JP2768961B2 - Piezoelectric actuator with position detection function - Google Patents

Description

The present invention relates to a piezoelectric actuator having a position detecting function.

(B) Conventional technology Conventionally, as one form of a piezoelectric actuator, one side of a piezoelectric block for stroke is fixed to a fixed portion, a piezoelectric element for clamping is attached to the other side of the element, and a pulse-like drive is applied to each piezoelectric element. There is a piezoelectric actuator that moves the plunger largely by repeatedly applying and applying voltage to clamp the plunger with the piezoelectric element for clamping, extending and retracting the piezoelectric element for stroke to extend and retract the plunger. Since the amount is substantially proportional to the amount of electric charge applied to the stroke piezoelectric element and the number of pulses, some devices have made open-loop control possible.

However, there is a drawback that an error occurs in the position of the plunger due to a drive voltage error, a slip between the plunger and the piezoelectric element, and further, these errors accumulate to a large error.

Therefore, as a means for solving this drawback, a limit switch or a photo sensor is disposed at the stroke end position of the plunger, and when these switches or sensors detect the plunger, the position data of the plunger is updated. One that can be considered, or one that connects an encoder to the plunger to detect the position of the plunger.

(C) Problems to be Solved by the Invention However, in the position detecting means using the switch or the photo sensor, the plunger position data can be updated only when the plunger reaches the stroke end, and the plunger moves forward and backward at the intermediate position. If the operation is repeated, there is a drawback that errors gradually accumulate. Particularly, in the case of using a limit switch, there is a drawback that the position where the plunger is detected is different because the switch has hysteresis. .

Also, the means for connecting the encoder to the plunger is generally expensive, and the pulse counter type has the disadvantage that errors are accumulated unless the position is frequently calibrated. Calibration is necessary but very expensive.

(D) Means for Solving the Problems According to the present invention, in a linear drive actuator configured to linearly drive a plunger, a movable electrode is provided on the plunger, and the fixed electrode is provided on a fixed side of the actuator. Provided so as to face each other, one of the electrodes is divided and formed, and the other electrode is straddled between the divided electrodes to detect a change in capacitance between the respective electrodes due to the advance / retreat operation of the plunger. Accordingly, the present invention provides a piezoelectric actuator having a position detecting function, which is configured to detect the position of a plunger.

(E) Function / Effect According to the present invention, when the plunger moves forward and backward, the capacitance between the electrodes changes, and the position of the plunger can be detected from the change in capacitance.

Therefore, no matter where the plunger is,
The position can always be detected, and the disadvantage that the position can be detected only when the plunger reaches the end of the stroke in the related art is solved.

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

In addition, one of the electrodes is divided and formed, and the other electrode is laid across the divided electrodes. A change in the capacitance between the electrodes due to the reciprocating operation of the plunger is detected, and Since the position is detected, the capacitance between one electrode and the capacitance between the other electrodes increase and decrease complementarily with each other with the movement of the plunger. And the effect of a change in capacitance due to a change in temperature can be reduced.

(F) Embodiment (A) in FIG. 1 shows a piezoelectric actuator as a linear drive actuator, which moves in a casing (c) having front and rear walls (a) and (b) concentrically and along an axis. A plunger (P) as a driven body is freely attached, and three piezoelectric elements (e), (f), and (g) are concentrically arranged on the outer peripheral surface of the plunger (P).

In addition, (i) has its base end fixed to the support member (h), and (j) has its base end fixed to the piezoelectric element for stroke (g) and its front end faces the front and rear walls (a) and (b). It is a cantilevered elastic bridge that extends.

At the tip of the elastic bridge (i) (j), a clamping piezoelectric element (e) (f) is attached to the outer peripheral surface, and the clamp member (k) (l) is fixed to the inner peripheral surface. ing.

Among the piezoelectric elements (e), (f) and (g), the clamping piezoelectric elements (e) and (f) reduce the inner diameter in the state of applying a voltage to clamp the plunger (P),
When no voltage is applied, the inner diameter is increased to release the clamp to the plunger (P).

On the other hand, the stroke piezoelectric element (g) extends in the axial direction on the plunger (P) in a voltage applied state, and contracts in the axial direction on the plunger (P) in a non-voltage applied state.

Next, the piezoelectric actuator (A) having the above configuration
2 to 5 regarding the movement of the plunger (P) by
This will be described with reference to the drawings.

According to a drive program, a voltage is applied to the piezoelectric element (f) from a control device (C) to be described later to clamp the plunger (P) as shown in FIG.
The voltage applied to the plunger (P) is released to release the clamp of the plunger (P).

Next, as shown in FIG. 3, when the voltage of the piezoelectric element (g) is released and contracted, the piezoelectric element (f) moves in the direction of the arrow, and accordingly, the plunger (P) also moves in the direction of the arrow. Moving.

Thereafter, as shown in FIG. 4, a voltage is applied to the piezoelectric element (e) to clamp the plunger (P), and then the applied voltage to the piezoelectric element (f) is released to release the clamp of the plunger (P). Then, when a voltage is applied to the piezoelectric element (g),
The piezoelectric element (g) expands and the piezoelectric element (f) returns to the position shown in FIG.

After that, by repeating the above operation, the plunger (P) can be moved in the form of a worm with a stroke of the order of μm or sub-μm, and various operating devices connected to the tip of the plunger (P) can be precisely operated. Can be done.

The operation of the piezoelectric actuator (A) is controlled by a control device (C) shown in FIG.
Is composed of a microprocessor (MPU), an input / output interface (I) (O), and a memory (M) storing a driving program. The input interface (I) has a function for operating a plunger (P). The switch (Sw) is connected, and the clamp and stroke piezoelectric elements (e), (f), and (g) are connected to the output interface (O) via the drive circuit (D).

When a control command from the switch (Sw) to the plunger (P) is input to the control device (C), a pulse-like driving voltage is output according to the driving program, and the plunger (P) is operated as described above. Can be.

A moving electrode (pm) is provided at the rear end of the plunger (P) on the rear wall (b) of the piezoelectric actuator (A), and is opposed to the moving electrode (pm) and is insulated from the moving electrode (pm). A fixed electrode (ps) is provided, and the capacitance between the fixed electrode (ps) and the moving electrode (pm) is detected and input to the control device.

On the other hand, a routine for calculating the position of the plunger (P) from the capacitance is stored in the memory (M) of the control device (C).

To detect the capacitance between the moving electrode (pm) and the fixed electrode (ps), the following configuration can be considered.

That is, as shown in FIG. 7, an oscillation circuit (C1) in which the capacitance of the gap (G) between the moving electrode (pm) and the fixed electrode (ps) is one of the oscillation constants is configured. The oscillation frequency is converted into a voltage by the FV conversion circuit (C2) and input to the control device (C).

As shown in FIG. 8, an oscillation circuit (C3) having the capacitance of the gap (G) as one of oscillation constants is configured, and the oscillation frequency is directly input to the control device (C).
The frequency is digitally detected (for example, frequency count, etc.) inside the device (C).

The frequency detected in this way is the gap (G)
Is inversely proportional to the capacitance of the gap (G), and inversely proportional to the size of the gap (G), the size of the gap (G), that is, the position of the plunger (P) can be detected.

The above-described routine processes the capacitance data between the moving electrode (pm) and the fixed electrode (ps) input to the control device (C) as described above to calculate the position of the plunger (P). can do.

Using the position of the plunger (P) detected in this manner, the position of the plunger (P) can be controlled by closed loop, and the above-described control can be realized at low cost because no expensive encoder is required. It has the effect of cutting.

As described above, the piezoelectric actuator (A) capable of detecting the position of the plunger (P) can accurately control the same by connecting various devices to the tip of the plunger (P).

FIG. 9 shows an example in which the above-mentioned piezoelectric actuator (A) is applied to the operation control of the diaphragm valve (V) to open and close the valve (V) and adjust the flow rate.

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

In the piezoelectric actuator (B) shown in FIG. 10, a cylindrical moving electrode (pm) is provided on the outer peripheral surface of the rear end of the plunger (P), and a predetermined distance from the moving electrode (pm) is maintained. A cylindrical fixed electrode (ps) fixed to the fixed side of (B) is externally fitted, and the length of the wrapped portion of each electrode (pm) (ps) changes by movement of the plunger (P). Accordingly, the capacitance between the electrodes (pm) (ps) is changed.

In FIG. 11, the moving electrode (pm) and the fixed electrode (ps)
A dielectric material (E) such as a cylindrical alumina ceramic
Is interposed.

The gist of the present invention is to provide a linear drive actuator configured to linearly drive the plunger (P) as described above, in which the plunger (P) is disposed on the moving electrode (pm) and fixed on the fixed side of the actuator. An electrode (ps) is provided so as to face the moving electrode (pm), one of the electrodes is divided and formed, and the other electrode is straddled between the divided electrodes to move the plunger (P) forward and backward. , The change in the capacitance between the electrodes (pm) and (ps) is detected to detect the position of the plunger (P).

That is, as shown in FIG. 12, the first fixed electrode (ps1) in which the fixed electrodes (ps) are
The movable electrode (pm) is opposed to the above-mentioned space, and both ends of the movable electrode (pm) are wrapped with the first and second fixed electrodes (ps1) (ps2), and the plunger (P ), The capacitance between the first fixed electrode (ps1) and the moving electrode (pm) and the capacitance between the second fixed electrode (ps2) and the moving electrode (pm) complement each other. It is configured to increase or decrease.

Therefore, the position of the plunger (P) can be detected from the difference between the two capacitances, the accuracy of position detection can be improved, and the effect of the capacitance change due to temperature change can be reduced. it can.

Contrary to the above, one fixed electrode is provided on the fixed side of the piezoelectric actuator, and a movable electrode composed of the first and second movable electrodes is provided on the plunger, and the difference in capacitance between the electrodes is provided. , The position of the plunger can be detected.

 A dielectric (E) may be provided between the electrodes.

[Brief description of the drawings]

FIG. 1 is an explanatory sectional view of a piezoelectric actuator, FIGS. 2 to 5 are explanatory diagrams showing an operation sequence of the piezoelectric actuator, FIG. 6 is a block diagram showing a configuration of a control device, FIG.
FIG. 9 is a block diagram showing a circuit configuration for detecting capacitance, FIG. 9 is a cross-sectional explanatory diagram of a flow control valve, FIG. 10 is a cross-sectional explanatory diagram of a piezoelectric actuator, FIG. FIG. 12 is an explanatory sectional view of a piezoelectric actuator according to the present invention. (A): Piezoelectric actuator (P): Plunger (pm): Moving electrode (ps): Fixed electrode

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Takenori Fukushima 2-81-1, Honmura, Chigasaki-shi, Kanagawa Prefecture Inside the Toga Kikai Co., Ltd. Chigasaki Plant (72) Takao Yoshida 2-81-1, Motomura, Chigasaki-shi, Kanagawa Prefecture No. Tochiki Co., Ltd. Chigasaki Factory (72) Inventor Kinya 2-8-1, Honmura, Chigasaki-shi, Kanagawa Prefecture Tochiki Co., Ltd. Chigasaki Factory (72) Inventor Mikio Sawai 2-chome Honmura, Chigasaki-shi, Kanagawa No. 1 in the Toga Kiki Co., Ltd. Chigasaki Plant (72) Inventor Keishi Horiuchi 2-81-1, Honmura, Chigasaki-shi, Kanagawa Prefecture Toto Kiki Co., Ltd. Chigasaki Plant (56) References JP-A-62-288782 (JP) JP-A-63-67502 (JP, A) JP-A-63-115706 (JP, U) JP-A-63-75405 (JP, U) (58) nt.Cl. ⁶ , DB name) F16K 31/02 G01B 7/00

Claims (1)

(57) [Claims] In a linear drive actuator configured to linearly drive a plunger (P), a moving electrode (pm) is provided on the plunger (P) and a fixed electrode (ps) is provided on a fixed side of the actuator. The movable electrode (pm) is provided so as to face the electrode, one of the electrodes is divided and formed, and the other electrode is straddled between the divided electrodes. A piezoelectric actuator having a position detecting function, characterized in that a change in capacitance between pm) and (ps) is detected to detect the position of the plunger (P).