JP2844726B2 - 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 element for stroke is fixed to a fixed portion, a piezoelectric element for clamping is mounted on the other side of the same element, and each piezoelectric element is driven by pulses. There is a piezoelectric actuator in which a voltage is applied, a plunger is clamped by a clamping piezoelectric element, and a stroke piezoelectric element is expanded and contracted to largely move the plunger.

The operation control of the piezoelectric actuator is performed by open-loop control in consideration that the amount of movement of the plunger is substantially proportional to the amount of charge applied to the stroke piezoelectric element and the number of pulses.

However, in the operation of the piezoelectric actuator, 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 generate a large integration error, and as a result, the plunger moves forward and backward. Cannot be performed accurately.

Therefore, as a means for solving this problem, a limit switch or a photo sensor is disposed at the stroke end position of the plunger, and when these limit switches and sensors detect the plunger, the position data of the plunger is updated. It is conceivable to detect the plunger position by connecting an encoder to the plunger or to update the plunger position data.

(C) Problems to be Solved by the Invention However, in the position detecting means using the limit 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. There is a drawback that if the operation is repeated, errors gradually accumulate.

In particular, in the case of using a limit switch, there is a disadvantage that the position where the plunger is detected in the forward / backward movement 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 a disadvantage that errors are accumulated unless the position is frequently calibrated. Calibration is not necessary, but very expensive.

In addition, limit switches and encoders require a considerable amount of additional mounting space, resulting in an increase in the size of the piezoelectric actuator structure.

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

(D) Means for Solving the Problems The present invention relates to a linear drive type piezoelectric actuator configured to linearly drive a plunger, wherein a moving electrode is mounted on the plunger and a fixed electrode is mounted on a fixed side of the piezoelectric actuator. Attach, make both electrodes face each other, detect the change in capacitance between each electrode due to the plunger's reciprocating operation, calculate the position of the plunger based on the detected value, and move the moving electrode to the cylinder Another object of the present invention is to provide a piezoelectric actuator having a position detecting function, wherein the piezoelectric actuator is formed from a shape and can be fitted and attached to a moving electrode mounting portion of a plunger.

Further, according to the present invention, in the above configuration, the moving electrode mounting portion of the plunger is reduced in diameter from other portions to provide a step portion, and the moving electrode is moved while one end of the moving electrode is in contact with the step portion. There is also a feature in the configuration attached to the electrode attachment portion.

(E) Function / Effect In the present invention, when the plunger moves forward and backward, the capacitance between both electrodes changes. Therefore, the position of the plunger is detected from the change in the capacitance. Therefore, regardless of the position of the plunger, the position can always be detected, and the problem that the position of the plunger can be detected only when the conventional plunger reaches the stroke end can be solved.

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

Furthermore, since the movable electrode is formed from a cylindrical body and can be fitted and attached to the reduced-diameter movable electrode attaching portion of the plunger, the attaching operation of the movable electrode can be performed easily, quickly and reliably. The individual difference of the plunger with an electrode can be eliminated, and the controllability of the plunger advance / retreat movement by the microcomputer or the like can be improved.

In addition, since the movable electrode is formed from a cylindrical body and can be fitted and attached to the reduced-diameter movable electrode mounting portion of the plunger, the movable electrode mounting space can be minimized, and the control function can be improved. Meanwhile, the structure of the piezoelectric actuator can be kept as compact as possible.

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

In FIG. 1, A denotes a piezoelectric actuator as a linear drive actuator, and a plunger P as a driven body is provided concentrically and freely forward and backward along a shaft wash in a casing c having front and rear walls a and b. Three piezoelectric elements e, f, and g are arranged concentrically on the outer peripheral surface.

In addition, i is a cantilever-like elastic bridge whose base end is fixed to the support member h and j is fixed to its base end to the piezoelectric element g for stroke and whose front end extends toward the front and rear walls a and b. .

At the ends of the elastic bridges i, j, clamping piezoelectric elements e, f are attached to the outer peripheral surface, and clamp members k, l are fixed to the inner peripheral surface.

Among the piezoelectric elements e, f, g, the clamping element e, f clamps the plunger P by reducing the inner diameter in the voltage applied state and expands the inner diameter in the non-voltage applied state. 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 the voltage applied state, and contracts in the axial direction on the plunger P in the non-voltage applied state.

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

From a control device C described later, according to a drive program,
As shown in FIG. 2, a voltage is applied to the piezoelectric element f to clamp the plunger P, and the application of the voltage to the piezoelectric element e 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,
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, and then the applied voltage to the piezoelectric element f is released to release the clamp of the plunger P,
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.

Thereafter, by repeating the above-described operation, the plunger P can be moved like a scale with a stroke of the order of μm or subordination μm, and the various actuators connected to the tip of the plunger P can be operated precisely. You can do it.

The operation of the voltage actuator A is controlled by a control device C shown in FIG. 6, and the control device C is constituted by a microprocessor MPU, input / output interfaces I and O, and a memory M storing a drive program. Yes,
A switch Sw for operating a program is connected to the input interface I, and piezoelectric elements e, f, g for clamping and stroke are connected to the output interface O via a drive circuit D.

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

The present invention provides a plunger position sensor structure for accurately and reliably controlling the movement of the plunger P.
This is a gist thereof, and the structure will be specifically described below.

That is, as shown in FIG. 1 and FIG. 7, the piezoelectric actuator A has a cylindrical fixed electrode ps attached to the rear wall b and a rear end of the plunger P facing the fixed electrode ps. A moving electrode pm formed of a cylindrical body having an outer diameter smaller than the inner diameter of the fixed electrode ps is mounted on the moving electrode mounting portion m formed on the outer peripheral surface.

The movable electrode pm is partially disposed concentrically, that is, in the overlapped state within the fixed electrode ps, and has an annular shape for insulating between the fixed electrode ps and the movable electrode pm. A space is formed and constitutes a capacitor.

In such a configuration, the length of the overlap portion of the movable electrode pm with respect to the fixed electrode ps changes due to the movement of the plunger P in the axial direction, and the change in the amount of overlap also changes the capacitance of the capacitor.

Next, with reference to FIG. 7, a configuration for detecting the above-described change in capacitance and sending a detection output to the control device C will be described.

That is, as shown in FIG. 7, the oscillation circuit C1 is configured with the capacitance of the overlapping portion of the movable electrode pm, the fixed electrode ps and the overlap portion as one of the oscillation constants, and the oscillation frequency is applied to the voltage by the FV conversion circuit C2. , And input to the control device C.

Since the frequency thus detected is inversely proportional to the capacitance of the overlap portion and inversely proportional to the length of the overlap portion, the length of the overlap portion, that is, the position of the plunger P is detected. can do.

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

First, when the plunger P moves in one of the axial directions by applying a voltage to the piezoelectric elements e, f, and g, the amount of overlap between the moving electrode pm and the fixed electrode ps forming a capacitor, that is, both electrodes The capacitance between ps and pm changes.

The changing capacitance between the fixed electrode ps and the moving electrode pm is stored in a routine for calculating the position of the plunger P from the capacitance via the oscillation circuit C1 and the FV conversion circuit C2 described above. This is input to the control device C.

The position of the plunger P can be calculated by processing the capacitance data between the moving electrode pm and the fixed electrode ps input to the control device C as described above by the above-described routine.

Using the position of the plunger P detected in this way, the position of the plunger P can be controlled in a closed loop, and the above-mentioned control can be realized at low cost because no expensive encoder is required. Have.

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.

Further, in the present embodiment, the moving electrode pm is formed from a cylindrical body, and is configured to be fitted into the moving electrode mounting portion m having the reduced diameter of the plunger P.
This can be performed quickly and reliably, the individual difference of the plunger P with an electrode can be eliminated, and the controllability of the plunger advance / retreat movement by the microcomputer or the like can be enhanced. Further, the space for mounting the moving electrode pm can be minimized, and the control function can be improved, while the structure of the piezoelectric actuator A can be kept as compact as possible.

Further, as shown in FIG. 8, an oscillation circuit C3 in which the capacitance of the overlap portion is one of oscillation constants is configured,
The oscillation frequency is directly input to the control device C, and the control device C
Digitally inside (eg frequency counting, etc.)
The frequency may be detected.

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

In the figure, 1 is a valve body, 2 is an outflow passage, 3 is an inflow passage, 4 is a main toilet seat, 5 is a main valve body, 6 is a pilot valve seat, 7 is a diaphragm, 8 is an orifice, and 9 is a tip of a plunger P. It shows a pilot valve body connected continuously, and since the position of the plunger P is always detected, the position of the pilot 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.

FIG. 10 shows a second embodiment, in which a dielectric E such as a cylindrical alumina ceramic is opened between a moving electrode pm and a fixed electrode ps which are configured substantially in the same manner as the first embodiment. Thus, the same operation and effect as those of the second embodiment can be obtained.

In FIG. 11 shows a third embodiment, constituted by a fixed electrode ps and the first fixed electrode ps ₁ which is arranged to hold a predetermined distance between the second fixed electrode ps _2, the interval moving electrode pm And confront
Both ends of the movable electrode pm overlap with the first and second fixed electrodes ps ₁ and ps _2, and the capacitance between the first fixed electrode ps ₁ and the movable electrode pm and the second fixed Electrode ps ₂
And the capacitance between the moving electrode pm and the moving electrode pm are configured to increase and decrease in a complementary manner so that the position of the plunger P can be detected from the difference between the two capacitances. And the effect of the change in capacitance due to temperature change is reduced.

Although not shown, one fixed electrode ps is provided on the fixed side of the piezoelectric actuator A in a manner opposite to the above, and the plunger P
In addition, a movable electrode pm composed of the first and second movable electrodes may be provided, and the position of the plunger P may be detected from a difference in capacitance between the electrodes.

Also, in the third embodiment, the same dielectric E as in the second embodiment can be provided.

[Brief description of the drawings]

FIG. 1 is a cross-sectional explanatory view of a piezoelectric actuator having a position detecting function according to the present invention, FIGS. 2 to 5 are explanatory views showing an operation sequence of the piezoelectric actuator, and FIG. 6 is a block diagram showing a configuration of a control device. FIG. 7, FIG. 7 and FIG. 8 are block diagrams showing a circuit configuration for detecting the capacitance, FIG. 9 is a cross-sectional explanatory view of the flow regulating valve, FIG. 10 is a cross-sectional explanatory view of the second embodiment, FIG. FIG. 6 is an explanatory sectional view of the third embodiment. In the figure, A: Piezoelectric actuator P: Plunger pm: Moving electrode ps: Fixed electrode m: Moving electrode mounting part

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Takanori Matsuno 2-8-1, Honmura, Chigasaki-shi, Kanagawa Prefecture Inside the Toga Kikai Co., Ltd. Chigasaki Plant (72) Inventor Keishi Horiuchi 2-81-1, Honmura, Chigasaki-shi, Kanagawa Prefecture No. Toga Kikai Co., Ltd. Chigasaki Plant (58) Fields surveyed (Int. Cl. ⁶ , DB name) H01L 41/00-41/26

Claims (2)

(57) [Claims] A linear drive type piezoelectric actuator configured to linearly drive a plunger (P), wherein a moving electrode (pm) is mounted on the plunger (P) and a fixed electrode (ps) is mounted on a fixed side of the piezoelectric actuator. ), Make both electrodes (pm) (ps) face each other, and plunger (P)
It is configured to detect a change in the capacitance between the electrodes (pm) and (ps) due to the forward / backward movement of the plunger and calculate the position of the plunger (P) based on the detected value. ) Is formed from a cylindrical body, and can be fitted and mounted on the moving electrode mounting portion (m) of the plunger (P). 2. A moving electrode mounting portion (m) of a plunger (P).
Of the moving electrode (pm) is attached to the moving electrode mounting part (m) in a state where one end of the moving electrode (pm) is in contact with the step part by reducing the diameter of the moving electrode (pm) from the other part. The piezoelectric actuator according to claim 1, wherein the piezoelectric actuator has a position detecting function.