DEVICE FOR ADJUSTING FOCAL POINT OF AN OPTICAL PICKUP DEVICE.

摘要

The focal point adjusting mechanism is servo-controlled such that the deviation will become zero between the ratio of the amount of light received in the centre to the total amount of light received in the centre and periphery of the first light detector and the ratio of the amount of light in the centre to the total amount of light in the centre and periphery of the second detector. Even if the detectors receive different amounts of light, the difference is cancelled between the denominator and the numerator of the ratio of the amount of light in the centre to the total amount of light in the centre and periphery, and the device is not affected by the imbalance in the amount of light. Alternatively, the focal point adjusting mechanism is servo-controlled based on the difference between the amounts of light received in the centres of the two detectors. Here, the difference in the total mount of light received by the detectors is calculated throughout all stages, and the difference is used to calculate a correction value multiplied by the component ratio of the amount of light in the centre to the total mount of the light received in a focused condition. Since the calculated correction value is subtracted from the difference in the amount of light received in the centres, the servo output does not contain imbalance in the amount of light falling on the detectors of the two systems, and the device is not affected by the imbalance in the amount of incident light. @(35pp Dwg.No.5/11)@.