Displacement measuring apparatus and method
US4636076A · kind A · utility
Assignee
Inventor
Key dates
| Filing date | Jul 30, 1984 |
| Grant date | Jan 13, 1987 |
| Priority date | — |
| Expiry date | Jul 30, 2004 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG01D5/38
- WIPO fieldMeasurement
- WIPO sectorInstruments
Abstract
Apparatus for measuring displacement comprises a member, such as a reading head, which carries a stepped index diffraction grating (14) and is movable with respect to a reflective scale grating (16). The head also carries a source (10) and lens for directing light on to the index grating and then on to the scale grating for reflection to the index grating, with the resultant Moire bands detected by a photodetector (18) on the reading head. In order to determine the phase separation or offset, and to avoid high sensitivity thereof to the spacing between the gratings, the index grating (14) has a square-stepped profile resulting in graded, increasing thickness. Alternatively, a conventional index grating may be employed in conjunction with a stepped profile optical element interposed between the two gratings.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.