JP2024061618A - LIQUID EJECTION APPARATUS, PROGRAM, AND HEAD DRIVE CONTROL METHOD - Google Patents

Abstract

The present invention aims to realize high-frequency driving by suppressing the bending of droplets while reducing the generation of mist that accompanies the ejection of liquid.
SOLUTION
The liquid ejection device is equipped with a head drive control unit that outputs a drive waveform to the pressure generating unit, and when the drive waveform includes two or more of the pulses, it includes a final pulse at the end of the multiple pulses, and the final pulse includes a first expansion waveform element that expands the individual liquid chamber, a first contraction waveform element that is a waveform element after the first expansion waveform element and contracts the individual liquid chamber, a second expansion waveform element that is a waveform element after the first contraction waveform element and expands the individual liquid chamber, a second contraction waveform element that is a waveform element after the second expansion waveform element and contracts the individual liquid chamber, and a third expansion waveform element that is a waveform element after the second contraction waveform element and expands the individual liquid chamber.
[Selection diagram] Figure 9

Description

The present invention relates to a liquid ejection device, a program, and a head drive control method.

There are known liquid ejection devices equipped with a liquid ejection head that ejects droplets. Some of these liquid ejection devices output a drive waveform, which includes one or more pulses selected according to the droplet size, to a pressure generating unit (see, for example, Patent Document 1).

However, in the device of Patent Document 1, when the liquid ejection head is driven at high frequency to eject droplets, minute vibrations remain in the liquid in the individual liquid chambers of the liquid ejection head, which can cause the droplets to be ejected in a curved manner. Also, mist can be generated when droplets are ejected.

The present invention has been made in consideration of the above problems, and aims to provide a liquid ejection device that can perform high-frequency driving while suppressing the bending of droplets, while reducing the generation of mist that accompanies the ejection of droplets.

The liquid ejection device according to the present invention comprises a liquid ejection head having a plurality of nozzles for ejecting droplets, individual liquid chambers communicating with the nozzles, a pressure generating unit for generating pressure to pressurize the liquid in the individual liquid chambers, and a head drive control unit for outputting a drive waveform including one or more pulses selected according to a droplet size to the pressure generating unit, and when the drive waveform includes two or more of the pulses, the drive waveform includes a final pulse at the end of the plurality of pulses, and the final pulse is a first expansion waveform element that expands the individual liquid chambers, and a waveform element subsequent to the first expansion waveform element, which fills the individual liquid chambers. The waveform element includes a first contraction waveform element that contracts the individual liquid chamber, a second expansion waveform element that is a waveform element that comes after the first contraction waveform element and expands the individual liquid chamber, a second contraction waveform element that is a waveform element that comes after the second expansion waveform element and contracts the individual liquid chamber, and a third expansion waveform element that is a waveform element that comes after the second contraction waveform element and expands the individual liquid chamber, and is characterized in that the time from the start of the first contraction waveform element to the start of the second expansion waveform element is less than 0.5Tc, and the time from the start of the first contraction waveform element to the start of the second contraction waveform element is within the range of 0.5Tc to 0.6Tc.

The present invention provides a liquid ejection device that can perform high-frequency driving while suppressing the bending of droplets, while reducing the generation of mist that accompanies the ejection of droplets.

1 is a schematic side view illustrating an image forming apparatus according to an embodiment. 1 is a plan view of an image forming apparatus according to an embodiment; FIG. 2 is a cross-sectional view of a recording head. FIG. 2 is a cross-sectional view of a recording head. FIG. 2 is a block diagram showing a control unit of the image forming apparatus. FIG. 2 is a block diagram showing a print control unit and a head driver. FIG. 4 is a waveform diagram showing driving waveforms according to the first embodiment. FIG. 2 is a waveform diagram showing a drive waveform including multiple pulses, a droplet control signal, and pulses according to droplet size. FIG. 11 is a waveform diagram showing a final pulse P5 in the drive waveform according to the first embodiment. FIG. 2 is a diagram showing droplets ejected from a nozzle. FIG. 11 is a waveform diagram showing a driving waveform according to Comparative Example 1. 11 is a graph showing satellite lengths when droplets are ejected using driving waveforms according to Example 1, Example 2, and Comparative Example 1. 13 is a graph showing a change amount of a sub-scanning speed fluctuation ratio. FIG. 11 is a waveform diagram showing a pulse P3 in a driving waveform according to the first embodiment. FIG. 11 is a waveform diagram showing a pulse P5 in a drive waveform according to a second embodiment. 11 is a waveform diagram showing a pulse P13 in a drive waveform according to Comparative Example 1. FIG. FIG. 13 is a waveform diagram showing a pulse P15 in a drive waveform according to Comparative Example 1. FIG. 2 is a waveform diagram showing the waveform shape of a drive pulse, and is a waveform diagram showing a single pulse consisting of a single waveform. 13 is a graph showing the relationship between pulse width Pw and droplet velocity.

A liquid ejection device, a program, and a head drive control method according to an embodiment of the present invention will be described below with reference to the drawings. In this specification, an image forming device that forms an image on a medium using liquid will be described as an example of a liquid ejection device according to an embodiment.

<Overview of Image Forming Apparatus>
FIG. 1 is a schematic side view showing an image forming apparatus according to an embodiment. FIG. 2 is a plan view of the image forming apparatus according to an embodiment. The image forming apparatus 1 shown in FIG. 1 and FIG. 2 is a serial type inkjet recording apparatus. The image forming apparatus 1 includes a carriage 33 carrying recording heads 34a and 34b. The carriage 33 is slidably supported by a pair of guide rods 31 and 32 extending in the main scanning direction, and moves in the main scanning direction. The carriage 33 is capable of scanning in the main scanning direction. The pair of guide rods 31 and 32 are supported by left and right side plates 21A and 21B of the apparatus main body. The main scanning motor transmits power via a timing belt to move the carriage 33.

<Recording head>
The recording heads 34a and 34b are examples of liquid ejection heads. When there is no need to distinguish between the recording heads 34a and 34b, they will be referred to as recording heads 34. The recording heads 34 eject liquid droplets of each color, yellow (Y), cyan (C), magenta (M), and black (K). The liquid droplets may be ink droplets. The recording head 34 has a nozzle plate in which a plurality of nozzles that eject liquid droplets are formed. A plurality of nozzle rows are formed in the nozzle plate. The nozzle row has a plurality of nozzles aligned in the sub-scanning direction. The sub-scanning direction intersects with the main scanning direction. The recording head 34 ejects liquid droplets, for example, downward.

Each recording head 34 has two nozzle rows. Recording head 34a has a nozzle row that ejects black (K) droplets and a nozzle row that ejects cyan (C) droplets. Recording head 34b has a nozzle row that ejects magenta (M) droplets and a nozzle row that ejects yellow (Y) droplets. Note that recording head 34 may have one nozzle row or three or more nozzle rows.

<Head tank>
The carriage 33 is equipped with head tanks 35a and 35b. The head tanks 35a and 35b store inks corresponding to the respective colors. The head tanks 35a and 35b supply the inks of the respective colors to the recording head 34.

<Ink cartridge>
Ink cartridges 10y, 10m, 10c, and 10k of each color are removably mounted in the image forming device 1. When there is no need to distinguish between the ink cartridges 10y, 10m, 10c, and 10k, they will be referred to as ink cartridge 10. The ink cartridge 10 communicates with head tanks 35a and 35b via a supply tube 36. The ink cartridge 10 supplies ink of each color to the head tanks 35a and 35b.

<Paper Feeding Section>
The image forming apparatus 1 includes a paper feed section. The paper feed section supplies paper 42 to the recording head 34. The paper 42 is an example of a medium. The paper feed section has a paper feed tray 2 that holds a plurality of papers 42. The papers 42 are stacked on a paper stacking section 41 of the paper feed tray 2. The paper feed section includes a half-moon roller (paper feed roller) 43 and a separation pad 44. The half-moon roller 43 and the separation pad 44 are disposed opposite each other. The half-moon roller 43 and the separation pad 44 separate and transport the papers 42 one by one from the paper stacking section 41.

The paper feed section includes a guide member 45, a counter roller 46, a transport guide 47, and a pressing member 48 having a tip pressure roller 49. The paper feed section supplies paper 42 below the recording head 34.

<Transportation section>
The image forming apparatus 1 includes a transport unit. The transport unit includes a transport belt 51. The transport belt 51 electrostatically attracts the paper 42 and transports it to a position facing the recording head 34. The transport belt 51 transports the paper 42 by electrostatic attraction. The transport belt 51 is an endless belt, and is stretched between a transport roller 52 and a tension roller 53. The transport belt 51 transports the paper 42 in the sub-scanning direction. The transport belt 51 is driven by the transport roller 52.

The conveying section includes a charging roller 56 that charges the surface of the conveying belt 51. The charging roller 56 is arranged to contact the surface of the conveying belt 51 and rotate in response to the rotation of the conveying belt 51.

<Paper ejection section>
The image forming apparatus 1 includes a paper discharge section. The paper discharge section discharges paper 42 on which an image has been formed by droplets ejected from the recording head 34. The paper discharge section includes a separation claw 61, a paper discharge roller 62, and a spur 63 which is a paper discharge roller. The paper discharge section separates paper 42 from the conveyor belt 51. The paper discharge section includes a paper discharge tray 3. The paper discharge tray 3 receives paper 42 separated from the conveyor belt 51.

<Duplex unit>
The image forming apparatus 1 includes a duplex unit 71. The duplex unit 71 is detachably attached to the rear part of the main body of the image forming apparatus 1. The duplex unit 71 takes in and inverts the paper 42 returned by the reverse rotation of the conveyor belt 51. The duplex unit 71 again supplies the paper 42 between the counter roller 46 and the conveyor belt 51. The upper surface of the duplex unit 71 is used as a manual feed tray 72.

<Maintenance and recovery mechanism>
The image forming apparatus 1 includes a maintenance and recovery mechanism 81. The maintenance and recovery mechanism 81 is disposed in a non-printing region on one side in the main scanning direction. The maintenance and recovery mechanism 81 executes a maintenance operation for maintaining or recovering the state of the nozzles of the recording head 34. The maintenance and recovery mechanism 81 includes caps 82a and 82b for capping the nozzle surface of the recording head 34. The nozzle surface is the bottom surface of the nozzle plate, and is the surface on which the nozzles are formed.

The maintenance and recovery mechanism 81 includes a wiper member 83 and an empty discharge receiver 88. The wiper member 83 wipes the nozzle surface. The empty discharge receiver 88 receives droplets discharged from the recording head 34. The recording head 34 can perform empty discharge, which discharges viscous liquid. The droplets discharged by performing empty discharge do not contribute to image formation and are received by the empty discharge receiver 88.

The maintenance and recovery mechanism 81 includes a carriage lock 87 that locks the carriage 33. The image forming device 1 includes a waste liquid tank 100 for storing waste liquid generated by the maintenance and recovery operation. The waste liquid tank 100 is disposed below the maintenance and recovery mechanism 81. The waste liquid tank 100 is detachably attached to the device body.

The image forming device 1 is provided with an empty discharge receiver 88 arranged in a non-printing area on the other side of the main scanning direction. The empty discharge receiver 88 receives droplets discharged from the recording head 34 during empty discharge. An opening 89 is formed in the empty discharge receiver 88. The opening 89 is aligned along the direction in which the nozzle rows of the recording head 34 are arranged.

<Operation of Image Forming Apparatus 1>
In the image forming apparatus 1, paper 42 is fed from the paper feed tray 2. The paper 42 is guided by a guide member 45 and conveyed while being sandwiched between a conveyor belt 51 and a counter roller 46. The leading edge of the paper 42 is guided by a conveyor guide 47 and pressed against the conveyor belt 51 by a leading edge pressure roller 49. This changes the conveying direction of the paper 42 by approximately 90 degrees.

At this time, the conveyor belt 51 is charged with an alternating charging voltage pattern by the charging roller 56. When the paper 42 is fed onto the charged conveyor belt 51, the paper 42 is attracted to the conveyor belt 51, and the paper 42 is conveyed in the sub-scanning direction by the circular movement of the conveyor belt 51.

The image forming device 1 drives the recording head 34 in response to an image signal while moving the carriage 33. The recording head 34 ejects droplets onto the stationary paper 42 to record one line, and then records the next line after transporting the paper 42 a predetermined distance. The image forming device 1 ends the recording operation by receiving a recording end signal or a signal indicating that the rear end of the paper 42 has reached the recording area, and ejects the paper 42 onto the paper ejection tray 3.

<Recording head>
Next, the recording head will be described with reference to Fig. 3 and Fig. 4. Fig. 3 and Fig. 4 are cross-sectional views of the recording head. Fig. 3 and Fig. 4 are cross-sectional views along the longitudinal direction of an individual liquid chamber. The longitudinal direction of the individual liquid chamber is a direction perpendicular to the arrangement direction of the nozzle row.

This recording head 34 includes a flow path plate 101, a vibration plate member 102, and a nozzle plate 103. The flow path plate 101 is laminated on the nozzle plate 103. The vibration plate member 102 is laminated on the flow path plate 101.

The nozzle plate 103 has a nozzle 104 that ejects droplets. The flow path plate 101 has a through hole 105, an individual liquid chamber 106, a fluid resistance portion 107, and a liquid introduction portion 108. The through hole 105 communicates with the nozzle 104. The through hole 105, the individual liquid chamber 106, the fluid resistance portion 107, and the liquid introduction portion 108 communicate with each other.

The recording head 34 includes a frame member 117. The frame member 117 has a common liquid chamber 110. The vibration plate member 102 has a filter portion 109. The filter portion 109 is disposed between the common liquid chamber 110 and the liquid introduction portion 108. The common liquid chamber 110 supplies ink to the liquid introduction portion 108.

The ink in the liquid introduction section 108 flows through the fluid resistance section 107 and is supplied to the individual liquid chamber 106. The ink in the individual liquid chamber 106 flows through the through hole 105 and is ejected from the nozzle 104. Note that the "individual liquid chamber" may also be called a pressurized chamber, pressurized liquid chamber, pressure chamber, individual flow path, pressure generation chamber, etc.

The flow path plate 101 is formed by laminating metal plates such as SUS (stainless steel). Openings and grooves are formed in the flow path plate 101. These openings and grooves form the through holes 105, individual liquid chambers 106, fluid resistance sections 107, and liquid introduction sections 108.

The vibration plate member 102 forms the walls of each individual liquid chamber 106, the fluid resistance portion 107, and the liquid introduction portion 108. The vibration plate member 102 also forms the filter portion 109. Note that the flow path plate 101 is not limited to a metal plate such as SUS, but can also be formed by anisotropically etching a silicon substrate.

The recording head 34 includes a piezoelectric member 112. The piezoelectric member 112 is disposed on the surface of the vibration plate member 102 opposite the individual liquid chamber 106. The piezoelectric member 112 is an actuator (pressure generating unit) that generates energy for ejecting droplets. The piezoelectric member 112 is stacked to form a column. An FPC (Flexible Printed Circuits) 115 that transmits a drive waveform is connected to the piezoelectric member 112.

The piezoelectric member 112 is used in a d33 mode in which it expands and contracts in the stacking direction. The piezoelectric member 112 is not limited to being used in a d33 mode, but may be used in a d31 mode in which it expands and contracts in a direction perpendicular to the stacking direction.

The recording head 34 contracts the piezoelectric member 112 by lowering the voltage applied to the piezoelectric member 112 from the reference potential Ve. As the piezoelectric member 112 contracts, the vibration plate member 102 deforms and the volume of the individual liquid chamber 106 expands. This causes ink to flow from the fluid resistance portion 107 into the individual liquid chamber 106.

The recording head 34 contracts the piezoelectric member 112 and then expands it. As shown in FIG. 4, the recording head 34 increases the voltage applied to the piezoelectric member 112 to expand the piezoelectric member 112 in the stacking direction. By expanding the piezoelectric member 112 in the stacking direction, the vibration plate member 102 is deformed in the opposite direction to the piezoelectric member 112, causing the volume of the individual liquid chamber 106 to contract. This pressurizes the ink in the individual liquid chamber 106, causing droplets to be ejected from the nozzle 104.

The recording head 34 restores the vibration plate member 102 to its initial position by returning the voltage applied to the piezoelectric member 112 to the reference potential Ve. At this time, the individual liquid chamber 106 expands. This causes ink to fill the individual liquid chamber 106 from the common liquid chamber 110. After the vibration of the meniscus surface of the nozzle 104 has attenuated and stabilized, the operation proceeds to eject the next droplet.

<Natural vibration period Tc>
Next, the natural vibration period Tc of the individual liquid chamber 106 of the recording head will be described. As described above, the recording head 34 pressurizes the ink inside the individual liquid chamber 106 by varying the volume of the individual liquid chamber 106, and ejects droplets from the nozzle 104. At this time, when the ink inside the individual liquid chamber 106 is pressurized, pressure vibration occurs according to the natural vibration frequency of the individual liquid chamber 106. The period of this pressure vibration is called the natural vibration period Tc of the individual liquid chamber 106. In general, the natural vibration period Tc of the individual liquid chamber 106 corresponds to the natural vibration period of the ink pressure determined by the physical properties of the ink, the shapes of the individual liquid chamber 106 and the nozzle 104, the materials of the individual liquid chamber 106 and the flow path, etc., and is called the Helmholtz period.

<Image forming apparatus 1>
Next, an overview of the control section of the image forming apparatus 1 will be described with reference to Fig. 5. Fig. 5 is a block diagram of the control section. The image forming apparatus 1 includes a control section (control device).

This control unit 500 comprises a CPU (Central Processing Unit) 501 which controls the entire device, a ROM (Read Only Memory) 502 which stores fixed data such as various programs including those executed by the CPU 501, and a RAM (Random Access Memory) 503 which temporarily stores image data and the like. The control unit also comprises a rewritable non-volatile memory 504 for retaining data even when the power to the control unit is cut off, and an ASIC (Application Specific Integrated Circuit) 505 which processes input/output signals for image processing such as various signal processing and sorting of image data, and other control of the entire device.

The control unit 500 includes a print control unit 508. The print control unit 508 includes a data transfer unit and a drive signal generation unit for driving and controlling the recording head 34. The carriage 33 includes a head driver (driver IC) 509 for driving the recording head 34. The head driver 509 is an example of a head drive control unit. The head driver 509 can execute a head drive control method. Note that some or all of the processing executed by the head driver 509 may be executed by the control unit 500.

The control unit 500 includes a motor drive unit 510. The image forming apparatus 1 includes a main scanning motor 554, a sub-scanning motor 555, and a maintenance recovery motor 556. The main scanning motor 554 moves and scans the carriage 33. The sub-scanning motor 55 moves the conveyor belt 51 in a circular motion. The maintenance recovery motor 556 outputs power used for driving the cap 82 of the maintenance recovery mechanism 81, moving the wiper member 83, and suction by the suction pump. The motor drive unit 510 executes drive control of the main scanning motor 554, the sub-scanning motor 555, and the maintenance recovery motor 556.

The control unit 500 includes an AC bias supply unit 511 and a supply system drive unit 512. The AC bias supply unit 511 supplies an AC bias to the charging roller 56. The supply system drive unit 512 controls the drive of the liquid feed pump 241. The image forming apparatus 1 includes the liquid feed pump 241. The liquid feed pump 241 supplies ink in the ink cartridge 10 to the head tank 35.

An operation panel 514 is connected to the control unit 500 for inputting and displaying information required for this device.

The control unit 500 includes a host I/F 506. The host I/F 506 is an interface for transmitting and receiving data and signals to and from the host 600. The host 600 is, for example, an information processing device such as a personal computer, an image reading device, or an imaging device. The control unit 500 is connected to the host 600 via a cable or a network. The control unit 500 receives data and signals from the host 600 via the I/F 506.

The CPU 501 of the control unit 500 reads and analyzes the print data in the receive buffer included in the I/F 506. The ASIC 505 performs necessary image processing, data sorting, etc. on the analyzed print data. The control unit 500 transfers the image data processed by the ASIC 505 from the print control unit 508 to the head driver 509. The host 600 includes a printer driver 601. The printer driver 601 can generate dot pattern data to output an image. The control unit 500 may also generate the dot pattern data.

The print control unit 508 can transfer the image data described above as serial data. The print control unit 508 outputs a transfer clock, latch signal, control signal, and other signals required for transferring this image data and confirming the transfer to the head driver 509.

The control unit 500 includes a drive signal generating unit. The drive signal generating unit includes a D/A converter, a voltage amplifier, and a current amplifier. The drive signal generating unit performs D/A conversion of the drive waveform pattern data stored in the ROM. The drive waveform includes one or more drive pulses. The print control unit 508 outputs the drive waveform to the head driver 509.

The head driver 509 selects a drive pulse included in the drive waveform. The head driver 509 selects a drive pulse based on image data corresponding to one row of the recording head 34 that is serially input. The head driver 509 supplies the selected drive pulse to the piezoelectric member 112. The head driver 509 drives the recording head 34 by supplying the drive pulse to the piezoelectric member 112.

The head driver 509 can print dots of different sizes by selecting some or all of the drive pulses that make up the drive waveform. Dots of different sizes include large, medium, and small droplets, for example. The head driver 509 can print large, medium, and small droplets by selecting some or all of the waveform elements that make up the drive pulse.

The control unit 500 includes an I/O unit 513. The image forming device 1 includes a group of various sensors 515. The I/O unit 513 acquires information from the group of various sensors 515. The I/O unit 513 extracts information necessary for controlling the printer from the acquired information. The print control unit 508, the motor drive unit 510, and the AC bias supply unit 511 use the extracted information for various controls.

The image forming device 1 includes a sensor group 515, which includes an optical sensor for detecting the position of the paper, a thermistor for monitoring the temperature inside the device, a sensor for monitoring the voltage of the charged belt, and an interlock switch for detecting whether the cover is open or closed.

<Printing control unit and head driver>
Next, an example of the print control unit 508 and the head driver 509 will be described with reference to the block diagram of Fig. 6. Fig. 6 is a block diagram showing the print control unit and the head driver.

The print control unit 508 includes a drive waveform generation unit 701 and a data transfer unit 702. The drive waveform generation unit 701 generates and outputs a drive waveform (common drive waveform) consisting of multiple pulses (drive signals) within one printing cycle (one drive cycle) during image formation. The data transfer unit 702 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.

The droplet control signal is a two-bit signal that instructs the opening and closing of the analog switch 715 for each droplet. The analog switch 715 is a switch of the head driver 509. The droplet control signal transitions to an H level (ON) state when a pulse or waveform element that should be selected in accordance with the printing cycle of the common drive waveform is selected, and transitions to an L level (OFF) state when not selected.

The print control unit 508 selects a pulse for large droplets with the droplet control signal M3, selects a pulse for medium droplets with the droplet control signal M2, selects a pulse for small droplets with the droplet control signal M2, and selects a pulse for fine drive with the droplet control signal M0.

The head driver 509 has a shift register 711 and a latch circuit 712. The shift register 711 inputs a transfer clock (shift clock) and serial image data (gradation data: 2 bits/1 channel (1 nozzle) from the data transfer unit 702. The latch circuit 712 latches each register value of the shift register 711 by a latch signal.

The head driver 509 has a decoder 713 and a level shifter 714. The decoder 713 decodes the gradation data and the droplet control signals M0 to M3 and outputs the result. The level shifter 714 converts the level of the logic level voltage signal of the decoder 713. The level shifter 714 converts the logic level voltage signal of the decoder 713 to a level at which the analog switch 715 can operate. The analog switch 715 is turned on/off (opened/closed) by the output of the decoder 713 provided via the level shifter 714.

This analog switch 715 is connected to the selection electrode (individual electrode) of each piezoelectric member 112. The drive waveform generation unit 701 inputs the common drive waveform Pv to the analog switch 715. 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. When the analog switch 715 is turned on, the required pulses (or waveform elements) that make up the common drive waveform Pv pass (are selected), and the passed pulses are applied to the piezoelectric members 112.

Next, the drive waveform in the first embodiment will be described with reference to FIG. 7. FIG. 7 is a waveform diagram showing a drive waveform according to the embodiment. In FIG. 7, the horizontal axis indicates time, and the vertical axis indicates potential.

The term "pulse" is used to refer to a drive pulse that is an element that constitutes a drive waveform. The term "ejection pulse" is used to refer to a drive pulse that is given to the pressure generating unit to eject droplets. The term "non-ejection pulse" is used to refer to a drive pulse (micro drive pulse) that is given to the pressure generating unit but drives the pressure generating unit to the extent that it does not eject droplets (makes the ink in the nozzle flow). The drive waveforms and the pulses that are their components that are described below are examples and are not limiting.

The drive waveform (common drive waveform) Pv shown in FIG. 7 includes pulses P1 to P5 within one printing cycle (one drive cycle). Pulse P1 is a micro-drive pulse. Pulses P2 to P5 are ejection pulses. Pulses P1 to P5 are generated in time series.

Figure 8 shows a drive waveform including multiple pulses, a droplet control signal, and a pulse corresponding to the droplet size. In Figure 8, these are shown on the horizontal axis. From the top, Figure 8 shows the drive waveform Pv, droplet control signals M0 to M3, a waveform for large droplets, a waveform for medium droplets, a waveform for small droplets, and a waveform for fine drive.

The head driver 509 selects pulses P1 to P5 in response to the droplet control signals M3 to M0 shown in FIG. 8. The head driver 509 supplies the selected pulses P1 to P5 to the pressure generating section. Depending on the droplet size, one or more pulses are selected. As a result of this selection, a large droplet ejection drive waveform (large droplet waveform), a medium droplet ejection drive waveform (medium droplet waveform), a small droplet ejection drive waveform (small droplet waveform), and a fine drive waveform are obtained.

The large droplet waveform includes pulses P1 to P5. The large droplet waveform is obtained by selecting pulses P1 to P5. Pulses P2 to P5 are supplied to the pressure generating section, causing droplets to be ejected. The droplets ejected by selecting pulses P2 to P5 combine in flight to form a large droplet.

The waveform for medium droplets includes pulses P2 and P4. The waveform for medium droplets is obtained by selecting pulses P2 and P4. Pulses P2 and P4 are supplied to the pressure generating unit, causing droplets to be ejected. The droplets ejected by selecting pulses P2 and P4 combine in flight to form a medium droplet.

The small droplet waveform includes pulse P3. By selecting pulse P3, a small application waveform is obtained. By supplying pulse P3 to the pressure generating unit, droplets (small droplets) are ejected.

The micro-driving waveform includes a pulse P1. By selecting the pulse P1, the micro-driving waveform is obtained. By supplying the pulse P1 to the pressure generating section, the vibration plate member 102 vibrates micro-vibrations.

<Pulse P5>
Next, the final pulse P5, which is the last of the multiple pulses included in the large droplet waveform, will be described in detail with reference to Fig. 9. Fig. 9 is a waveform diagram showing the final pulse P5. In Fig. 9, the horizontal axis represents time, and the vertical axis represents potential. Times t0 to t11 pass in this order.

This pulse P5 has a first expansion waveform element (first retraction waveform element) a1, a hold waveform element b1, a first contraction waveform element (first push-in waveform element) c1, a hold waveform element b2, a second expansion waveform element (second retraction waveform element) a2, a hold waveform element b3, a second contraction waveform element (second push-in waveform element) c2, a hold waveform element b4, and a third expansion waveform element (third retraction waveform element) a3.

The first expansion waveform element a1 expands the individual liquid chamber 106 by decreasing from the reference potential Ve to a potential Vf. The potential Vf is a potential lower than the reference potential Ve. The first expansion waveform element a1 is at the reference potential Ve at time t1 and decreases to the potential Vf at time t2.

The hold waveform element b1 holds the potential Vf for a predetermined time. The hold waveform element b1 holds the potential Vf from time t2 to time t3.

The first contraction waveform element c1 rises from potential Vf to potential Vg (Vg>Ve), contracting the individual liquid chamber 106 and ejecting a droplet. The first contraction waveform element c1 is at potential Vf at time t3 and increases to potential Vg at time t4.

The hold waveform element b2 holds the rising potential Vg of the first contraction waveform element c1 for a predetermined time. The hold waveform element b2 holds the potential Vg from time t4 to time t5.

The second expansion waveform element a2 drops from potential Vg to potential Vf, expanding the individual liquid chamber 106 and tearing off a portion of the droplet ejected by the first contraction waveform element c1 and returning it to the nozzle 104. The second expansion waveform element a2 is at potential Vg at time t5 and drops to potential Vf at time t6.

The hold waveform element b3 holds the potential Vf for a predetermined time. The hold waveform element b3 holds the potential Vf from time t6 to time t7.

The second contraction waveform element c2 rises from potential Vf to potential Vh (Vg<Vh), contracting the individual liquid chamber 106 and ejecting a droplet. The second contraction waveform element c2 is at potential Vf at time t7 and increases to Vh at time t8.

The hold waveform element b4 holds the rising potential Vh of the second contraction waveform element c2 for a predetermined time. The hold waveform element b4 holds the potential Vh from time t8 to time t9.

The third expansion waveform element a3 decreases from potential Vh to potential Vi, expanding the individual liquid chamber 106 and tearing off a portion of the droplet ejected by the second contraction waveform element c2 and returning it to the nozzle 104. No droplets are ejected by this third expansion waveform element a3.

The first contraction waveform element c1 is a waveform element that contracts the individual liquid chamber 106 at a timing that resonates with the pressure fluctuation in the individual liquid chamber 106 caused by the first expansion waveform element a1.

The second contraction waveform element c2 is a vibration damping waveform element that suppresses the pressure fluctuations in the individual liquid chamber 106 caused by the first expansion waveform element a1, the first contraction waveform element c1, and the second expansion waveform element a2.

The third expansion waveform element a3 is a vibration damping waveform element that suppresses pressure fluctuations in the individual liquid chamber 106 that could not be suppressed by the second contraction waveform element c2.

<Method of measuring natural vibration period Tc>
Next, a method for measuring the natural vibration period Tc will be described before explaining the relationship between the start and end of each waveform element of the pulse P5 shown in FIG.

Figure 18 is a waveform diagram showing the waveform shape of a drive pulse, and is a waveform diagram showing a single pulse consisting of a single waveform. The drive pulse includes a waveform element Tf in which the potential falls from a reference potential Ve. The falling waveform element Tf may be a fall time. When the waveform element Tf in which the potential falls from the reference potential Ve is supplied to the piezoelectric member 112, the piezoelectric member 112 contracts and the volume of the individual liquid chamber 106 expands.

The drive pulse includes a pulse width Pw. The pulse width Pw is the waveform element following the waveform element Tf. The pulse width Pw is a waveform element for maintaining the state of the piezoelectric element 112 as a hold state. The state of the piezoelectric element 112 is maintained by supplying the waveform element with the pulse width Pw to the piezoelectric element 112. This is called a hold state.

The drive pulse includes a waveform element Tr that rises from a potential that is in a hold state due to the pulse width Pw. The rising waveform element Tr may be the rising time. When the rising waveform element Tr is supplied to the piezoelectric member 112, the piezoelectric member 112 expands and the individual liquid chamber 106 contracts.

Figure 19 is a graph showing the relationship between pulse width Pw and droplet velocity. The relationship between pulse width Pw and droplet velocity is called the pulse width Pw characteristic. When the pulse width Pw supplied to the piezoelectric member 112 is changed, the meniscus vibrates at the resonance period of the Helmholtz natural vibration. The resonance period of the Helmholtz natural vibration is determined by the ink flow path system, vibration system, dimensions of the piezoelectric element, material system, physical properties, etc., which are made up of several types of bonded thin plates. When the timing at which the meniscus moves out of the nozzle coincides with the timing at which the meniscus is pushed out by the waveform element Tr, which is the rising element, the force pushing out the meniscus is maximized and the droplet velocity is maximized.

When the pulse width Pw is increased, multiple peaks appear. In FIG. 20, the first peak that appears is shown as the first peak Pw1, and the next peak that appears is shown as Pw2. The natural vibration period Tc of the pressure resonance is calculated from the difference between the first peak Pw1 and the second peak Pw2.

Next, we will explain the relationship between the start and end of each waveform element of pulse P5 shown in Figure 9 and the natural vibration period Tc.

The time T1 from the start of the first expansion waveform element a1 to the start of the first contraction waveform element c1 is 0.45Tc to 0.65. This improves the droplet ejection efficiency. Time T1 is from time t1 to time t3.

The time T2 from the start of the first contraction waveform element c1 to the start of the second expansion waveform element a2 is less than 0.5Tc. This allows the satellite length to be shortened. Time T2 is from time t3 to time t5.

The time T3 from the start of the first contraction waveform element c1 to the start of the second contraction waveform element c2 is in the range of 0.5Tc to 0.6Tc. The time T4 from the start of the first contraction waveform element c1 to the start of the third expansion waveform element a3 is 0.9Tc to 1.0Tc. As a result, the second contraction waveform element c2 and the third expansion waveform element a3 become vibration damping waveform elements that suppress the pressure fluctuations in the individual liquid chamber 106 that are caused by the first expansion waveform element a1, the first contraction waveform element c1, and the second expansion waveform element a2.

Note that times T1 to T4 are not limited to the above. For example, time T3 may be a time that allows the second contraction waveform element c2 to contract the individual liquid chamber 106 in the opposite phase to the pressure fluctuation in the individual liquid chamber 106.

Next, the droplet ejection state will be explained with reference to Figure 10. Figure 10 shows droplets ejected from a nozzle.

By applying the first expansion waveform element a1 from the state shown in FIG. 10(a), the meniscus 300 is drawn into the nozzle 104 as shown in FIG. 10(b), and after a predetermined time has passed, the first contraction waveform element c1 is applied, causing the portion that will become the droplet 301 to protrude as shown in FIG. 10(c). At this time, by applying the second expansion waveform element a2, a part of the droplet 301 is torn off and returned to the nozzle 104 as shown in FIG. 10(d).

As a result, the droplets 301 become smaller droplets, and the tail portions of the droplets 301 that become satellites or mist are torn off and returned to the nozzle 104, thereby reducing the amount of satellites and mist.

<Pulse P3>
Next, the pulse P3 will be described with reference to Fig. 14. Fig. 14 is a waveform diagram showing the pulse P3. In Fig. 14, the horizontal axis indicates time, and the vertical axis indicates potential. Times t31 to t38 shown on the horizontal axis pass in this order. As described above, the pulse P3 is included in the waveform for large droplets and the waveform for small droplets.

This pulse P3 has a first expansion waveform element a31, a hold waveform element b31, a first contraction waveform element c31, a hold waveform element b32, a second expansion waveform element a32, a hold waveform element b33, and a second contraction waveform element c32.

The first expansion waveform element a31 expands the individual liquid chamber 106 by decreasing from the reference potential Ve to a potential Vf3. The potential Vf3 is a potential lower than the reference potential Ve. The first expansion waveform element a31 is at the reference potential Ve at time t31 and decreases to the potential Vf3 at time t32.

The hold waveform element b31 holds the potential Vf3 for a predetermined time. The hold waveform element b31 holds the potential Vf3 from time t32 to time t33.

The first contraction waveform element c31 rises from potential Vf3 to potential Vg3 (Vg3<Ve), contracting the individual liquid chamber 106 and ejecting a droplet. The first contraction waveform element c31 is at potential Vf3 at time t33 and increases to potential Vg3 at time t34.

The hold waveform element b32 holds the rising potential Vg3 of the first contraction waveform element c31 for a predetermined time. The hold waveform element b32 holds the potential Vg3 from time t34 to time t35.

The second expansion waveform element a32 drops from potential Vg3 to potential Vf3, expanding the individual liquid chamber 106 and tearing off a portion of the droplet ejected by the first contraction waveform element c31 and returning it to the nozzle 104. The second expansion waveform element a32 is at potential Vg3 at time t35 and drops to potential Vf3 at time t36.

The hold waveform element b33 holds the potential Vf3 for a predetermined time. The hold waveform element b33 holds the potential Vf3 from time t36 to time t37.

The second contraction waveform element c32 rises from potential Vf3 to potential Ve, contracting the individual liquid chamber 106 and ejecting a droplet. The second contraction waveform element c32 is at potential Vf3 at time t37 and increases to the reference potential Ve at time t38.

The time T31 from the start of the first expansion waveform element a31 to the start of the first contraction waveform element c31 is in the range of 0.45Tc to 0.65Tc. This improves the droplet ejection efficiency. The time T31 is from time t31 to time t33.

The time T32 from the start of the first contraction waveform element c31 to the start of the second expansion waveform element a32 is less than 0.5Tc. This allows the satellite length to be shortened. The time T32 is from time t33 to time t35.

The time T33 from the start of the first contraction waveform element c31 to the start of the second contraction waveform element c32 is 0.5Tc. This allows the residual vibration generated in the first contraction waveform element c31 to be suppressed by the second contraction waveform element c32. The time T33 is from time t33 to time t37.

Note that times T31 to T33 are not limited to the above. For example, time T33 may be a time that allows contraction of the individual liquid chamber 106 by the second contraction waveform element c32 in the opposite phase to the pressure fluctuation of the individual liquid chamber 106.

[Functions and Effects of Image Forming Apparatus 1 According to the Embodiment]
The image forming apparatus (liquid ejection apparatus) 1 according to this embodiment generates a final pulse P5 including a first expansion waveform element a1 for expanding the individual liquid chamber 106, a first contraction waveform element c1 for contracting the individual liquid chamber 106, a second expansion waveform element a2 for expanding the individual liquid chamber 106, a second contraction waveform element c2 for contracting the individual liquid chamber 106, and a third expansion waveform element a3 for expanding the individual liquid chamber 106. The image forming apparatus 1 outputs a drive waveform including the final pulse P5 at the end of the time series of pulses P1 to P5 to the piezoelectric member 112 (pressure generating unit) by the head driver 509 (head drive control unit). As a result, in the image forming apparatus 1, ejection bending is suppressed during ejection at a high frequency, and the generation of mist is reduced, thereby reducing dirt inside the machine.

For example, the first contraction waveform element c1 contracts the individual liquid chamber 106 at a timing that resonates with the pressure fluctuation in the individual liquid chamber 106 caused by the first expansion waveform element a1, and the second contraction waveform element c2 suppresses the pressure fluctuation in the individual liquid chamber 106. By ejecting droplets using a drive waveform that includes a final pulse P5 that includes such waveform elements, residual vibration in the individual liquid chamber 106 can be suppressed.

The time T2 from the start of the first contraction waveform element c1 to the start of the second expansion waveform element a2 is less than 0.5Tc, and the time T3 from the start of the first contraction waveform element c1 to the start of the second contraction waveform element c2 is in the range of 0.5Tc to 0.6Tc. By ejecting droplets using a pulse P5 that includes such waveform elements, ejection bending can be suppressed during ejection at high frequencies, and the generation of mist can be reduced, reducing dirt inside the machine.

The time T1 from the start of the first expansion waveform element a1 to the start of the first contraction waveform element c1 may be in the range of 0.45 to 0.65 Tc. The time T4 from the start of the first contraction waveform element c1 to the start of the third expansion waveform element a3 may be in the range of 0.9 Tc to 1.0 Tc.

<Image forming apparatus according to the second embodiment>
Next, the driving waveform in the image forming apparatus 1 according to the second embodiment will be described. The driving waveform in the second embodiment includes pulses P1, P2, P3, P4, and P5, similar to the driving waveform in the first embodiment shown in Figs. 7 and 8. The time T31 of the pulse P3 in the driving waveform in the second embodiment is different in length from the time T31 of the pulse P3 in the driving waveform in the first embodiment. The times T1 and T4 of the pulse P5 in the driving waveform in the second embodiment are different in length from the times T1 and T4 of the pulse P5 in the driving waveform in the first embodiment. In the description of the second embodiment, the same description as in the first embodiment may be omitted.

<Pulse P3>
As described above, the pulse P3 of the second embodiment differs from the pulse P3 of the first embodiment in the length of the time T31. The pulse P3 of the second embodiment will be described with reference to FIG.

The time T31 from the start of the first expansion waveform element a31 to the start of the first contraction waveform element c31 is 0.3Tc. The time T31 of the pulse P3 in the second embodiment is shorter than the time T31 of the pulse P3 in the first embodiment.

In the pulse P3 according to the second embodiment, the time T32 is less than 0.5Tc, and the time T33 is 0.5Tc, so that the tail portion of the ejected droplet is torn off and returned to the nozzle 104, thereby reducing satellites and mist. With the pulse P3 according to the second embodiment, the same effect as the pulse P3 according to the first embodiment can be obtained. With the pulse P3 according to the second embodiment, even if the time T31 is 0.3Tc, the same effect as the pulse P3 according to the first embodiment can be obtained.

<Pulse P5>
Next, the pulse P5 of the drive waveform according to the second embodiment will be described with reference to Fig. 15. Fig. 15 is a waveform diagram showing the pulse P5 in the drive waveform according to the second embodiment. As described above, the pulse P5 of the second embodiment differs from the pulse P5 of the first embodiment in the lengths of the times T1 and T4.

The time T1 from the start of the first expansion waveform element a1 to the start of the first contraction waveform element c1 is 0.3Tc. This improves the droplet ejection efficiency. The time T1 from the start of the first expansion waveform element a1 to the start of the first contraction waveform element c1 is in the range of resonance timing that improves the droplet ejection efficiency, from time t1 to time t3.

The time T4 from the start of the first contraction waveform element c1 to the start of the third expansion waveform element a3 is 1.25Tc. As a result, the second contraction waveform element c2 and the third expansion waveform element a3 become vibration-damping waveform elements that suppress the pressure fluctuations in the individual liquid chamber 106 that have fluctuated due to the first expansion waveform element a1, the first contraction waveform element c1, and the second expansion waveform element a2. This time T4 is the time at which the second contraction waveform element c2 and the third expansion waveform element a3 become vibration-damping waveform elements that suppress the pressure fluctuations in the individual liquid chamber 106 that have fluctuated due to the first expansion waveform element a1, the first contraction waveform element c1, and the second expansion waveform element a2.

The pulse P5 according to the second embodiment has a time T2 of less than 0.5Tc and a time T3 of 0.5Tc (within the range of 0.5Tc to 0.6Tc), so that the tail portion of the ejected droplet is torn off and returned to the nozzle 104, thereby reducing satellites and mist. The pulse P5 according to the second embodiment has the same effect as the pulse P5 according to the first embodiment.

[Comparative Example 1]
Next, the drive waveform according to Comparative Example 1 will be described with reference to Fig. 11, Fig. 16, and Fig. 17. Fig. 11 is a waveform diagram showing the drive waveform according to Comparative Example 1. Fig. 11 shows the drive waveform Pv11 according to the comparative example. The drive waveform Pv11 includes pulses P1, P2, P13, P4, and P15. The drive waveform Pv11 differs from the drive waveform Pv shown in Fig. 8 in that it includes a pulse P13 instead of the pulse P3, and a pulse P15 instead of the pulse P5.

<Pulse P13 according to Comparative Example 1>
16 is a waveform diagram showing a pulse P13 in a drive waveform according to Comparative Example 1. The pulse P13 has an expansion waveform element a11, a hold waveform element b11, a contraction waveform element c11, a hold waveform element b12, a contraction waveform element c12, and a hold waveform element b13. As described below, the potential decreases in the expansion waveform element a11. The potential is maintained in the hold waveform elements b11, b12, and b13. The potential increases in the contraction waveform elements c11 and c12.

The expansion waveform element a11 drops from the reference potential Ve to a potential Vf13, causing the individual liquid chamber 106 to expand. The potential Vf13 is a potential lower than the reference potential Ve. The expansion waveform element a11 is at the reference potential Ve at time t131, and drops to the potential Vf13 at time t132.

The hold waveform element b11 holds the potential Vf13 for a predetermined time. The hold waveform element b11 holds the potential Vf13 from time t132 to time t133.

The contraction waveform element c11 rises from potential Vf13 to potential Vg13 (Vg13<Ve), contracting the individual liquid chamber 106 and ejecting a droplet. The contraction waveform element c11 is at potential Vf13 at time t133 and increases to potential Vg13 at time t134.

The hold waveform element b12 holds the rising potential Vg13 of the contraction waveform element c11 for a predetermined time. The hold waveform element b12 holds the potential Vg13 from time t134 to time t135.

The contraction waveform element c12 rises from potential Vg13 to the reference potential Ve, contracting the individual liquid chamber 106 and ejecting a droplet. The contraction waveform element c12 is at potential Vg13 at time t135 and increases to the reference potential Ve at time t136.

The time T131 from the start of the expansion waveform element a11 to the start of the contraction waveform element c11 in pulse P13 is 0.5Tc. The time T131 is from time t131 to time t133.

The time T12 from the start of contraction waveform element c11 to the start of contraction waveform element c12 in pulse P13 is 0.5Tc. Time T132 is from time t133 to time t135.

The time T133 from the end of contraction waveform element c11 to the end of contraction waveform element c12 in pulse P13 is 0.5Tc. Time T133 is from time t134 to time t136.

By using such a pulse P13, the piezoelectric element 112 of the individual liquid chamber 106 can be driven as a vibration damping timing that cancels the residual vibration after the droplet is ejected by the contraction waveform element c11. With such a pulse P13, the droplet ejected by the pulse P13 in the drive waveform of Comparative Example 1 can be made small, and the residual vibration due to the contraction waveform element c11 can be suppressed by the contraction waveform element c12.

However, with pulse P13 in Comparative Example 1, the tail of the ejected droplet cannot be torn off and then returned to the nozzle, so satellites and mist cannot be sufficiently reduced.

<Pulse P15 according to Comparative Example 1>
17 is a waveform diagram showing a pulse P15 in a drive waveform according to Comparative Example 1. The pulse P15 has an expansion waveform element a21, a hold waveform element b21, a contraction waveform element c21, a hold waveform element b22, a contraction waveform element c22, a hold waveform element b23, and an expansion waveform element a22. As described below, the potential decreases in the expansion waveform elements a21 and a22. The potential is maintained in the hold waveform elements b21, b22, and b23. The potential increases in the contraction waveform elements c21 and c22.

The expansion waveform element a21 expands the individual liquid chamber 106 by decreasing from the reference potential Ve to a potential Vf15. The potential Vf15 is a potential lower than the reference potential Ve. The expansion waveform element a21 is at the reference potential Ve at time t151 and decreases to the potential Vf15 at time t152.

The hold waveform element b21 holds the potential Vf15 for a predetermined time. The hold waveform element b21 holds the potential Vf15 from time t152 to time t153.

The contraction waveform element c21 rises from potential Vf15 to potential Vg15 (Vg15>Ve), contracting the individual liquid chamber 106 and ejecting a droplet. The contraction waveform element c21 is at potential Vf15 at time t153 and increases to potential Vg15 at time t154.

The hold waveform element b22 holds the rising potential Vg15 of the contraction waveform element c21 for a predetermined time. The hold waveform element b22 holds the potential Vg15 from time t154 to time t155.

The contraction waveform element c22 rises from potential Vg15 to potential Vh15, contracting the individual liquid chamber 106 and ejecting a droplet. The contraction waveform element c22 is at potential Vg15 at time t155 and increases to potential Vh15 at time t156.

The hold waveform element b23 holds the potential Vh15 for a predetermined time. The hold waveform element b23 holds the potential Vh15 from time t156 to time t157.

The expansion waveform element a22 drops from potential Vh15 to potential Vi15 (Vf15<Vi15<Ve) to expand the individual liquid chamber 106. The expansion waveform element a22 is at potential Vh15 at time t157 and drops to potential Vi15 at time t158.

The time T151 from the start of the expansion waveform element a21 to the start of the contraction waveform element c21 in pulse 15 is 0.5Tc. The time T151 is from time t151 to time t153.

The time T152 from the start of contraction waveform element c21 to the start of contraction waveform element c22 is 0.5Tc. Time T152 is from time t153 to time t155.

The time T153 from the end of contraction waveform element c21 to the end of contraction waveform element c22 is 0.5Tc.

The time T154 from the end of the contraction waveform element c21 to the end of the expansion waveform element a22 is Tc.

By using this type of pulse P15, droplets can be ejected at high speed, and residual vibrations caused by the contraction waveform element c21 can be suppressed by the contraction waveform element c22.

However, with pulse P15 in Comparative Example 1, the tail of the ejected droplet cannot be torn off and then returned to the nozzle, so satellites and mist cannot be sufficiently reduced.

The waveform for large droplets in Comparative Example 1 includes pulses P1, P2, P13, P4, and P15. The waveform for small droplets in Comparative Example 1 includes pulse P13.

[Example 1, Example 2, and Comparative Example 1]
Next, the results of measuring the satellite length when droplets are ejected using the drive waveforms of Example 1, Example 2, and Comparative Example 1 will be described. The drive waveform Pv of Example 1 is the drive waveform Pv of the above-mentioned first embodiment, and is shown in Figures 8, 9, and 14. The drive waveform of Example 2 is the drive waveform Pv of the above-mentioned second embodiment, and is shown in Figures 8, 14, and 15. The drive waveform Pv11 of Comparative Example 1 is shown in Figures 11, 16, and 17, as described above. Figure 12 is a graph showing the satellite length when droplets are ejected using the drive waveforms according to Example 1, Example 2, and Comparative Example 1.

<Satellite Head>
12, bar graphs are shown showing the satellite lengths of, from the left, a large droplet of Example 1, a large droplet of the Example, a large droplet of Comparative Example 1, a small droplet of Example 1, a small droplet of Example 2, and a small droplet of Comparative Example 1. The satellite lengths were measured by actually taking photographs.

The satellite length is measured as the difference (Tjs-Tj) between the time Tj when the main droplet (the leading large droplet) of the ejected droplet reaches the position on the paper 42 and the time Tjs when the tail of the main droplet or a small droplet that arrives at the position on the paper 42 after the main droplet reaches the position on the paper 42. Therefore, the satellite length is expressed in time (μs).

The satellite length of the droplets in Comparative Example 1 was approximately 100 μs. The satellite length of the droplets in Example 1 was approximately 40 μs. The satellite length of the droplets in Example 1 was shorter than the satellite length of the droplets in Comparative Example 1. The satellite length of the droplets in Example 2 was approximately 60 μs. The satellite length of the droplets in Example 1 was shorter than the satellite length of the droplets in Example 2.

These results confirmed that the satellite length can be shortened by using pulse P3 for ejecting droplets in Examples 1 and 2. In other words, it was confirmed that the satellite length can be shortened by setting the time T32 from the start of the first contraction waveform element c31 to the start of the second expansion waveform element a32 of pulse P3 to less than 0.5Tc, and setting the time T33 from the start of the first contraction waveform element c31 to the start of the second contraction waveform element c32 to 0.5Tc.

The satellite length of the large droplets in Comparative Example 1 was approximately 350 μs. The satellite length of the large droplets in Example 1 was approximately 98 μs. The satellite length of Example 2 was 140 μs. The satellite lengths of the large droplets in Examples 1 and 2 were shorter than the satellite length of the large droplets in Comparative Example 1.

These results confirmed that the satellite length can be shortened by using pulse P5, which ejects large droplets in Examples 1 and 2. In other words, it was confirmed that the satellite length of large droplets can be shortened by setting the time T2 from the start of the first contraction waveform element c1 to the start of the second expansion waveform element a2 of pulse P5, which is the final pulse, to less than 0.5Tc, and setting the time T3 from the start of the first contraction waveform element c1 to the start of the second contraction waveform element c2 in the range of 0.5Tc to 0.6Tc.

The satellite length of the large droplets in Example 1 was shorter than that of the large droplets in Example 2. Therefore, it was confirmed that the satellite length can be further shortened by setting the time T1 from the start of the first expansion waveform element a1 to the start of the first contraction waveform element c1 of pulse P5 in the range of 0.45Tc to 0.65Tc, and setting the time T4 from the start of the first contraction waveform element c1 to the start of the third expansion waveform element a3 in the range of 0.9Tc to 1.0Tc.

In the case of the large droplets in Comparative Example 1, when the frequency was 12 kHz, the main droplets were deflected by several tens of μm. The spacing between the multiple nozzles was 169.3 μm. In this case, the deflection of the main droplets affects image formation. In the case of the small droplets in Comparative Example 1, no deflection of the main droplets was detected.

In the case of small droplets in Examples 1 and 2, no deflection of the ejection was detected. In the case of large droplets in Examples 1 and 2, no deflection of the main droplet was observed at a frequency of 12 kHz. Furthermore, in the case of large droplets in the Example, no deflection of the main droplet was observed even when the frequency was increased to a maximum of 24 kHz.

Next, the amount of change in the sub-scanning speed fluctuation ratio will be described with reference to FIG. 13. FIG. 13 is a graph showing the amount of change in the sub-scanning speed fluctuation ratio. The sub-scanning speed is the medium transport speed. When the image forming device 1 is in use, if mist of droplets adheres to the encoder that detects the medium transport speed, the medium transport speed will fluctuate. The amount of change in the sub-scanning speed fluctuation ratio gradually worsens as the number of printed sheets increases. Specifically, the difference between the actual transport speed and the measured transport speed becomes larger.

Figure 13 shows the relationship between the number of printed sheets and the degree of dirt on the encoder (change in the sub-scanning speed fluctuation ratio) when used in actual printing. In Figure 13, the horizontal axis shows the number of printed sheets, and the vertical axis shows the change in the sub-scanning speed fluctuation ratio. As the dirt on the encoder increases, the change in the sub-scanning speed fluctuation ratio increases (becomes a higher value).

In the measurement experiment, the distance between the nozzle surface of the recording head and the medium was increased from normal to increase the amount of dirt. The charts used for printing generally contain figures and text, and large, medium and small droplets were all used.

The large drop waveform, medium drop waveform, small application waveform, and fine drive waveform of Example 1 are shown in Figures 8, 9, and 14, as described above. The large drop waveform, medium drop waveform, small application waveform, and fine drive waveform of Example 2 are shown in Figures 8, 14, and 15, as described above. The large drop waveform, medium drop waveform, small application waveform, and fine drive waveform of Comparative Example 1 are shown in Figures 11, 16, and 17, as described above. The fine drive waveform of Comparative Example 1 is pulse P1, and is the same as the fine drive waveform of Examples 1 and 2. The medium drop waveform of Comparative Example 1 includes pulses P2 and P4, and is the same as the medium drop waveform of Examples 1 and 2.

The amount of change in the sub-scanning speed fluctuation ratio is the amount of deterioration in the variability of the encoder reading, and is aggravated by mist contamination inside the machine. When mist adheres to the encoder, the contamination accumulates. When contamination accumulates on the encoder, the reading of the scale on the encoder becomes inaccurate, the media cannot be transported accurately, and the device cannot be used as an image forming device.

In the case of Example 1, even when the number of printed sheets was 2000, the sub-scanning speed fluctuation ratio change amount (%) was 0.5% or less. In the case of Example 2, even when the number of printed sheets was 2000, the sub-scanning speed fluctuation ratio change amount (%) was 1.5% or less. In the case of Comparative Example 1, when the number of printed sheets was 500, the sub-scanning speed fluctuation ratio change amount was about 2.0%. In the case of Comparative Example 1, when the number of printed sheets was 1000, the sub-scanning speed fluctuation ratio change amount was about 3.2%. In Example 1, the encoder is less dirty than in Comparative Example 1, and the life of the device can be extended. In Examples 1 and 2, the encoder is less dirty than in Comparative Example 1, and the conveying speed is accurately maintained, thereby suppressing the deterioration of print quality.

Furthermore, the sub-scanning speed fluctuation ratio change amount (%) of Example 1 is smaller than the sub-scanning speed fluctuation ratio change amount (%) of Example 2. Therefore, by setting the time T1 from the start of the first expansion waveform element a1 to the start of the first contraction waveform element c1 of pulse P5 in the range of 0.45Tc to 0.65Tc, and setting the time T4 from the start of the first contraction waveform element c1 to the start of the third expansion waveform element a3 in the range of 0.9Tc to 1.0Tc, it was confirmed that the generation of mist can be further reduced and the dirt on the encoder can be reduced. As a result, in Example 1, the dirt on the encoder is further reduced and the conveying speed is accurately maintained, thereby suppressing the deterioration of print quality.

In this application, "paper" does not mean limited to paper, but includes overhead projectors, cloth, glass, substrates, etc., and refers to anything onto which ink droplets or other liquids can be attached. In this application, media includes those referred to as recording media, recording paper, recording paper, etc.

"Image forming device" refers to a device that forms an image by ejecting liquid onto a medium such as paper, thread, fiber, cloth, leather, metal, plastic, glass, wood, ceramics, etc. "Image formation" refers not only to applying meaningful images such as letters or figures onto a medium, but also to applying meaningless images such as patterns onto a medium (simply causing droplets to land on the medium).

In addition, unless otherwise specified, the term "ink" is used as a general term for all liquids capable of forming images, including not only those called ink, but also those called recording liquid, fixing treatment liquid, liquid, etc. For example, it also includes DNA samples, resists, pattern materials, resins, etc.

In addition, "images" are not limited to flat objects, but also include images attached to objects formed in a three-dimensional form, and images formed by modeling the object itself in three dimensions.

Additionally, unless otherwise specified, image forming devices include both serial type image forming devices and line type image forming devices.

Although the preferred embodiment has been described above in detail, the present invention is not limited to the above-described embodiment, and various modifications and substitutions can be made to the above-described embodiment without departing from the scope of the claims.

For example, in the above embodiment, an image forming apparatus equipped with a recording head according to the present invention has been described, but the recording head and its control according to the present invention can be widely applied to devices that eject liquid, including image forming apparatuses.

In this application, a "liquid ejection device" is a device that includes a liquid ejection head or a liquid ejection unit, and ejects liquid by driving the liquid ejection head. A liquid ejection device includes not only a device that can eject liquid onto an object onto which the liquid can adhere, but also a device that ejects liquid into air or liquid.

This "liquid ejecting device" can also include means for feeding, transporting, and discharging items onto which liquid can be attached, as well as pre-processing devices and post-processing devices.

For example, examples of "devices that eject liquid" include image forming devices that eject ink to form an image on paper, and three-dimensional modeling devices that eject modeling liquid onto a powder layer formed by layering powder to form a three-dimensional object.

In addition, a "liquid ejecting device" is not limited to devices that use ejected liquid to visualize meaningful images such as letters and figures. For example, it also includes devices that form patterns that have no meaning in themselves, and devices that create three-dimensional images.

The above phrase "something to which liquid can adhere" refers to something to which liquid can adhere at least temporarily, and to which the liquid adheres and sticks, or adheres and penetrates. Specific examples include media such as paper, recording paper, film, and cloth, electronic circuit boards, electronic components such as piezoelectric elements, powder layers, organ models, and testing cells, and unless otherwise specified, includes all things to which liquid can adhere.

The above-mentioned "materials to which liquid can adhere" include paper, thread, fiber, cloth, leather, metal, plastic, glass, wood, ceramics, and other materials to which liquid can adhere even temporarily.

In addition, the pressure generating means used in the "liquid ejection head" is not limited. For example, a piezoelectric actuator (which may use a laminated piezoelectric element), a thermal actuator using an electrothermal conversion element such as a heating resistor, an electrostatic actuator consisting of a vibration plate and an opposing electrode, etc. can be used.

In addition, in this application, the terms image formation, recording, printing, copying, printing, modeling, etc. are all synonymous.

Each function executed by the control unit 500 in the embodiment described above can be realized by one or more processing circuits. Here, the term "processing circuit" in this specification includes a processor programmed to execute each function by software, such as a CPU implemented by electronic circuits, and devices such as an ASIC (Application Specific Integrated Circuit), DSP (digital signal processor), FPGA (field programmable gate array), and conventional circuit modules designed to execute each function described above.

1. Image forming apparatus (liquid ejection apparatus)
34 (34a, 34b) recording head (liquid ejection head)
42 Paper (medium)
104 Nozzle 106 Individual liquid chamber 112 Piezoelectric member (pressure generating section)
500 Control unit 508 Print control unit 509 Head driver (head drive control unit)
701 Drive waveform generating unit Tc Natural vibration period

JP 2014-184658 A

Claims (7)

a liquid ejection head including a plurality of nozzles for ejecting liquid droplets, individual liquid chambers communicating with the nozzles, and a pressure generating unit for generating pressure to pressurize liquid in the individual liquid chambers;
a head drive control unit that outputs to the pressure generating unit a drive waveform including one or more pulses selected according to a droplet size,
When the drive waveform includes two or more of the pulses, the drive waveform includes a final pulse at the end of the plurality of pulses,
The final pulse is
A first expansion corrugated element that expands the individual liquid chamber;
a first contraction waveform element that is a waveform element subsequent to the first expansion waveform element and contracts the individual liquid chamber;
a second expansion waveform element that is a waveform element subsequent to the first contraction waveform element and expands the individual liquid chamber;
a second contraction waveform element that is a waveform element subsequent to the second expansion waveform element and contracts the individual liquid chamber;
a third expansion waveform element which is a waveform element subsequent to the second contraction waveform element and expands the individual liquid chamber;
the time from the start of the first contraction waveform element to the start of the second expansion waveform element is less than 0.5Tc;
A liquid ejection device, characterized in that the time from the start of the first contraction waveform element to the start of the second contraction waveform element is within a range of 0.5Tc to 0.6Tc. The time from the start of the first expansion waveform element to the start of the first contraction waveform element is in the range of 0.45Tc to 0.65Tc;
2. The liquid ejection device according to claim 1, wherein the time from the start of the first contraction waveform element to the start of the third expansion waveform element is within a range of 0.9Tc to 1.0Tc. a conveyor belt that conveys a medium on which an image is formed by the liquid discharged from the liquid discharge head;
3. The liquid ejection apparatus according to claim 1, wherein the transport belt transports the medium by electrostatic attraction. A program for causing a computer to execute a process for ejecting liquid from a plurality of nozzles of a liquid ejection head,
The program is
outputting, to a pressure generating unit, a drive waveform including one or more pulses selected according to a droplet size;
When the drive waveform includes two or more of the pulses, the drive waveform includes a final pulse at the end of the plurality of pulses,
The final pulse is
A first expansion waveform element that expands an individual liquid chamber of the liquid ejection head;
a first contraction waveform element that is a waveform element subsequent to the first expansion waveform element and contracts the individual liquid chamber;
a second expansion waveform element that is a waveform element subsequent to the first contraction waveform element and expands the individual liquid chamber;
a second contraction waveform element that is a waveform element subsequent to the second expansion waveform element and contracts the individual liquid chamber;
a third expansion waveform element which is a waveform element subsequent to the second contraction waveform element and expands the individual liquid chamber;
the time from the start of the first contraction waveform element to the start of the second expansion waveform element is less than 0.5Tc;
A program characterized in that the time from the start of the first contraction waveform element to the start of the second contraction waveform element is within the range of 0.5Tc to 0.6Tc. The time from the start of the first expansion waveform element to the start of the first contraction waveform element is in the range of 0.45Tc to 0.65Tc;
5. The program according to claim 4, wherein the time from the start of the first contraction waveform element to the start of the third expansion waveform element is within a range of 0.9Tc to 1.0Tc. 1. A head drive control method for driving and controlling a liquid ejection head having a plurality of nozzles for ejecting liquid droplets, individual liquid chambers communicating with the nozzles, and a pressure generating unit for generating pressure to pressurize liquid in the individual liquid chambers, comprising:
outputting a drive waveform including one or more pulses selected according to a droplet size to the pressure generating unit;
When the drive waveform includes two or more of the pulses, the drive waveform includes a final pulse at the end of the plurality of pulses,
The final pulse is
A first expansion corrugated element that expands the individual liquid chamber;
a first contraction waveform element that is a waveform element subsequent to the first expansion waveform element and contracts the individual liquid chamber;
a second expansion waveform element that is a waveform element subsequent to the first contraction waveform element and expands the individual liquid chamber;
a second contraction waveform element that is a waveform element subsequent to the second expansion waveform element and contracts the individual liquid chamber;
a third expansion waveform element which is a waveform element subsequent to the second contraction waveform element and expands the individual liquid chamber;
the time from the start of the first contraction waveform element to the start of the second expansion waveform element is less than 0.5Tc;
A head drive control method, characterized in that the time from the start of the first contraction waveform element to the start of the second contraction waveform element is within a range of 0.5Tc to 0.6Tc. The time from the start of the first expansion waveform element to the start of the first contraction waveform element is in the range of 0.45Tc to 0.65Tc;
7. The head drive control method according to claim 6, wherein the time from the start of the first contraction waveform element to the start of the third expansion waveform element is within a range of 0.9Tc to 1.0Tc.

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