Apparatus for reading a disk-shaped record carrier

Claim 1

An apparatus for reading a disk-shaped record carrier having substantially concentric information tracks, which apparatus comprises an optical system for producing three radiation beams and projecting said radiation beams onto the record carrier as a first, second and third radiation spot, the second and third radiation spot being disposed on opposite sides of the first radiation spot in a direction transverse to the track direction and the distance between their respective centres and the axis which extends through the centre of the first radiation spot and parallel to the information tracks being at least substantially 1/4 of the track pitch of the information tracks, a first, second and third detector for detecting the amount of luminous energy in the emerging radiation beams corresponding to the first, the second and the third radiation spot respectively and for converting this luminous energy into corresponding electric output signals, a tracking system, which co-operates with the radiation beams, for centring the first radiation spot at an information track, and a control device, coupled to the second and the third detector, for generating a tracking-system control signal which depends on the difference between the output signals of the second and the third detector, characterized in that the control device is also coupled to the first detector and is adapted to supply a control signal V c which complies with the formula: ##EQU7## where V s , V R1 and V R2 are the output signals of the first, the second and the third detector respectively, α is an adjustment factor, and V ref is a reference signal.

Claim 2

An apparatus for reading a disk-shaped record carrier having substantially concentric information tracks, which apparatus comprises an optical system for producing three radiation beams and projecting said radiation beams onto the record carrier as a first, second and third radiation spot, the second and third radiation spot being disposed on opposite sides of the first radiation spot in a direction transverse to the track direction and the distance between their respective centres and the axis which extends through the centre of the first radiation spot and parallel to the information tracks being at least substantially 1/4 of the track pitch of the information tracks, a first, second and third detector for detecting the amount of luminous energy in the emerging radiation beams corresponding to the first, the second and the third radiation spot respectively and for converting this luminous energy into corresponding electric output signals, a tracking system, which co-operates with the radiation beams, for centring the first radiation spot at an information track, and a control device, coupled to the second and the third detector, for generating a tracking-system control signal which depends on the difference between the output signals of the second and the third detector, characterized in that the control device is also coupled to the first detector and is adapted to supply a control signal V c which complies with the formula: ##EQU7## where V s , V R1 and V R2 are the output signals of the first, the second and the third detector respectively, α is an adjustment factor, and V ref is a reference signal.