write enable signal DEN, and a write clock signal WCLK for forming a drive signal, which will be described later, to the inkjet head driver 35. Further, the control unit 31 clears the first clock signal ACLK that sets the timing for latching the drive waveform data DATA, the second clock signal BCLK that sets the timing for adding the latched multiplication output, and the latch data. The clear signal CLER to be output is output to the inkjet head driver 35.

  The inkjet head driver 35 includes a drive signal generation circuit 70 that generates a drive signal COM and an oscillation circuit 71 that outputs a clock signal SCK. As shown in FIG. 5, the drive signal generation circuit 70 includes a waveform memory 701 that stores waveform formation data DATA for generating a drive signal input from the control unit 31 in a storage element corresponding to a predetermined address, A latch circuit 702 that latches the waveform forming data DATA read from the waveform memory 701 by the first clock signal ACLK described above, an output of the latch circuit 702, and waveform generation data WDATA output from a latch circuit 704 described later. An adder 703 for adding, a latch circuit 704 for latching the addition output of the adder 703 by the above-described second clock signal BCLK, and D for converting the waveform generation data WDATA output from the latch circuit 704 into an analog signal / A converter 705 and the analog output from this D / A converter 705 A voltage amplifier 706 amplifies the voltage signal, and a current amplifier 707 for outputting a drive signal COM output signal of the voltage amplifier 706 current amplification to. Here, the clear signal CLER output from the control unit 31 is input to the latch circuits 702 and 704, and the latch data is cleared when the clear signal CLER is turned off.

  As shown in FIG. 6, in the waveform memory 701, memory elements each having several bits are arranged at the designated address, and waveform data DATA is stored together with the addresses A0 to A3. Specifically, the waveform data DATA is input together with the clock signal WCLK to the addresses A0 to A3 instructed from the control unit 31, and the waveform data DATA is stored in the memory element by the input of the write enable signal DEN.

  The inkjet head 34 receives the drive signal COM generated by the drive signal generation circuit 70, the data signal SI for selecting the nozzles to be ejected based on the print data, and the nozzle selection data for all the nozzles. A latch signal LAT for connecting the drive signal COM and the piezoelectric element 71 of the inkjet head 34 and a clock signal SCK for transmitting these selection data signals SI as serial signals to the inkjet head 34 are input.

  Next, a configuration for connecting the drive signal COM output from the drive signal generation circuit 70 and the piezoelectric element 71 will be described. FIG. 7 is a block diagram of a selection unit that connects the drive signal COM and the piezoelectric element 71. The selection unit includes a shift register 211 that stores data specifying the piezoelectric element 71 corresponding to the nozzle 5 that should eject ink droplets, a latch circuit 212 that temporarily stores data in the shift register 211, and a latch circuit 212. The level shifter 213 converts the level of the output of the output signal and the selection switch 201 that connects the drive signal COM to the piezoelectric element 71 in accordance with the level shifter output.

  A data signal SI is sequentially input to the shift register 211 as print data, and the storage area is sequentially shifted from the initial stage to the subsequent stage in response to an input pulse of the clock signal SCK. The latch circuit 212 latches each output signal of the shift register 211 by the input latch signal LAT after print data for the number of nozzles is stored in the shift register 211. The signal stored in the latch circuit 212 is converted by the level shifter 213 to a voltage level at which the selection switch 201 at the next stage can be turned on / off. This is because the drive signal COM is higher than the output voltage of the latch circuit 212, and the operating voltage range of the selection switch 201 is set higher accordingly. The selection switch 201 is composed of an analog switch having a transmission gate in which a P-channel FET and an N-channel FET are combined, and the gate voltage is level-converted to a high value in order to sufficiently operate the analog switch. Then, the piezoelectric element 71 of the nozzle to which the gate voltage of the selection switch 201 is applied by the level shifter 213 is connected to the drive signal COM.

  Further, after the print data signal SI of the shift register 211 is stored in the latch circuit 212, the next print information is input to the shift register 211, and the stored data of the latch circuit 212 is sequentially updated in accordance with the ink droplet ejection timing. . Reference numeral HGND in the figure is the ground end of the piezoelectric actuator 22.

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

  From this state, for example, as shown in FIG. 8, when the waveform data at the address A1 is read and the first clock signal ACLK is input, the digital data of + ΔV1 is stored in the latch circuit 702. The stored digital data of + ΔV1 is input to the latch circuit 704 via the adder 703, and the latch circuit 704 stores the output of the adder 703 in synchronization with the rise of the second clock signal BCLK. Since the output of the latch circuit 704 is also input to the adder 703, the output (COM) of the latch circuit 704 is added by + ΔV1 at the rising timing of the second clock signal BCLK. In this example, the waveform data at the address A1 is read during the time width T1, and as a result, the digital data of + ΔV1 is added until it is tripled.

  Next, when the waveform data at the address A0 is read and the first clock signal ACLK is input, the digital data stored in the latch circuit 702 is switched to zero. The digital data of 0 is added at the rising timing of the second clock signal BCLK through the adder 703 as described above, but since the digital data is 0, the value before that is substantially the same. Is retained. In this example, the drive signal COM is held at a constant value during the time width T0.

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

  The drive signal COM thus generated and output after being subjected to analog conversion and voltage-current amplification is a waveform signal as shown in FIG. Among them, the rising portion of the drive signal COM is a stage where the volume of the cavity 75 is enlarged and ink is drawn (which can be said to draw a meniscus in consideration of the ink discharge surface), and the falling portion of the drive signal COM is the volume of the cavity 75. Is reduced and the ink droplets are ejected (it can be said that the meniscus is extruded if the ink ejection surface is considered). Incidentally, the waveform of the drive signal COM is, as easily guessed from the above, the waveform data 0, + ΔV1, −ΔV2, + ΔV3, the first clock signal ACLK, and the second clock signal BCLK written to the addresses A0 to A3. Can be adjusted by. That is, the larger the inclination and time when the volume of the cavity 75 is enlarged or reduced, the larger the amount of ink droplets ejected.

  In this embodiment, for example, the waveform data 0, + ΔV1, −ΔV2, + ΔV3, the first clock signal ACLK, and the second clock signal BCLK written to the addresses A0 to A3 are changed variously, for example, as shown in FIG. 9a. Drive waveforms (microvibration to M26) are arranged in time series to form a series of drive signals. The drive signal generation circuit 70 and the piezoelectric element 71 are connected at a necessary timing, and the drive waveforms at that time are connected. Ink droplets are ejected from the corresponding nozzle 5 by the drive signal consisting of In this embodiment, there are a total of 11 drive waveforms from micro vibration to M26, and one or more of them can be selected and supplied to the piezoelectric element 71. The selection pattern is shown in FIG. 9b. In this waveform selection table, for example, only the fine vibration driving waveform is selected at waveform selection number 0, only the S19 driving waveform is selected at waveform selection number 1, and the S19 driving waveform and the S21 driving waveform are selected at waveform selection number 6. The waveform selection number 20 selects the drive waveform according to the waveform selection number, such as selecting the M18 drive waveform and the M20 drive waveform, and supplies the drive signal composed of these drive waveforms to the piezoelectric element 71. When two or more drive waveforms are selected, ink droplets are ejected by the number of drive waveforms. If the ink droplets are ejected twice or more before the ink is dried, a large ink droplet is ejected on the printing medium 102, and as a result, a large ink dot id can be formed. Further, ink droplets are not ejected only by the minute vibration driving waveform.

  Therefore, if the waveform selection number is determined according to the required gradation, ink dots corresponding to the required gradation can be formed. FIG. 10 represents a total of eight gradation levels including gradation 0 where no ink dot is formed. For the required gradation, it is ideal that ink dots of the same size are formed from all nozzles. However, as described above, the amount of ink droplets ejected from each nozzle varies depending on, for example, individual differences between the piezoelectric elements 71 and the nozzles 5 and differences in ink viscosity in the cavity 75. The size is different. FIG. 11 a shows variations in the size of ink dots generated between a plurality of inkjet nozzles formed on one inkjet head. Further, FIG. 11b shows the variation in the size of the ink dots generated in the ink jet nozzles between the ink jet heads arranged side by side. Therefore, in this embodiment, the size of the ink dot id formed from each nozzle 5, specifically the area S, is measured by the image sensor 6 and the image processing circuit 9, and a drive signal (drive) corresponding to the area is measured. Waveform) is set to adjust the size of the ink dot id, that is, the amount of ink droplets. When measuring the area S of the ink dot id, in order to avoid the overlap of the ink dots id due to the above-mentioned flight curve, the ink dot id is spaced at least one interval as shown in FIG. It is desirable to form.

  FIG. 12A shows an ink dot id area (hereinafter also referred to as a dot area) for each gradation degree for yellow (Y) nozzle numbers Y (1) to Y (n) in an inkjet head 34 as shown in FIG. 12B, for example. ) S is measured. In this example, the nozzles at both ends vary as a whole while showing a tendency that the dot area S slightly increases. Further, the tendency of variation between the gradations is the same. In order to suppress variations in ink dot size by adjusting the amount of ink droplets, it is necessary to prevent the ink dot size from being reversed between the gradation levels. In addition, since it is difficult to accurately correct the ink dot size for all nozzles, a reference nozzle is set for each gradation, and the inks of other nozzles are set based on the measurement data of the reference nozzle. What is necessary is just to correct | amend the magnitude | size of a dot, ie, the quantity of an ink drop. Further, the number of reference nozzles is not necessarily one, and the average value of the ink dot sizes of a plurality of nozzles may be used as the reference value, or may be determined by weighting each.

  In the present embodiment, as described above, the drive waveform selected for each required gradation is stored in the gradation corresponding drive waveform selection table. The so-called default gradation corresponding drive waveform selection table that is set in advance is a set value, but since there is variation in the size of the ink dot as described above, the amount of ink droplets is set to suppress this variation. The adjusted result is updated and stored in the gradation corresponding drive waveform selection table. This ink droplet amount adjustment is referred to as gradation correction processing. For example, when the temperature change amount detected by the temperature sensor 14 and the temperature detection opening 15 is equal to or greater than a predetermined value after the power is turned on and before printing, the gradation correction processing is performed when the print medium sensor 10 and the print medium When the change of the type of the print medium 102 is detected by the change detection circuit 11, the ink cartridge 111 is replaced by detecting that the ink remaining amount sensor 12 and the ink remaining amount detection circuit 13 have increased the ink remaining amount. When it is determined, it is performed either before power-off or in combination.

FIG. 13 is a flowchart of calculation processing performed by the control unit 31 for gradation correction processing. In this calculation process, first, the gradation is designated in step S1.
Next, the process proceeds to step S <b> 2, and the reference dot area Sd and the reference range ΔSd as the reference for the ink dot corresponding to the specified gradation are read from the memory 33.
Next, the process proceeds to step S3, and the gradation level corresponding driving waveform number N is read from the gradation level corresponding driving waveform selection table that has been updated and stored.

Next, the process proceeds to step S4, where a combination of drive waveforms is read from the waveform selection table as shown in FIG. 9b based on the read gradation waveform corresponding drive waveform selection number N.
Next, the process proceeds to step S5, and ink dots are formed based on the drive waveform read out in step S4.
Next, the process proceeds to step S6, and the dot area S of the formed ink dots is measured.

Next, the process proceeds to step S7, and the dot area difference ΔS is calculated by subtracting the measured dot area S from the reference dot area Sd read in step S2.
Next, the process proceeds to step S8, where it is determined whether or not the dot area difference ΔS calculated in step S7 is within the reference range ΔSd read in step S4, and the dot area difference ΔS is within the reference range ΔSd. If it is within the range, the process proceeds to step S12, and if not, the process proceeds to step S9.

In step S9, it is determined whether or not the dot area difference ΔS calculated in step S7 is a positive value. If the dot area difference ΔS is a positive value, the process proceeds to step S10; If it is a value, the process proceeds to step S11.
In step S10, a value obtained by subtracting 1 from the current gradation level driving waveform selection number N is set as a new gradation level corresponding driving waveform selection number N, and then the process proceeds to step S12.

In step S11, a value obtained by adding 1 to the current gradation level driving waveform selection number N is set as a new gradation level corresponding driving waveform selection number N, and then the process proceeds to step S12.
In step S12, the gradation corresponding drive waveform selection number N is updated and stored in the gradation corresponding drive waveform selection table.
Next, the process proceeds to step S13, where it is determined whether or not the gradation correction processing for all ink dots at the current gradation degree is completed, and the gradation correction processing for all ink dots at the current gradation degree is completed. If so, the process proceeds to step S14. If not, the process proceeds to step S16.

In step S16, after moving to the next tone correction process target ink dot, the process proceeds to step S6.
In step S14, it is determined whether or not the dot area difference ΔS of all ink dots at the current gradation is within the reference range ΔSd, and the dot area difference ΔS of all ink dots at the current gradation is the reference. If it is within the range ΔSd, the process proceeds to step S15. Otherwise, the process proceeds to step S4 for the nozzle corresponding to the ink dot that is not within the range.

In step S15, it is determined whether or not gradation correction processing has been completed for all gradation levels. If gradation correction processing has been completed for all gradation degrees, the process returns to the main program; In this case, the process proceeds to step S17.
In step S17, after specifying the next gradation, the process proceeds to step S2.
According to this arithmetic processing, for example, when a so-called default gradation-corresponding drive waveform selection table that is initially set is as shown in FIG. 14a, all nozzles for all colors and all gradations are used. 14 is measured to correct the gradation corresponding drive waveform selection number N and update and store it in the gradation corresponding drive waveform selection table. Therefore, the gradation corresponding drive waveform selection table is shown in FIG. It becomes like this. This gray level drive waveform selection table looks complicated at first glance, but if there is a gray level drive waveform selection table and a waveform selection table below it, all the colors and all the gray levels can be obtained. The variation in the size of the ink dots of the nozzles, that is, the variation in the amount of ink droplets can be suppressed. That is, the storage capacity is much smaller than when all the drive signals for all the nozzles are stored for all the colors and all the gradations.

FIG. 15A shows a result of measuring the dot area S by selecting a drive waveform in order from the waveform selection number 1 in the waveform selection table of FIG. 9B, supplying a drive signal having the corresponding drive waveform to the piezoelectric element 71, and FIG. . The black circles in FIG. 15b are obtained by setting the waveform selection number close to the median value of the dot area range of each gradation degree among the waveform selection numbers in FIG. 15a as the gradation corresponding drive waveform number.
By setting the number of combinations of drive waveforms that can be selected in this way to be greater than the required number of gradations, the number of drive waveform selection patterns increases, and variations in ink droplets ejected from inkjet nozzles or print media It is possible to reliably suppress variations in the ink dots formed on the top.

  As described above, according to the non-ink jet printer of the present embodiment, the size of the ink dot id on the print medium 102 is detected, and based on the detected size of the ink dot id on the print medium 102. Since the amount of ink droplets ejected from the inkjet nozzle 5 is adjusted, variations in the ink droplets ejected from the inkjet nozzle 5 or variations in the ink dots id formed on the print medium 102 can be reliably suppressed. It becomes.

  In addition, by changing the drive signal to the piezoelectric element 71 as an actuator, the amount of ink droplets ejected from the inkjet nozzle 5 is changed, and the size of the ink dots on the print medium 102 is changed to two or more gradation levels. And the drive signal to the piezoelectric element 71 is set based on the dot area S of the ink dot id on the print medium 102 detected by the image processing circuit 10. It is possible to reliably suppress variations in ink droplets ejected from the inkjet nozzle 5 or variations in ink dots id formed on the print medium 102.

  Further, when a combination of one or more drive waveforms is selected from the drive waveform selection table corresponding to the gradation, and a drive signal corresponding to the required gradation is created, the image on the print medium 102 detected by the image processing circuit 10 is generated. Based on the dot area S of the ink dot id, the gradation-corresponding drive waveform selection table is updated. Therefore, the variation of the ink droplets ejected from the inkjet nozzle 5 or the variation of the ink dot id formed on the print medium 102 is changed. It is possible to suppress the storage capacity of the drive signal when trying to suppress the above.

In addition, since the number of combinations of drive waveforms that can be selected is larger than the required number of gradation levels, the number of drive waveform selection patterns increases, resulting in variations in ink droplets ejected from inkjet nozzles or on print media. It is possible to reliably suppress variations in ink dots.
Also, after the power is turned on and before printing, when the amount of change in temperature exceeds a predetermined value, that is, when the viscosity of ink changes, when the type of print medium is changed, that is, formed on the print medium When the ink dot size changes, when the ink cartridge filled with ink is replaced, that is, when the viscosity of the ink changes, it is discharged from the inkjet nozzle either before power-off or when they are combined Since the amount of ink droplets to be adjusted is adjusted, variations in the ink droplets ejected from the inkjet nozzles or variations in the ink dots formed on the print medium can be suppressed at an appropriate timing.

  FIG. 16 shows an example in which an ink dot detection device 3 is provided in a multi-pass ink jet printer as a second embodiment of the ink jet printer of the present invention. FIG. 16A is a plan view showing an overall image of the multi-pass ink jet printer of the present embodiment. In the ink jet printer of this embodiment, a carriage 321 provided integrally with an ink cartridge and an ink jet head 34 is reciprocated in the width direction of the print medium 102 and in the horizontal direction of the figure, and the print medium 22 is moved in the longitudinal direction. The ink droplets are ejected from the nozzles of the inkjet head 34 while being conveyed in the vertical direction, and minute ink dot ids are formed and output on the print medium 102, thereby drawing predetermined characters and images on the print medium 102. To produce a desired printed matter. The reciprocating direction of the carriage 321 is also referred to as a main scanning direction, and the paper feeding direction of the printing medium 102 is also referred to as a sub-scanning direction.

  Reference numeral 322 in FIG. 16 is a carriage motor as an actuator for reciprocating the carriage 321 in the main scanning direction, reference numeral 323 is a driving pulley for transmitting the driving force of the carriage motor 322, and reference numeral 324 is for sandwiching the print medium 102. A driven pulley disposed on the opposite side of the drive pulley 323 and a reference numeral 325 is a conveyor belt wound around the drive pulley 323 and the driven pulley 324 and connected to the carriage 321. In the figure, reference numeral 326 denotes a carriage shaft that guides the carriage 321, reference numeral 327 denotes a carriage encoder arranged in parallel to the carriage shaft 326, and reference numeral 328 denotes a carriage encoder sensor that reads the carriage encoder 327. Reference numeral 303 denotes a cap for cleaning the nozzles of the inkjet head 34 mounted on the carriage 321, and reference numeral 330 denotes a wiper for stroking the nozzles to adjust the meniscus of the nozzles. Reference numeral 329 denotes a cable for connecting the inkjet head 34 and the inkjet printer main body.

  FIG. 16 b shows details of the ink dot detection device 3 provided in the ink jet printer of this embodiment. In the multi-pass ink jet printer as in the present embodiment, the carriage 321 mounted with the ink jet head 34 has to be reciprocated in the main scanning direction, so the weight of the carriage 321 cannot be increased. For this reason, in this embodiment, the image sensor 6 is provided separately, and a plurality of reflecting mirrors 331 are combined to measure the size of the ink dot id, specifically the area. The correction of the amount of ink droplets by the ink dot detection device 3 is the same as in the first embodiment.

BRIEF DESCRIPTION OF THE DRAWINGS It is a block diagram which shows 1st Embodiment of the inkjet printer of this invention, (a) is the whole front view of a line head type inkjet printer, (b) is a detailed drawing of an ink dot detection apparatus. It is a block diagram of the inkjet head provided in the inkjet printer of FIG. It is explanatory drawing of the area measurement of an ink dot. It is a printing system block diagram of the inkjet printer of FIG. FIG. 5 is a block diagram of the drive signal generation circuit of FIG. 4. It is explanatory drawing of the waveform memory of FIG. It is a block diagram of the selection part which connects a drive signal to a piezoelectric actuator. It is explanatory drawing of drive signal generation. It is explanatory drawing of the waveform selection table for selecting the drive signal which arranged the drive waveform in time series, and the drive waveform. It is explanatory drawing of the magnitude | size of the ink dot in each gradation degree. It is explanatory drawing of the variation in the magnitude | size of an ink dot. It is explanatory drawing of the variation in a dot area. It is a flowchart which shows the calculation process of the gradation correction process which suppresses the variation in a dot area. It is explanatory drawing of the drive waveform selection table corresponding to a gradation degree updated and memorize | stored by the arithmetic processing of FIG. It is explanatory drawing of the drive waveform number corresponding to the gradation degree updated and memorize | stored by the arithmetic processing of FIG. It is a block diagram which shows 2nd Embodiment of the inkjet printer of this invention, (a) is the whole front view of a multipass-type inkjet printer, (b) is a detailed figure of an ink dot detection apparatus.

Explanation of symbols

  1 is a host computer, 2 is an ink jet printer, 3 is an ink dot detection device, 4 is a nozzle surface, 5 is a nozzle, 6 is an image sensor, 7 is illumination, 8 is a carriage, 9 is an image processing circuit, and 10 is a print medium sensor , 11 is a print medium change detection circuit, 12 is an ink remaining amount sensor, 13 is an ink remaining amount detection circuit, 14 is a temperature sensor, 15 is a temperature detection circuit, 30 is a device driver, 31 is a control unit, and 34 is an inkjet head.

Claims (9)

  In an ink jet printer that performs printing by ejecting ink droplets from ink jet nozzles to form ink dots on a print medium, ink dot detection means for detecting the size of the ink dots on the print medium, and the ink dot detection means An ink-jet printer comprising: ink-drop adjusting means for adjusting the amount of ink droplets ejected from the ink-jet nozzle based on the size of ink dots on the printing medium detected in step 1).  Multi-tone output means for changing the amount of ink droplets ejected from the ink jet nozzles by changing the drive signal to the actuator and forming the size of the ink dots on the print medium at two or more gradations The ink dot detection means includes image processing means for detecting the area of the ink dots on the print medium, and the ink droplet adjustment means detects the area of the ink dots on the print medium detected by the image processing means. 2. The ink jet printer according to claim 1, further comprising drive signal setting means for setting a drive signal for the multi-gradation output means.  The multi-gradation output means creates a drive signal corresponding to a required gradation degree by selecting a combination of one or more drive waveforms from the gradation degree corresponding drive waveform selection table, and the drive signal setting means includes the image 3. The inkjet printer according to claim 2, wherein the gradation level corresponding drive waveform selection table of the multi-gradation output means is updated based on the area of the ink dots on the print medium detected by the processing means.   4. The ink jet printer according to claim 3, wherein the number of combinations of drive waveforms that can be selected is greater than the number of required gradation levels.   5. The ink jet printer according to claim 1, wherein the ink droplet adjusting unit adjusts an amount of ink droplets ejected from the ink jet nozzle after power-on and before printing. 6. .   6. The ink droplet adjusting unit according to claim 1, wherein the ink droplet adjusting unit adjusts an amount of ink droplets ejected from the inkjet nozzle when a temperature change amount exceeds a predetermined value. Inkjet printer.   The ink jet printer according to claim 1, wherein the ink droplet adjusting unit adjusts an amount of ink droplets ejected from the ink jet nozzle when a type of a printing medium is changed.   8. The ink droplet adjusting unit according to claim 1, wherein the ink droplet adjusting unit adjusts an amount of ink droplets discharged from the inkjet nozzle when an ink cartridge filled with ink is replaced. Inkjet printer. The ink jet printer according to claim 1, wherein the ink droplet adjusting unit adjusts an amount of ink droplets ejected from the ink jet nozzles before power is turned off.

Images