Control circuitry for preliminary focusing of light on a record medium surface in an optical reproducing apparatus

摘要

In an optical reproducing apparatus including an optical pickup device directing a light beam at a record medium surface and having at least one photodetector which produces a focus error signal in accordance with the state of focus of the light beam in respect to the record medium surface, and a focus control device responsive to a drive signal for controlling the focus of the light beam in respect to the record medium surface; there are provided a signal generator for producing a preliminary focusing signal which initially varies rapidly toward a first predetermined level of one polarity and then varies relatively slowly toward a second predetermined level of opposite polarity; a detecting device for detecting a zero crossover point of the focus error signal and producing an output signal which varies from a first level to a second level when the zero crossover point is detected; and switching circuitry for supplying the preliminary focusing signal to the focus control device as the drive signal for the latter when the output signal of the detecting device is at its first level and supplying the focus error signal to the focus control device as the drive signal for the latter when the output signal of the detecting device is at its second level.