Absolute optical encoder system

• US 4,445,110 A
• Filed: 07/28/1980
• Issued: 04/24/1984
• Est. Priority Date: 07/28/1980
• Status: Expired due to Term

• Current Assignee: Motion Systems LLC
• Original Assignee: Itek Corp (Northrop Grumman Corporation)
• Inventors: Breslow, Donald H.
• Primary Examiner(s): Sloyan, T. J.
• Application Number:
  US06/173,219
• Time in Patent Office: 1,366 Days
• Field of Search: 340/347 M, 340/347 P, 340/870.29, 250/231 SE, 250/237
• US Class Current: 341/10
• CPC Class Codes: G01D 5/34792 with only digital scales or both digital and incremental scales
• CPC Class Codes: H03M 1/143 in pattern-reading type converters, e.g. having both absolute and incremental tracks on one disc or strip H03M1/16 takes precedence
• CPC Class Codes: H03M 1/26 with weighted coding, i.e. the weight given to a digit depends on the position of the digit within the block or code word, e.g. there is a given radix and the weights are powers of this radix
• CPC Class Codes: H03M 1/285 of the unit Hamming distance type, e.g. Gray code
• CPC Class Codes: H03M 1/303 Circuits or methods for processing the quadrature signals

Abstract

An optical code disc includes a fine track which provides a high resolution signal, at least one V scan natural binary track synchronized to the fine track by lead and lag detectors, and Gray code tracks which provide the most significant bits of the digital output of the encoder system. The number of circuit elements in the multiplier circuitry associated with the fine track are reduced by means of a quadrant switching technique whereby the sinusoidal inputs to the multiplier are repeated through each quadrant of the fine track cycle. The V scan and Gray code tracks are optically multiplexed to reduce the number of leads from the optical detector. The use of both V scan and Gray code tracks minimizes the number of detectors required in the system while maintaining large detector signals from each track. The V scan and Gray code outputs are synchronized by the use of an overlapping bit.

Claims

1. An optical angular encoder system including a code disc having a plurality of concentric optical code tracks thereon, illuminating means for illuminating the code tracks, detecting means for detecting illumination which passes through the code tracks and decoding circuitry for providing an angular output in response to the output of the detecting means, the system characterized by:

the code tracks comprising a fine code track, at least one more significant track encoded for a natural binary output, and at least two most significant coarse tracks encoded for Gray code output;

a plurality of illuminators associated with respective groups of code tracks, each illuminator being optically isolated from those code tracks with which it is not associated;

means for sequentially enabling at least some of the illuminators to optically multiplex code track signals, common detector outputs associated with groups of multiplexed code tracks, and decoder circuitry for demultiplexing the common detector outputs;

multiplier circuitry for providing a multi-bit digital output from sinusoidal outputs of the fine track by deriving a family of phase shifted sinusoids in parallel circuits, converting the family of sinusoids to square waves and logically combining the square waves from parallel circuits, the multiplier circuitry being designed to provide a multi-bit digital output directly from the sinusoidal detector outputs only through one of a plurality of segments of the fine track cycle, there being means for selectively modifying the sinusoidal inputs to the multiplier circuitry such that those inputs are identical though each of said segments of the fine track cycle;

the detecting means associated with the more significant tracks including at least a lead detector and a lag detector, the locations of which are phased with respect to signals from said fine track, and which generate signals which, respectively, lead and lag the signal of the next lower order track, and the decoding circuitry associated with those tracks including means to select either the lead or the lag detector output as a function of the logic state of the next lower order track signal to synchronize each track to the preceding track; and

the decoding circuitry associated with the most significant Gray code tracks including means to synchronize those tracks to the natural binary tracks.