Displacement measurement apparatus having first and second servo control circuits and a zone decision circuit
US5475209A · kind A · utility
Assignee
Inventor
Key dates
| Filing date | Oct 5, 1994 |
| Grant date | Dec 12, 1995 |
| Priority date | — |
| Expiry date | Oct 5, 2014 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG11B7/0909
- WIPO fieldAudio-visual technology
- WIPO sectorElectrical engineering
Abstract
A displacement measurement apparatus utilizing an astigmatism, comprises an objective lens, an optical system detecting an offset distance between a relative distance of the objective lens to a measured surface and its focal distance by utilizing a reflection beam from the measured surface, to generate a focus-error signal, an actuator connected to the lens for moving the objective lens in a direction of an optical axis of the lens on the basis of the focus-error signal, so that the relative distance is maintained at the focal distance, and a linear scale and a detecting head cooperative with each other for detecting a displacement of the linear scale to the head. One of the linear scale and the head is integrally connected to the actuator for moving together with the lens and coaxially aligned with the optical axis, and the other is stationary. A first servo control circuit is arranged for executing a first feedback control based on a linear-scale displacement signal so that the linear-scale displacement signal is adjusted to zero. A second servo control circuit is arranged for executing a second feedback control based on the focus-error signal so that the focus-error signal is ad…
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.