JP2008023813A - Capacitive actuator driving circuit and inkjet head - Google Patents

Abstract

Disclosed is a capacitive actuator drive circuit and an inkjet head that drive an actuator so that energy consumption is sufficiently small and a drive waveform can be freely adjusted, and high-speed, high-reliability and print quality is improved. To do.
An electrostatic drive capacitive actuator drive circuit 100 comprising an inductor L that stores current energy from a power source and a capacitive actuator CL that is charged by the current stored in the inductor L is a static drive. After holding the voltage charged in the capacitive actuator CL for a predetermined time, the capacitive actuator CL is discharged.
[Selection] Figure 1

Description

  The present invention relates to a capacitive actuator drive circuit that drives an actuator and an inkjet head.

  In a high-performance inkjet head that drives a capacitive actuator such as a piezoelectric actuator at high speed, the actuator is generally based on the operation of deforming the actuator, maintaining the deformed state for a predetermined time, and then returning to the original state. It is adjusted so that desired ink ejection is performed by changing a parameter for operating, or putting another pause for a predetermined time. For this reason, in a high-performance inkjet head with high speed, high reliability and good print quality, how to adjust the operation of the actuator is the key to performance. That is, making it possible to freely adjust the operation of the actuator is an important problem for high-performance printing. Since the deformation of the capacitive actuator is proportional to the driving voltage, the voltage applied to the capacitive actuator is controlled in order to control the deformation amount of the actuator.

  However, capacitance means that the voltage has inertia. That is, for example, in order to instantaneously change the voltage across the capacitance, an infinite current is required. This is energy loss. Even if it is not instantaneous, if the voltage change is fast, a large current is required, and a relatively large loss occurs in a relatively short time. Conversely, if the battery is slowly charged, the charging current is reduced, but charging takes time and a relatively small loss occurs over a relatively long time.

  The following technologies are disclosed as techniques for reducing the energy consumption of an ink jet head using a piezoelectric actuator.

  A device that drives an actuator using resonance of electrostatic capacitance between an inductor and an actuator is known (for example, see Patent Document 1).

  A device that uses a transformer to return the energy stored in the capacitance of the actuator to a power source to reduce power consumption more than a general drive circuit is known (see, for example, Patent Document 2).

One that reduces power consumption by charging from a plurality of power sources is known (see, for example, Patent Document 3).
Japanese Patent Laid-Open No. 5-3683 JP-A-11-314364 JP 2005-288830 A

Consider the energy supplied and stored here. When the electrostatic capacity C is charged once from the power supply voltage V through a driving circuit such as a transistor, the energy supplied from the power supply voltage V is CV ² regardless of the charging speed. energy remains in the capacitor C is 1 / 2CV ^2. 1/2 CV ² of this difference is consumed by the dielectric loss of the actuator and the internal resistance of the drive circuit.

  When the voltage change is made faster, the internal resistance of the drive circuit is lowered. The energy loss at this time is mainly the dielectric loss of the actuator. When the voltage change is delayed, the internal resistance of the drive circuit is increased by giving a series resistance or current limit to the drive circuit. The energy loss at this time mainly occurs in the drive circuit. Therefore, even if the voltage change is made faster or slower, the loss ratio between the actuator and the drive circuit only changes, and the total energy loss does not change.

Further, the 1/2 CV ² remaining in the capacitance C is lost when the actuator that has maintained the deformation is returned. Therefore, a high-performance ink jet head using a piezoelectric actuator has a problem that energy efficiency is poor.

  In the device described in Patent Document 1, the power consumption is small, but the drive waveform is determined by the LC resonance waveform, and the waveform cannot be freely adjusted. Therefore, it is difficult to improve the ink ejection performance of the inkjet head.

  In the device described in Patent Document 2, the power consumption can be reduced as compared with a general drive circuit. However, since there is no description about the energy loss at the time of charging as described above, the power consumption can be reduced. The effect is not enough.

In the device described in Patent Document 3, power consumption can be reduced by charging from a plurality of power sources, but the number of power sources that can be prepared is limited in view of size and cost.

  In addition, in the case of selectively driving a plurality of actuators, in Patent Documents 1 and 2, inductors are required as many as the number of actuators. It is not realistic in terms of point, and it has been hopelessly adopted for a recent inkjet head having hundreds of nozzles or more.

  The present invention has been made in view of the above circumstances, and the object thereof is to make it possible to freely adjust the drive waveform with a sufficiently small energy consumption and to improve the print quality at high speed and high reliability. It is an object of the present invention to provide a capacitive actuator driving circuit and an ink jet head for driving an actuator.

  The first aspect of the present invention includes an inductor that stores current energy from a power source and a capacitive actuator that is charged by the current stored in the inductor, and the voltage charged in the capacitive actuator is supplied for a predetermined time. It is a capacitive actuator drive circuit that discharges the capacitive actuator after being held.

  According to a second aspect of the present invention, an inductor that stores current energy from a power source, a capacitive actuator that is charged by a current stored in the inductor, and a voltage charged in the capacitive actuator are held for a predetermined time. And an electrostatic actuator driving circuit for discharging the electrostatic actuator.

  According to the present invention, a capacitive actuator driving circuit and an ink jet head that drive an actuator such that energy consumption is sufficiently small and a driving waveform can be freely adjusted, and high-speed, high-reliability and printing quality is improved. Can provide.

  Embodiments of the present invention will be described below with reference to the drawings.

(First embodiment)
First, the configuration of the capacitive actuator drive circuit will be described with reference to FIGS. As shown in FIG. 1, in the capacitive actuator drive circuit 100, a constant voltage power supply P, an inductor L, and a capacitive actuator CL are connected in series. A switch Q11 is provided in series between the constant voltage power supply P and the inductor L. A diode D11 is provided in parallel with the switch Q11. The anode of the diode D11 is connected to the inductor L side, and the cathode is connected to the constant voltage power supply P side.

  The switch Q12 is provided between the switch Q11 and the inductor L, and between the constant voltage power supply P and the capacitive actuator CL. A diode D12 is provided in parallel with the switch Q12. The anode side of the diode D12 is connected between the constant voltage power supply P and the capacitive actuator CL, and the cathode side is connected between the switch Q11 and the inductor L.

  Further, the switch Q13 is provided between the inductor L and the capacitive actuator CL and between the constant voltage power supply P and the capacitive actuator. A diode D3 is provided in parallel with the switch Q3. The anode side of the diode D3 is connected between the constant voltage power supply P and the capacitive actuator, and the cathode side is connected between the inductor L and the capacitive actuator CL.

  Next, the operation of the capacitive actuator drive circuit will be described. First, as shown in FIG. 1A, the switches Q11 and Q13 are turned on to store current energy in the inductor L. At this time, the current value stored in the inductor L can be adjusted in the time during which the switch Q11 is ON. Subsequently, as shown in FIG. 1B, when the switch Q11 is turned OFF, the current energy stored in the inductor L is held. As shown in FIG. 1C, when the switch Q13 is turned OFF, the capacitive actuator CL is charged by the current energy stored in the inductor L. As shown in FIG. 1C, when charging of the capacitive actuator CL is completed, no current flows through the diode D12 and the power is turned off, so that the voltage is held in the capacitive actuator CL. This charging voltage is determined by the current stored in the inductor L, the inductor L, and the capacitance C. When charging the capacitive actuator CL with a voltage higher than that of the constant voltage power supply P, a series switch is provided in the diode D11, and the charging voltage is held after the charging of the capacitive actuator CL is completed. The series switch is turned OFF only during

  In this state, when the switch Q12 is turned on, and when the series switch is provided, when the switch is turned on at the same time, as shown in FIG. 1 (e), the charge stored in the capacitive actuator CL is changed. It flows to the inductor L. Then, as shown in FIG. 1F, when the discharge of the capacitive actuator CL is completed, the diode D13 is turned on by the electromotive force of the inductor L, and current energy is held in the inductor L. Further, as shown in FIG. 1 (g), when the switch Q12 is turned OFF, the current energy stored in the inductor L is returned to the constant voltage power source P through the diode D11. During this time, the switch Q11 may be turned on to lower the ON resistance. When the current flowing through the inductor L decreases to 0, the diodes D11 and D13 are turned OFF and the process is terminated.

  According to this capacitive actuator drive circuit 100, current energy is stored in the inductor L from the constant voltage power supply P, and then the energy is transferred from the inductor L to the capacitive actuator CL to charge the capacitive actuator CL. . After charging is complete, the circuit is turned off to hold the voltage across the capacitive actuator CL. And it discharges, after hold | maintaining the required time with the capacitive actuator CL. A drive waveform required by combining this basic operation once or twice, for example, a drive waveform for ejecting ink when the capacitive actuator CL is provided in a mechanism for ejecting ink of an inkjet head. Generate.

  The loss in storing the power supply energy stored in the inductor L from the constant voltage power supply P is determined by the internal resistance of the circuit. The inductor L is an element that gives an inertia to the current and has no inertia in the voltage. Therefore, even if the voltage across the inductor is arbitrarily changed, the principle loss as in the case of the capacitor does not occur. Therefore, the loss of power source energy can be reduced by reducing the internal resistance of the circuit. The operation of transferring energy from the inductor L to the capacitive actuator CL is a part of the resonance operation of the LC resonance circuit. The energy loss at this time is determined by the resonance sharpness of the resonance circuit. Therefore, the loss can be reduced by increasing the resonance sharpness of the resonance circuit, that is, by reducing the internal resistance of the circuit. Therefore, both losses can be reduced as much as possible in principle by reducing the internal resistance of the circuit.

  Furthermore, with respect to the degree of freedom in generating the drive waveform, the charging voltage can be adjusted by adjusting the time for storing the current energy in the inductor L. After the charging is completed, the capacitive actuator driving circuit 100 is turned off to statically. Since the driving time can be freely adjusted by adjusting the holding time in the capacitive actuator CL, a free waveform can be generated.

  In addition, although the above-mentioned capacitive actuator CL is configured only with an actuator as shown in FIG. 2, it may be configured with a switching element as shown in FIG. In this way, the charging direction may be switched using the switching element. As shown in FIG. 3, in FIG. 3A and FIG. 3B, the charging direction of the capacitive actuator CL is switched by ON / OFF of the switching elements Q21, Q22, Q23, and Q24.

  For example, when the capacitive actuator drive circuit 100 is used in a mechanism for ejecting ink of an ink jet head, the capacitive actuator CL is not only closed in order to eject ink but also in a direction in which the space is expanded. If it is also operated, the discharge performance can be further improved. As shown in FIG. 3, the switching direction can be switched using the switching elements Q21, Q22, Q23, and Q24, so that the capacitive actuator can be quickly switched to charge the capacitive actuator.

  The drive circuit using the sequence of the capacitive actuator driving circuit 100 described with reference to FIG. 1 and using the polarity reversing mechanism (switching element) for switching the polarity described in FIG. The case where a predetermined drive waveform is obtained will be described. FIG. 4 is a diagram for explaining changes in voltage and current waveforms for obtaining the predetermined drive waveform in the drive circuit.

  The drive waveform shown in FIG. 4 is often used as a high-speed drive waveform of a piezoelectric inkjet head. The configuration of the piezoelectric ink jet head is the same as that of the conventional one, and the description thereof is omitted. The piezoelectric ink jet head expands the ink chamber by the charging waveform (moves the actuator in the direction of expanding), calls the ink, returns the capacitive actuator CL at t5, discharges the ink, and waits for a pause. The residual vibration is dumped by the reverse charge waveform.

  The main parameters of this drive waveform are the charging voltage, energizing time, rest time, reverse charging voltage, and reverse energizing time. In order to drive the piezoelectric inkjet head at high speed, stably, and with high quality, these parameters must be adjusted in accordance with the resonance frequency and damping characteristics of the vibration system formed by the ink and the capacitive actuator CL. By using the above drive circuit, it is possible to freely adjust the drive waveform, and by switching the charging direction using a switching element, depending on the resonance frequency and damping characteristics of the vibration system while maintaining low power consumption. Thus, it is possible to adjust the drive waveform.

  First, current accumulation in L is started at t1. The current waveform of L increases linearly if the internal resistance of the circuit is sufficiently low. The circuit operation during this period is shown in FIG. Next, current accumulation is stopped at t2 (FIG. 1 (b)). Immediately after that, charging to the capacitive actuator CL is started at t3 (FIG. 2C). The shape of the charging waveform is a part of the LC resonance waveform. The time point at which the charging is completed is t4, from which the state automatically shifts to the voltage holding state (FIG. 1 (d)).

  After holding the voltage for the necessary time, discharge from the capacitive actuator CL to the inductor L is started at t5 (FIG. 1 (e)). The shape of the discharge becomes a part of the LC resonance waveform. The time point at which the discharge is completed is t6, and at this time, a loop current flows through the inductor L (FIG. 1 (f)).

  Immediately after that, the current stored in the constant voltage power supply P from the inductor L is returned at t7 (FIG. 1 (g)). If the internal resistance of the circuit is low enough, the current will decrease linearly. When the return of the current is completed and the current flowing through the inductor L becomes zero, the circuit returns to the initial state. This time is t8.

  Thereafter, at t9, the operations of the switching elements Q21, Q22, Q23, Q23 are reversed, and the state shown in FIG. 3A is shifted to the state shown in FIG. When the same operation as that started at t1 is repeated again from t10, since the switching elements Q21, Q22, Q23, and Q23 are inverted, a waveform having a polarity opposite to that of the previous one is given to the capacitive actuator CL. It is done. By operating as described above, the drive waveform shown in FIG. 4 can be created.

  Further, the charging voltage and the reverse charging voltage can be increased or decreased by shortening the times T1 and T2 shown in FIG. Furthermore, in order to adjust the energization time, the rest time, and the reverse energization time, the timings of t5, t12, and t14 may be changed, respectively. That is, each waveform parameter can be freely controlled, and the drive waveform can be easily optimized. In addition, during this time, since the operation of losing charges in principle is not performed in the past, the power consumption is reduced as much as the impedance of the circuit and the loss of the capacitive actuator CL can be reduced.

  Moreover, although the case where there is one capacitive actuator CL has been described in the above case, it may be a capacitive actuator CL in which a plurality of capacitive actuators are arranged as shown in FIG.

  By the way, when the circuit for charging the capacitive actuator CL as described above is realized by the capacitive actuator driving circuit for driving a plurality of actuators, the inductors L are prepared by the number of the capacitive actuators CL. However, it is necessary to prepare as many inductors L as the capacitive actuators CL in terms of cost. Therefore, a method of dividing the capacitive actuator drive circuit 101 into a common part composed of the inductor L and the switching element and a part for selecting the capacitive actuator CL to be operated can be considered. At this time, since the number of capacitive actuators CL driven at the same time is generally arbitrary, the capacitance viewed from the inductor L changes depending on the number of capacitive actuators CL driven simultaneously. Therefore, the charging voltage cannot be made constant.

  Therefore, a method of adjusting the time for storing current energy in the inductor L according to the number of driving of the capacitive actuator CL can be considered. However, although this method can make the charging voltage constant, there remains a problem that the time required for charging changes depending on the number of driving of the capacitive actuator CL.

  Therefore, the most desirable method is to add a capacitor according to the number of driving of the capacitive actuator, and always make the capacitance as viewed from the inductor L constant. FIG. 6 is a diagram showing a circuit configuration of a capacitive actuator drive circuit in the case where the capacitance viewed from the inductor L is constant.

  According to the capacitive actuator driving circuit 101 shown in FIG. 6, the counter counts the input DATA, calculates the number of capacitive actuators CX that are driven simultaneously, latches the inversion of the numerical values, and switches Qc0 to Qc0. By turning on Qc5, it is possible to add an amount of capacitance that supplements the number of capacitive actuators CX to be driven, and the capacitance seen from the inductor L can be kept constant. Capacitance values of the capacitors (C0 to C5) to be added are different from each other, and the different capacitance values are the smallest capacitance value C0 = Cx and the smallest capacitance value of 2. The power is n (n is a natural number).

  Furthermore, the total value of the capacitances of the capacitors to be added may be calculated and added by correcting the capacitance value calculated from the number of capacitive actuators CL that are simultaneously driven. Further, a configuration for detecting the temperature may be added, and correction may be performed based on the detected temperature.

  The idea of adding capacitors according to the number of drives described above has the advantage of stabilizing the operation even when applied to a conventional drive circuit. Moreover, if it applies to what was described in patent document 2, since one transformer can be shared with respect to several actuators, a merit is large.

(Second Embodiment)
Next, a second embodiment will be described. In the second embodiment, a capacitive actuator driving circuit 200 configured to be able to be charged immediately when the charging direction of the capacitive actuator CL is changed and charged will be described.

  In the above embodiment, the current stored in the inductor L at t7 is returned to the constant voltage power supply P, and then the current is stored in the inductor L again at t11. Although this method has an advantage that the circuit configuration and control are simplified, it is disadvantageous in terms of efficiency, and there is a problem that the pause time cannot be made very small because t7 to t11 must be incorporated within the pause time. . A second embodiment describing a method for solving this problem will be described below.

  In the second embodiment, as shown in FIG. 7, when the discharge of the capacitive actuator CL is completed, the current stored in the inductor L is returned to the power source and terminated, or the current from the power source is terminated. It is possible to select whether to increase by replenishing or to restart.

  For example, if the operation of the switching elements Q21, Q22, Q23, Q23 is reversed at the same time as the discharge is completed and re-driven at the same time, the current stored in the inductor L is not directly returned to the constant voltage power supply P as a direct reverse charging current. Can be used.

  At this time, if the reverse charge voltage is insufficient, it is sufficient to replenish the current once from the constant voltage power source P and increase the voltage, and then reverse drive current. The operation of returning to the power supply P may be performed for a short time and then restarted.

  The circuit configuration of the second embodiment is more complicated in circuit and control than the circuit configuration of the first embodiment, but is advantageous in terms of efficiency because wasteful discharge is reduced, and There is an advantage that restrictions on the driving waveform are reduced.

  FIG. 7 is a diagram for explaining charging and discharging of the capacitive actuator CL in the capacitive actuator drive circuit 200 according to the second embodiment. As shown in FIG. 7A, the switches Q31 and Q33 are turned on to store current in the inductor L. At this time, the current value to be stored is determined by the time for which the switch Q31 is ON. 7B, when the switch Q31 is turned off, the stored current energy is held in the inductor L. Subsequently, as shown in FIG. 7C, after the switch Q34 is turned on and then the switch Q33 is turned off, the capacitive actuator CL is charged by the current energy stored in the inductor L.

  When the charging is completed, as shown in FIG. 7 (d), the diode D36 is turned OFF, so that the voltage is held in the capacitive actuator CL. Since the charging voltage is determined by the current energy stored in the inductor L, the inductor L, and the capacitance C, it is possible to charge a voltage higher than that of the constant voltage power supply P. Thereafter, the switch Q34 is turned off. 7E, after the switch Q33 is turned on and then the switch Q35 is turned on, the charge stored in the capacitive actuator CL flows to the inductor L. When the discharge of the capacitive actuator CL is completed, the diode D36 is turned on by the electromotive force of the inductor L, and current energy is held in the inductor L, as shown in FIG. Thereafter, the switch Q35 is turned off.

  The subsequent operation is one of the following three. First, in order to reversely drive the capacitive actuator CL, charging is performed by changing the charging direction of the capacitive actuator CL (the capacitive actuator CL is reversed using the switching element shown in FIG. 3). In the case of having a mechanism), as shown in FIG. 8, after the switch Q34 is turned on, the switch Q33 is turned off. Thereby, the charging direction in the case shown in FIG. 7D is switched by the current energy stored in the inductor L, and the capacitive actuator CL is charged. As described above, since the capacitive actuator CL can be charged by changing the charging direction without returning the charge to the constant voltage power supply P, the capacitive actuator driving circuit 200 is charged in the charging direction of the capacitive actuator CL. You can charge immediately when you replace and charge.

  Second, in the state of FIG. 7 (f), when it is desired to replenish the inductor L with current energy lost due to circuit resistance or the like prior to reverse driving of the capacitive actuator CL, as shown in FIG. First, the switch Q31 is turned on. Then, the current energy can be additionally stored in the inductor L. As a result, it is possible to charge the capacitive actuator CL after supplementing the current energy lost due to the circuit resistance or the like.

  Third, when driving the capacitive actuator CL is stopped in the state of FIG. 7F, the switch Q33 is turned off after the switch Q32 is turned on as shown in FIG. Then, the current energy stored in the inductor L is returned to the constant voltage power supply P. By returning the current energy to the constant voltage power supply P in this way, the driving of the capacitive actuator CL can be stopped.

  Note that the present invention is not limited to the above-described embodiments as they are, and can be embodied by modifying constituent elements without departing from the scope of the invention in the implementation stage.

The figure which shows the structure of the capacitive actuator drive circuit in the 1st Embodiment of this invention. The figure which shows an example of the capacitive actuator CL in the embodiment. The figure which shows an example of the capacitive actuator CL containing the switching element in the embodiment. The figure for demonstrating the change of the waveform of the voltage for obtaining the predetermined drive waveform in the embodiment, and an electric current. The figure which shows the capacitive actuator CL which has arrange | positioned multiple capacitive actuators in the embodiment. The figure which shows the circuit structure of the capacitive actuator drive circuit in the case of making the electrostatic capacitance seen from the inductor L constant in the embodiment. The figure which shows the structure of the capacitive actuator drive circuit in the 2nd Embodiment of this invention. The figure for demonstrating the operation | movement in the case of charging by changing the charging direction of the capacitive actuator CL in the embodiment. The figure for demonstrating the operation | movement which supplements the current energy lost with the circuit resistance etc. in the embodiment. The figure for demonstrating operation | movement in the case of stopping the drive of the capacitive actuator CL in the embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100,101,200 ... Capacitive actuator drive circuit, Q ... Switch, D ... Diode, P ... Constant voltage power supply, CL ... Capacitive actuator

Claims (7)

An inductor that stores current energy from the power source;
Means for charging the capacitive actuator with the current stored in the inductor,
A capacitive actuator drive circuit which discharges the capacitive actuator after holding the voltage charged in the capacitive actuator for a predetermined time.   2. The capacitive actuator according to claim 1, wherein discharging of the capacitive actuator is performed by storing current energy in the inductor, and the current energy stored in the inductor is returned to the power source. Driving circuit.   The reversing mechanism for reversing the connection between two electrodes forming the capacitive actuator and a drive circuit for driving the capacitive actuator is further provided. Capacitive actuator drive circuit. Comprising a plurality of the capacitive actuators;
When selectively driving the plurality of capacitive actuators, the number of the capacitive actuators to be driven is detected, and a capacitor selected from the plurality of capacitors according to the number is added, and the electrostatic actuator is added. 3. The capacitive actuator drive circuit according to claim 1, wherein when the capacitive actuator is driven, control is performed so that a capacitance value of the plurality of capacitive actuators with respect to the power source is constant. 4.   The capacitance values of the capacitors to be added are different from each other, and the different capacitance values are the smallest capacitance value and the 2nd power of the smallest capacitance value (n is a natural number). 5. The capacitive actuator drive circuit according to claim 4, wherein   5. The total capacitance value of the added capacitors is calculated by correcting the capacitance value calculated from the number of capacitive actuators that are driven simultaneously. The capacitive actuator drive circuit described. An inductor that stores current energy from the power source;
A capacitive actuator that is charged by the current stored in the inductor;
An inkjet head comprising: a capacitive actuator drive circuit that discharges the capacitive actuator after holding a voltage charged in the capacitive actuator for a predetermined time.

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