System for detecting the position of an objective lens

An apparatus for controlling the status of tracking of a light beam on an information recording medium having a tracking guide, comprising:

• first generating means for generating a first light beam;
• lens means, having an optical axis, for converging the first light beam onto the information recording medium;
• means for converting the first light beam emanating from the information recording medium into a tracking signal representing a tracking state of the lens means;
• means for movably suspending the lens means, the lens means being movable along a predetermined direction substantially perpendicular to the optical axis;
• a plane mirror movable with the lens means;
• second generating means facing the plane mirror for generating a divergent light beam;
• first and second photodetector means for detecting the light rays reflected from the plane mirror, and converting the light rays into electric signals, said photodetector means being arranged along the predetermined direction, located at respective sides of the light emitting means, said plane mirror being disposed facing said first and second photodetector means and substantially parallel thereto and the light rays detected by the photodetector means being varied in accordance with the movement of the plane mirror, the levels of the electric signals being representative of the movement of the plane mirror;
• means for converting the electric signals generated from the photodetector means into a positional signal corresponding to the position of the lens means;
• means for driving the lens means along the predetermined direction in response to the tracking signal and the positional signal to direct the light beam emergent from said lens means onto the tracking guide so that the tracking guide is traced by the light beam.

An apparatus for controlling the status of focus and tracking of a light beam on an information recording medium having a tracking guide, comprising:

• first generating means for generating a first light beam;
• lens means, having an optical axis, for converging the first light beam to form a beam spot on the information recording medium, a minimum beam spot being formed on the information recording medium when the lens means is in a focused state and a beam spot larger than the minimum beam spot being formed on the information recording medium when the lens means is in a defocused state;
• means for converting the first light beam emanating from the recording medium into a focusing signal representing a focusing state of the objective lens;
• means for movably suspending the lens means, the lens being movable along the optical axis and in a predetermined direction perpendicular to the optical axis;
• a plane mirror movable with the lens means;
• second generating means facing the plane mirror for generating a divergent light beam;
• first and second photodetector means for detecting the light rays reflected from the plane mirror and converting the light rays into electric signals, said first and second photodetector means being arranged along the predetermined direction and located at respective sides of the light emitting means, said plane mirror facing said first and second photodetector means and being disposed substantially parallel thereto and the light rays detected by the photodetector means being varied in accordance with the movement of the plane mirror so that the levels of the electric signals are changed in response to the movement of the plane mirror;
• means for converting the electric signals generated from the photodetector means into a positional signal corresponding to the position of the lens means;
• means for driving the lens means along the optical axis in response to the focusing signal to maintain the lens means in a focused state and along the predetermined direction in response to the positional signal to direct the light beam emerged from the lens means onto the tracking guide so that the tracking guide is traced by the light beam.