Optical position sensor

• US 5,973,320 A
• Filed: 12/10/1997
• Issued: 10/26/1999
• Est. Priority Date: 12/25/1996
• Status: Expired due to Term

• Current Assignee: Harmonic Drive Systems Inc.
• Original Assignee: Harmonic Drive Systems Inc.
• Inventors: Maruyama, Toshiki, Akahane, Akira, Asawa, Hideo
• Primary Examiner(s): Westin, Edward P.
• Assistant Examiner(s): Luu, Thanh X.
• Application Number:
  US08/988,535
• Time in Patent Office: 685 Days
• Field of Search: 250/231.13, 250/231.14, 250/231.18, 250/214 C, 250/214 PR, 356/141.4, 356/141.5
• US Class Current: 250/231.13
• CPC Class Codes: G01B 11/26 for measuring angles or tapers; for testing the alignment of axes
• CPC Class Codes: G01D 5/2449 using hard-stored calibration data
• CPC Class Codes: G01D 5/3473 Circular or rotary encoders

Abstract

An optical position sensor comprises a linearity correction circuit 20 having ROM 22 in which a corresponding table between compensation values and respective rotational angular position of a rotational disk 51. The compensation values are obtained such that an actual relationship is measured between the rotational angular positions of the rotational disk 51 and the output B of a semiconductor position sensing device 54, deviation of the output B of the device 54 from a predetermined linearity relationship (A) is calculated, and compensation values are determined for eliminating the deviation of the output B of the device 54 at respective rotational angular positions of the rotational disk 51. The linearity correction circuit 20 retrieves a compensation value E from ROM 22 based on the output B of the device 54, and compensates the output A so as to produce the sensing output E which has a linearity relationship to the rotational angle of the rotational disk 51.

Claims

1. An optical position sensor which comprises:

a light emitting means, a light receiving means, and a rotational disk arranged between the light emitting and light receiving means and formed with a spiral slit encompassing a prescribed angular range, wherein a light emitted from the light emitting means and passed through the spiral slit is received by a light receiving surface of the light receiving means, a position where the light is received on the light receiving surface moves in a radial direction of the rotational disk in accordance with a rotational angle of the rotational disk, thereby producing a sensing output corresponding to the rotational angle of the rotational disk;

a linearity correction circuit for compensating an output from the light receiving means so as to establish a linearity relationship between the sensing output and the rotational angle of the rotational disk;

the linearity correction circuit has a memory means for storing a corresponding table in which compensation values are assigned to respective rotational angular positions of the rotational disk and for generating one of the compensation values in response to the output from the light receiving means; and

the compensation values are obtained by measuring an actual relationship between the rotational angle of the rotational disk and the output of the light receiving means, calculating deviation of the output of the light receiving means from a predetermined linearity relationship between the rotational angle of the rotational disk and the output of the light receiving means, and determining compensation values for eliminating the deviation of the output of the light receiving means at respective rotational angular positions of the rotational disk, wherein

the linearity correction circuit retrieves a compensation value from the memory means based on the output of the light receiving means, and compensates the output of the light receiving means so as to produce the sensing output which has a linearity relationship to the rotational angle of the rotational disk.

2. An optical position sensor according to claim 1, wherein the light receiving means comprises a semiconductor position sensing device which has a light receiving surface arranged in a radial direction of the rotational disk, output current signals from both ends of which varies in an inversely proportional relationship with each other in responsive of a light receiving position on the light receiving surface.