Process for searching for a track on a rotating plate-like infor

Details Process for searching for a track on a rotating plate-like infor Process for searching for a track on a rotating plate-like infor

1987-08-24

1989-07-11

LaRoche, Eugene R.

Dynamic information storage or retrieval

Information location or remote operator actuated control

Selective addressing of storage medium

369 44, G11B 1722

Patent

active

048478210

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

The invention concerns a method of searching for a track on a rotating disk-like data carrier with tracks that data can be written into and/or read out of by means of a read-and-write head that can be positioned over any track on the data carrier by means of a controlled coarse drive mechanism and of a controlled fine drive mechanism that is mechanically connected to the coarse drive mechanism.
Rotating data carriers that can be read with a reading head provided with an optical system for reading data are employed for example in CD players. The use of such rotating disk-like data carriers, which are read optically, is, however, in no way restricted to record players. Videorecorders with optically scanned disks are also available. In one case we speak of audio disks and in the other of video disks.
The data carrier--the CD (CD stands for compact disk)--rotates at a speed that is relatively higher than that of a conventional record player. The information--sound, picture signals, or both for example--which are stored on the CD along a spiral or in concentric circles, is read out by means of an optical system in the reading head, which usually operates with lasers. The individual windings of the spirals or the individual concentric circles constitute the tracks.
The article, "The Compact Disk Digital Audio System," by X. G. Carasso, J. B. H. Peek, and J. P. Sinjou in Philips Technical Review, Vol. 40, No. 6 (1982) describes the design of a CD player.
The reading head must be accurately guided from track to track in order to scan the data carrier--the CD. In order to read out any desired data, it must also be possible to position the reading head precisely at any desired track. The reading head is guided and positioned by means of a controlled coarse drive mechanism and of a controlled fine drive mechanism that is mechanically connected to the coarse drive mechanism. The coarse drive mechanism can for example be a spindle driven by a servomotor that carries out the coarse positioning, whereas the fine drive mechanism, which entrained as a result of the mechanical connection, assumes the function of precise positioning. The coarse drive mechanism moves radially in relation to the center--the point of rotation, that is--of the rotating disk. The fine drive mechanism is mechanically mounted and is deflected by means of electromagnets such that the scanned beam of light is radially diverted to a prescribed extent out of the vertical both toward and away from the point of rotation. This deflection results in fine adjustment at the desired track.
FIG. 3 illustrates the system. A CD is driven by a motor M. The reading head, often called the optical scanning system or optical pick-up, is coarsely positioned by means of a spindle SP. A servomotor SM, which is governed by the same controls RG as the coarse drive mechanism, drives spindle SP. The controls RF for the fine drive mechanism also govern electromagnets EM that divert a beam L of light out of the vertical.
When tracks are being searched for, tracks that are not too remote from one another can be located with the fine drive mechanism. When, however, data are to be read out of a track that is farther away, the coarse drive mechanism must be activated. To keep access times brief the coarse drive mechanism must be guided over the tracks at high speed.
EPA 0 090 379 describes a device with a coarse drive mechanism and a fine drive mechanism for reading a rotating data carrier. The application mentions that high speeds on the part of the coarse drive mechanism can as a result of the inertia that occurs lead to undesired mechanical oscillations on the part of the fine drive mechanism, so that the fine drive-mechanism control loop can no longer engage. The fine drive-mechanism control loop is accordingly interrupted while the coarse drive mechanism is in operation. An acceleration signal generated by a device that measures acceleration and speed and corresponding to the instantaneous motion of the coarse drive mechanism is simultaneously su

REFERENCES:
patent: 3906326 (1975-09-01), Chur
patent: 4236232 (1980-11-01), Jansen et al.
patent: 4397009 (1983-08-01), Eriksson
patent: 4561081 (1985-12-01), Janssen et al.
patent: 4745587 (1988-05-01), Maeda et al.

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