JPH02177382A - Piezoelectric actuator - Google Patents

Abstract

PURPOSE:To keep the stoke per one pulse of a piezoelectric element constant by a method wherein a piezoelectric actuator is provided with a plunger position detecting device and the amount of a charge to apply to the element is adjusted on the basis of the result detected by the device. CONSTITUTION:With a moving electrode Pm provided at the rear end of a plunger P, a fixed electrode Ps, which faces the electrode Pm and is insulated from the electrode Pm, is arranged and a gap G is formed to detect an electrostatic capacity between the electrode Ps to fluctuate with the movement of the electrode Pm and the electrode Pm. Then, the position of the plunger P is detected on the basis of the detected electrostatic capacity and further, the actual stroke of the plunger P per one pulse is detected to adjust a voltage applying time to a piezoelectric element (g) for stroke use having a previously set reference stroke as an object or an applying voltage is adjusted to perform a feedback control and the stroke per one pulse of the element (g) is kept constant.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention relates to a piezoelectric actuator having an automatic correction function for actuation resolution.

(B) Conventional technology Conventionally, as a form of piezoelectric actuator, one side of a piezoelectric element for stroke is fixed to a fixed part, a piezoelectric element for clamping is attached to the other side of the same element, and each piezoelectric element is driven in a pulsed manner. There is a piezoelectric actuator that moves the plunger over a large distance by repeatedly applying a voltage, clamping the plunger with a clamping piezoelectric element, and expanding and contracting the stroke piezoelectric element to move the plunger forward and backward. Since the amount of charge is approximately proportional to the amount of charge applied to the stroke piezoelectric element and the number of pulses, there are some devices that enable open-loop control.

(c) Problem to be solved by the invention However, even if the piezoelectric elements have the same specifications, there are variations in operating characteristics between the piezoelectric elements, and this causes the stroke per pulse between piezoelectric actuators with the same specifications to vary. In addition, even if the piezoelectric actuator is the same, there will be differences in the stroke of one plunger per pulse due to load fluctuations, errors in drive voltage, and slip between the plunger and piezoelectric element. This has the disadvantage that accurate operation cannot be expected because the accumulation of errors results in large errors.

(d) Means for solving WIJi In the present invention,
A piezoelectric actuator is equipped with a piezoelectric element for stroke and a piezoelectric element for clamping, and applies a pulse-like drive voltage to each piezoelectric element to move one plunger forward and backward. It is an object of the present invention to provide a piezoelectric actuator configured to adjust the amount of charge applied to a piezoelectric element based on the detection result of the device.

(E) Effects and Effects According to the present invention, since the stroke of the piezoelectric element is approximately proportional to the amount of electric charge applied to the piezoelectric element, the stroke of the plunger per one pulse is determined by the detection result of the plunger position detection device. By detecting this and adjusting the amount of charge applied to the piezoelectric element based on the detection result, the stroke per pulse of the piezoelectric element can be made constant.

Note that in order to adjust the amount of charge, a constant current may be supplied to the piezoelectric element via a constant current circuit or the like, and the time for which this current is applied may be adjusted.

(f) Embodiment The first embodiment of the present invention will be described in detail based on the drawings.
In the figure, (A) shows a piezoelectric actuator, front and back ri (a
) (b) A plunger (P) as a limb driving body is installed concentrically and movably back and forth along the axis, and a plunger (P) is installed concentrically on the outer peripheral surface of the plunger (P). , three piezoelectric elements (e), (f), and (g) are arranged.

In addition, (i) has its base end fixed to the support material fh), and (j) has its base end fixed to the piezoelectric element (C1) for strut 17-, and its tips are fixed to the front and rear walls (a) (1)). It is a cantilever-like elastic bridge that extends toward the

A piezoelectric cord for clamping (ELF) is attached to the outer circumferential surface of the tip of the elastic bridge (iHj), and a clamping member (k) (1) is fixed to the inner circumferential surface thereof. .

Among these piezoelectric elements (e), (f), and (Q), the clamping piezoelectric element to)m reduces its inner diameter to clamp the 1-lunger (P) when a voltage is applied, and when no voltage is applied, Expand the inner diameter and release the clamp on the plunger (P).

On the other hand, the stroke piezoelectric element (1g) extends in the axial direction on the plunger (P) when no voltage is applied, and contracts in the axial direction on the plunger (P) when a voltage is applied.

Next, the movement of the plunger (P) by the piezoelectric actuator (A) having such a structure will be explained with reference to FIGS. 2 to 5.

From the control device (C) described in t&, a voltage is applied to the element m according to the drive program, and as shown in FIG. 2, the plunger (P) is clamped and the pressure is applied to the element (e). Release the application and release the clamp on the plunger (P).

Next, as shown in FIG. 3, when a voltage is applied to the piezoelectric element (9) to cause it to contract, the piezoelectric cord (if) moves in the direction of the arrow, and along with this, the plunger (P) also moves in the direction of the arrow. Moving.

Then, as shown in Figure 4, a voltage is applied to the piezoelectric element (C) to clamp the plunger (P), and then the voltage applied to the piezoelectric element (f) is released to release the clamp on the plunger (P). However, when the voltage applied to the piezoelectric element (a) is released, the piezoelectric element (g) expands and returns to the position shown in FIG. 5.

By repeating the above-mentioned movement (j), the plunger (P) can be moved like a scale wheel with a stroke on the order of μm or sub-μm, and various actuating devices connected to the tip of the plunger (P) This means that it can be operated precisely.

The operation of the piezoelectric actuator (8) is controlled by a control device (C) shown in FIG.
Microprocessor (HPU), input/output interface [100], memory storing drive program (100)
4), and an input interface (
A switch (Sv) for operating the plunger (P) is connected to 1), and a piezoelectric cord (e) for clamping and stroke is connected to the output interface (0) via a drive circuit (D). (f) (g) are connected.

When a control command from the switch (Sv) to the plunger (P) is input to the control device (C), a pulsed drive voltage is output according to the drive program, and the plunger (P) is controlled as described above. It is possible to activate it.

This piezoelectric actuator (^) is provided with a position detection device (S) for the plunger (P), and as shown in FIG. 1, a moving electrode (pl) is provided at the rear end of the plunger (P). A moving electrode (pm
), a fixed electrode (aS) insulated from the fixed electrode (aS) is arranged to form a gap (G), and the fixed electrode (pl and the moving type @ (ρ1) is detected.

FIG. 7 shows a piezoelectric actuator (A) configured almost in the same way as above, with a cylindrical moving electrode (pl) provided on the outer peripheral surface of the rear end of the plunger (P), and a predetermined interval maintained between the moving electrodes (pl). Then, a cylindrical fixed type li! is made up of a first fixed voltage (psl) and a second fixed voltage 1 (ps2) arranged at a predetermined distance in the axial direction. ([)S) and connect both ends of the moving electrode (ara) to the first and second fixed electrodes (pst) (
ps2) and fl to move the plunger (P).
The capacitance between the first fixed electrode (psi) and the moving electrode (all), and the capacitance between the second fixed electrode (ps2) and the moving electrode (p
411! so that the capacitance between lJ increases and decreases in a complementary manner to each other! From the difference in both capacitances, the grandger (P
) to improve the accuracy of position detection.

FIG. 8 shows a disc-shaped moving zone (llll11) with a predetermined distance from the rear end surface at the f& end of the granger CP) of the piezoelectric actuator (A) configured almost in the same manner as described above.
A plunger (P) is arranged in series, and disk-shaped first and second fixed electrodes (PSL) (PS2) are arranged parallel to the moving electrode with a predetermined interval maintained before and after the moving electrode. The changes in capacitance between the first and second fixed voltages Bi (psl) (ps2) and the moving electrode (pl) due to the movement of the electrodes are detected, and the position of the plunger (P) is determined from the ratio of each capacitance. It is designed to detect.

In order to detect the capacitance between the moving electrode (pl) and the fixed electrode (ps), the following configuration can be considered.

That is, as shown in FIG. 9, there is a moving pole (pm) and a fixed type M! (ρS) is one of the oscillation constants, and the oscillation frequency is F.
The V conversion circuit (C2) converts it into a voltage and inputs it to the control device (C).

In addition, as shown in FIG. 10, an oscillation circuit (C3) with the above-mentioned capacitance as one of the oscillation constants is constructed, and its oscillation frequency is directly input to the control device (C). ), the frequency is detected digitally (for example, by frequency counting).

The electrostatic capacitance can be detected by calculating backward from the frequency detected in this way, and then the position of the plunger can be detected.

From the position of 1 lange (P) detected in this way,
The actual rotor of the plunger (P) per pulse can be detected, and the voltage application time to the piezoelectric element (1) for stroke can be adjusted to achieve a preset standard stroke. Or, by adjusting the applied voltage, feedback control can be performed to maintain a constant value of S1-L7- per pulse.

FIG. 11 is a block diagram conceptually showing the flow of the feedback control described above, in which the position of the plunger (P) of the piezoelectric actuator (A) is detected by the position detection device (S), and this detection result is transmitted to the transducer ( It) via comparator (■)
and compare it with the setting device (old standard stroke) inputted to the same pipe (T) via the converter (U), input this comparison result to the control device, and output from the same control device. The driving circuit is controlled to input the current application time or the applied voltage to control the feedback of the stroke per pulse, thereby automatically correcting the operating resolution.

As mentioned above, the piezoelectric actuator (Δ) that can automatically correct the operating resolution of the plunger (P) is
Various devices can be connected to the tip of P) to control the devices extremely accurately.

FIG. 12 shows the above piezoelectric actuator (8) applied to control the operation of a diaphragm valve (V) to open/close the volume valve (V) and adjust the flow rate.

In the figure, (1) is the valve body, (2) is the inflow path, (3) is the outflow path, (4) is the main valve seat, (5) is the main valve body, (6) is the pilot valve seat, and (7) is the main valve seat. ) indicates the diaphragm, (8) indicates the orifice, and (9) indicates the pilot valve body connected to the tip of the plunger (P).Since the position of the plunger (P) is always detected, the pilot valve The position of the body (9) is accurately controlled, and therefore the position of the main valve body (5) is also accurate, allowing accurate flow rate adjustment.

6 is a block diagram showing the configuration of the control device, FIGS. 7 and 8 are cross-sectional views showing the form of the music of the position detection device, and FIGS. 9 and 10. does not indicate the vPI configuration for detecting capacitance. 11 is a conceptual block diagram of the feedback control system, and FIG. 12 is a cross-sectional explanatory diagram of the flow rate regulating valve.

A: Piezoelectric actuator P Nibranja S: Position detection device e): Piezoelectric element for clamping g: Piezoelectric element for stroke

[Brief explanation of the drawing]

Claims (1)

[Claims] 1) Each piezoelectric element (e) (f) (g) is equipped with a piezoelectric element (g) for stroke and a piezoelectric element (e) (f) for clamping.
), the piezoelectric actuator (A) is configured to move the plunger forward and backward by applying a pulsed drive voltage to the piezoelectric actuator (A), and is provided with a position detection device for the plunger (P), which applies a pulsed drive voltage to the piezoelectric element based on the detection result of the plunger (P). A piezoelectric actuator configured to adjust the amount of electric charge.