Liquid dispensing head

Abstract

To provide a liquid discharge head that enables a gradation expression range to broaden and can secure discharge stability.SOLUTION: A liquid discharge head comprises: a pressure chamber communicating with a nozzle that discharges liquid; an actuator that changes the volume of the pressure chamber in accordance with an electric signal; and a driving circuit that generates an electric signal for driving the actuator. A driving waveform that is outputted by the driving circuit has an ejection waveform part that has n-1 time discharge pulses including: a first discharge pulse which has an expanding element for expanding the pressure chamber and a contracting element for contracting the expanded pressure chamber to an intermediate voltage; and a second discharge pulse which has an expanding element for expanding the pressure chamber and a contacting element for contracting the expanded pressure chamber to a voltage higher than the intermediate voltage at the when discharging ink droplets n-times (n is three or more integer) to perform printing in three or more gradations, at an interval of 0.8-1.2 λ where a period of primary natural vibration in a state where the pressure chamber is filled with ink is defined as λ.SELECTED DRAWING: Figure 6

Description

Technical Field

[0001] Embodiments of the present invention relate to a liquid ejection head.

Background Art

[0002] In recent years, in liquid ejection devices such as inkjet heads, various printing performances such as high image quality, high resolution, high productivity, and increased droplet volume have been demanded.

[0003] For example, in order to achieve high speed and ejection of a large number of droplets, a technique of supplying a drive signal having a plurality of ejection pulses for ejecting ink droplets within one printing cycle based on an intermediate voltage is known. For example, in order to suppress residual vibration generated by the ejection pulse, an expansion element that expands the pressure chamber after the final ejection pulse and a contraction element that contracts the pressure chamber expanded by the expansion element again to return to the intermediate voltage are provided. A drive waveform is adopted.

[0004] In such an inkjet head, an expansion of the gradation expression range and stability are demanded.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] The problem to be solved by the present invention is to provide a liquid ejection head that can expand the gradation expression range and ensure ejection stability.

Means for Solving the Problems

[0007] The liquid discharge head according to this embodiment includes a pressure chamber communicating with a nozzle for discharging liquid, an actuator that changes the volume of the pressure chamber in response to an electrical signal, and a drive circuit that generates an electrical signal to drive the actuator. The drive waveform output by the drive circuit includes a discharge waveform section having n discharge pulses at intervals of 0.8 to 1.2λ, where λ is the period of the first natural vibration when the pressure chamber is filled with ink, when discharging ink droplets n times (an integer of 3 or more) to print three or more grayscale levels, and a cancellation waveform section following the discharge waveform section. The discharge waveform section includes a discharge pulse having an element that reduces the voltage to a first voltage and then an element that raises it to a second voltage higher than the first voltage, and a discharge pulse having an element that reduces the voltage to the first voltage and then an element that raises it to a third voltage higher than the second voltage. The cancellation waveform section includes a cancellation pulse having an element that reduces the voltage to the first voltage and then an element that raises it to the second voltage. The final discharge pulse in the discharge waveform section is a discharge pulse having an element that lowers the voltage to the first voltage and an element that then raises it to a third voltage higher than the second voltage, and the cancellation pulse is a waveform that lowers the voltage from the state where the voltage became the third voltage due to the final discharge pulse to the first voltage and then returns it to the second voltage. [Brief explanation of the drawing]

[0008] [Figure 1] A perspective view showing the configuration of a liquid dispensing head according to the first embodiment. [Figure 2] A perspective view showing the configuration of the head body of the liquid discharge head according to the first embodiment. [Figure 3] A bottom view showing the configuration of the liquid discharge head according to the first embodiment, with some parts omitted. [Figure 4] A cross-sectional view showing the configuration of the head body according to the first embodiment, with some parts omitted. [Figure 5] An explanatory diagram showing the configuration of a liquid dispensing device according to the first embodiment. [Figure 6] An explanatory diagram showing the drive waveform according to Example 1. [Figure 7] A graph showing the simulation results of the flow velocity in Example 1. [Figure 8] A graph showing the simulation results of the meniscus position in Example 1. [Figure 9] An explanatory diagram showing the drive waveform according to Example 2. [Figure 10] A graph showing the simulation results of the flow velocity in Example 2. [Figure 11] A graph showing the simulation results of the meniscus position in Example 2. [Figure 12] An explanatory diagram showing the drive waveform according to Example 3. [Figure 13] A graph showing the simulation results of the flow velocity in Example 3. [Figure 14] A graph showing the simulation results of the meniscus position in Example 3. [Figure 15] An explanatory diagram showing the drive waveform according to Example 4. [Figure 16] An explanatory diagram showing the drive waveform according to Example 5. [Figure 17] An explanatory diagram showing the drive waveform according to Example 6. [Modes for carrying out the invention]

[0009] Below, a liquid discharge head 1 and a liquid discharge device 2 using the liquid discharge head 1 according to the first embodiment will be described with reference to Figures 1 to 5. Figure 1 is a perspective view showing the configuration of the liquid discharge head 1 according to the first embodiment. Figure 2 is a perspective view showing the configuration of the head body 11 of the liquid discharge head 1 with a part of the nozzle plate 114 cut out. Figure 3 is a bottom view showing the configuration of the liquid discharge head 1 with the nozzle plate 114 omitted. Figure 4 is a cross-sectional view showing the configuration of the head body 11. Figure 5 is an explanatory diagram showing the configuration of the liquid discharge device 2 using the liquid discharge head 1. Note that in each figure, the configuration is enlarged, reduced, or omitted as appropriate for explanatory purposes.

[0010] The liquid ejection head 1 is a shear-mode sheared-wall type inkjet head provided in a liquid ejection device 2, such as the inkjet recording device shown in Figure 5. The liquid ejection head 1 is provided in a head unit 2130 which includes a supply tank 2132 as a liquid storage section provided in the liquid ejection device 2.

[0011] The liquid ejection head 1 is supplied with ink as the liquid stored in the supply tank 2132. Note that the liquid ejection head 1 may be a non-circulating head that does not circulate the ink, or may be a circulating head that circulates the ink. In the present embodiment, the liquid ejection head 1 will be described using an example of a non-circulating head.

[0012] As shown in FIGS. 1 to 4, the liquid ejection head 1 includes a head body 11, a manifold unit 12, a drive circuit 13, and a cover 14. For example, the liquid ejection head 1 is a side shooter type four-row integrated structure head having two sets of head bodies 11 each having a pair of actuators 113.

[0013] The head body 11 ejects liquid. The head body 11 includes a substrate 111, a frame body 112, an actuator 113 having a plurality of pressure chambers 1131, and a nozzle plate 114.

[0014] The head body 11 has a common liquid chamber 116 that communicates with the plurality of pressure chambers 1131 of the actuator 113. The primary side of the plurality of pressure chambers 1131 is the upstream side of the plurality of pressure chambers 1131 in the direction of liquid flow. The secondary side of the plurality of pressure chambers 1131 is the downstream side of the plurality of pressure chambers 1131 in the direction of liquid flow.

[0015] Further, the head body 11 has a plurality of individual electrodes 118 (electrode portions) for driving the plurality of pressure chambers 1131 of the actuator 113 on the substrate 111 and the actuator 113.

[0016] In this embodiment, the head body 11 has two actuators 113, and the common liquid chamber 116 has one first common liquid chamber 1161 and two second common liquid chambers 1162. The common liquid chamber 116 includes, for example, a first common liquid chamber 1161 that communicates with the primary side openings (inlets of the pressure chambers 1131) of the multiple pressure chambers 1131 of the actuator 113, and a second common liquid chamber 1162 that communicates with the secondary side openings (outlets of the pressure chambers 1131) of the multiple pressure chambers 1131 of the actuator 113.

[0017] The substrate 111 is formed in the shape of a rectangular plate, for example, from a ceramic material. The substrate 111 is formed in the shape of a rectangle that is elongated in one direction, for example.

[0018] On one side of the substrate 111, the wiring surface 115, wiring 1181 is formed, which constitutes part of a plurality of individual electrodes 118. The wiring on the substrate 111 is formed, for example, from a thin nickel film. The wiring 1181 has a predetermined pattern shape that connects to the wiring formed on the actuator 113.

[0019] A pair of actuators 113 are provided side by side along the shorter side of the substrate 111. One side of the substrate 111 is one of the surfaces of the substrate 111. The substrate 111 has a single supply port 1111 and a plurality of discharge ports 1112. The supply port 1111 and the discharge ports 1112 are through holes that penetrate between the two main surfaces of the substrate 111.

[0020] The supply port 1111 is an inlet for supplying ink to the first common liquid chamber 1161. The supply port 1111 is a through-hole formed in the center of the substrate 111 in the short direction. The supply port 1111 extends along the longitudinal direction of the substrate 111. In other words, the supply port 1111 is an elongated hole that is long in one direction, for example, along the longitudinal direction of the actuator 113 and the longitudinal direction of the first common liquid chamber 1161. The supply port 1111 is located between a pair of actuators 113 and opens in a position opposite the first common liquid chamber 1161.

[0021] The discharge port 1112 is an outlet for discharging ink from the second common liquid chamber 1162. Multiple discharge ports 1112 are provided, for example, four. Each discharge port 1112 is located, for example, between the first common liquid chamber 1161 and each of the second common liquid chambers 1162, and is adjacent to each of the longitudinal ends of the pair of actuators 113. Note that multiple discharge ports 1112 may also be provided in the second common liquid chamber 1162.

[0022] The frame 112 is fixed to one main surface of the substrate 111 with adhesive or the like. The frame 112 surrounds the supply port 1111, the multiple discharge ports 1112, and the actuator 113 provided on the substrate 111.

[0023] For example, the frame 112 is formed in a rectangular shape, thereby forming a long opening in one direction along the longitudinal direction of the frame 112. A pair of actuators 113, a supply port 1111, and four discharge ports 1112 are arranged in the opening of the frame 112.

[0024] A pair of actuators 113 are bonded to the mounting surface of the substrate 111. The pair of actuators 113 are arranged in two rows on the substrate 111, with the supply port 111 in between. The actuators 113 are formed in a long, plate-like shape in one direction. The actuators 113 are placed within the opening of the frame 112 and bonded to the main surface of the substrate 111.

[0025] As shown in Figure 3, the actuator 113 has a plurality of pressure chambers 1131 arranged at equal intervals along its longitudinal direction, located towards the center of its longitudinal direction. In other words, the actuator 113 has a plurality of pressure chambers 1131 arranged along its longitudinal direction.

[0026] The top surface of the actuator 113, which is the side opposite to the substrate 111, is bonded to the nozzle plate 114. The actuators 113 are arranged at equal intervals in the longitudinal direction, and multiple grooves are formed along a direction perpendicular to the longitudinal direction. The multiple grooves form multiple pressure chambers 1131. In other words, the actuator 113 has multiple piezoelectric pillars 1133, which are driving elements that constitute a wall forming grooves between them, arranged at equal intervals in the longitudinal direction. The multiple piezoelectric pillars 1133 form multiple pressure chambers 1131 between adjacent piezoelectric pillars 1133, and the volume of the pressure chambers 1131 is changed by applying a driving voltage. That is, the actuator 113 changes the volume of the pressure chambers in response to an electrical signal.

[0027] The actuator 113 has a width in the shorter direction that gradually increases from the top side toward the substrate 111 side. The cross-sectional shape of the actuator 113 along the direction perpendicular to the longitudinal direction (shorter direction) is formed as a trapezoid. That is, the actuator 113 has an inclined surface 1134 that slopes toward the side surface in the shorter direction. The side surface (inclined surface 1134) is positioned opposite the first common liquid chamber 1161 and the second common liquid chamber 1162.

[0028] The pressure chamber 1131 deforms during printing or other operations by the liquid ejection head 1, thereby ejecting ink from the nozzle 1141. The pressure chamber 1131 has an inlet that opens into the first common liquid chamber 1161 and an outlet that opens into the second common liquid chamber 1162. Ink flows into the pressure chamber 1131 from the inlet and flows out from the outlet. The pressure chamber 1131 may also be configured so that ink flows in from both openings described as the inlet and outlet.

[0029] The nozzle plate 114 is formed in a plate shape. The nozzle plate 114 is fixed to the main surface of the frame 112 opposite to the substrate 111 with an adhesive or the like. The nozzle plate 114 has a plurality of nozzles 1141 formed at positions opposite to a plurality of pressure chambers 1131. In this embodiment, the nozzle plate 114 has two rows of nozzle rows 1142 in which the plurality of nozzles 1141 are arranged in one direction.

[0030] The first common liquid chamber 1161 is formed between the central sides of a pair of actuators 113, excluding both ends, and constitutes the flow path for ink from the supply port 1111 to the primary side openings (inlets) of the multiple pressure chambers 1131 of each actuator 113. The first common liquid chamber 1161 extends along the longitudinal direction of the actuators 113.

[0031] The second common liquid chamber 1162 is formed between each actuator 113 and the frame 112. The second common liquid chamber 1162 forms the flow path for ink from the secondary openings (outlets) of the multiple pressure chambers 1131 to the discharge port 1112. The second common liquid chamber 1162 extends along the longitudinal direction of the actuator 113.

[0032] The multiple individual electrodes 118 are individual electrodes that apply a drive voltage individually to the multiple piezoelectric columns 1133, which are piezoelectric materials. The multiple individual electrodes 118 individually deform each pressure chamber 1131. The individual electrodes 118 are composed of wiring formed on the actuator 113 and the substrate 111, respectively.

[0033] The individual electrodes 118 are drawn out from the inner surface of the pressure chamber 1131 to the inclined surface 1134 and the wiring surface 115 of the substrate 111, extending to the short-side end of the substrate 111 and connected to the drive circuit 13. The individual electrodes 118 are formed of, for example, a thin nickel film. However, the individual electrodes 118 are not limited to a thin nickel film; they may also be formed of, for example, a thin gold or copper film. Furthermore, a portion of the individual electrodes 118 may be covered on the lower surface of the frame 112 with an adhesive used to bond the frame 112 to the substrate 111.

[0034] The individual electrodes 118 are connected, for example, to the drive circuit 13. For example, each individual electrode 118 is connected by wiring to the control unit 2118, which acts as a drive unit, via a driver described later in the drive circuit 13, and is configured to be controllable by control of the processor.

[0035] As shown in Figures 1 and 3, the manifold unit 12 comprises a manifold 121, an ink supply pipe 123, an ink discharge pipe 124, and a pair of temperature control pipes, namely a temperature-controlled water supply pipe 125 and a temperature-controlled water discharge pipe. The number of ink supply pipes 123, ink discharge pipes 124, temperature-controlled water supply pipes 125, and temperature-controlled water discharge pipes can be set as appropriate.

[0036] The manifold 121 is formed in the shape of a plate or a block. The manifold 121 includes a supply channel that is continuous with the supply port 1111 of the substrate 111 and forms a liquid supply channel, a discharge channel that is continuous with the discharge port 1112 of the substrate 111 and forms a liquid discharge channel, and a temperature control channel that forms a channel for a temperature control fluid.

[0037] One main surface of the manifold 121 is fixed to the main surface of the substrate 111. In addition, an ink supply pipe 123, an ink discharge pipe 124, a temperature-controlled water supply pipe 125, and a temperature-controlled water discharge pipe are fixed to the manifold 121, for example.

[0038] The supply channel is a channel formed in the manifold 121 by holes or grooves. The supply channel fluidly connects the ink supply pipe 123 and the supply port 1111 of the substrate 111.

[0039] The discharge channel is a channel formed in the manifold 121 by holes or grooves. The discharge channel fluidly connects the ink discharge pipe 124 and the discharge port 1112 of the substrate 111.

[0040] The temperature control channel is a channel formed in the manifold 121 by holes or grooves. The temperature control channel fluidically connects the temperature-controlled water supply pipe 125 and the temperature-controlled water discharge pipe.

[0041] Both ends of the temperature control channel are openings that connect to a temperature-controlled water supply pipe 125 and a temperature-controlled water discharge pipe, which are provided on one main surface of the manifold 121. The temperature control channel is also formed to allow heat exchange with the substrate 111 fixed to the manifold 121.

[0042] The ink supply pipe 123 is connected to the supply channel. The ink discharge pipe 124 is connected to the discharge channel. The temperature-controlled water supply pipe 125 and the temperature-controlled water discharge pipe are connected to the primary and secondary sides of the temperature-controlled channel.

[0043] As shown in Figure 2, the drive circuit 13 comprises a wiring film 131 with one end connected to the substrate 111, a driver IC 132 mounted on the wiring film 131, and a printed circuit board 133 mounted on the other end of the wiring film 131.

[0044] The drive circuit 13 drives the actuator 113 by applying a drive voltage to the wiring pattern of the actuator 113 using the driver IC 132, thereby increasing or decreasing the volume of the pressure chamber 1131 and causing droplets to be discharged from the nozzle 1141.

[0045] The wiring film 131 is connected to a plurality of individual electrodes 118. For example, the wiring film 131 is an ACF (anisotropic conductive film) fixed to the connection part of the substrate 111 by thermocompression or the like. Multiple wiring films 131 are provided for a single head body 11, for example. In this embodiment, two wiring films 131 are connected to a single actuator 113. The wiring film 131 is, for example, a COF (Chip on Film) on which a driver IC 132 is mounted.

[0046] The driver IC 132 is connected to a plurality of individual electrodes 118 via a wiring film 131. Alternatively, the driver IC 132 may be connected to the plurality of individual electrodes 118 by means other than the wiring film 131, such as ACP (anisotropic conductive paste), NCF (non-conductive film), and NCP (non-conductive paste).

[0047] The driver IC 132 generates control signals and drive signals to operate the piezoelectric poles 1133, which act as driving elements. The driver IC 132 generates control signals for control purposes, such as selecting the timing for ink ejection and the piezoelectric pole 1133 from which to eject ink, according to the image signal input from the control unit 2118 of the liquid ejection device 2. The driver IC 132 also generates a voltage to be applied to the piezoelectric pole 1133, i.e., a drive signal (electrical signal), according to the control signals. When the driver IC 132 applies a drive signal to the piezoelectric pole 1133, the piezoelectric pole 1133 is driven to change the volume of the pressure chamber 1131. As a result, the ink filled in the pressure chamber 1131 is ejected from the nozzle 1141 that communicates with the pressure chamber 1131. The liquid ejection head 1 may be configured to achieve gradation expression by changing the amount of ink droplets that land on one pixel. Alternatively, the liquid ejection head 1 may be configured to change the amount of ink droplets that land on one pixel by changing the number of times the ink is ejected. Thus, the driver IC 132 is an example of an application unit that applies a drive signal to the piezoelectric pole 1133.

[0048] For example, the driver IC 132 includes a data buffer, a decoder, and a driver. The data buffer stores print data chronologically for each piezoelectric pole 1133. The decoder controls the driver for each piezoelectric pole 1133 based on the print data stored in the data buffer. Based on the decoder's control, the driver outputs a drive signal to operate each piezoelectric pole 1133. The drive signal is the voltage applied to each piezoelectric pole 1133.

[0049] The printed wiring board 133 is a PWA (Printed Wiring Assembly) on which various electronic components and connectors are mounted.

[0050] The cover 14 includes, for example, an outer casing 141 that covers the sides of the pair of head bodies 11, the manifold unit 12 and the drive circuit 13, and a mask plate that covers a portion of the nozzle plate 114 side of the pair of head bodies 11.

[0051] The outer casing 141 exposes, for example, the ink supply pipe 123, ink discharge pipe 124, temperature-controlled water supply pipe 125, and temperature-controlled water discharge pipe of the manifold unit 12, as well as the end of the drive circuit 13, to the outside.

[0052] The mask plate covers the portion of the pair of head bodies 11 excluding the multiple nozzles 1141 and the area around the multiple nozzles 1141 of the nozzle plate 114.

[0053] The liquid ejection device 2, which has a liquid ejection head 1, will be described below with reference to Figure 5. The liquid ejection device 2 comprises a housing 2111, a media supply unit 2112, an image forming unit 2113, a media discharge unit 2114, a transport device 2115 which is a support device, a maintenance device 2117, and a control unit 2118. The liquid ejection device 2 also includes a temperature control device that adjusts the temperature of the ink supplied to the liquid ejection head 1.

[0054] The liquid ejection device 2 is an inkjet printer that performs image formation processing on paper P by ejecting a liquid such as ink while transporting paper P, which is the recording medium to be ejected, along a predetermined transport path 2001 from the media supply unit 2112 through the image forming unit 2113 to the media discharge unit 2114.

[0055] The media supply unit 2112 includes a plurality of paper feed cassettes 21121. The image forming unit 2113 includes a support unit 2120 for supporting paper and a plurality of head units 2130 positioned opposite each other above the support unit 2120. The media discharge unit 2114 includes a paper output tray 21141.

[0056] The support unit 2120 includes a conveyor belt 21201 provided in a loop shape in a predetermined area where image formation is performed, a support plate 21202 that supports the conveyor belt 21201 from the back, and a plurality of belt rollers 21203 provided on the back of the conveyor belt 21201.

[0057] The head unit 2130 comprises a liquid ejection head 1 which is a plurality of inkjet heads, a plurality of supply tanks 2132 which are liquid tanks mounted on each liquid ejection head 1, a pump 2134 which supplies ink, and a connecting channel 2135 which connects the liquid ejection head 1 and the supply tanks 2132.

[0058] In this embodiment, the liquid ejection head 1 comprises four liquid ejection heads 1 for cyan, magenta, yellow, and black, and four supply tanks 2132 each containing ink of one of these colors. The supply tanks 2132 are connected to the liquid ejection head 1 by a connecting channel 2135.

[0059] Pump 2134 is a liquid transfer pump, for example, a piezoelectric pump. Pump 2134 is connected to the control unit 2118 and is driven and controlled by the control unit 2118.

[0060] The connecting channel 2135 includes a supply channel connected to the ink supply pipe 123 of the liquid ejection head 1. The connecting channel 2135 also includes a recovery channel connected to the ink discharge pipe 124 of the liquid ejection head 1. For example, if the liquid ejection head 1 is a non-circulating type, the recovery circuit is connected to the maintenance device 2117, and if the liquid ejection head 1 is a circulating type, the recovery channel is connected to the supply tank 2132.

[0061] The transport device 2115 transports the paper P along a transport path 2001 from the paper feed cassette 21121 of the media supply unit 2112, through the image forming unit 2113, to the paper output tray 21141 of the media discharge unit 2114. The transport device 2115 comprises a plurality of guide plate pairs 21211 to 21218 and a plurality of transport rollers 21221 to 21228 arranged along the transport path 2001. The transport device 2115 supports the paper P so that it can move relative to the liquid discharge head 1.

[0062] The maintenance device 2117, for example, sucks up and recovers ink remaining on the outer surface of the nozzle plate 114 during maintenance. Furthermore, if the liquid discharge head 1 is a non-circulating type, the maintenance device 2117 recovers ink from within the head body 11 during maintenance. Such a maintenance device 2117 includes a tray or tank for storing the recovered ink.

[0063] The control unit 2118 is, for example, a control board. The control unit 2118 is equipped with a processor, ROM (Read Only Memory), RAM (Random Access Memory), I / O ports (input / output ports), and image memory.

[0064] The processor is a processing circuit such as a CPU (Central Processing Unit) which acts as a controller. The processor controls the head unit 2130, drive motor, operating unit, and various sensors provided in the liquid dispensing device 2 via I / O ports. The processor transmits the print data stored in the image memory to the drive circuit 13 in the order of drawing.

[0065] ROM stores various programs and other data. RAM temporarily stores various variable data and image data. I / O ports are interface units that input data from and output data to external devices. Print data from externally connected devices is transmitted to the control unit via the I / O ports and stored in image memory.

[0066] The following describes the characteristics of the liquid discharge head 1 used in the liquid discharge device 2 according to the embodiment, and the drive waveform generated by the drive signal in the drive circuit 13 of the liquid discharge head 1. For example, the drive waveform of the liquid discharge head 1 is multidrop drive and comprises a discharge waveform section having multiple discharge pulses and a cancellation waveform section having a cancellation pulse following the discharge waveform section.

[0067] The discharge waveform section comprises multiple discharge pulses Pa, Pb, and Pc. Each discharge pulse Pa, Pb, and Pc has an expansion element that lowers the voltage and a contraction element that increases the voltage following the expansion element. In the drive waveform of the liquid discharge device 2 according to this embodiment, the pressurized voltage in the contraction elements of the multiple discharge pulses is set in two stages. That is, the drive waveform has at least two contraction elements that pressurize with different voltages.

[0068] For example, when printing three or more shades by ejecting ink droplets n times (where n is an integer greater than or equal to 3), the ejection waveform section includes (n-1) expansion elements that expand the pressure chamber by lowering the voltage from the first drop to the (n-1)th drop, using a first intermediate voltage Vb as a reference; contraction elements that contract the pressure chamber expanded by each expansion element to the first intermediate voltage Vb, which is the intermediate voltage, and eject the ink; and contraction elements that contract the pressure chamber expanded by the expansion elements to a second intermediate voltage Vc, which is higher than the first intermediate voltage Vb, and eject the ink. For example, voltage Va = 0V.

[0069] In this embodiment, the print waveform, which includes n ejection pulses and cancellation pulses for one printing cycle, fits within a time shorter than (n+1, 5)λ. Furthermore, in the drive waveform, the print waveform, which includes n ejection pulses and cancellation pulses for one printing cycle, fits within a time shorter than (n+1)λ.

[0070] In this embodiment, the drive waveform is configured such that the period of the first natural vibration when the pressure chamber 1131 is filled with ink is λ, and the centers of each ejection pulse Pa, Pb, Pc and the center of the cancellation pulse Pd are set with a period of 0.8 to 1.2λ (λ ± variation). Furthermore, the overall configuration of the drive waveform, including the ejection waveform section and the cancellation waveform section, is shorter than (n+1)λ. By adopting such a configuration, the range in which the size of the ink droplet can be increased or decreased can be expanded, and the ejection of ink droplets can be stabilized for gradation printing. [Example 1] Figure 6 shows the drive waveform according to Embodiment 1. This drive waveform is a 3-drop waveform, with three discharge pulses that perform expansion and contraction respectively, arranged with a constant period λ. The three discharge pulses Pa, Pb, and Pc each have an expansion element that expands the pressure chamber 1131 and draws liquid into the pressure chamber 1131, and a contraction element that contracts the pressure chamber 1131 and discharges the liquid. In this embodiment, the first discharge pulse Pa has an expansion element that lowers the voltage from the first intermediate voltage Vb to the expansion voltage Va and a contraction element that raises the voltage to a second intermediate voltage Vc that is higher than the first intermediate voltage Vb. For example, the second intermediate voltage Vc is greater than the first intermediate voltage Vb. That is, in this waveform, the first discharge pulse Pa lowers the voltage from the first intermediate voltage Vb to the expansion voltage Va (=0V), and then raises the voltage to a second intermediate voltage Vc that is greater than the first intermediate voltage Vb. Then, in the second discharge pulse Pb, the voltage is lowered again to the expansion voltage Va, and then raised to the first intermediate voltage Vb. Furthermore, in the third discharge pulse Pc, the voltage is lowered to the extended voltage Va, and then raised again to the first intermediate voltage Vb.

[0071] The cancellation waveform section of Example 1 has a cancellation pulse Pd that, following the final discharge pulse Pc, sequentially includes a contraction element that increases the voltage from a first intermediate voltage Vb to a larger second intermediate voltage Vc, and an expansion element that decreases the voltage back to the first intermediate voltage Vb. In this example, the multiple discharge pulses Pa, Pb, Pc and the cancellation pulse Pd are arranged with a constant period λ. In each discharge pulse Pa, Pb, Pc, the period from expansion to contraction and from contraction to expansion is λ / 2. In the cancellation pulse Pd, the period from the contraction of the discharge pulse Pc to the contraction of the cancellation pulse Pd, and the period from the contraction to the expansion of the cancellation pulse Pd are both λ / 2.

[0072] Figures 7 and 8 show the simulation results when the meniscus was operated with a voltage that did not cause discharge in Example 1. Figure 7 shows the time change of flow velocity when Vc / Vb = 1.4 and when Vc / Vb = 2.0. The simulation condition is λ = 4 μs. Figure 8 shows the time change of the meniscus position when Vc / Vb = 1.4 and when Vc / Vb = 2.0. According to this embodiment, both stabilization of ink droplet ejection and expansion of the tonal range can be achieved. Furthermore, as shown in Figures 7 and 8, residual vibration can be suppressed by adjusting the voltage ratio Vc / Vb. [Example 2] Figure 9 shows the drive waveform according to Embodiment 2. This drive waveform is a 3-drop waveform, with three discharge pulses that perform expansion and contraction respectively, arranged with a constant period λ. The three discharge pulses Pa, Pb, and Pc each have an expansion element that expands the pressure chamber 1131 and draws liquid into the pressure chamber 1131, and a contraction element that contracts the pressure chamber 1131 and discharges the liquid. In this embodiment, the first discharge pulse Pa has an expansion element that lowers the voltage from the first intermediate voltage Vb to the expansion voltage Va and a contraction element that raises the voltage to a second intermediate voltage Vc which is higher than the first intermediate voltage Vb. For example, the second intermediate voltage Vc is greater than the first intermediate voltage Vb. That is, in this waveform, the first discharge pulse Pa lowers the voltage from the first intermediate voltage Vb to the expansion voltage Va (=0V), and then raises the voltage to a second intermediate voltage Vc which is greater than the first intermediate voltage Vb. Then, in the second discharge pulse Pb, the voltage is lowered again to the expansion voltage Va, and then raised to the first intermediate voltage Vb. Furthermore, in the third discharge pulse Pc, the voltage is lowered to the extended voltage Va, and then raised again to the second intermediate voltage Vc. In this embodiment, the voltage is raised to the maximum voltage Vc in the final discharge pulse, and the final drop is accelerated, thereby merging the multiple discharged drops.

[0073] The cancellation waveform section of Embodiment 2 has a cancellation pulse Pd that sequentially includes an expansion element that expands the contracted pressure chamber 1131 again by setting a second intermediate voltage Vc higher than the first intermediate voltage Vb in the contraction element of the final discharge pulse Pc, thereby changing it to an expanded voltage Va lower than the first intermediate voltage Vb, and a contraction element that contracts the pressure chamber 1131 expanded by the expansion element of the cancellation pulse section again, returning it to the first intermediate voltage Vb.

[0074] In this embodiment, multiple discharge pulses Pa, Pb, and Pc are arranged with a period of λ. In each discharge pulse Pa, Pb, and Pc, the period from expansion to contraction and from contraction to expansion is λ / 2. In the cancellation waveform section, the distance from the contraction element of discharge pulse Pc to the expansion element of cancellation pulse Pd is λ, and the period from expansion to contraction of cancellation pulse Pd is 0.1λ to 0.4λ.

[0075] Figures 10 and 11 show the simulation results when the meniscus was operated with a voltage that did not cause discharge in Example 2. Figure 10 shows the time change of flow velocity when Vc / Vb = 1.4 and when Vc / Vb = 2.0. The simulation condition is λ = 4 μs. Figure 11 shows the time change of the meniscus position when Vc / Vb = 1.4 and when Vc / Vb = 2.0. According to this embodiment, it is possible to achieve both stabilization of ink droplet ejection and an expansion of the gradation range. Furthermore, as shown in Figures 10 and 11, residual vibration can be suppressed by adjusting the voltage ratio Vc / Vb.

[0076] [Example 3] Figure 12 shows the drive waveform of Example 3. The drive waveform of Example 3 is a modified version of the drive waveform of Example 2, and has a step waveform in which the timing of starting some of the pulses in the cancellation pulse section is adjusted and the expansion of the cancellation pulse Pd is performed in two stages.

[0077] The cancellation waveform section of Embodiment 3 has a cancellation pulse Pd that sequentially includes an expansion element including a step waveform, which expands the contracted pressure chamber 1131 again to the first intermediate voltage Vb by setting a second intermediate voltage Vc higher than the first intermediate voltage Vb in the contraction element of the final discharge pulse Pc, and then changes it to an expansion voltage Va lower than the first intermediate voltage Vb, and a contraction element that contracts the pressure chamber 1131 expanded by the expansion element of the cancellation pulse section again to return it to the first intermediate voltage Vb.

[0078] In the cancellation waveform section, the distance from the contraction element of the final discharge pulse Pc to the expansion element of the cancellation pulse Pd is λ, and the period from expansion to contraction of the cancellation pulse Pd is 0.1λ to 0.4λ. The other waveforms are the same as in Example 2. In this embodiment as well, it is possible to achieve both stabilization of ink droplet ejection and an expansion of the tonal range.

[0079] Figures 13 and 14 show the simulation results when the meniscus was operated with a voltage that did not cause discharge in Example 3. Figure 13 shows the time change in flow velocity when Vc / Vb = 1.4 and when Vc / Vb = 2.0. The simulation condition is λ = 4 μs. Figure 14 shows the time change in meniscus position when Vc / Vb = 1.4 and when Vc / Vb = 2.0. As shown in Figures 13 and 14, residual vibration can be suppressed by adjusting the voltage ratio Vc / Vb.

[0080] [Example 4] Figure 15 shows the drive waveform of Example 4. The drive waveform of Example 4 is a modified version of the drive waveform of Example 2, and is an example in which the voltage of the Pa and Pb contraction elements is switched.

[0081] The drive waveform of Example 4 is a 3-drop waveform, with three ejection pulses that perform expansion and contraction, each arranged with a constant period λ. The three ejection pulses Pa, Pb, and Pc each have an expansion element that expands the pressure chamber 1131 and draws liquid into the pressure chamber 1131, and a contraction element that contracts the pressure chamber 1131 and ejects the liquid. In this example, the first ejection pulse Pa has an expansion element that lowers the voltage from the first intermediate voltage Vb to the expansion voltage Va and a contraction element that raises the voltage to the first intermediate voltage Vb. The second ejection pulse Pb lowers the voltage again to the expansion voltage Va, and then raises the voltage to the second intermediate voltage Vc, which is greater than the first intermediate voltage Vb. Furthermore, in the third ejection pulse Pc, the voltage is lowered to the expansion voltage Va, and then raised again to the second intermediate voltage Vc. The other waveforms are the same as in Example 2. In this example as well, both stabilization of ink droplet ejection and expansion of the gradation range can be achieved. [Example 5] Figure 16 shows the drive waveform of Example 5. The drive waveform of Example 5 is a modified version of the drive waveform of Example 2, and has a step waveform section that includes an element that maintains an intermediate voltage for a certain period of time at Pa and Pb, and is an example in which the voltage is applied in steps. In this example, the contraction element of the first discharge pulse Pa has a step waveform that increases the voltage in steps, and the expansion element of the second discharge pulse Pb has a step waveform that decreases the voltage in steps.

[0082] Example 5 has a 3-drop waveform, in which three discharge pulses that perform expansion and contraction are arranged with a constant period λ. The three discharge pulses Pa, Pb, and Pc each have an expansion element that expands the pressure chamber 1131 and draws liquid into the pressure chamber 1131, and a contraction element that contracts the pressure chamber 1131 and discharges the liquid. In this example, the first discharge pulse Pa has an expansion element that lowers the voltage from the first intermediate voltage Vb to the expansion voltage Va, and a contraction element that gradually increases the voltage to the second intermediate voltage Vc which is greater than the first intermediate voltage Vb. For example, the second intermediate voltage Vc is greater than the first intermediate voltage Vb. The first discharge pulse Pa has a step waveform in which the voltage is increased from the expansion voltage Va to the first intermediate voltage Vb, the first intermediate voltage Vb is maintained for a certain period of time, and then gradually increased to the second intermediate voltage Vc. In this waveform, the first discharge pulse Pa lowers the voltage from the first intermediate voltage Vb to the extended voltage Va (=0V), then raises the voltage back to the first intermediate voltage Vb, and further raises the voltage to the second intermediate voltage Vc, which is greater than the first intermediate voltage Vb. The second discharge pulse Pb includes an extension element that lowers the voltage from the second intermediate voltage Vc to the first intermediate voltage Vb, maintains the first intermediate voltage Vb for a certain period of time, and then lowers the voltage further to the extended voltage Va, and a contraction element that raises the voltage back to the first intermediate voltage Vb. The third discharge pulse Pc has an extension element that lowers the voltage from the first intermediate voltage Vb to the extended voltage Va, and a contraction element that raises the voltage back to the first intermediate voltage Vb. Furthermore, as shown in Figure 16, the cancellation waveform section of this embodiment has a step waveform that maintains the first intermediate voltage Vb for a certain period of time. Specifically, the cancellation waveform section includes, in order, a contraction element of the final discharge pulse Pc that raises the voltage to the first intermediate voltage Vb, maintains the first intermediate voltage Vb for a certain period of time, and then gradually increases the voltage to the second intermediate voltage Vc; an expansion element that expands the pressure chamber 1131 that has contracted at the second intermediate voltage Vc to the first intermediate voltage Vb, maintains this state for a certain period of time, and then gradually changes it to the expanded voltage Va; and a contraction element that contracts the expanded pressure chamber 1131 again to return it to the first intermediate voltage Vb. Other waveforms are the same as in Example 2. In this example as well, it is possible to stabilize ink droplet ejection and expand the range of gradation simultaneously.

[0083] [Example 6] Figure 17 shows the drive waveform of Example 6. The drive waveform of Example 6 is a modified version of the drive waveform of Example 2, and is an example in which an auxiliary waveform section is included before the discharge waveform section. That is, in this embodiment, the auxiliary waveform section has an auxiliary pulse Pe which has a contraction element that raises the voltage from a first intermediate voltage Vb to a second intermediate voltage Vc before the expansion element of the first discharge pulse Pa. The other waveforms are the same as in Example 2. The auxiliary pulse can increase the speed of the first drop of ink droplet.

[0084] In the liquid ejection head 1 and liquid ejection device configured in this way, gradation can be achieved by increasing the intermediate voltage of the contraction element in the ejection pulse. That is, for example, if the voltage of the ejection pulses from the 1st drop to the (n-1)th drop is the same, there is a limit to the size of the ink droplet that can be ejected. Therefore, for example, when printing a multi-gradation image by changing the size of the print dots, the range in which the ink droplet size can be increased or decreased is narrow, and there is a limit to the expression of gradation. In contrast, according to this embodiment, the range of expression of gradation can be expanded by controlling the intermediate potential in two or more stages. Furthermore, according to this embodiment, ejection stability can be ensured by having n-1 ejection pulses at intervals of 0.8 to 1.2λ, where λ is the period of the first natural vibration when the pressure chamber is filled with ink. Therefore, it is possible to achieve both an expanded range of expression of gradation and ejection stability.

[0085] The embodiments of the present invention are not limited to the configurations described above.

[0086] For example, we used 3 drops, but this is not limited to this; it could be 4 or more. Furthermore, in that case, the voltage of the contraction element may be set not only in 2 stages, but in 3 or more stages.

[0087] For example, the configuration of the liquid dispensing head 1 is not limited to the example above, and other types of heads may be used.

[0088] According to at least one embodiment described above, it is possible to stabilize the ejection of ink droplets and expand the range of gradation simultaneously.

[0089] While several embodiments of the present invention have been described, these embodiments are presented as examples only and are not intended to limit the scope of the invention. These novel embodiments can be carried out in a variety of other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, as well as in the claims of the invention and its equivalents. The following is an appended description equivalent to the invention described in the claims of the original application. (1) A pressure chamber connected to a nozzle that discharges liquid, An actuator that changes the volume of the pressure chamber in response to an electrical signal, The system includes a drive circuit that generates an electrical signal to drive the actuator, The drive waveform output by the aforementioned drive circuit is When printing with 3 or more grayscale levels by ejecting ink droplets n times (n = an integer of 3 or more), A liquid dispensing head has a dispensing waveform section that includes a first dispensing pulse having an expansion element for expanding the pressure chamber and a contraction element that sets the voltage to an intermediate voltage after expansion, and a second dispensing pulse having an expansion element for expanding the pressure chamber and a contraction element that sets the voltage to a higher voltage than the intermediate voltage after expansion, with n-1 dispensing pulses occurring at intervals of 0.8 to 1.2λ, where λ is the period of the first natural vibration when the pressure chamber is filled with ink. (2) The drive waveform includes a cancellation waveform section following the final discharge pulse in the discharge waveform section. The liquid discharge head according to (1), wherein the cancellation waveform section includes, in order, a contraction element that raises the voltage of the pressure chamber expanded by the expansion element of the final discharge pulse to a voltage higher than the intermediate voltage, and an expansion element that expands the pressure chamber contracted by the contraction back to the intermediate voltage. (3) The drive waveform includes a cancellation waveform section following the final discharge pulse in the discharge waveform section. The liquid discharge head according to (1), wherein the cancellation waveform section includes, in order, a contraction element that raises the voltage to a higher voltage than the intermediate voltage after the expansion element in the final discharge pulse, an expansion element that raises the pressure chamber again to a voltage lower than the intermediate voltage after the contraction, and a contraction element that lowers the expanded pressure chamber again to return it to the intermediate voltage. (4) The expansion element and contraction element in the discharge pulse are A liquid dispensing head according to any one of (1) to (3), comprising an element for maintaining an intermediate voltage for a certain period of time and having a step waveform section for gradually changing the voltage. (5) The aforementioned drive waveform is generated before the first discharge pulse of the discharge waveform section. The liquid discharge head according to (1), further comprising, in order, a contraction element that contracts the pressure chamber to a voltage higher than the intermediate voltage, and an expansion element that expands the contracted pressure chamber to return it to the intermediate voltage, as an auxiliary waveform section. [Explanation of symbols]

[0090] 1...Liquid ejection head (inkjet head), 2...Liquid ejection device (inkjet recording device), 11...Head body, 12...Manifold unit, 13...Drive circuit, 14...Cover, 111...Substrate, 112...Frame, 113...Actuator, 114...Nozzle plate, 116...Common liquid chamber, 118...Individual electrodes (electrode part), 121...Manifold, 123...Ink supply pipe, 124...Ink discharge pipe, 125...Temperature-controlled water supply pipe, 131...Wiring film, 133...Printed wiring board, 141...Outlet, 1111...Supply port, 1112...Discharge port, 1131...Pressure chamber, 1133...Piezoelectric column (drive element), 1134...Inclined surface, 1141...Nozzle, 114 2...Nozzle row, 1161...First common liquid chamber, 1162...Second common liquid chamber, 2001...Conveyor path, 2111...Housing, 2112...Media supply unit, 2113...Image forming unit, 2114...Media discharge unit, 2115...Conveyor device, 2117...Maintenance device, 2118...Control unit, 2120...Support unit, 2130...Head unit, 2132...Supply tank, 2134...Pump, 2135...Connecting channel, 21121...Paper feed cassette, 21141...Paper output tray, 21201...Conveyor belt, 21202...Support plate, 21203...Belt roller, 21211~21218...Guide plate pair, 21221~21228...Conveyor roller, 132...Driver IC, P...Paper.

Claims

1. A pressure chamber connected to a nozzle that discharges liquid, An actuator that changes the volume of the pressure chamber in response to an electrical signal, The system includes a drive circuit that generates an electrical signal to drive the actuator, The drive waveform output by the drive circuit comprises an ejection waveform section, which, when ejecting ink droplets n times (n = an integer of 3 or more) to print three or more grayscale levels, has n ejection pulses at intervals of 0.8 to 1.2λ, where λ is the period of the primary natural vibration when the pressure chamber is filled with ink; The system comprises a cancellation waveform section following the discharge waveform section, The discharge waveform section includes a discharge pulse having an element that reduces the voltage to a first voltage and an element that then increases it to a second voltage higher than the first voltage, and a discharge pulse having an element that reduces the voltage to the first voltage and then increases it to a third voltage higher than the second voltage, The cancellation waveform section comprises a cancellation pulse having an element that reduces the voltage to the first voltage and an element that then raises it to the second voltage. The final discharge pulse in the discharge waveform section is a discharge pulse having an element that reduces the voltage to the first voltage and an element that then raises it to a third voltage higher than the second voltage. The cancellation pulse is a waveform that lowers the voltage from the third voltage, which was reached by the final discharge pulse, to the first voltage, and then returns it to the second voltage, in the liquid discharge head.

2. The discharge waveform section or the cancellation waveform section The liquid discharge head according to claim 1, further comprising a step waveform section that maintains the second voltage for a certain period of time and changes the voltage in steps.

3. The liquid discharge head according to claim 1, wherein the drive waveform includes an auxiliary waveform section that raises the voltage to a level higher than the second voltage before the first discharge pulse of the discharge waveform section, and then returns it to the second voltage.

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