Rotary encoder in which an absolute position is defined using reference mark signals produced by each of at least two readheads and method of operating the same
First Claim
1. Rotary encoder apparatus comprising;
- an encoder scale comprising an incremental scale and one or more reference marks; and
an encoder scale reader comprising at least first and second readheads,the first and second readheads being arranged to read the incremental scale and generate incremental signals that vary periodically as the encoder scale rotates relative to the encoder scale reader, the incremental signals providing a measure of an amount of rotation of the encoder scale relative to the encoder scale reader,each of the first and second readheads also producing a reference mark signal when passed over one of said one or more reference marks of the encoder scale during rotation of the encoder scale relative to the encoder scale reader;
wherein the apparatus comprises a reference position setter for determining, as the encoder scale reader is rotated relative to the encoder scale, at least one angularly repeatable reference position of the encoder scale relative to the encoder scale reader,wherein each angularly repeatable reference position is determined using both a first reference mark signal produced by the first readhead and a second reference mark signal subsequently produced by the second readhead, the encoder scale having been rotated relative to the encoder scale reader between the production of the first reference mark signal and the subsequent production of the second reference mark signal.
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Abstract
Rotary encoder apparatus is described that comprises an encoder scale or ring and an encoder scale reader. The encoder scale includes an incremental scale and one or more reference marks. The encoder scale reader comprises at least a first readhead and a second readhead that each produce a reference mark signal when passed over a reference mark of the encoder scale. The apparatus also comprises a reference position setter for determining, as the encoder scale reader is rotated relative to the encoder scale, at least one angularly repeatable reference position of the encoder scale relative to the encoder scale reader using a first reference mark signal produced by the first readhead and second reference mark signal subsequently produced by the second readhead.
9 Citations
32 Claims
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1. Rotary encoder apparatus comprising;
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an encoder scale comprising an incremental scale and one or more reference marks; and an encoder scale reader comprising at least first and second readheads, the first and second readheads being arranged to read the incremental scale and generate incremental signals that vary periodically as the encoder scale rotates relative to the encoder scale reader, the incremental signals providing a measure of an amount of rotation of the encoder scale relative to the encoder scale reader, each of the first and second readheads also producing a reference mark signal when passed over one of said one or more reference marks of the encoder scale during rotation of the encoder scale relative to the encoder scale reader; wherein the apparatus comprises a reference position setter for determining, as the encoder scale reader is rotated relative to the encoder scale, at least one angularly repeatable reference position of the encoder scale relative to the encoder scale reader, wherein each angularly repeatable reference position is determined using both a first reference mark signal produced by the first readhead and a second reference mark signal subsequently produced by the second readhead, the encoder scale having been rotated relative to the encoder scale reader between the production of the first reference mark signal and the subsequent production of the second reference mark signal. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26)
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27. An interface for a rotary encoder, the rotary encoder comprising at least first and second readheads of an encoder scale reader, each readhead being arranged to read an incremental scale of an encoder sale and generate incremental signals that vary periodically as the encoder scale rotates relative to the encoder scale reader, the incremental signals providing a measure of an amount of rotation of the encoder scale relative to the encoder scale reader, each readhead also being arranged to generate a reference mark signal when passed over a reference mark of an associated encoder scale,
wherein the interface is arranged to establish an angularly repeatable reference position of the encoder scale relative to the encoder scale reader using both a first reference mark signal produced by the first readhead and a second reference mark signal subsequently produced by the second readhead, the encoder scale having been rotated relative to the encoder scale reader between the production of the first reference mark signal and the subsequent production of the second reference mark signal.
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28. A method of operating a rotary encoder comprising the steps of:
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(a) taking a rotary encoder having an encoder scale that is moveable relative to an encoder scale reader, the encoder scale reader comprising at least first and second readheads, and the encoder scale comprising a series of incremental marks and at least one reference mark, wherein the first and second readheads are arranged to read the encoder scale and generate incremental signals that vary periodically as the encoder scale rotates relative to the encoder scale reader, the incremental signals providing a measure of an amount of rotation of the encoder scale relative to the encoder scale reader, each of the first and second readheads also producing a reference mark signal when passed over one or more said at least one reference mark of the encoder scale; (b) rotating said encoder scale relative to the encoder scale reader such that a reference mark passes the first readhead thereby generating a first reference mark signal; (c) further rotating said encoder scale relative to the encoder scale reader such that a reference mark passes the second readhead thereby generating a second reference mark signal; and (d) establishing at least one absolute angular reference position of the encoder scale relative to the encoder scale reader, wherein each of the at least one absolute angular reference positions is established from both the first reference mark signal and the second reference mark signal. - View Dependent Claims (29, 30, 31, 32)
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Specification