Patent Description:
In recent years, improved printing performance with regard to such things as higher image quality, higher resolution, higher productivity (e.g., throughput), as well an increase in the amount of liquid droplets have been required in liquid ejection apparatuses, such as an ink jet head for printers. For example, <CIT> discloses an ink jet recording apparatus including an ink jet head and a drive circuit, wherein the ink jet head forms an image on a recording medium in response to a drive signal applied to multiple piezoelectric elements, and the drive signal causes multiple pressure chambers corresponding to the multiple piezoelectric elements to expand or to contract in volume and causes ink in the multiple pressure chambers to be discharged from multiple nozzles. <CIT> discloses a liquid ejection head including a pressure chamber that contains a liquid, an actuator to change the pressure in the pressure chamber according to an applied drive signal, and a drive circuit to apply a first drive signal to the actuator when a single droplet is to be ejected from the pressure chamber and a second drive signal to the actuator when two or more droplets are to be ejected in series from the pressure chamber.

In order to realize higher printing speeds and ejection of a large amount of droplets, a technique for supplying a drive signal including a plurality of ejection pulses for ejecting ink droplets within one printing period with an intermediate voltage as a reference is known. In order to suppress residual vibration generated by such an ejection pulse, a drive waveform including an expansion component that causes a pressure chamber to expand in volume after a final ejection pulse and a contraction component that contracts the pressure chamber after the expansion and returns the voltage of the drive signal to an intermediate voltage can be adopted.

In such an ink jet head, increasing the gradation expression range (an aspect of print quality) and the stability of ejection are required.

To this end, there is provided a liquid ejection head according to claim <NUM>, comprising: a nozzle from which a droplet of a liquid can be ejected; a pressure chamber for the liquid, the pressure chamber connected to the nozzle; an actuator configured to change a volume of the pressure chamber according to a voltage signal applied to the actuator; and a drive circuit configured to generate the voltage signal that includes (n-<NUM>) ejection pulses when droplets are to be ejected n times from the nozzle, where n is an integer of <NUM> or more. According to the preset invention, the ejection pulses include: a first ejection pulse that lowers a voltage applied to the actuator to a first voltage value to expand the pressure chamber and then raises the voltage to a second voltage value to contract the pressure chamber, and a second ejection pulse that lowers the voltage to the first voltage value and then raises the voltage to a third voltage value higher than the second voltage value, and the ejection pulses are separated by intervals of <NUM>. 8λ to <NUM>. 2λ, where λ is a period of a primary natural vibration for the pressure chamber filled with the liquid.

In the drive waveform according to an embodiment, the period of the primary natural vibration when the pressure chamber is filled with ink is λ, the centers of the ejection pulses are provided at a period of <NUM> to <NUM>. 2λ, (λ ± variation). By adopting such a configuration, the ejection of ink droplets in gradation printing can be stabilized to widen the range in which the size of ink droplets can be increased or decreased.

The voltage signal further includes a cancel pulse following the ejection pulses.

Preferably, the cancel pulse raises the voltage to a voltage value higher than the second voltage value and then lowers the voltage to the second voltage value.

Preferably, the voltage value higher than the second voltage value is the third voltage value.

A last ejection pulse of the ejection pulses is the second ejection pulse by which the voltage is raised to the third voltage value.

The cancel pulse lowers the voltage to a voltage value lower than the second voltage value and then raises the voltage to the second voltage value.

Preferably, the voltage value lower than the secondo voltage value is the first voltage value.

Preferably, the cancel pulse is input upon elapse of the period after the last ejection pulse.

The cancel pulse is input after the voltage is lowered from the third voltage value to the second voltage value.

Preferably, one of the ejection pulses changes the voltage stepwise.

Preferably, the voltage signal further includes an auxiliary pulse before the ejection pulses.

The auxiliary pulse may raise the voltage to a voltage value higher than the second voltage value and then lowers the voltage to the second voltage value.

Preferably, the liquid is ink for printing.

Preferably, the droplet ejected n times expresses n different gradation levels.

The present invention further relates to an image forming apparatus, comprising:
a conveyer by which a medium is conveyed; and an image forming unit configured to form an image on the medium and including the above-described ink ejection head.

Embodiments provide a liquid ejection head capable of expanding the gradation expression range and ensuring the stability of ejection.

In general, according to one embodiment, a liquid ejection head includes a nozzle from which a droplet of a liquid can be ejected, a pressure chamber connected to the nozzle, an actuator configured to change a volume of the pressure chamber according to a voltage signal applied thereto, and a drive circuit configured to generate the voltage signal when droplets are to be ejected n times, where n is an integer of <NUM> or more. The voltage signal includes (n-<NUM>) ejection pulses, comprising at least one first ejection pulse that lowers a voltage applied to the actuator to a first voltage value to expand the pressure chamber and then raises the voltage to a second voltage value to contract the pressure chamber, and at least one second ejection pulse that lowers the voltage to the first voltage value and then raises the voltage to a third voltage value higher than the second voltage value. The ejection pulses are spaced at intervals of <NUM>. 8λ to <NUM>. 2λ, where λ is a period of a primary natural vibration of the pressure chamber filled with the liquid.

Hereinafter, a liquid ejection head <NUM> and a liquid ejection apparatus <NUM> incorporating the liquid ejection head <NUM> according to an embodiment will be described with reference to <FIG>. <FIG> is a perspective view illustrating the liquid ejection head <NUM>. <FIG> is a perspective view illustrating a head body <NUM> of the liquid ejection head <NUM> in which a part of a nozzle plate <NUM> is cut away to show internal aspects of the liquid ejection head <NUM>. <FIG> is a bottom view illustrating the liquid ejection head <NUM> in which the nozzle plate <NUM> is omitted to show other aspects. <FIG> is a cross-sectional view illustrating the head body <NUM>. <FIG> is a diagram illustrating the liquid ejection apparatus <NUM> using the liquid ejection head <NUM>. For aiding description, parts of the liquid ejection head <NUM> or the liquid ejection apparatus <NUM> may be enlarged, reduced, or omitted as appropriate.

The liquid ejection head <NUM> is a shear-mode, shared wall type ink jet head provided in a liquid ejection apparatus <NUM> such as the ink jet recording device illustrated in <FIG>. The liquid ejection head <NUM> is provided in a head unit <NUM>, which includes a supply tank <NUM> (liquid storage unit).

The liquid ejection head <NUM> is supplied with ink from the supply tank <NUM>. The liquid ejection head <NUM> may be a non-circulating type head that does not circulate ink between the liquid ejection head <NUM> and the supply tank <NUM>, or may be a circulating type head that circulates ink between the between the liquid ejection head <NUM> and the supply tank <NUM>. In this example, the liquid ejection head <NUM> is a non-circulating type head.

As illustrated in <FIG>, the liquid ejection head <NUM> includes a head body <NUM>, a manifold unit <NUM>, a drive circuit <NUM>, and a cover <NUM>. For example, the liquid ejection head <NUM> is a side shooter type four-row integrated structure head including two pairs of head bodies <NUM> each of which has a pair of actuators <NUM>.

The head body <NUM> ejects the liquid (e.g., ink). The head body <NUM> includes a substrate <NUM>, a frame body <NUM>, an actuator <NUM>, and a nozzle plate <NUM>. The actuator <NUM> has a plurality of pressure chambers <NUM>.

The head body <NUM> includes a common liquid chamber <NUM> that communicates with (connects to) the plurality of pressure chambers <NUM> of an actuator <NUM>. The primary side of the plurality of pressure chambers <NUM> is an upstream side with respect to the direction in which the liquid flows from the supply tank <NUM> for ejection. The secondary side of the plurality of pressure chambers <NUM> is a downstream side.

The head body <NUM> includes a plurality of individual electrodes <NUM> on the substrate <NUM> and the actuator <NUM> for driving the plurality of pressure chambers <NUM>.

In this example, the head body <NUM> includes two actuators <NUM>, and one first common liquid chamber <NUM> and two second common liquid chambers <NUM> for each actuator <NUM>. The common liquid chamber <NUM> for an actuator <NUM> comprises a first common liquid chamber <NUM>, which communicates with openings (inlets) on the primary side of the plurality of pressure chambers <NUM> of the actuator <NUM> and two second common liquid chambers <NUM> (on opposite sides of the first common liquid chamber <NUM>) that communicates with openings (outlets) on the secondary side of the plurality of pressure chambers <NUM> of the actuator <NUM>.

The substrate <NUM> is, for example, a ceramic material formed in a rectangular plate shape. The substrate <NUM> is, for example, a rectangular shape that is long in one direction.

A wiring <NUM> forming a part of the plurality of individual electrodes <NUM> is formed on a wiring surface <NUM>, which is one surface of the substrate <NUM>. The wiring of the substrate <NUM> is formed of, for example, a nickel thin film. The wiring <NUM> has a predetermined pattern shape connected to a wiring formed in the actuator <NUM>.

A pair of actuators <NUM> are provided to be aligned in the lateral direction of the substrate <NUM>. The substrate <NUM> has a single supply port <NUM> and a plurality of discharge ports <NUM>. The supply port <NUM> and the discharge ports <NUM> are through-holes penetrating between both main surfaces of the substrate <NUM>.

The supply port <NUM> is an inlet for supplying ink to the first common liquid chamber <NUM>. The supply port <NUM> is a through-hole formed in the center of the substrate <NUM> in the lateral direction. The supply port <NUM> extends along the longitudinal direction of the substrate <NUM>. In other words, the supply port <NUM> is, for example, a long hole (e.g., a slot or groove shape) that is long in one direction along the longitudinal direction of the actuator <NUM> and the longitudinal direction of the first common liquid chamber <NUM>. The supply port <NUM> is provided between the pair of actuators <NUM> and opens at a position facing the first common liquid chamber <NUM>.

The discharge port <NUM> is an outlet for discharging ink from the second common liquid chamber <NUM>. A plurality of discharge ports <NUM>, for example, four discharge ports, are provided. Each discharge port <NUM> is located between the first common liquid chamber <NUM> and one of the second common liquid chamber <NUM>. A discharge port <NUM> is adjacent to each end in the longitudinal direction of each of the pair of actuators <NUM>. In some examples, the discharge ports <NUM> may be provided in the second common liquid chambers <NUM>.

The frame body <NUM> is fixed to one main surface of the substrate <NUM> with an adhesive or the like. The frame body <NUM> surrounds the supply port <NUM>, the plurality of discharge ports <NUM>, and the actuator <NUM> that are provided on the substrate <NUM>.

For example, the frame body <NUM> is formed in a rectangular frame shape. The pair of actuators <NUM>, the supply port <NUM>, and four discharge ports <NUM> are disposed in the opening of the frame body <NUM>.

The pair of actuators <NUM> are adhered to a mounting surface of the substrate <NUM>. The pair of actuators <NUM> are aligned in two rows with the supply port <NUM> interposed therebetween. Each actuator <NUM> is formed in a plate shape that is long in one direction. Each actuator <NUM> is disposed in the opening of the frame body <NUM> and adhered to the main surface of the substrate <NUM>.

As illustrated in <FIG>, an actuator <NUM> includes a plurality of pressure chambers <NUM> disposed at equal intervals in the longitudinal direction in two rows.

The top surface portion of the actuator <NUM>, which is a surface opposite to the substrate <NUM>, is adhered to the nozzle plate <NUM>. The actuators <NUM> are disposed to be aligned at equal intervals in the longitudinal direction, and each of the actuators <NUM> is formed with a plurality of grooves along a direction orthogonal to the longitudinal direction. The plurality of grooves form the plurality of pressure chambers <NUM>. In other words, the actuator <NUM> includes a plurality of piezoelectric columns <NUM> (walls) at equal intervals in the longitudinal direction and are drive elements that are the walls between the grooves. The adjacent piezoelectric columns <NUM> form of the sidewalls of a pressure chambers <NUM>, and a volume of the pressure chamber <NUM> can be changed by applying a driving voltage to the piezoelectric columns <NUM>. That is, the actuator <NUM> changes the volume of a pressure chamber <NUM> according to an electric signal applied to the piezoelectric columns <NUM> (walls) of the respective pressure chamber <NUM>.

For example, a width of the actuator <NUM> in the lateral direction gradually increases from the top side toward the substrate <NUM> side. A cross-sectional shape of a cross section along the direction orthogonal to the longitudinal direction of the actuator <NUM> is formed into a trapezoidal shape. That is, the actuator <NUM> has an inclined surface <NUM> that is inclined to a side surface portion in the lateral direction. The side surface portion (inclined surface <NUM>) is disposed so as to face the first common liquid chamber <NUM> and the second common liquid chamber <NUM>.

A pressure chamber <NUM> can be deformed so that ink is ejected from the nozzle <NUM> for printing by the liquid ejection head <NUM>. Each pressure chamber <NUM> has an inlet that opens to the first common liquid chamber <NUM> and an outlet that opens to a second common liquid chamber <NUM>. Ink flows into the pressure chamber <NUM> from the inlet and out from the outlet. In some examples, the pressure chamber <NUM> may be configured such that ink flows in from openings at both ends of the pressure chamber <NUM> rather than having either end serve as an outlet.

The nozzle plate <NUM> is formed in a plate shape. The nozzle plate <NUM> is fixed to the frame body <NUM> on the side opposite from the substrate <NUM> with an adhesive or the like. The nozzle plate <NUM> has a plurality of nozzles <NUM> formed at positions facing the plurality of pressure chambers <NUM>. In an embodiment, the nozzle plate <NUM> includes two nozzle rows <NUM> in which a plurality of nozzles <NUM> are aligned.

The first common liquid chamber <NUM> is formed between the central sides of the pair of actuators <NUM> except for both ends of the pair of actuators <NUM>, and forms an ink flow path from the supply port <NUM> to the openings (inlets) on the primary side of the pressure chambers <NUM> of each actuator <NUM>. The first common liquid chamber <NUM> extends along the longitudinal direction of the actuator <NUM>.

Each of the second common liquid chambers <NUM> is formed between an actuator <NUM> and the frame body <NUM>. Each of the second common liquid chambers <NUM> forms an ink flow path from the openings (outlets) on the secondary side of the plurality of pressure chambers <NUM> to the discharge port <NUM>. The second common liquid chambers <NUM> extend along the longitudinal direction of the actuator <NUM>.

The plurality of individual electrodes <NUM> are electrodes that can be used to individually apply a driving voltage to the plurality of piezoelectric columns <NUM>. The individual electrodes <NUM> may be used to individually deform any particular one of the pressure chambers <NUM>. Each electrode <NUM> comprises the wiring portions that are formed on the actuator <NUM> and on the substrate <NUM>.

Each individual electrode <NUM> is drawn out from the inner surface of the pressure chamber <NUM> to the inclined surface <NUM> and the wiring surface <NUM> of the substrate <NUM>, extends to the end in the lateral direction of the substrate <NUM>, and is connected to the drive circuit <NUM>. The individual electrodes <NUM> are formed of, for example, a nickel thin film. The individual electrodes <NUM> are not limited to being a nickel thin film, and may be formed of, for example, a thin film of gold or copper. A part of each electrode <NUM> may be covered with an adhesive that is used to adhere the bottom surface of the frame body <NUM> to the substrate <NUM>.

Each individual electrode <NUM> is connected to drive circuit <NUM>. For example, the individual electrodes <NUM> can be connected to a control unit <NUM> via a driver in the drive circuit <NUM> by a wiring. The individual electrodes <NUM> and the drive circuit <NUM> configured so that individual electrodes <NUM> may be addressable/controllable by a processor.

As illustrated in <FIG> and <FIG>, the manifold unit <NUM> includes a manifold <NUM>, ink supply pipes <NUM>, ink discharge pipes <NUM>, and a pair of temperature control pipes of a temperature control water supply pipe <NUM> and a temperature control water discharge pipe. The numbers of the ink supply pipes <NUM>, the ink discharge pipes <NUM>, the temperature control water supply pipes <NUM>, and the temperature control water discharge pipes can be appropriately set.

The manifold <NUM> is formed in a plate shape or a block shape. The manifold <NUM> includes a supply flow path, which is continuous with the supply port <NUM> of the substrate <NUM> and forms a liquid supply flow path, a discharge flow path, which is continuous with the discharge port <NUM> of the substrate <NUM> and forms a liquid discharge flow path, and a temperature control flow path which forms a fluid flow path for temperature control.

One main surface of the manifold <NUM> is fixed to the main surface of the substrate <NUM>. For example, the ink supply pipe <NUM>, the ink discharge pipe <NUM>, the temperature control water supply pipe <NUM>, and the temperature control water discharge pipe are fixed to the manifold <NUM>.

The supply flow path is formed in the manifold <NUM> by holes and grooves. The supply flow path fluidly connects the ink supply pipe <NUM> and the supply port <NUM> of the substrate <NUM>.

The discharge flow path is formed in the manifold <NUM> by holes and grooves. The discharge flow path fluidly connects the ink discharge pipe <NUM> and the discharge port <NUM> of the substrate <NUM>.

The temperature control flow path is formed in the manifold <NUM> by holes and grooves. The temperature control flow path fluidly connects the temperature control water supply pipe <NUM> and the temperature control water discharge pipe.

The temperature control flow path has openings connected to the temperature control water supply pipe <NUM> at one end and the temperature control water discharge pipe at the other. The temperature control flow path is capable of heat exchange with the substrate <NUM> fixed to the manifold <NUM>.

The ink supply pipe <NUM> is connected to the supply flow path. The ink discharge pipe <NUM> is connected to the discharge flow path. The temperature control water supply pipe <NUM> and temperature control water discharge pipe are connected to the primary side and the secondary side of the temperature control flow path, respectively.

As illustrated in <FIG>, the drive circuit <NUM> includes wiring films <NUM>, each of which has one end connected to the substrate <NUM>, driver ICs <NUM> mounted on the wiring film <NUM>, and a printed wiring board <NUM> mounted on the other end of each wiring film <NUM>.

The drive circuit <NUM> drives the actuator <NUM> by applying a drive voltage to a wiring pattern of the actuator <NUM> by the driver IC <NUM> to increase or decrease the volume of the pressure chamber <NUM> and eject droplets from the nozzle <NUM>.

The wiring film <NUM> is connected to the plurality of individual electrodes <NUM>. For example, the wiring film <NUM> is an anisotropic conductive film (ACF) fixed to a connection portion of the substrate <NUM> by thermos-compression bonding or the like. A plurality of wiring films <NUM> to be connected are provided for, for example, one head body <NUM>. In an embodiment, two wiring films <NUM> are connected to one actuator <NUM>. The wiring film <NUM> is, for example, a chip-on-film (COF) on which the driver IC <NUM> is mounted.

The driver IC <NUM> is connected to the plurality of individual electrodes <NUM> via the wiring film <NUM>. The driver IC <NUM> may be connected to the plurality of individual electrodes <NUM> by other means such as combination of an anisotropic conductive paste (ACP), a non-conductive film (NCF), and a non-conductive paste (NCP) instead of the wiring film <NUM>.

The driver IC <NUM> generates a control signal and a drive signal for operating the piezoelectric column <NUM> as each drive element. The driver IC <NUM> generates a control signal for control such as selecting the timing for ejecting ink and the piezoelectric column <NUM> for ejecting ink according to an image signal input from the control unit <NUM> of the liquid ejection apparatus <NUM>. The driver IC <NUM> generates a voltage applied to the piezoelectric column <NUM> according to the control signal, that is, a drive signal. If the driver IC <NUM> applies the drive signal (voltage) to the piezoelectric column <NUM>, the piezoelectric column <NUM> is driven so as to change the volume of the pressure chamber <NUM>. With this configuration, ink inside the pressure chamber <NUM> can be ejected from the nozzle <NUM> corresponding to the pressure chamber <NUM>. The liquid ejection head <NUM> may be capable of changing the amount (e.g., number) of ink droplets that land for printing one pixel for purposes of gradation expression (e.g., providing different levels of color saturation or shading). The liquid ejection head <NUM> may be capable of changing the amount of ink droplets that land on each pixel by changing the number of times the ink is ejected. Thus, the driver IC <NUM> applies the drive signal to the piezoelectric column <NUM> as appropriate.

For example, the driver IC <NUM> includes a data buffer, a decoder, and a driver. The data buffer stores print data in chronological order on a per piezoelectric column <NUM> basis. The decoder controls the driver based on the print data stored in the data buffer on the per piezoelectric column <NUM> basis. The driver outputs a drive signal to operate each piezoelectric column <NUM> under the control of the decoder. The drive signal is the voltage applied to each piezoelectric column <NUM>.

The printed wiring board <NUM> is a printed wiring assembly (PWA) on which various electronic components and connectors are mounted.

The cover <NUM> includes, for example, an outer shell <NUM> that covers the side surfaces of the pair of head bodies <NUM>, the manifold unit <NUM>, and the drive circuit <NUM>, and a mask plate that covers a part of the pair of head bodies <NUM> on the nozzle plate <NUM> side.

The outer shell <NUM> leaves exposed to the outside the ink supply pipe <NUM>, the ink discharge pipe <NUM>, the temperature control water supply pipe <NUM> and the temperature control water discharge pipe, and the end portion of the drive circuit <NUM>.

The mask plate covers a portion of the pair of head bodies <NUM> excluding the plurality of nozzles <NUM> and the periphery of the plurality of nozzles <NUM> of the nozzle plate <NUM>.

Hereinafter, the liquid ejection apparatus <NUM> including the liquid discharge head <NUM> will be described with reference to <FIG>. The liquid ejection apparatus <NUM> includes a casing <NUM>, a paper supply unit <NUM>, an image forming unit <NUM>, a paper discharge unit <NUM>, a conveyance device <NUM>, a maintenance device <NUM>, and a control unit <NUM>. The liquid ejection apparatus <NUM> includes a temperature control device that adjusts the temperature of ink supplied to the liquid ejection head <NUM>.

The liquid ejection apparatus <NUM> is an ink jet printer that performs an image forming processing on paper P by ejecting a liquid, such as an ink, onto the paper P as a recording medium while the paper P is conveyed along a predetermined conveyance path <NUM> from the paper supply unit <NUM> through the image forming unit <NUM> to the paper discharge unit <NUM>.

The paper supply unit <NUM> includes a plurality of paper feed cassettes <NUM>. The image forming unit <NUM> includes a support portion <NUM> that supports paper, and a plurality of head units <NUM> that are disposed so as to face each other above the support portion <NUM>. The paper discharge unit <NUM> includes a paper discharge tray <NUM>.

The support portion <NUM> includes a conveyance belt <NUM> provided in a loop shape in a predetermined area for which image formation is performed, a support plate <NUM> for supporting the conveyance belt <NUM> from the back side, and a plurality of belt rollers <NUM> provided on the back side of the conveyance belt <NUM>.

The head units <NUM> include the liquid ejection heads <NUM> which are a plurality of ink jet heads, a plurality of supply tanks <NUM> as liquid tanks mounted on the liquid ejection heads <NUM>, and pumps <NUM> for supplying ink, connection flow paths <NUM> for connecting the liquid ejection heads <NUM> and the supply tanks <NUM>.

In an embodiment, the liquid ejection heads <NUM> eject ink of four colors of cyan, magenta, yellow, and black, and include the supply tanks <NUM> for storing ink of these colors. The supply tank <NUM> is connected to the liquid ejection head <NUM> by the connection flow path <NUM>.

The pump <NUM> is a liquid feed pump such as a piezoelectric pump. The pump <NUM> is connected to the control unit <NUM> and is driven and controlled by the control unit <NUM>.

The connection flow path <NUM> includes a supply flow path connected to the ink supply pipe <NUM> of the liquid ejection head <NUM>. The connection flow path <NUM> includes a recovery flow path connected to the ink discharge pipe <NUM> of the liquid ejection head <NUM>. For example, if the liquid ejection head <NUM> is a non-circulating type liquid ejection head, the recovery flow path is connected to the maintenance device <NUM>, and if the liquid ejection head <NUM> is a circulating type liquid ejection head, the recovery flow path is connected to the supply tank <NUM>.

The conveyance device <NUM> conveys paper P along the conveyance path <NUM> from the paper feed cassette past the image forming unit <NUM> to the paper discharge tray <NUM>. The conveyance device <NUM> includes a plurality of guide plates (guide plate <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>) and a plurality of conveyance rollers pairs (conveyance roller pairs <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>) disposed along the conveyance path <NUM>. The conveyance device <NUM> guides paper P past the liquid ejection heads <NUM> for printing.

The maintenance device <NUM> suctions and recovers ink from the outer surface of the nozzle plate <NUM> during maintenance processing. If the liquid ejection head <NUM> is a non-circulating type liquid ejection head, the maintenance device <NUM> also recovers ink stored in the head body <NUM> during maintenance processing. Such a maintenance device <NUM> includes a tray, a tank, or the like for storing the recovered ink.

The control unit <NUM> is, for example, a control board. A processor, a read only memory (ROM), a random access memory (RAM), an I/O port as an input and output port, and an image memory are mounted on the control unit <NUM>.

The processor is a processing circuit such as a central processing unit (CPU) which can be a controller. The processor controls the head unit <NUM> provided in the liquid ejection apparatus <NUM>, a drive motor, an operation panel, various sensors, and the like through the I/O port. The processor transmits print data stored in the image memory to the drive circuit <NUM> in a drawing order.

The ROM stores various programs and the like. The RAM temporarily stores various variable data, image data, and the like. The I/O port is an interface unit that receives data from the outside and outputs data to the outside. Print data from an externally connected device is transmitted to the control unit through the I/O port and stored in the image memory.

Hereinafter, characteristics of the liquid ejection head <NUM> used in the liquid ejection apparatus <NUM> according to an embodiment and a drive waveform by the drive signal generated by the drive circuit <NUM> of the liquid ejection head <NUM> will be described. For example, the drive waveform of the liquid ejection head <NUM> is a multi-drop drive, and includes an ejection waveform portion having a plurality of ejection pulses and a cancel waveform portion having a cancel pulse following the ejection waveform portion.

The ejection waveform portion includes a plurality of ejection pulses Pa, Pb, and Pc. Each of the ejection pulses Pa, Pb, and Pc includes an expansion element that lowers a voltage and a contraction element that raises the voltage following the expansion element. Then, in the drive waveform of the liquid ejection apparatus <NUM> according to an embodiment, an applying voltage in the contraction elements of the plurality of ejection pulses is set in two steps. That is, the drive waveform includes at least two contraction elements that pressurize at different voltages.

For example, if ink droplets are ejected n times (where n is an integer of <NUM> or more) to print three or more gradations, the ejection waveform portion includes (n - <NUM>) expansion elements that expand the pressure chamber by lowering the voltage to voltage Va from a first drop to an (n - <NUM>)-th drop with first intermediate voltage Vb as a reference, a contraction element that contracts the pressure chamber after each expansion element until the voltage reaches the first intermediate voltage Vb, which is an intermediate voltage, and ejects ink, and a contraction element that contracts the pressure chamber after the expansion element until the voltage reaches to a second intermediate voltage Vc higher than the first intermediate voltage Vb, and ejects ink. For example, the voltage Va = <NUM> V.

In an embodiment, a print waveform including n ejection pulses and a cancel pulse in one printing period is within a time shorter than (n + <NUM>)λ. In the drive waveform in one embodiment, the print waveform including n ejection pulses and a cancel pulse in one printing cycle may be within a time shorter than (n + <NUM>)λ.

In the drive waveform according to an embodiment, the period of the primary natural vibration when the pressure chamber <NUM> is filled with ink is λ, the centers of the ejection pulses Pa, Pb, and Pc and the center of the cancel pulse Pd are provided at a period of <NUM> to <NUM>. 2λ, (λ ± variation). The configuration of the entire drive waveform including the ejection waveform portion and the cancel waveform portion is shorter than (n + <NUM>)λ. By adopting such a configuration, the ejection of ink droplets in gradation printing can be stabilized to widen the range in which the size of ink droplets can be increased or decreased.

<FIG> illustrates the drive waveform according to Example <NUM>. This drive waveform is a three-drop waveform, and three ejection pulses for expansion and contraction are aligned at a regular time period λ. Each of the three ejection pulses Pa, Pb, and Pc includes an expansion element that expands the pressure chamber <NUM> to draw liquid into the pressure chamber <NUM> and a contraction element that contracts the pressure chamber <NUM> to eject the liquid. In this example, the first ejection pulse Pa includes an expansion element that lowers the voltage from the first intermediate voltage Vb to expansion voltage Va and a contraction element that raises the voltage to second intermediate voltage Vc higher than the first intermediate voltage Vb. For example, the second intermediate voltage Vc is larger than the first intermediate voltage Vb. That is, in this waveform, the first ejection pulse Pa lowers the voltage from the first intermediate voltage Vb to the expansion voltage Va (= <NUM> V), and then raises the expansion voltage Va to the second intermediate voltage Vc (which is larger than the first intermediate voltage Vb). Then, in the second ejection pulse Pb, the second intermediate voltage Vc is lowered to the expansion voltage Va again and then raised to the first intermediate voltage Vb. In the third ejection pulse Pc, the first intermediate voltage Vb is lowered to the expansion voltage Va and then raised to the first intermediate voltage Vb again.

The cancel waveform portion of Example <NUM> has a cancel pulse Pd including a contraction element that raises the voltage from the first intermediate voltage Vb to a larger second intermediate voltage Vc following the final ejection pulse Pc, and then an expansion element that lowers the final ejection pulse Pc to the first intermediate voltage Vb. In this example, the plurality of ejection pulses Pa, Pb, and Pc and the cancel pulse Pd are aligned at a regular time period λ. In each of the ejection pulses Pa, Pb, and Pc, each of the periods from expansion to contraction and the period from contraction to expansion is λ/<NUM>. In the cancel pulse Pd, each of the periods from the contraction of the ejection pulse Pc to the contraction of the cancel pulse Pd and the period from the contraction to the expansion of the cancel pulse Pd is λ/<NUM>.

<FIG> illustrate simulation results if meniscus is operated at a voltage that does not cause ejection in Example <NUM>. <FIG> illustrates a temporal change in the flow velocity if Vc/Vb is <NUM> and if Vc/Vb is <NUM>. As a simulation condition, λ is set to <NUM>. <FIG> illustrates the temporal change in a meniscus position if Vc/Vb is <NUM> and if Vc/Vb is <NUM>.

According to this example, stabilization of ink droplet ejection and expansion of the range of gradation can be achieved. As illustrated in <FIG>, residual vibration can be suppressed by adjusting a voltage ratio Vc/Vb.

<FIG> illustrates the drive waveform according to Example <NUM>. This drive waveform is a three-drop waveform, and three ejection pulses for expansion and contraction are aligned at a regular time period λ. Each of the three ejection pulses Pa, Pb, and Pc includes an expansion element that expands the pressure chamber <NUM> to draw liquid into the pressure chamber <NUM> and a contraction element that contracts the pressure chamber <NUM> to eject the liquid. In this example, the first ejection pulse Pa includes 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 second intermediate voltage Vc higher than the first intermediate voltage Vb. For example, the second intermediate voltage Vc is larger than the first intermediate voltage Vb. That is, in this waveform, the first ejection pulse Pa lowers the voltage from the first intermediate voltage Vb to the expansion voltage Va (= <NUM> V), and then raises the expansion voltage Va to the second intermediate voltage Vc which is larger than the first intermediate voltage Vb. Then, in the second ejection pulse Pb, the voltage is lowered to the expansion voltage Va again and then raised to the first intermediate voltage Vb. Furthermore, in the third ejection pulse Pc, the first intermediate voltage Vb is lowered to the expansion voltage Va and then raised to the second intermediate voltage Vc again. In this example, in the final ejection pulse, by raising the first intermediate voltage Vb to the second intermediate voltage Vc, which is the maximum voltage, and speeding up the final drop, a plurality of ejected drops can be combined.

The cancel waveform portion of Example <NUM> has a cancel pulse Pd including an expansion element that expands the contracted pressure chamber <NUM> again by raising the first intermediate voltage Vb to the second intermediate voltage Vc higher than the first intermediate voltage Vb in the contraction element of the final ejection pulse Pc and changes the second intermediate voltage Vc to the expansion voltage Va lower than the first intermediate voltage Vb, and a contraction element that contracts the pressure chamber <NUM> again and then returns the expansion voltage Va to the first intermediate voltage Vb.

In this example, the plurality of ejection pulses Pa, Pb, and Pc are aligned at a regular time period λ. In each of the ejection pulses Pa, Pb, and Pc, each of the periods from expansion to contraction and the period from contraction to expansion is λ/<NUM>. In the cancel waveform portion, the spacing from the contraction element of the ejection pulse Pc to the expansion element of the cancel pulse Pd is λ, and the period from the expansion to the contraction of the cancel pulse Pd is <NUM>. 1λ to <NUM>.

<FIG> illustrate simulation results if the meniscus is operated at a voltage that does not cause ejection in Example <NUM>. <FIG> illustrates the temporal change in the flow velocity if Vc/Vb is <NUM> and if Vc/Vb is <NUM>. As a simulation condition, λ is set to <NUM>. <FIG> illustrates the temporal change in the meniscus position if Vc/Vb is <NUM> and if Vc/Vb is <NUM>.

According to this example, stabilization of ink droplet ejection and expansion of the range of gradation can be achieved. As illustrated in <FIG>, residual vibration can be suppressed by adjusting the voltage ratio Vc/Vb.

<FIG> illustrates the drive waveform of Example <NUM>. The drive waveform of Example <NUM> is a modification example of the drive waveform of Example <NUM>, and has a step waveform in which the timing of starting a part of the pulse of the cancel pulse portion is adjusted and the cancel pulse Pd is expanded in two steps.

The cancel waveform portion of Example <NUM> has a cancel pulse Pd that includes an expansion element including a step waveform that expands the pressure chamber <NUM>, which is contracted by raising the first intermediate voltage Vb to the second intermediate voltage Vc higher than the first intermediate voltage Vb in the contraction element of the final ejection pulse Pc, again to lower the second intermediate voltage Vc to the first intermediate voltage Vb, and subsequently further changes the first intermediate voltage Vb to the expansion voltage Va lower than the first intermediate voltage Vb and a contraction element that contracts the pressure chamber <NUM> again and returns the expansion voltage Va to the first intermediate voltage Vb.

In the cancel waveform portion, the period from the contraction element of the final ejection pulse Pc to the expansion element of the cancel pulse Pd is λ, and the period from the expansion to the contraction of the cancel pulse Pd is <NUM>. 1λ to <NUM>. Other waveforms are the same as in Example <NUM>.

Also in this example, stabilization of ink droplet ejection and expansion of the range of gradation can be achieved.

<FIG> illustrate simulation results if the meniscus is operated at a voltage that does not cause ejection in Example <NUM>. <FIG> illustrates the temporal change in the flow velocity if Vc/Vb is <NUM> and if Vc/Vb is <NUM>. As a simulation condition, λ is set to <NUM>. <FIG> illustrates the temporal change in the meniscus position if Vc/Vb is <NUM> and if Vc/Vb is <NUM>. As illustrated in <FIG>, residual vibration can be suppressed by adjusting the voltage ratio Vc/Vb.

<FIG> illustrates the drive waveform of Example <NUM>. The drive waveform of Example <NUM> is a modification example of the drive waveform of Example <NUM>, and is an example of switching the voltage of the contraction element of Pa and Pb.

The drive waveform of Example <NUM> is a three-drop waveform, and three ejection pulses for expansion and contraction are aligned at a regular time period λ. Each of the three ejection pulses Pa, Pb, and Pc includes an expansion element that expands the pressure chamber <NUM> to draw liquid into the pressure chamber <NUM> and a contraction element that contracts the pressure chamber <NUM> to eject the liquid. In this example, the first ejection pulse Pa includes 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 expansion voltage Va to the first intermediate voltage Vb. The second ejection pulse Pb lowers the first intermediate voltage Vb to the expansion voltage Va again, and then raises the expansion voltage Va to the second intermediate voltage Vc larger than the first intermediate voltage Vb. Furthermore, the second intermediate voltage Vc is lowered to the expansion voltage Va in the third ejection pulse Pc, and then raised to the second intermediate voltage Vc again. Other waveforms are the same as in Example <NUM>. Also in this example, stabilization of ink droplet ejection and expansion of the range of gradation can be achieved.

<FIG> is a drive waveform of Example <NUM>. The drive waveform of Example <NUM> is a modification example of the drive waveform of Example <NUM>, and is an example in which Pa and Pb include a step waveform portion that maintains an intermediate voltage for a certain period of time, and a voltage is applied stepwise. In this example, the contraction element of the first ejection pulse Pa has a step waveform that raises the voltage stepwise, and the expansion element of the second ejection pulse Pb has a step waveform that lowers the voltage stepwise.

This drive waveform of Example <NUM> is a three-drop waveform, and three ejection pulses for expansion and contraction are aligned at a regular time period λ. Each of the three ejection pulses Pa, Pb, and Pc includes an expansion element that expands the pressure chamber <NUM> to draw liquid into the pressure chamber <NUM> and a contraction element that contracts the pressure chamber <NUM> to eject the liquid. In this example, the first ejection pulse Pa includes 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 expansion voltage Va to the second intermediate voltage Vc, which is larger than the first intermediate voltage Vb, stepwise. For example, the second intermediate voltage Vc is larger than the first intermediate voltage Vb. The first ejection pulse Pa has a step waveform in which the voltage is raised 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 the first intermediate voltage Vb is raised to the second intermediate voltage Vc stepwise. In this waveform, the first ejection pulse Pa lowers the voltage from the first intermediate voltage Vb to the expansion voltage Va (= <NUM> V), then raises the voltage to the first intermediate voltage Vb, and further raises the voltage to the second intermediate voltage Vc larger than the first intermediate voltage Vb. The second ejection pulse Pb includes an expansion 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 further lowers the first intermediate voltage Vb to the expansion voltage Va, and a contraction element that raises the expansion voltage Va to the first intermediate voltage Vb again. The third ejection pulse Pc has the expansion element that lowers the voltage from the first intermediate voltage Vb to the expansion voltage Va, and the contraction element that raises the expansion voltage Va to the first intermediate voltage Vb again.

As illustrated in <FIG>, the cancel waveform portion of this example has the step waveform that maintains the first intermediate voltage Vb for a certain period of time. Specifically, the cancel waveform portion includes a contraction element that maintains the first intermediate voltage Vb for a certain period of time after raising the expansion voltage Va to the first intermediate voltage Vb in the contraction element of the final ejection pulse Pc and then raises the first intermediate voltage Vb to the second intermediate voltage Vc stepwise, an expansion element that expands the pressure chamber <NUM> contracted by the second intermediate voltage Vc again to maintain the state of the first intermediate voltage Vb for a certain period of time, and then changes the first intermediate voltage Vb to the expansion voltage Va in a stepwise manner, and a contraction element that contracts the expanded pressure chamber <NUM> again and then returns the expansion voltage Va to the first intermediate voltage Vb.

Other waveforms are the same as in Example <NUM>. Also in this example, stabilization of ink droplet ejection and expansion of the range of gradation can be achieved.

<FIG> is a drive waveform of Example <NUM>. The drive waveform of Example <NUM> is a modification example of the drive waveform of Example <NUM>, and is an example of including an auxiliary waveform portion before the ejection waveform portion. That is, in this example, the auxiliary waveform portion has an auxiliary pulse Pe (including a contraction element that raises the voltage from the first intermediate voltage Vb to the second intermediate voltage Vc) before the expansion element of the first ejection pulse Pa. Other waveforms are the same as in Example <NUM>. The auxiliary pulse can speed up the first drop of ink.

In the liquid ejection head <NUM> and the liquid ejection apparatus <NUM>, gradation can be provided by raising the intermediate voltage of the contraction element in the ejection pulse. That is, for example, if the voltage of the ejection pulse from the first drop to the (n - <NUM>) drop is the same, the size of the ink droplet that can be ejected is limited. Therefore, when printing a multi-gradation image by changing the size of print dots, the range in which the size of the ink droplet can be increased or decreased is fairly narrow, and the expression of gradation is limited. In contrast, according to the examples above, the range of the gradation expression can be expanded by controlling the intermediate voltage in two or more steps (increments). According to those examples, the ejection stability can be ensured by having (n - <NUM>) ejection pulses at intervals of <NUM> to <NUM>. 2λ, where λ is a period of a primary natural vibration when the pressure chamber is filled with ink. Therefore, both an expansion of the expression range of gradation and ejection stability can be achieved.

The liquid ejection head <NUM> or the liquid ejection apparatus <NUM> may have any configuration other than the ones described above.

For example, three-drop gradation is used as an example, but the disclosure is not limited thereto, and four or more-drop may be used. In such cases, steps for the voltage of the contraction element are not limited to two, but may be set to three or more.

The configuration of the liquid ejection head <NUM> is not limited to the examples described above, and may be used for other types of heads.

According to at least one embodiment described above, both the stabilization of ejection of ink droplets and the expansion of the range of gradation can be achieved.

While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions.

Claim 1:
A liquid ejection head (<NUM>), comprising:
a nozzle (<NUM>) from which a droplet of a liquid can be ejected;
a pressure chamber (<NUM>) for the liquid, the pressure chamber connected to the nozzle;
an actuator (<NUM>) configured to change a volume of the pressure chamber according to a voltage signal applied to the actuator; and
a drive circuit (<NUM>) configured to generate the voltage signal that includes n-<NUM> ejection pulses when droplets are to be ejected n times from the nozzle, where n is an integer of <NUM> or more, wherein
the ejection pulses include:
a first ejection pulse that lowers a voltage applied to the actuator to a first voltage value to expand the pressure chamber and then raises the voltage to a second voltage value to contract the pressure chamber, and
a second ejection pulse that lowers the voltage to the first voltage value and then raises the voltage to a third voltage value higher than the second voltage value, and
the ejection pulses are separated by intervals of <NUM>.8λ to <NUM>.2λ, where λ is a period of a primary natural vibration for the pressure chamber filled with the liquid,
the voltage signal further includes a cancel pulse following the ejection pulses,
a last ejection pulse of the ejection pulses is the second ejection pulse by which the voltage is raised to the third voltage value,
the cancel pulse lowers the voltage to a voltage value lower than the second voltage value and then raises the voltage to the second voltage value, characterised in that:
the cancel pulse is input after the voltage is lowered from the third voltage value to the second voltage value.