Tracking system for video disc player

Abstract

A video disc player is described for use with a video disc having frequency modulated video information recorded thereon in the form of a plurality of concentric circles or a single spiral. The information track comprises successively positioned light reflective and light non-reflective regions. A focused light beam is caused to be positioned over the center of an information track and the light reflected from the information track is gathered by an objective lens for application to electronic circuitry for recovering the recorded frequency modulated video signals. Radial tracking means are described for maintaining the focused light spot to impinge upon the center of an information track. Lens focusing means are described for positioning the objective lens at the optimum focused position above the information track for gathering the maximum amount of reflected light from the information track. FM processing means are described for reconstructing the recovered frequency modulated video information such that the ratio between the amplitude of the signals as recorded is essentially the same in the signals as recovered from the video disc member. Further servo means are described for handling the selective change of the intersection of the reading beam with the video disc member in a predetermined preferred mode of operation.

What is claimed is: 
     
       1. A method of tracking for use in a player for deriving information from spaced information tracks on an information bearing surface, the player including a source beam of radiation for impinging upon the information bearing surface and following an information track thereon, beam position control means having a first portion responsive to the position of the beam of radiation relative to an information track being followed to produce a tracking error signal and a second portion coupled to the first portion in a closed loop mode and responsive to the tracking error signal for controlling the position of the beam impingement point on the information carrier relative to the information track being followed, the method comprising the steps of: enabling the beam position control means to change from the closed loop mode to an open loop mode;   uncoupling the second portion from the first portion to establish the open loop mode;   driving the second portion in the open loop mode to move the source beam from a first one of the tracks towards a second one of the tracks;   .[.searching for a selected location of the source beam intermediate the first track and.]. .Iadd.moving the source beam towards .Iaddend.the second track; .[.and.].   .Iadd.determining when the beam is located at a prescribed point intermediate the first and second tracks; and, .Iaddend.   recoupling the second portion to the first portion to re-establish the closed loop mode and control the movement of the beam.[., in response to completing the search for the selected location, as the beam approaches the second track, whereby the beam then follows a path formed by the second track.]. .Iadd.a prescribed time after it is determined that said beam is located at said prescribed point.Iaddend..   
     
     
       2. In a player for recovering information from a selected one of a plurality of spaced information tracks on an information-bearing surface, the player including means for providing a beam of radiation to follow an information track, means for imparting relative movement between the surface and the beam along a selected track, a tracking system comprising: .Iadd.(a) .Iaddend.beam position control means having a first portion and a second portion, said first portion responsive to the position of the beam of radiation relative to an information track being followed to produce a tracking error signal indicative of the position of the beam of radiation relative to the information track, said second portion including means for controlling the latitudinal position of the beam of radiation relative to the track on the information-bearing surface;   .Iadd.(b) .Iaddend.control means for coupling the tracking error signal from the first portion to the second portion in a first mode of operation, to controllably position the beam of radiation in alignment with a first selected track on the surface; .[.and.].   .Iadd.(c) .Iaddend.means for producing a control pulse signal, the control means further operating, in a second mode of operation, to uncouple the first portion from the second portion, and to couple said control pulse signal to the second portion to controllably move the beam of radiation toward a second selected track on the surface;   .Iadd.(d) .Iaddend.means for producing a mode change enabling signal coupled to said control means for selectively causing said control means to change its operating mode from said first mode of operation to said second mode of operation;   .Iadd.(e) .Iaddend.the control means .[.including detector means responsive to the tracking error detector means.]. .Iadd.being arranged .Iaddend.for determining when the beam of radiation has been moved to a prescribed position intermediate the first track and the second track, and for terminating the control pulse signal at that time; and   .Iadd.(f) .Iaddend.the control means further operating to recouple the first portion to the second portion a prescribed time after terminating the control pulse signal.   
     
     
       3. In a player for recovering information from a selected one of plurality of spaced information tracks on an information-bearing surface, the player including means for providing a beam of radiation to follow an information track, means for imparting relative movement between the surface and the beam along a selected track, and tracking error detector means for producing a tracking error signal indicative of the position of the beam of radiation relative to an information track, a tracking system comprising: .Iadd.(a) .Iaddend.beam positioning means for controlling the latitudinal position of the beam of radiation relative to the track on the information-bearing surface;   .Iadd.(b) .Iaddend.control means for coupling the tracking error signal from the tracking error detector means to the beam positioning means, in a first mode of operation, to controllably position the beam of radiation in alignment with a first selected track on the surface; .[.and.].   .Iadd.(c) .Iaddend.means for producing a control pulse signal, the control means further operating, in a second mode of operation, to uncouple the tracking error signal from the beam positioning means, and to couple said control pulse signal to the beam positioning means, to controllably move the beam of radiation toward a second selected track on the surface;   .Iadd.(d) .Iaddend.means for producing a mode change enabling signal coupled to said control means for selectively causing said control means to change its operating mode efrom.]. .Iadd.from .Iaddend.said first mode of operation to said second mode of operation;   .Iadd.(e) .Iaddend.the control means .[.including detector means responsive to the tracking error detector means.]. .Iadd.being arranged .Iaddend.for determining when the beam of radiation has been moved to a prescribed position intermediate the first track and the second track, and for terminating the control pulse signal at that time; and   .Iadd.(f) .Iaddend.the control means further operating to recouple the tracking error signal to the beam positioning means a prescribed time after terminating the control pulse signal.   
     
     
       4. A tracking system as defined in claim 3, .[.wherein.]. .Iadd.further including detector means responsive to the tracking error detector means, .Iaddend.the detector means .[.terminates.]. .Iadd.terminating .Iaddend.the control pulse signal when the beam of radiation is located substantially midway between the first track and the second track. 
     
     
       5. A tracking system as defined in claim 3, wherein the control means recouples the tracking error signal to the beam positioning means before the beam of radiation reaches the second selected track. 
     
     
       6. In a player for recovering information from a selected one of a plurality of spaced information tracks on an information-bearing surface, the player including means for providing a beam of radiation to follow an information track, and means for imparting relative movement between the surface and the beam along a selected track, a tracking system comprising: a tracking error detector means responsive to the position of the beam of radiation relative to an information track being followed to produce a tracking error signal indicative of the position of the beam of radiation relative to the information track;   beam positioning means responsive to an input control signal for controllably moving the beam of radiation laterally relative to the track on the information-bearing surface;   control means for selectively coupling the tracking error signal from said error detector means to said beam positioning means in a first mode of operation, to controllably position the beam of radiation in a direction laterally of a first selected track on the surface to produce minimum tracking error and thereby maintain the position of the beam of radiation in alignment with the first selected track; .[.and.].   pulse generating means for producing a control pulse signal, the control means further operating, in a second mode of operation, to uncouple said tracking error detector means from said beam positioning means, and to couple said control pulse signal from said pulse generating means to said beam positioning means to controllably move the beam of radiation toward a second selected track on the surface;   means for producing a mode change enabling signal coupled to said control means for selectively causing said control means to change its operating mode from said first mode of operation to said second mode of operation;   said control means including .[.analyzing means responsive to the tracking error signal from said tracking error detector.]. means for determining when the beam of radiation has been moved to a prescribed position intermediate the first track and the second track, and further including means for terminating the control pulse signal .[.when the beam has moved to said prescribed position.]. .Iadd.in response to said determining means having determined that said beam of radiation has been moved to said prescribed position; and, .Iaddend.   said control means further operating to recouple said tracking error detector means to said beam positioning means a prescribed time after terminating the control pulse signal. .Iadd.   
     
     
       7.  A method for employing a player apparatus to repetitively follow at least one track of a plurality of substantially concentric information tracks recorded on an information-bearing surface of an optical disc, said player apparatus including means for rotating said disc; means for impinging an optical beam upon said information-bearing surface; means for radially translating said beam relative to said plurality of tracks; means for generating a tracking error signal indicative of the deviation of the radial position of said beam from a preferred radial position; tracking means, operatively associated with said radial translating means and responsive to said tracking error signal, during a closed loop mode of operation, to cause said beam to follow successive ones of said plurality of tracks; said method including the steps of: employing said tracking means, in said closed loop mode of operation, to cause said beam to follow a first one of said plurality of tracks;   uncoupling said tracking error signal from said tracking means, to thereby change the mode of operation of said tracking means from said closed loop of operation to an open loop mode of operation, whereby said tracking means is not responsive to said tracking error signal;   generating a control pulse signal and coupling said control pulse signal to said tracking means, in said open loop of mode of operation, said tracking means being responsive to said control pulse signal to move said beam from said first track towards a second one of said plurality of tracks;   terminating said control pulse signal and recoupling said tracking error signal to said tracking means before said beam reaches said second track, whereby said tracking means is responsive to said tracking error signal to cause said beam to follow at least said second track; and,   thereafter repeating, in a consecutive manner, said uncoupling, said generating, and said terminating and recoupling steps, a plurality of times, to thereby cause said beam to repetitively follow at least said second track. .Iaddend.  .Iadd.8. The method as set forth in claim 7, wherein said terminating and recoupling step includes the steps of:   determining when said beam has been moved to a prescribed position between said first track and said second track;   terminating said control pulse signal in response to said determining step; and,   recoupling said tracking error signal to said tracking means a prescribed time after terminating said control pulse signal. .Iaddend. .Iadd.9. The method as set forth in claim 7, wherein said first track and said second track are immediately adjacent to each other. .Iaddend. .Iadd.10. In a player apparatus of the type including a beam steering means operable in a closed loop of mode of operation, under the influence of a tracking error signal coupled thereto, for causing an optical beam to follow successive ones of a plurality of substantially concentric information tracks recorded on an information-bearing surface of an optical disc, a tracking system operable to repetitively follow at least one of said plurality of tracks, said tracking system including:   control means for uncoupling said tracking error signal from said beam steering means to thereby change the mode of operation of said beam steering means from said closed loop mode of operation to an open loop mode of operation, whereby said beam steering means is not responsive to said tracking error signal;   means for generating a control pulse signal, said control means functioning to couple said control pulse signal to said beam steering means, in said open loop mode of operation, said beam steering means being responsive to said control pulse signal to move said beam from a track being followed towards an adjacent track;   means for actuating said control means to uncouple said control pulse signal from and then recouple said tracking error signal to said beam steering means, before said beam reaches said adjacent track, to thereby return the mode of operation of said beam steering means from said open loop mode of operation back to said closed loop mode of operation, whereby said beam steering means is responsive to said tracking error signal to cause said beam to follow at least said adjacent track; and,   means for causing repetitive operation of said control means, said control pulse signal generating means, and said actuating means, in a consecutive manner, to thereby cause said beam to repetitively follow at least said second track. .Iaddend. .Iadd.11. The tracking system as set forth in claim 10, wherein said control means is configured to recouple said tracking error signal to said beam steering means a prescribed time after uncoupling said control pulse signal from said beam steering means. .Iaddend.