# US 10,768,026 B2 · Optical element > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 10,768,026 B2 - Document ID: US10768026B2 - Status: Granted - Kind: B2 - Application number: 15/925,002 - Filed: 2018-03-19 - Published: 2018-07-26 - Granted: 2020-09-08 - Earliest claimed: 2012-12-20 - Assignees: Renishaw PLC - Applicants: Renishaw PLC - Inventors: Jason Kempton Slack - Web page: https://patentgrep.com/patent/US10768026B2 ## CPC - G01D 5/38: by diffraction gratings - G01D 5/366: {Particular pulse shapes} - G01D: MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR ## Abstract An optical element for generating diffraction orders for an encoder apparatus, in which the optical element includes an array of diffraction features arranged such that the spacing between the centres of adjacent diffraction features varies irregularly from one pair of adjacent features to the next. ## Claims ### Claim 1 An encoder apparatus for determining movement between two relatively moveable parts of an apparatus, the encoder apparatus comprising: a detector; and at least one optical element comprising at least one series of consecutive diffraction features for diffracting electromagnetic radiation from a source into diffraction orders and which are for contributing to the production at the detector of an interference fringe varying with movement between the two parts, wherein the diffraction features in said at least one series are shifted from a nominally regular spacing such that the spacing between the centres of adjacent diffraction features selectively varies irregularly from one pair of adjacent diffraction features to the next so that harmonics in the interference fringe at the detector are reduced compared to a like encoder apparatus with a diffraction grating having a constant spacing between diffraction features. ### Claim 2 (depends on 1) An encoder apparatus as claimed in claim 1, further comprising a readhead including the detector and a diffraction grating, and wherein the encoder apparatus optionally comprises a scale and the diffraction grating is configured to interact with electromagnetic radiation from the scale to effect recombination of diffraction orders at the detector. ### Claim 3 (depends on 2) An encoder apparatus as claimed in claim 2, wherein the readhead's diffraction grating comprises the at least one optical element. ### Claim 4 (depends on 1) An encoder apparatus as claimed in claim 1, wherein the encoder apparatus comprises a scale that includes the at least one optical element. ### Claim 5 (depends on 3) An encoder apparatus as claimed in claim 3, wherein the scale comprises a reference mark between two series of consecutive diffraction features. ### Claim 6 (depends on 2) An encoder apparatus as claimed in claim 2, wherein a range of variation in the spacing between the centres of adjacent diffraction features in said at least one series of diffraction features is not less than 1/200th of the average period of the diffraction grating's features. ### Claim 7 (depends on 1) An encoder apparatus as claimed in claim 1, wherein the diffraction features are arranged such that a ratio of the intensity of the 1st diffraction order to the 5th diffraction order is at least 100:1. ### Claim 8 (depends on 1) An encoder apparatus as claimed in claim 1, wherein the diffraction features are arranged such that a ratio of the intensity of the 1st diffraction order to the 7th diffraction order is at least 150:1. ### Claim 9 (depends on 1) An encoder apparatus as claimed in claim 1, wherein the spacing between adjacent diffraction features are spaced so that the signal output by the detector is substantially harmonic free. ### Claim 10 (depends on 1) An encoder apparatus as claimed in claim 1, wherein the at least one series of diffraction features is repeated at least once along the length of the optical element. ### Claim 11 (depends on 1) An encoder apparatus as claimed in claim 1, wherein the at least one series of diffraction features comprises at least five diffraction features. ### Claim 12 (depends on 1) An encoder apparatus as claimed claim 1, wherein the spacing between the centres of adjacent diffraction features varies irregularly from one pair of adjacent diffraction features to the next along the entire length of the optical element. ### Claim 13 A readhead for an encoder apparatus comprising a detector and a diffraction grating comprising at least one series of consecutive diffraction features for diffracting electromagnetic radiation from a source into diffraction orders and which contribute to the production of an interference fringe at the detector, wherein the diffraction features in said at least one series are shifted from a nominally regular spacing such that the spacing between the centres of adjacent diffraction features selectively varies irregularly from one pair of adjacent diffraction features to the next so that harmonics in the interference fringe at the detector are reduced compared to a like readhead with a diffraction grating having a constant spacing between diffraction features. ### Claim 14 (depends on 13) A readhead as claimed in claim 13, in which a range of variation in the spacing between the centres of adjacent diffraction features is not less than 1/200th of the average period of the diffraction grating's features. ### Claim 15 (depends on 13) A readhead as claimed in claim 13, in which the diffraction features are arranged such that the ratio of the intensity of the 1st diffraction order to the 5th diffraction order is at least 100:1. ### Claim 16 (depends on 13) A readhead as claimed in claim 13, in which the diffraction features are arranged such that the ratio of the intensity of the 1st diffraction order to the 7th diffraction order is at least 150:1. ### Claim 17 (depends on 13) A readhead as claimed in claim 13, wherein the spacing between adjacent diffraction features are spaced so that the signal output by the detector is substantially harmonic free.