JPH05124227A - Piezoelectric element driver - Google Patents

Abstract

PURPOSE:To take an appropriate action by detecting a failure in electrically discharging a piezoelectric element in a piezoelectric element driver which expands/contracts the piezoelectric element by electrically charging/discharging the piezoelectric element for using the piezoelectric element as an actuator. CONSTITUTION:A title driver is provided with a piezoelectric element drive circuit 1 which electrically charges a piezoelectric element 2 by a charging drive pulse and discharges said element by a discharging drive pulse and an overvoltage detection circuit 3 which compares the voltage of the piezoelectric element 2 with a reference voltage and generates an alarm signal by said voltage not less than the reference voltage.

Description

Detailed Description of the Invention

(Table of Contents) Industrial Application Conventional Technology (FIG. 7) Problem to be Solved by the Invention Means for Solving the Problem (FIG. 1) Action Example (a) Description of the First Example ( 2 to 3) (b) Description of the second embodiment (FIG. 4) (c) Description of the third embodiment (FIG. 5) (d) Description of the fourth embodiment (FIG. 6) (e) ) Description of other embodiments Effect of the invention

[0002]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric element driving device for charging / discharging a piezoelectric element to expand / contract the piezoelectric element and use it as an actuator. Recently, in wire dot printers, wire dot line printers, etc.,
Piezoelectric elements are beginning to be used in print wire actuators.

In order to use this piezoelectric element in an actuator, it is necessary to charge the piezoelectric element, extend the piezoelectric element, and then discharge the piezoelectric element to shrink and restore the piezoelectric element. A drive circuit for charging and discharging is required. There is a demand for a technique for preventing smoking and ignition of the piezoelectric element due to the occurrence of an overvoltage state due to the charging / discharging of the piezoelectric element.

[0004]

2. Description of the Related Art FIG. 7 is an explanatory diagram of a conventional technique. The piezoelectric element drive circuit includes a transformer method, an inductance method, a totem pole method, and the like. Here, the transformer method will be described as an example.

As shown in FIG. 7A, in the transformer type drive circuit 1, the primary side of the transformer T has a power source E, a primary side winding (coil) L1, a switch Q1 and a regenerative diode D.
1 is connected in series, and the secondary side is the secondary side winding (coil)
A switch Q2 connected in parallel with L2 and the piezoelectric element 2 and a diode D2 are connected in series.

The operation of this circuit will be described with reference to FIG. 7B. A switch Q1 is turned on by a charging drive pulse P1 from a control unit (not shown), and a current I1 flows through the primary winding L1.
Flow through the secondary winding L1 to store a predetermined amount of energy in the primary winding L1, and at the moment when the switch Q1 is turned off, the energy is transferred to the secondary winding L1.
2, the current flows clockwise in the secondary winding L2, and the piezoelectric element 2 is charged as indicated by the piezoelectric element voltage Vp.

Next, when the switch Q2 is turned on by the discharge driving pulse P2 from the control section, the counter electromotive force of the secondary winding L2 causes a current to flow counterclockwise and the piezoelectric element 2 is discharged.

As described above, in the wire dot printer, when the piezoelectric element 2 is charged, the piezoelectric element 2 expands and hits the print wire against the ink ribbon, and when the piezoelectric element 2 discharges, the piezoelectric element 2 contracts and the print wire is discharged. After that, this cycle is repeated to perform the printing operation and the like.

[0009]

However, the prior art has the following problems. When the piezoelectric element 2 is not discharged due to an abnormality of the piezoelectric element drive circuit 1, for example, a failure of the switch Q2, or the discharge drive pulse P2 is not output due to a failure of the software of the control unit, the piezoelectric element 2 expands. For example, in a wire dot printer, the ink ribbon and the paper are damaged by the print wire.

When the battery is further charged without being discharged, the voltage Vp of the piezoelectric element 2 is added to the previous voltage as shown by the dotted line in FIG. 7 (B), an overvoltage is applied, and the piezoelectric element 2 emits smoke. In addition to destroying the piezoelectric element 2 by firing or igniting, there is a danger of fire of the device. Therefore, an object of the present invention is to provide a piezoelectric element drive device that can detect a state in which a piezoelectric element is not discharged and can take appropriate measures.

It is another object of the present invention to provide a piezoelectric element driving device capable of discharging the piezoelectric element even if the piezoelectric element is not discharged. Further, it is an object of the present invention to provide a piezoelectric element driving device that can continue to operate with another piezoelectric element even if the piezoelectric element is not discharged.

[0012]

FIG. 1 shows the principle of the present invention. According to claim 1 of the present invention, the piezoelectric element drive circuit 1 that charges the piezoelectric element 2 with a charge drive pulse and discharges it with a discharge drive pulse is compared with the piezoelectric of the piezoelectric element 2 and a reference piezoelectric. And an overvoltage detection circuit 3 which generates an alarm signal when the voltage is equal to or higher than the reference voltage.

According to claim 2 of the present invention, in claim 1,
A plurality of the piezoelectric elements 2 and the piezoelectric element drive circuit 1 are provided, and the plurality of piezoelectric elements 2 are respectively connected to the diodes d1 to dn.
It is characterized in that it is connected to the overvoltage detection circuit 3 through a common connection.

According to a third aspect of the present invention, in the first or second aspect, the overvoltage detection circuit 3 divides the piezoelectric of the piezoelectric element 2 by voltage dividing resistors R1 and R2, and the voltage dividing resistors R1 and R.
It is characterized by including a comparison circuit CMP for comparing the divided voltage by 2 and the reference voltage, and a capacitor C provided in parallel with either of the voltage dividing resistors R1 and R2.

According to a fourth aspect of the present invention, in the first, second or third aspect, a discharge circuit 5 for discharging the piezoelectric element 2 is provided, and the discharge circuit 5 is operated by an alarm signal of the overvoltage detection circuit 3. Is characterized by.

According to a fifth aspect of the present invention, in the first, second, third or fourth aspect, the piezoelectric element drive circuit 1 is provided with a control section 4 for outputting the charge drive pulse and the discharge drive pulse. An alarm signal of the overvoltage detection circuit 3 is input to the control unit 4 to stop the output of both drive pulses.

According to a sixth aspect of the present invention, in the second, third or fourth aspect, the piezoelectric element drive circuit 1 is provided with a control section 4 for outputting the charge drive pulse and the discharge drive pulse, and the overvoltage detection. An alarm signal of the circuit 3 is input to the control unit 4 to stop the output of both drive pulses of the overvoltage piezoelectric element 2 to the piezoelectric element drive circuit 1.

According to claim 7 of the present invention, in claim 6,
The diodes d1 to dn of the plurality of piezoelectric elements 2 are connected to the overvoltage detection circuit 3 via a selection circuit 7, and the control unit 4 causes the selection circuit 7 to sequentially connect the piezoelectric elements 2 to the overvoltage detection circuit 3. And detecting the overvoltage piezoelectric element 2.

According to claim 8 of the present invention, in claim 6,
The control unit 4 detects the overvoltage piezoelectric element 2 by driving each of the piezoelectric element driving circuits 1 with the charging driving pulse and the discharging driving pulse at the time of initializing before the operation of the apparatus. To do.

A ninth aspect of the present invention is based on the sixth, seventh or eighth aspect, wherein each of the piezoelectric element drive circuits 1 of the control section 4 is provided.
Gate circuits 8a to 8n and 9a to 9n for prohibiting the charging drive pulse and the discharge drive pulse output to the piezoelectric element drive circuit 1 from being input to the control unit 4
Are the gate circuits 8a to 8n and 9a to 9n corresponding to the piezoelectric element drive circuit 1 of the detected piezoelectric element 2 of the overvoltage.
The output of the charging drive pulse and the discharging drive pulse is prohibited.

According to a tenth aspect of the present invention, in the sixth, seventh, eighth or ninth aspect, the piezoelectric element 2 is an actuator for driving a print wire 16 in a wire dot print head, and the control section 4 is a printing unit. The charge drive pulse and the discharge drive pulse are output to the piezoelectric element drive circuit 1 according to the dot information.

[0022]

According to the first aspect of the present invention, since the voltage of the piezoelectric element 2 is compared with the reference voltage, and the overvoltage detection circuit 3 which generates an alarm signal when the voltage is equal to or higher than the reference voltage is provided, It is possible to detect an overvoltage state due to discharge abnormality of the element 2 at an early stage, take appropriate measures such as stopping the device, and prevent a situation such as smoking without continuing the abnormal state.

According to claim 2 of the present invention, a plurality of piezoelectric elements 2 are provided.
Are commonly connected to each other through the diodes d1 to da and are connected to the overvoltage detection circuit 3, so that the overvoltage state due to the discharge abnormality of the plurality of piezoelectric elements 2 can be detected early by one overvoltage detection circuit 3.

According to claim 3 of the present invention, the overvoltage detection circuit 3 is provided.
Are voltage dividing resistors R1 and R2 for dividing the voltage of the piezoelectric element 2.
And a comparison circuit CMP for comparing the divided voltage by the voltage dividing resistors R1 and R2 with the reference voltage, it is possible to detect a high voltage (about 130 V) of the piezoelectric element 2 as an overvoltage.
The overvoltage detection circuit can be constructed at low cost, and since the capacitor C is provided in parallel with either of the voltage dividing resistors R1 and R2, noise components can be absorbed and overvoltage detection can be performed accurately.

According to the fourth aspect of the present invention, since the discharge circuit 5 for discharging the piezoelectric element 2 is provided and the discharge circuit 5 is operated by the alarm signal of the overvoltage detection circuit 3, the overvoltage state of the piezoelectric element 2 can be eliminated. it can.

According to a fifth aspect of the present invention, the piezoelectric element drive circuit 1 is provided with a control section 4 for outputting a charge drive pulse and a discharge drive pulse, and an alarm signal of the overvoltage detection circuit 3 is input to the control section 4. Since the output of both drive pulses is stopped, the overvoltage state of the piezoelectric element 2 is not further deteriorated, and the smoking of the piezoelectric element 2 or the like can be prevented.

In the sixth aspect of the present invention, the overvoltage detection circuit 3
The alarm signal is input to the control unit 4 and the output of both drive pulses to the piezoelectric element drive circuit 1 of the overvoltage piezoelectric element 2 is stopped, so that the operation of other piezoelectric elements 2 can be continued. For example, in the wire dot printer, You can continue printing with one print wire except one.

According to the seventh aspect of the present invention, the control unit 4 sequentially connects the piezoelectric elements 2 to the overvoltage detection circuit 3 by the selection circuit 7 to detect the overvoltage piezoelectric element 2. Therefore, one overvoltage detection is performed. The circuit 3 can detect the overvoltage piezoelectric element 2 among the plurality of piezoelectric elements 2.

In the eighth aspect of the present invention, the control unit 4 drives each piezoelectric element drive circuit 1 by the charge drive pulse and the discharge drive pulse at the time of initializing before the operation of the device, and drives the piezoelectric element 2 having an overvoltage. Since the detection is performed, one overvoltage detection circuit 3 can detect the overvoltage piezoelectric element 2 among the plurality of piezoelectric elements 2.

According to a ninth aspect of the present invention, gate circuits 8a to 8n and 9a to 9n are provided for inhibiting input of the charge driving pulse and the discharge driving pulse to each piezoelectric element driving circuit 1,
The control unit 4 controls the gate circuits 8a to 8n and 9a to 9n corresponding to the piezoelectric element driving circuit 1 of the piezoelectric element 2 having the detected overvoltage.
Since the output of the charging drive pulse and the discharge drive pulse is prohibited, the output of the charge drive pulse and the discharge drive pulse to the piezoelectric element drive circuit 1 of the overvoltage piezoelectric element 2 is prohibited without changing the drive sequence of the control unit 4. it can.

In claim 10 of the present invention, the piezoelectric element 2 is
It is an actuator that drives the print wire 16 in the wire dot print head, and the control unit 4 outputs the charge drive pulse and the discharge drive pulse to the piezoelectric element drive circuit 1 according to the print dot information. Even if the operation of pin 1 of the wire is prohibited, the printing operation can be continued without significantly affecting the printing.

[0032]

【Example】

(a) Description of First Embodiment FIG. 2 is an explanatory diagram of a printing element to which an embodiment of the present invention is applied.

In FIG. 2, a print element 10 of a wire dot print head holds a beam 15 supporting a print wire 16 and an armature 13 on a base 12 by an expanding spring 14, and an actuator (piezoelectric element) is attached to the base 12 and the armature 13. Element 2 is provided, and the actuator 2 rotates the armature 13 about the expansion spring 14 as a fulcrum to reciprocate the print wire 16 to perform dot printing.

In this actuator 2, the piezoelectric element 2 is provided between the pair of block members 17 and 18, and the compression spring member 19 is provided to the pair of block members 17 and 18.
The piezoelectric element 2 is compressed in advance, the piezoelectric element 2 is charged, the compressed piezoelectric element 2 is stretched against the compression spring member 19, the print wire 16 is struck on the paper, the piezoelectric element 2 is discharged, and the piezoelectric element 2 is discharged. Is compressed and compressed by the compression spring member 19, and the printing wire 16 is returned.

With a 24-pin wire dot print head,
Twenty-four printing elements 10 are provided. FIG. 3 is an explanatory view of the first embodiment of the present invention, and shows a transformer type drive circuit. In FIG. 3, the same components as those shown in FIGS. 1 and 7 are designated by the same symbols.

Reference numeral 3 denotes an overvoltage detection circuit, which divides the voltage Vp of the piezoelectric element 2 by voltage dividing resistors R1 and R2 and a voltage dividing resistor R.
2, a capacitor C connected in parallel, and voltage dividing resistors R1 and R
The divided voltage by 2 is compared with the reference voltage Vref, and when the divided voltage exceeds the reference voltage Vref, the alarm signal AL
Is provided to the control unit 4 (not shown).

In this embodiment, as shown in FIG. 3 (B), when the piezoelectric element 2 is not discharged after being charged and is charged again, the divided voltage of the voltage Vp of the piezoelectric element 2 becomes the reference voltage. V
When it exceeds ref, the comparison circuit CMP outputs an alarm signal A
L is output to the control unit 4.

As a result, the overvoltage state due to the discharge abnormality of the piezoelectric element 2 can be detected at an early stage, and appropriate measures such as driving stoppage can be taken. In this example, voltage dividing resistors R1 and R2
The voltage (about 130 V) of the piezoelectric element 2 is divided by the voltage and compared with the reference voltage Vref.
It suffices that f is small, and the withstand voltage of the comparison circuit CMP is also small.

A capacitor C is connected in parallel with the voltage dividing resistor R2.
Since it is provided, the noise component due to the operation of the piezoelectric element 2 can be absorbed, and the malfunction of the overvoltage detection by the voltage comparison can be prevented.

(B) Description of Second Embodiment FIG. 4 is a configuration diagram of a second embodiment of the present invention, which is applied to a plurality of piezoelectric elements 2.

In FIG. 4, the same components as those shown in FIG. 3 are designated by the same symbols, 1a to 1n are piezoelectric element driving circuits, and the charging driving pulse P1 from the control unit 4 is used.
1 to P1n charge the piezoelectric elements 2a to 2n, and discharge driving pulses P21 to P2n charge the piezoelectric elements 2a to 2n.
Is to be discharged.

Reference numerals d1 to dn denote diodes, respectively, which connect the piezoelectric elements 2a to 2n in common and connect them to the overvoltage detection circuit 3. In this example, one for each of the plurality of piezoelectric element drive circuits 1a to 1n and each of the plurality of piezoelectric elements 2a to 2n.
The overvoltage detection circuit 3 detects overvoltage.

Since the backflow is prevented by the diodes d1 to dn, the overvoltage can be detected by the voltage of the one piezoelectric element 2a to 2n without unnecessarily charging the other piezoelectric element. .. Furthermore, the noise absorbing capacitor C can absorb noise even if it is provided in parallel with the voltage dividing resistor R1.

Explaining an example in which the piezoelectric elements 2a to 2n are used in the actuator of the above-mentioned wire dot print head, the control section 4 makes the piezoelectric element drive circuits 1a to 1n simultaneously at the initial stage before the operation of the apparatus. Alternatively, the charge driving pulses Pll to Pln and the discharge driving pulse P21 to
P2n is output to charge and discharge the piezoelectric elements 2a to 2n, and then to the piezoelectric element drive circuits 1a to 1n, respectively.
Charge drive pulses Pll to P1n and discharge drive pulse P21
To P2n are output to monitor the alarm signal AL of the overvoltage detection circuit 3.

At this time, in the piezoelectric element which has not been discharged the first time, the voltage Vp of the piezoelectric element exceeds the reference voltage Vref as shown in FIG. The signal AL rises, whereby the control unit 4 can identify the piezoelectric element having the abnormal discharge and prohibit the operation of the device.

If the alarm signal does not rise, the operation of the apparatus is started, and the control unit 4 causes the corresponding piezoelectric element drive circuits 1a to 1n to charge drive pulses P11 to P according to the print information.
1n and discharge drive pulses P21 to P2n are used to perform dot printing using wire dots.

Even after the printing operation is started, the control unit 4 monitors the alarm signal AL of the overvoltage detection circuit 3, and when the alarm signal AL is generated, the operation of the apparatus is stopped and the operator is notified.

In this way, the plurality of piezoelectric elements 2a-2
For n, one overvoltage detection circuit 3 can detect the overvoltage state of each piezoelectric element 2a to 2n, and the control unit 4 controls the alarm signal AL of one overvoltage detection circuit 3 to detect the piezoelectric element in the overvoltage state. It can be specified and preventive measures can be taken.

(C) Description of Third Embodiment FIG. 5 is a block diagram of the third embodiment of the present invention. In FIG. 5, the same components as those shown in FIGS. 1, 2 and 4 are represented by the same symbols, 5 is a forced discharge circuit, and between the diode d and the overvoltage detection circuit 3, Current limiting resistor R3
And a switch (transistor) Q3 whose emitter is grounded
6 is a latch circuit for latching the alarm signal AL of the overvoltage detection circuit 3,
The base of the switch Q3 is controlled to turn on the switch Q3.

In this embodiment, if the piezoelectric element 2 is left in an overvoltage state, the piezoelectric element 2 may be destroyed, so that the piezoelectric element 2 is forcibly discharged. When the piezoelectric element 2 is in the overvoltage state and the alarm signal AL is generated from the overvoltage detection circuit 3, it is latched by the latch circuit 6, the switch Q3 of the forced discharge circuit 5 is turned on, and the piezoelectric element 2 is connected to the diode d-
The resistor R3-switch Q3-is forcibly discharged along the route of ground.

In this embodiment, the latch circuit 6 and the switch Q3 can be replaced with a thyristor. or,
When this embodiment is applied to the embodiment of FIG. 4 and the control unit 4 controls the switch Q3 of the forced discharge circuit 5 instead of the latch circuit 6, even if the piezoelectric element 2 with abnormal discharge is detected, the device operation Can continue.

That is, the control section 4 outputs the charge driving pulses P11 to P1n and the discharge driving pulses P21 to P2n to the respective piezoelectric element driving circuits 1a to 1n simultaneously or sequentially at the time of initializing before the operation of the apparatus. , The piezoelectric elements 2a to 2n are charged and discharged, and then the piezoelectric element drive circuits 1a to 1
The charging drive pulses P11 to P1n and the discharging drive pulses P21 to P2n are sequentially output to n, and the alarm signal AL of the overvoltage detection circuit 3 is monitored.

At this time, in the piezoelectric element which has not been discharged the first time, the voltage Vp of the piezoelectric element exceeds the reference voltage Vref as shown in FIG. The signal AL rises, whereby the control unit 4 can identify the piezoelectric element having the abnormal discharge, and the forced discharge circuit 5 discharges the piezoelectric element having the abnormal discharge and prohibits the driving of the piezoelectric element drive circuit. ..

Then, the operation of the apparatus is started, and the control unit 4
Corresponds to the piezoelectric element drive circuit 1a to
1n is driven by the charge driving pulses P11 to P1n and the discharge driving pulses P21 to P2n to perform dot printing by wire dots.

At this time, if there is only one piezoelectric element with abnormal discharge, of the wire dots of 24 pins, 1 pin cannot be printed, but even if about 1 dot is missing, the printing result is not so noticeable It doesn't matter if you start.

Even after the printing operation is started, the control section 4 monitors the alarm signal AL of the overvoltage detection circuit 3 and when the alarm signal AL is generated, all the forced discharge circuits 5 are operated to operate each piezoelectric element. After discharging, the operation of the device is stopped and the operator is notified.

In this way, the plurality of piezoelectric elements 2a-2
For n, one overvoltage detection circuit 3 can detect the overvoltage state of each piezoelectric element 2a to 2n, and the control unit 4 controls the alarm signal AL of one overvoltage detection circuit 3 to detect the piezoelectric element in the overvoltage state. It is possible to identify and take preventive measures against destruction due to forced discharge.

(D) Description of the Fourth Embodiment FIG. 6 is a block diagram of the fourth embodiment of the present invention. In FIG. 6, the same components as those shown in FIG. 4 are designated by the same symbols, 7 is a selection circuit, and the voltages of the respective piezoelectric elements 2a to 2n are input in parallel via the diodes d1 to dn. , The overvoltage detection circuit 3 depending on the selection signal SL of the control unit 4.
, 8a to 8n are gate circuits, and control of input of charging drive pulses P11 to P1n from the control unit 4 to the piezoelectric element drive circuits 1a to 1n by the gate signals G1 to Gn of the control unit 4, respectively. 9a to 9n are gate circuits, which control the input of discharge drive pulses P21 to P2n from the control unit 4 to the piezoelectric element drive circuits 1a to 1n by the gate signals G1 to Gn of the control unit 4, respectively. Is.

In this embodiment, the control unit 4 controls each of the piezoelectric element drive circuits 1a to 1n at the time of initializing before the operation of the apparatus.
, Simultaneously or sequentially, the charging drive pulses P11 to P1n
And discharge driving pulses P21 to P2n are output to charge and discharge the piezoelectric elements 2a to 2n. Then, the piezoelectric element driving circuits 1a to 1n are sequentially charged to the charging driving pulses P11 to P1.
n and discharge drive pulses P21 to P2n are output, the selection circuit 7 sequentially selects the piezoelectric elements 2a to 2n, and the alarm signal AL of the overvoltage detection circuit 3 is monitored.

At this time, in the piezoelectric element which has not been discharged for the first time, the voltage Vp of the piezoelectric element exceeds the reference voltage Vref as shown in FIG. The signal AL rises, whereby the control unit 4 can identify the piezoelectric element having the abnormal discharge, set the gate signals G1 to Gn to the low level, and the gate circuits 8a to 8n.
n, 9a to 9n, and charging drive pulses P11 to P1
The input of n and the discharge drive pulses P21 to P2n to the piezoelectric element drive circuit is prohibited, and the driving of the piezoelectric element drive circuit is prohibited.

Then, the operation of the apparatus is started, and the control unit 4
Corresponds to the piezoelectric element drive circuit 1a to
1n is driven by the charge driving pulses P11 to P1n and the discharge driving pulses P21 to P1n to perform dot printing by wire dots.

At this time, if there is only one piezoelectric element with abnormal discharge, one of the 24 dot wire dots cannot be printed, but even if about 1 dot is missing, the printed result is not so conspicuous. It doesn't matter if you start.

Even after the printing operation is started, the control section 4 sequentially selects the piezoelectric elements 2a to 2n by the selection circuit 7 to monitor the alarm signal AL of the overvoltage detection circuit 3 and when the alarm signal AL is generated, The piezoelectric element in which the discharge is abnormal is specified from the selection signal at the special point where the alarm signal is generated, the gate signals G1 to Gn are set to the low level, and the gate circuit 8a thereof is set.
8n and 9a to 9n are closed, and charging drive pulse P11 to
The input of P1n and the discharge driving pulses P21 to P2n to the piezoelectric element driving circuit is prohibited, the driving of the piezoelectric element driving circuit is prohibited, and then the operation is continued.

In this way, the plurality of piezoelectric elements 2a-2
For n, one overvoltage detection circuit 3 can detect the overvoltage state of each piezoelectric element 2a to 2n, and the control unit 4 controls the alarm signal AL of one overvoltage detection circuit 3 to detect the piezoelectric element in the overvoltage state. The operation of the specified piezoelectric element drive circuit is prohibited by gate control, and the printing operation is continued.

In this example, the drive of the piezoelectric element in the overvoltage state can be prohibited by gate control without changing the drive program of the control section 4. Also in this example, the forced discharge circuit 5 of FIG. 5 can be added to each of the piezoelectric elements 2a to 2n.

(E) Description of Other Embodiments In addition to the above embodiments, the present invention can be modified as follows. In the third embodiment, the forced discharge circuit 5 of all the piezoelectric elements 2a to 2n may be operated by the generation of the alarm signal AL.

In the fourth embodiment, the apparatus may be stopped when the number of piezoelectric elements having abnormal discharge reaches, for example, two or more. Although the example of the serial dot printer has been described, the present invention may be applied to a line dot printer and is not limited to a printer, and may be applied to other devices.

Although the piezoelectric element drive circuit has been described as the transformer type, other types of drive circuits such as an inductance type and a totem pole type can be used. Although the present invention has been described with reference to the embodiments, various modifications are possible within the scope of the gist of the present invention, and these modifications are not excluded from the scope of the present invention.

[0069]

As described above, according to the present invention,
It has the following effects. It is possible to detect an overvoltage state due to abnormal discharge of the piezoelectric element and prevent the piezoelectric element from being broken. Since the overvoltage state due to the abnormal discharge of the piezoelectric element can be detected at an early stage, it is possible to prevent the piezoelectric element from smoking and igniting, and also prevent the danger of igniting the device or the like.

[Brief description of drawings]

FIG. 1 is a principle diagram of the present invention.

FIG. 2 is a configuration diagram of a print element applied to an embodiment of the present invention.

FIG. 3 is an explanatory diagram of the first embodiment of the present invention.

FIG. 4 is a configuration diagram of a second embodiment of the present invention.

FIG. 5 is a configuration diagram of a third embodiment of the present invention.

FIG. 6 is a configuration diagram of a fourth embodiment of the present invention.

FIG. 7 is an explanatory diagram of a conventional technique.

[Explanation of symbols]

 1, 1a to 1n Piezoelectric element drive circuit 2, 2a to 2n Piezoelectric element 3 Overvoltage detection circuit 4 Control unit

Claims (10)

[Claims] 1. A piezoelectric element drive circuit (1) that charges a piezoelectric element (2) with a charge drive pulse and discharges it with a discharge drive pulse, and compares the voltage of the piezoelectric element (2) with a reference voltage. A piezoelectric element drive device, comprising: an overvoltage detection circuit (3) that generates an alarm signal when the voltage is equal to or higher than the reference voltage. 2. The overvoltage is provided by providing a plurality of the piezoelectric elements (2) and a plurality of the piezoelectric element drive circuits (1) and commonly connecting the plurality of piezoelectric elements (2) through diodes (d1 to dn). The piezoelectric element drive device according to claim 1, wherein the piezoelectric element drive device is connected to a detection circuit (3). 3. The voltage dividing resistors (R1, R2) for dividing the voltage of the piezoelectric element (2) in the overvoltage detection circuit (3).
And a comparison circuit (CMP) for comparing the divided voltage by the voltage dividing resistors (R1, R2) with the reference voltage, and a capacitor (C) provided in parallel with either of the voltage dividing resistors (R1, R2). ) And The piezoelectric element drive device of Claim 1 or 2 characterized by the above-mentioned. 4. A discharge circuit (5) for discharging the piezoelectric element (2) is provided, and the discharge circuit (5) is operated by an alarm signal of the overvoltage detection circuit (3). Alternatively, 2 or 3 of the piezoelectric element driving device. 5. The piezoelectric element drive circuit (1) is provided with a control section (4) for outputting the charge drive pulse and the discharge drive pulse, and an alarm signal of the overvoltage detection circuit (3) is sent to the control section. 5. The piezoelectric element driving device according to claim 1, wherein the output of both drive pulses is stopped by inputting to (4). 6. The piezoelectric element drive circuit (1) is provided with a control section (4) for outputting the charge drive pulse and the discharge drive pulse, and an alarm signal of the overvoltage detection circuit (3) is sent to the control section. 5. The piezoelectric element drive according to claim 2, 3 or 4, characterized in that the output of both drive pulses to the piezoelectric element drive circuit (1) of the piezoelectric element (2) having an overvoltage is stopped by inputting to (4). apparatus. 7. The diodes (d1 to dn) of the plurality of piezoelectric elements (2) are connected to the overvoltage detection circuit (3) via a selection circuit (7), and the control unit (4) performs the selection. 7. The piezoelectric element driving device according to claim 6, wherein the circuit (7) sequentially connects each piezoelectric element (2) to the overvoltage detection circuit (3) to detect the piezoelectric element (2) having the overvoltage. .. 8. The control section (4) drives each of the piezoelectric element drive circuits (1) by the charge drive pulse and the discharge drive pulse at the time of initializing before the operation of the device, and thereby the piezoelectric element of the overvoltage. 7. The piezoelectric element driving device according to claim 6, wherein the element (2) is detected. 9. In order to prohibit the charge drive pulse and the discharge drive pulse output to each piezoelectric element drive circuit (1) of the control section (4) from being input to each piezoelectric element drive circuit (1). Gate circuits (8a to 8n, 9a to 9n) are provided, and the control section (4) corresponds to the piezoelectric element drive circuit (1) of the detected piezoelectric element (2) of the overvoltage. 9. The piezoelectric element drive device according to claim 6, wherein output of the charging drive pulse and the discharging drive pulse of 8n, 9a to 9n) is prohibited. 10. The piezoelectric element (2) is an actuator for driving a print wire (16) in a wire dot print head, and the control unit (4) responds to print dot information by the piezoelectric element drive circuit. 10. The piezoelectric element drive device according to claim 6, wherein the charge drive pulse and the discharge drive pulse are output to (1).