JPH05268781A - Position detecting method for electrostatic motor - Google Patents

Abstract

PURPOSE:To provide a position detecting method for electrostatic motor having simple constitution for facilitating downsizing wherein a stator electrode is provided with two functions as a driving electrode and a position detecting sensor and no independent position detector is required. CONSTITUTION:In order to detect the position of the mover 2 in an electrostatic motor, a plurality of stator electrodes 11 are arranged at a predetermined pitch in the moving direction on the surface of a stator 1 and a plurality of mover electrodes 21 are arranged at a predetermined pitch on the surface of a mover 2 while opposing through a micro gap to the stator electrode 11. A rectangular driving voltage and a high frequency exciting voltage are applied, while being superposed, onto the stator electrode 11 and an output voltage corresponding to the variation of capacitance between the stator electrode 11 and the mover electrode 21 due to movement of the mover 2 is detected and employed in the determination of the moving amount of the mover.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for detecting the position of an electrostatic motor that moves a mover by using electrostatic force.

[0002]

2. Description of the Related Art Conventionally, a strip-shaped mover electrode made of a ferroelectric material and an insulator having a low dielectric constant are alternately arranged at equal pitches in the moving direction and are movably supported. , A multi-phase drive power supply, which includes a stator facing the mover electrode through a minute gap and having stator electrodes arranged at a predetermined pitch, and a position detector for detecting the moving amount of the mover on the stator. There has been disclosed an electrostatic motor that drives a mover by sequentially applying a drive voltage to a stator electrode by using an electromagnetic wave (for example, JP-A-62-4).
No. 4079). Here, the position in the moving direction is detected from the outside by a displacement sensor or the like, but at that time, the mover requires a measurement surface such as a sensor target.

[0003]

However, in the method of detecting the amount of movement from the outside, the mover needs to have a measuring surface such as a sensor target, which hinders downsizing of the electrostatic motor and its mounting accuracy. There was a drawback that it took a lot of time to maintain. SUMMARY OF THE INVENTION It is an object of the present invention to provide an electrostatic motor having a simple structure and easily miniaturized without separately providing a position detector for a mover.

[0004]

According to the present invention, a stator in which a plurality of stator electrodes are arranged at a predetermined pitch in a moving direction on a surface is opposed to the stator electrode with a minute gap therebetween. In a method of detecting the position of the mover of an electrostatic motor having a mover in which a plurality of mover electrodes are arranged at a predetermined pitch on the surface, a rectangular wave is formed between the stator electrode and the mover electrode. The driving voltage and the high-frequency excitation voltage are superimposed and applied, and the mover is generated from the output voltage generated by the change in the capacitance of the capacitor formed by the stator electrode and the mover electrode as the mover moves. Is to detect the movement amount of.

[0005]

When the mover moves from an arbitrary position, the facing area between the stator electrode and the mover electrode changes,
A capacitor is formed by the stator electrode and the mover electrode. Therefore, the driving voltage and the high-frequency excitation voltage are applied to the stator electrode of the electrostatic motor in a superimposed manner, and the capacitance of the capacitor changes due to the change in the area where the two electrodes of the stator and the mover face each other. Is detected as a change in the output voltage of the capacitor, and the position of the mover is detected from the amount of change in the output voltage. Therefore, the position of the mover can be detected without specially providing a measurement surface such as a sensor target.

[0006]

Embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a side view showing an embodiment of the present invention, in which a stator electrode 11 is provided on the surface of a stator 1 at a predetermined pitch in the moving direction.
The movable element 2 is provided so as to face the stator electrode 11 via a minute gap, and the surface of the movable element 2 facing the stator electrode 11 is made of a ferroelectric substance alternately at equal intervals. A child electrode 21 and an insulator 22 made of a low dielectric material are arranged in the moving direction. Each stator electrode 11 is connected to each phase of a three-phase power source, and by sequentially energizing each phase, an electrostatic force is sequentially generated in the stator electrode 11 and the mover electrode 21 to move the mover. I am allowed to do it. The voltage applied to each stator electrode 11 is such that the high-frequency excitation voltage V ₂ sin ωt for position detection is superimposed on the three-phase (R, S, T) drive voltage V ₁ (t) and applied. is there. A capacitor having an electrostatic capacity corresponding to the opposing area is formed between each stator electrode 11 and the mover electrode 21.
Since the facing area changes due to the movement, the capacitance C changes. The output voltage V ₃ is output from the change in the capacitance C due to the facing area in each phase, and the output voltage V ₃ is converted into a rectangular wave by using the bandpass filter 4 and the Schmitt trigger circuit 5, and moved as a pulsed voltage. The child 2 is driven. On the other hand, the moving amount Δx is detected by counting the number of pulses of the pulsed voltage output by the pulse counter 6. Here, the principle showing the relationship between the change in the capacitance C and the movement amount of the mover 2 will be described. The applied voltage V ₀ between the stator electrode 11 and the mover electrode 21 is expressed by the following mathematical formula 1.

[0007]

[Equation 1]

The electrostatic energy U at that time is given by the following equation 2 from the capacitance C and the applied voltage V ₀ .

[0009]

[Equation 2]

The electrostatic thrust F when the stator electrode 11 and the mover electrode 21 partially overlap each other is given by the following formula 3 from the law of conservation of energy.

[0011]

[Equation 3]

Here, the electrode length is L, the electrode width facing each other when the stator electrode 11 and the mover electrode 21 partially overlap with each other, x is the length of a minute gap between the stator electrode 11 and the mover electrode 21. Where d is the permittivity and ε is the permittivity of the minute voids, the capacitance C (x) is obtained by the following mathematical formula 4.

[0013]

[Equation 4]

When the electrostatic thrust F is calculated by substituting the equation 4 into the equation 3, the electrostatic thrust F is expressed by the following equation 5 and is constant regardless of the opposing electrode width x.

[0015]

[Equation 5]

Further, by substituting the equation 1 into the equation 5, the electrostatic thrust F is expressed by the following equation 6.

[0017]

[Equation 6]

[0018] Here, since the high frequency excitation voltage V ₂ is used to detect, by setting sufficiently smaller than the drive voltage V ₁ (t), the mover 2 is driven only by the driving voltage V ₁ (t) You can think of it. The position of the mover 2 is detected by utilizing the change in the capacitance C due to the change in the area where the electrodes face each other when the mover 2 moves from an arbitrary position by the movement amount Δx. That is, in order to detect a position with a long stroke, as shown in FIG. 1, the electrodes 3 are considered to be capacitors 3 and the high frequency excitation voltage V ₂ si is applied to all three phases.
By applying nωt, the output voltage V ₃ is output from the change of the capacitance C due to the facing area in each phase. In this case, the output voltage V ₃ is represented by the following Equation 7.

[0019]

[Equation 7]

When rationalization is performed and the absolute value is taken, the output voltage V ₃ is represented as the output voltage V ₄ by the following formulas 8 and 9.

[0021]

[Equation 8]

[0022]

[Equation 9]

Here, although the amount of movement of the mover 2 can be detected by the change of the output voltage V ₄ , only the high frequency component is taken out to improve the detection accuracy. That is, the drive voltage V
The frequency ω of the high-frequency excitation voltage V ₂ sinωt for position detection is made sufficiently large as compared with the response frequency of ₁ (t), the high-frequency component is extracted through the bandpass filter 4, and converted into a rectangular wave using the Schmitt trigger circuit 5. Then, the mover 2 is driven with a pulsed voltage, while the pulsed voltage output is counted by the pulse counter 6 to detect the movement amount Δx. After passing through an appropriate high-pass filter or band-pass filter, the output voltage V ₄ is given as the output voltage V _{5 by the} following formula 10.

[0024]

[Equation 10]

Substituting equation 4 into equation 10, the output voltage V ₅ is expressed as the output voltage V ₆ in the following equation 11. The relationship between the applied voltages V ₁ and V ₂ and the output voltages V ₄ and V ₆ during the movement of the mover 2 is as shown in FIG.

[0026]

[Equation 11]

Here, the opposed electrode width x is represented by the following formula 12 obtained from formula 11.

[0028]

[Equation 12]

Therefore, since the amount of change in the electrode width x facing each other becomes the movement amount Δx, when the output voltage at rest is V ₆₁ and the output voltage at the time of slight movement is V ₆₂ , the movement amount Δx is Equation 13 is given.

[0030]

[Equation 13]

For example, assuming that a three-phase electrostatic motor is used,
, Reference resistance R = 22 MΩ, excitation frequency ω = 10
KHz, electrode length L = 10 mm, electrode width w = 10 μm,
Electrode pitch = 20 μm, high frequency excitation voltage V ₂ = 10 V
The respective output voltages of the three phases are as shown in Fig. 3,
The change in the output voltage when the mover 2 moves by one pitch is shown. Here, the moving distance of the movable element 2 is shown in FIG. 3 at time t _a is 0 .mu.m, time t _b in the moving distance is 5 [mu] m, the output voltage V of the R-phase when the movement distance is stopped respectively 10μm at time t _{c If 66} is V _6a , V _6b and V _6c respectively,
The magnitudes of the output voltages and the positional relationship between the R-phase mover electrode 21 and the stator electrode 11 are shown in FIGS.
As shown in (c). Therefore, the movement distance traveled from time t _a to time t _b is obtained as a value proportional to V _6b -V _6a, the configuration shown in FIG. 1 is obtained by the seek the value in the number of pulses is there. Since the detection voltage for one pitch is repeated during a long stroke movement, the movement distance in a long stroke is detected by converting the magnitude of the output voltage of each phase into a pulse by the above method and counting the number of pulses. can do. In addition, the moving direction can be confirmed by detecting the rising order between the three phases. That is, the three phases R, S, T are detected in this order,
The moving direction of the mover 2 can be detected by the rising order depending on whether the T phase, the S phase, and the R phase are detected in this order. FIG. 3 is a graph showing the output voltage of the R phase, S phase, and T phase with respect to the moving amount when the mover 2 moves. In the case of the solid line, the R phase, S phase, and T phase of the moving direction are shown. It can be confirmed that it moves to the right because it rises in order, and in the case of the broken line, it can be confirmed that it moves to the left because it rises in the order of T phase, S phase, and R phase. Although the electrostatic motor that moves linearly has been described above,
The present invention can also be applied to an electrostatic motor that rotates by forming the stator and the mover in a disk shape or a cylindrical shape.

[0032]

As described above, according to the present invention, the position of the mover can be detected by applying the drive voltage and the high frequency excitation voltage in a superimposed manner to the stator electrode of the electrostatic motor. Therefore, the stator electrode can have two functions of a drive electrode and a position detection sensor, and it is not necessary to separately provide a position detector, and the structure is simple and the effect of facilitating downsizing can be achieved. is there.

[Brief description of drawings]

FIG. 1 is a side sectional view showing an embodiment of the present invention.

FIG. 2 is a graph showing an output waveform of the present invention.

FIG. 3 is an explanatory diagram showing a relationship between an output voltage of each phase and a movement amount.

FIG. 4 is an explanatory diagram showing an output voltage at a moved position of an R phase and a relative positional relationship between a mover and a stator.

[Explanation of symbols]

1 Stator 11 Stator Electrode 2 Mover 21 Mover Electrode 3 Capacitor 4 Band Pass Filter 5 Schmidt Trigger Circuit 6 Pulse Counter

Claims (1)

[Claims] 1. A stator having a plurality of stator electrodes arranged at a predetermined pitch in the moving direction on the surface, and a plurality of mover electrodes on the surface so as to face the stator electrodes with a minute gap therebetween. In the method of detecting the position of the mover of the electrostatic motor having the mover arranged at a predetermined pitch above, a rectangular-wave drive voltage and a high-frequency excitation voltage are provided between the stator electrode and the mover electrode. Is superimposed and applied, and the moving amount of the mover is detected from the output voltage generated by the change in the capacitance of the capacitor formed by the stator electrode and the mover electrode that accompanies the move of the mover. Characteristic electrostatic motor position detection method.