JPH02119276A - Drive circuit of piezoelectric element - Google Patents

Abstract

PURPOSE:To generate a driving force of a definite magnitude at a piezoelectric element for a definite time and easily by a method wherein a first state-control means, a second state-control means and a voltage-limiting means, which are individually specific, are formed at a drive circuit, for the piezoelectric element, which is provided with a direct-current power-supply, a coil and the piezoelectric element. CONSTITUTION:The following are installed in a drive circuit, for a piezoelectric element, provided with a direct-current power supply E, a coil L and the piezoelectric element P which is resonated at a prescribed frequency together with the coil L: first state-control means TR1, TC which are always in a state to prevent a charging operation, are set to a state to permit the charging operation at an input of a driving command and are returned to an original state at one time after the passage of a time when a voltage of the piezoelectric element P has reached a definite value of a power-supply voltage or lower; second state-control means TR2, TC which are always in a state to prevent a discharge operation, are set to a state to permit the discharge operation simultaneously with one time from the input of the driving command or when a prescribed time has elapsed after time and are returned to an original state by a time when at least the first state-control means TR1, TC are set to the state to permit the charging operation; prescribed voltage-limiting means D1, D2.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a drive circuit for a piezoelectric element, and particularly to a technique for controlling the displacement state of a piezoelectric element.

[Background of the invention]

The piezoelectric element can resonate at a predetermined frequency while repeating charging and discharging together with the coil, but it is sometimes desirable that the displacement state duration time for one displacement of the piezoelectric element be longer than a certain period of time. One example is when piezoelectric elements are used in actuators such as print heads of printers.

Therefore, in view of these circumstances, the present applicant has developed a drive circuit for a piezoelectric element that can set the displacement state duration time to a large value without deteriorating the operational response of the piezoelectric element. The application is currently being filed as An example of this drive circuit is shown in FIG. In this development device,
DC power supply E.

The transistor TR, the coil, and the piezoelectric element P are connected in series, and the negative electrode side of the DC power source E and the electrode side of the piezoelectric element P that should become the negative electrode are grounded. The forward direction of the transistor TR is a forward direction (hereinafter referred to as the forward direction of the circuit) from the positive electrode side of the DC power supply E to the electrode side that should become the positive electrode of the piezoelectric element P. The electrode side of the piezoelectric element P that is to become the positive electrode is grounded via a resistor R and a transistor TR, and the forward direction of the transistor TR is directed from the resistor R toward the ground point.

Switching of the transistors TR+ and TRz between a cutoff state and a conduction state is performed by a transistor control circuit TC (hereinafter simply referred to as control circuit TC). When a drive command is input to the control circuit TC, the transistor TR is switched from a cutoff state to a conduction state, and as a result, the electric charge of the DC power supply E is transferred to the piezoelectric element P via the transistor TR and the coil L, and the piezoelectric The element P is charged while resonating with the coil L, and the voltage VP of the piezoelectric element P starts rising from a value of 0 as shown by the solid line in the ninth graph. After half of the cycle time corresponding to the resonance period determined by the product of the equivalent capacitance of the piezoelectric element P and the coil resistance actance after the piezoelectric element P starts charging or a longer time, the control circuit TC starts charging. transistor TR
, from the conductive state to the cut-off state, the voltage VP of the piezoelectric element P reaches a maximum value which is approximately twice the power supply voltage V of the DC power source E, and charging is completed.

At a certain point after the completion of charging of the piezoelectric element P, the transistor T
Even if R, is in a conductive state, transistor TR prevents current from flowing in the direction opposite to the forward direction of the circuit, so discharging of piezoelectric element P is prevented, and the voltage of piezoelectric element P is will be kept constant. transistor TR,
The charging period during which the is in a conductive state is represented by T in the same graph. After charging is completed, the transistor TR, which is in the cut-off state,
The voltage of the piezoelectric element P is kept constant by preventing both charging and discharging of the piezoelectric element P.

After a predetermined period of time has elapsed since the input of the drive command, the control circuit TC switches the transistor TR from the cutoff state to the conduction state, and as a result, the electrical energy stored in the piezoelectric element P and the coil L is extinguished by the resistor R. .

The control circuit TC returns the transistor TR to its cut-off state at a time when the electrical energy should be completely extinguished.

The discharge period during which the transistor TR is in a conductive state is represented by T in the same graph.

[Problem to be solved by the invention]

As is clear from the above explanation, in the development equipment,
The piezoelectric element P is designed to be able to apply a fixed amount of driving force to the driven object over a fixed period of time by maintaining the piezoelectric element P in a maximum displacement state from the completion of charging to the start of discharging. .

However, subsequent research by the applicant revealed that the developed device had the following problems. That is,
Since the piezoelectric element P is prevented from being charged in the maximum displacement state, if the electrical energy of the piezoelectric element P is consumed due to the piezoelectric element P performing work on the driven object, the piezoelectric element The voltage (2) of P gradually decreases as shown by the two-dot chain line in the same graph, and as a result, the displacement of the piezoelectric element P and, as a result, the driving force decreases.

In addition, in the developed device, for some reason the piezoelectric element P
If the discharging is not performed normally and electrical energy may remain in the piezoelectric element P at the start of the subsequent charging, the amplitude of the resonance between the coil L and the piezoelectric element P becomes small, and the piezoelectric element P The voltage ■, can reach the maximum value that can be reached when charging is started with no electrical energy remaining in the piezoelectric element P, and as a result, the maximum displacement position of the piezoelectric element P reaches its normal position. Therefore, the driving force of the piezoelectric element P is insufficient. Therefore, like an actuator for a print head, it is necessary to alternately charge and discharge the piezoelectric element P many times, and it is not allowed to take sufficient time for discharging, and the time between discharging and charging is If the intervals are different, the maximum displacement position of the piezoelectric element P may vary depending on whether the electrical energy remains in the piezoelectric element P at the start of charging or not, or if it remains, the amount is large or small. This will vary depending on the displacement, resulting in a situation where the driving force of the piezoelectric element fluctuates. Therefore, the developed device also has the problem that it is necessary to design the piezoelectric element P to ensure that the piezoelectric element P is discharged before charging starts, for example by setting a long discharge time.

Therefore, the present invention has been made with the object of solving these problems.

[Means to solve the problem]

The gist of the present invention is to provide a piezoelectric element drive circuit including the above-mentioned DC power supply, coil, and piezoelectric element, (a) which is normally in a state of blocking the charging, but allows charging upon input of a drive command; (b) a first state control means that returns to the original state after a period when the voltage of the piezoelectric element reaches a certain value equal to or lower than the power supply voltage; , the state is set to permit discharging at the same time as a period of time from the input of the drive command, or a predetermined period of time after that period has elapsed, and the state is returned to the original state at least by the time when the first state control means next enters the state of permitting charging. (C) by preventing excessive electrical energy from the DC power supply from being stored in the piezoelectric element, which would cause the voltage of the piezoelectric element to exceed a certain value;
A voltage limiting means is provided to prevent the voltage of the piezoelectric element from exceeding a certain value.

[Effect]

In the piezoelectric element drive circuit according to the present invention, charging of the piezoelectric element is started upon input of a drive command, and charging is stopped for a period of time after the voltage of the piezoelectric element reaches a certain value below the power supply voltage. Ru. During the period from when the voltage of the piezoelectric element reaches a certain value until charging is stopped, even if the electrical energy of the piezoelectric element is consumed, the consumed amount is compensated for by the DC power supply, and the voltage limiting means Since the voltage is prevented from exceeding a certain value, the voltage of the piezoelectric element is kept constant during the period. Then, when a predetermined period of time has elapsed since the input of the drive command, the piezoelectric element starts discharging, and the displacement of the piezoelectric element disappears.

Furthermore, even if the piezoelectric element is not discharged normally and electrical energy remains in the piezoelectric element when the next charging starts, charging may be started before the displacement of the piezoelectric element has completely disappeared. The maximum voltage across the piezoelectric element is the same at each displacement, regardless of whether or not electrical energy remains, and if so, regardless of how much of it remains.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to easily generate a driving force of a constant magnitude in a piezoelectric element over a constant period of time.

Furthermore, regardless of whether or not electrical energy remains in the piezoelectric element at the start of charging, and regardless of the amount of electrical energy remaining, the maximum displacement position of the piezoelectric element is the same at each displacement, so for example, When charging and discharging a piezoelectric element alternately many times, even if the discharging time is set short and the discharging does not occur properly,
This provides the effect that fluctuations in the magnitude of the driving force that can be taken out from the piezoelectric element are suppressed to a small level at each displacement.

In addition, in order to prevent excess electrical energy from the DC power supply that would cause the voltage of the piezoelectric element to exceed a certain value from being accumulated in the piezoelectric element, for example, the excess electrical energy may be extinguished with a resistor, etc. It is possible to return it to a DC power source. In the latter case, the returned electrical energy can be reused, eliminating waste and reducing the power consumption required to drive the piezoelectric element.

〔Example〕

Hereinafter, two or three embodiments in which the present invention is applied to a drive circuit for a piezoelectric element, which is a drive source of a piezoelectric actuator that drives a print wire of a print head for an impact-type dot printer, will be explained in detail based on the drawings. do.

As shown in FIG. 2, the piezoelectric actuator includes a laminated piezoelectric element 10 in which a large number of piezoelectric elements P are laminated in a straight line direction (vertical direction in the figure). Each of the laminated piezoelectric elements 10 extends parallel to the laminated piezoelectric element 10,
It is supported by two frames 12 and 14 that are arranged in a direction perpendicular to the lamination direction with the laminated piezoelectric element lO at the center.

A movable element I6 and a temperature compensating member 18, both of which form a rectangular parallelepiped shape, are fixed to both end surfaces of the laminated piezoelectric element 10, respectively. One side surface of the movable element 16 parallel to the stacking direction is connected to the frame 1 through a pair of leaf springs 20 and 22 that are stacked on top of each other.
2, and the back surface of the temperature compensating material 18 opposite to the surface to which the laminated piezoelectric element 10 is fixed is opposed to the surface 26 of the frame 12. The movable member 16 and the leaf spring 20, and the leaf spring 22 and the surface 24 of the frame 12 are fixed to each other, but the leaf springs 20 and 22 are slidably in contact with each other along these surfaces. .

Further, a pin 28 is fixed to the frame 12 to contact the temperature compensation material 18 and bring it closer to the movable element 16. Thereby, the laminated piezoelectric element 10 is attached to the frame 12.14 with a slight compressive force remaining in the lamination direction. Therefore, if a voltage is applied to the laminated piezoelectric element 10 and the laminated piezoelectric element 10 extends in the lamination direction, the leaf spring 2
0 moves in the positive direction (upward in the figure) relative to the leaf spring 22, and on the other hand, if the voltage is removed from the laminated piezoelectric element 10 and the laminated piezoelectric element 10 contracts, the leaf spring 20 moves to the leaf spring 22. It will move in the opposite direction.

Note that even if the voltage is completely removed from the laminated piezoelectric element 10, residual strain in the positive direction remains in the laminated piezoelectric element 10.
This residual strain becomes smaller as the temperature of the laminated piezoelectric element 10 becomes higher. Therefore, even if the magnitude of the voltage applied to the laminated piezoelectric element 10 is controlled to be constant and the amount of displacement of the laminated piezoelectric element 10 is controlled to be constant, if the temperature is high, the laminated piezoelectric element 1
The maximum displacement position of 0 can reach the normal position, and the higher the temperature, the greater the unreached distance remaining between the normal position and the maximum displacement position. The temperature compensating material 18 is provided to avoid such a situation. The temperature compensating material 18 expands more as its temperature increases, and the temperature compensating material 18 is arranged in series in the direction of displacement of the laminated piezoelectric element 10.

In other words, by compensating for the unreached distance of the laminated piezoelectric element 10 with the expansion length of the temperature compensating material 18, the maximum displacement position of the laminated piezoelectric element 10 is prevented from changing due to temperature changes. There is.

The frame 14 is composed of an elastically deformable plate having a longitudinal shape longer than the laminated piezoelectric element 10, and the frame 14 connects a portion of the frame 12 close to the temperature compensation material 18 and the movable element 16. The function of frame 14 will be explained later.

A holding member 34 having a linearly extending groove 32 is fitted to the end of the pair of leaf springs 20 and 22 opposite to the end on the side of the laminated piezoelectric element 10 (the upper end in the figure). ing. The width of the groove 32 is made larger than the sum of the plate thicknesses of the leaf springs 20.22, and each leaf spring 20.22 and the side surface of the groove 32 facing the leaf spring 20.22 are fixed to each other. Holding member 34
An arm 36 is extended from the holder, and a printing wire 38 is fixed to the tip of the arm 36.

This printing wire 38 is opposed to the printing paper via a printing ribbon.

Therefore, when the laminated piezoelectric element 10 is extended and the leaf spring 20 slides upward relative to the leaf spring 22, and the holding member 34 is rotated counterclockwise approximately about the center line of the groove 32 in the figure. , the printing wire 38 is pressed against the printing paper via the printing ribbon, and dots are printed on the printing paper. When the laminated piezoelectric element 10 contracts from this state, the holding member 34 is rotated clockwise, and as a result, the printing wire 38 returns to the non-operating position. The non-active position of the printing wire 38 is defined by the abutment of the arm 36 against a low resilience rubber stopper 40 fixed to the frame 14.

As is clear from the above description, the piezoelectric actuator uses a pair of leaf springs 20, 22 to control the displacement of the laminated piezoelectric element 10.
．． It is expanded by the holding member 34 and arm 36 and transmitted to the print wire 3 days later.

In addition, if the printing wire 3 days is pressed against the printing paper,
A moment is generated in the movable element 16 in a direction that causes the movable element 16 to rotate counterclockwise approximately around its center, and the laminated piezoelectric element 10 may be bent in a direction crossing the lamination direction. . However, in this embodiment, when the laminated piezoelectric element 10 stretches, the frame 14 elastically stretches accordingly, and as a result, a moment is generated in the movable element 16 in the direction of rotating it clockwise.
The moments in opposite directions cancel each other out, allowing the laminated piezoelectric element 10 to expand and contract linearly without bending.

FIG. 1 shows a drive circuit for the laminated piezoelectric element 10. As shown in FIG.

This is because a diode D1 is provided between the transistor TR and the coil in the development device (shown in FIG. 8) to bypass them in the opposite direction, and the coil L is connected to the positive terminal side of the DC power supply E. The opposite side is grounded via diode D2. Diode D2
The forward direction is defined as the direction from the grounding point to the coiling point. Note that the figure depicts one piezoelectric element P as a representative, and a large number of piezoelectric elements P constituting the laminated piezoelectric element 10.
are connected in parallel with each other.

Switching of the transistors TR+ and TRz between the cutoff state and the conduction state is performed by the control circuit TC.

When a dot printing command (command to print dots) is input to the control circuit TC, the transistors TR,
As a result, the electric charge of the DC power source E is transferred to the transistor TR.

and moves to the piezoelectric element P via the coil L, and the piezoelectric element P
is charged while resonating with the coil L, and the voltage (2) of the piezoelectric element P starts to rise from a value of 0, as shown in the graph of FIG. 3, and eventually reaches the power supply voltage (2).

reaches a size equal to . After that, diode D,
Since the voltage on the piezoelectric element P side becomes higher than the voltage on the DC power supply E side, the current flowing from the coil L to the piezoelectric element P flows back to the coil via the diode D and the transistor TR, and electrical energy is transferred to the coil. accumulated, piezoelectric element P
is not accumulated in the piezoelectric element P, and the voltage of the piezoelectric element P is the power supply voltage ■6
In this state, even if the electrical energy of the piezoelectric element P is consumed by pressing the printing wire 38 against the printing paper, the electric charge from the DC power source E is transferred to the transistor TR and the coil. Since it is supplemented by being supplied to the piezoelectric element P via L, the voltage (2) of the piezoelectric element P is kept at a constant level.

In the control circuit TC, the voltage ■ of the piezoelectric element P is the power supply voltage ■,
Transistor TR when a predetermined period of time 1+ has elapsed from the input of the dot printing command.

to return to the cut-off state. As a result, the coil.

Diode D1. A closed circuit including a DC power source E and a diode D2 converts the electrical energy of the coil L into a DC type a.
It will be returned to E. Furthermore, when the transistor TR is in a cut-off state, even if the voltage 7 of the piezoelectric element P becomes smaller than the magnitude equal to the power supply voltage 2, electric energy is not replenished by the DC power supply E, so the piezoelectric element P If the electrical energy of is consumed, the voltage of the piezoelectric element P decreases. In addition, in the graph of FIG. 3, the transistors TR,
After returning to the cut-off state, there is a period in which the voltage of the piezoelectric element P, ■, is kept equal to the power supply voltage, ■;
This is because the electrical energy of the coil L is transferred to the piezoelectric element P by the current flowing through the closed circuit including the piezoelectric element P, thereby replenishing the consumed electrical energy of the piezoelectric element P.

The control circuit TC also controls the transistor TR, when a predetermined time t2 has elapsed from the input of the dot printing command, either at the same time as the time when the electric energy of the coil L should be completely extinguished, or after that time. Switch from cutoff state to conduction state. As a result, the piezoelectric element P has a resistance R
The electric energy of the piezoelectric element P is consumed by the resistor R, and the voltage P of the piezoelectric element P decreases. The control circuit TC controls the transistor T when a predetermined time t3 has elapsed from the input of the dot printing command, either at the same time as or after the time when the voltage of the piezoelectric element P should become completely zero. Rt is returned to the cut-off state.

As described above, in this embodiment, the voltage V of the piezoelectric element P is maintained at least during the period from when the voltage V of the piezoelectric element P reaches a magnitude equal to the power supply voltage V until the charging period Tc expires. Since the magnitude of the voltage V is kept constant and the magnitude of the voltage V at that time does not change for each dot printing, the maximum displacement position of the piezoelectric element P becomes equal for each dot printing, and The maximum displacement state duration time of the piezoelectric element P can be set to a sufficient length.

Furthermore, in this embodiment, charging of the piezoelectric element P in the next dot printing is started after waiting for the electric energy of the piezoelectric element P to be completely released.
The amount of displacement (difference between the initial position and the maximum displacement position of the piezoelectric element P just before charging starts) is also the same for each dot printing, and the magnitude of the driving force of the piezoelectric element P and, by extension, the height of the printing pressure is It becomes constant, and the print quality becomes good.

As is clear from the above explanation, in this example,
The transistor T RI and a portion of the control circuit TC that controls the transistor TR constitute a first state control means, and the resistor R and the transistor TR constitute a first state control means.

and a portion of the control circuit TC that controls the transistor TRz constitute a second state control means, and the diodes D and D2 constitute a voltage limiting means.

As a different aspect from the above embodiment of the control circuit TC, after returning the transistor TRI from the conductive state to the cut-off state,
Transistor TR Switches transistor TR to conduction again at a certain period of time before the time when transistor TR should be switched to conduction, and then switches transistor TR to conduction at the same time as transistor TR returns to cut-off state. It can be done. In this way, each time a dot printing command is input, the voltage V of the piezoelectric element P reaches a level equal to the power supply voltage Vi by at least the first charging, as shown in the graph of FIG. Not only the period from then until the charging period T'c+ expires, but also the period from when the voltage V of the piezoelectric element P reaches a magnitude equal to the power supply voltage ■ due to the second charging to the charging period T' Even in the period until ez expires, a constant level of printing pressure can be obtained, and if the dot printing command is input to the control circuit TC at the same timing as in the previous embodiment, this embodiment In this case, the time required to obtain a constant level of printing pressure during each dot printing is longer than in the case of the above embodiment. Therefore, normally it is charged only once for each dot printing, but by charging it twice as necessary, it is possible to print darker than usual. In this embodiment, since discharging is started at the same time as the second charging ends, electrical energy remains in the coil at the start of discharging, and the electrical energy of the piezoelectric element P and the DC power source of the coil L are Since the remaining electric energy that has not been returned is also consumed by the resistor R, - the time it takes for the piezoelectric element P to be completely discharged is longer than in the case of the above embodiment; Since the amount of charge is relatively small, the discharging time does not need to be extended.

As yet another aspect of the control circuit TC, a transistor T
R, may be kept conductive until such time as transistor T Rz is switched conductive. In this way, the voltage of the piezoelectric element P becomes the power supply voltage V.

If the electrical energy of the piezoelectric element P is consumed during the period from when it reaches a size equal to , until the charging period T expires (until the start of discharging), the consumed amount is replenished from the DC power supply E, and the piezoelectric element P As shown in the graph of FIG. It remains at a constant size from the time it reaches a size equal to , until the discharge starts. In this embodiment, since electrical energy remains in the coil at the start of discharge, the electrical energy stored in the piezoelectric element P and the coil L is consumed by the common resistor R, and the discharge time is It will be a little longer.

FIG. 6 shows a piezoelectric element drive circuit different from the above embodiment. This corresponds to the diode D in the embodiment shown in FIG.
, and a transistor TR is connected in parallel with the transistors TR. The forward direction of transistor TR is opposite to the forward direction of diode D.

Transistors TR, , TR, and TR are control circuit T
Controlled by C. When a dot printing command is input to the control circuit TC, the transistor TR is switched from a cut-off state to a conduction state, thereby charging the piezoelectric element P, and the voltage thereof is shown in the graph of FIG. to rise like that. When the voltage (2) of the piezoelectric element P becomes equal to the power supply voltage V, a current flows through the diode D+, and the voltage vP of the piezoelectric element P is kept equal to the power supply voltage vE. The control circuit TC also controls the transistor T after the voltage V, of the piezoelectric element P becomes equal to the power supply voltage V,
At the same time, the transistor TR is returned to the cut-off state.
, switches from the cutoff state to the conduction state. therefore,
When the electrical energy of the piezoelectric element P is consumed, the electric charge of the DC power source E is transferred to the piezoelectric element P via the transistor TR, without passing through the coil L, unlike the previous embodiment.

On the other hand, the electric energy accumulated in the coil is returned to the DC power supply through a closed circuit including the diode DI, the DC power supply E, and the diode Dz, so that the control circuit TC changes the transistor TR1 from the conductive state to the cutoff state. At the start of discharging when the transistor TR is switched from the cut-off state to the conductive state at the same time as the piezoelectric element P returns to the current state, no electrical energy remains in the coil, and the discharge of the piezoelectric element P is completed in a relatively short time. The period during which the transistor T R3 is in a conductive state is Tc in the graph of FIG. During the period, the voltage V of the piezoelectric element P is kept constant.

As is clear from the above explanation, in this example,
The transistors TR, TR, and a portion of the control circuit TC that controls the transistors TR, TR constitute a first state control means, which controls the resistor R, the transistor TRz, and the transistor TR of the control circuit TC. portion constitutes the second state control means, and the diodes D and D2 constitute the voltage limiting means.

In the embodiment described above, the present invention is applied to a drive circuit in which the electrical energy of the piezoelectric element P is transferred to the resistor R without resonance with the coil L and is consumed by the resistor R when the piezoelectric element P is discharged. For example, as in the embodiments shown in FIGS. 6 and 8 of the above-mentioned Japanese Patent Application No. 114397/1982, the electric energy of the piezoelectric element P is transmitted with resonance with the coil L. The present invention can also be applied to a drive circuit of the type that discharges by returning to the DC power source E.

Furthermore, in all of the above embodiments, when a dot printing command is input to the control circuit TC, the control circuit TC itself returns the TRI to the cut-off state after a predetermined time has elapsed in response to the transistor TR. , transistor TR
, and TR, respectively. At the same time, the control circuit TC is changed so that a command that triggers the switching of the conduction/cutoff state of each of the transistors TR or TR is inputted, and the control circuit TC is changed to switch the conduction or cutoff state of each of the transistors TR or TR in accordance with these commands. It can be changed to one that switches the cut-off state.

Further, in each of the above embodiments, the transistor TR is used to switch between a state of blocking and a state of allowing charging and discharging of the piezoelectric element P, respectively.

or TR3 are used, but instead of them,
It is also possible to use, for example, an analog switch that can be switched between a blocking state and a conducting state that allows current to flow in either the forward or reverse direction of the circuit.

In addition to these, the present invention can be implemented with various modifications, improvements, etc. based on the knowledge of those skilled in the art.

[Brief explanation of drawings]

FIG. 1 is an electric circuit diagram showing a drive circuit of a piezoelectric element of a piezoelectric actuator for a print head of an impact-type dot printer according to an embodiment of the present invention, and FIG. FIG. 3 is a graph showing voltage changes of the piezoelectric element in this example. FIGS. 4 and 5 are graphs showing voltage changes of piezoelectric elements different from those of the above embodiments, respectively. FIG. 6 is an electric circuit diagram showing a piezoelectric element drive circuit different from that of the above embodiment, and FIG. 7 is a graph showing voltage changes of the piezoelectric element in this embodiment. FIG. 8 is an electric circuit diagram showing a piezoelectric element drive circuit previously developed by the applicant, and FIG. 9 is a graph showing voltage changes of the piezoelectric element in the drive circuit. lO: Laminated piezoelectric element 20, 22: Leaf spring 34: Holding member 36: Arm 38: Print wire E: DC power supply TR0, TRz, TRz: Transistor: Coil P: Piezoelectric element R: Low resistance C:) Transistor control circuit Figure 1: Diode

Claims (1)

[Claims] A piezoelectric element comprising a DC power source, a coil, and a piezoelectric element that can resonate at a predetermined frequency with the coil while repeatedly charging and discharging, and the piezoelectric elements are connected in series. The drive circuit is always in a state of blocking the charging, but becomes a state of allowing charging when a drive command is input, and determines when the voltage of the piezoelectric element reaches a certain value below the power supply voltage. a first state control means that returns to the original state after a certain period of time has elapsed; a second state control means that returns to the original state at least by the time when the first state control means next becomes a state that allows charging; and a voltage of the piezoelectric element is set to the constant value. and voltage limiting means for preventing the voltage of the piezoelectric element from exceeding the predetermined value by preventing excess electrical energy from the DC power supply that would exceed the voltage from being accumulated in the piezoelectric element. A drive circuit for a piezoelectric element.