JPH0471859A - Driving device of piezoelectric element - Google Patents

Abstract

PURPOSE:To obtain a piezoelectric element driving device of low power consumption by a method wherein one end of a coil is connected to the piezoelectric element, the other end is connected to a switch together with the piezoelectric element and said coil composing a resonance circuit, and when displacement of the piezoelectric element is released, a switch is made to conduct and after specific time, is intercepted with a timer. CONSTITUTION:In the case where, for instance, the invention is applied on a driving circuit of a piezoelectric type actuator of a dot printer, a control circuit 55 makes a transistor (Tr)1 conduct by an indication of driving in the circuit as given in the figure and after accumulating enough charges in a piezoelectric element P, Tr1 is intercepted, and Tr3 is made to conduct. After time necessary for printing has elapsed, when Tr3 is intercepted and Tr2 is made to conduct, all electric energy accumulated by the charges in the element P is accumulated in a coil L as magnetic energy near the coil 53. When Tr2 is intercepted at this instant, all electric energy accumulated by action of the coil 53 is returned to d.c power source 51. Conductive time of Tr2 is indicated with a timer 55a and where inductance of the coil 53 is L and electric capacity of the element P is C, is expressed by (pi/3) (LC)<1/2>.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a piezoelectric element drive device, and more particularly to a piezoelectric element drive device that can realize low power consumption, low heat generation, and low cost.

[Prior Art] A piezoelectric element can resonate at a predetermined frequency while repeating charging and discharging together with a coil.

However, in some cases, such as when used to drive a print wire in a printer, it is necessary to maintain the displacement state of - times of displacement for a predetermined period of time. As a drive device for such a case, for example, a device disclosed in Japanese Patent Application Laid-Open No. 130357/1983 is known.

This device is constructed as shown in FIG. That is, piezoelectric element 1
02 is connected to the power supply terminal of the power supply 101 via the emitter-collector of the switching transistor 103. This switching transistor 103 receives a drive signal v
2 is input, a power supply voltage is applied to the piezoelectric element 102. Further, a diode 110 is connected in parallel to the piezoelectric element 102 in such a direction that a voltage is applied in the opposite direction when the switching transistor 103 is in an on state. Further, one end of a coil 105 is connected to the non-ground terminal of the piezoelectric element 102, and the other end of the coil 105 is connected to a power terminal of the power source 101 via a diode 109.

This diode 109 is oriented to allow current to flow only from the piezoelectric element 102 to the power supply terminal side.

A connecting line between the diode 109 and the coil 105 is connected to the collector of the switching transistor 106. The emitter of this switching transistor is connected to ground, and the base of the switching transistor 108
connected to the collector. The emitter of this switching transistor 108 is connected to the piezoelectric element 102 via a resistor.
connected to the non-ground terminal of the The emitter of the switching transistor 108 is connected to the collector of the switching transistor 107, and the emitter is connected to ground. Also, this switching transistor 1
The release signal V3 is input to the base of 07.

In the device described above, when the drive signal V2 becomes high, the switching transistor 103 becomes conductive.

Then, the electric charge from the power supply terminal is charged to the piezoelectric element 102 via the switching transistor 103, and the piezoelectric element 102 is displaced.

When canceling the displacement of the piezoelectric element 102, the drive signal V
2 is set low, and the release signal V3 is set high. Then, the supply of new charge is cut off, and the switching transistor 107 becomes conductive. Then, the base voltage of the switching transistor 108 becomes OV. On the other hand, since the emitter of the switching transistor 108 is connected to the charged piezoelectric element, a predetermined voltage is applied thereto. Therefore, a predetermined voltage is applied between the base and emitter of the switching transistor 108, and the switching transistor 108 becomes conductive.

Therefore, a voltage equivalent to the terminal voltage of the piezoelectric element 102 is applied to the base of the switching transistor 106, and the switching transistor 106 becomes conductive. Therefore, the piezoelectric element 102 (here equivalent to a capacitor) and the coil 105 form a resonant circuit arranged in series.

Therefore, the current and voltage flowing through coil 105 are
It becomes a sine wave with a predetermined period determined by the inductance of the piezoelectric element 102 and the capacitance of the piezoelectric element 102, and its phase difference is 90 degrees if the pure resistance component in the circuit is ignored.

Also, at this time, there is almost no pure resistance in the circuit, so there is no loss in the circuit. Since the voltage applied to the coil 105 is sinusoidal in this way, the voltage applied to the coil becomes zero when a quarter of the period has elapsed after the release signal becomes high. At this time, since the emitter of the switching transistor 108 becomes OV, the switching transistor 108 is turned off, and at the same time, the switching transistor 106 is also turned off. Then coil 105
All of the current accumulated in the diode 109 flows into the power supply. Therefore, the discharged charges are not dissipated by heat, achieving low heat generation and low power consumption.

[Problems to be Solved by the Invention] However, in the above-mentioned device, many switching transistors are used, which makes the device complicated, and it is difficult to provide the device at a low cost. Furthermore, since a large number of switching transistors are used in this way, there is a loss due to each switching transistor, and the reduction in power consumption is not satisfactory.

The present invention has been made to solve the above problems,
The purpose is to provide a piezoelectric element drive device with low power consumption at low cost.

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a method in which one terminal A is electrically connected to the terminal B of the piezoelectric element, and the other terminal C is electrically connected to the power source. a coil, a switch means electrically connected to a terminal C of the coil and the other terminal of the piezoelectric element to constitute a resonant circuit with the piezoelectric element and the coil, and capable of measuring a predetermined time. timer and
The control means includes a control means that makes the switch means conductive when an instruction is given to cancel the displacement of the piezoelectric element, and then cuts off the switch means when a timer indicates that a predetermined time has elapsed.

In this case, it is preferable that a microcomputer is used as the control means, and that the timer is built into the microcomputer or configured by its program. Further, in this case, it is desirable that the microcomputer also controls the device itself in which the piezoelectric element and the drive device are incorporated.

[Operation] In the present invention having the above configuration, when the displacement of the piezoelectric element is released, the switch means is brought into a conductive state. In this state, the piezoelectric element and the coil constitute a resonant circuit, and the charge accumulated in the piezoelectric element flows out through the coil.

Then, the timer waits until the electrostatic energy due to the charge has been substantially converted into current energy flowing through the coil, and the control means shuts off the switch means. The current flowing through the coil then flows into the power source.

[Example] Hereinafter, an example in which the present invention is applied to a drive circuit for a piezoelectric element that is a drive source for a piezoelectric actuator that drives a print wire of a print head for an impact-type dot printer will be described in detail based on the drawings. do.

A piezoelectric actuator consists of a large number of piezoelectric elements P shown in FIG.
Laminated piezoelectric element 10 made up of layers laminated along a straight line direction
It is equipped with As shown in FIG. 2, the laminated piezoelectric element 10 is supported by two frames 12.degree. There is.

A movable member 16 and a temperature compensating member 18, each having a rectangular parallelepiped shape, are fixed to both end faces of the laminated piezoelectric element 10, respectively.

One side surface of the mover 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 element 16 and the leaf spring 20, and the leaf spring 22 and the surface 24 of the frame 12 are respectively fixed to each other, but the leaf springs 20, 22 are brought into sliding contact 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, when a voltage is applied to the laminated piezoelectric element 10 and the laminated piezoelectric element 10 extends in the lamination direction, the leaf spring 20 moves in the positive direction (upward in the figure) relative to the leaf spring 22, and on the other hand, When the voltage is removed from the laminated piezoelectric element 10 and the laminated piezoelectric element 10 contracts, the leaf spring 20 moves in the opposite direction to the leaf spring 22.

Note that even if the voltage is completely removed from the laminated piezoelectric element 10,
A residual strain in the positive direction remains in the laminated piezoelectric element 10, and this residual strain becomes smaller as the temperature of the laminated piezoelectric element 10 increases. 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 10
The maximum displacement position of 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. That is, by compensating for the unreached distance of the laminated piezoelectric element 10 by 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. It is.

The frame 14 is made of an elastically deformable plate having a longitudinal shape longer than the laminated piezoelectric element 10, and 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 groove 32 extending linearly 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). There is. The width of the groove 32 is made larger than the sum of the plate thicknesses of the leaf springs 20 and 22, and the side surfaces of the groove 32 and the leaf springs 20 and 22 facing each other 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 extends and slides upwardly relative to the leaf spring 20 or 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 3
8 returns to the non-active position. The non-active position of the printing wire 38 is located at a low-repulsion rubber stopper 4 fixed to the frame 14.
It is defined by the arm 36 coming into contact with the point 0.

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.
, is expanded by the holding member 34 and the arm 36 and transmitted to the printing wire 38.

Note that when the printing wire 38 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 in the figure approximately around its center, causing the laminated piezoelectric element 10 to rotate. There is a risk that it will be bent in a direction that intersects with the stacking direction. However, in this embodiment, when the laminated piezoelectric element 10 extends, the frame 14 elastically extends accordingly, and as a result, a moment is generated in the movable element 16 in the direction of rotating it clockwise. The directional moments cancel each other out, making it possible for the laminated piezoelectric element 10 to expand and contract linearly without bending.

Next, a drive circuit for the laminated piezoelectric element 10 is shown in FIG. In this embodiment, a DC power source 51 with an output voltage E, a transistor Trl, a coil 53, and a piezoelectric element P are connected in series, and the negative electrode side of the DC power source 51 and the electrode side that should become the negative electrode of the piezoelectric element P are grounded. ing. transistor T
The forward direction of rl is defined as the forward direction from the positive electrode side of the DC power supply 51 to the electrode side that should become the positive electrode of the piezoelectric element P (hereinafter referred to as the forward direction of the circuit).

Furthermore, the connection point between the transistor Trl and the coil 53 is grounded via the transistor Tr2.

The forward direction of the transistor Tr2 is the direction from the connection point between the transistor Tr1 and the coil 53 toward the ground point. Diodes DI and D2 are connected in parallel to the transistors Trl and Tr2, respectively, and the forward directions of the diodes DI and D2 are opposite to the forward direction of the transistors to which the respective diodes are connected in parallel. .

The positive electrode side of the DC power supply 51 and the electrode side of the piezoelectric element P that should become the positive electrode are connected by a diode D3, and the forward direction of the diode D3 is opposite to the forward direction of the circuit. Further, a transistor Tr3 is connected in the opposite direction to the diode D3. Further, a diode D4 is connected in parallel to the piezoelectric element P, and its forward direction is a forward direction from the electrode side of the piezoelectric element P that should be the negative electrode to the electrode side that should be the positive electrode. Note that a large number of piezoelectric elements P constituting the laminated piezoelectric element 10 are connected in parallel to each other.

Transistors Tri, Tr2. Switching between the cutoff state and the conduction state of Tr3 is performed by a transistor control circuit 55 (hereinafter simply referred to as control circuit 55). This control circuit 55 is also responsible for the overall control of the impact type printer in which this device is mounted, and is composed of a microcomputer. This control circuit 55 includes a timer 55a
Built-in.

Next, control of the control circuit 55 will be explained. Figure 3 shows
2 is a flowchart showing an excerpt of the control of driving a predetermined printing element for printing a predetermined dot of the printer. In addition to the control shown in this flowchart, this control circuit simultaneously drives other printing elements and controls other printers.

First, when the printing element is instructed to be driven, the control circuit 55 turns on the transistor Trl (Sl). Then, the charge generated by the DC power supply 51 flows into the piezoelectric element P via the transistor Trl and the coil 53. This piezoelectric element P is therefore displaced, and this displacement causes the printing wire 38 to protrude. This printing wire 38 presses the printing paper placed on the platen through the printing ribbon.

The control circuit 51 waits until sufficient charge is accumulated in the piezoelectric element P (S2). Then, due to the action of the coil 53, the current continues to flow through the closed current loop via the diode D3 and the transistor Trl, and the current flowing through the coil 53 is maintained.

After a sufficient charge is accumulated in the piezoelectric element P, the control device 51 turns off the transistor Tri and turns on the transistor Tr3 (S3). Then, a current continues to flow through the coil 53 due to the action of the coil 53, and the current flows through the diode D3. DC power supply 51. It continues to flow in the closed current loop via diode D2 and eventually attenuates.

During this time, a small amount of current is consumed by the piezoelectric element P, but this current is transferred from the DC power supply 51 to the transistor Tr3.
is supplied to the piezoelectric element P via.

That is, during this period, the displacement of the piezoelectric element P remains maintained.

The control circuit 55 attenuates the current flowing through the coil 53 and waits for a displacement time necessary for printing (S4). After that, the control circuit 55 shuts off the transistor Tr3 and turns on the transistor Tr2 after a slight delay. is made conductive (S5). Then, the charge accumulated in the piezoelectric element flows through a closed current loop via the coil 53 and the transistor Tr2. At this time, there is almost no pure resistance in this closed current loop, so there is almost no heat consumption of electrical energy. All of the electrical energy resulting from the charges accumulated in the piezoelectric element P is accumulated in the coil as magnetic energy near the coil 53 after a predetermined period of time to be described later.

Then, the control circuit 55 waits until this moment in step S6.
), the transistor Tr2 is cut off (S7). Then, because the current in the coil 53 tends to continue flowing due to the action of the coil 53, this current is returned to the DC power source E via the diode D1. In other words, all the electrical energy stored in the coil is returned to the DC power source 51.

Next, in order to discharge the piezoelectric element P, the transistor T
The time to close r2, that is, the waiting time in S6 will be explained.

First, when transistor Tr2 is closed (time is 10),
A closed circuit consisting of the piezoelectric element P (capacitance C), the coil 53 and the transistor Tr2 is formed, and the piezoelectric element P
Due to the electrostatic energy stored in the piezoelectric element P
A current flows through the coil 53. The time when this transistor is closed is set to t-〇, and the transistor Tr is connected to the coil 53.
If the current flowing from the 2 side to the piezoelectric element P side is i (t), then by assuming that there is no resistance component in the transistor Tr2 etc., the following equation can be obtained from Kirchhoff's second law from the above-mentioned closed circuit. I can do it.

However, here, L is the inductance of the coil 53, and C
represents the capacitance of the piezoelectric element P.

Now, if the charge of the piezoelectric element P is q (t), then
q (t) becomes the following formula.

Q(t)=5i(t)dt (2)i
(t)-dQ(t) (3)d
t By substituting these equations (2) and (3) into equation (1), the following equation is obtained.

L q(t)+19(t) −0(4)t2c Solve this differential equation (4) to obtain q(t). In order to solve this equation, a differential operator p is introduced. This differential operator p is expressed by the following equation.

1)-d (5) By substituting equation (5) into equation (4), the following equation is obtained.

Lp2 +’O Solving equation (6) yields the following equation.

Here, j is an imaginary unit. If the constant A1°A2 is introduced here, g(t) will be expressed by the following equation.

Jam 1 By equations (9), (10), and (11),
Equation (8) is transformed as follows.

q(t) = Acos ωOt +Bs1n u
Ot (12) By substituting this equation (12) into equation (3), the following equation is obtained.

1(t)-ωo [Beos ωOt-Asin
Next, consider the initial conditions at time t'-Q. Before time 1-0, charge is stored in the piezoelectric element P in order to perform printing. At this time, the potential difference between both ends of the piezoelectric element P is equal to the power supply voltage E. Since the capacitance of the piezoelectric element P is C, at time 1-
The charge stored in the piezoelectric element P at 0 is expressed by the following equation.

Now, further define the following equation.

A − A, 10A 2 B=j(A+A2) Furthermore, since the transistor Tr2 is closed at time t-0, no current is flowing through the coil 53 yet at time tQ. Therefore, the current flowing through the coil 53 at time t-0 is expressed by the following equation.

(14), (15) and t-0 as (12).

By substituting into equation (13), constants A and B become as follows.

A-CE (16)
B −0 (17) By giving equations (16) and (17) to equations (12) and (13), the following equation is obtained.

q(t)-CEcos 'L'Ot
(1g)i(t) −−ω□ CEs1n ωOt
(19) On the other hand, if the potential difference between both ends of the piezoelectric element P is v (t), v (t) is expressed by the following equation.

Ru.

v(t) = Ecos ωo t
(21) Therefore, at time t-0, transistor T
When r2 is closed, the potential difference v (t) across the piezoelectric element P
will take the value expressed by equation (21) until it reaches zero.

On the other hand, the time when the potential difference v (t) between both ends of the piezoelectric element P reaches zero can be obtained by solving the equation (21) with the left side set to zero.

Ecos uOt -0 (22) π 3 5.

uOt-Knee Earth-π Earth-π-Fist (23) t, -
+1. π 3 π , , , (24) ten
〇2 ωo, 2 ω0 Here, it can be seen from equation (24) that the potential difference v (t) between both ends of the piezoelectric element P reaches zero for the first time from time 1-0 at a time of 1 π -. . The 2ω0 value of ω0 was defined in equation (11), so by substituting this value, we get (2
By substituting the equation (18) into the equation (0), the following equation is obtained. If the transistor Tr2 is opened at this time t-"%,
The current i (t) due to the current energy of the coil 53 is
Since the current cannot flow through the transistor Tr2,
Coil 53. Diode DI, DC power supply 51. Current now flows through the closed circuit consisting of diode D4. Time t is defined as the time when transistor Tr2 is opened, that is, as shown in the following equation.

tShinito L C (25) On the other hand, from the above-mentioned closed circuit, the following equation holds true according to Kirchhoff's second law.

E--L di (t) (2B) t Solving equation (26) yields the following equation.

i (t) −−Et+K (27)
Considering the initial condition of equation (27), it is sufficient to substitute t in equation (25) for t in equation (19). Therefore, the value i(t+) of i(t) at time t1 is as follows.

~ωo CE (2g) Using equation (28), if the constant K in equation (27) is eliminated, 1-1. It can be seen that the subsequent i (t) is as shown in the following equation.

Next, from equation (29), t such that i (t)=0 is calculated as follows.

One ω. LC+t.

−fτC+t, (30) Therefore, time 1
-1. When the transistor Tr2 is opened at time I, the current energy of the coil 53 is regenerated to the DC power supply 51.

During these operations, the potential difference V(1) across the piezoelectric element P and the current i (t) flowing through the coil 53 are as shown in FIG. 4(a).

According to the above, if the transistor Tr2 is closed for a period of time ττ, the piezoelectric This is the same as opening the switching transistor 06 when the potential difference between both ends of the element P becomes zero, and according to the embodiment, the potential detection means required in the device of the above-mentioned publication is not required, so an equivalent circuit can be constructed at low cost. This means that it will be possible to realize this.

However, the following points need to be considered here. That is, according to this embodiment, since the period during which the transistor Tr2 is closed is controlled by time, the electric charge of the piezoelectric element P described above is discharged due to individual differences in the capacitance C of each piezoelectric element P and the inductance of the coil 53. time iJ
[E will vary depending on the individual circuit. Therefore,
Next, we will explain the case where it does not work.

The case where the time is opened will be explained.

Since this is similar to when the transistor Tr2 is closed at time t-0, no particular explanation will be given here.

At time t=iJ, the potential difference between both ends of the piezoelectric element P becomes zero. Then, since diode D4 closes, a closed circuit is formed between coil 53. Switching element Tr2. It is now composed of diode D4.

If the transistor Tr2 and the diode D4 are ideal switching elements, there is no factor that consumes the current energy of the coil 53, so the potential difference v (t) across the piezoelectric element P and the current i (t) of the coil 53 are as follows. It becomes like the solid line in FIG. 4(b).

However, in reality, transistor Tr2. Diode D4. Since the coil 53 and the like have a resistance component, the current energy of the coil 53 is consumed while the transistor Tr3 is closed, as shown by the broken line in FIG. 4(b).
converted into thermal energy. However, this converted thermal energy is minute, and the increase in heat generation from the drive circuit of this embodiment is also minute, so this does not pose a major problem.

= −(IJOCEsjn ω□ t H (31) On the other hand, when transistor Tr2 is opened at time 1-1.
The current energy in coil 53 causes coil 53. A current flows through a closed circuit consisting of the diode DI, the DC power supply 51, and the piezoelectric element P. Regarding this closed circuit, the following formula holds from Kirchhoff's second law.

By introducing q(t t+), the following equation is obtained.

The case where the period is closed will be explained.

Time t −t + <i, /T”El=transistor 9
When T r 2 is opened, the coil 53 at that time t1
The current i(t+) flowing in is calculated from equation (19) as follows.

Find Q (t) by solving the differential equation for "dt". First, the transient term qt (t t+) is expressed as the homogeneous equation (
4) This is the solution to the equation. Therefore, from equation (12), it becomes as follows.

q(t-t+) −Acos ωo(t-t+
)+Bs1n tl)Q (t-t+)
(34) On the other hand, the steady solution qs is as follows.

qs=cE (35) Therefore, the general solution q(t t+) is (34), (35)
From the formula, it becomes as follows.

q(t-t + )-Qs+qt(t-t, )-C
E + Acos ω□ t +Bs1n ωot
(3B) The following equation is obtained by using equation (3) in equation (36).

1(1-1+)-ωo tBcosωo (t-1+
)-Asjn (1,10(t-t+)l
(37) From the initial conditions at time t-tl, the following results.

CEcos (JJOt + -CE+A
(3g) −ωOCEs1nω□ t l −(J
JOB From equations (39), (38), and (39), the following is obtained.

A-CE(cos ωo t-1)
(40) B = -CEsln ωOt 1 (41
)(40), (41) into (3B), (37
), we get the following:

q(t-t,) -CE+CE(cos (IJOt+-1)co
s ωo(t-tl)-CEsin ω□ t 1
sinω0 (t-tl) (42)+(1
−1+ ) −−<IJOCEs1n ω(3(t−t+ )−(I
JOCE(cosω□ t + -1) sinω0
(t-t+) (43) The following equation is obtained from equations (42) and (20).

v(t-t+)=E+E(cosωOt 1-1)cosωo(t
-t+ )-Esinωot+sjnωo (t-11
) (44) Therefore, the potential difference v (t) across the piezoelectric element P and the current i (t) of the coil 53 are as shown in FIG. 4(C). Here, at time t-t2 when v(t-t,) becomes minimum, the following equation holds true.

The left side of equation (45) can be transformed as follows.

1 (t-t 1) −-ω□ CEs1n (IJOt + cosω0
(t2-t+)+ω□ CE(1-cosωot
+) sinωo(t2t+)=-(IJOCE['
sin (IJOlt+ +(t 2-t+month+'
sin ω□ fh −t+ )l]+(AJOCEs
jn ω0 (t2−t+)−1ω. CE[1si
n O0f(t 2 −t+ )+t +
]cosωO(+2-1t+1+1sin O01(t2-tl)+t+1mω
OCEs1n ωo (+2-t+)-(IJOCE
s1n ωo t 2・sin 1 (JJOt
1=0 Therefore, one of the following two equations will hold true.

= 2 ω□ CEcos[1ωo I(t 2-t+
)+121]cosωo(+2-1t+)-0(5
1) sin [斐ω. f(t2-t+)-t2+
1-2ωOCEcosω. 1t2-1t + 1si
n 1 (1, 10t, -0 Now, what we are discussing here is the transistor T, 1' Sin ωot+ 2 (4
B) Now, the following formula holds true.

ω0≠○ (47)C≠
0(48) E≠0 (49) Therefore, from equations (45) and (4B), it becomes as follows.

When r3 is open for a shorter time than yrFτ (because it is a trick, the following equation holds true).

Therefore, equation (52) does not hold true, and equation (51) holds true. Therefore, it becomes as follows.

ωo (+2-' t+l-π (54
)+ 'Ecos[ +2= lt+”l
(55) 2 O0 Next, as shown in FIG. 4(d), at time t-t2, tl at which the value of the potential difference v(t t, ) across the piezoelectric element P becomes zero is determined.

The value of v(t t+) in 1-12 is as follows.

v(t-t 1) t-t 2 =E+E(cos ωOt + -1)CO8(JJO
(+2-tl) Esjn ωOt 2 ・5in(
t 2-t+ )E +Ecosωot+ ・cosωo (+2-t+
) −Ecosωo (h −t+ ) −Esin ω(, t 2 fist sin ωo(+2−t+
)E −Ecos ωo (+2−t+ )”−IEcos
[ωo It+ −(t+ ′ Ecos[ E +Ecos ωat E −22sin ′ω(.

2-Ecos 2+(t sin 1(, Joit 2- t -E-2E-sin (AJOl+2'(+2-t+ -tl + ' Ecos[O0(t+ -(t 2-h ) 1
1・ 1' Sin O0 = E-2E-sin ωo (' t 1 + 11t1
) ωo2 ΦSin ω01l -E-2E-sin 7r-sin ωOt H=E-
2Esin ω□ t +
(5G) Since equation (56) is zero, it becomes as follows.

E-2Esin ωOt + -0 (57) From equation (49), equation (57) becomes as follows.

sinωot + -' (58
) (53) gives the following.

Therefore, if the transistor Tr2 is opened after time t-1fET, the potential difference v (t) across the piezoelectric element will reach zero, as shown in FIG. 4(e).

By the way, consider the value of t2 when the transistor Tr2 is opened at time t-"f"te.

Substituting equation (59) into equation (55) yields the following.

By the way, if the transistor Tr2 is closed for 1JLC as shown in Fig. 4(a), the current i (t) in the coil 5π3 will continue to increase until the current i (t) becomes zero (C2+l) JT
: It takes time, but if the transistor Tr2 is closed only for if 100 as shown in FIG. 4(d), the coil 53
It takes only 4τ〒 for the current i (t) to become zero. Until the current i (t) of this coil 53 becomes zero,
Since the next drive cannot be performed, a drive time shorter than the IP fU is useful for speeding up the drive of the piezoelectric element P.

As explained above, in the present invention, it is always necessary to close the transistor Tr2 for the times i and b[i].

Note that the present invention is not limited to the above configuration, and various modifications are possible. For example, in this embodiment, a bipolar transistor is used as a switching element, but a field effect transistor can also be used to further reduce power consumption.

[Effects of the Invention] As described in detail above, the present invention does not require a device for detecting current, so the circuit configuration can be significantly simplified. Furthermore, by using the timer used in the present invention, which is built into a control device normally used in printing devices, etc., it is possible to configure a device using the present invention without preparing new parts. I can do it. In this manner, the device of the present invention can reduce the number of parts and significantly reduce manufacturing costs.

[Brief explanation of drawings]

The drawings show one embodiment of the present invention. Fig. 1 is a circuit diagram showing the electrical configuration of the device of the above embodiment, and Fig. 2 is a circuit diagram showing the electrical configuration of the device of the above embodiment. A front view showing the configuration of the printing element of the impact type dot printer.
FIG. 3 is a flowchart showing an excerpt of the control of the control circuit, and FIG. 4 is a diagram showing changes in current and voltage. FIG. 5 is a circuit diagram showing the electrical configuration of a conventional device. In the figure, Tr2 is a transistor constituting a switch means;
53 is a coil, 55a is a timer, and 55 is a control circuit constituting a control means.

Claims (1)

[Claims] 1. A coil whose one terminal A is electrically connected to the terminal B of the piezoelectric element and whose other terminal C is electrically connected to a power supply; a switch means that can be electrically connected to the other terminal D of the piezoelectric element to configure a resonant circuit with the piezoelectric element and the coil; a timer that can measure a predetermined time; and a timer that can cancel the displacement of the piezoelectric element. A driving device for a piezoelectric element, comprising: control means that turns on the switch means when instructed to do so, and then cuts off the switch means when a timer indicates that a predetermined time has elapsed.