JP4975258B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus.

  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 discharge head, or a head driving apparatus or a head driving method in such an image forming apparatus, for example, Patent Document 1 discloses a liquid in an outward path and a return path in an apparatus that performs bidirectional jetting of droplets In order to make the droplet ejection amounts uniform, the drive signal generation circuit generates the forward drive signal COM1 in which the small dot ejection pulse DP1 is arranged after the medium dot ejection pulse DP1 during the forward scanning of the recording head, and returns the recording head in the backward direction. During the scanning, the ejection pulses DP1 and DP2 are arranged in the reverse order of the forward scanning, and the backward driving signal COM2 in which the fine vibration pulse VP is arranged between the ejection pulses is generated. When the discharge pulses DP1 and DP2 are continuously supplied, the fine vibration pulse is generated before the medium dot discharge pulse DP1. There is a thing which was to be supplied to.
JP 2004-074500 A

Further, as described in Patent Document 2, the landing position of the liquid droplet ejected from the reciprocating nozzle opening can be suitably adjusted without having to switch the drive signal between the forward movement and the backward movement. Therefore, the drive signal generating means generates a common drive signal in the forward path and the return path, the drive signal is a periodic signal of the pulse train, and the pulse train includes the first pulse waveform PS01 and the second pulse waveform PS02. The first pulse waveform PS01 is a pulse waveform for ejecting liquid droplets at a relatively slow ejection speed, and the second pulse waveform PS02 ejects liquid droplets at a relatively fast ejection speed. There is a configuration that has a pulse waveform for the purpose.
JP 2004-058606 A

Furthermore, as described in Patent Document 3, a first drive waveform for ejecting ink droplets and a second drive waveform for vibrating a meniscus without ejecting ink droplets are referred to as a second drive waveform and a first drive waveform. There is a device provided with means for generating and outputting in time series.
JP 2002-144563 A

  However, in the above-described patent document 1, it is necessary to use different driving signals for the forward path and the backward path, and the landing positions of the small dots and the medium dots on the recording medium are different. There is a problem that it is difficult to achieve high image quality, such as separation into a plurality of parts.

  In addition, in the case of ejecting a large ink droplet with a single drive signal, the one described in Patent Document 2 has a limit on the amount of the droplet, and when forming a large dot with a plurality of drive signals, Due to the landing on the recording medium, there is a problem that it is difficult to form clean dots, and similarly, it is difficult to achieve high image quality.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide an image forming apparatus capable of forming high-quality images at high speed so that droplets of different sizes can be ejected with high accuracy in a short cycle. And

In order to solve the above problems, an image forming apparatus according to the present invention provides:
A liquid discharge head having pressure generating means for generating pressure to pressurize a liquid chamber communicating with a nozzle for discharging droplets is mounted, and a drive signal constituting a drive waveform is selectively discharged based on an image signal In an image forming apparatus that is applied to a head and driven to form an image on a recording medium.
A drive waveform including at least first, second, and third drive signals generated in time series within one drive cycle,
The first drive signal is a drive signal for finely moving the liquid chamber without discharging a droplet,
The second drive signal and the third drive signal are drive signals for discharging droplets,
When the second drive signal is applied alone, the second drive signal is applied when the first to third drive signals are continuously applied, rather than the ejection speed of the droplets ejected by the second drive signal. The ejection speed of the droplets ejected by the drive signal is relatively slow, and by continuously applying the first to third drive signals , a drive waveform is generated in which the ejected droplets coalesce during flight. It was set as the structure provided with the means to do.

Here, before Symbol second driving signal, the first to form a relatively large dot second, than the droplets of the third driving signal is the driving signal for forming a relatively small dot Can be configured. The second drive signal may be a drive signal that is applied when a meniscus in the nozzle is raised by the first drive signal.

The second drive signal may be a drive signal that is applied when the phase of the pressure generated by the first drive signal is reversed. Also, the time from the start of application of the drive waveform to the time when the droplet ejected by the second drive signal and the droplet ejected by the first to third drive signals land on the recording medium. It can be set as the structure which is substantially the same .

A landing position on the recording medium of the droplet discharged by the second driving signal; a landing position on the recording medium of the droplet discharged by the first to third driving signals; and the landing position on the recording medium more ejected droplets to a third driving signal can be configured to be substantially the same.

According to the image forming apparatus of the present invention, a drive waveform including at least first, second, and third drive signals generated in time series within one drive cycle, wherein the first drive signal is a droplet. The second drive signal and the third drive signal are drive signals for ejecting liquid droplets, and the second drive signal is applied when the second drive signal is applied alone. When the first to third drive signals are continuously applied, the discharge speed of the droplets discharged by the second drive signal is relatively slower than the discharge speed of the droplets discharged by the drive signal of Since the first to third drive signals are continuously applied, the structure is provided with means for generating a drive waveform in which the ejected liquid droplets are combined during flight. Can be landed as a single droplet on the recording medium, and of different sizes Droplets be discharged in a short period with high accuracy can be formed a high quality image at a high speed that.

  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 or 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. Further, as a material for forming the conductive layer of the transport belt 31 having a multi-layer structure, it is preferable that carbon is contained in the resin or elastomer so that the volume resistivity is 10 ⁵ to 10 ⁷ Ωcm.

The charging roller 34 is disposed so as to come into contact with an insulating layer (in the case of a multilayer belt) that forms the surface layer of the transport belt 31 and to rotate following the rotation of the transport belt 31. 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, a 2 kV positive / 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.

  As shown in FIG. 1, the carriage 4 is provided with a paper sensor 71 for detecting the presence or absence of the paper 22. Further, the sheet sensor 71 is provided on the recording region (image forming region) side (conveying belt 31 side) when the carriage 4 is at the home position, and upstream of the recording head 11 in the sheet 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. In addition, the piezoelectric element member forms the piezoelectric element 121 and the support | pillar part 123 in the comb-tooth shape by performing the dicing process of a half cut.

  Further, the above-described 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 case, the electrode of the piezoelectric element member on the side that becomes the individual electrode 153 is divided into individual electrodes when divided by the above-described half-cut dicing by limiting the length by processing such as a notch, and the common electrode 154 The electrode of the piezoelectric element member on the side is formed so as not to be completely divided by half-cut dicing.

  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. Sub-scan motor drive unit 211, AC bias supply unit 212 for supplying AC bias to charging roller 34, detection pulse from linear encoder 74 and wheel encoder 236, detection signal from temperature sensor 215 for detecting environmental temperature, paper I / O 213 for inputting detection signals from the sensor 71 and detection signals from various other sensors. It is equipped with a. 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, the head drive control unit 207 and the head driver 28 will be described with reference to FIG.
As described above, the head drive control unit 207 generates a drive waveform (common drive waveform) composed of a plurality of drive pulses (drive signals) within one ejection cycle (drive cycle) and outputs the drive waveform. And a data transfer unit 302 that outputs image data (print data), a transfer clock (not shown), a latch signal, and a droplet control signal. The droplet control signals M0 to M3 are signals for instructing the opening and closing of an analog switch 316, which will be described later, of the head driver 208 for each droplet. The state transitions, and when not selected, the state transitions to the L level.

  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 droplet control signals M0 to M3 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 level shifter 314 And an analog switch 316 that is turned on / off (opened / closed) by an output of a given decoder 313.

  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.

Next, an example of a drive waveform generated and output by the drive waveform generation unit 301 will be described with reference to FIG.
This drive waveform is composed of first, second, and third drive signals P1, P2, and P3 that are generated and output within one drive cycle.

  Here, the first drive signal P1 is a reference from the waveform element a falling from the reference potential (intermediate potential) V, the waveform element b maintaining the hold state at the falling potential of the waveform element a, and the hold potential of the waveform element b. It is a signal including a waveform element c that rises to the potential V. When the first drive signal P1 is applied to the piezoelectric element 121, a minute vibration is generated in the liquid chamber 106 to vibrate the nozzle meniscus, and no droplet is ejected from the nozzle 104.

  The reference potential V is a potential at which the piezoelectric element 112 pushes the diaphragm 102 toward the liquid chamber 106 and keeps the liquid chamber 106 contracted when the potential V1 is applied. Falling down deforms the piezoelectric element 112 in the direction in which the diaphragm 102 expands the liquid chamber 106.

  The second drive signal P2 includes a waveform element d falling from the reference potential (intermediate potential) V, a waveform element e maintaining the hold state at the falling potential of the waveform element d, and a waveform rising from the hold state to the middle of the reference potential V. The signal includes the element f, the waveform element g that maintains the hold state at the rising potential of the waveform element f, and the waveform element h that rises from the hold potential of the waveform element g to the reference potential V.

  In this second drive signal P2, the pressure generated in the liquid chamber 106 when the first drive signal P1 is applied and the pressure generated when the second drive signal P2 is applied are in opposite phases. That is, in other words, the discharge speed of the liquid droplets discharged by the first and second drive signals P1 and P2 is higher than the discharge speed of the liquid droplets discharged by contracting the liquid chamber 6 by the second drive signal. The time (interval) T1 between the first drive signal P1 and the second drive signal P2 is set so as to be relatively slow.

  The third drive signal P3 includes a waveform element i falling from the reference potential (intermediate potential) V, a waveform element j that maintains the hold state at the falling potential of the waveform element i, and from the hold potential of the waveform element j to the reference potential V. It is a signal including a rising waveform element k.

  By selecting the first to third drive signals P1 to P3 of this drive waveform and applying them to the liquid discharge head, droplets are not discharged from the liquid discharge head, and the dots ( Here, it is possible to perform droplet discharge capable of forming three types of large dots, medium dots, and small dots having relatively different sizes.

  That is, as shown in FIG. 10A, by selecting and applying only the first drive signal P1, the nozzle meniscus can be vibrated without performing droplet discharge, and ink thickening can be prevented. it can. This fine driving is usually performed in a non-printing area.

  As shown in FIG. 10B, small dots can be formed by selecting and applying only the second drive signal P2. That is, the second drive signal P2 is used as a droplet waveform for forming small dots.

  As shown in FIG. 10C, medium dots can be formed by selecting and applying only the third drive signal 3. That is, the third drive signal P3 is used as a medium droplet waveform for forming a medium dot.

  As shown in FIG. 10D, the first, second, and third drive signals P1, P2, and P3 are applied to use as a large droplet waveform for forming a large dot.

  Waveforms are selected so that the landing positions of these small dots, medium dots, and large dots on the recording medium (paper) are substantially the same.

  Further, by ejecting a droplet by the second drive signal P within the time of the phase opposite to the pressure by the first drive signal P1, a small dot is formed by the second drive signal P2 in FIG. 10B. Compared to the droplet discharge speed, the droplet discharge speed is higher when the first drive signal P1 and the second drive signal P2 are sequentially applied and the droplet is discharged with the second drive signal P2 as shown in FIG. Becomes slower.

  Accordingly, as shown in FIG. 10D, when the first to third drive signals P1 to P3 are sequentially applied, the first drive signal P1 and the second drive signal P2 are sequentially applied to the second drive signal P1 to P3. The droplets ejected with the drive signal P2 can be combined with the droplets ejected with the third drive signal P3 during flight to land on the recording medium, and the small dots And matching the landing positions of medium dots and large dots.

  As described above, the drive waveform includes at least the first, second, and third drive signals generated in time series within one drive cycle, and is higher than the ejection speed of the droplets ejected by the second drive signal. The first and second drive signals are sequentially applied to eject the droplets ejected in a relatively slow manner, and the droplets ejected by the first to third drive signals are combined in flight. By providing a means for generating a waveform, a droplet having a desired droplet amount can be landed on the recording medium as a single droplet, and droplets of different sizes can be accurately and shortly cycled. Can be discharged at high speed, and a high-quality image can be formed at high speed.

  In this case, the drive waveform length can be shortened by using the first drive signal used when forming a relatively large dot as the drive signal for finely moving the liquid chamber without discharging a droplet.

  Further, the second drive signal is driven by using a drive signal for forming a relatively small dot as compared to a droplet by the first, second, and third drive signals for forming a relatively large dot. The waveform length can be shortened.

  In addition, the second drive signal is a drive signal that is applied when the pressure generated by the first drive signal is in the opposite phase, so that the discharge efficiency is relatively slowed by a decrease in drive efficiency, A desired droplet amount can be landed as a single droplet at a desired position on the recording medium.

  Further, the landing position on the recording medium of the droplet ejected by the second drive signal is substantially the same as the landing position on the recording medium of the droplet ejected by the first to third driving signals. By using the waveform, droplets that form relatively large dots and small dots can be landed on the recording medium with high accuracy, and high image quality can be achieved, and deterioration in image quality in bidirectional printing can be suppressed. it can.

Next, drive waveforms in the second embodiment of the present invention will be described with reference to FIG.
In this embodiment, the interval T2 between the first drive signal P1 and the second drive signal P2 is shortened (T2 <T1) compared to the drive waveform of the embodiment described in FIG.

  With this configuration, the droplets generated by the second drive signal P in a state where the meniscus of the nozzle 104 is raised by refilling by the first drive signal P1 (the recording liquid is supplied into the liquid chamber 106). Discharging can be performed. As a result, the weight of the ejected droplet (droplet ejection amount) increases, and droplet ejection by the first drive signal P1 and the second drive signal P2 is faster than the droplet ejection speed by only the second drive signal P2. The speed can be relatively slow. In addition, the length of the drive waveform shown in FIG. 9 can be shortened (time can be shortened). In other words, one drive cycle can be shortened and the speed can be increased.

  In this way, the second drive signal is a drive signal that is applied when the meniscus in the nozzle is raised by the first drive signal, so that the amount of ejected droplets increases and the droplet ejection speed is relatively slow. Thus, a desired droplet amount can be landed as a single droplet at a desired position on the recording medium.

Next, drive waveforms in the third embodiment of the present invention will be described with reference to FIG.
In this embodiment, the third drive signal P3 is composed of two signals of the drive signal P31 and the drive signal P31. The drive signal P31 includes a waveform element l that falls from the reference potential (intermediate potential) V, a waveform element m that maintains the hold state at the falling potential of the waveform element l, and a waveform element that rises from the hold potential of the waveform element m to the reference potential V. It is a signal containing n. The drive signal P32 includes a waveform element o falling from the reference potential (intermediate potential) V, a waveform element p that maintains the hold state at the falling potential of the waveform element o, and a potential higher than the reference potential V from the hold potential of the waveform element p. The waveform element q rises up to, the waveform element r that maintains the hold state at the rising potential of the waveform element q, and the waveform element s that falls from the waveform element r to the reference potential V. ,

  In this driving waveform, the first driving signal P1 is used as a fine driving waveform for performing fine driving in the non-printing region, and the second driving signal P2 is used as a droplet waveform for forming small dots. The drive signal P31 of the drive signal P3 is used as a medium droplet waveform for forming a medium dot. For the large droplet waveform for forming a large dot, all of the drive signals P31 and P32 constituting the first and second drive signals P1 and P2 and the third drive signal P3 are used. Thereby, a larger large dot can be formed.

  In this way, by configuring the third drive signal with a plurality of drive signals, it is easy to adjust the amount of droplets that form a relatively large dot.

  In addition, when forming large, medium, and small dots using the first to third drive signals, either all or a part of the third drive signal or the second drive signal is used. The drive waveform length can be shortened by using one as a drive signal for forming small dots and the other as a drive signal for forming medium dots.

  Further, the landing position on the recording medium of the droplet discharged by the second driving signal, the landing position on the recording medium of the droplet discharged by the first to third driving signals, A relatively large dot, medium dot, and small dot are formed by setting the waveform so that the landing position on the recording medium of the droplets ejected by all or part of the drive signal is substantially the same. By causing the droplets to land on the recording medium with high accuracy, it is possible to improve the image quality and to suppress the deterioration of the image quality in bidirectional printing.

  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 which shows 1st Embodiment of the drive waveform produced | generated by the drive waveform production | generation part. It is explanatory drawing with which it uses for description of selection of each drive signal of the same drive waveform. It is explanatory drawing which shows 2nd Embodiment of the drive waveform produced | generated by the drive waveform production | generation part. It is explanatory drawing which shows 3rd Embodiment of the drive waveform produced | generated by the drive waveform production | generation part.

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 (6)

A liquid discharge head having pressure generating means for generating pressure to pressurize a liquid chamber communicating with a nozzle for discharging droplets is mounted, and a drive signal constituting a drive waveform is selectively discharged based on an image signal In an image forming apparatus that is applied to a head and driven to form an image on a recording medium.
A drive waveform including at least first, second, and third drive signals generated in time series within one drive cycle,
The first drive signal is a drive signal for finely moving the liquid chamber without discharging a droplet,
The second drive signal and the third drive signal are drive signals for discharging droplets,
When the second drive signal is applied alone, the second drive signal is applied when the first to third drive signals are continuously applied, rather than the ejection speed of the droplets ejected by the second drive signal. The ejection speed of the droplets ejected by the drive signal is relatively slow, and by continuously applying the first to third drive signals , a drive waveform is generated in which the ejected droplets coalesce during flight. An image forming apparatus comprising:   2. The image forming apparatus according to claim 1, wherein the second driving signal is a dot that is relatively smaller than droplets generated by the first, second, and third driving signals that form relatively large dots. An image forming apparatus characterized in that the image forming apparatus is a drive signal for forming the image. 3. The image forming apparatus according to claim 1, wherein the second drive signal is a drive signal that is applied when a meniscus in the nozzle is raised by the first drive signal. Image forming apparatus. 3. The image forming apparatus according to claim 1, wherein the second drive signal is a drive signal applied when the pressure generated by the first drive signal is opposite in phase. 4. Forming equipment. The image forming apparatus according to any one of claims 1 to 4, the droplets ejected by the second driving signal, the droplet ejected by the first to third drive signals, the drive waveform An image forming apparatus characterized in that the time from the start of application to landing on a recording medium is substantially the same. The image forming apparatus according to any one of claims 1 to 5, and the landing position on the recording medium of the droplets ejected by the second driving signal, and discharged by the first to third drive signals An image forming apparatus, wherein a landing position of a droplet on a recording medium and a landing position of a droplet ejected by the third drive signal on the recording medium are substantially the same.

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