JPH0349575A - Piezoelectric actuator having function of detecting operation origin - Google Patents

Abstract

PURPOSE:To improve control accuracy by providing a stopper for regulating the operation range and a position sensor. CONSTITUTION:For a piezoelectric actuator, a plunger A as a substance to be driven is attached freely in advance and retreat inside a casing c, and three pieces of piezoelectric elements e-g are arranged on this periphery. Moreover, clamping members K-l are fixed to the tops of elastic bridges i-j. And a stopper S is formed at the inner face of the front wall a of the casing, and it contacts with the bottom flange of the plunger and regulates the downward operation. Moreover, a position sensor Sp is provided so as to detect the position of the plunger P, and it makes a controller store the position so as to make it an operation orgin.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Industrial Application Field The present invention has an operation origin detection function.4. This invention relates to piezoelectric actuators.

(B) Conventional technology Conventionally, there is a piezoelectric actuator as one form of pulse-driven actuator. In this piezoelectric actuator, one side of a piezoelectric element for stroke is fixed to a fixed part, and a piezoelectric element for clamping is attached to the other side of the same element. Attach the element, apply a pulsed drive voltage to each piezoelectric element, clamp the plunger with the clamping piezoelectric element, expand and contract the stroke piezoelectric element to move the plunger forward and backward repeatedly, and move the plunger over a large distance. There are piezoelectric actuators that allow oven loop control because the amount of movement of the plunger is proportional to the drive voltage applied to the stroke piezoelectric element and the number of pulses.

However, there is a drawback that an error occurs in the position of the plunger due to an error in the driving voltage, a slip between the plunger and the piezoelectric element, and this error accumulates to become a large error.

Therefore, in order to solve this problem, we installed a micro switch with a contact point at the stroke end position of the plunger of the actuator, and when the plunger comes into contact with the switch and performs switching, the plunger returns to the home position. There is one that updates plunger position data.

(c) Problems to be Solved by the Invention However, contact switches have variations in their switching operating points, and in particular, those that operate at low speeds, such as piezoelectric actuators, are strongly affected by vibrations and the above-mentioned variations occur. This has the disadvantage that the origin becomes inaccurate because the value becomes even larger.

Note that there are position sensors that can detect absolute position, such as absolute encoders, but those that precisely control the plunger position, such as piezoelectric actuators, cannot ignore fluctuations due to temperature, changes over time, etc. Since this is not possible, even if an absolute encoder is used, the operating origin must be corrected as necessary.

(2) Means for Solving the Problems In the present invention, a pulse voltage is applied from a control device to a piezoelectric element for clamping and a piezoelectric element for stroke to cause the plunger to reciprocate. In this piezoelectric actuator, a stopper is installed on the actuator to mechanically restrict the operating range of the plunger to serve as the origin of plunger operation, and a position sensor is attached to detect the position of the plunger, so that the output of the position sensor changes. It is an object of the present invention to provide a piezoelectric actuator having an operation origin detection function, which operates a plunger in one direction until it stops moving, and uses the output of a position sensor at this time as position data of the plunger operation origin. .

(E) Functions and Effects According to the present invention, even if the plunger is once operated in the direction of the stopper, and the plunger reaches the origin, and the control device outputs a driving output in the direction of the stopper, the operation of the plunger is not performed in the direction of the stopper. Drive the plunger until it stops moving.

Then, at the same time as the plunger stops moving, the position sensor output also stops changing.

As mentioned above, the arrival of the plunger at the origin and the phenomenon in which the change in the position sensor output stops occurs simultaneously, so the position sensor output at the time when the change in the position sensor output stops is used as the position data of the plunger operation origin. It can be done.

In particular, since a contact switch or the like is not used, the position sensor output is stable without variations even with a plunger operating at low speed, and the operating origin can be detected precisely.

If the position data of the plunger operation origin detected in this manner is stored in the control device, the operation of the plunger can be controlled based on this position data.

In addition, the position data of the operating origin can be updated by returning the plunger to the origin as needed or periodically, and furthermore, the data on the position of the operating origin can be updated by returning the plunger to the origin while the piezoelectric actuator is operating. can be updated.

As described above, since the operation of the plunger is controlled based on the updated position data of the operation origin, the precision of control can be improved.

(F) Embodiment An embodiment of the present invention will be described in detail with reference to the drawings. In FIG. 1, (A) shows a piezoelectric actuator as a pulse drive actuator, and a casing ( A plunger (P) as a driven body is mounted concentrically and movably back and forth along the axis within e), and three piezoelectric elements (c) are mounted concentrically on the outer peripheral surface of the plunger (P). )((')(g) is provided.

In addition, (1) has its base end fixed to the support member (h), and (j) has its base end fixed to the stroke piezoelectric element (g), and its tips are directed toward the front and rear walls (a) and (b). It is an elastic bridge in the form of a cantilevered beam.

At the tip of the elastic bridge (1) (j), piezoelectric elements (e) (f') for clamping are attached to the outer circumferential surface, and clamping members (k) (+) are fixed to the inner circumferential surface. are doing.

In addition, a stopper (S) is formed on the inner surface of the front wall (a), and a flange (F) is formed at the lower end of the plunger (P).
The downward movement of the plunger (P) is restricted by contact with the plunger (P), and in this state, the plunger (P)
The position is set as the operating origin of the plunger (P).

Next, we will explain the action of each piezoelectric element (e), (f), and The plunger (P) is clamped by contracting the diameter of the plunger (P), while expanding its inner diameter and releasing 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 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 configuration will be explained with reference to FIGS. 2 to 5.

A voltage is applied to the piezoelectric element (f') from a control device (C), which will be described later, according to a drive program, and as shown in FIG. 2, the plunger (P) is clamped and the piezoelectric element (e)
The clamp of the plunger (P) is released by removing the voltage from the plunger (P).

Next, as shown in Figure 3, when a voltage is applied to the piezoelectric element (g) to cause it to contract, the piezoelectric element (f) moves in the direction of the arrow, and the plunger (P) also moves in the direction of the arrow. Moving.

Thereafter, as shown in Figure 4, a voltage is applied to the piezoelectric element (e) to clamp the plunger (P), and then the voltage applied to the piezoelectric element (f') is released to unclamp the plunger (P). When the voltage applied to the piezoelectric element (g) is released, the piezoelectric element (g) expands and the piezoelectric element (f')
Return to the position shown in the figure.

After that, by repeating the above operation, the plunger (
P) can be moved like an inchworm with a stroke on the μm order or sub-μm order, and various actuating devices connected to the tip of the plunger (P) can be precisely operated.

The operation of the piezoelectric actuator (A) is controlled by a control device (C) shown in FIG.
It consists of a microprocessor (MPU), an input/output interface (+) (0), and a memory (M) that stores a drive program.The input interface (1) includes a switch ( Sv) is connected to the output interface (0), and piezoelectric elements (e) (f') (g) for clamping and stroke are connected to the output interface (0) via the drive circuit (I)).

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 actuated as described above. I can do it.

As shown in FIG. 1, this piezoelectric actuator (A) is provided with a position sensor (Sp) to detect the position of the plunger (P).

That is, a cylindrical moving electrode (pm) is provided on the outer peripheral surface of the rear end of the plunger (P), and a cylindrical dielectric material (E) such as alumina ceramics is provided at a predetermined distance from the moving electrode (pm). Fit the rear end surface of the dielectric (E) onto the rear wall (
b) A first fixed electrode (psl) and a second fixed electrode (ps2) each having a cylindrical shape are fixed to the inner surface of the dielectric (E) and are arranged on the outer periphery of the dielectric (E).
are fitted onto the outside while maintaining a predetermined interval in the axial direction, and both ends of the movable electrode (pm) are connected to the first and second fixed electrodes (psi) (
ps2) and the first fixed electrode (psi) and the moving electrode (pI!l) by changing the length of the wrapped portion of each electrode (pm) (psi) (ps2) as the plunger (P) moves. and the capacitance between the second fixed electrode (ps
2) and the electrostatic capacitance between the moving electrode (pm) are configured to increase and decrease in a complementary manner to each other.

As shown in FIG. 7, each electrode (pm) (psl
) (ps2) as one of the oscillation constants, and the oscillation wave is input to the mixer (C3), and the high frequency output of the mixer (C3) is Cut the area with a low-pass filter (C4),
Convert to voltage with FV conversion circuit (C5) and convert to A-D converter
C6> is configured to be manually input to the control device (C).

The position of the plunger (P) can be calculated by processing the output of the AD converter (C6) input to the control device (C) as described above.

That is, as described above, the capacitance between the first fixed electrode <psi) and the moving electrode (pm) and the second fixed electrode (ps2
) and the electrostatic capacitance between the moving electrode (pm) and the plunger (
In response to the movement of P), the oscillation circuit (CI) is configured to increase or decrease in a complementary manner to each other.
Regarding the oscillation frequency of (C2), when one becomes high, the other becomes low.

By mixing the oscillation frequency of the oscillation circuit (Cl) (C2), which changes in response to the movement of the plunger (P) as described above, with the mixer (C3), the sum and difference of the two oscillation frequencies are synthesized. The frequency is output, the high frequency region of the sum of the synthesized frequencies is cut by a low-pass filter (C4), only the low frequency region of the difference of the synthesized frequencies is converted to voltage by the FV conversion circuit (C5), and the AD By inputting to the control device (C) via the converter (C6), the plunger (P
) position can be detected.

It is also possible to shape the output waveform of the low-pass filter (C4) and manually input it to the control device (C), and then digitally detect the frequency (for example, by frequency counting) inside the equipment 1 (C).

The embodiment of the present invention is configured as described above, and when the piezoelectric actuator (A) and the control device (C) are connected to the power source, the piezoelectric actuator (A) is loaded with a load as part of initialization or power-on reset. Before this occurs, move the plunger (P) forward until its operation is regulated by the stopper (S) and there is no change in the output of the position sensor (Sp), and then record the output of the A-D converter (C6) at that time. By storing it in the memory (M), the position where the operation is regulated by the stopper (S) can be used as the starting point for the operation of the plunger (P).

Then, the current position of the plunger (P) detected from the position data of the operating origin of the plunger (P), the amount of movement of the plunger (P) per one drive pulse, and the output of the A-D converter (C6). Refer to the data and plunger (P
), the operation of the plunger (P) can be controlled in a closed loop.

In addition, in order to update the position data of the operating origin, similarly to the above, move the plunger (P) forward until the operation is regulated by the stopper (S) and there is no change in the position sensor (Sp) output, and then The output of the A-D converter (C6) may be stored in the memory (}4).

In particular, by using the output of the position sensor (Sp) when there is no change in the output of the position sensor (Sp) as the position data of the operating origin of the plunger (P), it is possible to detect fj1 dense position data without variation. As a result, the plunger (P) can be precisely controlled.

The detection and updating of the position data of the operating origin is always performed when the power is turned on as described above, but if necessary, the user may issue a command to update the position data to the control device (C) or perform the control You can set a timer during the program and update it at regular intervals, or as described in the application example below, you can update it by seizing the opportunity to operate until the plunger (P) is regulated by the stopper (S). can.

Also, when the plunger (I') reaches the operating origin and comes into contact with the stopper (S) and stops operating, the position sensor (
Since there will be no change in the output of Sp), if the driving of the plunger (P) in the stopper direction is stopped at this point, the plunger (P) will be prevented from being driven forcefully, and the piezoelectric element for clamping due to forced driving will be prevented. (e), (f) and harmful effects such as wear of the plunger (P) can be prevented.

The piezoelectric actuator (^) above is a plunger (1')
Various devices can be connected to the tip of the device to accurately control the devices.

Figure 8 shows the above piezoelectric actuator (A) applied to control the operation of a diaphragm-type flow rate regulating valve (■).
v), which is configured to open/close 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). To open the valve body (1),
Operate the plunger (P) upward to remove the pilot valve seat (6).
) is opened and closed by operating the plunger (P) downward to close the pilot valve seat (6).

In particular, when the valve body (1) is closed, the main valve body (5) is connected to the main valve seat (4), and the pilot valve body (9) connected to the tip of the plunger (P) is connected to the pilot valve seat (6). >, the downward movement of the plunger (P) is restricted and there is no change in the output of the position sensor (Sp), so set this position as the operating origin of the plunger (P). , the detection output of the position sensor (Sp) in this state is taken as the position data of the operating origin of the plunger (P).

Therefore, one upright position data of the operating origin of the plunger (P) can be updated every time the main valve body (5) closes the valve.

In addition, since the position of the plunger CP is corrected using the closed state of the main valve body (5) as the operating origin, the valve close position and open position due to fatigue of the main valve body (5), pilot valve body (9), etc. The degree deviation will also be automatically corrected.

As mentioned above, the position of the plunger (P) in the closed state of the main valve body (5) is set as the operating origin, and the plunger (P)
Since the position of the plunger (P) is frequently corrected, the position of the plunger (P) can be accurately controlled and the flow rate can be adjusted accurately.

[Brief explanation of drawings]

Figure 1 is based on the present invention. A cross-sectional explanatory diagram of the II electric actuator, FIGS. 2 to 5 are explanatory diagrams showing the operating order of the piezoelectric actuator, FIG. 6 is a block diagram showing the configuration of the control device, and FIG. 7 is a capacitance detection diagram. A block diagram showing the circuit groove, and FIG. 8 is a cross-sectional explanatory diagram of the flow ffi adjustment valve. (A): Piezoelectric actuator (C) Two-control device (P): Plunger (S): Stopper (Sp): Position sensor (e) (f'): Piezoelectric element for clamp (g) Piezoelectric element for two-stroke

Claims (1)

[Scope of Claims] 1) A piezoelectric actuator configured to reciprocate a plunger by applying a pulse voltage from a control device to a piezoelectric element for clamping and a piezoelectric element for stroke, comprising: A stopper is installed to mechanically restrict the operating range of the plunger to serve as the origin of plunger operation, and a position sensor is installed to detect the position of the plunger, and the plunger is moved in the direction of the stop until the output of the position sensor stops changing. 1. A piezoelectric actuator having an operation origin detection function, characterized in that the piezoelectric actuator is actuated at this time, and the output of the position sensor at this time is used as position data of the plunger operation origin.