Patent ID: 6985412

Claim:
A focus servo controller comprising: an optical pickup, having a photodetector including a plurality of photodetector elements, for irradiating a light beam on an optical recording medium and detecting a reflected light beam from the optical recording medium by means of said photodetector, amplifying means for amplifying the respective ones of two sum output signals from two sets of the photodetector elements located symmetrically with respect to a light-receiving center of said photodetector, focus servo control means for generating a focus error signal in accordance with a difference between respective output levels of said amplifying means and for performing focus servo control by moving an objective lens in said optical pickup in an optical axis direction of said light beam in accordance with the focus error signal when a focus servo operation start-up command is supplied, a lock-in state detecting portion for detecting a lock-in state of said focus servo control means, focus balance adjusting means for adjusting gains of said amplifying means in accordance with the focus error signal to perform focus balance adjustment, bias applying means for applying a bias voltage to a focus error signal line in said focus servo control means in accordance with said focus error signal, said bias voltage being a voltage for eliminating an electrical offset component in the focus error signal, and a bias correcting voltage generator which adds a bias correcting voltage to said bias voltage in response to a detection of the lock-in state by said lock-in state detecting portion, said bias correcting voltage being a voltage for shifting said objective lens such that said objective lens maintains at least a predetermined distance from the optical recording medium to avoid a collision with the optical recording medium.