JPH08201107A - Electrostatic capacitance type encoder - Google Patents

Abstract

PURPOSE: To provide a long-life highly reliable electrostatic capacitance type encoder with limited friction of an electrode surface. CONSTITUTION: This electrostatic capacitahce type encoder comprises a stator 1 which has at least two stator electrodes 2 at a fixed interval on the surface of an insulating base body and a rotor or a moving element 3 having a moving element electrode 4 on the surface of the insulating base body to measure a change in the electrostatic capacitance determined by areas of the moving element electrode 4 and the stator electrode 2 as opposed to each other when the stator electrode 2 and the moving element electrode 4 are made to face each other maintaining a fixed interval therebetween. In the electrostatic capacitance type encoder, at least one of the moving element electrode 4 and the stator electrode 2 is buried into polytetrafluoroethylene to be molded integral and the surface of the moving element electrode 4 or the stator electrode 2 is covered with the polytetrafluoroethylene.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a capacitance type encoder for detecting a rotation angle, a position, a speed, etc. of a motor or a linear motor by a capacitance.

[0002]

2. Description of the Related Art As a conventional capacitance type encoder, FIG.
There is a structure shown in (Japanese Patent Laid-Open No. 56-8508). The mover electrode 4 and the stator electrodes 2a and 2b are pattern-printed on the surface of the printed board. The electrode patterns 2a and 2b on the stator are separately electrically connected alternately for each voltage phase, and a voltage is applied. Wiring of the mover electrode is performed on the opposite surface facing the stator electrode through the through hole. When the mover moves in the direction of the arrow, when the mover electrode and the stator electrode face each other, the mover electrode −
The capacitance between the stator electrodes is maximized, and when the mover electrode and the stator electrode do not face each other, the capacitance between the mover electrode and the stator electrode is minimized. The detection principle of the electrostatic capacity encoder is to detect the rotation angle or the moving distance of the moving element from the change of the electrostatic capacity. Further, it is known that an insulating film is formed on the surface of the capacitance type encoder to prevent a short circuit. (Published by the Management Development Center, "Development of new sensor technology, optimal selection and usage")

[0003]

However, when the conventional electrostatic capacity type encoder is attached to the motor or the linear motor, when the load is applied to the motor or the linear motor, the distance between the mover electrode and the stator electrode is reduced due to mechanical play. It may change, the insulating film coated on the mover electrode and the insulating film coated on the stator electrode may come into contact with each other, and may slide between the insulating films. there were. on the other hand,
Although it is easy to consider a method of reducing the friction coefficient between the stator and the mover by forming the insulating film with polytetrafluoroethylene, polytetrafluoroethylene with a low friction coefficient is used in thin film forming technology such as sputtering or plasma polymerization. An all-ethylene film has not been produced. Further, even if an attempt is made to adhere a polytetrafluoroethylene film onto an electrode, polytetrafluoroethylene is originally a material that is difficult to adhere to other materials, and it is difficult to form it on the electrode. Recently, there is a method of surface-treating polytetrafluoroethylene to facilitate adhesion to different materials. However, as the temperature changes, stress due to the difference in thermal expansion between the electrode and polytetrafluoroethylene acts on the adhesive surface, and the polytetrafluoroethylene film may peel off. That is, it is difficult to form polytetrafluoroethylene on the electrode, and it cannot be used for the insulating film on the electrode of the capacitance type encoder. Therefore, it is an object of the present invention to provide a capacitive encoder having a long life and high reliability by reducing friction on the electrode surface.

[0004]

In order to solve the above-mentioned problems, the present invention provides a stator having at least two stator electrodes at regular intervals on the surface of an insulating substrate, and a mover on the surface of the insulating substrate. A rotor or a mover having an electrode, and the stator electrode and the mover electrode are opposed to each other with a fixed space therebetween, and the static electrode is determined by the area where the mover electrode and the stator electrode are opposed to each other. In a capacitance type encoder for measuring a change in capacitance, at least one of the mover electrode or the stator electrode is embedded in polytetrafluoroethylene and integrally molded, and the surface of the mover electrode or the stator electrode is The structure is covered with tetrafluoroethylene.

[0005]

In the electrostatic capacity type encoder of the present invention, since the polytetrafluoroethylene is not coated or adhered on the mover electrode and is continuously connected to the whole mover and integrally molded, the mover and the stator are integrally formed. However, even if they are in contact with each other and a large load is applied, the insulating film is not peeled off as in the prior art. Also, even if the temperature changes and the adhesive force between the electrode and polytetrafluoroethylene disappears,
The polytetrafluoroethylene insulating film on the electrode does not peel off. In addition to these, since polytetrafluoroethylene is used, the slidability between the mover and the stator is extremely good.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view showing the configuration of the capacitance type encoder of the present invention. In the figure, 1 is a stator, 2 is a stator electrode, 3 is a mover, and 4 is a mover electrode. 2 is a plan view of the mover 3, and FIG. 3 is a plan view of the stator 1. The mover 3 has a structure in which the mover electrode 4 is embedded with polytetrafluoroethylene, and was manufactured by the molding method shown in FIG. That is, polytetrafluoroethylene powder (not shown) is uniformly filled in the cylindrical female die 5b of the die 5, and the semicircular mover electrode 4 made of a thin copper plate is placed thereon. Then, a circular polytetrafluoroethylene sheet 6 was placed thereon, and a cylindrical male die 5a was press-fitted and integrally molded by a heating press. The stator electrode 2 is formed in a 90 ° fan shape at diagonal positions by a normal patterning method by etching a copper plate. Now, with the mover electrode 4 and the stator electrodes 2a, 2b facing each other, the stator electrodes 2a, 2b
It was found that when an excitation voltage is applied to the moving element 3 to rotate the moving element 3, the electrostatic capacity changes as shown in FIG. 5, and the element has a function as an encoder. Next, the durability of the capacitance type encoder of the present invention was examined. First, even if this encoder is attached to a motor and a large load is applied to bring the stator 1 and the mover 3 into contact with each other and rotate, the tetrafluoroethylene of the mover electrode 4 of the capacitance type encoder of the present invention peels off. I didn't do it. Furthermore, in order to quantitatively investigate the effect of the capacitance type encoder of the present invention, comparison was made with a conventional encoder. Each of the electrostatic capacity encoder of the present invention and the conventional electrostatic capacity encoder is brought into contact with the moving element 3 and the stator 1, and a static load of ² kg / cm ² is applied to the contact surface so as to be static at a rotational speed of 100 rpm. The capacitance type encoder was rotated, and the time until the mover electrode 4 and the stator electrode 2 were short-circuited was measured. As a test condition, an oil-impregnated polyacetal having a thickness of 100 μm was used as the insulating film for the moving electrode of the conventional electrostatic capacity encoder, and 10% was used as the insulating film for the stator.
0 μm thick polyacetal was used. In the conventional electrostatic capacity type encoder, 70 out of 100 pieces peeled off the insulating film within 1 hour and caused a short circuit, 19 pieces failed in 1 to 2 hours, and all remaining in 3 hours. Broke down.
On the other hand, as a result of testing five capacitance type encoders of the present invention, it took an average of 3004 hours to fail. That is, it was found that the electrostatic capacity encoder of the present invention has a much longer life than the conventional electrostatic capacity encoder. The reason for this is that the polytetrafluoroethylene 6 on the moving element electrode 4 of the capacitance type encoder of the present invention does not exist alone but is continuously connected to the entire moving element 3. . Further, it is considered that the excellent friction property of polytetrafluoroethylene 6 is also the reason for the long life. In addition to the above-mentioned durability test, as a result of performing a heat cycle test at -30 to 80 ° C., in the conventional capacitive encoder, the insulating film was completely peeled off in the heat cycle test of 100 times. The capacitive encoder did not show any damage. In this embodiment, the entire mover electrode 4 is embedded in polytetrafluoroethylene, but the same effect as in this embodiment can be obtained by embedding the stator electrode and performing the same test. Further, if both the stator electrode and the mover electrode are embedded in polytetrafluoroethylene, the life becomes even longer.

[0007]

As described above, according to the present invention, since at least one of the mover electrode and the stator electrode is embedded in polytetrafluoroethylene, the life is extremely long and the reliability is high. There is an effect that it is possible to provide a capacitive encoder having high property.

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of a capacitance type encoder of the present invention.

FIG. 2 is a plan view of a mover of the present invention.

FIG. 3 is a plan view of a stator of the present invention.

FIG. 4 is a perspective view showing a method of molding a moving element according to the present invention.

FIG. 5 is a voltage characteristic diagram showing a capacitance change of the capacitance type encoder of the present invention.

FIG. 6 is a cross-sectional view showing a configuration of a conventional capacitance type encoder.

[Explanation of symbols]

 1: Stator 2, 2a, 2b: Stator electrode 3: Moving element 4: Moving element electrode 5: Mold 5a: Male type 5b: Female type 6: Polytetrafluoroethylene sheet

Claims (1)

[Claims] 1. A stator comprising an insulative base surface having at least two stator electrodes at regular intervals, and a rotor or a mover having an insulative base surface having mover electrodes. In the electrostatic capacity encoder for measuring the capacitance change determined by the area where the mover electrode and the stator electrode are opposed to each other, the mover electrode and the mover electrode are opposed to each other with a constant gap, At least one of the electrode or the stator electrode is embedded in polytetrafluoroethylene and integrally molded, and the surface of the mover electrode or the stator electrode is covered with polytetrafluoroethylene. Capacitive encoder.