Beam focus control system for optical record carrier scanning ap

Details Beam focus control system for optical record carrier scanning ap Beam focus control system for optical record carrier scanning ap

1989-05-16

1992-04-07

Envall, Jr., Roy N.

Dynamic information storage or retrieval

With servo positioning of transducer assembly over track...

Optical servo system

369 4429, 369 4435, G11B 700

Patent

active

051034395

ABSTRACT:
A focus control system for optical record carrier scanning apparatus includes a mechanical actuator (13) for moving the focus of the scanning beam relative to a recording layer of the record carrier, a focus-error detection circuit (15, 16, 17) for generating a focus-error signal (FE), and a control circuit (26) for generating a first control signal (AS') for the actuator (13) which is proportional to the focus-error signal (FE). In order to ensure that the actuator is within its generating range when it locks-in to the focus-error signal, the system also includes a lock-in circuit (20) having a signal generator (21) and an integrator (23) for generating an additional control signal (AS') for the actuator (13) prior to lock-in. A lock-in detection circuit (25) generates a lock-in signal (IN FOCUS) when the focus error is in the operation range, which causes a switch (22) to change-over the input to integrator (23) to the focus-error signal (FE) and also enables the control circuit (26) to provide the first control signal (AS'). Thus, after lock-in the integrator (23) and the control circuit (26) constitute a controller for controlling actuator (13) in accordance with both the focus-error signal and the integral thereof. This compensates for low-frequency disturbances and renders the control system more immune to variations in the parameters affecting correct beam focus position.

REFERENCES:
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patent: 4561080 (1985-12-01), Yamazaki
patent: 4627041 (1986-12-01), Uemara
patent: 4636625 (1987-01-01), Emoto et al.
patent: 4669074 (1987-05-01), Hsieh et al.
patent: 4677605 (1987-06-01), Abed
patent: 4683561 (1987-07-01), Bierhoff et al.

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