Transducer positioning servo mechanisms employing digital and analog circuits
AssigneeInternational Business Machines Corporation
InventorsKarl A. Belser, Paul J. Dounn, Ian E. Henderson, Ronald J. Kadlec, Spencer D. Roberts
Life of this patent
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Abstract
A track-seeking system for an optical disk using a velocity control loop with partially-digitized velocity measurement. A quadrature signal is generated based on summing the halves of a position error signal to give directionality to track-crossing counts. A so-called piggy-back construction, wherein a fine positioner is carried by a coarse positioner, is employed. Feed-forward controls are provided from the fine to the coarse positioner. At track-capture time, the dynamic range of the fine positioner is momentarily increased.
Claims27
In a positioning system, a track-seeking servo for an optical recorder operatively supporting an optical medium having a plurality of signal-storing elongated tracks which are sensible by an optical beam of a sensing means and having a coarse positioning carriage mounted with respect to the optical medium for relative radial movements across the tracks for seeking access to a target track and relatively movably carrying a fine positioning carriage such that the fine carriage moves radially of the disk about a reference point on the coarse carriage, a relative sensor mounted on the coarse positioning carriage and being operatively coupled to the fine positioning carriage for sensing and supplying an RPE (Relative Position Displacement Error) indication of the relative displacement of the fine carriage from the reference point, said sensing means having lens means mounted on the carriage for supplying a TES (Tracking Error Signal) indication of an absolute position of the fine carriage with respect to a track on the optical medium which is being scanned by said optical beam;
- the improvement including, in combination:
- first and second track-seeking servo-control loops operatively coupled, respectively, to said fine and coarse carriages for effecting relative positioning motions between the carriages and the optical medium such that the carriages can radially cross the tracks on the optical medium, said second track-seeking loop being operatively coupled to said relative sensor for receiving said RPE indication and responding thereto to effect a relative motion of the coarse carriage to follow the track-crossing motions of the fine carriage, each of said loops independently and respectively having error means for generating first and second drive signals and said loops respectively including first and second output means, respectively responsive to the first and second drive signals and being coupled to said fine and coarse carriages, respectively to effect respective relative motions;
- emphasis means in said first track-seeking loop and being coupled to said second track-seeking loop and receiving said first drive signal and being responsive to the first drive signal to supply an emphasized drive signal to said first and second output means;
- and
- first circuit means in said first servo loop coupled to the sensing means for receiving said TES indication and being responsive thereto to generate said first drive signal and including capture means coupled to the first output means for supplying a track-capture signal to the first output means for adjusting operation of the first output means upon imminent arrival of the fine carriage to said target track to enable said fine carriage to stop at said target track and including track crossing means for correcting the seek operation to accommodate track runout of the record medium such that the number of tracks yet to be traversed for the fine carriage to reach said target track is faithfully indicated in the first loop.
In a positioning servomechanism having a plurality of possible stop-lock positions between two relatively movable, members, motive means operatively coupled to said members for relatively moving same, a servo control circuit coupled to the motive means for effecting predetermined relative motions of said members to a succession of predetermined relative desired stop-lock positions;
- the improvement including, in combination:
- power amplifier means having a given dynamically alterable dynamic range of operations and being electrically interposed between said control circuit and said motive means for supplying a power current to the motive means in response to said control circuit and normally operating in a first predetermined dynamic range of operation;
- approach means in the control circuit for indicating an immediate proximity to approaching one of said stop-lock positions;
- and
- capture means electrically interposed between said approach means and said power amplifier means for responding to said immediate proximity indication to momentarily increase the dynamic range of operation of said power amplifier means.
In a machine-effected method of moving a transducer across a plurality of record tracks from an origin track to a target track, the method of measuring track-crossing velocity;
- the machine-executed steps of:
- detecting and indicating track-crossing velocity;
- when the track-crossing velocity exceeds a predetermined track-crossing velocity, measuring the track-crossing velocity in periods of time during which a predetermined number of tracks are crossed and selecting said number of tracks to be crossed in a given period to vary within a range having a plurality greater than two of a given number of track crossings, including adjusting the number of tracks crossed during each sample period for each of the velocity measurements in predetermined change increments with changes in said track-crossing velocity;
- and
- when the track-crossing velocity is less than or equal to said predetermined track-crossing velocity, measuring track-crossing velocity at each track crossing.
In a machine-effected method of moving an optical transducer across a plurality of optical record tracks on an optical medium from an origin track to a target track, the method of measuring track-crossing direction and velocity;
- the machine-executed steps of:
- providing a multiple-element detector arranged such that the optical record tracks lie along a line disposed between the predetermined ones of the elements in the detector;
- shining a light beam onto the medium such that light reflected from the medium impinges on the two-element detector and such that variations in light intensity indicates a spatial relationship of the transducer with a nearest one of the said optical record tracks;
- differentially comparing and electrically indicating the differential comparison of the light impinging respectively on the elements of the detector and indicating track crossings at determined zero axis crossing of the differential comparison electrical signal;
- summing the light impinging on the elements and supplying an electrical indication of the summing as a signal in quadrature to the differential comparison electrical signal;
- combining the electrical signals for indicating the relative direction of each of said track crossings;
- and
- counting the track crossings indicated by the differential comparison electrical signal and assigning a sign to the count representing a direction of track crossing as indicated by the phase relation of summed electrical signal to the differential signal.
In a servo-controlled positioning system having motive means for moving a sensing element across a plurality of machine-sensible indicia on a reference member and being evenly spaced apart along a path of travel of the sensing element, said positioning system being for stopping said sensing element on a first one of the indicia and for moving the sensing element along the path from the first one indicia as an origin indicia to a second one of the indicia spaced from the first indicia by a plurality of intervening ones of the indicia, said second one of the indicia being a target indicia;
- velocity servo means actuating the motive means to move the sensing element between said origin and said target indicia in accordance with a predetermined velocity profile directed along said path, velocity profile means indicating the desired velocity profile as a series of digital values;
- the improvement including, in combination:
- said sensing element supplying a tracking error signal TES indicating the relative position of the sensing element to the indicia along said path of travel having a sinusoidal shape during movement and having zero axis crossing of a first kind midway between the indicia and zero axis crossing of a second kind at the center of the indicia and supplying a second sinusoidal signal in quadrature with the TES signal;
- digital counting means connected to the sensing element for responding to said TES signal to digitally count the passed indicia and supplying the current digital count value to the velocity profile means and said velocity profile means responding to the supplied digital count value to generate and indicate a digital sample rate value, said sample rate value being linearly related to the velocity profile and being representative of a number of said indicia passed does not exceed a given modulus and is greater than a predetermined number;
- digital frequency dividing means connected to said velocity profile means for receiving said digital sample rate value and connected to said sensing means for receiving one of said sensing element supplied signals and responsive thereto to generate a digitally-indicated speed value which includes division of the number of zero axis crossings of said one sensing element supplied signal by said rate value;
- and
- said velocity servo means being connected to said frequency digital dividing means for receiving said speed value and being responsive to the digital speed value and to the desired velocity profile to servo the positioning of the sensing element close to the desired velocity profile.
In a track-seeking servo system which servo positions a transducer to seek for a track on a record medium, the record medium and transducer being relatively moving along a first direction along the track length wherein the transducer scans the track and being relatively movable in a second direction transversely to said first direction, the transducer being relatively movably carried by a first carriage, said first carriage being relatively movably carried by a second carriage, said second carriage being relatively movably mounted on a frame, said record medium being relatively movably mounted on said frame, means for sensing and indicating the relative position of the transducer and said record member track, first control means having motive means for relatively moving the first carriage with respect to the second carriage for positioning the transducer along motions in said second direction, second control means having motive means for relatively moving the second carriage with respect to the frame and being connected to the first control for causing the second carriage to follow the motions of the first carriage;
- the improvement including, in combination:
- difference means in the first control for sensing and indicating the direction in the second direction of the relative position of said first and second carriages;
- and
- the first control having means connected to said difference means for adjusting the operation of the motive means of the first control in a direction opposite to the direction of motion indicated by said difference means.
Dependencies are inferred from the claim text.