Radiant energy – Photocells; circuits and apparatus – Photocell controls its own optical systems
Patent
1994-10-05
1995-12-12
Westin, Edward P.
Radiant energy
Photocells; circuits and apparatus
Photocell controls its own optical systems
2502015, 369 4435, 369 4427, 369 4414, G01J 120
Patent
active
054752094
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 adjusted to zero. The first feedback control is executed when a signal level of the focus-error signal is shifted to a dead zone in which the focus-error signal is unuseable as a servo signal necessary for the second feedback control.
REFERENCES:
patent: 4542491 (1985-09-01), Takasago et al.
patent: 5146442 (1992-09-01), Shikichi
patent: 5247165 (1993-09-01), Hiruta et al.
patent: 5396477 (1995-03-01), Matsumoto et al.
Le Que T.
Sony Magnescale Inc.
Westin Edward P.
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