Patent Description:
In the use of an inkjet head, small droplets called satellites, ink mists, or the like may be generated along with the main ink droplets (main droplets) that are ejected from the nozzles of the inkjet head. These small droplets cause deterioration of print quality. Therefore, there is a demand for the development of an inkjet head that suppresses the generation of these small droplets.

<CIT> and <CIT> describe an inkjet head, comprising: a pressure chamber for ink; a nozzle plate including a nozzle for ejecting ink from the pressure chamber; an actuator configured to change a volume of the pressure chamber; and a drive circuit configured to drive the actuator according to a drive waveform, wherein the drive waveform includes: an expansion portion that drives the actuator in an expansion direction expanding the volume of the pressure chamber, a first weak contraction portion after the expansion portion that drives the actuator in a contraction direction contracting the volume of the pressure chamber, a contraction portion after the first weak contraction portion that drives the actuator in the contraction direction by an amount greater than the first weak contraction portion, and a second weak contraction portion after the contraction portion that drives the actuator in the contraction direction by an amount less than the contraction portion.

The drive waveform further includes a holding portion between the expansion portion and the first weak contraction portion, the holding portion not driving the actuator in either the contracting direction or the expansion direction.

The drive waveform comprises a first droplet ejection operation and a second droplet ejection operation after the first droplet ejection operation.

The holding portion, the first weak contraction portion, the contraction portion, and the second weak contraction portion are in the second droplet ejection operation.

A sum of a holding time of the holding portion and a first weak contraction time of the first weak contraction portion is greater than or equal to a holding time of a first droplet ejection operation holding portion plus <NUM> microseconds, but less than or equal to the holding time of the first droplet ejection operation holding portion plus <NUM> microseconds.

Preferably, a second weak contraction time of the second weak contraction portion is greater than or equal to an expansion time of a first droplet ejection operation expansion portion minus <NUM> microseconds, but less than or equal to the expansion time of the first droplet ejection operation expansion portion plus <NUM> microseconds.

Preferably, a contraction time of the contraction portion is equal to <NUM> times the expansion time of the first droplet ejection operation expansion portion minus the second weak contraction time and the sum of the holding time of the holding portion and the first weak contraction time.

Preferably, the actuator comprises a piezoelectric material.

The inkjet head may further comprise a plurality of pressure chambers for ink. The nozzle plate includes a nozzle for each of the plurality of pressure chambers.

Preferably, the drive circuit includes a first power source line connected to a positive terminal of a first power source, a second power source line connected to a negative terminal of a second power source, and a ground line connected to a ground terminal connected to a negative terminal of the first power source and a positive terminal of the second power source.

Preferably, the drive circuit further includes a plurality of switch elements, each switch element having at least one of a source or drain connected one of the first power source line, the second power source line, or the ground line.

An object of certain example embodiments described herein is to provide an inkjet head that suppresses generation of small, unintended droplets such as satellite droplets and the like.

In general, according to one embodiment, an inkjet head includes a pressure chamber for ink, a nozzle plate including a nozzle for ejecting ink from the pressure chamber, and an actuator configured to change a volume of the pressure chamber. A drive circuit is configured to drive the actuator according to a drive waveform. The drive waveform includes an expansion portion that drives the actuator in an expansion direction expanding the volume of the pressure chamber; a first weak contraction portion after the expansion portion that drives the actuator in a contraction direction contracting the volume of the pressure chamber; a contraction portion after the first weak contraction portion that drives the actuator in the contraction direction by an amount greater than the first weak contraction portion; and a second weak contraction portion after the contraction portion that drives the actuator in the contraction direction by an amount less than the contraction portion.

Hereinafter, example embodiments will be described with reference to the drawings.

The examples use a piezo type inkjet head as an on-demand type inkjet head.

<FIG> is a perspective view illustrating a piezo-type inkjet head <NUM>. The inkjet head <NUM> is of shared wall type. Hereinafter, the inkjet head <NUM> will be referred to as a head <NUM> for simplicity.

The head <NUM> includes a head main body <NUM> with a plurality of nozzles <NUM> for ejecting ink, a head driver <NUM> for generating a drive signal, and a manifold <NUM> with an ink supply port <NUM> and an ink discharge port <NUM>. The head driver <NUM> includes two driver ICs (IC driver <NUM> and IC driver <NUM>). Each of the driver ICs <NUM> and <NUM> has the same circuit configuration. Each of the driver ICs <NUM> and <NUM> includes a head drive circuit <NUM> which will be described below.

The head <NUM> ejects ink (which is supplied from the ink supply port <NUM>) from the nozzle <NUM> in response to a drive signal generated by the head driver <NUM>. Further, the head <NUM> discharges, from the ink discharge port <NUM>, the ink that flows in from the ink supply port <NUM> but is not ejected from a nozzle <NUM>.

<FIG> is a plan view illustrating the head main body <NUM>. <FIG> is a view taken along line A-A of the head main body <NUM> illustrated in <FIG>, and <FIG> is a view taken along line B-B of the head main body <NUM> illustrated in <FIG>.

As illustrated in <FIG>, the head main body <NUM> includes a piezoelectric member <NUM>, a base substrate <NUM>, a nozzle plate <NUM>, and a frame member <NUM>. The head main body <NUM> begins with the base substrate <NUM>. Then, the frame member <NUM> is joined onto the base substrate <NUM>, and the piezoelectric member <NUM> is joined into the frame member <NUM>. The nozzle plate <NUM> is adhered onto the frame member <NUM>. Additionally, as illustrated in <FIG>, a central space that is surrounded by portions of the base substrate <NUM>, the piezoelectric member <NUM>, and the nozzle plate <NUM> serves as an ink supply path <NUM>. Additionally, in the head main body <NUM>, a peripheral space surrounded by portions of the base substrate <NUM>, the piezoelectric member <NUM>, the frame member <NUM>, and the nozzle plate <NUM> serves as an ink discharge path <NUM>. In the nozzle plate <NUM>, a plurality of nozzles <NUM> are formed in a repeating pattern or the like.

The base substrate <NUM> includes a hole <NUM> communicating with (connecting to) the ink supply path <NUM> and a hole <NUM> communicating with (connecting to) the ink discharge path <NUM>. The hole <NUM> communicates with the ink supply port <NUM> through the manifold <NUM>. The hole <NUM> communicates with (connects to) the ink discharge port <NUM> through the manifold <NUM>.

As illustrated in <FIG>, in the piezoelectric member <NUM>, a first piezoelectric member <NUM> and a second piezoelectric member <NUM> (having a polarity opposite to that of the first piezoelectric member <NUM>) are stacked. The first piezoelectric member <NUM> and the second piezoelectric member <NUM> are adhered to each other.

As illustrated in <FIG>, in the piezoelectric member <NUM>, a plurality of elongated grooves <NUM> are formed in parallel. The grooves <NUM> extend from the ink supply path <NUM> to the ink discharge path <NUM>. Then, as illustrated in <FIG>, electrodes <NUM> are arranged on inner surfaces of the grooves <NUM>, respectively. As illustrated in <FIG>, the electrodes <NUM> are connected to the head driver <NUM> through wirings <NUM>, respectively. The spaces surrounded by each groove <NUM> and back surface of the nozzle plate <NUM> (which is adhered onto the second piezoelectric member <NUM> to cover the grooves <NUM>) are pressure chambers <NUM>, respectively. Additionally, the nozzles <NUM> each communicate with one of the pressure chambers <NUM> on a one-to-one basis.

As illustrated in <FIG>, a portion of piezoelectric member <NUM> forms a partition wall between adjacent pressure chambers <NUM>. The partition wall portion is interposed between the electrodes <NUM> of the respective adjacent pressure chambers <NUM>. An actuator <NUM> is formed by the portion of the piezoelectric member <NUM> between the electrodes <NUM> on both sides thereof. When an electric field is applied according to the drive signal generated by the head drive circuit <NUM>, the actuator <NUM> is shear deformed into a "<" or ">" shape with its ridge or apex portion corresponding to the joint point between the first piezoelectric member <NUM> and the second piezoelectric member <NUM>. When the actuator <NUM> is deformed, the volume of the pressure chamber <NUM> is changed, and the ink inside the pressure chamber <NUM> can be pressurized. The pressurized ink is ejected from the nozzle <NUM> connected to the pressure chamber <NUM>. That is, the head drive circuit <NUM> serves as a drive circuit for driving the actuator <NUM> for ejecting ink from a nozzle <NUM>.

A grouping of components including a pressure chamber <NUM>, the electrode <NUM> arranged in the pressure chamber <NUM>, and the nozzle <NUM> of the pressure chamber <NUM> can be referred to as a channel. That is, the head <NUM> includes as many channels as there are pressure chambers <NUM>. Hereinafter, a grouping of channels(e.g., a subset of the pressure chambers <NUM>) can be referred to as a channel group <NUM> (see <FIG>).

Next, the operating principle of the head <NUM> will be described with reference to <FIG>.

<FIG> illustrates a state in which all potentials of the electrodes <NUM> arranged on the wall surfaces of a central pressure chamber <NUM> and adjacent pressure chambers <NUM> and <NUM> on both sides of the central pressure chamber <NUM> respectively have the ground potential GND. In this state, neither the actuator <NUM> interposed between the pressure chamber <NUM> and the pressure chamber <NUM>, nor the actuator <NUM> interposed between the pressure chamber <NUM> and the pressure chamber <NUM> is subjected to any deforming action.

<FIG> illustrates a state in which a negative voltage ("-V") is applied to the electrode <NUM> of the central pressure chamber <NUM>, and a positive voltage ("+V") is applied to the electrodes <NUM> of the adjacent pressure chambers <NUM> and <NUM>. In this state, an electric field with a doubled net voltage acts on each of the actuators <NUM> and <NUM> in a direction orthogonal to the polarization direction of the piezoelectric members <NUM> and <NUM>. By this action, each of the actuators <NUM> and <NUM> is deformed outward so as to expand the volume of the pressure chamber <NUM>.

<FIG> illustrates a state in which a positive voltage ("+V") is applied to the electrode <NUM> of the central pressure chamber <NUM>, and a negative voltage ("-V") is applied to the electrodes <NUM> of the adjacent pressure chambers <NUM> and <NUM>. In this state, an electric field with a doubled net voltage acts on each of the actuators <NUM> and <NUM> in the direction opposite to that in <FIG>. By this action, each of the actuators <NUM> and <NUM> is deformed inward so as to contract the volume of the pressure chamber <NUM>.

When the volume of the pressure chamber <NUM> is expanded or contracted, a pressure vibration is generated in the pressure chamber <NUM>. By this pressure vibration, ink droplets can be ejected from the nozzle <NUM> communicating with the pressure chamber <NUM>.

As described above, the actuator <NUM> that separates the pressure chamber <NUM> and the pressure chamber <NUM>, and the actuator <NUM> that separates the pressure chamber <NUM> and the pressure chamber <NUM> apply the pressure vibration to the inside of the pressure chamber <NUM>. That is, the pressure chamber <NUM> shares an actuator <NUM> with each of its adjacent pressure chambers <NUM> and <NUM>. Therefore, the head drive circuit <NUM> cannot drive each of the pressure chambers <NUM> individually. In the head drive circuit <NUM>, the pressure chambers <NUM> are thus divided into groups of (n + <NUM>) (where n can be any integer of <NUM> or more) for driving. The members of each group are separated from each other by n other pressure chambers <NUM> which are not members of the group. In this example embodiment, the pressure chambers <NUM> are divided into a group of three chambers, which are separated from each other by two non-group chambers, that is, the case of the so-called <NUM>-division driving. The <NUM>-division driving is just an example, and accordingly, the driving may be <NUM>-division driving, <NUM>-division driving, or the like.

Next, an inkjet printer <NUM> using the head <NUM> will be described. Hereinafter, the inkjet printer <NUM> will be referred to as a printer <NUM>.

<FIG> is a block diagram illustrating the hardware configuration of the printer <NUM>. The printer <NUM> includes a processor <NUM>, a Read Only Memory (ROM) <NUM>, a Random Access Memory (RAM) <NUM>, an operation panel <NUM>, a communication interface <NUM>, a conveying motor <NUM>, a motor drive circuit <NUM>, a pump <NUM>, a pump drive circuit <NUM>, the head <NUM>, and the like. Further, the printer <NUM> includes a bus line <NUM> such as an address bus and a data bus. The processor <NUM>, the ROM <NUM>, the RAM <NUM>, the operation panel <NUM>, the communication interface <NUM>, the motor drive circuit <NUM>, the pump drive circuit <NUM>, the drive circuit <NUM> of the head <NUM> each connect to bus line <NUM> directly or through an input and output (I/O) circuit.

The processor <NUM> controls the other units and/or components to realize various functions of the printer <NUM> according to an operating system and/or an application program(s). The processor <NUM> is a central processing unit (CPU), for example.

The ROM <NUM> stores an operating system and/or an application program(s). The ROM <NUM> may store data necessary for the processor <NUM> to execute processes for controlling other units and/or components.

The RAM <NUM> stores data for the processor <NUM> to execute various processing. The RAM <NUM> is also used as a work area where information can be rewritten by the processor <NUM>. The work area includes an image memory in which print data can be loaded.

The operation panel <NUM> includes an input operation unit and a display unit. The input operation unit can include various function keys such as a power key, a paper feed key, an error release key, and the like. The display unit can display status indicators and/or information indicating various operating states of the printer <NUM>.

The communication interface <NUM> receives print data from a client terminal connected through a network such as Local Area Network (LAN) or the like. For example, if an error occurs in the printer <NUM>, the communication interface <NUM> transmits a signal notifying the error to the client terminal.

The motor drive circuit <NUM> controls the driving of the conveying motor <NUM>. The conveying motor <NUM> serves as a drive source for a conveyance mechanism that conveys a recording medium such as printer paper. Once the conveying motor <NUM> is activated, the conveyance mechanism starts to convey the recording medium. The conveyance mechanism conveys the recording medium to the printing position near the head <NUM>. The conveyance mechanism eventually discharges the printed recording medium to the outside of the printer <NUM> from a discharge port.

The pump drive circuit <NUM> controls the driving of the pump <NUM>. When the pump <NUM> is driven, ink from an ink tank or the like is supplied to the head <NUM>.

The head drive circuit <NUM> drives a channel group <NUM> of the head <NUM> based on the print data.

<FIG> is a diagram illustrating aspects of a circuit configuration of the head drive circuit <NUM>. The head drive circuit <NUM> includes a charge and discharge circuit <NUM>, a waveform generation circuit <NUM>, and a power supply circuit <NUM>. The charge and discharge circuit <NUM> electrically connects the waveform generation circuit <NUM> and the power supply circuit <NUM>. Note that in some examples the waveform generation circuit <NUM> and the power supply circuit <NUM> may be physically separated from the head <NUM> and electrically connected to the charge and discharge circuit <NUM>.

In the power supply circuit <NUM>, a first voltage source <NUM> and a second voltage source <NUM> are connected in series. Specifically, a negative electrode of the first voltage source <NUM> and a positive electrode of the second voltage source <NUM> are connected to each other and a connection point therebetween is grounded(zero V). Both the first voltage source <NUM> and the second voltage source <NUM> output a DC voltage E/<NUM>, which is half of the maximum voltage E, which is the charging target of the charge and discharge circuit <NUM>. A power supply line La connected to a positive electrode of the first voltage source <NUM> is a positive power supply line at +E/<NUM>. A power supply line Lb connected to a negative electrode of the second voltage source <NUM> is a negative power supply line at -E/<NUM>. A power supply line Lc connected to the connection point between the negative electrode of the first voltage source <NUM> and the positive electrode of the second voltage source <NUM> is a ground line (zero V).

The charge and discharge circuit <NUM> is connected to the first voltage source <NUM> and the second voltage source <NUM> through the power supply line La, the power supply line Lb, and the power supply line Lc. The charge and discharge circuit <NUM> is also connected to a reference power supply VBG at +24V through a power supply line Ld.

In the charge and discharge circuit <NUM>, a number of switch series circuits are connected between the positive power supply line La and the negative power supply line Lb. Specifically, in the charge and discharge circuit <NUM>, a switch series circuit including a switch element <NUM> and a switch element <NUM>, a switch series circuit including a switch element <NUM> and a switch element <NUM>,. and a switch series circuit including a switch element <NUM> and a switch element <NUM> are connected between the positive power supply line La and the negative power supply line Lb.

Furthermore, a switch element <NUM>, a switch element <NUM>,. and a switch element <NUM> are connected respectively between a switch element interconnection point of each of the switch series circuits and the ground line Lc. The actuators <NUM>, <NUM>,. <NUM> are capacitive actuators including piezoelectric elements and are connected between the switch element interconnection points of adjacent switch series circuits.

Since the actuators (<NUM>,. <NUM>) are connected between the switch element interconnection points of the adjacent switch series circuits, the total number of actuators is one less than the total number of the switch series circuits. The number of switch series circuits is not limited to nine as depicted in the figure, nor is the number of limited to eight.

The switch elements <NUM>, <NUM>,. <NUM> connected to the positive power supply line La are P-type channel MOS transistors. The switch elements <NUM>, <NUM>,. <NUM> connected to the negative power supply line Lb are N-type channel MOS transistors. Therefore, in the charge and discharge circuit <NUM>, a large number of series circuits of the sources and drains of the P-type channel MOS transistors and the sources and drains of the N-type channel MOS transistors are connected between the positive power supply line La and the negative power supply line Lb.

The switch elements <NUM>, <NUM>,. <NUM> are N-type channel MOS transistors. Therefore, in the charge and discharge circuit <NUM>, the sources and drains of the N-type channel MOS transistors are connected between the switch element interconnection point of each of the switch series circuits and the ground line Lc.

Back gates of the P-type channel MOS transistors (the switch elements <NUM>, <NUM>,. <NUM>) are connected to a reference power supply line Ld of +24V. Back gates of the N-type channel MOS transistors (the switch elements <NUM>, <NUM>,. <NUM> and switch elements <NUM>, <NUM>,. <NUM>) are connected to a negative power supply line Lb of -E/<NUM>. All the gates of the P-type channel MOS transistors (the switch elements <NUM>, <NUM>,. <NUM>) and the gates of the N-type channel MOS transistors (the switch elements <NUM>, <NUM>,. <NUM> and switch elements <NUM>, <NUM>,. <NUM>) are connected to the waveform generation circuit <NUM>.

The waveform generation circuit <NUM> generates a control waveform for controlling on and off switching of each of these switch elements (<NUM>, <NUM>,. <NUM>; <NUM>, <NUM>,. <NUM>; and <NUM>, <NUM>,. Each of the switch elements is switched on and off according to the control waveform output from the waveform generation circuit <NUM>. By switching on and off of these switch elements, each of the actuators <NUM>, <NUM>,. <NUM> can be charged and discharged.

In this example, the switch element <NUM>, the switch element <NUM> and the switch element <NUM> on one side, and the switch element <NUM>, the switch element <NUM> and the switch element <NUM> one the other, with the actuator <NUM> interposed therebetween, form an energization path for charging and discharging the actuator <NUM>. Similarly, switch element <NUM>, the switch element <NUM> and the switch element <NUM> on one side, and a switch element <NUM>, a switch element <NUM> and a switch element <NUM> on the other, with the actuator <NUM> interposed therebetween, form an energization path for charging and discharging the actuator <NUM>. The same applies to similarly the other actuators including actuator <NUM>. Therefore, in the following, there will be a focus on the actuator <NUM> and the corresponding six switch elements <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM> that form the energization path to the actuator <NUM> as representative of the operations of the other switch elements and actuators.

<FIG> is a block diagram illustrating aspects of a circuit configuration of the waveform generation circuit <NUM>. The waveform generation circuit <NUM> includes a time setting register <NUM>, a selector <NUM>, a timer <NUM>, a state counter <NUM>, and a drive pattern memory <NUM>.

The time setting register <NUM> includes a first setting register <NUM>, a second setting register <NUM>, a third setting register <NUM>, a fourth setting register <NUM>, a fifth setting register <NUM>, a sixth setting register <NUM>, and a seventh setting register <NUM>. The value for time Ta is set in the first setting register <NUM>. The value for time Tb is set in the second setting register <NUM>. The value for time Tc is set in the third setting register <NUM>. The value for time Td is set in the fourth setting register <NUM>. The value for time Te is set in the fifth setting register <NUM>. The value for time Tf is set in the sixth setting register <NUM>. The value for time Tg is set in the seventh setting register <NUM>.

The selector <NUM> selects one of the time Ta, the time Tb, the time Tc, the time Td, the time Te, the time Tf, and the time Tg as set in the first to seventh setting registers <NUM> to <NUM> according to the state data ST output from the state counter <NUM>. The selector <NUM> sets the selected time in the timer <NUM>.

The timer <NUM> counts the time set by the selector <NUM>. Then, when the set time is finished, the timer <NUM> outputs a state update signal SA to the state counter <NUM>.

The state counter <NUM> is an octal counter, and in the initial state, the state data ST value is "<NUM>". In this initial state, if a trigger signal for starting waveform output is input from the printer <NUM>, the state counter <NUM> increments the state data ST value by one. After that, each time the state update signal SA is received from the timer <NUM>, the state counter <NUM> increments the state data ST value by one. Then, if the state data ST value has reached the upper limit value (here seven because the state counter <NUM> is an octal counter), the state counter <NUM> resets the state data ST back to "<NUM>" by transmission of the state update signal SA. The state counter <NUM> outputs the present state data ST value to the selector <NUM> and the drive pattern memory <NUM>.

In the following description, the state data ST value in the initial state is referred to as state data Sta, the next state data ST value (incremented value) is state data STb, and so forth for subsequent (incremented) state data ST values of state data STc, STd, STe STf, STg, and STh.

The drive pattern memory <NUM> stores the drive pattern data in association with the state data STa to STh, respectively. The drive pattern data is data for controlling the on and off switching of the six switch elements <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM> for the actuator <NUM>. The drive pattern data is also data for controlling the on and off switching of the six switch elements <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM> for the actuator <NUM>.

Each time the state data STa to STh are sent from the state counter <NUM>, the drive pattern memory <NUM> generates a drive waveform for controlling the switch elements <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and so on according to the drive pattern data corresponding to the state data STa to STh.

<FIG> is a diagram illustrating the correspondence relationship between the state data STa to STh and the drive pattern data. In the initial state (state data Sta), the switch elements <NUM> and <NUM> are turned on, and the switch elements <NUM>, <NUM>, <NUM>, and <NUM> are turned off.

In this initial state, if a trigger signal for starting waveform output is sent to the state counter <NUM> so the state data is updated from STa to STb (at time point ta), the switch element <NUM> is turned off and the switch element <NUM> is turned on by the drive waveform of the drive pattern data for the state data STb period from the drive pattern memory <NUM>. At this time, a closed circuit including the first voltage source <NUM>, the switch element <NUM>, the actuator <NUM>, and the switch element <NUM> is formed. As a result, the actuator <NUM> is energized and charged with a voltage E/<NUM> (intermediate voltage E/<NUM>) in the forward direction.

As described above, the actuator <NUM> is charged with the electric charge with an intermediate voltage E/<NUM>, which is half of a maximum voltage E, by using the positive first voltage source <NUM>. The maximum voltage E is the charging target value. The actuator <NUM> may be said to be "half-charged" at this point.

When the state data is updated from STa to STb, the selector <NUM> selects the first setting register <NUM>. As a result, the timer <NUM> times the time Ta. Then, when the time Ta has been timed and the timer <NUM> times out, the state data is updated from STb to STc.

When the state data is updated from STb to STc (at time point tb), the switch element <NUM> is turned off and the switch element <NUM> is turned on by the drive waveform of the drive pattern data corresponding to the state data STc. At this time, a closed circuit including the first voltage source <NUM>, the switch element <NUM>, the actuator <NUM>, the switch element <NUM>, and the second voltage source <NUM> is formed. As a result, the actuator <NUM> is energized and further charged to the maximum voltage E in the forward direction.

As described above, in the latter half of charging, the actuator <NUM> is charged to the maximum voltage E by using the positive first voltage source <NUM> and the negative second voltage source <NUM>. The actuator <NUM> the actuator <NUM> is considered fully charged when charged to the maximum voltage E.

When the state data is updated from STb to STc, the selector <NUM> selects the second setting register <NUM>. As a result, the timer <NUM> times the time Tb. Then, when the time Tb has been timed and the timer <NUM> times out, the state data is updated from STc to STd.

When the state data is updated from STc to STd (at time point tc), the switch element <NUM> is turned off and the switch element <NUM> is turned on by the drive waveform of the drive pattern data corresponding to the state data STd. At this time, a closed circuit including the actuator <NUM>, the switch element <NUM>, the first voltage source <NUM>, and the switch element <NUM>, is formed. As a result, the actuator <NUM> is discharged.

As described above, in the first half of discharging, the electric charge is returned from the actuator <NUM> to the positive first voltage source <NUM>, and the actuator <NUM> is discharged while the first voltage source <NUM> is charged.

When the state data is updated from STc to STd, the selector <NUM> selects the third setting register <NUM>. As a result, the timer <NUM> times the time Tc. Then, when the time Tc has been timed and the timer <NUM> times out, the state data is updated from STd to STe.

When the state data is updated from STd to STe (at time point td), the switch element <NUM> is turned off and the switch element <NUM> is turned on by the drive waveform of the drive pattern data corresponding to the state data STe. At this time, a closed circuit including the actuator <NUM>, the switch element <NUM>, and the switch element <NUM> is formed. As a result, the actuator <NUM> is further discharged.

As described above, in the latter half of discharging, the actuator <NUM> is fully discharged by forming a closed loop between the terminals of the actuator <NUM>.

In the charging and discharging operation described above, the volume of a pressure chamber <NUM> is first expanded and ink is replenished (refilled into the pressure chamber), and the volume of the pressure chamber is then restored to its original (relaxed or steady) state. However, this operation causes a pressure vibration in the pressure chamber <NUM> by which ink droplets are ejected from the nozzle <NUM> associated with the pressure chamber <NUM>. The ejection occurs at the time of discharging operation.

When the state data is updated from STd to STe, the selector <NUM> selects the fourth setting register <NUM>. As a result, the timer <NUM> times the time Td. Then, when the time Td has been timed and the timer <NUM> times out, the state data is updated from STe to STf.

When the state data is updated from STe to STf (at time point te), the switch element <NUM> is turned off and the switch element <NUM> is turned on by the drive waveform of the drive pattern data corresponding to the state data STf. At this time, a closed circuit including the first voltage source <NUM>, the switch element <NUM>, the actuator <NUM>, and the switch element <NUM> is formed. As a result, the actuator <NUM> is energized and charged with intermediate voltage E/<NUM> in the opposite direction.

As described above, in the first half of this "opposite charging," the actuator <NUM> is charged with electric charge in the opposite direction from the expansion operation to the intermediate voltage E/<NUM>, which is half of the maximum voltage E, by using the positive first voltage source <NUM>.

When the state data is updated from STe to STf, the selector <NUM> selects the fifth setting register <NUM>. As a result, the timer <NUM> times the time Te. Then, when the time Te has been timed and the timer <NUM> times out, the state data is updated from STf to STg.

When the state data is updated from STf to STg (at time point tf), the switch element <NUM> is turned off and the switch element <NUM> is turned on by the drive waveform of the drive pattern data corresponding to the state data STg. At this time, a closed circuit including the first voltage source <NUM>, the switch element <NUM>, the actuator <NUM>, the switch element <NUM>, and the second voltage source <NUM> is formed. As a result, the actuator <NUM> is further charged to maximum voltage E in the opposite direction.

As described above, in the latter half of the opposite charging, the actuator <NUM> is fully charged to the maximum voltage E (but in the opposite direction from the expansion operation) by using the positive first voltage source <NUM> and the negative second voltage source <NUM>.

When the state data is updated from STf to STg, the selector <NUM> selects the sixth setting register <NUM>. As a result, the timer <NUM> times the time Tf. Then, when the time Tf has been timed and the timer <NUM> times out, the state data is updated from STg to STh.

When the state data is updated from STg to STh (at time point tg), the switch element <NUM> is turned off and the switch element <NUM> is turned on by the drive waveform of the drive pattern data corresponding to the state data STh. At this time, a closed circuit including the actuator <NUM>, the switch element <NUM>, the first voltage source <NUM>, and the switch element <NUM> is formed. As a result, the actuator <NUM> is discharged.

When the state data is updated from STg to STh, the selector <NUM> selects the seventh setting register <NUM>. As a result, the timer <NUM> times the time Tg. Then, when the time Tg has been timed and the timer <NUM> times out, the state data returns from STh to STa.

When the state data returns from STh to STa (at time point th), the switch element <NUM> is turned off and the switch element <NUM> is turned on by the drive waveform of the drive pattern data corresponding to the state data STa. At this time, a closed circuit including the actuator <NUM>, the switch element <NUM>, and the switch element <NUM> is formed. As a result, the actuator <NUM> is further discharged.

As described above, in the latter half of discharging, the actuator <NUM> is completely discharged by forming a closed loop between the terminals of the actuator <NUM>.

By this opposite charging and discharging operation as described above, , the volume of a pressure chamber <NUM> is contracted and then restored to its original state. By this operation, a residual vibration in the pressure chamber <NUM> can be canceled.

After this, each time a trigger signal for starting the waveform output is input to the state counter <NUM>, the waveform generation circuit <NUM> executes the same operation again. By such an operation of the waveform generation circuit <NUM>, the charge and discharge circuit <NUM> switches on and off the switch elements <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM> forming the energization path to the actuator <NUM>.

In this case, the electrode <NUM> of which applied voltage is controlled by switching on and off of the three switch elements <NUM>, <NUM>, and <NUM> is an electrode of one channel for ejecting ink (hereinafter referred to as ejection channel Ch. The electrode <NUM> of which applied voltage is controlled by switching on and off of the remaining three switch elements <NUM>, <NUM>, <NUM> is an electrode of a channel adjacent to the ejection channel Ch. X (hereinafter referred to as adjacent channel Ch. The actuator <NUM> is interposed between the electrode <NUM> of the ejection channel Ch. X and the electrode <NUM> of the adjacent channel Ch. Accordingly, the actuator <NUM> is driven by the difference between the voltage applied to the electrode <NUM> of the ejection channel Ch. X and the voltage applied to the electrode <NUM> of the adjacent channel Ch. By appropriately controlling the driving of the actuator <NUM>, it is possible to eject <NUM> ink droplet from the nozzle <NUM> of the ejection channel Ch. As described above, the waveform that controls the driving of the actuator <NUM> is referred to as a drive waveform.

<FIG> is an explanatory diagram illustrating the drive waveform used in an embodiment. In this example, a first drive waveform (I) and a second drive waveform (II) are used.

The first drive waveform (I) includes an expansion waveform in time period D, a holding waveform in time period R, and a contraction waveform in time period P. For the expansion waveform, a first pulse Pa that changes from the steady state value ("0V") to a negative maximum voltage -E is applied to the actuator <NUM>. By applying the first pulse Pa to the actuator <NUM>, the actuator <NUM> is driven in the direction of expanding the pressure chamber <NUM> of the ejection channel Ch.

The expansion waveform returns towards the steady state value ("0V") after a time corresponding to the length of time period D elapses. As the voltage applied to the actuator <NUM> returns towards the steady state value, the actuator <NUM> is driven in the direction of restoring the pressure chamber <NUM> to its non-expanded state.

In time period D, the pressure chamber <NUM> of the ejection channel Ch. X is first expanded, maintained in this expanded state (expansion state), and then restored to its non-expanded (steady-state) state. By such a change in the volume of the pressure chamber <NUM>, ink droplets are ejected from the nozzle <NUM> associated with the pressure chamber <NUM>. In addition, if the time the expansion state of the pressure chamber <NUM> is maintained in time period D is set to be <NUM>/<NUM> of the pressure vibration cycle <NUM> AL (Acoustic Length) of the pressure chamber <NUM>, the ink ejection volume reaches a maximum value. The time Dt may be adjusted by adjusting the time Ta set in the first setting register <NUM> and/or the time Tb set in the second setting register <NUM>. The expansion waveform in time period D can be referred to as a compression pulse, an ejection pulse, or the like.

After the expansion waveform returns to the steady state value, the first drive waveform (I) becomes a holding waveform in time period R, which holds the steady state value ("0V")for the time corresponding to length of time period R. After the steady state value ("0V") is held, the first drive waveform (I) becomes a contraction waveform in time period P.

For the contraction waveform, a second pulse Pb that changes from 0V to a positive maximum voltage +E is applied to the actuator <NUM>. By applying the second pulse Pb to the actuator <NUM>, the actuator <NUM> is driven in the direction of contracting the pressure chamber <NUM> of the ejection channel Ch.

The contraction waveform becomes 0V after a time corresponding to time period P elapses. Once the voltage applied to the actuator <NUM> becomes the steady state value ("0V"), the actuator <NUM> can be driven in the direction of restoring the pressure chamber <NUM>.

As described above, in time period P, the pressure chamber <NUM> of the ejection channel Ch. X is first contracted, maintained in the contraction state, and then restored. By such a volume change of the pressure chamber <NUM>, the residual vibration of the pressure chamber <NUM> can be canceled. Specifically, by adjusting the time corresponding to the time period R of the holding waveform and the time corresponding to time period P of the contraction waveform to appropriate values, the residual vibration of the pressure chamber <NUM> is canceled at the trailing edge of the contraction waveform. The time Rt may be adjusted by adjusting the time Td set in the fourth setting register <NUM>. The time period P may be adjusted by adjusting the times Te, Tf, and Tg set in the fifth setting register <NUM>, the sixth setting register <NUM>, and the seventh setting register <NUM>. Here, the contraction waveform of time period P is referred to as a contraction pulse, a cancel pulse, or the like.

As described above, the first drive waveform (I) can cancel the residual vibration of the pressure chamber <NUM> in the ejection channel Ch. X, so that good ejection efficiency can be obtained. In addition, the landing performance of ink droplets is also excellent.

However, in the head <NUM>, usually, if the ink droplet is ejected from the nozzle <NUM>, the ink droplet is ejected from the nozzle <NUM> with a tail behind. Then, at the time the ink droplet separates from the ink in the nozzle <NUM>, this tailing part, or the so-called liquid column becomes a spherical satellite and flies following the main ink droplet (main droplet). Since this satellite is a minute droplet, its flight speed is slower than that of the main ink droplet. For this reason, the satellite may land on the recording medium apart from the main ink droplet, causing deterioration of print quality such as density unevenness and ghost. In addition, some satellites stall and float in the printer <NUM>, which is a so-called ink mist. If the ink mist adheres to the head <NUM> or surrounding circuit members and the like, it may cause a malfunction of the printer <NUM>. The first drive waveform (I) cannot suppress the generation of small droplets such as the satellites and the ink mist described above.

The second drive waveform (II) includes an expansion waveform in time period D, a holding waveform in time period R', a first weak contraction waveform in time period H, a contraction waveform in time period P', and a second contraction waveform in time period W. The expansion waveform in the second drive waveform (II) can be the same as the expansion waveform of the first drive waveform (I). That is, for the expansion waveform, a first pulse Pa that changes from the steady state value of 0V to the negative maximum voltage -E is applied to the actuator <NUM>, and when the time corresponding to time period D elapses, it returns to the steady state of 0V.

Also in the second drive waveform (II), in time period D, the pressure chamber <NUM> of the ejection channel Ch. X is first expanded, maintained in the expansion state, and then restored. By such a change in the volume of the pressure chamber <NUM>, ink droplets are ejected from the nozzle <NUM> communicating with the pressure chamber <NUM>. In addition, when the time period D (time the expansion state of the pressure chamber <NUM> is maintained) is <NUM>/<NUM> of the pressure vibration cycle <NUM> AL of the pressure chamber <NUM>, the ink ejection volume reaches the maximum. If the expansion waveform becomes the steady state value of 0V, the second drive waveform (II) becomes a holding waveform. The holding waveform holds the steady state value of 0V for a time corresponding to time period R'. When time period R' of the holding waveform ends, the second drive waveform (II) becomes the first weak contraction waveform.

For the first weak contraction waveform, a third pulse Pc that changes from the steady state value of 0V to an intermediate voltage +E/<NUM> is applied to the actuator <NUM>. By applying the third pulse Pc to the actuator <NUM>, the actuator <NUM> is driven in the direction of contracting the pressure chamber <NUM> of the ejection channel Ch. However, the degree of contraction is smaller than the degree of contraction of the pressure chamber <NUM> by the second pulse Pb of the first drive waveform (I). Hereinafter, the degree of contraction of the pressure chamber <NUM> by the third pulse Pc is referred to as a weak contraction, and this state of weak contraction is referred to as a weak contraction state.

When the time corresponding to time period H of the weak contraction waveform elapses, the second drive waveform (II) becomes a contraction waveform. For the contraction waveform, a fourth pulse Pd that changes from the intermediate voltage +E/<NUM> to the positive maximum voltage +E is applied to the actuator <NUM>. By applying the fourth pulse Pd to the actuator <NUM>, the actuator <NUM> is driven in the direction of further contracting the pressure chamber <NUM> of the ejection channel Ch. The degree of contraction is equal to the degree of contraction of the pressure chamber <NUM> by the second pulse Pb of the first drive waveform (I).

When the time corresponding to time period P' of the contraction waveform elapses, the second drive waveform (II) becomes a second weak contraction waveform. For the second weak contraction waveform, a fifth pulse Pe that changes from the maximum voltage +E to the intermediate voltage +E/<NUM> is applied to the actuator <NUM>. By applying the fifth pulse Pe to the actuator <NUM>, the actuator <NUM> is driven in the direction of restoring the pressure chamber <NUM> of the ejection channel Ch. However, the pressure chamber <NUM> is not completely restored. If the voltage applied to the actuator <NUM> becomes the intermediate voltage +E/<NUM>, the pressure chamber <NUM> becomes a weak contraction state.

When a time corresponding to time period W of the second weak contraction waveform elapses, the second drive waveform (II) becomes the steady state value of 0V. If the voltage applied to the actuator <NUM> becomes the steady state value 0V, the pressure chamber <NUM>, which is in the weak contraction state, is completely restored.

The second drive waveform (II) can suppress the generation of small droplets such as satellites, ink mists, and the like. Specifically, the time corresponding to time period R' of the holding waveform, the time corresponding to time period H of the first weak contraction waveform, the time corresponding to time period P' of a strong contraction waveform and the time corresponding to time period W of the second weak contraction waveform are adjusted to appropriate values. By doing so, the generation of small droplets called satellites, ink mists, and the like can be suppressed. The time of time period R' may be adjusted by adjusting the time Td set in the fourth setting register <NUM>. The time of the time period H may be adjusted by adjusting the time Te set in the fifth setting register <NUM>. The time of the time period P' may be adjusted by adjusting the time Tf set in the sixth setting register <NUM>. The time of the time period W may be adjusted by adjusting the time Tg set in the seventh setting register <NUM>.

Next, the setting of appropriate values for various time periods of the second drive waveform (II) will be described.

The length of time period D (time Dt) is the time from time point ta to time point tc.

The length of time period R' (time R't) is the time from the time point tc (at the starting of discharge of the actuator <NUM> that has been charged with the negative maximum voltage -E by the first pulse Pa) to the time point te (at the starting of charging the actuator <NUM> with the intermediate voltage E/<NUM> by the third pulse Pc).

The length of time period H (time Ht) is the time from the time point te (at the starting of charging the actuator <NUM> with the intermediate voltage E/<NUM> by the third pulse Pc) to the time point tf (at the starting of charging the actuator <NUM> with the positive maximum voltage +E by the fourth pulse Pd).

The length of time period P' (time P't) is the time from the time point tf (at the starting of charging the actuator <NUM> with the positive maximum voltage +E by the fourth pulse Pd) to the time point tg (at the starting of discharge of the actuator <NUM> by the fifth pulse Pe).

The length of time period W (time Wt) is the time from the time point tg (at the starting of discharge of the actuator <NUM> by the fifth pulse Pe) to the time point th (at the completing of the discharging).

By setting these time values according to the relationship of Equations (<NUM>) to (<NUM>) below, it is possible to suppress the generation of small droplets called satellites, ink mists, and the like. <MAT> <MAT> <MAT>.

Equation (<NUM>) can be expressed in different notation as: Rt + <NUM> ≤ (R't + Ht) ≤ Rt + <NUM>. Equation (<NUM>) can be expressed in different notation as: Dt - <NUM> ≤ Wt ≤ Dt + <NUM>.

In Equation (<NUM>), the variable Rt is a time corresponding to the length of time period R of the holding waveform in the first drive waveform (I). The sum total time of the time R't and the time Ht is obtained by adding a value of <NUM> to <NUM> to the time Rt. The time Wt is a value obtained by adding between -<NUM> to <NUM> to the time Dt corresponding to time period D of the expansion waveform. The time P't is the time obtained by subtracting the time Wt and the sum of time R't and time Ht from four times the value of time Dt.

<FIG> is a timing diagram illustrating the pressure waveform of the pressure chamber <NUM> and the flow rate waveform of the ink in the ejection channel Ch. X, if the second drive waveform (II) is applied to the actuator <NUM>, where the total time of time R't and time Ht is time Rt + <NUM>, and the time Wt is time Dt + <NUM>. In <FIG>, the solid line "Drive Voltage" represents the voltage waveform of the second drive waveform (II). The alternate long and short dash line "Pressure" represents a pressure waveform generated in the pressure chamber <NUM>. The alternate long and two short dash line "Flow Rate" represents a flow rate waveform of the ink flowing into the nozzle <NUM>. The horizontal axis represents the passage of time (µs). The vertical axis represents the drive voltage, pressure, flow rate and size of waveform, in which the numerical values are normalized.

As illustrated in <FIG>, the pressure in the pressure chamber <NUM>, which is decreased by the expansion of the pressure chamber <NUM> at the leading edge (first pulse Pa) of the expansion waveform in the second drive waveform (II) between the time point ta and the time point tb, is increased while the expansion state is maintained. Then, if the pressure chamber <NUM> is restored at the trailing edge of the expansion waveforms between the time point tc and the time point td, the pressure is increased sharply. As a result, ink droplets are ejected from the nozzle <NUM> communicating with the pressure chamber <NUM>.

After the ink droplets are ejected, the pressure reaches a positive peak value at the time point te of the leading edge (third pulse Pc) of the first weak contraction waveform in the second drive waveform (II). The pressure is decreased from the positive peak value while the pressure chamber <NUM> is maintained in the weak contraction state, changes to negative pressure, reaches a negative peak value, and then increased. Then, the pressure changes to the positive pressure at the time tf of the leading edge (fourth pulse Pd) of the contraction waveform in the second drive waveform (II). The pressure changed to the positive pressure reaches the second positive peak value while the pressure chamber <NUM> is maintained in the contraction state, and then decreased again and changed to the negative pressure. Then, the pressure at the second negative peak value is increased again and changes to the positive pressure. The pressure, which is the positive pressure, changes to the negative pressure at the time point tg of the leading edge (fifth pulse Pe) of the second weak contraction waveform in the second drive waveform (II). The pressure, which is the negative pressure, is increased while the pressure chamber <NUM> is maintained in the weak contraction state, and changes back to the positive pressure.

The flow rate of the ink flowing into the nozzle <NUM> has a positive peak value after the ink droplets are ejected. After that, the flow rate decreases and reaches a negative peak value at the time tf of the leading edge (fourth pulse Pd) of the contraction waveform in the second drive waveform (II). Upon reaching the negative peak value, the flow rate changes to increase and reaches a second positive peak value while the pressure chamber <NUM> is maintained in the contraction state, after which the flow rate decreases again and reaches a second negative peak value at the time point tg of the leading edge (fifth pulse Pe) of the second weak contraction waveform in the second drive waveform (II). When reaching the negative peak value, the flow rate starts to increase. Then, at the time point th if the flow rate becomes zero, that is, at the time point th when discharging the actuator <NUM> is completed, the pressure chamber <NUM> is completely restored from the weak contraction state. At this time, the pressure in the pressure chamber <NUM>, which is the positive pressure, decreases and becomes substantially zero.

As described above, for the second drive waveform (II), the pressure chamber <NUM> after ejecting the ink droplet is maintained in the weak contraction state for the time Ht. Furthermore, in order to cancel the residual vibration of the pressure chamber, after the pressure chamber <NUM> is changed to the contraction state, the weak contraction state is maintained for the time Wt. By such a change of state in the pressure chamber <NUM>, the meniscus of the ink is increased to the extent that the ink droplets are not ejected from the nozzle <NUM> communicating with the pressure chamber <NUM>. This increase of the meniscus shortens the tailing, which is the main cause of satellite generation. As a result, the generation of small droplets to become satellites or ink mists is suppressed. Further, the residual vibration of the pressure chamber <NUM> is also canceled by restoring the state of the pressure chamber <NUM> from the contraction state. Thus, by using the second drive waveform (II) as the drive waveform for controlling the driving of the actuator <NUM>, it is possible to suppress the generation of small droplets while suppressing the residual vibration. As a result, there is no concern that the satellite lands on the recording medium, causing deterioration of print quality such as density unevenness and ghost, or that ink mist adheres to the head <NUM> and circuit members therearound, causing a malfunction of the printer <NUM>.

However, the second drive waveform (II) has a longer waveform length compared to the first drive waveform (I). For this reason, if gradation printing is performed by a multi-drop method in which <NUM> dot is formed with a plurality of continuously ejected ink droplets (drops), ejecting all ink droplets according to the second drive waveform (II) will take time to form <NUM> dot, causing a concern that the drive frequency may be affected.

Therefore, in the case of the multi-drop method, the ink droplets ejected according to the first drive waveform (I) and the ink droplets ejected according to the second drive waveform (II) are combined to form <NUM> dot. As an example, a combination of drive waveforms for a multi-drop method with a maximum of <NUM> drops will be described with reference to <FIG>.

<FIG> illustrates a matrix-format data table in which the columns denote the number of drops and the rows denote the frame numbers. Since there are a maximum of <NUM> drops, the number of drops includes <NUM> types including "<NUM> drop", "<NUM> drop", and "<NUM> drop". The frame number includes "<NUM> frame" indicating the first drop of <NUM> drops, "<NUM> frame" indicating the second drop of <NUM> drops, and "<NUM> frame" indicating the third drop of <NUM> drops.

If <NUM> dot is formed by <NUM> drop, that is, in the case of "<NUM> drop", the <NUM> drop corresponds to "<NUM> frame" which is the third drop in <NUM> drops. In the present embodiment, the ink droplet of "<NUM> frame" is ejected according to the second drive waveform (II).

If <NUM> dot is formed by <NUM> drops, that is, in the case of "<NUM> drop", the first drop corresponds to the "<NUM> frame" which is the second drop in the <NUM> drops, and the second drop corresponds to the "<NUM> frame" which is the third drop in the <NUM> drops. In an embodiment, the ink droplet of "<NUM> frames" and the ink droplet of "<NUM> frames" are ejected according to the second drive waveform (II), respectively. As described above, even if all the <NUM> drops are ejected according to the second drive waveform (II), the time required for forming <NUM> dot does not affect the drive frequency.

If <NUM> dot is formed with <NUM> drops, that is, in the case of "<NUM> drop", the ink droplet of "<NUM> frame" which is the first drop is ejected according to the first drive waveform (I). The ink droplets of the "<NUM> frame" which is the second drop and the "<NUM> frame" which is the third drop are ejected according to the second drive waveform (II), respectively. Even if the first drop is ejected according to the first drive waveform (I), the satellites generated by the ejection are extremely small as compared with the case where all <NUM> drops are ejected according to the first drive waveform (I). In addition, the ink mist may adhere to the ink droplets of the second drop or the third drop and land on the recording medium. Therefore, the print quality does not deteriorate. Moreover, the time required to form <NUM> dot can be reduced to such an extent that the drive frequency is not affected.

<FIG> shows results related to a flying state of ejected ink. In the <FIG>, photograph PHa shows the flying state of the ink if the first drive waveform (I) is applied and printing is performed by a single drop method with <NUM> drop. Photograph PHb shows the flying state of the ink if the first drive waveform (I) is applied and printing is performed by a multi-drop method with <NUM> drops. Photograph PHc shows the flying state of the ink if the first drive waveform (I) is applied and printing is performed by a multi-drop method with <NUM> drops. Photograph PHd shows the flying state of the ink if the second drive waveform (II) is applied and printing is performed by a single drop method with <NUM> drop. Photograph PHe shows the flying state of the ink if the second drive waveform (II) is applied and printing is performed by a multi-drop method with <NUM> drops. Photograph PHf shows the flying state of the ink if printing is performed by a multi-drop method with <NUM> drops in which the first drive waveform (I) is applied and the first drop is ejected, and the second drive waveform (II) is subsequently applied and the second drop and the third drop are ejected.

As is clear from comparing the photographs PHa and PHd, the photographs PHb and PHe, and the photographs PHc and PHf, respectively, if the second drive waveform (II) is not applied, many satellites land on the recording medium apart from the main ink droplets, causing deterioration of print quality such as density unevenness and ghost images. On the other hand, if the second drive waveform (II) is applied, the generation of satellites can be almost entirely suppressed. Therefore, it is possible to improve the print quality without causing density unevenness and ghost images. Further, since the generation of ink mist is also suppressed, there is less concern that the printer <NUM> may malfunction.

In the embodiments described above, each time element of the holding time R't, the first weak contraction time Ht, the contraction time P't, and the second weak contraction time Wt is set according to the relationship of Equations (<NUM>) to (<NUM>) described above, respectively. As another embodiment, Equation (<NUM>) may have instead the relationship of Equation (<NUM>) below: <MAT>.

Equation (<NUM>) can be expressed in alternative notation as: Rt + <NUM> ≤ Ht ≤ Rt + <NUM>. Thus, according to Equation (<NUM>), the time R't of the holding section corresponding to time period R' from the second drive waveform (II) may be set to zero. Even with such a drive waveform, by adjusting values of each of the first weak contraction time Ht, the contraction time P't, and the second weak contraction time Wt, it is still possible to suppress the amount of satellites accompanying the ink droplets ejected from the nozzle.

In the case of a multi-drop method in which one printed dot (<NUM> dot)is formed by three ejected drops (<NUM> drops), the first drive waveform (I) can be used for the first drop, and the second drive waveform (II) can be used for the second and third drops. In some examples, the first drive waveform (I) may be used for the first and second drops, and the second drive waveform (II) may be used for the third drop. Such concepts are also equally applicable to a multi-drop method of four drops (<NUM> drops) or more.

The first drive waveform (I) is not limited to that illustrated in <FIG>. However, even when other drive waveform are adopted as the first drive waveform (I), it is possible to obtain the effect of suppressing the generation of small droplets such as satellites, ink mist, and the like by using the second drive waveform (II) for at least the ejection of the ink droplets of the final drop in a series of drops.

The head <NUM> is not limited to the shared wall type. The disclosure can also be applied to other types of piezo-type inkjet heads.

Claim 1:
An inkjet head (<NUM>), comprising:
a pressure chamber (<NUM>) for ink;
a nozzle plate (<NUM>) including a nozzle (<NUM>) for ejecting ink from the pressure chamber;
an actuator (<NUM>) configured to change a volume of the pressure chamber; and
a drive circuit (<NUM>) configured to drive the actuator according to a drive waveform, wherein the drive waveform includes:
an expansion portion that drives the actuator in an expansion direction expanding the volume of the pressure chamber,
a first weak contraction portion after the expansion portion that drives the actuator in a contraction direction contracting the volume of the pressure chamber,
a contraction portion after the first weak contraction portion that drives the actuator in the contraction direction by an amount greater than the first weak contraction portion, and
a second weak contraction portion after the contraction portion that drives the actuator in the contraction direction by an amount less than the contraction portion,
wherein the drive waveform further includes a holding portion between the expansion portion and the first weak contraction portion, the holding portion not driving the actuator in either the contracting direction or the expansion direction,
characterized in that
the drive waveform comprises a first droplet ejection operation and a second droplet ejection operation after the first droplet ejection operation,
the holding portion, the first weak contraction portion, the contraction portion, and the second weak contraction portion are in the second droplet ejection operation, and
a sum of a holding time of the holding portion and a first weak contraction time of the first weak contraction portion is greater than or equal to a holding time of a first droplet ejection operation holding portion plus <NUM> microseconds, but less than or equal to the holding time of the first droplet ejection operation holding portion plus <NUM> microseconds.