Document Type and Number:
Japanese Patent JPS5433724
Kind Code:
B2
Abstract:
An apparatus for reading a record carrier in the form of a disk on which are stored signals on tangentially arranged tracks, which apparatus includes an optical reading unit with a radiation source, a director system and a reading detector, whose source of radiation emits a beam of radiation that is projected onto the record carrier as a reading radiation point and which, through the director system, transfers to the reading detector the information contained in the scanning point of the record carrier or carrier, a control system for controlling the radial position of the scanning point on the desired track, whose control system includes driving means for the steering system and a first measuring system for measuring the radial position of the scanning point and supplying the means of drive a corresponding first control signal, whose first measurement system employs a first plot od ison of radiation points projected onto the record carrier, from which trace the image is formed on a first measurement detector and whose first measurement system supplies a first control signal, which, during a radial movement of the scanning point on a certain number of track distances, includes a periodic alternating component whose period is equal to the distance of tracks, the control system being stable during a half-period of said alternating current component and being unstable during the other half-period of the control system, characterized in that to ensure the stability of the control system a second measuring system is arranged which uses a second tracing of radiation points projecting on the record carrier and from which the image is formed on a second measurement detector, whose second measurement system supplies a second control signal, which, if take place, a movement r adial of the scanning point on a certain number of track distances, contains an alternate periodic component whose period is equal to the distance of tracks, but whose component alternates, as a result of a radial position deviated from the second trace of radiation points in relation to to that of the first tracing of radiation points, it has a phase shift substantially equal to a quarter of a period in relation to the alternating component of the first control signal, and because the control system has a variable transfer function which is controlled by a control unit that receives a third control signal that is derived from the second control signal, and whose control unit, upon a movement of the scanning point over a certain number of track distances, controls the transfer function to order to stabilize the control system. (Machine-translation by Google Translate, not legally binding)
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Application Number:
JP12763274A
Publication Date:
October 23, 1979
Filing Date:
November 07, 1974
Export Citation:
International Classes:
H04N5/85; G11B7/085; G11B7/09