Variable capacitance type encoder

• US 4,879,552 A
• Filed: 04/20/1988
• Issued: 11/07/1989
• Est. Priority Date: 05/23/1985
• Status: Expired due to Term

• Current Assignee: Mitutoyo Mfg. Co., Ltd.
• Original Assignee: Mitutoyo Mfg. Co., Ltd.
• Inventors: Arai, Yoshihiro, Sasaki, Kouji, Ohsaki, Takanori
• Primary Examiner(s): Moore, David K.
• Assistant Examiner(s): Oberley, Alvin
• Application Number:
  US07/185,348
• Time in Patent Office: 566 Days
• Field of Search: 340/870.37, 340/347 M, 340/562, 324/61 R, 324/60 R, 324/60 C
• US Class Current: 340/870.37
• CPC Class Codes: G01B 7/003 for measuring position, not involving coordinate determination coordinate measuring G01B7/004
• CPC Class Codes: G01D 5/2415 adapted for encoders

Abstract

Disclosed is a variable capacitance type encoder for measuring the length of an object to be measured on the basis of the amount of a probe which is brought into contact with the object. The amount of the movement of the probe is detected by the variation of electrostatic capacity between a rotary disc which is secured to the shaft, e.g., threaded shaft of the probe, and fixed plates which are secured to a baseplate so as to be opposed to the rotary disc. Two fixed plates are opposed to the rotary disc, and at least one fixed plate is provided with first and second transmitting electrodes composed of a pluarlity of electrode elements to which voltages of different phases are applied and which are annularly arranged at regular intervals in the circumferential direction of the fixed plate. The phase difference between the voltages which are applied to both transmitting electrodes is 180°. On the other hand, the rotary disc is provided with first and second receiving electrodes for receiving signals of a common phase by electrostatic coupling with both transmitting electrodes. Each fixed plate is provided with an output electrode which electrostatically couples with the respective receiving electrode for fetching a signal through electrostatic coupling.

Claims

1. A variable capacitance type encoder comprising:

a rotary disc which is rotatably mounted on a frame body and rotates in accordance with the amount of movement of a probe; and

first and second fixed plates which are secured to said frame body such as to be opposed to each other with said rotary disc therebetween;

wherein at least one of said first and second fixed plates is provided with a first transmitting electrode composed of a plurality of consecutive electrode elements to which alternating voltages of different phases are applied and which are annularly arranged at regular intervals in the circumferential direction of said at least one of said fixed plates;

at least one of said first and second fixed plates is provided with a second transmitting electrode which is composed of a plurality of consecutive electrode elements aligned in the radial direction, with respect to the center of said at least one fixed plate, with a corresponding electrode of said first transmitting electrode and to each of said second transmitting electrode is applied an alternating voltage 180°

out-of-phase with respect to that applied to its corresponding electrode element of said first transmitting electrode and which are annularly arranged at regular intervals in the circumferential direction of said at least one of said fixed plates;

wherein said rotary disc is provided with first and second receiving electrodes which are opposed to a plurality of said consecutive first and second transmitting electrodes, respectively, and which receive signals of a common phase by electrostatic coupling, said first and second receiving electrodes being disposed at positions which are spaced from each other at a predetermined phase interval in terms of mechanical angle with respect to the center of rotation;

wherein an output electrode is provided on a surface of at least one of said fixed plates for fetching the receiving signals from said first and second receiving electrodes, whereby the rotary displacement of the rotary disc is detected on the basis of the output signal of said output electrode which varies in accordance with the rotation of said rotary disc;

wherein said first fixed plate is provided with said first transmitting electrode composed of said plurality of electrode elements to which alternating voltages of different phases are applied and which are annularly arranged at regular intervals in the circumferential direction of said first fixed plate, and said second transmitting electrode composed of said plurality of electrode elements to each of which an alternating voltage 180°

out of phase with respect to that applied to each electrode element of said first transmitting electrode and which are annularly arranged on the inside of said first transmitting electrode at regular intervals in the circumferential direction of said first fixed plate; and

wherein the electrode elements of the first and second transmitting electrodes and the first and second receiving electrodes each form concentric rings with one on the outer peripheral side of a surface of said first fixed plate and other on the inner peripheral side of said surface;

whereby displacement of the rotary disk is detected precisely without being effected by eccentricity, whirling or offset which may exist among the fixed plates and rotary disk.

2. A variable capacitance type encoder according to claim 1, wherein said rotary disk is provided with a coupling electrode which is electrically coupled with said first and second receiving electrodes and is opposed to said second fixed plate;

and

said second fixed plate is provided with said output electrode which is opposed to said coupling electrode.

3. An encoder according to claim 2, wherein

said first transmitting electrode is composed of 16 electrode elements to each of which an alternating voltage 45°

out-of-phase with respect to each other is applied; and

said second transmitting electrode is composed of 16 electrode elements to each of which said

alternating voltage 180°

out-of-phase with respect to that applied to the electrode element of said first transmitting electrode is applied.

4. An encoder according to claim 3, wherein

said first receiving electrode is composed of two electrode elements which are disposed on the surface of said rotary disc at diametrically opposite positions with respect to the center of rotation and each of which is so constructed as to be opposed to four consecutive electrode elements of said first transmitting electrodes;

and

said second receiving electrode is composed of two electrode elements which are disposed on the surface of said rotary disc at diametrically opposite positions with respect to the center of rotation which are spaced at a 90°

phase interval, and each of which is so constructed as to be opposed to four consecutive electrode elements of said second transmitting electrodes.

5. A variable capacitance encoder comprising:

a rotary disc which is rotatably mounted on a frame body and rotates in accordance with the amount of movement of a probe; and

first second fixed plates which are secured to said frame body such as to be opposed to each other with said rotary disc therebetween;

wherein at least one of said first and second fixed plates is provided with a first transmitting electrode composed of a plurality of consecutive electrode elements to which alternating voltages of different phases are applied and which are annularly arranged at regular intervals in the circumferential direction of said at least one of said fixed plates;

at least one of said first and second fixed plates is provided with a second transmitting electrode which is composed of a plurality of consecutive electrode elements aligned in the radial direction, with respect to the center of said at least one of said fixed plates, with a corresponding electrode of said first transmitting electrode and to each of said second transmitting electrodes is applied an alternating voltage 180°

out-of-phase with respect to that applied to its corresponding electrode element of said first transmitting electrode and which are annularly arranged at regular intervals in the circumferential direction of said at least one of said fixed plates;

wherein an output electrode is provided on a surface of at least one of said fixed plates;

wherein said first fixed plate is provided with said first transmitting electrode composed of said plurality of electrode elements to which alternating voltages of different phases are applied and which are annularly arranged at regular intervals in the circumferential direction of said first fixed plate, and said second transmitting electrode composed of said plurality of electrode elements to each of which an alternating voltage 180°

out of phase with respect to that applied to each electrode element of said first transmitting electrode and which are annularly arranged on the inside of said first transmitting electrode at regular intervals in the circumferential direction of said first fixed plate;

wherein said second fixed plate is provided with said output electrode which is provided extendingly in the radial direction so as to be opposed to both of said first transmitting electrode and said second transmitting electrode;

wherein said rotary disk is provided with a shielding portion which allows an electrostatic coupling only between predetermined electrode elements of said first and second transmitting electrodes to which alternating voltages of a common phase are applied and said output electrode, and shields the other electrode elements,

wherein said output electrode is for fetching the receiving signal from non-shielded portions of said first and second transmitting electrodes, whereby the rotary displacement of the rotary disk is detected on the basis of the output signal of said output electrode which is varies in accordance with the rotation of said rotary disk; and

wherein the electrode elements of the first and second transmitting electrodes form concentric rings with one on the outer peripheral side of a surface of said first fixed plate and the other on the inner peripheral side of said surface;

whereby displacement of the rotary disk is detected precisely without being effected by eccentricity, whirling or offset which may exist among the fixed plates and the rotary disk.