JP6024906B2 - Image forming apparatus, head drive control device, and head drive control method - Google Patents

Description

  The present invention relates to an image forming apparatus, an image forming apparatus, a head drive control device, and a liquid ejection head drive control method.

  As an image forming apparatus such as a printer, a facsimile machine, a copying machine, a plotter, and a complex machine of these, for example, an ink jet recording apparatus is known as a liquid discharge recording type image forming apparatus using a liquid discharge head for discharging droplets as a recording head. It has been.

  In such an image forming apparatus, for example, a plurality of driving pulses (ejection pulses) for ejecting droplets within one driving cycle are generated in time series and output as a common driving waveform. It is known to form dots of a plurality of sizes by selecting two or more drive pulses when ejecting and ejecting a plurality of droplets so that the plurality of droplets combine and land during flight. ing.

  Conventionally, as a head drive control device or method, for example, a discharge waveform is a first waveform section that operates a pressure generating section to reduce the pressure chamber by changing the potential from a reference potential to an operating potential with a constant gradient, A second waveform section that maintains the potential for a certain period of time, and a third waveform section that operates the pressure generating section to pressurize the pressure chamber by changing the potential from the operating potential to the reference potential with a constant gradient, and within a unit cycle It is known that the interval between the previous discharge pulse and the next discharge pulse generated following the previous discharge pulse is set based on the natural vibration period Tc generated in the liquid in the pressure chamber ( Patent Document 1).

JP 2011-084028 A

  By the way, the ink droplets ejected from the nozzles fly with a tail, and a time difference and a speed difference are generated between the head portion (main droplet) and the tail portion of the flying ink droplets. For this reason, unnecessary fine droplets (satellite) may be generated accompanying the preceding main droplet. In particular, satellites become more prominent as the drop velocity increases.

  On the other hand, when adopting a configuration in which ink droplets are ejected by two drive pulses and merged into one droplet during flight, the droplet velocity of the trailing droplet must be higher than the droplet velocity of the preceding droplet.

  For this reason, the following droplets are in a state where satellites are likely to be generated, and as a result, there is a problem that the satellites cannot be suppressed even if they are merged.

  The present invention has been made in view of the above problems, and an object of the present invention is to suppress the generation of satellites with a simple configuration when forming one drop with two drive pulses.

In order to solve the above problems, an image forming apparatus according to the present invention provides:
A recording head having pressure generating means for generating pressure for pressurizing the liquid in the individual liquid chamber through which the nozzle for discharging the droplets communicates;
Drive waveform generating means for generating and outputting a drive waveform including at least a first drive pulse and a second drive pulse in time series, which are given to the pressure generating means of the recording head within one drive cycle;
The first drive pulse includes at least a drawing waveform element that expands the individual liquid chamber, and a pushing waveform element that contracts the expanded individual liquid chamber,
The second drive pulse includes at least a drawing waveform element that expands the individual liquid chamber, and a pushing waveform element that contracts the expanded individual liquid chamber,
The time from the end point of the pushing waveform element of the first driving pulse to the starting point of the drawing waveform element of the second driving pulse is an integral multiple of the natural vibration period of the individual liquid chamber.

  According to the present invention, when one drop is formed with two drive pulses, the generation of satellites can be suppressed with a simple configuration.

FIG. 3 is a side explanatory view illustrating a mechanism unit of an example of an image forming apparatus according to the present invention. It is principal part plane explanatory drawing of the mechanism part. FIG. 4 is a cross-sectional explanatory view in the longitudinal direction of the liquid chamber showing an example of a liquid discharge head constituting the recording head of the image forming apparatus. It is sectional explanatory drawing similarly used for description of droplet discharge operation | movement. FIG. 2 is a block explanatory diagram illustrating an overview of a control unit of the image forming apparatus. FIG. 3 is a block explanatory diagram illustrating an example of a print control unit and a head driver of the control unit. It is explanatory drawing of the drive waveform in 1st Embodiment of this invention. It is explanatory drawing which shows the waveform shape of a single pulse. It is explanatory drawing explaining an example of the change of the droplet speed when changing the hold period (pulse width Pw) of the same single pulse. It is explanatory drawing with which it uses for description of the basic composition of the drive waveform which makes two drops merge during flight and makes it one drop. It is explanatory drawing explaining an example of the change of the voltage of the satellite Tj and the 1st drive pulse P1 with respect to pulse interval (time) Td. It is typical explanatory drawing with which it uses for description of satellite Tj. It is explanatory drawing of the drive waveform in 2nd Embodiment of this invention. It is explanatory drawing explaining the mode from droplet discharge to merge. It is explanatory drawing of the drive waveform in 3rd Embodiment of this invention. It is explanatory drawing of the drive waveform in 4th Embodiment of this invention.

  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 of a mechanism portion of the image forming apparatus, and FIG.

  This image forming apparatus is a serial type ink jet recording apparatus. The carriage 33 is slidably held in the main scanning direction by main and sub guide rods 31 and 32 which are guide members laid over the left and right side plates 21A and 21B of the apparatus main body 1. The carriage 33 is moved and scanned in a direction indicated by an arrow (carriage main scanning direction) in FIG. 2 via a timing belt by a main scanning motor (not shown).

  The carriage 33 is equipped with recording heads 34a and 34b (referred to as “recording head 34” when not distinguished from each other) composed of liquid ejection heads. For example, yellow (Y), cyan (C), magenta (M), and black (K) ink droplets are ejected by the two recording heads 34. The recording head 34 is mounted with a nozzle row composed of a plurality of nozzles arranged in the sub-scanning direction orthogonal to the main scanning direction and the ink droplet ejection direction facing downward.

  Each recording head 34 has two nozzle rows. One nozzle row of the recording head 34a discharges black (K) droplets, and the other nozzle row discharges cyan (C) droplets. Also, one nozzle row of the recording head 34b discharges magenta (M) droplets, and the other nozzle row discharges yellow (Y) droplets. As the recording head 34, a recording head having a nozzle row of each color in which a plurality of nozzles are arranged on one nozzle surface can be used.

  The carriage 33 has head tanks 35a and 35b as second ink supply units for supplying ink of each color corresponding to the nozzle rows of the recording head 34 (referred to as “head tank 35” when not distinguished). It is equipped with. Ink is supplied to the head tank 35 from ink cartridges (main tanks) 10 of various colors that are detachably attached to the cartridge loading unit 4. The supply pump unit 24 sends ink of each color of the ink cartridge 10 to the head tank 35 via the supply tube 36.

  On the other hand, sheets 42 are stacked on a sheet stacking portion (pressure plate) 41 of the sheet feeding tray 2. The paper 42 faces the half-moon roller (paper feeding roller) 43 and the paper feeding roller 43 and is separated and fed one by one by a separation pad 44 made of a material having a large friction coefficient. The separation pad 44 is urged toward the paper feed roller 43 side.

  The fed paper 42 is interposed between a conveying belt 51 serving as a conveying means and a pressure roller 49 via a guide member 45 that guides the paper 42, a counter roller 46, and a conveying guide member 47. It is sent. The transport belt 51 electrostatically attracts the paper 42 and transports it to a position facing the recording head 34.

  The conveyance belt 51 is an endless belt, and is configured to wrap around the conveyance roller 52 and the tension roller 53 and circulate in the belt conveyance direction (sub-scanning direction). Further, a charging roller 56 that is a charging unit for charging the surface of the transport belt 51 is provided. The charging roller 56 is disposed so as to come into contact with the surface layer of the transport belt 51 and to rotate following the rotation of the transport belt 51.

  Further, the conveyance belt 51 rotates in the belt conveyance direction of FIG. 2 when the conveyance roller 52 is rotationally driven through timing by a sub-scanning motor (not shown).

  Further, as a paper discharge unit for discharging the paper 42 recorded by the recording head 34, a separation claw 61 for separating the paper 42 from the conveying belt 51, a paper discharge roller 62, and a spur 63 that is a paper discharge roller. And a paper discharge tray 3 below the paper discharge roller 62.

  A duplex unit 71 is detachably mounted on the back surface of the apparatus body 1. The duplex unit 71 takes in the paper 42 returned by the reverse rotation of the conveyance belt 51, reverses it, and feeds it again between the counter roller 46 and the conveyance belt 51. The upper surface of the duplex unit 71 is a manual feed tray 72.

  Further, a maintenance / recovery mechanism 81 for maintaining and recovering the nozzle state of the recording head 34 is disposed in the non-printing area on one side of the carriage 33 in the scanning direction.

  The maintenance / recovery mechanism 81 includes cap members (hereinafter referred to as “caps”) 82a and 82b (hereinafter referred to as “caps 82” when not distinguished) for capping the nozzle surfaces of the recording head 34.

  The maintenance / recovery mechanism 81 includes a wiper member (wiper blade) 83 for wiping the nozzle surface. Further, the maintenance / recovery mechanism 81 includes an empty discharge receiver 84 that receives droplets when performing empty discharge for discharging droplets that do not contribute to recording in order to discharge the thickened recording liquid, and a carriage lock that locks the carriage 33. 87 and the like.

  Further, a waste liquid tank 99 for storing waste liquid generated by the maintenance recovery operation is mounted on the lower side of the maintenance recovery mechanism 81 in a replaceable manner with respect to the apparatus main body.

  Further, in the non-printing area on the other side of the carriage 33 in the scanning direction, there is an empty space for receiving liquid droplets when performing empty discharge for discharging liquid droplets that do not contribute to recording in order to discharge the recording liquid thickened during recording or the like. A discharge receiver 88 is disposed. The idle discharge receiver 88 is provided with an opening 89 along the nozzle row direction of the recording head 34.

  In the image forming apparatus configured as described above, the sheets 42 are separated and fed one by one from the sheet feeding tray 2, and the sheets 42 fed substantially vertically upward are guided by the guide unit 45, It is sandwiched between the counter roller 46 and conveyed. Then, the leading edge of the paper 42 is guided by the conveying guide 37 and pressed against the conveying belt 51 by the leading pressure roller 49, and the conveying direction is changed by approximately 90 °.

  At this time, a voltage is applied to the charging roller 56 so that positive output and negative output are alternately repeated, and the conveying belt 51 is charged with an alternating charging voltage pattern. When the sheet 42 is fed onto the charged conveying belt 51, the sheet 42 is attracted to the conveying belt 51, and the sheet 42 is conveyed in the sub-scanning direction by the circular movement of the conveying belt 51.

  Therefore, by driving the recording head 34 according to the image signal while moving the carriage 33, ink droplets are ejected onto the stopped paper 42 to record one line, and after the paper 42 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 42 has reached the recording area, the recording operation is finished and the paper 42 is discharged onto the paper discharge tray 3.

  Further, when performing the maintenance recovery of the nozzles of the recording head 34, the carriage 33 is moved to a position facing the maintenance recovery mechanism 81 which is the home position. Then, by performing maintenance and recovery operations such as nozzle suction for performing capping by the cap member 82 to perform suction from the nozzles and idle ejection for ejecting droplets that do not contribute to image formation, image formation by stable droplet ejection It can be performed.

  Next, an example of the liquid discharge head constituting the recording head 34 will be described with reference to FIGS. 3 and 4 are cross-sectional explanatory views along the liquid chamber longitudinal direction (direction perpendicular to the nozzle arrangement direction) of the head.

  In the liquid discharge head, the flow path plate 101, the vibration plate member 102, and the nozzle plate 103 are joined. Thereby, the individual liquid chamber 106 through which the nozzle 104 that discharges the liquid droplets communicates through the through hole 105, the fluid resistance portion 107 that supplies the liquid to the liquid chamber 106, and the liquid introduction portion 108 are formed. Then, liquid (ink) is introduced from the common liquid chamber 110 formed in the frame member 117 into the liquid introduction unit 108 through the filter unit 109 formed in the diaphragm member 102, and the fluid resistance unit 107 is introduced from the liquid introduction unit 108. Through this, ink is supplied to the liquid chamber 106.

  The flow path plate 101 is formed by laminating metal plates such as SUS to form openings and groove portions such as the through hole 105, the liquid chamber 106, the fluid resistance portion 107, and the liquid introduction portion 108. The diaphragm member 102 is a wall surface member that forms the wall surface of each liquid chamber 106, fluid resistance portion 107, liquid introduction portion 108, and the like, and a member that forms the filter portion 109. The flow path plate 101 is not limited to a metal plate such as SUS, and may be formed by anisotropic etching of a silicon substrate.

  A columnar laminated piezoelectric member 112 is joined to the diaphragm member 102 on the side opposite to the liquid chamber 106. One end of the piezoelectric member 112 is joined to the base member 113, and the FPC 115 that transmits a driving waveform is connected to the piezoelectric member 112. Thus, a piezoelectric actuator 111 is configured as a pressure generating unit that generates pressure to pressurize the ink in the liquid chamber 106 and eject droplets from the nozzle 104.

  In this example, the piezoelectric member 112 is used in the d33 mode that expands and contracts in the stacking direction, but it may be in the d31 mode that expands and contracts in the direction orthogonal to the stacking direction.

  In the liquid discharge head configured as described above, for example, as shown in FIG. 3, the voltage applied to the piezoelectric member 112 is lowered from the reference potential Ve. As a result, the piezoelectric member 112 contracts, the diaphragm member 102 deforms, and the volume of the liquid chamber 106 expands, so that ink flows into the liquid chamber 106. Thereafter, as shown in FIG. 4, the voltage applied to the piezoelectric member 112 is increased. As a result, the piezoelectric member 112 extends in the stacking direction, deforms the diaphragm member 102 in the direction of the nozzle 104, and contracts the volume of the liquid chamber 106. By contracting the volume of the liquid chamber 106, the ink in the liquid chamber 106 is pressurized, and the droplets 301 are ejected from the nozzle 104.

  Then, by returning the voltage applied to the piezoelectric member 112 to the reference potential Ve, the diaphragm member 102 is restored to the initial position, and the liquid chamber 106 expands to generate a negative pressure. At this time, ink is filled from the common liquid chamber 110 into the liquid chamber 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.

  Next, an outline of the control unit of the image forming apparatus will be described with reference to FIG. FIG. 5 is a block diagram of the control unit.

  The control unit 500 includes a CPU 501 that controls the entire apparatus, a ROM 502 that stores fixed data such as various programs including programs executed by the CPU 501, and a RAM 503 that temporarily stores image data and the like. In addition, the control unit 500 includes a rewritable nonvolatile memory 504 for holding data even while the apparatus is powered off. Further, the control unit 500 includes an ASIC 505 that processes various signal processing on image data, image processing that performs rearrangement, and other input / output signals for controlling the entire apparatus.

  The control unit 500 also includes a print control unit 508 including a data transfer unit for driving and controlling the recording head 34 and a driving signal generation unit, and a head driver (driver) for driving the recording head 34 provided on the carriage 33 side. IC) 509. In addition, the control unit 500 includes a main scanning motor 554 that moves and scans the carriage 33 and a sub-scanning motor 555 that moves the conveyor belt 51 around. Further, the control unit 500 includes a motor drive unit 510 for driving a maintenance / recovery motor 556 that moves the cap 82 and the wiper member 83 of the maintenance / recovery mechanism 81, the suction pump 812, and the like. The control unit 500 also includes an AC bias supply unit 511 that supplies an AC bias to the charging roller 56, a supply system drive unit 512 that drives the liquid feed pump 241, and the like.

  The control unit 500 is connected to an operation panel 514 for inputting and displaying information necessary for the apparatus.

  The control unit 500 has an I / F 506 for transmitting and receiving data and signals to and from the host side. The control unit 500 receives the I / F 506 from the host 900 side such as an information processing apparatus such as a personal computer or an image reading apparatus such as an image scanner via the I / F 506 via a cable or a network.

  Here, the CPU 501 of the control unit 500 reads and analyzes the print data in the reception buffer included in the I / F 506, performs necessary image processing, data rearrangement processing, and the like in the ASIC 505, and prints this image data. The data is transferred from the control unit 508 to the head driver 509. In order to output an image, dot pattern data can be generated by the printer driver 901 on the host 900 side or by the control unit 500.

  The print control unit 508 transfers the above-described image data as serial data. Further, the print control unit 508 outputs a transfer clock, a latch signal, a control signal, and the like necessary for image data transfer and transfer confirmation to the head driver 509. Further, the print control unit 508 includes a drive signal generation unit including a D / A converter that converts D / A conversion of drive pulse pattern data stored in the ROM 502, a voltage amplifier, a current amplifier, and the like. Then, the print control unit 508 outputs a drive waveform composed of one drive pulse or a plurality of drive pulses to the head driver 509.

  The head driver 509 selects a drive pulse constituting a drive waveform supplied from the print control unit 508 based on image data corresponding to one line of the print head 34 input serially, and generates a pressure in the print head 34. The recording head 34 is driven by giving to the means. At this time, by selecting part or all of the pulses constituting the drive waveform or all or part of the waveform elements forming the pulses, for example, dots of different sizes such as large drops, medium drops, and small drops Can be sorted out.

  The I / O unit 513 acquires information from various sensor groups 515 mounted on the apparatus, extracts information necessary for controlling the printer, a print control unit 508, a motor drive unit 510, and an AC bias supply unit. Used to control 511. A sensor group 515 is an optical sensor for detecting the position of the paper, a thermistor for monitoring the temperature in the machine, a sensor for monitoring the voltage of the charging belt, and the I / O unit 513 processes various sensor information. Can do.

  Next, an example of the print control unit 508 and the head driver 509 constituting the head drive control device will be described with reference to the block explanatory diagram of FIG.

  The print control unit 508 includes a drive waveform generation unit 701 that generates and outputs a drive waveform (common drive waveform) composed of a plurality of pulses (drive signals) within one print cycle (one drive cycle) during image formation. ing. The print control unit 508 outputs 2-bit image data (gradation signals 0 and 1) corresponding to the print image, a clock signal, a latch signal (LAT), and droplet control signals M0 to M3. It has.

  The droplet control signal is a 2-bit signal that instructs each droplet to open and close an analog switch 715 that is a switch unit of the head driver 509 described later. This droplet control signal makes a state transition to the H level (ON) at a pulse or waveform element to be selected in accordance with the printing cycle of the common drive waveform, and makes a state transition to the L level (OFF) when not selected.

  The head driver 509 includes a shift register 711 that inputs a transfer clock (shift clock) from the data transfer unit 702 and serial image data (gradation data: 2 bits / 1 channel (1 nozzle)). 509 includes a latch circuit 712 for latching each resist value of the shift register 711 by a latch signal, and a decoder 713 for decoding the gradation data and the droplet control signals M0 to M3 and outputting the result. The head driver 509 includes a level shifter 714 that converts the logic level voltage signal of the decoder 713 to a level at which the analog switch 715 can operate, and the head driver 509 includes the decoder 713 provided via the level shifter 714. Output on / off (open / close) And a analog switch 715.

  The analog switch 715 is connected to the selection electrode (individual electrode) of each piezoelectric member 112, and the common drive waveform Pv from the drive waveform generation unit 701 is input. Accordingly, the analog switch 715 is turned on according to the result of decoding the serially transferred image data (gradation data) and the droplet control signals M0 to M3 by the decoder 713. Thereby, a required pulse (or waveform element) constituting the common drive waveform Pv passes (is selected) and is applied to the piezoelectric member 112 of the recording head 34.

  Next, a first embodiment of the present invention will be described with reference to FIG. FIG. 7 is an explanatory diagram of drive waveforms in the same embodiment.

  This drive waveform Pv1 is a waveform including at least the first drive pulse P1 and the second drive pulse P2 given in time series to the pressure generating means (piezoelectric member 112) of the recording head 34 within one drive cycle.

  Here, the first drive pulse P1 includes a first waveform element a1 that is a lead-in waveform element, a second waveform element b1 that is a hold waveform element following the first waveform element a1, and a push waveform that follows the second waveform element b1. And a third waveform element c1 which is an element.

  The first waveform element a1 is a falling waveform element that contracts the piezoelectric member 112 and expands the individual liquid chamber 106 by falling from the reference potential (here, intermediate potential) Ve by the potential V1. The second waveform element b1 is a hold waveform element that holds the potential falling at the first waveform element a1 for a predetermined time (pulse width Pw1). The third waveform element c1 is a rising waveform element that elongates the piezoelectric member 112 and contracts the individual liquid chamber 106 by rising for the potential V1 from the potential held in the second waveform element b1 to the reference potential (intermediate potential) Ve. is there.

  The second drive pulse P2 is a first waveform element a2 that is a pulling waveform element, a second waveform element b2 that is a holding waveform element following the first waveform element a2, and a pushing waveform element that follows the second waveform element b2. And a third waveform element c2.

  The first waveform element a2 is a falling waveform element that contracts the piezoelectric member 112 and expands the individual liquid chamber 106 by falling from the reference potential (here, intermediate potential) Ve by the potential V2. The second waveform element b2 is a hold waveform element that holds the potential falling at the first waveform element a2 for a predetermined time (pulse width Pw2). The third waveform element c2 is a rising waveform element that elongates the piezoelectric member 112 and contracts the individual liquid chamber 106 by rising for a potential V2 from the potential held in the second waveform element b2 to the reference potential (intermediate potential) Ve. is there.

  In the present embodiment, the first drive pulse P1 and the second drive pulse P2 have the same waveform, and therefore have a relationship of potential V1 = V2. The potentials V1 and V2 can be adjusted according to the target droplet speed.

  In this case, the droplet velocity Vj1 ejected by the first drive pulse P1 and the droplet velocity Vj2 ejected by the second drive pulse P2 are such that Vj1 <Vj2. A potential V, a falling time Tf, a rising time Tr, and a pulse width (holding time) Pw relating to the waveforms of the first driving pulse P1 and the second driving pulse P2 are set.

  Further, here, the first drive pulse P1 and the second drive pulse P1 and the second drive pulse P2 are merged into one droplet during flight, so that the droplets ejected by the first drive pulse P1 and the second drive pulse P2 merge. A potential V, a falling time Tf, a rising time Tr, and a pulse width (holding time) Pw relating to the waveform of the drive pulse P2 are set.

  The drive waveform Pv of the present embodiment has a start point T2 of the first waveform element a2 that is the pull-in waveform element of the second drive pulse P2 from the end point T1 of the third waveform element c1 that is the push-in waveform element of the first drive pulse P1. The time (pulse interval) Td until is an integer multiple of the natural vibration period Tc of the individual liquid chamber 106 (here, Td = 1 × Tc).

  Thus, the pulse interval Td between the first drive pulse P1 and the second drive pulse P2, that is, from the end point of the third waveform element c1 of the first drive pulse P1 to the start point of the first waveform element a2 of the second drive pulse P2. Is set to a waveform that is an integral multiple of the natural vibration period Tc of the individual liquid chamber 106, and the formation of satellites can be suppressed with a simple configuration when one drop is formed by two drive pulses.

  This point will be specifically described. First, the configuration of one pulse (single pulse) will be described with reference to FIGS. FIG. 8 is an explanatory view showing the waveform shape of a single pulse, and FIG. 9 is an explanatory view for explaining an example of a change in droplet velocity when the hold period (pulse width Pw) of the single pulse is changed.

  A single pulse for ejecting droplets is composed of a drawing waveform element a, a holding waveform element b, and a pushing waveform element c.

  Here, the drawing waveform element (falling waveform element) a falls from the reference potential Ve and contracts the piezoelectric member 112 to expand the individual liquid chamber 106. Let the fall time Tf be from the start point to the end point of the falling waveform element a.

  The hold waveform element b holds the falling potential of the falling waveform element a for a predetermined time. A holding time (hold time) by the hold waveform element b is referred to as a pulse width Pw.

  The pushing waveform element (rising waveform element) c rises from the potential held by the hold waveform element b and expands the piezoelectric member 112 to contract the individual liquid chamber 106. The time from the start point to the end point of the rising waveform element c is set as a rising time Tr.

  The droplet discharge speed is changed by changing the pulse width Pw of the single pulse. In this case, as shown in FIG. 9, the natural vibration period Tc of the individual liquid chamber 106 can be calculated from the difference between the pulse widths Pwa and Pwb.

  Next, a basic configuration of a driving waveform in which two droplets are merged during flight to form one droplet will be described with reference to FIG.

  This drive waveform has the same configuration as the drive waveform described with reference to FIG. 7, and the droplet ejected by the first drive pulse P1 and the droplet ejected by the second drive pulse P2 are in flight. Merge to make one drop and land on the recording medium.

  Here, the time from the end point of the third waveform element c1 of the first drive pulse P1 to the start point of the first waveform element a2 of the second drive pulse P2 is defined as a pulse interval Td. The change in the pulse interval Td means that the timing at which the second drive pulse P2 is applied changes, and the drop velocity of the droplets ejected by the second drive pulse P2 is greatly affected.

  Changes in the voltages of the satellite Tj and the first drive pulse P1 with respect to the pulse interval (time) Td from the end point of the third waveform element c1 of the first drive pulse P1 to the start point of the first waveform element a2 of the second drive pulse P2 An example is shown in FIG.

  Here, the satellite Tj will be described with reference to the schematic explanatory view of FIG. Note that FIG. 12 shows a case where the number of ejected droplets is one for easy understanding. The satellite Tj is the time from the start of ejection to landing.

  First, a single pulse is applied, and the ink droplet 600 starts to be ejected from the nozzle surface 103a. Let this time be t1. Next, as time t2 and t3 elapse, the ink droplet 600 gradually approaches the virtual recording medium 42a. Here, the distance G from the nozzle surface 103a to the recording medium 42a is set to be the same as the distance between the actually used nozzle surface and the recording medium.

  As shown, at time t4, the ink droplet 600 reaches the line of the recording medium 42a.

  Further, at time t5, the satellite 601 following the ink droplet 600 (main droplet) reaches the line of the recording medium 42a.

  Here, the time Tj of the ink droplet 600 is the time from when the ink droplet 600 is ejected until it reaches the line of the recording medium 42a, that is, time (t4-t1).

  The satellite Tj is the time from when the ink droplet 600 is ejected until the satellite that follows the ink droplet 600 reaches the line of the recording medium 42a, that is, time (t5-t1).

  The longer this time (t5-t1), the slower the satellite speed and the greater the speed difference from the main droplet. This actually works in the direction of deterioration of the image when landing on the recording medium, so that the satellite Tj needs to be shortened in order to form a high-quality image.

  Here, referring back to FIG. 11, as the measurement conditions of FIG. 11, first, the voltage V2 is fixed so that the satellite Tj of the ink droplet when given by the second drive pulse P2 alone is 200 μs.

  Next, when the first drive pulse P1 and the second drive pulse P2 are continuously applied, the ink droplets ejected by the respective drive pulses are merged during the flight, and the satellite Tj of the ink droplet becomes 200 μs. The voltage is adjusted. That is, the second drive pulse P2 has a fixed waveform regardless of the pulse interval Td, and the voltage V1 of the first drive pulse P1 is adjusted simultaneously with changing the pulse interval Td.

  Here, the broken line 700 in FIG. 11 indicates that the voltage V1 of the first drive pulse P1 decreases in a certain cycle. In other words, the fact that the voltage is small means that ink droplets can be ejected efficiently, and this point is the resonance point.

  Focusing on this, it can be seen that the satellite Tj tends to become smaller at the resonance point. Further, it can be read that the satellite Tj can be made smaller at the resonance point in the direction in which the time Td becomes longer, such as second and third.

  As described above, as in the present embodiment, the pulse interval Td that is the time from the end point T1 of the third waveform element c1 of the first drive pulse P1 to the start point T2 of the first waveform element a2 of the second drive pulse P2 is individually determined. By making the waveform the same as the natural vibration period Tc of the liquid chamber 106 (Td = 1 · Tc), the generation of satellites can be suppressed with a simple configuration when one drop is formed by two drive pulses. That is, satellites can be suppressed more than when the time (pulse interval) Td is a waveform shorter than the length of the natural vibration period Tc.

  Next, a second embodiment of the present invention will be described with reference to FIG. FIG. 13 is an explanatory diagram of drive waveforms in the same embodiment.

  In this embodiment, the time (pulse interval) Td from the end point T1 of the third waveform element c1 of the first drive pulse P1 to the start point T2 of the first waveform element a2 of the second drive pulse P2 is unique to the individual liquid chamber 106. The waveform is twice the vibration period Tc (Td = 2 · Tc).

  With this configuration, as described with reference to FIG. 11, satellites can be suppressed as compared with the case where the pulse interval Td is the natural vibration period Tc.

  This point will be described with reference to FIG. FIG. 14A shows a state from droplet discharge to merge in the first embodiment, and FIG. 14B shows a state from droplet discharge to merge in the second embodiment.

  Here, as shown in FIG. 14A, the droplet velocity of the droplet 611 ejected by the first drive pulse P1 in the first embodiment is Vj1, and the droplet velocity of the droplet 612 ejected by the second drive pulse P2 is set. Let Vj2. As shown in FIG. 14B, the droplet velocity of the droplet 611 ejected by the first drive pulse P1 in the second embodiment is Vj12, and the droplet velocity of the droplet 612 ejected by the second drive pulse P2 is Vj22. And Times Ta1 and Ta2 indicate time intervals at which the droplets 611 and 612 are ejected.

  The voltage of the second drive pulse P2 is set to such a voltage that the satellite Tj becomes 200 μs when the second drive pulse P2 is applied alone, and the drop speed of the second drop depends on the pulse interval Td. Will do.

  Naturally, since the meniscus vibration is larger in the natural vibration period Tc than in the time point of the natural vibration period Tc twice, the relationship of Vj2> Vj22 is established when the drop speeds of the second drop are compared.

  That is, when the pulse interval Td = 2 × Tc, the drop speed of the second drop is slower than when Td = Tc.

  Furthermore, when the pulse interval Td is set to 2 × Tc, the time required until the second droplet is ejected naturally becomes longer.

  Therefore, considering that two drops must be merged during flight, the drop speed of the first drop needs to be set slower than the drop speed at the interval of the natural vibration period Tc. That is, the relationship Vj1> Vj12 is established.

  Here, if the droplet velocity Vj12 is too slow, a desired satellite Tj cannot be obtained even if merged, and a certain droplet velocity is necessary.

  Therefore, it is necessary to adjust the voltage of the first drive pulse P1 with a good balance. As a result, as shown in FIG. 14, the interval of the natural vibration period Tc (2Tc) is doubled as in the second embodiment rather than the merge position L1 in the interval of the natural vibration period Tc as in the first embodiment. The merge position L2 at [time td] is closer to the landing position plane. That is, the relationship L1 <L2 is established.

  From these facts, it can be seen that the velocity difference between the droplet velocity Vj12 and the droplet velocity Vj22 of the second embodiment is inevitably small.

  In addition, regarding the two patterns of FIGS. 14A and 14B, the relationship with the satellite can be estimated from the viewpoint of pressure vibration.

  When the time Td is the interval of the natural vibration period Tc, the pressure vibration is larger than the interval of 2 × Tc, so that the satellite of the second drop is likely to appear. This is synonymous with an increase in the drop speed of the second drop. On the other hand, when the pulse interval Td is twice (= 2 × Tc) the natural vibration period Tc, the pressure vibration is small, so that the satellite of the second drop is hardly produced.

  Therefore, in the second embodiment, there is an effect that further satellites can be suppressed than in the first embodiment.

  Next, a third embodiment of the present invention will be described with reference to FIG. FIG. 15 is an explanatory diagram of drive waveforms in the same embodiment.

  In the present embodiment, the second drive pulse P2 follows the first waveform element a2 that is the pulling waveform element, the second waveform element b2 that is the holding waveform element following the first waveform element a2, and the second waveform element b2. A third waveform element c2 that is a push waveform element, a fourth waveform element d2 that follows the third waveform element c2, a fifth waveform element e2 that is a push waveform element that follows the fourth waveform element d2, and a fifth waveform element e2. Includes a sixth waveform element f2 and a seventh waveform element g2 following the sixth waveform element f2.

  The first waveform element a2 is a falling waveform element that contracts the piezoelectric member 112 and expands the individual liquid chamber 106 by falling from the reference potential (here, intermediate potential) Ve by the potential V2. The second waveform element b2 is a hold waveform element that holds the potential falling at the first waveform element a2 for a predetermined time (pulse width Pw2). The third waveform element c2 rises from the potential held in the second waveform element b2 to the potential Ve2 higher than the reference potential (intermediate potential) Ve, thereby extending the piezoelectric member 112 and contracting the individual liquid chamber 106. This is a rising waveform element.

  The fourth waveform element d2 is a hold waveform element that holds the potential rising at the third waveform element c2 for a predetermined time Tw2. The fifth waveform element e2 rises from the potential held in the fourth waveform element d2 to the potential Ve3 higher than the potential Ve2 by a potential V4, thereby extending the piezoelectric member 112 and further contracting the individual liquid chamber 106. Is an element.

  The sixth waveform element f2 is a hold waveform element that holds the potential rising at the fifth waveform element e2 for a predetermined time. The seventh waveform element g2 is a falling waveform element that falls from the potential held in the sixth waveform element f2 to the reference potential Ve.

  Thus, by making the second drive pulse P2 into a two-stage pushing shape, the speed of the satellite can be increased, and the satellite catches up and is absorbed by the main droplet before landing on the recording medium.

  Here, since the degree of suppression of the satellite varies depending on the length of the waveform hold time Tw2 and the magnitude of the potential V22 between the potential Ve2 and the potential Ve3, it needs to be optimized.

  By using such a driving waveform of the third embodiment, it is possible to further suppress the generation of the second drop of satellites, and thus it is possible to create a higher quality image.

  Further, by using only the second drive pulse P2, it is possible to form dots smaller than the droplet diameter of two pulses and one dot. Since the second drive pulse P2 originally has a two-stage push shape that suppresses the generation of satellites, it is possible to form beautiful small dots.

  Next, a fourth embodiment of the present invention will be described with reference to FIG. FIG. 16 is an explanatory diagram of drive waveforms in the same embodiment.

  The drive waveform of this embodiment is composed of 5 pulses of drive pulses P11 to P15. By selecting these five drive pulses P11 to P15 based on the image data and the droplet control signal described above, three types of droplets such as a large droplet, a medium droplet, and a small droplet can be distinguished. Note that the number of pulses is not limited to five, but may be three, or six or more pulses may be generated.

  Here, for example, a large droplet uses all the driving pulses P11 to P15, a medium droplet uses two driving pulses P13 and P15, and a small droplet uses one of the driving pulses P15. Form using pulses.

  In this drive waveform, the drive pulse P13 corresponds to the first drive pulse of the present invention, the drive pulse P15 also corresponds to the second drive pulse, and the interval between the drive pulse P13 and the drive pulse P15 is twice the natural vibration period Tc. (2 × Tc) is set.

  A drive pulse P14 as a third drive pulse is interposed between the drive pulse P13 and the drive pulse P15.

  As described above, the medium droplet is formed by the drive pulse P13 and the drive pulse P15, and the pulse interval is 2 × Tc. Therefore, it is possible to suppress the satellite generation and form a beautiful medium dot. Become.

  Then, by inserting the drive pulse P14 between the drive pulse P13 and the drive pulse P15, various types of efficient waveforms can be obtained without increasing the overall waveform length.

  That is, as described above, the large droplet uses all five pulses of the drive pulses P11 to P15. Here, when another drive pulse is not inserted between the drive pulse P13 and the drive pulse P15, the entire waveform length of the drive waveform for one pulse becomes long.

  In this way, in the method in which various droplet types are divided in one cycle, the maximum driveable frequency is determined by the entire waveform length, and therefore the waveform length is an important factor. By shortening the overall waveform length, it is possible to drive at a higher frequency, so that the printing speed can be increased.

  In the present application, the “paper” is not limited to paper, but includes OHP, cloth, glass, a substrate, etc., and means a material to which ink droplets or other liquids can be attached. , Recording media, recording paper, recording paper, and the like. In addition, image formation, recording, printing, printing, and printing are all synonymous.

  The “image forming apparatus” means an apparatus that forms an image by discharging a liquid onto a medium such as paper, thread, fiber, fabric, leather, metal, plastic, glass, wood, ceramics or the like. In addition, “image formation” not only applies an image having a meaning such as a character or a figure to a medium but also applies an image having no meaning such as a pattern to the medium (simply applying a droplet to the medium). It also means to land on.

  The “ink” is not limited to an ink unless otherwise specified, but includes any liquid that can form an image, such as a recording liquid, a fixing processing liquid, or a liquid. Used generically. For example, DNA samples, resists, pattern materials, resins and the like are also included.

  In addition, the “image” is not limited to a planar image, and includes an image given to a three-dimensionally formed image and an image formed by three-dimensionally modeling a solid itself.

  Further, the image forming apparatus includes both a serial type image forming apparatus and a line type image forming apparatus, unless otherwise limited.

33 Carriage 34, 34a, 34b Recording head (liquid ejection head)
500 Control Unit 508 Print Control Unit 701 Drive Waveform Generation Unit 702 Data Transfer Unit

Claims (8)

A recording head having pressure generating means for generating pressure for pressurizing the liquid in the individual liquid chamber through which the nozzle for discharging the droplets communicates;
Drive waveform generating means for generating and outputting a drive waveform including at least a first drive pulse and a second drive pulse in time series, which are given to the pressure generating means of the recording head within one drive cycle;
The first drive pulse includes at least a drawing waveform element that expands the individual liquid chamber, and a pushing waveform element that contracts the expanded individual liquid chamber,
The second drive pulse includes at least a drawing waveform element that expands the individual liquid chamber, and a pushing waveform element that contracts the expanded individual liquid chamber,
The image formation characterized in that the time from the end point of the push-in waveform element of the first drive pulse to the start point of the pull-in waveform element of the second drive pulse is an integral multiple of the natural vibration period of the individual liquid chamber apparatus. The droplet velocity Vj1 ejected by the first drive pulse and the droplet velocity Vj2 ejected by the second drive pulse have a relationship of Vj1 <Vj2. The image forming apparatus according to 1. The image forming apparatus according to claim 2, wherein the droplet ejected by the first drive pulse and the droplet ejected by the second drive pulse are merged into one droplet during flight. . Between the first drive pulse and the second drive pulse, a liquid that forms dots having a size different from the size of the dots formed by the droplets ejected by the first drive pulse and the second drive pulse. The image forming apparatus according to claim 1, further comprising a third drive pulse used when ejecting a droplet.   The dot formed by the droplet ejected by the third driving pulse is smaller than the dot formed by the droplet ejected by the first driving pulse and the second driving pulse. The image forming apparatus described. The time from the end point of the push-in waveform element of the first drive pulse to the start point of the pull-in waveform element of the second drive pulse is at least twice the natural vibration period of the individual liquid chamber. Item 6. The image forming apparatus according to any one of Items 1 to 5. A head drive control device for driving and controlling a recording head having a pressure generating means for generating a pressure for pressurizing a liquid in an individual liquid chamber through which a nozzle for discharging a droplet communicates,
Drive waveform generation means for generating and outputting a drive waveform including at least a first drive pulse and a second drive pulse in time series, which are given to the pressure generation means of the recording head within one drive cycle;
The first drive pulse includes at least a drawing waveform element that expands the individual liquid chamber, and a pushing waveform element that contracts the expanded individual liquid chamber,
The second drive pulse includes at least a drawing waveform element that expands the individual liquid chamber, and a pushing waveform element that contracts the expanded individual liquid chamber,
The head drive characterized in that the time from the end point of the push-in waveform element of the first drive pulse to the start point of the pull-in waveform element of the second drive pulse is an integral multiple of the natural vibration period of the individual liquid chamber Control device. A head driving control method for driving and controlling a recording head having a pressure generating means for generating a pressure for pressurizing a liquid in an individual liquid chamber through which a nozzle for discharging a droplet is communicated,
Generate and output a drive waveform including at least a first drive pulse and a second drive pulse in time series, which are given to the pressure generating means of the recording head within one drive cycle,
The first drive pulse includes at least a drawing waveform element that expands the individual liquid chamber, and a pushing waveform element that contracts the expanded individual liquid chamber,
The second drive pulse includes at least a drawing waveform element that expands the individual liquid chamber, and a pushing waveform element that contracts the expanded individual liquid chamber,
The head drive characterized in that the time from the end point of the push-in waveform element of the first drive pulse to the start point of the pull-in waveform element of the second drive pulse is an integral multiple of the natural vibration period of the individual liquid chamber Control method.

Images