Absolute encoder using interpolation to obtain high resolution

• US 5,252,825 A
• Filed: 07/11/1991
• Issued: 10/12/1993
• Est. Priority Date: 07/18/1990
• Status: Expired due to Term

• Current Assignee: Nikon Corporation
• Original Assignee: Nikon Corporation
• Inventors: Matsumoto, Tsuyoshi, Imai, Motokatsu, Ohno, Koh
• Primary Examiner(s): Willis, Davis L.
• Assistant Examiner(s): Pham, Hoa Q.
• Application Number:
  US07/728,269
• Time in Patent Office: 824 Days
• Field of Search: 250/231.14, 250/231.16, 250/231.18, 250/237 G, 341/13, 341/11, 356/375, 356/373
• US Class Current: 250/231.18
• 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 1/203 using an analogue interpolation circuit
• 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 1/30 incremental
• CPC Class Codes: H03M 1/303 Circuits or methods for processing the quadrature signals

Abstract

An absolute encoder device comprises a code plate having a 1-track type absolute pattern whose minimum reading unit length is λ, a first incremental pattern with a pitch λ, and a second incremental pattern with pitch 2^-n λ. The device also comprises a detector section, which is movable relative to the code plate, which includes a detector detecting the absolute pattern and obtaining an absolute pattern signal, a detector detecting a first incremental pattern and obtaining a first incremental signal, and a detector detecting a second incremental pattern and obtaining a second incremental pattern signal. A shorter cyclic incremental signal is generated from the first incremental signal by interpolating and the shorter cyclic signal is synchronized with the second incremental signal. The absolute pattern signal, the second incremental signal and the synchronized first incremental signal represent the relative positional relationship between the code plate and the detector section.

Claims

1. An absolute encoder comprising:

a code plate having a 1-track type absolute pattern whose minimum read unit length is λ

, a first incremental pattern with a pitch λ

, and a second incremental pattern with a pitch 2^-n λ

, each of which patterns is formed on said code plate;

a detector section including means for detecting the absolute pattern and thereby obtain an absolute pattern signal, means for detecting said first incremental pattern and thereby obtain a first incremental signal, and means for detecting said second incremental pattern and thereby obtain a second incremental signal, said detector section being movable relative to said code plate;

first interpolation means for producing, by interpolating said first incremental signal, an absolute position signal indicating an absolute position within one pitch of said first incremental signal, minimum read unit of said absolute position signal being shorter than the pitch 2^-n λ

of said second incremental signal; and

synchronization means for synchronizing said absolute position signal obtained by said first interpolation means to said second incremental signal and thereby obtain a synchronized absolute position signal;

wherein said absolute pattern signal, said second incremental signal and said synchronized absolute position signal indicate a relative positional relationship between said code plate and said detector section.