JPH02145344A - Piezoelectric actuator exciting system - Google Patents

Abstract

PURPOSE:To reduce in size and cost by controlling the conduction and interruption of a discharge current by employing a closed circuit of a piezoelectric actuator, a coil and a reverse current preventive diode when stored charge charged in the actuator is discharged. CONSTITUTION:A piezoelectric actuator 1 is charged until the terminal voltage Vb of the actuator 1 arrives at a peak, and a current is returned to an exciting power source through a diode 7 in a discharging step until the voltage Vb of the actuator 1 becomes equal to an exciting voltage. In this case, switch circuits 4, 5 are interrupted. Then, when the circuit 5 is conducted by a control signal, one end of a reverse current preventive diode 6 is grounded. Thus, a series closed circuit of the actuator 1, the coil 3 and the diode 6 is formed, and charge stored in the actuator 1 is discharged through the closed circuit. The signal is operated to regulate the times in which the circuit 5 is conducted and the repetition period of the conduction of the circuit 5 to alter the amount of the discharging current, thereby controlling the voltage Vb.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a line dot matrix type impact printing device, and particularly to an excitation method for a piezoelectric actuator used as a drive source for a print head.

[Conventional technology]

An example of an excitation method for a piezoelectric actuator conventionally used in a dot matrix impact print head is shown in the fourth example.
It is shown and explained in the figure.

In the figure, 21 is a piezoelectric actuator using a piezoelectric material, one electrode of this piezoelectric actuator 21 is grounded, and the other electrode is connected to a switch circuit 2 through a coil 22.
3 and is also connected to the switch circuit 25 via a discharge line 324.

Then, the switch circuit 23 applies the excitation voltage to the piezoelectric actuator 21 via the coil 22 only during the rising time of the pulse of the drive signal, for example. When an excitation voltage is applied to the series circuit of the coil 22 and the piezoelectric actuator 21, the charging current starts to flow gradually, and after reaching the peak, it gradually starts to decrease and passes through zero, and then discharges in the opposite direction. Current begins to flow.

On the other hand, the terminal voltage of the piezoelectric actuator 21 gradually increases as the charging current flows, and reaches the peak voltage when the current reaches zero. After the peak voltage, the terminal voltage of the piezoelectric actuator 21 gradually decreases as a discharge current flows. In the process of discharging, the switch circuit 25 becomes conductive by operating the braking signal, forming a series circuit of the discharging resistor 24, the coil 22, and the piezoelectric actuator 21. A discharge current flows through this closed circuit, and the piezoelectric The energy stored in the actuator 21 is converted into thermal energy and consumed by the discharge resistor 24.

In this way, the piezoelectric actuator 21 is charged and discharged at one time.
One dot is printed depending on the period.

[Problem to be solved by the invention]

In the conventional piezoelectric actuator excitation method described above, the piezoelectric actuator, a coil, and a discharge resistor form a closed circuit, and by passing a discharge current, the electrostatic energy accumulated in the piezoelectric actuator is consumed by the discharge resistor and heat is generated. It was converted into energy.

For this reason, a resistor for discharging is required to have a large power resistance and high reliability, which poses a problem in that printers cannot be miniaturized and costs are high.

[Means to solve the problem]

The piezoelectric actuator excitation method of the present invention includes: a piezoelectric actuator that is connected to a mechanical mechanism that performs reciprocating motion, generates dimensional strain according to an excitation voltage applied between electrodes, and drives the reciprocating motion of the mechanical mechanism; a coil connected in series to the electrode of the piezoelectric actuator, and a first switch means for applying the excitation voltage to the piezoelectric actuator via the coil in response to a drive signal indicating the application timing of the excitation voltage; a second switch means for discharging the charge in the piezoelectric actuator through the coil in response to a braking signal indicating a braking timing for dimensional distortion, and capable of programmably setting a repetition period of opening/closing, a number of repetitions, and a time ratio; and means for controlling conduction and interruption of discharge current through a closed circuit formed by the piezoelectric actuator, the coil, and a reverse current prevention diode, and the discharge of the charge of the piezoelectric actuator is completed at least from the start of the braking signal. The opening and closing of the circuit by the second switch means is repeated at least once during the period of time.

[Effect]

In the present invention, when discharging the charge charged to the piezoelectric actuator, conduction and interruption of the discharge current is controlled using a closed circuit including the piezoelectric actuator, a coil, and a reverse current prevention diode.

〔Example〕

Embodiments of the present invention will be described in detail below based on the drawings.

FIG. 1 is a block diagram showing an embodiment of a piezoelectric actuator excitation method according to the present invention.

In the figure, 1 is a piezoelectric actuator using a piezoelectric material,
This piezoelectric actuator 1 is connected to a mechanical mechanism 2 that performs reciprocating motion, and is configured to generate dimensional distortion in response to an excitation voltage applied between nine electrodes, thereby driving the reciprocating motion of the mechanical mechanism 2. . 3 is a coil connected in series to the electrode of this piezoelectric actuator 1; 4 is a switch circuit; this switch circuit 4 applies an excitation voltage to the piezoelectric actuator 1 via the coil 3 in response to a drive signal indicating the application timing of the excitation voltage. It constitutes a switch means for Reference numeral 5 denotes a switch circuit, which discharges the charge of the piezoelectric actuator 1 through the coil 3 in response to a braking signal indicating the braking timing for dimensional distortion, and also controls the cycle of opening/closing, the number of repetitions, and the time ratio. It constitutes a switch means that can be set programmably. Reference numeral 6 denotes a reverse current prevention diode, and a closed circuit consisting of the reverse current prevention diode 6, the piezoelectric actuator 1, and the coil 3 constitutes means for controlling conduction and interruption of the discharge current.

Here, one electrode of the piezoelectric actuator 1 is grounded,
The other electrode is connected to a switch circuit 4 via a coil 3 and further connected to a switch circuit 5 via a reverse current prevention diode 6.

In the process of charging the piezoelectric actuator 1, the coil 3 and the piezoelectric actuator 1 form a series circuit, and an excitation voltage is applied by the switch circuit 4 operated by the drive signal, and in the process of discharging, the piezoelectric actuator 1
and filter 3 form a closed circuit, and has a switch circuit 5 that opens and closes this circuit using a braking signal. Furthermore, the terminal voltage of the piezoelectric actuator 1 is controlled by repeating opening and closing of the switch circuit 5 at least once.

In this way, the circuit is configured to be repeatedly opened and closed by the switch means of the switch circuit 5 at least once during the period from the start of the braking signal until at least the discharge of the charge in the piezoelectric actuator 1 is completed. .

Since an alternating current flows through the switch circuit 4 or 5, a diode 7 or 8 is connected to bypass (side flow) the reverse current to these switch circuits 4 and 5, and the alternating current is passed through the switch circuit 4 or 5. The switch circuit 4 or the switch circuit 5 is configured to allow the current to flow. Furthermore, a diode 9 is connected in parallel to the piezoelectric actuator 1 as shown in FIG. .

Figure 2 is a time chart used to explain the operation of Figure 1.
(ω indicates the drive signal, cb) is the braking signal, (C) is the voltage Vb s (d> is the current I, (e)
represents the dimensional distortion of the piezoelectric actuator 1.

Next, the operation of the embodiment shown in FIG. 1 will be explained with reference to FIG. 2.

First, assuming that the switch circuit 4 is in a conductive state only during the rising time of the drive signal (see FIG. 2(a)) and is in a fast-acting state during the falling time, the switch circuit 4 is When in the conductive state, an excitation voltage is applied to the piezoelectric actuator 1 via the coil 3, and when the switch circuit 4 is in the cutoff state, the voltage Va at the output terminal of the switch circuit 4 becomes zero. It is assumed that, like the switch circuit 4, the switch circuit 5 is also in a conductive state during the rising time and is in a cut-off state during the falling time.

Then, when the switch circuit 5 is in a cut-off state, the switch circuit 5
When the switch circuit 4 becomes conductive due to a high-level (H) voltage drive signal, a voltage approximately equal in height to the excitation voltage is generated at the output terminal of the switch circuit 4 in response.

Since the coil 3 is connected in series to the piezoelectric actuator 1, the current flowing to the piezoelectric actuator 1 via this coil 3 is a sinusoidal current. In addition, the pulse width of the drive signal is selected to be approximately half of one cycle of the reciprocating motion of the piezoelectric actuator 1 due to dimensional strain (see Fig. 2(e)), and this is determined by the terminal voltage vb of the piezoelectric actuator 1 ( (see Figure 2 (c)) almost coincides with the time when it reaches its peak.

As described above, the charging process is until the terminal voltage vb of the piezoelectric actuator 1 reaches its peak.

On the other hand, during the discharge process, the current returns to the excitation power source through the diode 7 until the terminal voltage vb of the piezoelectric actuator 1 becomes equal to the excitation voltage.

At this time, switch circuit 4 and switch circuit 5 are in a cutoff state.

Next, the switch circuit 5 is brought into a conductive state by the control signal, so that one end of the reverse current prevention diode 6 is grounded. As a result, a series closed circuit consisting of the piezoelectric actuator 1, the coil 3, and the reverse current prevention diode 6 is formed, and the electric charge accumulated in the piezoelectric actuator 1 is discharged through this closed circuit. The terminal voltage b of the piezoelectric actuator 1 is controlled by controlling the amount of current to be discharged by manipulating this braking signal and adjusting the time period in which the switch circuit 5 is in a conductive state and the repetition period in which the switch circuit 5 is in a conductive state. be able to.

FIG. 3 is a block diagram showing an embodiment in which the switch circuit 5 in FIG. 1 is opened and closed by a control signal.

In FIG. 3, the same symbols as in FIG. 1 indicate corresponding parts, 10 is a programmable timer, 11 is an oscillator,
12 is a programmable multipipulator. By the configuration of the programmable timer 10, the oscillator 11, and the programmable multipipulator 12, it is possible to arbitrarily set the repeat period, number of repeats, and time ratio of opening and closing of the switch circuit 5.

〔Effect of the invention〕

As explained above, the present invention controls conduction and interruption of the discharge current using a closed circuit formed by the piezoelectric actuator, a coil, and a reverse current prevention diode when discharging the charge charged to the piezoelectric actuator. It becomes possible to configure a piezoelectric actuator excitation circuit without using the conventionally used discharge resistor with high power resistance and high reliability. Therefore, there is an effect that the printer device can be made smaller and lower in cost.

Furthermore, since a part of the charged charge is returned to the excitation power source side during discharging, there is an effect that the supply efficiency of the excitation power source can be improved.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing an embodiment of the piezoelectric actuator excitation method according to the present invention, Fig. 2 is a time chart for explaining the operation of Fig. 1, and Fig. 3 shows the opening/closing of the second switch circuit in Fig. 1. FIG. 4 is a block diagram showing an example of a conventional piezoelectric actuator excitation system. 1... Piezoelectric actuator, 2... 411 machines, 3... Coil, 4, 5... Switch circuit, 6
...Diode for preventing reverse current.

Claims (1)

[Claims] A piezoelectric actuator that is connected to a mechanical mechanism that performs reciprocating motion and that generates dimensional distortion according to the excitation voltage applied between the electrodes to drive the reciprocating motion of the mechanical mechanism, and a coil that is connected in series to the electrodes of this piezoelectric actuator. a first switch means for applying the excitation voltage to the piezoelectric actuator via the coil in response to a drive signal indicating application timing of the excitation voltage; a second switch means for discharging the charge of the piezoelectric actuator through the coil and programmably setting the repetition period, number of repetitions, and time ratio of opening and closing; means for controlling conduction and interruption of the discharge current by a closed circuit using a diode, and the circuit is controlled by the second switch means during the period from the start of the braking signal until at least the discharge of the charge of the piezoelectric actuator is completed. A piezoelectric actuator excitation method characterized in that opening and closing are repeated at least once or more.