JP2005088436A - Image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming device that can correct variations in droplet ejection characteristics even if a head is lengthened by a simple structure. <P>SOLUTION: Four heads HBk, HC, HM and HY are split into three driving units 111a, 111b and 111c and driven and three driving circuits 88a, 88b and 88c individually outputting driving waveforms Vcoma, Vcomb, and Vcomc to the driving units 111a, 111b and 111c are provided to apply driving waveforms Vcoma, Vcomb and Vcomc in which variations in droplet ejection characteristics among the driving units 111a, 111b and 111c are corrected. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus having a plurality of heads.

  An ink jet recording apparatus used as an image forming apparatus such as a printer, a facsimile, a copying apparatus, or a plotter has a nozzle for discharging ink droplets and a pressurized liquid chamber (discharge chamber, pressure chamber, pressure chamber, liquid chamber) that communicates with the nozzle. And an ink flow path, a flow path, etc.) and a pressure generating means for pressurizing the ink in the pressurized liquid chamber.

As a head drive control device in an ink jet recording apparatus in which such an ink jet head is mounted as a recording head, for example, each of at least some of the plurality of drive signal generators and at least one of the plurality of nozzles There is known a device including a selection unit that arbitrarily selects and executes connection with each of specific drive elements for driving some nozzles.
JP 2002-103617 A

In addition, each head of black (Bk), cyan (C), magenta (M), and yellow (Y) is mounted, and each head includes a waveform generation unit that generates a drive waveform and a low impedance output circuit. Also known is a drive waveform from a low impedance output circuit in which a common drive waveform is applied to all piezoelectric elements for each head.
JP-A-10-157102

  In recent ink jet recording apparatuses, the number of nozzles of the head has increased with the increase in speed, and the head dimensions have also become longer. In this case, since the mechanical rigidity differs between the central portion and the end portion of the nozzle array due to the lengthening of the head, a difference occurs in the ink droplet ejection characteristics between the nozzles.

  Here, as described in Patent Document 1, each of at least some of the plurality of drive signal generators and a specific for driving at least some of the plurality of nozzles By providing a selection unit that arbitrarily selects and executes connection with each of the drive elements, the nozzle row divided for each color can be made into one group, and the drive signal generation unit can be selected for each group. Variations can be corrected by applying different waveforms between nozzle rows (between colors).

  However, even in the apparatus described in Patent Document 1, variations in ink droplet ejection characteristics caused by a physical nozzle arrangement are corrected in the head (in the same color nozzle row) as described above. It is not possible.

  SUMMARY An advantage of some aspects of the invention is that it provides an image forming apparatus capable of correcting variations in droplet ejection characteristics even when the head is elongated with a simple configuration.

  In order to solve the above problems, an image forming apparatus according to the present invention includes a plurality of heads each having a pressure generating unit provided corresponding to each liquid chamber in communication with a plurality of nozzles for discharging droplets. A plurality of driving circuits for driving the pressure generating means, and each of the plurality of heads is divided into a plurality of driving units, and each of the divided driving units is divided into different driving circuits. Connected configuration.

  Here, it is preferable that the plurality of drive circuits include a voltage amplification unit and a current amplification unit that amplify the drive waveform. Moreover, it is preferable that the drive waveforms for the plurality of divided drive units can be independently adjusted. Furthermore, it is preferable that a plurality of heads are provided for each liquid of different colors, and one drive circuit drives a drive unit of liquids of different colors.

  The plurality of driving circuits are connected to a head substrate having a pressure generating means constituting a driving unit of each head and a selection circuit for selecting the driving pressure generating means via a relay substrate, and the relay substrate is connected to the input / output connection unit. Both of these patterns are preferably wired in the substrate so that they can be connected by straight wiring. In this case, it is preferable that the head substrate is connected to the relay substrate, and the drive waveform signal wiring in the head substrate does not intersect with other signal wiring.

  According to the image forming apparatus of the present invention, the inside of one head is divided into a plurality of drive units, and each has a drive circuit independently, so that they differ from each other depending on the difference in droplet ejection characteristics in the head. By driving with a drive waveform and adjusting the drive waveform so as to correct variations in the head, density unevenness can be eliminated and high image quality can be obtained.

  Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a schematic perspective explanatory view of a mechanism part of an ink jet recording apparatus as an image recording apparatus according to the present invention, and FIG. 2 is a side explanatory view of the mechanism part.

  The ink jet recording apparatus includes a carriage that is movable in the main scanning direction inside the recording apparatus main body 1, a recording head that includes an ink jet head mounted on the carriage, an ink cartridge that supplies ink to the recording head, and the like. 2 and the like, the paper 3 fed from the paper feed cassette 4 or the manual feed tray 5 is taken in, a required image is recorded by the printing mechanism unit 2, and then discharged to the paper discharge tray 6 mounted on the rear side. Make paper.

  The printing mechanism section 2 holds a carriage 13 slidably in the main scanning direction by a main guide rod 11 and a sub guide rod 12 which are guide members horizontally mounted on left and right side plates (not shown). A recording head 14 composed of an inkjet head that ejects ink droplets of each color (Y), cyan (C), magenta (M), and black (Bk) is mounted with the ink droplet ejection direction facing downward. Each ink tank (ink cartridge) 15 for supplying each color ink to the recording head 14 is replaceably mounted.

  The ink cartridge 15 has an air port that communicates with the atmosphere upward, a supply port that supplies ink to the recording head 14 below, and a porous body filled with ink inside. The ink supplied to the recording head 14 by the force is maintained at a slight negative pressure. Ink is supplied from the ink cartridge 15 into the recording head 14.

  Here, the carriage 13 is slidably fitted to the main guide rod 11 on the rear side (downstream side in the paper conveyance direction), and is slidably mounted on the secondary guide rod 12 on the front side (upstream side in the paper conveyance direction). doing. In order to move and scan the carriage 13 in the main scanning direction, a timing belt 20 is stretched between a driving pulley 18 and a driven pulley 19 that are rotationally driven by a main scanning motor 17. The carriage 13 is reciprocally driven by forward and reverse rotation of the main scanning motor 17.

  Further, although each color, that is, four ink jet heads are used here as the recording head 14, one ink jet head having a plurality of nozzle rows composed of a plurality of nozzles that eject ink droplets of each color may be used. Further, as the recording head 14, as will be described later, a vibration plate that forms at least a part of the wall surface of the ink flow path and a piezoelectric ink jet head that deforms the vibration plate with a piezoelectric element are used. Without limitation, a thermal head, an electrostatic head, or the like can also be used.

  On the other hand, in order to convey the paper 3 set in the paper feed cassette 4 to the lower side of the recording head 14, the paper feed roller 21 and the friction pad 22 for separating and feeding the paper 3 from the paper feed cassette 4 and the paper 3 are guided. The guide member 23 that performs the above operation, the transport roller 24 that transports the fed paper 3 in an inverted manner, the transport roller 25 that is pressed against the peripheral surface of the transport roller 24, and the feed angle of the paper 3 from the transport roller 24 are defined. A tip roller 26 is provided. The transport roller 24 is rotationally driven by a sub-scanning motor 27 through a gear train.

  A printing receiving member 29 is provided as a paper guide member for guiding the paper 3 fed from the transport roller 24 below the recording head 14 in accordance with the range of movement of the carriage 13 in the main scanning direction. A conveyance roller 31 and a spur 32 that are rotationally driven to send the paper 3 in the paper discharge direction are provided on the downstream side of the printing receiving member 29 in the paper conveyance direction, and the paper 3 is further delivered to the paper discharge tray 6. A roller 33 and a spur 34, and guide members 35 and 36 that form a paper discharge path are disposed.

  At the time of recording, the recording head 14 is driven according to the image signal while moving the carriage 13 to eject ink onto the stopped paper 3 to record one line, and after the paper 3 is conveyed by a predetermined amount, Record the line. Upon receiving a recording end signal or a signal that the trailing edge of the sheet 3 has reached the recording area, the recording operation is terminated and the sheet 3 is discharged.

  Further, a recovery device 37 for recovering defective ejection of the recording head 14 is disposed at a position outside the recording area on the right end side in the movement direction of the carriage 13. The recovery device 37 includes a cap unit, a suction unit, and a cleaning unit. While waiting for printing, the carriage 13 is moved to the recovery device 37 side and the recording head 14 is capped by the capping means, and the ejection port (nozzle hole) is kept in a wet state to prevent ejection failure due to ink drying. Further, by ejecting (purging) ink not related to recording during recording or the like, the ink viscosity of all the ejection ports is made constant and stable ejection performance is maintained.

  When ejection failure occurs, etc., the ejection port (nozzle) of each inkjet head of the recording head 14 is sealed with a capping unit, and bubbles and the like are sucked out from the ejection port with the suction unit through the tube, and adhere to the ejection port surface. The discharged ink, dust, etc. are removed by the cleaning means, and the ejection failure is recovered. Further, the sucked ink is discharged to a waste ink reservoir (not shown) installed at the lower part of the main body and absorbed and held by an ink absorber inside the waste ink reservoir.

  Next, an ink jet head constituting the recording head 14 of the ink jet recording apparatus will be described with reference to FIGS. 3 is an explanatory sectional view along the longitudinal direction of the liquid chamber of the head, FIG. 4 is an explanatory sectional view along the lateral direction of the liquid chamber of the head, and FIG. 5 is an explanatory plan view of the main part of the head.

  The inkjet head includes a flow path plate 41 formed of a single crystal silicon substrate, a vibration plate 42 bonded to the lower surface of the flow path plate 41, and a nozzle plate 43 bonded to the upper surface of the flow path plate 41. As a result, the nozzle 45 that discharges ink droplets as droplets is an ink in a pressure chamber 46 that is an ink flow path that communicates via a nozzle communication path 45a, and a common liquid chamber 48 that supplies ink to the pressure chamber 46. An ink supply path 47 serving as a fluid resistance portion communicating with the supply port 49 is formed.

  An electromechanical conversion which is a pressure generating means (actuator means) for pressurizing the ink in the pressurizing chamber 46 corresponding to each pressurizing chamber 46 on the outer surface side (the surface opposite to the liquid chamber) of the vibration plate 42. A laminated piezoelectric element 52 as an element is bonded, and the piezoelectric element 52 is bonded to a base substrate 53. Further, between the piezoelectric elements 52, support columns 54 are provided corresponding to the partition walls 41 a between the pressurizing chambers 46 and 46. Here, the piezoelectric element member is divided into comb teeth by performing slit processing by half-cut dicing, and each piezoelectric element 52 is formed as a piezoelectric element 52 and a column portion 54. The column portion 54 has the same configuration as that of the piezoelectric element 51, but is a simple column because no driving voltage is applied.

  Further, the outer peripheral portion of the diaphragm 42 is joined to the frame member 44 by an adhesive 50 including a gap material. The frame member 44 is formed with a recess serving as a common liquid chamber 48 and an ink supply hole (not shown) for supplying ink to the common liquid chamber 48 from the outside. The frame member 44 is formed of, for example, an epoxy resin or polyphenylene sulfite by injection molding.

  Here, the channel plate 41 is formed by, for example, anisotropically etching a single crystal silicon substrate having a crystal plane orientation (110) using an alkaline etching solution such as an aqueous potassium hydroxide solution (KOH), so that the nozzle communication path 45a, The pressurization chamber 46 and the ink supply passage 47 are formed with recesses and holes. However, the pressurization chamber 46 and the ink supply path 47 are not limited to single crystal silicon substrates, and other stainless steel substrates, photosensitive resins, and the like can also be used.

  The vibration plate 42 is formed of a nickel metal plate, and is manufactured by, for example, an electroforming method (electroforming method). Other metal plates, resin plates, or a joining member between a metal and a resin plate, or the like may be used. It can also be used. This diaphragm 42 forms a thin part (diaphragm part) 55 for facilitating deformation and a thick part (island-like convex part) 56 for joining with the piezoelectric element 52 in a part corresponding to the pressurizing chamber 46. At the same time, a thick portion 57 is formed at a portion corresponding to the column portion 54 and a joint portion with the frame member 44, the flat surface side is adhesively joined to the flow path plate 41, and the island-like convex portion 56 is joined to the piezoelectric element 52. Further, the thick portion 57 is joined to the support portion 54 and the frame member 44 with the adhesive 50. Here, the diaphragm 42 is formed by nickel electroforming with a two-layer structure. In this case, the diaphragm portion 55 has a thickness of 3 μm and a width of 35 μm (one side).

  The nozzle plate 43 forms a nozzle 45 having a diameter of 10 to 35 μm corresponding to each pressurizing chamber 46 and is bonded to the flow path plate 41 with an adhesive. The nozzle plate 43 may be made of a metal such as stainless steel or nickel, a combination of a metal and a resin such as a polyimide resin film, silicon, or a combination thereof. Here, it forms with the Ni plating film | membrane etc. by the electroforming method. Further, the inner shape (inner shape) of the nozzle 43 is formed in a horn shape (may be a substantially columnar shape or a substantially frustum shape), and the hole diameter of the nozzle 45 is approximately 20 to 20 on the ink droplet outlet side. 35 μm. Furthermore, the nozzle pitch of each row was 150 dpi.

  Further, a water repellent treatment layer (not shown) subjected to a water repellent surface treatment is provided on the nozzle surface (surface in the ejection direction: ejection surface) of the nozzle plate 43. Examples of the water-repellent treatment layer include PTFE-Ni eutectoid plating, fluororesin electrodeposition coating, vapor-deposited fluororesin (e.g., fluorinated pitch), silicon resin / fluorine resin A water-repellent treatment film selected according to the ink physical properties such as baking after solvent application is provided to stabilize the ink droplet shape and flying characteristics so that high-quality image quality can be obtained.

  The piezoelectric element 52 includes a lead zirconate titanate (PZT) piezoelectric layer 61 having a thickness of 10 to 50 μm / layer, and an internal electrode layer 62 made of silver and palladium (AgPd) having a thickness of several μm / layer. The internal electrodes 62 are alternately stacked, and are electrically connected to the individual electrodes 63 and the common electrode 64 which are the end face electrodes (external electrodes) of the end face alternately. The pressurizing chamber 46 is contracted and expanded by expansion and contraction of the piezoelectric element 52 whose piezoelectric constant is d33. The piezoelectric element 52 expands when a drive signal is applied and is charged, and contracts in the opposite direction when the charge charged in the piezoelectric element 52 is discharged.

  Note that the end face electrode on one end face of the piezoelectric element member is divided by dicing by half-cut to become individual electrodes 63, and the end face electrode on the other end face is not divided by the restriction by notching or the like and is divided by all the piezoelectric elements 52. The common electrode 64 becomes conductive.

  An FPC cable 65 is connected to the individual electrode 63 of the piezoelectric element 52 by solder bonding, ACF (anisotropic conductive film) bonding, or wire bonding in order to give a drive signal, and each piezoelectric element 52 is connected to the FPC cable 65. A drive circuit (driver IC) for selectively applying a drive waveform is connected. The common electrode 64 is connected to the ground (GND) electrode of the FPC cable 65 by providing an electrode layer at the end of the piezoelectric element and turning it around.

  In the ink jet head configured as described above, for example, by applying a drive waveform (pulse voltage of 10 to 50 V) to the piezoelectric element 52 in accordance with a recording signal, displacement in the stacking direction occurs in the piezoelectric element 52 and vibration occurs. Ink in the pressurizing chamber 46 is pressurized through the plate 42 to increase the pressure, and ink droplets are ejected from the nozzle 45.

  Thereafter, the ink pressure in the pressurizing chamber 46 decreases with the end of ink droplet ejection, and a negative pressure is generated in the pressurizing chamber 46 due to the inertia of the ink flow and the discharge process of the drive pulse, and the ink filling process is started. Transition. At this time, ink supplied from an ink tank (not shown) flows into the common liquid chamber 48 and is filled from the common liquid chamber 47 through the ink supply port 49 through the fluid resistance portion 47 into the pressurizing chamber 46.

  The fluid resistance portion 47 is effective in damping residual pressure vibration after ejection, but is resistant to refilling due to surface tension. By appropriately selecting the fluid resistance value of the fluid resistance unit 47, it is possible to balance the attenuation of the residual pressure and the refill time, and to shorten the time (drive cycle) until the transition to the next ink droplet ejection operation.

Next, an outline of the control unit of the ink jet recording apparatus will be described with reference to FIG.
The control unit includes a microcomputer (hereinafter referred to as “CPU”) 80 that controls the entire recording apparatus, a ROM 81 that stores necessary fixed information, a RAM 82 that is used as a working memory, and the like from the host side. An image memory (lass data memory) 83 for storing transferred image data (referred to as dot data or dot pattern data), a parallel input / output (PIO) port 84, a parallel input / output (PIO) port 86, a head A drive circuit 88 and a driver 89 are provided.

  Here, the PIO port 84 receives various information and data such as image data transferred from the printer driver side of the host, various instructions from the operation panel 90, selection information, various sensors such as a temperature sensor 92 that detects the environmental temperature. And the necessary information is sent to the host side and the operation panel 90 side via the PIO port 84.

  The head driving circuit 88 selectively applies a driving waveform to the piezoelectric elements 52 of the respective ink-jet heads constituting the recording head 14 based on various data and signals given through the PIO port 86 to generate ink droplets. Discharge. Further, the driver 89 drives and controls the main scanning motor 17 and the sub-scanning motor 27 in accordance with driving data given through the PIO port 86, thereby moving and scanning the carriage 13 in the main scanning direction. Is rotated to convey the paper 3 by a predetermined amount.

A portion of the control unit related to the head drive control device will be described with reference to FIG. In the figure, only the part related to the drive control of one drive unit of one head of the present invention is shown.
Here, the four inkjet heads H constituting the recording head 14 have the piezoelectric elements 52 that are 128 pressure generating means corresponding to a plurality of (here, 128) nozzles 45 as described above. One electrode of each piezoelectric element 52 is made common and connected to the ground as a common electrode Com (the common electrode 64), and the other electrode is individualized for each piezoelectric element 52 to select the selection electrode SEL (above Individual electrode 63.). Actually, since the nozzles 45 are provided in two rows, 256 nozzles 45 are provided.

  The head drive control unit includes a main control unit 101 including the CPU, ROM, RAM, and peripheral circuits, and a head drive unit 88A for driving an inkjet head constituting the recording head 14.

  The main control unit 101 inputs image information given from the host side such as an information processing terminal such as a personal computer, an image processing terminal device such as a digital camera or a scanner, and the timing for driving the head to the head driving unit 88A. The 8-bit voltage data is sequentially output to the D / A conversion circuit (DAC) 103 which is a waveform generation unit.

  The DAC 103 outputs the given voltage data in an output range of 0V to 2V, for example, with a resolution of 8 bits. When the 8-bit data input step is 250 ns, when the drive waveform (drive signal) has a rising time constant tr = 5 μs and the drive voltage Vp = 30 V (full scale), the output of the DAC 103 is in steps of 20 steps. It rises to 0-2V at about 0.1V / step.

  Similarly, when the drive waveform falls, if the fall time constant tf = 10 μs, the voltage drops to 5 to 3 V in 40 steps. Further, if the time required for the drive waveform (the time from the start of rise to the end of fall) is 50 μs, a drive waveform of full scale 5V is formed in 200 steps, and is repeatedly output in accordance with the drive timing of the head.

  The drive waveform output from the DAC 103 is amplified by the amplifier 104 in accordance with the DAC output level in the range of 3 to 30 V (at full scale). The voltage-amplified driving waveform is applied to the PZT selection circuit 106, which is a selection circuit, via a current amplification unit 105 including a low impedance circuit including a SEPP circuit (NPN transistor Q1 and PNP transistor Q2). .

  Here, an example of the drive waveform is shown in FIG. In the head driving method in this embodiment, the piezoelectric element 52 contracts and displaces in the direction of the head substrate (base substrate) 53 at the time of the falling waveform element (a → b) of the driving waveform. And the pressurized liquid chamber 46 is depressurized. The enlarged pressurized liquid chamber 46 is held for the hold waveform element (b → c) time of the drive waveform, and then the piezoelectric element 52 is connected to the nozzle plate 43 at the time of the rising waveform element (c → d). Since the pressure liquid chamber 46 is enlarged and displaced in the direction, the pressure liquid chamber 46 is reduced, and an ink droplet is ejected from the nozzle 45 with the generated pressure pressure.

  On the other hand, the main control unit 101 inputs serial data SD (nozzle data), a shift clock SCLK, and a latch signal / LAT for designating the nozzles 45 for ejecting ink droplets to the PZT selection circuit 106.

  The PZT selection circuit 106 includes a shift register circuit (256 bits) that receives the shift clock SCLK and the nozzle data SD, a latch circuit (256 bits) for latching each resist value of the shift register circuit using a latch signal / LAT, It consists of a 256-bit level shifter circuit and an analog switch group whose on / off is controlled by the level shifter circuit.

  The analog switch group is connected to the selection electrode 63 of each piezoelectric element 52, and a drive waveform is input. Then, the shift clock SCLK and the nozzle data SD are taken into the shift register circuit, and the serial data taken in by the latch signal / LAT is latched by the latch circuit and inputted to the level shifter circuit. This level shifter circuit applies a drive waveform to the selected piezoelectric element 52 by turning on an analog switch connected to each piezoelectric element 52 according to the content of the data.

  As described above, the drive waveform applied to each piezoelectric element is controlled by the 8-bit voltage data value input to the DAC 103 in increments of 250 ns, so that the drive voltage Vp and the rise time constant tr are determined by the DAC 103. It can be easily controlled by varying the voltage data input to the.

  8 and FIG. 8 show the overall configuration of the head drive unit that drives the four inkjet heads (hereinafter referred to as “head HBk, head HC, head HM, and head HY”) of the recording head 14 in the inkjet recording apparatus described above. This will be described with reference to FIG.

  Here, for each of the four heads HBk, HC, HM, and HY, one head is divided into a plurality (three in this example) of drive units 111a, 111b, and 111c. That is, an example will be described in which a plurality of piezoelectric elements 52 corresponding to the nozzles of the nozzle rows of the heads HBk, HC, HM, and HY are grouped for each required number, and each group serves as one drive unit.

  The head drive unit is connected to each of the drive units 111a, 111b, and 111c in order to drive the drive units 111a, 111b, and 111c that are divided into four heads HBk, HC, HM, and HY. Circuits 88a, 88b and 88c are provided.

  Each drive circuit 88a, 88b, 88c is a voltage amplifying unit constituted by a DAC 103 and an OP amplifier as waveform generating means for generating a drive waveform by D / A converting the voltage data from the main control unit 101 described above. 104 and three current amplifying units 105 each including an NPN transistor Q1, a PNP transistor Q2, and the like that amplify the output of the voltage amplifying unit 104no. From the current amplifying unit 105 to each of the drive units 111a, 111b, and 111c. In contrast, drive waveforms Vcoma, Vcomb, and Vcomc are output, respectively.

  The output Vcoma from the drive circuit 88a is connected (applied) to each PZT selection circuit 106a corresponding to the drive unit 111a of each head HBk, HC, HM, HY. Similarly, the output Vcomb from the drive circuit 88b is connected to each PZT selection circuit 106b corresponding to the drive unit 111b of each head HBk, HC, HM, and HY. Further, the output Vcomc from the drive circuit 88c is connected to each PZT selection circuit 106c corresponding to the drive unit 111c of each head HBk, HC, HM, and HY. Therefore, a drive unit that spans different heads is driven by the output of one drive circuit.

  On the other hand, the PZT selection circuits 106a, 106b, 106c included in one head of each head HBk, HC, HM, HY have a shift clock SCLK1 corresponding to each head HBk, HC, HM, HY from the main control unit 101. ˜4, nozzle data SD1˜4, and latch signals / LAT1˜4 are individually inputted.

Here, an example of nozzle division by the head drive unit will be described with reference to FIG.
In the example shown in FIG. 10, as described above, each head HBk, HC, HM, and HY that ejects ink of each color constitutes a recording head. In this example, the drive units are divided into three, so that the numbers of nozzles in the nozzle areas Na, Nb, and Nc corresponding to the drive units 111a, 111b, and 111c are substantially equal. In this case, the power capacities of the transistors constituting each current amplification unit 105 of each drive circuit 88a, 88b, 88c may be substantially the same. Of course, it may be divided into two or more than four.

The operation of the head driving unit configured as described above will be described with reference to FIGS.
First, the droplet ejection characteristics of the head generally depend on the rigidity of the pressurized liquid chamber even when driven with the same drive waveform, and a liquid chamber having higher rigidity can eject ink droplets more efficiently. Here, as shown in FIG. 10, when each of the heads HBk, HC, HM, and HY is divided into three drive units 111a, 111b, and 111c, the drive unit 111b in the central portion has the drive units 111a, The rigidity of the pressurized liquid chamber is lower than that of 111c.

  Therefore, when these three drive units 111a, 111b, and 111c are driven using a common drive waveform as shown in FIG. 11, for example, the ink ejection amount Mj of the head is the same as that of the drive unit 111b as shown in FIG. Only the ejection amount Mj of the ink droplets ejected from the nozzles is lower than the ejection amount Mj of the ink droplets ejected from the nozzles of the other drive units 111a and 111c.

  In contrast, in the present invention, the drive waveforms Vcoma, Vcomb, and Vcomc from the different drive circuits 88a, 88b, and 88c for the three drive units 111a, 111b, and 111c of the heads HBk, HC, HM, and HY, respectively. Therefore, the drive units 111a, 111b, and 111c can be driven with different drive waveforms.

  Therefore, as shown in FIG. 13, the drive waveform Vcomb given to the drive unit 111b can be made higher than the drive waveforms Vcoma and Vcomc given to the drive units 111a and 111c. As a result, even when the droplet discharge characteristics from the nozzles included in the drive unit 111b are relatively poor with respect to the droplet discharge characteristics from the nozzles included in the drive units 111a and 111c, as shown in FIG. Mj can be made uniform to the injection amount Mj0, that is, within 20% of the target injection amount Mj0.

  Here, the variation is corrected by varying the voltages Vp of the drive waveforms Vcoma, Vcomb, and Vcomc. However, the pulse width, the rise time, the fall time, etc. are not limited to the voltage, but depending on the ejection characteristics of the head. It is also possible to correct the variation by making the difference for each drive unit.

  In this way, since one head is divided into a plurality of drive units and each has a drive circuit independently, it can be driven with different drive waveforms according to the difference in ink ejection characteristics in the head. it can. As a result, the drive waveform can be adjusted so as to correct variations in one head, so that ink density unevenness can be eliminated and high image quality can be obtained.

  In addition, as the printing speed increases, the head becomes longer and the number of nozzles tends to increase. However, the longer the head, the more the nozzles located at the center of the head and the nozzles located at the end of the head. Since the variation amount of the injection characteristics is large, the effect of applying the present invention is great. Therefore, the present invention can also be applied to an image forming apparatus using a full line type head.

  Further, as shown in FIG. 15, a recording head is constituted by a head HBk that discharges black ink and a color head HCA that discharges cyan, magenta, and yellow ink, and the head HCA is more than the number of nozzles of the head HBk. Even when there are a large number of nozzles, the drive waveforms can be easily varied by dividing the drive units into the drive units a, b, and c.

  In the above embodiment, the number of nozzles of the divided drive units is almost the same, but in carrying out the present invention. The number need not be the same, and the number of nozzles of each drive unit may be determined according to the ejection variation between the nozzles of the head. In this case, the current capacity of the transistors constituting the current amplifying unit is such that a transistor having a larger current capacity is used as the number of nozzles is larger, and that a drive unit having a smaller number of nozzles is a transistor having a smaller current capacity in terms of cost. preferable.

  Further, the number of divisions of the drive unit in one head is not limited to three, and if the number of divisions is large, the droplet ejection amount Mj can be brought closer to the target value Mj0 with higher accuracy.

Next, an embodiment will be described with reference to FIG.
First, the main control unit 101 and the drive circuits 88a to 88c (the waveform generation unit (DAC) 103, the voltage amplification unit 104, and the current amplification unit 105) described above are mounted on the main body side control board, and from the main body side control board side, The drive waveform signals Vcoma, Vcomb, and Vcomc are transmitted to a relay board 122 provided in the carriage 13 via a transmission means 121 such as FFC or FPC.

  On the other hand, each head substrate 123Bk, 123C, 123M, 123Y on which the piezoelectric element (PZT) 52 and the PZT selection circuits 106a, 106b, 106c are mounted has wiring (pattern) for supplying the drive waveform signals Vcoma, Vcomb, Vcomc. It is patterned so as to be straight, that is, it does not cross three-dimensionally with other signal wiring (pattern) through the back surface of the substrate through the through hole, and transmitting means 124Bk, 124C such as FFC or FPC. , 124M, 124Y to the relay board 122. The control signals other than the drive waveform signal Vcom are not shown.

  Further, the relay board 122 is wired so that the drive waveforms Vcoma, Vcomb, and Vcomc input from the main body side control board 121 are distributed to the output connect part 123a for outputting to the head boards 123Bk, 123C, 123M, and 123Y. Has been. In this case, if a multilayer substrate such as a double-sided substrate or a four-layer substrate is used as the relay substrate 122, patterning can be easily performed. Further, since the head substrates 123Bk, 123C, 123M, and 123Y need only be patterned by straight wiring, patterning only on one side is sufficient.

  In this way, the relay board is wired in the board so that both of the patterns of the input / output connection section can be connected by straight wiring, so that a general-purpose and inexpensive FFC or FPC can be used as the input / output cable. Since the connection can be made, the harness cost can be reduced. In addition, since the driving waveform signal (output of the current amplification unit) does not intersect with other signals, the head substrate is less susceptible to interference (noise) between signals, and waveform quality can be improved.

  In the description here, the voltage amplifying unit and the current amplifying unit are mounted on the main body control board. However, the voltage amplifying section and the current amplifying section can be mounted on the relay board as necessary, and the present invention is applied also in this case. Can do.

  In the above embodiment, the driving of the inkjet head using the electromechanical conversion element has been described. However, the present invention is not limited to this, and as described above, an electrostatic head, a thermal head, a head using a shape memory alloy, etc. The present invention can also be applied to driving a head using other pressure generating means. Even when a thermal head is used, it is possible to correct variations in the head by dividing the head into a plurality of drive units and adjusting the drive voltage or pulse width (voltage application time) for each drive unit.

FIG. 3 is a perspective explanatory view showing an example of a mechanism part of an ink jet recording apparatus as an image forming apparatus according to the present invention. FIG. 3 is an explanatory side sectional view of a mechanism unit of the recording apparatus. FIG. 4 is a cross-sectional explanatory diagram along the long side direction of the liquid chamber of the head for explaining an example of an ink jet head constituting the recording head of the recording apparatus. It is sectional explanatory drawing in alignment with the liquid chamber short side direction of the head. It is principal part plane explanatory drawing of the head. FIG. 2 is a block diagram illustrating an overview of a control unit of the recording apparatus. It is a block diagram for 1 head of the part concerning the head drive control of the same control part. It is a block diagram similarly provided for description of a head drive part. It is a block diagram similarly provided for description of a head drive part. It is explanatory drawing with which it uses for description of the division example of a nozzle area | region and a drive unit. It is explanatory drawing which shows an example of a drive waveform. It is explanatory drawing explaining the change of the droplet ejection amount when three drive units are driven with the same drive waveform. It is explanatory drawing explaining an example of the drive waveform of this invention. It is explanatory drawing explaining the change of the droplet ejection amount when three drive units are driven with the drive waveform of FIG. It is explanatory drawing with which it uses for description of the form of mounting of the head drive part. It is explanatory drawing with which it uses for description of the other division example of a nozzle area | region and a drive unit.

Explanation of symbols

DESCRIPTION OF SYMBOLS 13 ... Carriage 14 ... Recording head 41 ... Flow path plate 42 ... Vibrating plate 43 ... Nozzle plate 45 ... Nozzle 46 ... Pressurizing chamber 52 ... Piezoelectric element,
88: Head drive unit 88a, 88b, 88c ... Head drive circuit 103 ... DAC (waveform generation unit)
104 ... Voltage amplifier 105 ... Current amplifier 111a, 111b, 111c ... Drive unit

Claims (6)

  A plurality of heads each having pressure generating means provided corresponding to each liquid chamber communicating with a plurality of nozzles for discharging droplets, and a plurality of drive circuits for driving the pressure generating means, An image forming apparatus, wherein each of the plurality of heads is divided into a plurality of drive units, and each of the divided drive units is connected to a different drive circuit.   2. The image forming apparatus according to claim 1, wherein the plurality of driving circuits include a voltage amplifying unit and a current amplifying unit that amplify a driving waveform.   3. The image forming apparatus according to claim 1, wherein drive waveforms for the plurality of divided drive units can be independently adjusted.   4. The image forming apparatus according to claim 1, wherein the plurality of heads are provided for liquids of different colors, and the one drive circuit drives drive units of liquids of different colors. Inkjet recording apparatus.   5. The image forming apparatus according to claim 1, wherein the plurality of driving circuits are provided on a head substrate having a pressure generating unit that constitutes a driving unit of each head and a selection circuit that selects the driving pressure generating unit. An image forming apparatus characterized in that wiring is performed via a relay board, and the pattern of the input / output connection portion of the relay board is wired in the board so that both can be connected by straight wiring. 6. The image forming apparatus according to claim 5, wherein the head substrate is connected to the relay substrate, and a drive waveform signal wiring in the head substrate does not intersect with other signal wirings.

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