JPH034080A - Piezoelectric actuator having position detecting function - Google Patents

Abstract

PURPOSE:To contrive the possibility of detecting a position over a full stroke by mounting moving electrodes and capacitors to both end parts of a plunger and fixed electrodes to an actuator fixed side and calculating a plunger position from a difference of electrostatic capacity between both the capacitors. CONSTITUTION:Moving electrodes pm1, pm2 are provided and capacitors Q1, Q2 are formed in both end parts of a plunger P, and fixed electrodes ps1, ps2 are provided in the fixed side of a piezoelectric actuator A. While a change of electrostatic capacity of both the capacitors Q1, Q2, following a longitudinal movement of the plunger P, is detected by a control unit, and being based on a difference between the electrostatic capacity, a drive signal is generated. Further elastic bridges (i), (j), in which the base end is mounted to a supporting material (h) and a stroke piezoelectric element (g) and the top end is mounted to clamping piezoelectric elements (e), (f), are provided. Accordingly, by moving the plunger P in a measuring worm state by the drive signal applied to the piezoelectric elements (e), (f), (g), a position can be detected over a full stroke, and accurate driving can be attained.

Description

DETAILED DESCRIPTION OF THE INVENTION (A) Field of Industrial Application The present invention relates to a piezoelectric actuator having a position detection function.

(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 by a pulse. There is a piezoelectric actuator in which a voltage is applied to clamp a plunger with a piezoelectric clamping element, and a piezoelectric stroke element expands and contracts to move the plunger over a large distance.

The operation of the piezoelectric actuator is controlled by open loop control in view of the fact that the amount of movement of the plunger is approximately proportional to the amount of charge applied to the stroke piezoelectric element and the number of pulses.

However, in the operation of piezoelectric actuators, errors in drive voltage, slips between the plunger and piezoelectric element, etc.
An error occurs in the position of the plunger, and furthermore, this error accumulates, resulting in a large integrated error, resulting in a problem that the plunger cannot be moved back and forth accurately.

Therefore, as a means to solve this problem, a limit switch or photo sensor is installed at the stroke end position of the plunger, and when these limit switches or sensors detect the plunger, the plunger position data is updated. Alternatively, an encoder may be connected to the plunger to detect the plunger position and update the plunger position data.

(C) Problems to be Solved by the Invention However, with the above-mentioned position detection means using limit switches or photosensors, plunger position data can only be updated when the plunger reaches the end of its stroke, and the plunger moves back and forth at an intermediate position. The disadvantage is that as the operation is repeated, errors gradually accumulate.

Particularly, in the case of a limit switch, the switch has hysteresis, so the plunger is detected at a different position during forward and backward movement.

In addition, encoders are generally expensive, pulse counter types have the disadvantage of accumulating errors unless the position is frequently calibrated, and absolute types have the drawback of connecting encoders to plungers. 1 calibration is not necessary but is very expensive.

Furthermore, the limit switch and encoder require a considerable amount of separate installation space, which increases the structure of the piezoelectric actuator.

An object of the present invention is to provide a piezoelectric actuator that can solve the above problems.

(d) Means for Solving Problems This invention provides a linear drive type piezoelectric actuator configured to linearly drive a plunger, in which movable electrodes are attached to both ends of the plunger, and the piezoelectric actuator is fixed. Fixed electrodes are attached to the sides facing the removable electrodes, capacitors are formed at both ends of the plunger, and changes in the capacitance of both capacitors as the plunger advances and retreats are detected. The present invention relates to a piezoelectric actuator having a position detection function, characterized in that it is configured to calculate the position of a plunger based on a difference.

(E) Function/Effect ■ In the present invention, when the plunger moves forward or backward, the capacitance between the two electrodes changes, so the position of the plunger is detected from this capacitance change. Therefore, no matter what position the plunger is in, it can always be detected, and it is possible to solve the conventional problem that the position of the plunger can only be detected when the plunger reaches the end of its stroke.

■In particular, the configuration is such that capacitors are formed at both ends of the plunger, changes in the capacitance of both capacitors are detected as the plunger advances and retreats, and the position of the plunger is calculated based on the difference between the detected values. , it is possible to increase the change in capacitance with respect to the movement of the plunger, allowing delicate position detection.

- Also, since an expensive encoder is not required, there is an advantage that the position of the plunger can be detected at low cost.

(F) Embodiment A first embodiment of the present invention will be specifically described with reference to FIGS. 1 to 7.

In FIG. 1, A indicates a piezoelectric actuator as a linear drive actuator, and the front and rear walls a.

Three piezoelectric elements e, f, and g are arranged concentrically on the outer peripheral surface of a plunger P as a driven body so as to be movable back and forth along the axis in a casing C equipped with b. ing.

In addition, l is a cantilever-shaped elastic bridge whose base end is used as a support member, and j is a cantilever-shaped elastic bridge whose base end is fixed to the stroke piezoelectric element g and whose tips extend toward the front and rear walls a and b. .

At the tips of the elastic bridges t and J, a piezoelectric element e1 for clamping is attached to the outer peripheral surface thereof, and a clamping member 1 is fixed to the inner peripheral surface thereof.

Among the piezoelectric elements e, f, and g, the clamping piezoelectric elements e and f have their inner diameters reduced to 1 when a voltage is applied.
While clamping the plunger P, the inner diameter is expanded to release the clamp on the plunger P when no voltage is applied.

On the other hand, the stroke piezoelectric element g extends in the axial direction on the plunger P when a voltage is applied, and contracts in the axial direction on the plunger P when a voltage is not applied.

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

A control device C, which will be described later, applies a voltage to the piezoelectric element f according to a drive program to clamp the plunger P, as shown in FIG. 2, and releases the voltage application to the piezoelectric element e to clamp the plunger P. Release.

Next, as shown in FIG. 3, when the voltage on the piezoelectric element g is released to cause it to contract, the piezoelectric element r moves in the direction of the arrow, and accordingly, the plunger P also moves in the direction of the arrow.

Thereafter, as shown in FIG. 4, a voltage is applied to the piezoelectric element e to clamp the plunger P, then the voltage applied to the piezoelectric element f is released to release the clamp on the plunger P, and a voltage is applied to the piezoelectric element g. When the voltage is applied, the piezoelectric element g expands and the piezoelectric element f returns to the position shown in FIG.

After that, by repeating the above operation, plunger P
can be moved in a linear manner with a stroke of the μm order or suborder IIm order, and various actuating devices connected to the tip of the plunger P can be operated precisely.

The operation of the piezoelectric actuator A is controlled by a control device C shown in FIG.
, a memory M that stores a drive program, an input interface I is connected to a switch S- for operating the program, and an output interface O is connected to a drive circuit for clamping and stroke. piezoelectric elements e, f, and g are connected.

When a control command signal from the switch S- to the plunger P is input to the control device C, a pulsed drive voltage is output according to the drive program, and the program can be operated as described above.

The present invention provides the i! The plunger position sensor structure is designed to accurately and reliably control retraction movement.
This is the gist, and the structure will be specifically explained below.

That is, as shown in FIGS. 1 and 7, the piezoelectric actuator A has disk-shaped fixed electrodes PS+ and 91 attached to its front wall a and rear wall, respectively, and the same fixed electrodes 1) and 3.
At the front and rear ends of the plunger P facing 1,931, annular and disk-shaped moving electrodes p■l+pH! is installed.

And fixed electrode 1)! + and the moving electrode pH+ and the fixed amount I! jrps□ and moving electrode p11! Insulating gaps G, , Gt are formed between the plunger P and capacitors Q1 . It constitutes Q-will.

In such a configuration, by moving the plunger P in the axial direction, the fixed electrodes 9SI, p of the moving electrodes f1m+, Pl
s! The lengths of the insulation gaps Gl and Gt for
The capacitance of Qt will also change.

Therefore, since the capacitors Ql and Qyo are formed at both ends of the plunger P, as the length of the insulation gap G1 increases, the length of the insulation gap G decreases, and the static of the capacitors Q, Q, It creates a capacitance and changes dynamically.

Next, referring to FIG. 7, the above-mentioned capacitor Q+,
A configuration for detecting a change in the capacitance of Qt and sending a detection output to the control device C will be described.

That is, as shown in FIG. 7, the capacitor Q1 and the moving electrode 1ull! are composed of a moving electrode ρ-1 and a fixed electrode ps. The oscillation circuits Cl-1 and Cl-2 are configured using the capacitance of the capacitor 08, which is composed of the fixed electrode pSg and the fixed electrode pSg, as one of the oscillation constants.

Then, each of the oscillation circuits C1 to C1. Cl-2 oscillates frequencies f, f, corresponding to the capacitances of the capacitors Q, Q, described above, and these oscillation frequencies r1°f8 are mixed in a mixer C3, and then passed through a low-pass filter LF. Output frequency 1r+- generated through
rgl is converted into a voltage by the FV conversion circuit C2, and the control device C
I am trying to input it into .

Next, positioning control of the plunger P using the plunger position sensor having the above configuration will be explained.

First, when the plunger P moves in any axial direction by applying voltage to the piezoelectric elements e, r, and g, the movement 11
The insulating gap G between fii p * + and the fixed electrode p4+ and the insulating gear knob G between the movable electrode pm and the fixed electrode Pat, that is, the capacitance of the capacitors Q+ and Qz change.

The changing capacitances of the capacitors Ql and Q-2 are determined by the above-mentioned oscillation circuits Cl-1 and Cl-2, which output frequencies f, f, which are proportional to their respective capacitances. The frequencies f,, f, are input to the control device C which stores a routine for calculating the position of the plunger P from the output frequency 1 r+-rx l via the mixer C3, low-pass filter LP and FV conversion circuit C2. will be done.

The capacitance data or output frequency data between the movable electrode p plow and the fixed electrode ps inputted to the control device C as described above can be processed by the above-mentioned routine to calculate the position of the plunger p. can.

Using the position of plunger p detected in this way,
The position of the plunger P can be controlled in a closed loop.

Therefore, in this embodiment, the position of the plunger P is detected based on the output frequency 1f+-ftl which is proportional to the difference in capacitance between the two capacitors Q, .

Therefore, as shown in FIG. 8, the output frequency 1r+-f! with respect to the change in the position of the plunger P! The rate of change (slope) of l is simply expressed as the frequency f based on the capacitance change of either capacitor Q1 or Q8, or the rate of change of frequency f8 (
(gradient) can be made significantly larger than in the case of (gradient).

Therefore, it is possible to detect subtle changes in the position of the plunger P, and the position controllability of the plunger P of the piezoelectric actuator A can be improved.

As described above, the piezoelectric actuator A that can detect the position of the plunger P can be connected to the tip of the plunger P to accurately control various devices.

Furthermore, the piezoelectric actuator A in this embodiment has the advantage that an expensive encoder is not required to detect the position of the plunger P, so that the above control can be realized at low cost.

FIG. 9 shows an arrangement in which the piezoelectric actuator A described above is applied to control the operation of a diaphragm valve V to open and close the facing valve V and adjust the flow rate.

In the figure, l is the valve body, 2 is the outflow path, 3 is the inflow path, 4 is the main toilet seat, 5 is the main valve body, 6 is the pilot valve seat, 7 is the Guyaflame, 8 is the orifice, and 9 is the tip of the plunger P. Since the pilot valve bodies are shown in series and the position of the plunger P is constantly detected, the position of the viroft valve body 9 is accurately controlled, and therefore the position of the main valve body 5 is also accurate. , accurate flow rate adjustment can be performed.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional explanatory diagram of a piezoelectric actuator having a position detection function according to the present invention, FIGS. 2 to 5 are explanatory diagrams showing the operating order of the piezoelectric actuator, and FIG. 6 is a block diagram showing the configuration of a control device. Figure 7 is a block diagram showing the circuit configuration for detecting capacitance, Figure 8 is a diagram showing the relationship between plunger position and output frequency, and Figure 9 is a flow regulating valve equipped with the piezoelectric actuator described above. FIG. In the figure, A: piezoelectric actuator P nrrp-t: moving electrode ps+, l) 3 snow: fixed electrode Q,, Ql: capacitor (■) Figure 7 (Figure 7) Output frequency f. Origin 7° Runcie IitJ

Claims (1)

[Claims] 1. In a linear drive type piezoelectric actuator configured to linearly drive a plunger (P), movable electrodes (pm_
1) Attach (pm_2) and both moving electrodes (pm_1) (pm_2) on the fixed side of the same piezoelectric actuator.
A fixed electrode (ps_1) (ps
_2) is installed, capacitors (Q_1) (Q_2) are formed at both ends of the plunger (P), and changes in the capacitance of both capacitors (Q_1) (Q_2) are detected as the plunger (P) advances and retreats. A piezoelectric actuator having a position detection function, characterized in that the position of the plunger (P) is calculated based on the difference between the detected values.