Patent Description:
A liquid discharge apparatus called valved nozzle type is known in the art, in which a valve opens and closes a discharge port from which a liquid is discharged. For example, <CIT> proposes a method of changing a pulse width of a drive waveform for controlling a discharge operation of the liquid to an optimum value in accordance with environmental conditions to solve a problem that a discharge amount of the liquid varies due to environmental fluctuations or the like.

However, if the method in <CIT> is applied to the valved nozzle type liquid discharge apparatus, when the pulse width of the drive waveform for driving the valve is changed, a discharge speed of the liquid is also changed, so that a position of an object onto which the liquid is landed may deviate, and the liquid may not be attached to a desired position.

<CIT> discloses a fluid ejection device which allows to vary a valve-closing speed.

<CIT> discloses a valve encased nozzle device comprising a valve chamber having an introduction port for introducing pressurized liquid, and an opening for injecting the liquid, and a valve for closing and opening one or both of the introduction port and the injecting port, wherein the valve is disposed together with a valve driving mechanism in the valve chamber, whereby the introduction port or the injecting port or both are closed or opened by movement of the valve driven by the driving mechanism.

The present disclosure has an object to reduce a variation in a discharge speed of liquid.

Embodiments of the present disclosure describe an improved drive controller that includes circuitry. The circuitry generates multiple types of drive pulses to be applied to a driver of a liquid discharge head including a valve to open and close a discharge port, and applies the multiple types of drive pulses to the driver to cause the driver to move the valve to open and close the discharge port. Each of the multiple types of drive pulses causes the valve to move away from the discharge port at a valve-opening speed to open the discharge port, keep opening the discharge port for an open time, and move toward the discharge port at a valve-closing speed to close the discharge port. Further, the circuitry generates the multiple types of drive pulses, the open time and the valve-closing speed of which are different, and changes the valve-closing speed according to the open time.

As a result, according to the present disclosure, the variation in the discharge speed of liquid can be reduced.

Embodiments of the present disclosure are described below with reference to the drawings. In the following description, as a drive controller according to an embodiment of the present disclosure, the drive controller that drives a valve provided in a liquid discharge head is described. The liquid discharge head discharges ink as a liquid.

<FIG> is an entire perspective view of a liquid discharge head <NUM>. The liquid discharge head <NUM> includes a housing <NUM>. The housing <NUM> is made of metal or resin. The housing <NUM> includes a connector <NUM> for communication of electrical signals at an upper portion thereof. A supply port <NUM> and a collection port <NUM> are disposed on the left and right sides of the housing <NUM> in <FIG> and <FIG>. Ink is supplied into the liquid discharge head <NUM> through the supply port <NUM> and drained from the liquid discharge head <NUM> through the collection port <NUM>.

<FIG> is a schematic view of a head unit <NUM>, which also illustrates a cross section of the liquid discharge head <NUM> taken along line A-A in <FIG> as viewed in the direction indicated by arrows in <FIG>. The head unit <NUM> includes the liquid discharge head <NUM> and a drive controller <NUM>.

The liquid discharge head <NUM> includes a nozzle plate <NUM>. The nozzle plate <NUM> is joined to the housing <NUM>. The nozzle plate <NUM> has a nozzle <NUM> from which ink is discharged. The housing <NUM> includes a channel <NUM>. The channel <NUM> is a flow path through which the ink is fed from the supply port <NUM> to the collection port <NUM> over the nozzle plate <NUM>. The ink is fed in the channel <NUM> in a direction indicated by arrows a1 to a3 in <FIG>.

Liquid discharge modules <NUM> are disposed between the supply port <NUM> and the collection port <NUM>. Each of the liquid discharge modules <NUM> discharges the ink in the channel <NUM> from the nozzle <NUM>. The number of the liquid discharge modules <NUM> matches the number of the nozzles <NUM>. In the present embodiment, the eight liquid discharge modules <NUM> correspond to the eight nozzles <NUM> arranged in a row, respectively. The number and an arrangement of the nozzles <NUM> and the liquid discharge modules <NUM> are not limited to eight as described above. For example, the number of nozzles <NUM> and the number of liquid discharge modules <NUM> may be one instead of plural. The nozzles <NUM> and the liquid discharge modules <NUM> may be arranged in multiple rows instead of one row.

With the above-described configuration, the supply port <NUM> takes in pressurized ink from the outside of the liquid discharge head <NUM>, feeds the ink in the direction indicated by arrow a1, and supplies the ink to the channel <NUM>. The channel <NUM> feeds the ink from the supply port <NUM> in the direction indicated by arrow a2. Then, the collection port <NUM> drains the ink that is not discharged from the nozzles <NUM> in the direction indicated by arrow a3. The nozzles <NUM> are arranged along the channel <NUM>.

The liquid discharge module <NUM> includes a needle valve <NUM> and a piezoelectric element <NUM>. The needle valve <NUM> opens and closes the nozzle <NUM>, and the piezoelectric element <NUM> drives (moves) the needle valve <NUM>. The housing <NUM> includes a restraint <NUM> at a position facing an upper end of the piezoelectric element <NUM> in <FIG>. The restraint <NUM> is in contact with the upper end of the piezoelectric element <NUM> to define a fixing point of the piezoelectric element <NUM>.

The nozzle <NUM> is an example of a discharge port, the nozzle plate <NUM> is an example of a discharge port forming component, the needle valve <NUM> is an example of an opening and closing valve (also simply referred to as a valve), and the piezoelectric element <NUM> is an example of a driver.

As the piezoelectric element <NUM> is operated to move the needle valve <NUM> upward, the nozzle <NUM> that has been closed by the needle valve <NUM> is opened, so that ink is discharged from the nozzle <NUM>. As the piezoelectric element <NUM> is operated to move the needle valve <NUM> downward, a leading end of the needle valve <NUM> comes into contact with the nozzle <NUM> to close the nozzle <NUM>, so that the ink is not discharged from the nozzle <NUM>. The liquid discharge head <NUM> may temporarily stops draining ink from the collection port <NUM> while discharging the ink to a liquid discharge target to prevent a decrease in an ink discharge efficiency from the nozzles <NUM>.

<FIG> are schematic cross-sectional views of one liquid discharge module <NUM> of the liquid discharge head <NUM>. <FIG> is an overall cross-sectional view of the liquid discharge module <NUM>, and <FIG> is an enlarged view of a portion B in <FIG>. The channel <NUM> is shared with the multiple liquid discharge modules <NUM> in the housing <NUM> (see <FIG>).

The needle valve <NUM> includes an elastic member 17a at the leading end thereof. When the leading end of the needle valve <NUM> is pressed against the nozzle plate <NUM>, the elastic member 17a is compressed. As a result, the needle valve <NUM> closes the nozzle <NUM>. A bearing portion <NUM> is disposed between the needle valve <NUM> and the housing <NUM>. A seal <NUM> such as an O-ring is disposed between the bearing portion <NUM> and the needle valve <NUM>.

The piezoelectric element <NUM> is accommodated in a space inside the housing <NUM>. A holder <NUM> holds the piezoelectric element <NUM> in a central space 23a. The piezoelectric element <NUM> and the needle valve <NUM> are coaxially coupled to each other via a front end 23b of the holder <NUM>. The front end 23b of the holder <NUM> is coupled to the needle valve <NUM>, and a rear end 23c of the holder <NUM> is fixed by the restraint <NUM> attached to the housing <NUM>.

When the drive controller <NUM> applies a voltage to the piezoelectric element <NUM>, the piezoelectric element <NUM> contracts and pulls the needle valve <NUM> via the holder <NUM>. Accordingly, the needle valve <NUM> moves away from the nozzle <NUM> to open the nozzle <NUM>. As a result, pressurized ink supplied to the channel <NUM> is discharged from the nozzle <NUM>. When the drive controller <NUM> applies no voltage to the piezoelectric element <NUM>, the needle valve <NUM> closes the nozzle <NUM>. In this state, even if the pressurized ink is supplied to the channel <NUM>, the ink is not discharged from the nozzle <NUM>.

The drive controller <NUM> includes a waveform generation circuit <NUM> serving as a drive pulse generator and an amplification circuit <NUM>. The waveform generation circuit <NUM> as circuitry generates a waveform having a drive pulse to be described later, and the amplification circuit <NUM> amplifies the voltage to a desired value. Then, the amplified voltage is applied to the piezoelectric element <NUM>. The drive controller <NUM> applies the voltage to the piezoelectric element <NUM> to cause the piezoelectric element <NUM> to move the needle valve <NUM> to open and close the nozzle <NUM>, thereby controlling a discharge operation of ink from the liquid discharge head <NUM>. When the waveform generation circuit <NUM> can apply a voltage of a sufficient value, the amplification circuit <NUM> may be omitted from the drive controller <NUM>.

The waveform generation circuit <NUM> generates the drive pulse of the waveform in which the voltage applied to the piezoelectric element <NUM> is changed with time. The waveform generation circuit <NUM> receives print data from an external personal computer (PC) or a microcomputer in the drive controller <NUM>, and generates the drive pulse based on the received print data. The waveform generation circuit <NUM> can change the voltage applied to the piezoelectric element <NUM> and generate multiple types of drive pulses. As described above, the waveform generation circuit <NUM> generates the drive pulse so that the piezoelectric element <NUM> expands and contracts in response to the drive pulse to move the needle valve <NUM> to open and close the nozzle <NUM>.

<FIG> is a schematic view of a liquid supply device <NUM> according to the present embodiment. A liquid discharge apparatus <NUM> (see <FIG>) includes tanks 31a to 31d as closed containers that accommodates inks 90a to 90d respectively to be discharged from liquid discharge heads 10a to 10d. In the following descriptions, the inks 90a to 90d are collectively referred to as ink <NUM>. The tanks 31a to 31d are collectively referred to as tanks <NUM>.

The tanks <NUM> and inlets of the liquid discharge heads <NUM> (i.e., the supply port <NUM> in <FIG> and <FIG>) are respectively connected to each other via tubes <NUM>. The tanks <NUM> are coupled to a compressor <NUM> via a pipe <NUM> including an air regulator <NUM>. The compressor <NUM> supplies pressurized air to the tanks <NUM> to pressurize the ink <NUM>. Thus, the ink <NUM> is discharged from the nozzle <NUM> when the needle valve <NUM> described above opens the nozzle <NUM> since the ink <NUM> in the liquid discharge head <NUM> is in a pressurized state.

The compressor <NUM>, the pipe <NUM> including the air regulator <NUM>, the tanks <NUM>, and the tubes <NUM> collectively construct the liquid supply device <NUM> that pressurizes and supplies the ink <NUM> to the liquid discharge head <NUM>, for example.

States in which the drive controller <NUM> applies the voltage to the piezoelectric element <NUM> to drive the needle valve <NUM> are described below with reference to <FIG>. Parts (a) to (c) of <FIG> are diagrams of the liquid discharge module <NUM> illustrating the states in which the needle valve <NUM> opens and closes the nozzle <NUM>. A part (d) of <FIG> is a graph of an amount of displacement of the needle valve <NUM> at that time. The horizontal axis represents time t (s), and the vertical axis represents the amount of displacement C (mm) of the needle valve <NUM>. The amount of displacement of the needle valve <NUM> indicates an amount of movement of the needle valve <NUM> from a position "<NUM>" at which the needle valve <NUM> contacts the nozzle plate <NUM> to close the nozzle <NUM> as illustrated in the part (a) of <FIG> toward an upper position in an opening direction to open the nozzle <NUM>, which is an upward direction in the parts (a), (b), and (c) of <FIG>.

The drive controller <NUM> applies the drive pulse to the piezoelectric element <NUM> to expand and contract the piezoelectric element <NUM> to drive the needle valve <NUM>. The drive pulse is a pulse of the voltage applied to the piezoelectric element <NUM>. The drive pulse is substantially proportional to the amount of displacement of the needle valve <NUM> when the piezoelectric element <NUM> can respond sufficiently fast to the drive pulse. That is, the waveform of the drive pulse, generated by the drive controller <NUM>, with respect to the time "t" has substantially the same shape as a transition of the amount of displacement of the needle valve <NUM> changing with the time "t" in the part (d) of <FIG>. The waveform of the amount of displacement C illustrated the part (d) of <FIG> coincides with (is equal to) the waveform of the drive pulse in the following description.

When the voltage applied to the piezoelectric element <NUM> is <NUM> V, the piezoelectric element <NUM> expands and the needle valve <NUM> contacts the nozzle plate <NUM> as illustrated in the part (a) of <FIG>. As a result, the needle valve <NUM> closes the nozzle <NUM>. In the part (d) of <FIG> and the subsequent drawings, the amount of displacement of the needle valve <NUM> is <NUM> when the needle valve <NUM> closes the nozzle <NUM>, and the amount of displacement C is defined as a distance the needle valve <NUM> is displaced from the position "<NUM>. " The voltage is set to <NUM> V when the nozzle <NUM> is closed in the present embodiment. However, a voltage other than <NUM> V may be used as long as the voltage is smaller than a predetermined voltage.

As the voltage is applied to the piezoelectric element <NUM>, the piezoelectric element <NUM> contracts. As a result, as illustrated in the part (b) of <FIG>, the needle valve <NUM> moves upward in the part (b) of <FIG>, and a gap region <NUM> is formed between the needle valve <NUM> and the nozzle plate <NUM>. Then, as illustrated in the part (c) of <FIG>, the needle valve <NUM> comes into contact with the nozzle plate <NUM> again to close the nozzle <NUM> by stopping the application of the voltage to the piezoelectric element <NUM> or reducing the voltage applied to the piezoelectric element <NUM>.

As illustrated in the part (d) of <FIG>, opening and closing operations of the nozzle <NUM> by the needle valve <NUM> is divided into three sections: an ascending section D1 in which the amount of displacement of the needle valve <NUM> increases; a holding section D2 in which the amount of displacement of the needle valve <NUM> is held in a range between <NUM> times a maximum displacement Cmax and the maximum displacement Cmax; and a descending section D3 in which the amount of displacement of the needle valve <NUM> decreases.

Since the ink <NUM> in the housing <NUM> of the liquid discharge head <NUM> is pressurized by the compressor <NUM> (see <FIG>), when the needle valve <NUM> moves upward to open the nozzle <NUM> as illustrated in the part (b) of <FIG>, the ink <NUM> enters the gap region <NUM> between the needle valve <NUM> and the nozzle plate <NUM>. Then, in the ascending section D1 in which the amount of displacement of the needle valve <NUM> increases and the subsequent holding section D2, the ink <NUM> starts to be discharged from the nozzle <NUM> due to a liquid pressure applied to the ink <NUM>. Thereafter, when the needle valve <NUM> starts to move downward, in the descending section D3, the ink <NUM> in the gap region <NUM> is further pushed out and discharged from the nozzle <NUM> due to a pressure force received from the needle valve <NUM> moving downward in addition to the liquid pressure of the ink <NUM> pressurized by the compressor <NUM>.

As described above, in the configuration in which the needle valve <NUM> is driven to open and close the nozzle <NUM>, in addition to the liquid pressure applied to the ink <NUM>, the pressure force accompanying the closing operation of the needle valve <NUM> to close the nozzle <NUM> contributes to the ink <NUM> discharged from the nozzle <NUM> (i.e., ink discharge).

A contribution ratio of the liquid pressure to the ink discharge and the contribution ratio of the pressure force of the needle valve <NUM> to the ink discharge differ depending on an open time during which the needle valve <NUM> opens the nozzle <NUM>.

Specifically, when a small droplet of the ink <NUM> is discharged, since the open time of the needle valve <NUM> is set to be short, the contribution ratio to the ink discharge is dominated by the pressure force of the needle valve <NUM> rather than the liquid pressure of the ink <NUM>. That is, when the nozzle <NUM> is opened for a short time, since the nozzle <NUM> is closed immediately after being opened, the ink <NUM> is pushed out by the pressure force accompanying the closing operation of the needle valve <NUM> before the liquid pressure propagates to the ink <NUM> in the liquid chamber (i.e., in the gap region <NUM> between the needle valve <NUM> and the nozzle plate <NUM> illustrated in the part (b) of <FIG>). Accordingly, in this case, since the ink <NUM> is pushed out mainly by the needle valve <NUM> moving at high speed, a discharge speed of the ink <NUM> is increased.

On the other hand, when a large droplet of the ink <NUM> is discharged, since the open time of the needle valve <NUM> is set to be long, unlike the case of the small droplet, the contribution ratio to the ink discharge is dominated by the liquid pressure of the ink <NUM> rather than the pressure force of the needle valve <NUM>. That is, in this case, since the nozzle <NUM> is opened for a long time, the liquid pressure sufficiently propagates to the ink <NUM> in the liquid chamber, and the ink <NUM> is pushed out by the propagated liquid pressure. In this case, the ink <NUM> in the liquid chamber also receives the pressure force accompanying the closing operation of the needle valve <NUM>, but since the ink <NUM> is pushed out by the liquid pressure before the ink <NUM> is pushed out by the pressure force received from the needle valve <NUM>, the ink discharge by the liquid pressure of the ink <NUM> becomes dominant, and as a result, the discharge speed of the ink <NUM> becomes slow.

<FIG> illustrate an example of the opening and closing operations of the needle valve <NUM> in a liquid discharge head according to a comparative example. <FIG> are diagrams illustrating the opening and closing operations of the needle valve <NUM>, <FIG> is a graph of the amount of displacement of the needle valve <NUM>, and <FIG> is a graph of the voltage applied to the piezoelectric element <NUM> when the open time is short. On the other hand, <FIG> are diagrams illustrating the opening and closing operations of the needle valve <NUM>, <FIG> is a graph of the amount of displacement of the needle valve <NUM>, and <FIG> is a graph of the voltage applied to the piezoelectric element <NUM> when the open time is long. Timings A to G on horizontal axes in <FIG> correspond to the operations of the needle valve <NUM> illustrated in <FIG>, respectively, and timings A to G on horizontal axes in <FIG> correspond to the operations of the needle valve <NUM> illustrated in <FIG>, respectively.

When the piezoelectric element <NUM> does not respond sufficiently fast to the drive pulse, it is possible to adjust the drive pulse according to a change in the amount of displacement of the needle valve <NUM> desired. In this case, the voltage applied to the piezoelectric element <NUM> illustrated in <FIG> and <FIG> is adjusted so that the needle valve <NUM> is displaced by the amount of displacement illustrated in <FIG> and <FIG>.

First, a case where the open time is short is described. In this case, when a voltage is applied to the piezoelectric element <NUM> in a state where the nozzle <NUM> is closed by the needle valve <NUM> as illustrated in <FIG>, the needle valve <NUM> starts the opening operation as illustrated in <FIG>. As a result, the gap region <NUM> is formed between the needle valve <NUM> and the nozzle <NUM>, and the ink <NUM> enters the gap region <NUM> as illustrated in <FIG>. Then, the liquid pressure starts to propagate to the ink <NUM> in the gap region <NUM>, but when the open time is short, the closing operation of the needle valve <NUM> starts immediately as illustrated in <FIG>. That is, the applied voltage is lowered immediately after the amount of displacement of the needle valve <NUM> becomes maximum to start the closing operation of the needle valve <NUM>. As a result, the pressure force is applied to the ink <NUM> by the closing operation of the needle valve <NUM> moving at high speed before the liquid pressure completely propagates to the ink <NUM> in the gap region <NUM> as illustrated in <FIG>. Therefore, the discharge speed of the ink <NUM> is increased.

On the other hand, when the open time is long, a period from when the needle valve <NUM> becomes in an open state to when the closing operation of the needle valve <NUM> starts is long as illustrated in <FIG>, and thus the liquid pressure sufficiently propagates to the ink <NUM> in the liquid chamber. Accordingly, in this case, since the ink <NUM> is pushed out from the nozzle <NUM> mainly by the propagated liquid pressure as illustrated in <FIG>, the discharge speed of the ink <NUM> becomes slow.

As described above, when the open time of the needle valve <NUM> is long, the discharge speed of the ink <NUM> is likely to be slower than when the open time is short. Further, since the open time of the needle valve <NUM> correspond to a width of the drive pulse of the voltage applied to the piezoelectric element <NUM> (i.e., the driver) that drives the needle valve <NUM>, the discharge speed of the ink <NUM> is also changed as the width of drive pulse is changed.

<FIG> is a graph schematically illustrating a relation between the width and drive frequency of the drive pulse and the discharge speed of the ink <NUM>. A horizontal axis in <FIG> represents the drive frequency of the drive pulse repeatedly applied to the piezoelectric element <NUM>. The drive frequency increases from left to right on the horizontal axis in <FIG>. A vertical axis in <FIG> represents the discharge speed of the ink <NUM>. The discharge speed increases from bottom to top on the vertical axis in <FIG>. Among three lines illustrated in <FIG>, a line plotted with circle marks corresponds to the largest width of the drive pulse, a line plotted with triangle marks correspond to a middle width of the drive pulse, and a line plotted with square marks correspond to the smallest width of the drive pulse.

As illustrated in <FIG>, the discharge speed of the ink <NUM> is likely to decrease with an increase in the width of the drive pulse (as illustrated in a lower portion of the graph in <FIG>), and conversely, the discharge speed of the ink <NUM> is likely to increase with a decrease in the width of the drive pulse (as illustrated in an upper portion of the graph in <FIG>).

As described above, in the liquid discharge head according to the comparative example, when the open time or the width of the drive pulse of the needle valve <NUM> is changed in response to the size of the droplet of the ink <NUM>, the discharge speed of the ink <NUM> is also changed. For this reason, a position of the object onto which the droplet of the ink <NUM> is landed and attached may deviate from a desired position depending on the size of the droplet.

Therefore, in the present disclosure, in order to reduce a variation of the discharge speed of the ink <NUM> as described above, the following control method of the valve (i.e., the needle valve <NUM>) is adopted. A method of controlling the valve is described below with reference to the liquid discharge head <NUM> according to the above-described embodiment.

As described above, the closing operation of the needle valve <NUM> affects the discharge speed of the ink <NUM> in addition to the liquid pressure of the ink <NUM>. Accordingly, if a drive speed of the needle valve <NUM> during the closing operation is changed, the discharge speed of the ink <NUM> can be changed, thereby reducing the variation of the discharge speed. Focusing on this point, in the present disclosure, the drive speed of the valve (i.e., the needle valve <NUM>) is changed in response to the open time of the valve.

Therefore, in the above-described embodiment of the present disclosure, the drive controller <NUM> (see <FIG>) to control the drive of the needle valve <NUM> includes the waveform generation circuit <NUM> (drive pulse generator) that can generate multiple types of drive pulses. The waveform generation circuit <NUM> can generate the multiple types of drive pulses. Each of the multiple types of drive pulses causes the needle valve <NUM> to open the nozzle <NUM> for the open time. The open time and the drive speed of the needle valve <NUM> are different in each of the multiple types of drive pulses.

<FIG> and <FIG> are diagrams illustrating the opening and closing operations of the needle valve <NUM> controlled by the drive controller <NUM> (the waveform generation circuit <NUM>), <FIG> and <FIG> are graphs of the amount of displacement of the needle valve <NUM>, and <FIG> and <FIG> are graphs of the voltage applied to the piezoelectric element <NUM>. <FIG> illustrate control when the open time is short, and <FIG> illustrate control when the open time is long. Timings A to G on horizontal axes in <FIG> correspond to the operations of the needle valve <NUM> illustrated in <FIG>, respectively, and timings A to G on horizontal axes in <FIG> correspond to the operations of the needle valve <NUM> illustrated in <FIG>, respectively.

The open time during which the needle valve <NUM> is kept in the open state is different between when the open time is short as illustrated in <FIG> and when the open time is long as illustrated in <FIG>. For this reason, a hold time of the applied voltage that keeps the needle valve <NUM> in the open state is also different therebetween (see the holding section D2 illustrated in <FIG> and <FIG> or a holding section E2 illustrated in <FIG> and <FIG>). In the present embodiment, the "open state" of the needle valve <NUM> means a state in which the amount of displacement of the needle valve <NUM> is held in the range between <NUM> times the maximum displacement Cmax and the maximum displacement amount Cmax, and the "open time" of the needle valve <NUM> means the period of the holding section D2 in which the open state is held (see <FIG> and <FIG>). Alternatively, the "open state" of the needle valve <NUM> means a state in which the voltage applied to the piezoelectric element <NUM> is held in the range between <NUM> times the maximum voltage Vmax and the maximum voltage Vmax, and the "open time" of the needle valve <NUM> means the period of a holding section E2 in which the open state is held (see <FIG> and <FIG>).

As illustrated in <FIG> and <FIG>, in the present embodiment, the drive speed of the needle valve <NUM> and the slew rate of the applied voltage during the closing operation is changed in response to the open time (see the descending section D3 or E3 illustrated in <FIG>, <FIG>). In the present embodiment, the "drive speed" of the needle valve <NUM> during the closing operation is the drive speed (i.e., the amount of displacement of the needle valve <NUM> per unit time) when the amount of displacement of the needle valve <NUM> drops below <NUM> times the maximum displacement Cmax (i.e., the descending section D3). The "slew rate" of the applied voltage during the closing operation is the slew rate of the applied voltage (i.e., an amount of change in the applied voltage per unit time) when the voltage applied to the piezoelectric element <NUM> drops below <NUM> times the maximum voltage Vmax (i.e., the descending section E3).

In the amount of displacement of the needle valve <NUM> during the closing operation illustrated in <FIG> and <FIG>, the drive speed is constant (proportional to time) in the descending section D3 in the present embodiment, but the drive speed may be changed in the descending section D3 in another embodiment. In such a case, a value obtained by dividing the amount of displacement of the needle valve <NUM> in the descending section D3 by the time of the descending section D3 may be used as the drive speed during the closing operation. In the applied voltage during the closing operation illustrated in <FIG> and <FIG>, the amount of change in the applied voltage per unit time decreases with time in the descending section E3. In such a case, a value obtained by dividing the amount of change in the applied voltage in the descending section E3 by the time of the descending section E3 (i.e., an average of the slew rate in the descending section E3) may be used as the slew rate of the applied voltage during the closing operation.

Specifically, in the present embodiment, when the open time is long as illustrated in <FIG>, the slew rate of the applied voltage during the closing operation is increased and the drive speed of the needle valve <NUM> during the closing operation is increased as compared to when the open time is short as illustrated in <FIG>. Accordingly, in the present embodiment, the waveform generation circuit <NUM> of the drive controller <NUM> selectively generates a first drive pulse and a second drive pulse. The first drive pulse causes the piezoelectric element <NUM> to drive the needle valve <NUM> when the open time of the needle valve <NUM> is relatively short as illustrated in <FIG>. The second drive pulse causes the piezoelectric element <NUM> to drive the needle valve <NUM> to open the nozzle <NUM> for the longer open time of the needle valve <NUM> than the first drive pulse as illustrated in <FIG> and to move the needle valve <NUM> at the faster drive speed than the first drive pulse as illustrated in <FIG> during the closing operation of the needle valve <NUM>. In other words, the waveform generation circuit <NUM> selectively generates the first drive pulse (in the case of <FIG>) and the second drive pulse (in the case of <FIG>) having the longer hold time of the applied voltage to keep the needle valve <NUM> in the open state than the first drive pulse and the larger slew rate of the applied voltage during the closing operation of the needle valve <NUM> than the first drive pulse.

As described above, in the present embodiment, the drive controller <NUM> increases the drive speed (i.e., a nozzle-closing drive speed) of the needle valve <NUM> when the open time is long. As a result, the speed of the ink <NUM> pushed out by the needle valve <NUM> is also increased, so that the discharge speed of the ink <NUM> discharged from the nozzle <NUM> can be increased. Accordingly, the discharge speed of the ink <NUM> is not decreased when the open time is long, and a variation in the discharge speed of the ink <NUM> accompanying a change in the open time of the needle valve <NUM> is reduced. Thus, a control method according to the present embodiment can reduce the variation in landing positions of the ink <NUM> on the object. Further, the drive controller <NUM> increases the slew rate of the applied voltage during the closing operation of the needle valve <NUM>. As a result, a control period (i.e., the width of the drive pulse) of the applied voltage can be shortened when the open time is long, and the opening and closing operations of the nozzle <NUM> by the needle valve <NUM> can be controlled in a short period.

Another embodiment different from the above-described embodiment is described below. Portions different from the above-described embodiment are mainly described, and descriptions of the same portions are appropriately omitted.

<FIG> are diagrams illustrating the opening and closing operations of the needle valve <NUM>, <FIG> is a graph of the amount of displacement of the needle valve <NUM>, and <FIG> is a graph of the voltage applied to the piezoelectric element <NUM>. <FIG> illustrate the control when the open time is long, and the control when the open time is short is the same as the control (the control illustrated in <FIG>) in the above-described embodiment, and drawings thereof are omitted.

When the piezoelectric element <NUM> does not respond sufficiently fast to the drive pulse, it is possible to adjust the drive pulse according to a change in the amount of displacement of the needle valve <NUM> desired. In this case, similarly to the control described in the above second embodiment with reference to <FIG>, the voltage applied to the piezoelectric element <NUM> illustrated in <FIG> is adjusted so that the needle valve <NUM> is displaced by the amount of displacement illustrated in <FIG>.

In another embodiment of the present disclosure illustrated in <FIG>, when the open time is long (in the case of <FIG>), the drive speed of the needle valve <NUM> during the closing operation is increased, and the drive speed of the needle valve <NUM> during the opening operation is also increased as compared to when the open time is short (in the case of <FIG>). That is, in the present embodiment, the waveform generation circuit <NUM> selectively generates the first drive pulse and the second drive pulse. The first drive pulse causes the piezoelectric element <NUM> to drive the needle valve <NUM> when the open time of the needle valve <NUM> is relatively short as illustrated in <FIG>. The second drive pulse causes the piezoelectric element <NUM> to drive the needle valve <NUM> to open the nozzle <NUM> for the longer open time of the needle valve <NUM> than the first drive pulse as illustrated in <FIG> and to move the needle valve <NUM> at the faster drive speed than the first drive pulse as illustrated in <FIG> during both the opening operation and the closing operation of the needle valve <NUM>. In other words, the waveform generation circuit <NUM> selectively generates the first drive pulse and the second drive pulse (in the case of <FIG>) having the longer hold time of the applied voltage to keep the needle valve <NUM> in the open state than the first drive pulse and the larger slew rate of the applied voltage during both the opening operation and the closing operation of the needle valve <NUM> than the first drive pulse. In the present embodiment, the "drive speed" of the needle valve <NUM> during the opening operation is the drive speed (i.e., the amount of displacement of the needle valve <NUM> per unit time) before the amount of displacement of the needle valve <NUM> reaches <NUM> times the maximum displacement Cmax (i.e., the ascending section D1). The "slew rate" of the applied voltage during the opening operation is the slew rate of the applied voltage (i.e., the amount of change of the applied voltage per unit time) before the voltage applied to the piezoelectric element <NUM> reaches <NUM> times the maximum voltage Vmax (i.e., the ascending section E1).

In the amount of displacement of the needle valve <NUM> during the opening operation illustrated in <FIG>, the drive speed is constant (proportional to time) in the ascending section D1 in the present embodiment, but the drive speed may be changed in the ascending section D1 in another embodiment. In such a case, a value obtained by dividing the amount of displacement of the needle valve <NUM> in the ascending section D1 by the time of the ascending section D1 may be used as the drive speed during the opening operation. In the applied voltage during the opening operation illustrated in <FIG>, the amount of change in the applied voltage per unit time decreases with time in the ascending section E1. In such a case, a value obtained by dividing the amount of change in the applied voltage in the ascending section E1 by the time of the ascending section E1 (i.e., an average of the slew rate in the ascending section E1) may be used as the slew rate of the applied voltage during the opening operation.

As described above, in the embodiment illustrated in <FIG>, the drive speed of the needle valve <NUM> during the opening operation (i.e., a nozzle-opening drive speed) is increased in addition to the drive speed of the needle valve <NUM> during the closing operation (i.e., the nozzle-closing drive speed), and the control period (the width of the drive pulse) of the applied voltage when the open time is long can be further shortened. Accordingly, the opening and closing operations of the nozzle <NUM> by the needle valve <NUM> can be controlled in a shorter period. The drive speeds (the slew rates of the applied voltage) during the opening operation and the closing operation of the needle valve <NUM> may be individually controlled in response to the open time of the needle valve <NUM> (the hold time of the applied voltage to keep the needle valve <NUM> in the open state). When the drive speed of the needle valve <NUM> is increased, an amount of heat generated by the driver such as the piezoelectric element <NUM> that drives the needle valve <NUM> increases. Accordingly, when the heat is transferred to the ink <NUM>, the viscosity of the ink <NUM> may increase, and discharge properties of the ink <NUM> may change. For this reason, a heat radiator to dissipate the heat from the driver or a cooling device to cool the driver is preferably provided.

The liquid discharge apparatus <NUM> including the head unit <NUM> including the drive controller <NUM> according to the above embodiments is described below with reference to <FIG>. The liquid discharge apparatus <NUM> illustrated in <FIG> is installed so as to face an object <NUM> onto which the ink <NUM> (liquid) is discharged. The liquid discharge apparatus <NUM> includes an X-axis rail <NUM>, a Y-axis rail <NUM> intersecting the X-axis rail <NUM>, and a Z-axis rail <NUM> intersecting the X-axis rail <NUM> and the Y-axis rail <NUM>.

The Y-axis rail <NUM> movably holds the X-axis rail <NUM> in the Y direction. The X-axis rail <NUM> movably holds the Z-axis rail <NUM> in the X direction. The Z-axis rail <NUM> movably holds a carriage <NUM> in the Z direction. The carriage <NUM> is an example of the head unit <NUM>, and includes the drive controller <NUM> and the liquid discharge head <NUM> described above.

Further, the liquid discharge apparatus <NUM> includes a first Z-direction driver <NUM> and an X-direction driver <NUM>. The first Z-direction driver <NUM> moves the carriage <NUM> in the Z direction along the Z-axis rail <NUM>. The X-direction driver <NUM> moves the Z-axis rail <NUM> in the X direction along the X-axis rail <NUM>. The liquid discharge apparatus <NUM> further includes a Y-direction driver <NUM> that moves the X-axis rail <NUM> in the Y direction along the Y-axis rail <NUM>. Further, the liquid discharge apparatus <NUM> includes a second Z-direction driver <NUM> that moves a head holder <NUM> relative to the carriage <NUM> in the Z direction.

The carriage <NUM> includes the head holder <NUM>. The head holder <NUM> is an example of a holding body. The carriage <NUM> is movable in the Z direction along the Z-axis rail <NUM> by driving force of the first Z-direction driver <NUM> illustrated in <FIG>. Further, the head holder <NUM> is movable relative to the carriage <NUM> in the Z direction by driving force of the second Z-direction driver <NUM> illustrated in <FIG>.

The liquid discharge apparatus <NUM> described above discharges the ink <NUM> from the liquid discharge head <NUM> mounted on the head holder <NUM> while moving the carriage <NUM> along the X-axis, the Y-axis, and the-Z axis, thereby drawing images on the object <NUM>. The ink <NUM> is an example of liquid. The movement of the carriage <NUM> and the head holder <NUM> in the Z direction may not be parallel to the Z direction, and may be an oblique movement including at least a Z direction component. Although the object <NUM> is flat in <FIG>, the object <NUM> may have a surface shape which is nearly vertical or a curved surface with the large radius of curvature, such as a body of a car, a truck, or an aircraft.

The term "liquid" includes not only ink but also paint.

In the above description, the embodiments in which the drive controller <NUM> applies a voltage to the driver such as the piezoelectric element <NUM> to open and close the valve such as the needle valve <NUM> has been described. However, the present disclosure is not limited thereto, and the valve may be opened and closed by pneumatic pressure or hydraulic pressure. In such a case, the drive pulse generated by the drive controller <NUM> is a drive waveform for driving the valve with a pressure set by a pneumatic or hydraulic pressurizing mechanism.

In the present disclosure, the term "liquid discharge apparatus" includes a liquid discharge head or a head unit and drives the liquid discharge head to discharge liquid. The term "liquid discharge apparatus" used here includes, in addition to apparatuses to discharge liquid to materials onto which liquid can adhere, apparatuses to discharge the liquid into gas (air) or liquid.

The "liquid discharge apparatus" may further include devices relating to feeding, conveying, and ejecting of the material onto which liquid can adhere and also include a pretreatment device and an aftertreatment device.

The "liquid discharge apparatus" may be, for example, an image forming apparatus to form an image on a sheet by discharging ink, or a three-dimensional fabrication apparatus to discharge fabrication liquid to a powder layer in which powder material is formed in layers to form a three-dimensional object.

The "liquid discharge apparatus" is not limited to an apparatus that discharges liquid to visualize meaningful images such as letters or figures. For example, the liquid discharge apparatus may be an apparatus that forms meaningless images such as meaningless patterns or an apparatus that fabricates three-dimensional images.

The above-described term "material onto which liquid can adhere" serves as the object onto which liquid is discharged as described above and represents a material on which liquid is at least temporarily adhered, a material on which liquid is adhered and fixed, or a material into which liquid is adhered to permeate. Specific examples of the "material onto which liquid can adhere" include, but are not limited to, a recording medium such as a paper sheet, recording paper, a recording sheet of paper, a film, or cloth, an electronic component such as an electronic substrate or a piezoelectric element, and a medium such as layered powder, an organ model, or a testing cell. The "material onto which liquid can adhere" includes any material to which liquid adheres, unless particularly limited.

Examples of the "material onto which liquid can adhere" include any materials to which liquid can adhere even temporarily, such as paper, thread, fiber, fabric, leather, metal, plastic, glass, wood, and ceramic.

The term "liquid discharge apparatus" may be an apparatus to relatively move the liquid discharge head and the material onto which liquid can adhere. However, the liquid discharge apparatus is not limited to such an apparatus. For example, the liquid discharge apparatus may be a serial head apparatus that moves the liquid discharge head or a line head apparatus that does not move the liquid discharge head.

Examples of the liquid discharge apparatus further include: a treatment liquid applying apparatus that discharges a treatment liquid onto a paper sheet to apply the treatment liquid to the surface of the paper sheet, for reforming the surface of the paper sheet; and an injection granulation apparatus that injects a composition liquid, in which a raw material is dispersed in a solution, through a nozzle to granulate fine particle of the raw material.

The terms "image formation," "recording," "printing," "image printing," and "fabricating" used in the present disclosure may be used synonymously with each other.

Claim 1:
A drive controller (<NUM>) comprising:
circuitry (<NUM>) configured to:
generate multiple types of drive pulses to be applied to a driver (<NUM>) of a liquid discharge head (<NUM>) including a valve (<NUM>) configured to open and close a discharge port (<NUM>);
apply the multiple types of drive pulses to the driver (<NUM>) to cause the driver (<NUM>) to move the valve (<NUM>) to open and close the discharge port (<NUM>), wherein each of the multiple types of drive pulses causes the valve (<NUM>) to:
move away from the discharge port (<NUM>) at a valve-opening speed to open the discharge port (<NUM>);
keep opening the discharge port (<NUM>) for an open time; and
move toward the discharge port (<NUM>) at a valve-closing speed to close the discharge port (<NUM>), and
the circuitry (<NUM>) is further configured to
generate the multiple types of drive pulses, the open time and the valve-closing speed of which are different,
characterized in that
the circuitry (<NUM>) is further configured to increase the valve-closing speed and the valve-opening speed with an increase in the open time.