JP4662830B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus, and more particularly, to an image forming apparatus including a recording head that discharges droplets of a recording liquid.

  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 provided with a line type head.

  In order to perform gradation printing in such an image forming apparatus, for example, a common drive waveform composed of a plurality of drive signals (drive pulses) is generated within one print cycle (within one drive cycle). 1 or a plurality of drive signals are selected and applied to pressure generating means (actuator means) for generating energy for ejecting droplets of the recording head, so that the droplet size is the same or different from the recording head. There are some which form dots of different sizes by ejecting droplets and combining them during flight, or by firing a plurality of droplets at the same landing position.

By the way, with regard to the drive waveform in such an image forming apparatus, for example, Patent Document 1 discloses a plurality of ejection drive pulses that are output in time series in order to eject droplets and eject droplets within one printing cycle. As a non-ejection drive pulse that causes the meniscus to vibrate to such an extent that it does not occur, a first signal for expanding the pressure generating chamber, a second signal for maintaining the expanded state of the pressure generating chamber after the first signal, It is described that a drive pulse including a third signal for contracting the pressure generating chamber is generated after the second signal.
JP 2005-041039 A

In Patent Document 2, a first potential VL that increases the volume of the pressure chamber, a second potential VH that decreases the volume of the pressure chamber, and an intermediate potential VM between the first potential VL and the second potential VH are disclosed. A signal supply means for supplying a drive signal including a temperature detection means for detecting an environmental temperature or an ink temperature, and the signal supply means includes an intermediate potential VM, a first potential VL, a second potential VH, At least a main drive signal whose potential changes in the order of the intermediate potential VM is supplied, and the ratio H = (VM−VL) of the difference between the intermediate potential VM and the first potential VL with respect to the difference between the second potential VH and the first potential VL. It is described that / (VH−VL) is changed between 0.5 and 1 according to the detected temperature so that it is closer to 1 as the detected temperature of the temperature detecting means is lower.
JP 2003-127369 A

Patent Document 3 describes that the drive waveform for forming one dot is changed based on the presence or absence of an ejection pulse signal immediately before and after one dot and the shape of the drive waveform of the ejection pulse signal. .
JP 2001-301206 A

  By the way, as described above, in order to achieve both high printing speed and high image quality, a plurality of types of droplets having different droplet amounts are ejected from the same nozzle, and a plurality of drive signals are output within one drive cycle. By generating a drive waveform including the signal and selectively applying a drive signal, small dots to large dots are formed.

  In addition, since the recording head and the recording medium move in the serial type image forming apparatus and the recording medium moves in the line type image forming apparatus, respectively, by adjusting the droplet discharge timing and the droplet speed, the target pixel position is adjusted. The droplet must land.

  On the other hand, in order to further increase the printing speed by increasing the printing drive frequency, a refill amount (filling amount of recording liquid into the pressure generating chamber) that can continuously eject large dots at a high frequency is required. It becomes. Here, since the amount of refill decreases in a low temperature environment where the viscosity of the recording liquid increases, in order to obtain high speed and high image quality regardless of the temperature environment, a fluid resistance portion that has a sufficient amount of refill in a low temperature environment. It needs to be shaped. When the pressure generating chamber is expanded, the recording liquid flows in by refilling from the common liquid chamber to the pressure generating chamber through the fluid resistance portion at the same time as the meniscus is drawn.

  However, as the recording liquid temperature rises, the amount of refill increases, and the recording liquid flows into the pressure generating chamber more than the amount of ejected droplets. As a result, the meniscus after droplet ejection becomes a raised state, and when the next droplet is ejected in that state, ejection becomes unstable or the amount of ejected droplet increases. . Further, since the refill amount varies depending on the viscosity of the recording liquid, there is a problem that the amount of ejected droplets varies depending on the temperature environment when high frequency driving is performed.

  In the head described in Patent Document 2 described above, although the temperature is considered, no change in the refill amount is taken into consideration, so that a large dot is generated by a plurality of pulses (drive signals) as described above. However, it is difficult to stably discharge droplets regardless of the temperature environment when droplets are discharged at a high frequency.

  Further, in the droplet discharge method described in Patent Document 3, for each of large, medium, and small dots and non-ejection, the drive waveform is set according to the presence or absence of the immediately preceding and immediately following dots and the type of drive waveform. In order to change, the number of drive waveforms increases, leading to an increase in design cost. Furthermore, the configuration for selecting the drive waveform for each discharge channel is complicated, leading to an increase in cost, and selecting the drive waveform according to the printing pattern also increases the printing processing time. ing.

  The present invention has been made in view of the above problems, and can reduce the difference in the amount of ejected droplets during low-frequency driving and high-frequency driving so that stable droplet ejection during high-frequency driving can be performed at high speed. An object of the present invention is to provide an image forming apparatus capable of forming a high quality image.

In order to solve the above problems, an image forming apparatus according to the present invention provides:
A recording head having a nozzle for discharging a droplet of the recording liquid, a pressure generating chamber in communication with the nozzle, and a pressure generating means for generating a pressure for pressurizing the recording liquid in the pressure generating chamber;
Drive waveform generating means for generating a drive waveform composed of a plurality of time-series drive signals applied to the pressure generating means of the recording head;
In an image forming apparatus comprising:
The drive waveform generating means may include one or a plurality of preliminary drive signals that do not eject a droplet or have a droplet velocity relatively slower than the droplet velocity of the droplet to be ejected before the droplet ejection drive signal that ejects the droplet. Means for generating a drive waveform including:
The droplet discharge drive signal is:
An expansion waveform element that expands the pressure generating chamber and a contraction waveform element that contracts after expansion,
The potential difference of the contraction waveform element is larger than the potential difference of the expansion waveform element,
In addition, the contraction waveform element is output at a timing that is in phase with the pressure fluctuation in the pressure generation chamber generated by the preliminary drive signal .

Here, the preliminary drive signal includes an expansion waveform element that expands the pressure generation chamber, and the droplet discharge drive signal includes an expansion waveform element that expands the pressure generation chamber and a contraction waveform element that contracts after expansion. The potential difference of the expansion waveform element of the droplet ejection drive signal can be made smaller than the potential difference of the expansion waveform element of the drive signal .

The droplet discharge drive signal includes a waveform element that expands the pressure generation chamber in a contracted state after droplet discharge, and the waveform element has a positive pressure change in the pressure generation chamber due to the previous waveform element. configuration outputted by comprising timing, or the droplet ejection driving signal includes the pressure generating chamber further waveform element and a waveform element which expands after shrinkage to shrink its contracted state after ejection, the pressure generating chamber The waveform element to be further contracted is output at a timing when the pressure fluctuation of the pressure generating chamber due to the waveform element up to the waveform element for discharging the droplet becomes negative pressure, and the waveform element to be expanded after contraction is the pressure generating chamber. It is possible to output at a timing when the pressure fluctuation becomes positive pressure .

Also, more than twice configuration of the potential difference of the potential difference is the expansion waveform element of the contraction wave element, or the potential difference of the contraction waveform element is cut with configuration and is at least 3 times the potential difference of the expansion wave element. Further, based on the environmental temperature, the drive waveform has a small ratio of the potential difference of the expansion waveform element to the potential difference of the contraction waveform element at a low temperature, and the ratio of the potential difference of the expansion waveform element to the potential difference of the contraction waveform element at a high temperature. A large drive waveform can be output .

According to the image forming apparatus of the present invention, the drive waveform generation unit does not eject the droplet or has a droplet velocity higher than the droplet velocity of the droplet to be ejected before the droplet ejection drive signal for ejecting the droplet. Means for generating a drive waveform including one or more relatively slow preliminary drive signals, wherein the drop ejection drive signal includes an expansion waveform element for expanding the pressure generating chamber and a contraction waveform element for contracting after expansion, The contraction waveform element is output at a timing when the potential difference of the contraction waveform element is larger than the potential difference of the expansion waveform element and is in phase with the pressure fluctuation in the pressure generating chamber generated by the preliminary drive signal. since a configuration which is a signal, it is possible to reduce the protrusion of the meniscus and the small refill amount by the drive signal for discharging large dots, the discharge at the time of high frequency driving The change in volume can be suppressed, the difference in ejected droplet volume between low-frequency driving and high-frequency driving can be reduced, stable droplet ejection during high-frequency driving can be performed, and high-quality images can be formed at high speed. .

Embodiments of the present invention will be described below with reference to the accompanying drawings. First, an example of a mechanism part of the 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, and FIG. 2 is a plan explanatory view of the mechanism section.
In this image forming apparatus, a carriage 3 is slidably held in a main scanning direction by a guide rod 1 and a guide rail 2 which are guide members horizontally mounted on left and right side plates (not shown), and a driving pulley 6A is driven by a main scanning motor 4. 2 is moved and scanned in the direction indicated by the arrow (main scanning direction) in FIG. 2 via a timing belt 5 stretched between the roller and the driven pulley 6B.

  The carriage 3 includes, for example, four recording heads 7y, 7c, and 7m including droplet discharge heads that discharge yellow (Y), cyan (C), magenta (M), and black (K) ink droplets, respectively. , 7k (referred to as “recording head 7” when colors are not distinguished) are arranged in a direction crossing the main scanning direction with a plurality of ink ejection openings, and the ink droplet ejection direction is directed downward.

  The carriage 3 is equipped with sub-tanks 8 for each color for supplying ink of each color to the recording head 7. Ink is supplied to the sub tank 8 from a main tank (ink cartridge) (not shown) via an ink supply tube 9.

  On the other hand, as a paper feeding unit for feeding paper 12 stacked on a paper stacking unit (pressure plate) 11 such as a paper feeding cassette 10, a half-moon roller (for separating and feeding the paper 12 one by one from the paper stacking unit 11) A separation pad 14 made of a material having a large friction coefficient is provided facing the sheet feeding roller 13 and the sheet feeding roller 13, and the separation pad 14 is urged toward the sheet feeding roller 13 side.

  In order to convey the sheet 12 fed from the sheet feeding unit below the recording head 7, a conveyance belt 21 for electrostatically attracting and conveying the sheet 12 and a guide 15 from the sheet feeding unit. A counter roller 22 for transporting the sheet 12 fed between the conveyor belt 21 and the conveyor belt 21, and for shifting the sheet 12 fed substantially vertically upward by approximately 90 ° to follow the conveyor belt 21. A conveyance guide 23 and a pressing roller 25 urged toward the conveyance belt 21 by a pressing member 24 are provided. In addition, a charging roller 26 as a charging unit for charging the surface of the transport belt 21 is provided.

  Here, the conveyance belt 21 is an endless belt, is stretched between the conveyance roller 27 and the tension roller 28, and the conveyance roller 27 rotates from the sub-scanning motor 31 via the timing belt 32 and the timing roller 33. By doing so, it is configured to circulate in the belt conveyance direction (sub-scanning direction) of FIG. A guide member 29 is disposed on the back side of the conveying belt 21 corresponding to the image forming area by the recording head 7. The charging roller 26 is disposed so as to come into contact with the surface layer of the transport belt 21 and rotate following the rotation of the transport belt 21.

  Further, as shown in FIG. 2, a slit disk 34 is attached to the shaft of the transport roller 27, and a sensor 35 for detecting the slit of the slit disk 34 is provided. A rotary encoder 36 is configured.

  Further, as a paper discharge unit for discharging the paper 12 recorded by the recording head 7, a separation claw 51 for separating the paper 12 from the transport belt 21, a paper discharge roller 52 and a paper discharge roller 53, and a discharge And a paper discharge tray 54 for stocking the paper 12 to be printed.

  A double-sided paper feeding unit 55 is detachably mounted on the back. The double-sided paper feeding unit 55 takes in the paper 12 returned by the reverse rotation of the transport belt 21, reverses it, and feeds it again between the counter roller 22 and the transport belt 21.

  Further, as shown in FIG. 2, a maintenance / recovery mechanism 56 for maintaining and recovering the nozzle state of the recording head 7 is disposed in the non-printing area on one side of the carriage 3 in the scanning direction.

  The maintenance / recovery machine 56 is provided with caps 57 for capping each nozzle surface of the recording head 7, a wiper blade 58 as a blade member for wiping the nozzle surface, and for discharging the thickened recording liquid. An empty discharge receiver 59 for receiving droplets when performing empty discharge for discharging droplets that do not contribute to recording is provided.

  In the image forming apparatus configured as described above, the sheets 12 are separated and fed one by one from the sheet feeding unit, and the sheet 12 fed substantially vertically upward is guided by the guide 15, and includes the transport belt 21 and the counter roller 22. The leading end is guided by the conveying guide 23 and pressed against the conveying belt 21 by the pressing roller 25, and the conveying direction is changed by approximately 90 °.

  At this time, a charging voltage pattern in which a positive output and a negative output are alternately repeated from the AC bias supply unit to the charging roller 26 by a control unit (not shown), that is, an alternating voltage is applied and the conveying belt 21 is alternated. That is, plus and minus are alternately charged in a band shape with a predetermined width in the sub-scanning direction which is the circumferential direction. When the sheet 12 is fed onto the conveyance belt 21 charged alternately with plus and minus, the sheet 12 is attracted to the conveyance belt 21 by electrostatic force, and the sheet 12 is conveyed in the sub-scanning direction by the circular movement of the conveyance belt 21. Is done.

  Therefore, by driving the recording head 7 according to the image signal while moving the carriage 3 in the forward and backward directions, ink droplets are ejected onto the stopped paper 12 to record one line. After transporting a predetermined amount, the next line is recorded. Upon receiving a recording end signal or a signal that the trailing edge of the paper 12 has reached the recording area, the recording operation is finished and the paper 12 is discharged onto the paper discharge tray 54.

  In the case of double-sided printing, when recording on the front surface (surface to be printed first) is completed, the recording belt 12 is fed into the double-sided paper feeding unit 61 by rotating the conveyor belt 21 in the reverse direction. The paper 12 is reversed (with the back surface being the printing surface), fed again between the counter roller 22 and the transport belt 21, controlled in timing, and transported onto the transport bell 21 as described above. After recording on the back side, the sheet is discharged onto the discharge tray 54.

  During printing (recording) standby, the carriage 3 is moved to the maintenance / recovery mechanism 55 side, and the nozzle surface of the recording head 7 is capped by the cap 57, and the nozzles are kept in a wet state. To prevent. In addition, the recording liquid is sucked from the nozzle in a state where the recording head 7 is capped by the cap 57 (referred to as “nozzle suction” or “head suction”), and a recovery operation is performed to discharge the thickened recording liquid or bubbles. Wiping is performed by the wiper blade 58 in order to clean and remove ink adhering to the nozzle surface of the recording head 7 by this recovery operation. In addition, an idle ejection operation for ejecting ink not related to recording is performed before the start of recording or during recording. Thereby, the stable ejection performance of the recording head 7 is maintained.

  Next, an example of the liquid discharge head constituting the recording head 7 will be described with reference to FIGS. 3 is a cross-sectional explanatory diagram along the longitudinal direction of the liquid chamber of the head, and FIG. 4 is a cross-sectional explanatory diagram 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. The nozzle plate 103 bonded to the upper surface of the path plate 101 is bonded and stacked, and the nozzle communication path 105 that is a flow path through which the nozzle 104 that discharges droplets (ink droplets) communicates therewith and the liquid that is the pressure generation chamber. An ink supply port 109 communicating with a common liquid chamber 108 for supplying ink to the chamber 106 and the liquid chamber 106 through a fluid resistance portion (supply path) 107 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.

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 also includes an I / F 206 for transmitting and receiving data and signals to and from the host side, data transfer means for driving and controlling the recording head 7, and a driving waveform for generating a driving waveform according to the present invention. A printing control unit 207 including a generating unit, a head driver (driver IC) 208 for driving the recording head 107 provided on the carriage 3 side, and a motor driving unit 210 for driving the main scanning motor 4 and the sub-scanning motor 31. And an AC bias supply unit 212 that supplies an AC bias to the charging roller 34, detection signals from the encoder sensors 43 and 35, and detection signals from various sensors such as a temperature sensor 215 that detects the environmental temperature. I / O 213 and the like are 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. Note that generation of dot pattern data for outputting an image is performed by a printer driver on the host side.

  The print control unit 207 transfers the above-described image data as serial data, and transfers to the head driver 208 a transfer clock, a latch signal, a droplet control signal (mask signal), and the like necessary to transfer the image data and confirm the transfer. In addition to output, the drive waveform to be supplied to the drive waveform generator and head driver composed of a D / A converter, a voltage amplifier, a current amplifier, etc. for D / A converting the pattern data of the drive signal stored in the ROM It includes selection means, and includes drive waveform generation means for generating a drive waveform composed of one drive pulse (drive signal) or a plurality of drive pulses (drive signals), and outputs the drive waveform to the head driver 208.

  The head driver 208 selectively selects droplets of the recording head 7 based on image data corresponding to one line of the recording head 7 input serially, and forms a driving signal provided from the print control unit 207. The recording head 7 is driven by applying it to a driving element (for example, a piezoelectric element) that generates energy to be discharged. At this time, by selecting a driving pulse constituting the driving waveform, for example, dots having different sizes such as large droplets, medium droplets, and small droplets can be sorted.

  Further, the CPU 201 detects a speed detection value and a position detection value obtained by sampling a detection pulse from the encoder sensor 43 constituting the linear encoder, and a speed target value and a position target value obtained from a previously stored speed / position profile. Based on this, a drive output value (control value) for the main scanning motor 4 is calculated, and the main scanning motor 4 is driven via the motor driving unit 210. Similarly, based on the speed detection value and position detection value obtained by sampling the detection pulse from the encoder sensor 35 constituting the rotary encoder, and the speed target value and position target value obtained from the previously stored speed / position profile. Then, a drive output value (control value) for the sub-scanning motor 31 is calculated, and the sub-scanning motor 31 is driven via the motor driver 210 and the motor driver.

Next, an example of the print control unit 207 and the head driver 208 will be described with reference to FIG.
As described above, the print control unit 207 generates a drive waveform (common drive waveform) composed of a plurality of drive pulses (drive signals) within one printing cycle, and outputs a print waveform. And a data transfer unit 302 that outputs a clock signal, a latch signal (LAT), and droplet control signals M0 to M3.

  The droplet control signal is a 2-bit signal that instructs each droplet to open and close an analog switch 317, which will be described later, of the head driver 208. The droplet control signal is a waveform to be selected according to the printing cycle of the common drive waveform. State transition is made to level (ON), and state transition is made to L level (OFF) when not selected.

  The head driver 208 receives a transfer clock (shift clock) and serial image data (gradation data: 2 bits / CH) from the data transfer unit 302, and each register value of the shift register 311 by a latch signal. A latch circuit 312 for latching, a decoder 313 that decodes gradation data and control signals M0 to M3 and outputs the result, and a logic level voltage signal of the decoder 313 is converted to a level at which the analog switch 315 can operate. Level shifter 314, and an analog switch 316 that is turned on / off (opened / closed) by the output of the decoder 313 provided via the level shifter 314.

  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 switch 316 is turned on in accordance with the result of decoding the serially transferred image data (gradation data) and the control signals MN0 to MN3 by the decoder 313, a required drive signal constituting the common drive waveform is obtained. Passing (selected) is applied to the piezoelectric element 121.

Next, the drive waveform according to the first embodiment of the present invention generated and output by the drive waveform generation unit in this image forming apparatus will be described with reference to FIG.
Here, the drive waveform generation unit 301 generates and outputs a plurality of drive signals P1 to P5 in time series, for example, as shown in FIG. Therefore, a plurality of drive signals P1 to P5 can be selected and applied to the piezoelectric element 121 by outputting droplet control signals M0 to M3 as shown in FIG. The drive signal P4 is a preliminary drive signal in the present invention, and the drive signal P5 is a droplet discharge drive signal.

  That is, the droplet control signal M1 selects the drive signal P2, and the recording head 7 discharges droplets (small droplets) that form small dots, and the droplet control signal M2 selects the drive signals P1 and P2 to record the recording head. 7, two droplets are ejected and merged during flight to eject droplets (medium droplets) that form medium dots, and the droplet control signal M3 selects the drive signals P1 to P5 to select the recording head 7. The four droplets are ejected in response to the drive signals P1, P2, P3, and P5, and the droplets (large droplets) forming a large dot are ejected by combining them in flight.

The details of the preliminary drive signal P4 and the droplet discharge drive signal P5 in the present invention will be described with reference to FIG.
The droplet discharge by the driving signal P5 is performed by lowering the potential from the state where the intermediate potential VM is previously applied to the piezoelectric element 121 and expanding the liquid chamber 106, and then setting the potential VH higher than the intermediate potential VM. It is assumed that the chamber 106 is contracted by pulling and pushing to discharge a droplet.

  The pre-driving signal P4 falls from the intermediate potential VM, so that the expansion waveform element a that expands the liquid chamber 106, the waveform element b that holds the potential subsequent to the waveform element a, and the intermediate potential subsequent to the waveform element b. The waveform element c rises up to the VM. Here, the waveform elements are such that droplet ejection is not performed even when the preliminary drive signal P4 is applied, but droplet ejection is performed at a slower droplet speed than when the droplet ejection drive signal P5 is applied following the preliminary drive signal P4. It can also be a waveform element to be performed.

  The droplet discharge drive signal P5 falls from the intermediate potential VM, expands the liquid chamber 106 by expanding, the waveform element e holding the potential following the waveform element d, and the intermediate following the waveform element e. The waveform element f that contracts the liquid chamber 106 by rising to the potential VH over the potential VM, the waveform element g that holds the potential following the waveform element f, and the intermediate potential VM that falls after the waveform element g. In this way, the liquid chamber 106 is made up of a wave element h that expands.

  Here, the droplet velocity when the droplet is ejected with the droplet ejection drive signal P5 that follows the preliminary drive signal P4 is relative to the droplet velocity when the droplet is ejected with the droplet ejection drive signal P5 alone. Waveform elements that become faster.

  The droplet discharge drive signal P5 has a waveform in which the waveform element f is output at the same timing as the pressure fluctuation in the liquid chamber 106 generated by the preliminary drive signal P4. That is, the droplet discharge drive signal P5 is configured to discharge a droplet at the resonance timing of the pressure fluctuation caused by the preliminary drive signal P4 (see FIG. 9). Further, the potential difference of the expansion waveform element d of the droplet discharge drive signal P5 is made smaller than the potential difference of the expansion waveform element a of the preliminary drive signal P4.

  Therefore, by applying the preliminary drive signal P4, the liquid chamber 106 expands to generate pressure vibration, and at the same time, ink flows into the liquid chamber 106 through the fluid resistance portion 107. Ink flows into the liquid chamber 106 and the ink meniscus of the nozzle 104 is raised. By applying the droplet ejection drive signal P5 at this timing, it is possible to eject the ink droplets accumulated in the meniscus (see FIG. 9).

  As described above, the droplet discharge drive signal P5 uses the pressure wave generated by the preliminary drive signal P4, so that even if the falling potential VL of the expansion waveform sheet d that expands the liquid chamber 106 from the intermediate potential VM is small, the required value is required. Droplets can be ejected at a drop speed.

  In addition, since the waveform element d that expands the liquid chamber 106 is small, the inflow of ink into the liquid chamber 106 due to the droplet ejection drive signal P5 is reduced, the rise of the meniscus after the droplet ejection is reduced, and even during high frequency driving. The discharged droplet amount can be kept constant.

  The timing of the expansion waveform element h that expands the liquid chamber 106 by returning the potential after droplet ejection of the droplet ejection drive signal P5 from the potential VH to the intermediate potential VM, and the residual pressure in the liquid chamber 106 after droplet ejection is When it comes to positive pressure. That is, by setting the timing at which the pressure is in the opposite phase, a vibration damping effect can be produced and the meniscus state can be stabilized. That is, by expanding the pressure generating chamber so as to have a phase opposite to the residual pressure vibration after droplet ejection, the residual pressure vibration is quickly suppressed, and the stability of droplet ejection during high frequency driving is further improved.

  In this way, before the droplet ejection driving signal for ejecting the droplet, a driving waveform including one or a plurality of preliminary driving signals that do not eject the droplet or has a relatively slow droplet velocity is generated, and the droplet ejection driving signal alone is generated. Since the droplet velocity when the droplet is ejected with the droplet ejection drive signal that follows the preliminary drive signal is relatively faster than the droplet velocity when the droplet is ejected with The amount of ejected droplets can be kept substantially constant during low frequency driving and high frequency driving. In other words, the last droplet ejection drive is used to keep the ejection droplet volume substantially constant by reducing the pull of the droplet ejection drive signal for ejecting the last droplet as much as possible, reducing the refill amount, and increasing the push as much as possible. By using the preliminary vibration before the signal, the droplet when the droplet is ejected with the droplet ejection drive signal that follows the preliminary drive signal rather than the droplet velocity when the droplet ejection drive signal alone ejects the droplet Make the speed relatively faster.

  In addition, since the droplet ejection drive signal can be efficiently ejected by utilizing the resonance of pressure by ejecting droplets at the resonance timing of the pressure fluctuation due to the preliminary drive signal, in particular, the pressure is determined by the last drive signal. When the generation chamber is expanded, the amount of ink flowing from the common liquid chamber is reduced, the difference in the amount of ejected droplets during low frequency driving and high frequency driving is reduced, and stable ejection during high frequency driving can be performed. .

  Furthermore, the drop speed that is ejected when the preliminary drive signal and the drop ejection drive signal are applied in sequence is the target drop speed, thereby reducing the difference in ejected drop volume between low-frequency driving and high-frequency driving. Stable ejection during high frequency driving can be performed.

  The preliminary drive signal includes an expansion waveform element that expands the pressure generation chamber, and the droplet discharge drive signal includes an expansion waveform element that expands the pressure generation chamber and a contraction waveform element that contracts after expansion, and the expansion waveform element of the preliminary drive signal Since the potential difference of the expansion waveform element of the droplet ejection drive signal is smaller than the potential difference of the ink, the amount of ink flowing from the common liquid chamber is reduced when the pressure generating chamber is expanded by the last drive signal as described above. It is possible to reduce the difference in ejected droplet amount between frequency driving and high frequency driving, and to perform stable ejection during high frequency driving.

Next, drive waveforms according to the second embodiment of the present invention will be described with reference to FIG.
Here, the droplet driving signal P5 further increases the potential of the contracted liquid chamber 106 from the potential VH to the potential VH2 after the waveform element g that is held following the waveform element f that contracts the liquid chamber 106 to discharge the droplet. A waveform element i to be contracted and a waveform element h2 falling from the potential VH2 to the intermediate potential VM following the waveform element i are included.

  In other words, in the first embodiment, the liquid chamber 106 is expanded (by the waveform element h) to suppress vibration when the pressure after droplet ejection is positive, but in the second embodiment, after the droplet ejection, After the potential VH, the potential VH2 that further contracts the liquid chamber 106 at the timing when the residual pressure becomes negative (with the waveform element i), and the intermediate potential VM so that the liquid chamber 106 expands at the timing when the residual pressure becomes positive. (With waveform element h2).

  As a result, a stronger vibration damping effect than that of the first embodiment can be obtained. In other words, the pressure generation chamber is further contracted and expanded so as to have an opposite phase to the residual pressure vibration after droplet ejection, thereby further suppressing the residual pressure vibration and performing more stable ejection during high frequency driving. be able to.

Next, drive waveforms according to the third embodiment of the present invention will be described with reference to FIG.
Here, the waveform is such that a plurality (three in this case) of preliminary drive signals P41, P42, and P43 are given before the droplet discharge drive signal P5. The waveform elements a, b, and c of the preliminary drive signals P41, P42, and P43 are assigned sub-codes “1”, “2”, and “3”, respectively. These preliminary drive signals P41, P42, and P43 may have the same waveform or different waveforms.

  In this manner, by applying a plurality of preliminary drive waveforms, it is possible to arbitrarily eject a larger droplet amount than in the first and second embodiments.

Next, drive waveforms according to the fourth embodiment of the present invention will be described with reference to FIG.
In this embodiment, the low temperature drive waveform PL composed of the preliminary drive signal P401 and the droplet discharge drive signal P501 shown in FIG. 5A, and the preliminary drive signal P402 and the droplet discharge drive signal P502 shown in FIG. And a means for generating and outputting a drive waveform PM for normal temperature and a drive waveform PH for high temperature consisting of a preliminary drive signal P403 and a droplet discharge drive signal P503 shown in FIG.

  Here, the droplet ejection drive signals P501, P502, and P503 are from the potential VL corresponding to the potential difference of the potential VL of the waveform element d that expands the liquid chamber 106 from the intermediate potential VM to the potential VH of the waveform element f that contracts the liquid chamber 106. The ratio of the potential difference is made different so that the ratio of the high-temperature driving waveform PH is 2 times or more, preferably 3 times or more.

  Specifically, the potential difference between the waveform element a of the preliminary drive signal P401 of the low temperature drive waveform PL and the waveform element d of the droplet discharge drive signal P501 is the waveform element a of the preliminary drive signal P402 of the room temperature drive waveform PM and the droplet discharge drive. The potential difference between the waveform element d of the signal 502 and the waveform element a of the preliminary drive signal P403 of the high temperature drive waveform PH and the waveform element d of the droplet ejection drive signal P503 is larger than the potential difference of the waveform element d of the signal 502. The potential difference between the waveform element a and the waveform element d of the droplet ejection drive signal 502 is smaller.

  As described above, the viscosity of the recording liquid (ink) increases as the environmental temperature decreases, that is, the fluidity decreases. Therefore, the refill amount decreases in a low-temperature environment where the viscosity of the recording liquid increases. It increases in a high temperature environment where the liquid becomes low. Therefore, in the low temperature drive waveform PL used in the low temperature environment, the potential difference for expanding the liquid chamber 106 is increased (more expanded) to secure the refill amount, and in the high temperature drive waveform PH used in the high temperature environment, the liquid chamber 106 is used. By lowering the potential difference that expands the liquid (without further expansion) and limiting the amount of refill, the meniscus state after discharge can be made constant regardless of the temperature environment, and even droplets can be discharged regardless of temperature. Can be done.

  Here, as shown in FIG. 13, the driving waveform is switched by detecting the environmental temperature based on the detection signal from the temperature sensor 215, and detecting the detected temperature in a predetermined low temperature, normal temperature, or high temperature range (section). In comparison, it is determined whether the temperature is low temperature, normal temperature, or high temperature, and according to the determined result, the drive waveform data that generates the low temperature drive waveform PL is selected in the case of low temperature, and in the case of normal temperature The drive waveform data for generating the room temperature drive waveform PM is selected. When the temperature is high, the drive waveform data for generating the high temperature drive waveform PH is selected, and the drive waveform is generated and output.

Next, drive waveforms according to the fifth embodiment of the present invention will be described with reference to FIG.
This drive waveform is a waveform that does not have the waveform element e that expands the liquid chamber 106 before the waveform element f that contracts the liquid chamber 106 of the preliminary drive signal P4 and the droplet discharge drive signal P5 and discharges the droplet.

  As described above, since the refill amount varies depending on the temperature, depending on the recording liquid to be used, the waveform does not have the waveform element e that expands the liquid chamber 106 before the waveform element f in this way. The recording liquid is prevented from flowing into the chamber 106, the difference between the ejection droplet amounts during low frequency driving and high frequency driving is reduced, and stable ejection during high frequency driving is performed.

  In the above-described embodiment, the present invention has been described with the serial type image forming apparatus having a printer configuration. However, the present invention is not limited to this, and the serial type image forming apparatus having a printer / facsimile / copier multifunction peripheral (MFP) configuration, etc. It can also be applied to a line type image forming apparatus.

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. 4 is a cross-sectional explanatory view along the longitudinal direction of the liquid chamber showing an example of a liquid discharge head constituting the recording head in the image forming apparatus. It is a cross-sectional explanatory drawing along a liquid chamber short direction similarly. 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 print control unit and a head driver. It is explanatory drawing explaining the drive waveform which concerns on 1st Embodiment of this invention. FIG. 6 is an enlarged explanatory view of a preliminary drive signal and a droplet discharge drive signal of the same drive waveform. It is explanatory drawing with which it uses for description of the relationship between the preliminary drive signal and droplet discharge drive signal, and a liquid chamber pressure change. FIG. 10 is an enlarged explanatory diagram of a preliminary drive signal and a droplet discharge drive signal portion of a drive waveform according to a second embodiment of the present invention. FIG. 10 is an enlarged explanatory diagram of a preliminary drive signal and a droplet discharge drive signal portion of a drive waveform according to a third embodiment of the present invention. FIG. 10 is an enlarged explanatory view of a preliminary drive signal and a droplet discharge drive signal portion of a drive waveform corresponding to a temperature according to a fourth embodiment of the present invention. It is a flowchart with which it uses for description of a drive waveform selection process for the embodiment. FIG. 12 is an enlarged explanatory diagram of a preliminary drive signal and a droplet discharge drive signal portion of a drive waveform according to a fifth embodiment of the present invention.

Explanation of symbols

3 ... carriage 7 ... recording head 7k, 7c, 7m, 7y ... recording head 104 ... nozzle 106 ... liquid chamber (pressure generating chamber)
121 ... Piezoelectric element (pressure generating means)
207 ... Print control unit 208 ... Head driver 301 ... Drive waveform generation unit 302 ... Data transfer unit

Claims (7)

A recording head having a nozzle for discharging a droplet of the recording liquid, a pressure generating chamber in communication with the nozzle, and a pressure generating means for generating a pressure for pressurizing the recording liquid in the pressure generating chamber;
In an image forming apparatus comprising: a drive waveform generating unit configured to generate a drive waveform composed of a plurality of time-series drive signals applied to the pressure generating unit of the recording head;
The drive waveform generating means may include one or a plurality of preliminary drive signals that do not eject a droplet or have a droplet velocity relatively slower than the droplet velocity of the droplet to be ejected before the droplet ejection drive signal that ejects the droplet. Means for generating a drive waveform including:
The droplet discharge drive signal is:
An expansion waveform element that expands the pressure generating chamber and a contraction waveform element that contracts after expansion,
The potential difference of the contraction waveform element is larger than the potential difference of the expansion waveform element,
The image forming apparatus , wherein the contraction waveform element is output at a timing that is in phase with a pressure fluctuation in the pressure generating chamber generated by the preliminary drive signal . 2. The image forming apparatus according to claim 1 , wherein the preliminary drive signal includes an expansion waveform element that expands the pressure generation chamber, and the droplet discharge drive signal expands the pressure generation chamber and contracts after expansion. An image forming apparatus comprising a contraction waveform element, wherein the potential difference of the expansion waveform element of the droplet ejection drive signal is smaller than the potential difference of the expansion waveform element of the preliminary drive signal. 3. The image forming apparatus according to claim 1, wherein the droplet ejection drive signal includes a waveform element that expands the pressure generation chamber in a contracted state after droplet ejection, and the waveform element is based on a waveform element before that. An image forming apparatus, wherein the pressure generation chamber outputs a pressure at a timing when the pressure fluctuation becomes a positive pressure. 3. The image forming apparatus according to claim 1, wherein the droplet discharge driving signal includes a waveform element that further contracts the pressure generating chamber in a contracted state after droplet discharge and a waveform element that expands after contraction, and the pressure The waveform element that further contracts the generation chamber is output at a timing when the pressure fluctuation of the pressure generation chamber due to the waveform element up to the waveform element that discharges the droplet becomes negative pressure. An image forming apparatus, wherein a pressure fluctuation in a pressure generating chamber is output at a timing when the pressure becomes positive . 5. The image forming apparatus according to claim 1 , wherein the potential difference of the contraction waveform element is at least twice the potential difference of the expansion waveform element . 5. The image forming apparatus according to claim 1 , wherein the potential difference of the contraction waveform element is three times or more than the potential difference of the expansion waveform element. 6. The image forming apparatus according to any one of claims 1 to 6, the potential difference ratio is small driving waveform of the expansion waveform element at low temperatures on the basis of the environmental temperature for the potential difference of the contraction wave element, the high temperature at the time of the contraction An image forming apparatus that outputs drive waveforms each having a large ratio of the potential difference of the expansion waveform element to the potential difference of the waveform element.

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