JP2006231539A - Head driving unit and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that a noise and a transient current value are increased because the number of switch means for concurrently performing switching is increased, when multivalued control is performed by selecting a required driving signal from a driving waveform including a plurality of driving signals within one driving period. <P>SOLUTION: When the switching means for selecting the driving signal from a common driving waveform including the plurality of driving signals within one driving period is opened/closed by a part for connecting the driving signals together, so that the selection/nonselection of the driving signal can be performed, selection starting timing for selecting the driving signal, and selection terminating timing for setting the driving signal to be in an unselected state are made different from each other. This reduces the number of the switch means to be simultaneously opened/closed. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a head drive device and an image forming apparatus, and more particularly to a head drive device that drives a liquid discharge head that discharges liquid droplets of a recording liquid and an image forming apparatus that includes the liquid discharge head.

  As various image forming apparatuses such as printers, facsimiles, copying machines, plotters, printer / fax / copier multifunction machines, etc., recording heads (printing heads) constituted by droplet discharging heads that discharge recording liquid (for example, ink) droplets are used. ) Is mounted on a carriage, and the carriage is a recording medium (hereinafter referred to as “paper”, but the material is not limited to paper, and is also referred to as recording medium, recording paper, transfer material, etc.). In addition to serial scanning in a direction orthogonal to the conveyance direction, the recording medium is intermittently conveyed according to the recording width, and an image is formed on the recording medium by repeating conveyance and recording (recording, printing, Printing and printing are also used synonymously.) There is a serial type image forming apparatus or a line type image forming apparatus equipped with a line type recording head.

As an image forming apparatus using such a liquid ejection head or a head driving device or a head driving method in such an image forming apparatus, for example, Patent Document 1 discloses a plurality of waveform data corresponding to a plurality of types of driving waveforms. There is described a drawing apparatus having storage means for storing in advance, sequentially reading out any waveform data from the storage means based on a drawing signal, converting the waveform data into a driving waveform of an analog signal, and supplying the waveform to the ink ejection head. Yes.
JP 2004-255789 A

Patent Document 2 discloses a head capable of ejecting and non-ejection of ink droplets from a nozzle with a constant driving period T by n piezoelectric elements, and a driving voltage applied to the piezoelectric element during ejection within the driving period T. It has waveform generating means for individually generating a fluctuation part in which the voltage value fluctuates in time and a steady part having a constant value, and the signal of the waveform generation means can be selectively applied to each piezoelectric element. There is described a head driving method that has a signal switching means, controls the signal switching means in accordance with a print signal, and applies a drive voltage waveform to each piezoelectric element.
JP 2001-129991 A

  Thus, in an image forming apparatus using a liquid discharge head, in order to perform gradation reproduction, one or a plurality of liquid droplets are discharged within one driving cycle and combined in flight or at a landing position. It is known to form droplets.

In general, as described in Patent Document 3, a head driving device or a head driving method for performing multi-value control of droplets ejected from a liquid ejection head includes one ejection cycle (one driving cycle, one printing cycle). The drive waveform in FIG. 2 is composed of a plurality of pulses (drive signals), and the given image data is decoded into ejection data (drive data) and a required drive signal is selected according to the gradation value. What is applied to the pressure generating means of the liquid discharge head is generally used.
Japanese Patent Laid-Open No. 10-8102

An outline of a head drive control device that realizes such a head drive method will be described with reference to FIGS.
As shown in FIG. 14 (a), this head drive control device has a plurality of drives for discharging three types of droplets, large droplets, medium droplets, and small droplets, within one discharge cycle as shown in FIG. 14 (a). A common drive waveform including the signals P51, P52, and P53 is generated and output to the head driver 502 that is a head drive device.

  The head driver 502 includes a control logic 503, a level shifter 504, and an analog switch 505. The head driver 502 includes ejection data representing ejection droplets for each nozzle and droplet types as shown in FIGS. 14 (c), (e), and (g). In response to the droplet control signals M0 to M3 (not shown for the non-ejection droplet control signal M3), the analog switch 505 is turned on / off (opened / closed).

  When the analog switch 505 is in the on state, the common drive waveform from the common drive waveform generation circuit 501 is applied to the piezoelectric element 506 of each channel, and when it is in the off state, the analog switch 505 is charged so as to maintain the electric charge stored in the piezoelectric element 506. Breaks the discharge current path.

  The analog switch 505 of the head driver 502 includes a pair of P-channel transistors 521 and N-channel transistors 522 as shown in FIG. 16, for example, and the gates of the transistors 521 and 522 are driven by inverter circuits 523 and 524. The inverters 523 and 524 are driven by a signal from the level shifter 504. The level shifter 504 amplifies the signal level of the 5V to 3.3V channel indicating the switch state output from the control logic 503. In the circuit configuration of FIG. 14, the analog switch 505 is turned on when the output A of the level shifter 504 is L (low) level and the output B is H (high) level. The size of the transistor constituting the analog switch 505 is designed in consideration of the response time delay of the output current and the output load.

  Here, the opening / closing (ON / OFF) of the analog switch 505 is switched after a certain delay time from the input transition timing of the actual droplet control signal. The delay time is determined by the size of the transistor constituting the analog switch 505 and the output drive capability of the inverter circuit. To reduce the delay time, the transistor size of the inverter circuit may be increased. There is a problem such as a large value, so it is necessary to keep it to the minimum necessary. Here, it is assumed that the state transition of the analog switch is set to actually occur after the time tsw from the state transition of the droplet control signal.

  The potential V1 in the common drive waveform shown in FIG. 14A is an intermediate potential and is a potential that is maintained when the piezoelectric element is in the OFF state, and is the potential level at the beginning and end of each pulse. For example, a large droplet control signal M0 as shown in FIG. 5C is input to the channel to which large droplet ejection data is input so that the drive signals P51 and P52 of the sections T51 and T52 are selected.

  The control logic 502 performs control so that the analog switch 505 of the nozzle is turned on when the droplet control signal is at the H level for the channel in which a large droplet is instructed. More specifically, a large droplet control signal M0 that changes to the on state at time t51 and changes to the off state that maintains the on state until time t53 is output.

  Here, details of the operation at the switching timing will be described with reference to FIG. FIG. 15 shows the output potential of the channel for ejecting large drops and medium drops near the time t53 and the state of the analog switch 505.

  As shown in FIG. 15A, when the common drive waveform is increasing toward the intermediate potential V1 before time t3, the output of the channel that ejects large droplets is as shown in FIG. 15B. The voltage rises later than the common drive waveform. This is a delay due to the ON resistance of the analog switch 505 and the capacitive component of the piezoelectric element that is the output load.

  When the common drive waveform reaches the intermediate potential V1, the voltage level is maintained constant. Even after the voltage level becomes constant, the potential of the channel output for large droplet discharge continues to rise, and reaches a level at which it can be considered to be almost the same as the intermediate potential V1, at time t53, as shown in FIG. 15 (c). The large droplet control signal M0 transitions to the L level so that the analog switch 505 of the channel that discharges large droplets is turned off. After the time tsw elapses after receiving the L level instruction, the analog switch 505 of the channel for ejecting large droplets is switched to the OFF state as shown in FIG.

  On the other hand, at time t53, the droplet control signal M2 for small droplets also changes so as to turn on the analog switch 505. As shown in FIG. 15E, the analog switch 505 of the channel for ejecting a small droplet also transitions from the OFF state to the ON state after time tsw has elapsed from time t53. The common drive waveform starts a transition for ejecting a droplet after time tsw has elapsed from time t53.

  By the way, in an image forming apparatus using a liquid discharge head, the number of nozzles of the liquid discharge head is increased in order to improve the recording speed and improve the image quality.

  In this case, in order to select a required drive signal from the drive waveform when droplets of different sizes are ejected using the conventional head drive apparatus or method described in Patent Document 3 described above. The selection timing of the switching means, that is, the state transition timing of the switch means is the same as the connection state of each drive signal of the common drive waveform. As a result, there is a problem that radiation noise and transient current increase occur.

  SUMMARY An advantage of some aspects of the invention is that it provides a head drive device and an image forming apparatus that suppress radiation noise and transient current increase by reducing the number of circuits that are simultaneously switched. To do.

  In order to solve the above problems, the head drive device according to the present invention has a configuration in which the selection timing for selecting a required drive signal from the drive waveform is different at the start and end of the selection.

  Here, the switch means has a delay time until the state actually transitions with respect to the state transition of the signal instructing opening and closing, and this delay time is longer from the OFF state than the time to transition from the ON state to the OFF state. It can be set as the structure where the time which changes to ON state is shorter.

  Moreover, it is preferable that the selection end timing varies depending on the voltage transition state immediately before the end of the selected drive signal.

  Further, a drop control signal for instructing opening / closing of the switch means is input for each size of the droplet to be ejected from the liquid ejection head, and an edge for instructing the selection end of the droplet control signal is detected to delay the timing of the selection end. It can be set as the structure provided with a means.

  The image forming apparatus according to the present invention includes the head driving device according to the present invention.

  According to the head drive device and the image forming apparatus of the present invention, the selection timing for selecting a required drive signal from the drive waveform is different between the selection start and the selection end, so the number of circuits that are switched at a time is reduced. Radiating noise and transient current can be reduced.

  Embodiments of the present invention will be described below with reference to the accompanying drawings. First, an example of an image forming apparatus according to the present invention will be described with reference to FIGS. FIG. 1 is an explanatory side view for explaining the overall structure of the mechanism section of the image forming apparatus, and FIG. 2 is a plan view for explaining the mechanism section.

  In this image forming apparatus, a carriage 4 is slidably held in a main scanning direction by a guide rod 2 and a stay 3 which are guide members horizontally mounted on left and right side plates 1A and 1B constituting a frame 1, and a main scanning motor. 5 is moved and scanned in the direction indicated by the arrow (main scanning direction) in FIG. 2 via the timing belt 7 spanned between the driving pulley 6A and the driven pulley 6B.

  The carriage 4 includes, for example, four droplet ejection heads 11k, 11c, 11m, and 11y that eject ink droplets of each color of yellow (Y), cyan (C), magenta (M), and black (Bk). The recording head 11 is mounted with the nozzle row of the nozzle surface 11a on which a plurality of ink discharge ports (nozzles) are formed arranged in a direction (sub-scanning direction) orthogonal to the main scanning direction, and the ink discharging direction is directed downward. . Although an independent droplet discharge head is used here, a configuration in which one or a plurality of heads having a plurality of nozzle rows that discharge droplets of recording liquid of each color can be used. Further, the number of colors and the arrangement order are not limited to this.

  Here, as described above, the recording head 11 is composed of four separate heads 11k, 11c, 11m, and 11y that discharge droplets of the respective colors, and the heads 11k, 11c, 11m, and 11y are shown in FIG. As described above, the nozzle array is formed by arranging two nozzles n for discharging droplets side by side (each nozzle array is referred to as nozzle arrays NA and NB). Not limited to this, as shown in FIG. 4, two nozzle rows 11 kA, 11 kB, 11 cA, 11 cB, 11 mA, 11 mB, 11 yA, and 11 yB that discharge droplets of each color are arranged in one recording head 11. It can also be constituted by a head having one or a plurality of nozzle rows that eject black ink and a head having one or a plurality of nozzle rows for each color that ejects color ink.

  As the ink jet head constituting the recording head 11, a head provided with a piezoelectric actuator such as a piezoelectric element as pressure generating means (actuator means) for generating pressure for discharging droplets is used.

  A driver IC is mounted on the recording head 11 and connected to a control unit (not shown) via a harness (flexible print cable: FPC cable) 12.

  In addition, the carriage 4 is equipped with a sub tank 15 for each color for supplying ink of each color to the recording head 11. Each color sub-tank 15 is supplementarily supplied with ink of each color from the ink cartridge 10 of each color mounted in the cartridge loading unit 9 via the ink supply tube 16 of each color. The cartridge loading 9 is provided with a supply pump unit 17 for feeding ink in the ink cartridge 10, and the ink supply tube 16 is engaged with the rear plate 1C constituting the frame 1 in the middle of turning. It is held by a stop member 18.

  On the other hand, as a paper feed unit for feeding the paper 22 stacked on the paper stacking unit (pressure plate) 21 of the paper feed tray 20, a half-moon roller (feed) that separates and feeds the paper 22 one by one from the paper stacking unit 21. A separation pad 24 made of a material having a large friction coefficient is provided opposite to the sheet roller 23 and the sheet feeding roller 23, and the separation pad 24 is biased toward the sheet feeding roller 23 side.

  In order to feed the paper 22 fed from the paper feeding unit to the lower side of the recording head 11, a guide member 25 for guiding the paper 22, a counter roller 26, a conveyance guide member 27, and a tip pressure roller. And a holding belt 28 as a conveying means for electrostatically attracting the fed paper 22 and conveying it at a position facing the recording head 11.

  The conveyance belt 31 is an endless belt, is configured to wrap around the conveyance roller 32 and the tension roller 33 and circulate in the belt conveyance direction (sub-scanning direction). 34 is charged (charged).

  The transport belt 31 may be a single-layer belt or a multi-layer (two or more layers) belt. In the case of the conveyance belt 31 having a one-layer structure, the entire layer is formed of an insulating material because it contacts the paper 32 and the charging row 34. In the case of the transport belt 31 having a multi-layer structure, the side that contacts the paper 22 and the charging roller 34 is preferably formed of an insulating layer, and the side that does not contact the paper 22 and the charging roller 34 is preferably formed of a conductive layer. .

As an insulating material for forming the transport belt 31 having a single layer structure and an insulating material for forming the insulating layer of the transport belt 31 having a multi-layer structure, for example, a conductive material such as PET, PEI, PVDF, PC, ETFE, or PTFE is used. It is preferable that the material does not contain a control material, and the volume resistivity is 10 ¹² Ωcm or more, preferably 10 ¹⁵ Ωcm. In addition, as a material for forming the conductive layer of the transport belt 31 having a multilayer structure, it is preferable that the resin or elastomer contains carbon and has a volume resistivity of 10 ⁵ to 10 ⁷ Ωcm.

The charging roller 34 is arranged so as to come into contact with an insulating layer (in the case of a multilayer belt) forming the surface layer of the transport belt 31 and to rotate following the rotation of the transport belt 31, and to apply pressure to both ends of the shaft. It is over. The charging roller 34 is formed of a conductive member having a volume resistivity of 10 ⁶ to 10 ⁹ Ω / □. As will be described later, for example, 2 kV positive and negative AC bias (high voltage) is applied to the charging roller 34 from an AC bias supply unit (high voltage power supply). The AC bias may be a sine wave or a triangular wave, but a square wave is more preferable.

  In addition, a guide member 35 is disposed on the back side of the conveyance belt 31 so as to correspond to a printing area by the recording head 11. The guide member 35 has an upper surface that protrudes toward the recording head 11 from the tangent line of the two rollers (the conveyance roller 32 and the tension roller 33) that support the conveyance belt 31, thereby maintaining high-precision flatness of the conveyance belt 31. Like to do.

  The transport belt 31 rotates in the belt transport direction of FIG. 2 when the transport roller 32 is rotationally driven by the sub-scanning motor 36 via the drive belt 37 and the timing roller 38. Although not shown, an encoder wheel having a slit is attached to the shaft of the conveying roller 32, and a transmission type photosensor for detecting the slit of the encoder wheel is provided, and the wheel encoder is configured by the encoder wheel and the photosensor. It is composed.

  Further, as a paper discharge unit for discharging the paper 22 recorded by the recording head 11 to the paper discharge tray 40, a separation claw 41 for separating the paper 22 from the transport belt 31, a paper discharge roller 42, and paper discharge The roller 43 is provided.

  A duplex unit 51 is detachably mounted on the back surface of the apparatus body 1. The duplex unit 51 takes in the paper 22 returned by the reverse rotation of the transport belt 31, reverses it, and feeds it again between the counter roller 26 and the transport belt 31. The upper surface of the duplex unit 51 is a manual feed tray 52.

  Further, a maintenance / recovery mechanism 61 for maintaining and recovering the state of the nozzles of the recording head 11 is disposed in a non-printing area on one side in the scanning direction of the carriage 4. The maintenance / recovery mechanism 61 includes cap members (hereinafter referred to as “caps”) 62 a to 62 d (hereinafter referred to as “caps 62” when not distinguished) and nozzles for capping the nozzle surfaces 11 a of the recording head 11. A wiper blade 63 that is a blade member for wiping the surface 11a, an empty discharge receiver 64 that receives liquid droplets when performing empty discharge for discharging liquid droplets that do not contribute to recording in order to discharge the thickened recording liquid, and the like It has. Here, the cap 62a is a suction and moisture retention cap, and the other caps 62b to 62d are moisture retention caps.

  Further, in the non-printing area on the other side of the carriage 4 in the scanning direction, there is an empty space for receiving a liquid droplet when performing an empty discharge for discharging a liquid droplet that does not contribute to recording in order to discharge the recording liquid thickened during recording or the like. A discharge receiver 68 is disposed, and the idle discharge receiver 68 is provided with an opening 69 along the nozzle row direction of the recording head 11.

  Further, as shown in FIG. 1, a density sensor 71 including an infrared sensor (a type of sensor is not limited to the infrared sensor) which is a medium detecting unit for detecting the presence or absence of the paper 22 in the carriage 4. Is provided. The density sensor 71 is provided on the recording area (image forming area) side (conveying belt 31 side) side of the carriage 4 at the home position and upstream of the recording head 11 in the paper conveying direction. .

  Further, an encoder scale 72 having slits is provided on the front side of the carriage 4 along the main scanning direction, and an encoder sensor 73 including a transmission type photosensor for detecting the slits of the encoder scale 72 is provided on the front side of the carriage 4. These components constitute a linear encoder 74 for detecting the position of the carriage 4 in the main scanning direction.

  Next, an example of a droplet discharge head constituting the recording head in this image forming apparatus will be described with reference to FIGS. 5 is a cross-sectional explanatory view along the longitudinal direction of the liquid chamber of the head, and FIG. 6 is a cross-sectional explanatory view of the head along the lateral direction of the liquid chamber (nozzle arrangement direction).

  The droplet discharge head includes a flow channel plate 101 formed by anisotropic etching of a single crystal silicon substrate, a vibration plate 102 formed by nickel electroforming, for example, bonded to the lower surface of the flow channel plate 101, and a flow plate. A nozzle plate 103 bonded to the upper surface of the path plate 101 is bonded and stacked, and a nozzle communication path 105, a liquid chamber 106, and a liquid chamber, which are channels through which the nozzles 104 that discharge liquid droplets (ink droplets) communicate with each other. An ink supply port 109 communicating with a common liquid chamber 108 for supplying ink to 106 is formed.

  In addition, two rows (only one row is shown in FIG. 6) of stacked piezoelectric elements as electromechanical conversion elements that are pressure generating means (actuator means) for pressurizing ink in the liquid chamber 106 by deforming the diaphragm 102. An element 121 and a base substrate 122 to which the piezoelectric element 121 is bonded and fixed are provided. Note that a column portion 123 is provided between the piezoelectric elements 121. This support portion 123 is a portion formed simultaneously with the piezoelectric element 121 by dividing and processing the piezoelectric element member. However, since the drive voltage is not applied, the support portion 123 becomes a simple support.

  Further, an FPC cable 12 equipped with a drive circuit (drive IC) (not shown) is connected to the piezoelectric element 121.

  The peripheral edge of the diaphragm 102 is joined to a frame member 130, and the frame member 130 serves as a through-hole 131 and a common liquid chamber 108 that house an actuator unit composed of the piezoelectric element 121 and the base substrate 122. A recess and an ink supply hole 132 for supplying ink from the outside to the common liquid chamber 108 are formed. The frame member 130 is formed by injection molding with a thermosetting resin such as an epoxy resin or polyphenylene sulfite, for example.

  Here, the flow path plate 101 is formed by, for example, subjecting the single crystal silicon substrate having a crystal plane orientation (110) to anisotropic etching using an alkaline etching solution such as an aqueous potassium hydroxide solution (KOH), so that the nozzle communication path 105, Although a recess or a hole serving as the liquid chamber 106 is formed, the invention is not limited to a single crystal silicon substrate, and other stainless steel substrates, photosensitive resins, and the like can also be used.

  The vibration plate 102 is formed from a nickel metal plate, and is manufactured by, for example, an electroforming method (electroforming method). Alternatively, a metal plate or a joining member between a metal and a resin plate may be used. it can. The piezoelectric element 121 and the support post 123 are bonded to the diaphragm 102 with an adhesive, and the frame member 130 is further bonded with an adhesive.

  The nozzle plate 103 forms a nozzle 104 having a diameter of 10 to 30 μm corresponding to each liquid chamber 106 and is bonded to the flow path plate 101 with an adhesive. The nozzle plate 103 is formed by forming a water repellent layer on the outermost surface of a nozzle forming member made of a metal member via a required layer. The surface of the nozzle plate 103 is the nozzle surface 34a described above.

  The piezoelectric element 121 is a stacked piezoelectric element (here, PZT) in which piezoelectric materials 151 and internal electrodes 152 are alternately stacked. An individual electrode 153 and a common electrode 154 are connected to each internal electrode 152 drawn out to different end faces of the piezoelectric element 121 alternately. In this embodiment, the ink in the liquid chamber 106 is pressurized using the displacement in the d33 direction as the piezoelectric direction of the piezoelectric element 121. However, the pressure in the d31 direction is used as the piezoelectric direction of the piezoelectric element 121. The ink in the liquid chamber 106 may be pressurized. Alternatively, a structure in which one row of piezoelectric elements 121 is provided on one substrate 122 may be employed.

  In the droplet discharge head configured as described above, for example, by lowering the voltage applied to the piezoelectric element 121 from the reference potential, the piezoelectric element 121 contracts, and the vibration plate 102 descends to expand the volume of the liquid chamber 106. As a result, the ink flows into the liquid chamber 106, and then the voltage applied to the piezoelectric element 121 is increased to extend the piezoelectric element 121 in the stacking direction, and the diaphragm 102 is deformed in the direction of the nozzle 104 to change the volume of the liquid chamber 106. / By contracting the volume, the recording liquid in the liquid chamber 106 is pressurized, and droplets of the recording liquid are ejected (jetted) from the nozzle 104.

  Then, by returning the voltage applied to the piezoelectric element 121 to the reference potential, the diaphragm 102 is restored to the initial position, and the liquid chamber 106 expands to generate a negative pressure. The recording liquid is filled in 106. Therefore, after the vibration of the meniscus surface of the nozzle 104 is attenuated and stabilized, the operation proceeds to the next droplet discharge.

  Note that the driving method of the head is not limited to the above example (pulling-pushing), and it is also possible to perform striking or pushing depending on the direction to which the driving waveform is given.

  In the image forming apparatus configured as described above, the sheets 22 are separated and fed one by one from the sheet feeding unit, and the sheets 22 fed substantially vertically upward are guided by the guide 25, and the conveyance belt 31 and the counter roller 26, and the leading end is guided by a conveying guide 27 and pressed against the conveying belt 31 by a leading end pressing roller 29, and the conveying direction is changed by approximately 90 °.

  At this time, a positive output and a negative output are alternately and repeatedly applied to the charging roller 34 from an AC bias supply unit, which will be described later, that is, an alternating voltage is applied, and a charging voltage pattern in which the conveying belt 31 alternates, that is, a loop In the sub-scanning direction, which is the direction, plus and minus are alternately charged in a band shape with a predetermined width. When the paper 32 is fed onto the conveying belt 31 that is alternately charged with plus and minus, the paper 22 is attracted to the conveying belt 31 by electrostatic force, and the paper 22 is conveyed in the sub-scanning direction by the circular movement of the conveying belt 31. Is done.

  Therefore, by driving the recording head 11 according to the image signal while moving the carriage 4, ink droplets are ejected onto the stopped paper 22 to record one line, and after the paper 22 is conveyed by a predetermined amount, Record the next line. Upon receiving a recording end signal or a signal that the trailing edge of the paper 22 has reached the recording area, the recording operation is finished and the paper 22 is discharged onto the paper discharge tray 40.

  In the case of double-sided printing, when recording on the front surface (surface to be printed first) is completed, the recording belt 32 is fed into the double-sided paper feeding unit 51 by rotating the conveyor belt 31 in reverse. The paper 22 is reversed (with the back surface being the printing surface), fed again between the counter roller 26 and the conveyor belt 31, controlled in timing, and conveyed by the conveyor bell 31 as described above. After recording on the back surface, the paper is discharged onto the paper discharge tray 40.

Next, an outline of the control unit of the image forming apparatus will be described with reference to the block diagram of FIG.
In the control unit 200, the CPU 211 that controls the entire apparatus, the ROM 202 that stores programs executed by the CPU 211 and other fixed data, the RAM 203 that temporarily stores image data and the like, and the power supply of the apparatus are cut off. A rewritable non-volatile memory 204 for holding data in between, an image processing for performing various signal processing and rearrangement on image data, and an ASIC 205 for processing input / output signals for controlling the entire apparatus. ing.

  The control unit 200 includes an I / F 206 for transmitting and receiving data and signals to and from the host side, a head drive control unit 207 including a data transfer unit for driving and controlling the recording head 11, and a carriage 4 side. A head driver (driver IC) 208, which is a head driving device for driving the provided recording head 11, a main scanning motor driving unit 210 for driving the main scanning motor 5, and a sub scanning motor 36 are driven. A sub-scanning motor drive unit 211, an AC bias supply unit 212 that supplies an AC bias to the charging roller 34, detection pulses from the linear encoder 74 and the wheel encoder 236, a detection signal from the temperature sensor 215 that detects the environmental temperature, and An I / O 213 for inputting detection signals from other various sensors is provided. The control unit 200 is connected to an operation panel 214 for inputting and displaying information necessary for the apparatus.

  Here, the control unit 200 transmits print data from the host side such as an information processing device such as a personal computer, an image reading device such as an image scanner, an imaging device such as a digital camera, etc. via an I / F 206 via a cable or a network. Receive.

  Then, the CPU 201 of the control unit 200 reads and analyzes the print data in the reception buffer included in the I / F 206, performs necessary image processing, data rearrangement processing, and the like in the ASIC 205, and this image data is head-driven. The data is transferred from the control unit 207 to the head driver 208. The dot pattern data for image output may be generated by storing font data in the ROM 202, for example, or the image data is developed into bitmap data by a host-side printer driver and transferred to this apparatus. You may do it.

  The head drive control unit 207 transfers the above-described image data as serial data, and outputs a transfer clock, a latch signal, a control signal, and the like necessary for transferring the image data and confirming the transfer to the head driver 208. Includes a drive waveform generation unit including a D / A converter and an amplifier that D / A converts drive pulse pattern data stored in the ROM 202 and read out by the CPU 201. One drive pulse or a plurality of drive pulses A drive waveform composed of (drive signal) is output to the head driver 208.

  The head driver 208 selectively selects the drive pulse constituting the drive waveform supplied from the head drive control 207 based on the image data corresponding to one line of the print head 11 inputted serially (actuator means of the print head 11 ( In the head configuration described above, the head 11 is driven by being applied to the piezoelectric element 121).

  The main scanning motor driving unit 210 calculates a control value based on a target value given from the CPU 201 side and a speed detection value obtained by sampling a detection pulse from the linear encoder 74, and performs main scanning via an internal motor driver. The motor 5 is driven.

  Similarly, the sub-scanning motor drive control unit 211 calculates a control value based on a target value given from the CPU 101 side and a speed detection value obtained by sampling a detection pulse from the wheel encoder 136 to determine an internal motor driver. And the sub-scanning motor 36 is driven.

Next, an example of the configuration of the head drive control unit 207 and the head driver 28 which is the head drive device according to the present invention will be described with reference to FIG.
As described above, the head drive control unit 207 generates and outputs a drive waveform (common drive waveform) composed of a plurality of drive pulses (drive signals) within one ejection cycle, and the image A data transfer unit 302 that outputs data (print data), a transfer clock (not shown), a latch signal, and a droplet control signal. Droplet control signals M0 to M3 (non-ejection control signal M3 is not shown) are signals for instructing opening / closing of an analog switch 316, which will be described later, of the head driver 208 for each drop, and are commonly driven. The state transitions to the H level with a waveform to be selected in accordance with the waveform ejection cycle, and the state transitions to the L level when not selected.

  The head driver 208 includes a shift register 311 for inputting a transfer clock (shift clock) and serial image data from the data transfer unit 302, a latch circuit 312 for latching each register value of the shift register 311 with a latch signal, and an image. A decoder 313 that decodes data and control signals and outputs a result, a level shifter 314 that converts the logic level voltage signal of the decoder 313 to a level at which the analog switch 315 can operate, and a decoder 313 that is provided via the level shifter 314 And an analog switch 316 which is turned on / off (opened / closed) by the output of

  The analog switch 316 is connected to the selection electrode (individual electrode) 154 of each piezoelectric element 121, and the common drive waveform from the drive waveform generation unit 301 is input thereto. Therefore, when the analog 316 is turned on according to the result of decoding the serially transferred image data and the control signal by the decoder 313, a required drive signal constituting the common drive waveform passes (is selected) and is piezoelectric. Applied to the element 121.

  The analog switch 316 is composed of a CMOS analog switch in the same manner as the conventional analog switch described above. That is, as shown in FIG. 9, a pair of P-channel transistors 321 and N-channel transistors 322 are provided, and the gates of the transistors 321 and 322 are driven by inverter circuits 323 and 324, and the inverters 323 and 324 are level shifters 314. It is driven by the signal. In this setting, the output A of the level shifter 314 is L (low) level, the output B is H (high) level, and the analog switch 315 is turned on. Further, the opening / closing (on / off) of the analog switch 315 is switched after a certain delay time from the input transition timing of the actual droplet control signals M0 to M2, and actually from the state transition of the droplet control signals M0 to M2. It is set so that the state transition of the analog switch 315 occurs after the time tsw. Cost reduction can be achieved by using a CMOS analog switch.

  The head driver 208 includes an edge detection circuit 317 that is an edge detection unit that detects falling edges (selection end timing) of the droplet control signals M0 to M2 from the data transfer unit 302, and an edge detection circuit 317. A delay setting circuit 318 is provided as delay setting means for delaying the falling edge of the droplet control signal by a predetermined time based on the output and outputting the delayed control signal to the decoder 313.

Next, the operation of the head driver 208 will be described with reference to FIG.
First, as shown in FIG. 10A, the drive waveform generation unit 301 falls from the reference potential (intermediate potential) V1 (in a direction in which the liquid chamber volume is expanded) within a single discharge period, and a predetermined hold time. After passing through, a common drive waveform including a plurality of pulses (drive signals) P1, P2, and P3 is output that rises toward the reference potential V1 (in the direction of contracting the liquid chamber volume).

  Here, a large droplet is formed by ejecting two droplets with pulses P1 and P2 and combining them during flight, and the waveform element of pulse P2 has a falling potential lower than that of pulse P1. The medium droplet can be ejected only by the pulse P2, and the waveform element of the pulse P3 can eject a small droplet only by the pulse P3 by setting the falling potential lower than that of the pulse P2 and rising in a stepwise manner. I am doing so.

  Further, when a large droplet is selected from the drive waveform generation unit 301, as shown in FIGS. 10B and 10C, a large droplet control signal M0 that becomes H level in the sections T1 and T2 corresponding to the pulses P1 and P2. When selecting a medium droplet, as shown in FIGS. 10 (e) and 10 (f), the medium droplet control signal M1 that becomes H level in the section T2 corresponding to the pulse P2 as shown in FIG. ) And (i), the droplet control signal M2 that becomes H level in the section T3 is output.

  Here, the state transition of each control signal M0, M1, M2 from the L level to the H level and the state transition from the H level to the L level (timing for instructing selection start or end) are the connected portions of the drive pulses ( This is set immediately after the drive pulse voltage rises to the intermediate potential V1. In this case, the time of the section T1 is set shorter than the time of the section T51 of FIG.

  Then, the edge detection circuit 317 of the head driver 208 detects a state transition (an edge for instructing selection completion) of these control signals M0, M1, and M2 from the H level to the L level, and the delay setting circuit 318 is an edge detection circuit. After the edge 317 detects the edges of the control signals M0, M1, and M2, the edge is delayed by a predetermined time rd, that is, the selection end timing is delayed and output to the decoder 313. As a result, the selection end timing instructed by the transition from the H level to the L level of the control signals M0, M1, and M2 input to the decoder 313 is actually delayed by a predetermined time td.

  Here, the delay time td is set in advance to a value that takes into account the delay time of the drive signal due to the ON resistance of the analog switch 315 and the capacitance of the piezoelectric element 121 of the output load.

  Next, the details of the operation near time t3 in FIG. 10 will be described with reference to FIG. FIG. 10 shows the output potential of the channel for ejecting large droplets and medium droplets and the state of the analog switch 315 near time t3.

  As shown in FIG. 11A, when the pulse P1 of the common drive waveform is increasing toward the intermediate potential V1 before the time t3, a channel that ejects large droplets as shown in FIG. 11B. Output (response waveform) rises later than the common drive waveform. This is a delay due to the ON resistance of the analog switch 315 and the capacitive component of the piezoelectric element 121 which is an output load.

  When the pulse P1 of the common drive waveform reaches the intermediate potential V1, the state of the large droplet control signal M0 changes (falls) from the H level to the L level, that is, the analog switch 315 that discharges the large droplet is turned off. It will be in the state which instruct | indicates the selection end to make into a state. At this time, as described above, the falling edge of the large droplet control signal M0 is delayed by the edge detection circuit 317 and the delay setting circuit 318, and when the delay time td has actually elapsed since time t3, that is, the large droplet discharge The output of the delay setting circuit 318 is changed from the H level so that the state of the analog switch 315 is changed from the ON state to the OFF state after the channel output potential continues to rise and reaches a level that can be regarded as substantially the same as the reference potential V1. Transition to L level.

  As a result, the analog switch 315 of the channel for ejecting large droplets receives an instruction for state transition (selection end) from the H level to the L level of the delayed large droplet control signal M0, as shown in FIG. 11C. Will be switched to the OFF state after elapse of time tsw.

  On the other hand, at time t3, the state of the droplet control signal M2 also changes so that the analog switch 315 is turned on. Since there is no delay with respect to the rise (state transition) of the droplet control signal M1 from the L level to the H level, the analog switch 313 of the droplet ejection channel is set to the time as shown in FIG. Transition from the OFF state to the ON state after the elapse of time tsw from t3. The common drive waveform starts a transition for ejecting a droplet after time tsw has elapsed from time t3.

  Therefore, the state transition at the end of selection of the analog switch for the channel that discharges large droplets is different from the state transition at the start of selection of the analog switch for the channel that discharges small droplets, that is, the selection timing for selecting the drive signal is driven. The timing at which signal selection starts and the end of selection of drive signals are different, and the number of circuits that switch simultaneously decreases.

  As described above, the selection timing for selecting a required drive signal from a drive waveform including a plurality of drive signals input within one ejection cycle differs between the selection start and the selection end. As a result, radiation noise and a transient increase in current can be suppressed, an increase in the number of nozzles can be accommodated, and a higher recording speed and higher image quality can be achieved.

  In this case, an edge detection unit that inputs a droplet control signal for instructing opening / closing of the switch unit for each droplet size to be ejected from the liquid ejection head, and detects an edge (state transition) for instructing the end of selection of the droplet control signal. And a delay means for delaying a state transition for instructing the switch means to end selection of the drop control signal in accordance with a detection result of the edge detecting means, and a selection switching timing at one location corresponding to the connection portion of the drive signals The selection start timing and the selection end timing can be made different with a simple configuration without increasing the number of signal lines to the head drive device by making the selection start timing different from the selection end timing by delaying Can do.

  Here, the drive capacity of the inverters 323 and 324 that drive the above-described transistor of FIG. 9 constituting the analog switch 315 is changed, and the delay time Tswoff until the transition from the ON state to the OFF state and the OFF state to the ON state are performed. It can also be configured such that the relationship of the following equation (1) is established during the delay time tswon when transitioning to.

  By configuring the analog switch in this manner, the state transition of the analog switch is the same as that described with reference to FIG. 11 without providing the edge detection circuit and the delay setting circuit described above, and the circuit configuration is further simplified.

Next, when the slope of the pulse (drive signal) constituting the common drive waveform is gentle, the delay amount of the delay setting circuit 318 can be reduced. The operation in this case will be described with reference to FIG.
As shown in FIG. 12A, the common drive waveform used here is a waveform element with a gentler transition than the transition of the rising voltage in the section T2 of the common drive waveform shown in FIG. At this time, the difference between the response waveform of the channel for ejecting large droplets and the common drive waveform is smaller than when the common drive waveform of FIG. 10 is used, and the time to reach the intermediate potential (reference potential) V1 is also shown in FIG. It becomes shorter than the waveform.

  Here, the delay setting circuit 318 performs the delay setting so that ts> ts1, and as a result, the time for maintaining the intermediate potential V1 is shortened by (ts−ts1), and the drive waveform can be shortened. It becomes. In this case, the delay amount may be determined for each selected waveform in advance, and the delay amount may be given to the delay setting circuit 318 each time from the control unit side.

  In other words, the selection end timing varies depending on the voltage transition state immediately before the end of the selected drive signal. Thereby, since the waveform selection timing can be selected in consideration of the voltage difference between the output drive voltage due to the ON resistance of the piezoelectric element and the analog switch and the common drive waveform, the waveform can be shortened and the speed can be increased.

  In the above embodiment, the image forming apparatus having a printer configuration has been described as an example. However, the present invention can be similarly applied to a multifunction type image forming apparatus in which a printer / FAX / copier is combined. Further, the present invention can be similarly applied to an image forming apparatus that uses recording liquids and liquids other than ink.

1 is an explanatory side view illustrating an overall configuration of a mechanism unit of an image forming apparatus according to the present invention. It is a plane explanatory view of the mechanism part. FIG. 3 is an explanatory diagram illustrating an example of a recording head configuration of the image forming apparatus. FIG. 6 is an explanatory diagram illustrating another example of the recording head configuration. FIG. 6 is a cross-sectional explanatory view along the longitudinal direction of the liquid chamber showing an example of a droplet discharge head that also constitutes a recording head. FIG. 5 is a cross-sectional explanatory view along the lateral direction of the liquid chamber showing an example of a droplet discharge head that also constitutes a recording head. FIG. 2 is a block explanatory diagram illustrating an overview of a control unit in the image forming apparatus. FIG. 3 is a block explanatory diagram illustrating an example of a head drive control unit and a head driver in the control unit. It is explanatory drawing explaining an example of the analog switch part of the head driver. It is explanatory drawing with which it uses for operation | movement description of a head driver similarly. It is explanatory drawing explaining the detail in the time t3 vicinity of FIG. Similarly, it is explanatory drawing explaining the detail in the vicinity of the time t3 of FIG. 9 in another example. FIG. 10 is a block diagram for explaining a conventional head driver. It is explanatory drawing with which it uses for operation | movement description of a head driver similarly. It is explanatory drawing explaining the detail in the time t3 vicinity of FIG. It is explanatory drawing explaining an example of the analog switch part of a head driver similarly.

Explanation of symbols

DESCRIPTION OF SYMBOLS 4 ... Carriage 5 ... Main scanning motor 11 ... Recording head 11k, 11c, 11m, 11y ... Head NA, NB ... Nozzle row 22 ... Recording medium (paper)
DESCRIPTION OF SYMBOLS 31 ... Conveyance belt 32 ... Conveyance roller 36 ... Sub-scanning motor 121 ... Piezoelectric element 200 ... Control part 207 ... Head drive control part 208 ... Head driver

Claims (5)

  For a liquid discharge head that discharges droplets, a required drive signal is selected via a switch means that opens and closes according to drive data from among drive waveforms including a plurality of drive signals input within one discharge cycle. In the head driving device to be applied, a selection timing for selecting a required driving signal from the driving waveform is different between selection start and selection end.   2. The head driving device according to claim 1, wherein the switch means has a delay time until the state actually changes with respect to the state transition of the signal instructing opening and closing, and the delay time is changed from the ON state to the OFF state. A head driving device characterized in that the time to transition from the OFF state to the ON state is shorter than the time to transition to.   2. The head driving device according to claim 1, wherein the timing of completion of selection varies depending on a voltage transition state immediately before the end of the selected driving signal.   2. The head drive device according to claim 1, wherein a drop control signal for instructing opening / closing of the switch means is input for each size of a droplet to be ejected from the liquid ejection head, and an edge for instructing the end of selection of the droplet control signal. And a means for delaying the timing of completion of selection. 5. An image forming apparatus for forming an image on a recording medium by a liquid discharge head that discharges liquid droplets of a recording liquid, comprising the head driving device according to any one of claims 1 to 4. apparatus.

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