Direction sensitive optical shaft encoder

• US 4,827,123 A
• Filed: 11/07/1988
• Issued: 05/02/1989
• Est. Priority Date: 04/11/1986
• Status: Expired due to Term

• Current Assignee: Itron, Inc.
• Original Assignee: Sangamo Weston, Inc. (Atos SE)
• Inventors: Gray, Donald E.
• Primary Examiner(s): Westin, Edward P.
• Assistant Examiner(s): Shami, Khaled
• Application Number:
  US07/268,615
• Time in Patent Office: 176 Days
• Field of Search: 250/231 SE, 250/237 G, 356/395, 33/125 C, 341/13, 341/97, 324/175
• US Class Current: 250/231.14
• CPC Class Codes: G01P 13/045 with speed indication
• CPC Class Codes: H03M 1/1076 Detection or location of converter hardware failure, e.g. power supply failure, open or short circuit
• CPC Class Codes: H03M 1/305 for detecting the direction of movement

Abstract

A direction sensitive optical shaft encoder includes an optical shutter disk mounted to a shaft for rotation therewith, the optical shutter disk bearing at least first and second radially concentric tracks having alternating light transmissive and light blocking areas formed thereon. The light transmissive and light blocking areas of one track are angularly offset with respect to the light transmissive and light blocking areas of an adjacent track. A pair of light emitters and light detectors are disposed on opposite sides of the optical shutter disk and aligned with the first and second concentric tracks, respectively. Because the pattern of light transmissive and light blocking areas on the two tracks are angularly offset, the output of the light detectors follows a unique pattern which is dependent upon the direction of rotation of the optical shutter. The frequency of repetition of the pattern of outputs by the light detectors is indicative of the speed of rotation of the optical shutter. A suitably programmed microprocessor can be used to detect the frequency and pattern of outputs of the light detectors to determine the angular speed of rotation of the optical shutter and its direction of rotation. If the pattern of detector outputs does not follow an expected pattern an alarm condition is generated indicative of a failure of one of the light emitters and/or light detectors or possible tampering with the optical shutter. The optical shutter may be used, for example, to determine the angular speed and direction of rotation of the eddy disk of an electricity meter.

Claims

1. A direction sensitive optical encoder comprising:

(a) a rotatable optical shutter, the shutter having first and second radially concentric tracks each of said tracks having a respective identical series of alternating light transmissive and light blocking areas formed thereon, the series of light transmissive and light blocking areas of one track being angularly offset with respect to the series of light transmissive and light blocking areas of the other track, there being a like number of light transmissive and light blocking areas on each of said tracks;

(b) first illuminating means disposed on a first side of the optical shutter and aligned with the first track, for illuminating the area of the first concentric track;

(c) second illuminating means disposed on a second side of the optical shutter and aligned with the second track, for illuminating the area of the second concentric track;

(d) first light detector means disposed on the second side of the optical shutter opposite said first illuminating means and aligned with said first concentric track;

(e) second light detector means disposed on the first side of the optical shutter opposite said second illuminating means and aligned with said second concentric track;

(f) means for detecting the frequency and pattern of outputs of said first and second light detector means in response solely to illumination passing through the light transmissive areas of the tracks of the optical shutter from said first and second illuminating means, said light transmissive and light blocking areas of said concentric tracks being arranged in a disposition such that the outputs of the first and second light detector means change state in a unique pattern as the optical shutter is rotated past said illuminating means and said light detector means;

(g) means for detecting whether the detected pattern of outputs of the light detectors follows a predetermined order; and

(h) means for generating an alarm condition if said predetermined order is not detected, wherein the pattern of outputs of the first and second light detector means is indicative of the direction of rotation of the optical shutter, and the frequency of repetition of said predetermined pattern of outputs is indicative of the speed of rotation of the optical shutter.

2. The optical encoder of claim 1 wherein the optical shutter is a disk.

3. The optical encoder of claim 1 wherein the optical shutter is mounted to a shaft for rotation therewith.

4. The optical encoder of claim 1 wherein the pattern of light transmissive and light blocking areas are arranged such that the outputs of the first and second light detectors change state in accordance with a Gray Code.