JP2638392B2 - Piezo element drive circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a driving circuit for a piezoelectric element used as a driving source for a printing wire or the like of a wire dot printer, and more particularly to a technique for controlling the stop of driving of a piezoelectric element.

[0002]

2. Description of the Related Art Conventionally, there has been known a printer which performs printing by utilizing expansion and contraction movement by application of a voltage of a piezoelectric element. The charge / discharge circuits of the piezoelectric element in this type of printer are provided with the number of pins required for the circuit shown in FIG. 1 described later as an embodiment of the present invention. Here, an outline of a conventional general piezoelectric element drive circuit will be described with reference to FIG. The piezoelectric element drive circuit includes a charge / discharge circuit for the piezoelectric element P, a drive control unit 1 for controlling the drive of the charge / discharge circuit, and a control device (CPU) 2.
Having. The transistor Tr1, the coil L, and the piezoelectric element P are connected in series between the power supply Vp and GND to form a charging circuit for charging the piezoelectric element P with electric charge.
The transistor Tr2 is connected in parallel with the circuit of the coil L and a circuit of the coil L to form a discharge circuit for discharging the electric charge from the piezoelectric element P. The inverted CHG signal S1 controls a charging circuit for charging the piezoelectric element P with electric charge, and the inverted DCHG signal S2
Controls a discharge circuit for discharging electric charge from the piezoelectric element P, and expands and contracts the piezoelectric element P by these controls to perform a printing operation.

FIG. 4 is a block diagram of the drive control section 1 of the above-described piezoelectric element drive circuit. Upon receiving the print data from the CPU 2, the drive control unit 1 converts the print data into drive data in the print data control unit 3, and converts the drive data into a charge pulse generator 4 for generating a pulse of the inverted CHG signal S1 and a DCHG signal S2.
The pulse is transmitted to a discharge pulse generator 5 for generating a pulse signal, and the print timing control unit 6 checks the print timing, outputs each pulse, and outputs the inverted CHG signal S1 from the output control unit 7.
And the inverted DCHG signal S2. Reference numeral 8 denotes an oscillator made of a crystal oscillator or the like, and reference numeral 9 denotes a counter.

FIG. 5 is a time chart for driving the piezoelectric element during normal printing. Inverted CHG signal S1
Causes the piezoelectric element P to start charging, and a voltage Vc across the piezoelectric element P.
p reaches the power supply voltage Vp, and after a certain period of time in this state,
The inverted DCHG signal S2 is output. Thus, the piezoelectric element P is discharged and returns to the original state, and one printing operation is completed. The displacement of the piezoelectric element P during this period is as shown in the figure.

[0005]

By the way, the inverted CHG
When the signal S1 is in an active state (active when low), the state in which the inverted CHG signal S1 has transitioned from active to inactive, or the state in which the inverted DCHG signal S2 is inactive, that is, when the piezoelectric element P has a charge, the drive control is performed. A signal to stop printing immediately (drive stop signal), such as an inverted RESET signal S4 or CP
When the print stop command signal S3 is input from U2 (including the power-off), (1) the inverted CHG signal S1 and the inverted DCHG signal S2 are immediately set to the non-active state. Alternatively, (2) control such that the inverted CHG signal S1 is immediately set to the non-active state and the inverted CHHG signal S2 is set to the active state can be considered. FIG. 6 shows a time chart when the control of (1) is performed, and FIG. 7 shows a time chart when the control of (2) is performed.

However, it is not easy to immediately stop the carriage during the printing operation, and if this is to be carried out, it cannot be inexpensive. In the case of the control of the above (1), the electric charge in the piezoelectric element P is not discharged, and the print pin remains in the state of being exposed, and the ribbon may be hooked. It is difficult. In the case of the control of (2), the transistor Tr
If the discharge of the piezoelectric element P is started earlier than the stop of the charging due to the variation of the turn-on / off of the devices such as 1, Tr2 and Tr3, a through current flows for a moment and the transistors Tr1 and Tr2 are destroyed. There was a problem that it would.

The present invention solves the above-described problem. When a signal to stop printing is input to the drive control unit while the piezoelectric element has a charge, the ribbon is not caught and the penetrating is performed. It is an object of the present invention to provide a piezoelectric element drive circuit that can stop printing without breaking a device such as a transistor when a current flows.

[0008]

In order to achieve the above-mentioned object, a first aspect of the present invention is a charging circuit for charging an electric charge to a piezoelectric element, and a discharging circuit for discharging the electric charge charged to the piezoelectric element. And a driving circuit for the charging circuit and the discharging circuit.
In the piezoelectric element drive circuit and a drive control unit for outputting a signal for controlling the movement, when the drive stop signal is input to the drive control unit, the drive control unit, a signal to the charging circuit and the non-driven state And outputs a signal for driving the discharge circuit to a driving state after the output .

[0009]

According to the first aspect of the present invention, the charging circuit charges the piezoelectric element with electric charge, the discharging circuit discharges, and the drive control unit outputs a driving signal to the charging / discharging circuit. When a drive stop signal is input to the drive control unit , the drive control unit
, By outputting a signal to the <br/> conductive circuit discharge after outputting a signal to the charging circuit and the non-driven state to the drive state, discharges the piezoelectric element to its original state. That is, the piezoelectric element does not remain stretched and the elements of the drive circuit are not broken .

[0010]

An embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a circuit diagram showing a piezoelectric element driving circuit according to the present invention. The charge / discharge circuits of the piezoelectric element are mounted in the same number as the number of pins required for a dot matrix printer (not shown) that performs printing by using expansion and contraction movement by application of a voltage of the piezoelectric element. The piezoelectric element drive circuit includes a charge / discharge circuit for the piezoelectric element P, a drive control unit 1 for driving and controlling the charge / discharge circuit, and a control device (CP
U) 2. The inverted CHG signal S1 for charging controls a charging circuit for charging the piezoelectric element P with electric charge, and the inverted DCHG signal S2 for discharging controls a discharging circuit for discharging electric charge from the piezoelectric element P. The printing operation is performed by expanding and contracting the piezoelectric element P.

In the charging circuit, a power supply Vp, a transistor Tr1, which is a switching element, a coil L, and a piezoelectric element P are sequentially connected in series, and a negative electrode side of the power supply Vp and an electrode side to be a negative electrode of the piezoelectric element P are grounded. ing. The forward direction of the transistor Tr1 is a forward direction from the positive electrode side of the power supply Vp to the electrode side to be the positive electrode of the piezoelectric element P. Further, a connection point between the transistor Tr1 and the coil L is grounded via a transistor Tr2 which is a switch element, thereby forming a discharge circuit.

The forward direction of the transistor Tr2 is a direction from the connection point between the transistor Tr1 and the coil L to the ground point. Diodes D1 and D2 are connected in parallel to the transistors Tr1 and Tr2, respectively, and the forward direction of each diode D1 and D2 is opposite to the forward direction of each transistor. Further, the charging circuit includes a transistor Tr3 for turning on / off the transistor Tr1.
Is connected.

The positive electrode of the power supply Vp and the electrode of the piezoelectric element P, which is to be 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 diode D4 is connected in parallel with the piezoelectric element P, and the forward direction is a direction from the electrode side to be the negative electrode of the piezoelectric element P to the electrode side to be the positive electrode.

The operation of the piezoelectric element driving circuit having the above configuration will be described. When the drive control unit 1 outputs the inverted CHG signal S1, it turns on the transistor Tr3 and turns on the transistor Tr1. This allows the transistor T to be switched from the power supply Vp.
r1, a current flows into the piezoelectric element P via the coil L, and the coil L and the piezoelectric element P are charged while resonating, and the piezoelectric element P
Is displaced (extended).

The potential difference Vcp between both ends of the piezoelectric element P almost reaches the power supply voltage Vp. When the output time of the inverted CHG signal S1 has elapsed, the drive control unit 1 turns off the transistor Tr3 and turns off the transistor Tr1. If the potential difference of the piezoelectric element P reaches the power supply voltage Vp before the output time of the inverted CHG signal S1, the current continues to flow through the closed current loop via the diode D3 and the transistor Tr1 due to the action of the coil L. Is maintained. In this state, the electric energy of the coil L is regenerated to the power supply Vp by a closed circuit including the coil L, the diode D3, the power supply Vp, and the diode D2.

Thereafter, the drive control unit 1 outputs the inverted DCHG signal S2 to turn on the transistor Tr2. Thereby, the electric charge charged in the piezoelectric element P is discharged via the coil L and the transistor Tr2, and the displacement of the piezoelectric element P is returned to the initial position. After that, the transistor T
Turn off r2. By repeating the above charging and discharging, the piezoelectric element P can be driven.

FIG. 2 shows a block configuration of the drive control unit 1. Upon receiving the print data from the CPU 2, the drive control unit 1 converts the print data into drive data in the print data control unit 3, transmits the data to the charge pulse generator 4 and the discharge pulse generator 5, and controls the print timing in the print timing control unit 6. And outputs a pulse. The output controller 7 outputs the inverted CHG signal S1 and the inverted DCG signal.
The HG signal S2 is output. The inverted RESET signal S4 or the print stop command signal S3 from the CPU 2 is given to the print stop control unit 10. Reference numeral 8 denotes an oscillator made of a crystal oscillator or the like, and reference numeral 9 denotes a counter.

Next, the timing of driving the piezoelectric element in this embodiment will be described with reference to FIG. When the inverted CHG signal S1 is in the active state and the inverted CHG signal S1 has transitioned from active to non-active,
When the G signal S2 is in a non-active state, that is, when the piezoelectric element P has a charge, the drive control unit 1
When the ET signal S4 or the print stop command signal S3 from the CPU 2 is input, the print stop control unit 10 immediately sets the inverted CHG signal S1 to the non-active state, stops charging, and sets a fixed delay time (DELAY). And controls the output control unit 7 to make the inverted DCHG signal S2 active.

If the DELAY time is too long, the piezoelectric element P remains extended, that is, the time during which the print pin is extended becomes longer, and the ribbon may be hooked. ~ 15μs
And Normally, in the actual printing operation, the inverted DCHG signal S
2 is delayed from the active state, but the intention is different from the DELAY time of this embodiment. The DELAY time in this embodiment is provided when the inverted RESET signal S4 or the print stop command signal S3 is input. Thus, when the conventional inverted CHG signal S1 and the inverted DCHG signal S2 are set to the non-active state, or when the inverted CHG signal S1 is set to the non-active state and the inverted DCHG signal S2 is set to the active state at the same time. In this case, it is possible to prevent the print pins generated in the above state from being stuck and the ribbon being hooked, or to prevent the transistors Tr1 and Tr2 from being broken by the through current.

Next, a case where the power supply Vp is turned off while the piezoelectric element P is extended will be described. In this case, in the related art, since the transistors Tr1 and Tr2 are both turned off, the electric charge of the piezoelectric element P is not discharged. However, in the present embodiment, the electric charge stored in the capacitor C causes the transistor Tr2 to be very small. Since it is kept on for a time, the electric charge of the piezoelectric element P is discharged. The capacity of this capacitor C is
The amount is set to an amount that can keep the transistor Tr2 on for a time sufficient to discharge all the charges of the piezoelectric element P.

[0021]

As described above, according to the first aspect of the present invention,
When the drive stop signal is input to the drive control unit for driving the charging and discharging circuit for charging and discharging the electric charge to the piezoelectric element, the driving system
Control unit, by outputting a signal to the discharge circuit to the drive state after outputting a signal to the charging circuit and the non-driving state, to discharge the piezoelectric element, and returns the printing pins to its original state. Therefore, printing can be stopped without hooking the ribbon, and breakage of devices such as transistors can be prevented by preventing a through current from flowing through the circuit .

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a piezoelectric element driving circuit according to an embodiment of the present invention.

FIG. 2 is a block diagram illustrating a drive control unit according to the embodiment.

FIG. 3 is a time chart of driving of the piezoelectric element when the piezoelectric element driving circuit of the present embodiment is stopped.

FIG. 4 is a block diagram showing a conventional drive control unit.

FIG. 5 is a time chart for driving a piezoelectric element during normal printing.

FIG. 6 is a time chart of driving a piezoelectric element when a conventional piezoelectric element driving circuit is stopped.

FIG. 7 is a time chart of driving a piezoelectric element when a conventional piezoelectric element driving circuit is stopped.

[Explanation of symbols]

 P piezoelectric element Tr1 transistor Tr2 transistor 1 drive control unit 2 control device 10 print stop control unit

Continuation of front page (56) References JP-A-4-290794 (JP, A) JP-A-64-42252 (JP, A) JP-A-63-117143 (JP, A) JP-A-2-58282 (JP, A) JP-A-4-290754 (JP, A) JP-A-5-237050 (JP, A) JP-A-4-127881 (JP, A) JP-A-59-104955 (JP, A) 59-52666 (JP, A) JP-A 61-98045 (JP, U) JP-A 4-22242 (JP, U) JP 4-6918 (JP, B2)

Claims (1)

(57) [Claims] A charge circuit for charging the piezoelectric element with a charge; a discharge circuit for discharging the charge charged in the piezoelectric element; and a drive circuit for controlling the charge circuit and the discharge circuit.
A drive control unit that outputs a signal to control the driving of the piezoelectric element, when a drive stop signal is input to the drive control unit,
The control unit outputs a signal for bringing the charging circuit into a non-driving state.
And outputting a signal for setting the discharge circuit to a driving state after the driving.