Dynamic information storage or retrieval – Dynamic mechanism subsystem – Specific detail of storage medium support or motion production
Reexamination Certificate
1998-03-18
2003-03-11
Ometz, David L. (Department: 2653)
Dynamic information storage or retrieval
Dynamic mechanism subsystem
Specific detail of storage medium support or motion production
C369S266000, C369S248000, C360S099090
Reexamination Certificate
active
06532204
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the invention
The present invention relates to a disk recording system, for recording a disk such as a compact disk. The present invention also relates to a method of controlling the rotation of a turntable relative to a recording head in a disk recording system.
2. Summary of the Prior Art
Many systems are known in which information is recorded on a disk-shaped medium and may subsequently be played back. Generally the information is arranged either in substantially circular rings or in a continuous spiral track on the disk. An example of the former arrangement is the magnetic floppy disk or hard disk, where the information is divided into sectors lying in concentric tracks. Examples of the latter arrangement include the conventional gramophone record carrying sound information in analog form in the spiral groove in its surface, the optically read videodisk carrying video information in analog form in a series of pits arranged spirally on the surface (or on an interfacial boundary) of the disk, and the compact optical disk carrying audio or other information in digital form in a series of spirally-arranged pits. The gramophone record, the videodisk and the compact disk are all examples of media available to the consumer which cannot normally be recorded on by the consumer; recording takes place on a master disk which is subsequently replicated by various processes such that the disks bought by the consumer are close copies of the geometry and the information content of the master disk.
The process of recording information on any of these media usually shares in common the fact that the disk or master disk is rotated at a speed typically anywhere between 16⅔ r.p.m. (for some gramophone records) and 1,800 r.p.m. (or even higher for some videodisks) while the point of recording (which may be a magnetic head, a mechanical stylus, or a focused light beam) is traversed between the inside and outer edge of the disk at a slower rate. Normally it is a requirement of the recording system that the rotational motion of the disk may vary only slowly, if at all; generally this is easily ensured by the inertia of the disk itself, together with that of the mechanism which rotates it. The radial motion of the point of recording on the disk is, however, not so easily controlled. In the case of magnetic disk recording, it is usual that the recording head must move in discrete steps between the separate concentric tracks; by contrast, in the cases of gramophone records, videodisks, or compact disks, the recording head must move continuously relative to the disk in a generally radial direction in order to lay out the information in a spiral track, and it is characteristic of these cases that the smoothness of the radial motion is more important than the absolute accuracy of radial positioning. With a gramophone record, for example, any radial motion having significant energy in the audio frequency band, even if it represents only a small fraction of the average groove spacing, will appear as a corresponding lateral movement of the pickup when the final record copy is played, and this will be audible as a noise superimposed on the recorded audio signal. With videodisks and compact disks there is not only the possibility that any sudden radial motions of the recording head will cause the player to fail to follow the track on the final disk, but also the more serious likelihood that such motions will be dangerous simply because they will result in significant changes in spacing between successive turns of the spiral track. Since this spacing is typically only 1.6-1.7 &mgr;m, and any reduction in spacing has the effect of increasing the crosstalk between tracks (resulting in interference in the picture from a videodisk, or an increased likelihood of bit errors with a compact disk) it is desirable to maintain a tolerance of at most ±0.1 &mgr;m in the track spacing, and preferably a much closer tolerance than this.
To obtain the necessary radial tracking motion, it is usual to move the recording head along a straight line which passes through the axis of the disk, in other words radially. When recording gramophone record masters this is commonly achieved by mounting the recording head on a linear slide or rolling mount and moving it by means of a rotating leadscrew and nut. Satisfactory performance is achieved by careful engineering; the stiffness of the leadscrew drive is great enough to overcome residual friction in the mounting in videodisk and compact disk mastering (recording) a similar technique may be used, in which the optics which produce the focused beam are moved over the rotating master disk. To avoid the disadvantage that part of the optics are thus movable while the remainder (owing to the size of the light source, normally a laser) have to be fixed, it is alternatively possible to move the entire turntable (which carries the master disk) together with its rotary bearing along a straight line, using a leadscrew, while the recording head remains fixed.
In long-playing optical videodisks, or optical compact disks used for audio or other data in digital form, a constant linear velocity mode or recording is normally used because it allows the maximum recording time consistent with operation at the optimum linear velocity (which determines the bandwidth of the signal which can be recorded) throughout the recording.
Constant linear velocity recording, however, adds complications to the system, because neither the speed of rotation of the disk, nor the speed of radial motion of the recording or playback head relative to the disk is constant. In a playback-only system this may be no great problem because both rotational and radial motions are normally controlled by servos governed by the information already laid down on the disk. Record/playback systems (for example read/write data recording systems) using pre-grooved disks are also simply implemented by servos of this type. However, in the case of a master recording system for videodisk or compact disk, where the master disk is initially devoid of groove structure, there is a problem in generating the required motions as it were from first principles.
If information is to be recorded in a spiral track of pitch P at a linear velocity v then, if the instantaneous radius is R and the rotational speed is &ohgr; (radians/sec.) at time t,
ω
=
v
R
and
Equation
1
ⅆ
R
ⅆ
t
=
P
ω
2
π
Equation
2
from which
ⅆ
R
ⅆ
t
=
Pv
2
π
R
Equation
3
EP-A-011495 discloses, in the context of defining or following a plurality of substantially circular and concentric information tracks, an arrangement in which the relationship of Equation 1 is obtained by generating a signal dependent on the radius R, and generating therefrom an alternating current signal of frequency inversely proportional to the radius R. The angular rotational speed &ohgr; of the turntable is then synchronised to that alternating current signal. The same alternating current signal is used to control the radial velocity,
ⅆ
R
ⅆ
t
,
in accordance with Equation 2 using a lead screw drive. A similar method is described in EP-A-011493, in which an alternating current signal with a frequency inversely proportional to the radius R is generated, in this case by a digital division process.
It may be noted that the methods disclosed in EP-A-011495 and EP-A-011493 both require that an alternating current signal is generated first, to which the turntable rotation has to be synchronised.
SUMMARY OF THE PRESENT INVENTION
As discussed above, it is possible for either the recording head or the turntable bearing to be made the moving element. However, whichever is the moving element, a lead screw drive system is not completely satisfactory in videodisk or compact disk mastering because of the great smoothness of motion required. A very precisely ground lead screw would be needed, and sticking or sl
Halliday Jonathan
Labinsky Alexander Numa
Reynolds Gerald Alfred John
Reynolds M. A.
Larson & Taylor PLC
Nimbus Communications International Ltd.
Ometz David L.
Reynolds M. A.
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