Optical information reproducing apparatus with tilt correction including projection and detection of a same diffusely illuminated field

Claim 1

In an optical information reproducing apparatus for reproducing information recorded on a recording surface of a disc-shaped record medium and which comprises an optical pick up device mounted on a tiltable optical block and having an optical axis, a laser beam source for generating a laser beam directed along said optical axis and focused at said recording surface of said record medium and a photo detector for detecting the reflected laser beam from said recording surface and thereby reading the recorded information; a skew error detector mounted on said tiltable optical block for detecting a skew of the record medium; and a skew error corrector controlled by the output of said skew error detector for controlling said optical block so that the optical axis of said pick up device is maintained perpendicular to the recording surface: said skew error detector including light source means providing a diffusely illuminated field, a photo detector divided into a plurality of areas and a lens which is apart from said optical pick up device, said light source means and said divided photo detector being arranged symmetrically with respect to an axis parallel with said optical axis of said optical pick up device, light irradiated from said diffusely illuminated field and reflected from the recording surface being directed to said divided photo detector only through said lens which is dimensioned and positioned to provide a real image of said diffusely illuminated field on said divided photo detector, and the difference between the amounts of light detected by said areas of said divided photo detector represents the skew error output of said skew error detector.