For scanning a disc-shaped information carrier at a high average information rate with minimum access time, the angular velocity is decreased substantially as the radial distance to the scan location increases, while at the same time the linear velocity of track scanning increases substantially. The track may be divided into zones which are scanned with constant angular velocity. With respect to the inner tracks of at least two adjacent zones, or the innermost and the outermost tracks, the angular velocity decreases less than inversely with increase of radial distance, while the linear velocity increases less than proportionally with increase of radial distance.
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0. 70. A method comprising recording information in a plurality of recording zones on a disc-shaped information carrier, each recording zone being comprised of a plurality of information tracks spanning a radial distance, wherein an information density decreases in successive recording zones located at a successively greater radial distance from a center of the carrier, but the information density within each zone is substantially constant.
0. 100. A method for scanning a plurality of information tracks recorded on a disc-shaped information carrier, comprising:
scanning the information tracks with a scanning beam;
moving the scanning beam in a radial direction relative to the information tracks, to thereby vary a radial distance (r) between the scanning beam and a rotational axis; and,
rotating the carrier about the rotational axis at an angular velocity that decreases as the radial distance (r) increases, wherein the angular velocity is not inversely proportional to the radial distance (r).
0. 140. A device for recording information on a disc-shaped information carrier, comprising:
means for recording information in a plurality of recording zones on the carrier, each recording zone being compared of a plurality of information tracks spanning a radial distance; and,
means for controlling the means for recording in such a manner as to decrease an information density in successive recording zones located at a successively greater radial distance from a center of the carrier, while maintaining the information density within each zone substantially constant.
0. 161. A device for scanning a plurality of information tracks recorded on a disc-shaped information carrier, comprising:
means for scanning the information tracks with a scanning beam;
means for moving the scanning beam in a radial direction relative to the information tracks, to thereby vary a radial distance (r) between the scanning beam and a rotational axis; and,
means for rotating the carrier about the rotational axis at an angular velocity that decreases as the radial distance (r) increases, wherein the angular velocity is not inversely proportional to the radial distance (r).
0. 117. A method for scanning a plurality of information tracks recorded on a disc-shaped information carrier, comprising:
scanning the information tracks with a scanning beam;
imparting relative radial movement between the scanning beam and the carrier, to thereby vary a radial distance (r) between the scanning beam and a central axis of the carrier; and,
controlling the imparting in such a manner as to increase a linear velocity of the scanning beam relative to an information track being scanned as the radial distance (r) increases, wherein the linear velocity is not proportional to the radial distance (r).
0. 112. A method for scanning a plurality of information tracks recorded on a disc-shaped information carrier, comprising:
scanning the information tracks with a scanning beam;
rotating the carrier about a rotational axis; and,
moving the scanning beam in a radial direction relative to the information tracks, to thereby vary a radial distance (r) between the scanning beam and the rotational axis, wherein a linear velocity of the scanning beam relative to an information track being scanned increases as the radial distance (r) increases, and wherein further, the linear velocity is not proportional to the radial distance (r).
0. 145. A method for scanning a plurality of information tracks recorded on a disc-shaped information carrier, comprising:
scanning the information tracks with a scanning beam;
rotating the carrier about a rotational axis, at an angular velocity;
moving the scanning beam in a radial direction relative to the information tracks, to thereby vary a radial distance (r) between the scanning beam and the rotational axis; and,
controlling the rotating in such a manner as to cause the angular velocity to decrease as the radial distance (r) increases, wherein the angular velocity is not inversely proportional to the radial distance (r).
0. 20. A device for scanning a plurality of information tracks recorded on a disc-shaped information carrier, comprising:
a scan head that generates a scanning beam that scans the information tracks;
a scan head drive that moves the scan head in a radial direction relative to the information tracks, to thereby vary a radial distance (r) between the scanning beam and a rotational axis; and,
a carrier drive that imparts rotational movement of the carrier about the rotational axis at an angular velocity that decreases as the radial distance (r) increases, wherein the angular velocity is not inversely proportional to the radial distance (r).
0. 164. A device for scanning a plurality of information tracks recorded on a disc-shaped information carrier, comprising:
means for scanning the information tracks with a scanning beam;
means for rotating the carrier about a rotational axis; and,
means for moving the scanning beam in a radial direction relative to the information tracks, to thereby vary a radial distance (r) between the scanning beam and the rotational axis, wherein a linear velocity of the scanning beam relative to an information track being scanned increases as the radial distance (r) increases, wherein the linear velocity is not proportional to the radial distance (r).
0. 165. A device for scanning a plurality of information tracks recorded on a disc-shaped information carrier, comprising:
means for scanning the information tracks with a scanning beam;
means for imparting relative radial movement between the scanning beam and the carrier, to thereby vary a radial distance (r) between the scanning beam and a central axis of the carrier; and,
means for controlling the means for imparting in such a manner as to increase a linear velocity of the scanning beam relative to an information track being scanned as the radial distance (r) increases, wherein the linear velocity is not proportional to the radial distance (r).
0. 42. A device for scanning a plurality of information tracks recorded on a disc-shaped information carrier, comprising:
a scan head that generates a scanning beam that scans the information tracks;
a drive system that imparts relative radial movement between the scanning beam and the carrier, to thereby vary a radial distance (r) between the scanning beam and a central axis of the carrier; and,
a servo controller that controls the drive system to increase a linear velocity of the scanning beam relative to an information track being scanned as the radial distance (r) increases, wherein the linear velocity is not proportional to the radial distance (r).
0. 156. A method for scanning a plurality of information tracks recorded on a disc-shaped information carrier, comprising:
scanning the information tracks with a scanning beam;
rotating the carrier about a rotational axis;
moving the scanning beam in a radial direction relative to the information tracks, to thereby vary the distance (r) between the scanning beam and the rotational axis; and
controlling the rotating and moving in such a manner as to cause a linear velocity of the scanning beam relative to an information track being scanned to increase as the radial distance (r) increases, wherein the linear velocity is not proportional to the radial distance (r).
0. 35. A device for scanning a plurality of information tracks recorded on a disc-shaped information carrier, comprising:
a scan head that generates a scanning beam that scans the information tracks;
a carrier drive that imparts rotational movement of the carrier about a rotational axis; and,
a scan head drive that moves the scan head in a radial direction relative to the information tracks, so thereby vary a radial distance (r) between the scanning beam and the rotational axis, wherein a linear velocity of the scanning beam relative to an information track being scanned increases as the radial distance (r) increases, and wherein further, the linear velocity is not proportional to the radial distance (r).
0. 78. A device for scanning a plurality of information tracks recorded on a disc-shaped information carrier, comprising:
a scan head that generates a scanning beam that scans the information tracks;
a scan head drive that moves the scan head in a radial direction relative to the information tracks, to thereby vary a radial distance (r) between the scanning beam and a rotational axis;
a carrier drive that imparts rotational movement of the carrier about the rotational axis, at an angular velocity; and,
a servo controller that controls the carrier drive in such a manner as to cause the angular velocity to decrease as the radial distance (r) increases, wherein the angular velocity is not inversely proportional to the radial distance (r).
1. A device for scanning an information track on a disc-shaped information carrier, comprising:
scanning means for scanning a location on the information track,
drive means for causing relative rotation between the location and the information carrier, at an angular velocity about a point of rotation, the location thereby having a linear velocity of relative movement along the track,
means for varying a distance (r) between said location and the point of rotation, and
control means for controlling the drive means,
characterized in that said control means is arranged to control the drive means so as to cause the relative angular velocity to decrease substantially with increasing distance (r), and to cause the linear velocity to increase substantially with increasing distance (r).
0. 93. A device for scanning a plurality of information tracks recorded on a disc-shaped information carrier, comprising:
a scan head that generates a scanning beam that scans the information tracks;
a carrier drive that imparts rotational movement of the carrier about a rotational axis;
a scan head drive that moves the scan head in a radial direction relative to the information tracks, to thereby vary the distance (r) between the scanning beam and a rotational axis; and,
a servo controller that controls the scan head drive and the carrier device in such a manner as to cause a linear velocity of the scanning beam relative to an information track being scanned to increase as the radial distance (r) increases, wherein the linear velocity is not proportional to the radial distance (r).
0. 151. A method for scanning a plurality of information tracks recorded on a disc-shaped information carrier, comprising:
scanning the information tracks with a scanning beam;
rotating the carrier about a rotational axis, at an angular velocity;
moving the scanning beam in a radial direction relative to the information tracks, to thereby vary a radial distance (r) between the scanning beam and the rotational axis;
controlling the rotating in such a manner as to cause the angular velocity to decrease as the radial distance (r) increases, wherein the angular velocity is not inversely proportional to the radial distance (r); and,
controlling the moving in such a manner as to cause a linear velocity of the scanning beam relative to an information track being scanned to increase as the radial distance (r) increases, wherein the linear velocity is not proportional to the radial distance (r).
0. 106. A method for scanning a plurality of information tracks recorded on a disc-shaped information carrier, comprising:
scanning the information tracks with a scanning beam;
rotating the carrier about a rotational axis at an angular velocity that decreases as a radial distance (r) between the scanning beam and the rotational axis increases, but at a rate that is not inversely proportional to the radial distance (r), wherein the angular velocity is not inversely proportional to the radial distance (r); and,
moving the scanning beam in a radial direction relative to the information tracks, to thereby vary the radial distance (r) between the scanning beam and the rotational axis, wherein a linear velocity of the scanning beam relative to an information track being scanned increases as the radial distance (r) increases, and wherein further, the linear velocity is not proportional to the radial distance (r).
0. 28. A device for scanning a plurality of information tracks recorded on a disc-shaped information carrier, comprising:
a scan head that generates a scanning beam that scans the information tracks;
a carrier drive that imparts rotational movement of the carrier about a rotational axis at an angular velocity that decreases as a radial distance (r) between the scanning beam and the rotational axis increases, wherein the angular velocity is not inversely proportional to the radial distance (r); and,
a scan head drive that moves the scan head in a radial direction relative to the information tracks, to thereby vary the radial distance (r) between the scanning beam and the rotational axis, wherein a linear velocity of the scanning beam relative to an information track being scanned increases as the radial distance (r) increases, and wherein further, the linear velocity is not proportional to the radial distance (r).
0. 163. A device for scanning a plurality of information tracks recorded on a disc-shaped information carrier, comprising:
means for scanning the information tracks with a scanning beam;
means for rotating the carrier about a rotational axis at an angular velocity that decreases as a radial distance (r) between the scanning beam and the rotational axis increases, but at a rate that i snot inversely proportional to the radial distance (r), wherein the angular velocity is not inversely proportional to the radial distance (r); and,
means for moving the scanning beam in a radial direction relative to the information tracks, to thereby vary the radial distance (r) between the scanning beam and the rotational axis, wherein a linear velocity of the scanning beam relative to an information track being scanned increases as the radial distance (r) increases, wherein the linear velocity is not proportional to the radial distance (r).
0. 132. A method for scanning a multiplicity of information tracks recorded on a disc-shaped information carrier in a plurality of CLV zones each comprised of a plurality of information tracks spanning a radial portion of a surface of the carrier, the method comprising:
scanning the information tracks with a scanning beam;
imparting relative linear movement between the scanning beam and an information track being scanned, at a linear velocity; and,
controlling the imparting in such a manner as to increase the linear velocity in successive CLV zones located successively further from a central axis of the carrier, while maintaining a substantially constant linear velocity within each CLV zone, wherein the controlling is performed in such a manner as to cause an average linear velocity of the scanning beam relative to an information track being scanned to increase as the radial distance (r) increases, and wherein further, the average linear velocity is not proportional to the radial distance (r).
0. 86. A device for scanning a plurality of information tracks recorded on a disc-shaped information carrier, comprising:
a scan head that generates a scanning beam that scans the information tracks;
a carrier drive that imparts rotational movement of the carrier about a rotational axis, at an angular velocity;
a scan head drive that moves the scan head in a radial direction relative to the information tracks, to thereby vary a radial distance (r) between the scanning beam and the rotational axis;
a first servo controller that controls the carrier drive in such a manner as to cause the angular velocity to decrease as the radial distance (r) increases, wherein the angular velocity is not inversely proportional to the radial distance (r); and,
a second servo controller that controls the scan head drive in such a manner as to cause a linear velocity of the scanning beam to increase as the radial distance (r) increases, wherein the linear velocity is not proportional to the radial distance (r).
0. 123. A method for scanning a multiplicity of information tracks recorded on a disc-shaped information carrier having a plurality of CAV zones each comprised of a plurality of information tracks spanning a radial portion of a surface of the carrier, the method comprising:
scanning the information tracks with a scanning beam;
rotating the carrier about a rotational axis, at an angular velocity;
moving the scanning beam in a radial direction relative to the information tracks, to thereby vary a radial distance (r) between the scanning beam and the rotational axis; and,
controlling the rotating in such a manner as to cause the angular velocity to decrease in successive CAV zones located successively further from the rotational axis, while maintaining a substantially constant angular velocity within each CAV zone, wherein an average angular velocity increases as the radial distance (r) increases, and wherein further, the average angular velocity is not inversely proportional to the radial distance (r).
0. 172. A device for scanning a multiplicity of information tracks recorded on a disc-shaped information carrier in a plurality of CLV zones each comprised of a plurality of information tracks spanning a radial portion of a surface of the carrier, the device comprising:
means for scanning the information tracks with a scanning beam;
means for imparting relative linear movement between the scanning beam and an information track being scanned, at a linear velocity; and,
means for controlling the means for imparting in such a manner as to increase the linear velocity in successive CLV zones located successively further from a central axis of the carrier, while maintaining a substantially constant linear velocity within each CLV zone, wherein the means for controlling causes an average linear velocity of the scanning beam relative to an information track being scanned to increase as the radial distance (r) increases, and wherein further, the average linear velocity is not proportional to the radial distance (r).
0. 60. A device for scanning a multiplicity of information tracks recorded on a disc-shaped information carrier in a plurality of CLV zones each comprised of a plurality of information tracks spanning a radial portion of a surface of the carrier, the device comprising:
a scan head that generates a scanning beam that scans the information tracks;
a drive system that imparts relative linear movement between the scanning beam and an information track being scanned, at a linear velocity; and,
a servo controller that controls the drive system to increase the linear velocity in successive CLV zones located successively further from a central axis of the carrier, and that controls the drive system to maintain a substantially constant linear velocity within each CLV zone, wherein an average linear velocity of the scanning beam relative to an information track being scanned increases as a radial distance (r) between the scanning beam and the central axis increases, and wherein further, the average linear velocity is not proportional to the radial distance (r).
0. 167. A device for scanning a multiplicity of information tracks recorded on a disc-shaped information carrier having a plurality of CAV zones each comprised of a plurality of information tracks spanning a radial portion of a surface of the carrier, the device comprising:
means for scanning the information tracks with a scanning beam;
means for rotating the carrier about a rotational axis, at an angular velocity;
means for moving the scanning beam in a radial direction relative to the information tracks, to thereby vary a radial distance (r) between the scanning beam and the rotational axis; and,
means for controlling the means for rotating in such a manner as to cause the angular velocity to decrease in successive CAV zones located successively further from the rotational axis, while maintaining a substantially constant angular velocity within each CAV zone, wherein an average angular velocity increases as the radial distance (r) increases, and wherein further, the average angular velocity is not inversely proportional to the radial distance (r).
8. A device for scanning an information track on a disc-shaped information carrier, where said track includes an innermost track, an outermost track, and a multiplicity of tracks therebetween, comprising:
scanning means for scanning a location on the information track,
drive means for causing relative rotation between the location and the information carrier, at an angular velocity about a point of rotation, the location thereby having a linear velocity of relative movement along the track,
means for varying a distance (r) between said location and the point of rotation, and
control means for controlling the drive means,
characterized in that said control means is arranged to control the drive means so as to cause the relative angular velocity to decrease substantially, but less than inversely with the increase of distance (r), as said location is moved from said increment track to said outermost track; and to cause the linear velocity to increase substantially, but less than proportionally with the increase of distance (r), at said location is moved from said innermost track to said outermost track.
0. 188. A method for scanning a multiplicity of information tracks recorded on a disc-shaped information carrier in a plurality of CLV zones each comprised of a plurality of information tracks spanning a radial portion of a surface of the carrier, the method comprising:
generating a scanning beam for scanning the information tracks;
rotating the carrier about a rotational axis, at an angular velocity;
moving the scanning beam in a radial direction relative to the information tracks, to thereby vary a radial distance (r) between the scanning beam and the rotational axis; and,
controlling the rotating and the moving to substantially increase a linear velocity of the scanning beam relative to an information track being scanned as the scanning beam is moved from an innermost track towards an outermost track; to set the linear velocity at a substantially constant linear velocity determined by the CLV zone of the information track being scanned; and, to cause the angular velocity of the scanning beam relative to an information track being scanned to change substantially as the radial distance (r) increases.
0. 49. A device for scanning a multiplicity of information tracks recorded on a disc-shaped information carrier having a plurality of CAV zones each comprised of a plurality of information tracks spanning a radial portion of a surface of the carrier, the device comprising:
a scan head that generates a scanning beam that scans the information tracks;
a carrier drive that imparts rotational movement of the carrier about a rotational axis, at an angular velocity;
a scan head drive that moves the scan head in a radial direction relative to the information tracks, to thereby vary a radial distance (r) between the scanning beam and the rotational axis; and,
a servo controller that controls the carrier drive in such a manner as to cause the angular velocity to decrease in successive CAV zones located successively further from the rotational axis, and that control the carrier drive to maintain a substantially constant angular velocity within each CAV zone, wherein an average angular velocity decreases as the radial distance (r) increases, and wherein further, the average angular velocity is not inversely proportional to the radial distance (r).
0. 192. A method for scanning a multiplicity of information tracks recorded on a disc-shaped information carrier in a plurality of CLV zones each comprised of a plurality of information tracks spanning a radial portion of a surface of the carrier, the method comprising:
generating a scanning beam for scanning the information tracks;
rotating the carrier about a rotational axis, at an angular velocity;
moving the scanning beam in a radial direction relative to the information tracks, to thereby vary a radial distance (r) between the scanning beam and the rotational axis; and,
controlling the rotating and the moving to substantially increase a linear velocity of the scanning beam relative to an information track being scanned as the scanning beam is moved from an innermost track towards an outermost track, and to set the linear velocity at a substantially constant linear velocity determined by the CLV zone of the information track being scanned,
wherein the radial portion spanned by an outermost one of the CLV zones is greater than the radial portion spanned by an innermost one of the CLV zones; and,
wherein the angular velocity decreases substantially at least within the outermost one of the CLV zones.
0. 176. A device for scanning a multiplicity of information tracks recorded on a disc-shaped information carrier in a plurality of CLV zones each comprised of a plurality of information tracks spanning a radial portion of a surface of the carrier, the device comprising:
scanning means for generating a scanning beam for scanning the information tracks;
rotating means for rotating the carrier about a rotational axis, at an angular velocity;
moving means for moving the scanning beam in a radial direction relative to the information tracks, to thereby vary a radial distance (r) between the scanning beam and the rotational axis; and,
control means for controlling the rotating means and the moving means in such a manner as to substantially increase a linear velocity of the scanning beam relative to an information track being scanned as the scanning beam is moved from an innermost track towards an outermost track, the control means being arranged to set the linear velocity at a substantially constant linear velocity determined by the CLV zone of the information track being scanned,
wherein the control means causes the angular velocity of the scanning beam relative to an information track being scanned to change as the radial distance (r) increases.
0. 182. A device for scanning a multiplicity of information tracks recorded on a disc-shaped information carrier in a plurality of CLV zones each comprised of a plurality of information tracks spanning a radial portion of a surface of the carrier, the device comprising:
a scan head that generates a scanning beam that scans the information tracks;
a carrier drive that rotates the carrier about a rotational axis, at an angular velocity;
a scan head drive that moves the scan head in a radial direction relative to the information tracks, to thereby vary a radial distance (r) between the scanning beam and the rotational axis; and,
a servo controller that controls the carrier drive and the scan head drive in such a manner as to substantially increase a linear velocity of the scanning beam relative to an information track being scanned as the scanning beam is moved from an innermost track towards an outermost track, the servo controller being arranged to set the linear velocity at a substantially constant linear velocity determined by the CLV zone of the information track being scanned, wherein the servo controller causes the angular velocity of the scanning beam relative to an information track being scanned to change substantially as the radial distance (r) increases.
0. 180. A device for scanning a multiplicity of information tracks recorded on a disc-shaped information carrier in a plurality of CLV zones each comprised of a plurality of information tracks spanning a radial portion of a surface of the carrier, the device comprising:
scanning means for generating a scanning beam for scanning the information tracks;
rotating means for rotating the carrier about a rotational axis, at an angular velocity;
moving means for moving the scanning beam in a radial direction relative to the information tracks, to thereby vary a radial distance (r) between the scanning beam and the rotational axis; and,
control means for controlling the rotating means and the moving means in such a manner as to substantially increase a linear velocity of the scanning beam relative to an information track being scanned as the scanning beam is moved from an innermost track towards an outermost track, the control means being arranged to set the linear velocity at a substantially constant linear velocity determined by the CLV zone of the information track being scanned,
wherein the radial portion spanned by an outermost one of the CLV zones is greater than the radial portion spanned by an innermost one of the CLV zone; and,
wherein the angular velocity decreases substantially at least within the outermost one of the CLV zones.
0. 186. A device for scanning a multiplicity of information tracks recorded on a disc-shaped information carrier in a plurality of CLV zones each comprised of a plurality of information tracks spanning a radial portion of a surface of the carrier, the device comprising:
a scan head that generates a scanning beam that scans the information tracks;
a carrier drive that rotates the carrier about a rotational axis, at an angular velocity;
a scan head drive that moves the scan head in a radial direction relative to the information tracks, to thereby vary a radial distance (r) between the scanning beam and the rotational axis; and,
a servo controller that controls the carrier drive and the scan head drive in such a manner as to substantially increase the linear velocity of the scanning beam relative to an information track being scanned as the scanning beam is moved from an innermost track towards an outermost track, the servo controller being arranged to set the linear velocity at a substantially constant linear velocity determined by the CLV zone of the information track being scanned,
wherein the radial portion spanned by an outermost one of the CLV zones is greater than the radial portion spanned by an innermost one of the CLV zones; and,
wherein the angular velocity decreases substantially at least within the outermost one of the CLV zones.
2. A device as claimed in
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5. A device as claimed in
said control means are arranged to change said relative rotation such that a first period of time, required to allow said location to be moved to another part of the information track by a rapid variation of said distance, is equal to or longer than a second period of time required to change the relative rotation such that the linear velocity resulting from the changed relative rotation and said rapid variation corresponds to a linear velocity at which the information can be processed, and
the second distance is the smallest distance for which the first and second periods of time are substantially equal.
6. A device as claimed in
7. A device as claimed in
said control means are arranged to change said relative rotation such that a first period of time, required to allow said location to be moved to another part of the information track by a rapid variation of said distance, is equal to or longer than a second period of time required to change the relative rotation such that the linear velocity resulting from the changed relative rotation and said rapid variation corresponds to a linear velocity at which the information can be processed, and
said control means are arranged to set the linear velocity such that the first and second periods of time are substantially equal for locations between the second distance and the third distance.
9. A device as claimed in
10. A device as claimed in
the control means sets the angular velocity in dependence on the distance (r).
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15. A device as claimed in
said drive means is a means for rotating said information carrier about said point of rotation, and
the control means sets the linear velocity at a constant velocity determined by the zone, such that for at least one zone the angular velocity decreases less than inversely with increase of distance between the inner tracks on the at least one zone and an adjacent zone.
16. A device as claimed in
17. A device as claimed in
the second distance is the smallest distance for which the first and second periods of time are substantially equal.
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The invention relates to a device for reading and/or recording information from/in an information track on a disc-shaped information carrier, comprising scanning means for scanning the information track with a linear velocity at a variable distance (r) from a point of rotation of the information carrier, and comprising drive means for causing the information carrier to rotate at an angular velocity, and control means for controlling the drive means.
Such a device is known from U.S. Pat. No. 5,161,142. In the known device a so-termed CLV (Constant Linear Velocity) disc, which is a disc-shaped information carrier on which the information track is filled with information having a constant linear density, is scanned with a Constant Angular Velocity (CAV). If information is to be read from another part of the information track, the scanning means are moved as rapidly as possible to this part of the track by a skip across the tracks to a new radial position. In the known device the angular velocity remains unchanged, so that a short access time to information elsewhere on the disc is realised.
A problem of such a device is that the information scanning velocity close to the centre of the disc is considerably lower than near the outer edge. As a result, the average information scanning velocity is much lower than the maximum information scanning velocity. Also the information processing circuit in the device is required to have a large operational range; that is, to process data having widely varying data rates.
It is an object of the invention to provide, for example, a device that has a high average information scanning velocity, while the access time after a rapid displacement remains short.
This object is achieved by a device as defined in the opening paragraph, characterized in that the control means are arranged to cause the information carrier to be driven in such a way that the angular velocity of the information carrier substantially decreases with an increasing distance (r), and the linear scanning velocity substantially increases.
The invention is advantageous in that the difference between the minimum and maximum operational angular velocities is smaller than when recording or reading operations are carried out with a constant linear velocity, so that the adaptation of the angular velocity in the case of a rapid radial displacement remains limited. In a device according to the invention, a relatively low-power motor and motor drive may be used. This not only restricts the weight and size, but also the energy consumption, the heat build-up and mechanical vibrations.
A further embodiment for the device is characterized in that the control means are arranged to set the angular or linear velocity in such a way that a first period of time necessary for the pick-up means to reach another part of the information track by a rapid radial displacement is longer than or equal to a second period of time necessary to adapt the linear velocity for a rapid radial displacement to a speed at which the information can be processed. This embodiment is advantageous in that, given a specific maximum information processing rate and the physical parameters of the device, the optimum average information rate is obtained with a minimum access time.
A further embodiment for the device is characterized in that the control means are arranged for constant linear velocity scanning during information recording. This embodiment is advantageous in that the recording parameters, such as, for example, the laser power and the shape of the write pulse, need to be determined for only one fixed linear velocity. These parameters continue to be constant during the recording operation.
A further embodiment for the device is characterized in that the control means are arranged for deriving the distance (r) from information in the information track. This embodiment is advantageous in that the distance (r) can be derived from the available signals, for example, addresses, without the necessity of adding another pick-up to the device.
These and other aspect of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.
In the drawings:
In the drawing figures, elements corresponding to elements already described carry like reference characters.
During recording, information is fed via encoder 6 to modulator 5, which encoder encodes the information into an information stream with redundancy for error correction. The encoded and modulated information is recorded at a constant information rate determined by a clock signal. The tracking as well as the linear velocity are controlled via the tracking system and the control loop. For example, when a master disc is manufactured, which is subsequently to be used for manufacturing CD-ROMs, the angular velocity can be controlled by deriving a measuring signal 14 from the drive means 3 and allowing the desired angular velocity to decrease inversely proportionally to r. The recordable information carrier may beforehand be provided with patterns, such as in the sampled servosystem, or a wobbled pregroove, so that a control signal 15 is generated in the read/write head 2. For an extensive description of the manner in which the control signal is generated, reference be made to EP 03262006, or U.S. Pat. No. 4,901,300, which document is deemed incorporated in the description by reference. During recording, the control signal 15 is led to control unit 4 via switch 10, which unit maintains, in dependence on the control signal, a constant value for the linear velocity at which the information carrier 1 is scanned by the read/write head 2. In this manner an information carrier 1 is obtained, whose information density seen in the scanning direction is constant.
During reading, a reading signal produced by the read/write head 2 is decoded by a demodulator 7 and decoder 8 into an information signal while the clock signal 13 is being recovered. The frequency of this clock signal is indicative of the linear velocity at which the information pattern is scanned by the read/write head 2. Switch 10 leads the clock signal 13 to control unit 4 during the reading operation.
In the case of a reading operation according to the so-called CLV system, the rotation is controlled in such a way that a constant linear scanning velocity is obtained, as occurs in the known audio CD player for a CD-DA. For this purpose, the control means 4 are supplied via switch 10 with a linear scanning velocity signal 16, such as said control signal from the servotracking system during the recording operation, or with the recovered clock signal 13 from demodulator 7 during the reading operation. The information is recorded with a constant density in the information track. As a result, a maximum amount of information can be recorded on the disc. In the CLV system the angular velocity depends on the distance r. Since the angular velocity is to be adapted after a rapid displacement of the read/write head 2 to another part of the information track, the motor control will need some time to reach this velocity. For part of this time, that is, as long as the information rate lies outside the operational area of the information processing circuit (i.e. demodulator 7 and decoder 8, modulator 5 and encoder 6, respectively), no information can be processed. A strong motor and a strong motor drive are to be used to obtain a short access time.
During a scanning operation according to the so-called CAV system, the rotation is adjusted in such a way that a constant angular velocity of the information carrier 1 is obtained. For this purpose, the drive means 3 may comprise a sensor which produces a sensing signal 14 which is indicative of the angular velocity. The sensing angle 14 is then applied to the control means 4. When a recording operation is performed according to the CAV system, the information can be recorded at a constant clock rate, so that the density on the information carrier then decreases with an increasing distance r.
When a recording operation is performed according to the CAV system, a constant information density may be obtained by allowing the information rate of the information to be recorded to increase proportionally to the distance r. However, this poses strict requirements on the operational area of the information processing circuit. In addition, the information transfer rate in the case of a small distance r is much smaller than along the outer edge. As a result, the average information transfer rate is much lower than the maximum information transfer rate. The access time after a rapid displacement only depends on the time necessary for reaching the desired part of the information track. A scanning operation according to the CAV system for reading information carriers which have a constant information density in the scanning direction is known from U.S. Pat. No. 5,161,142.
In a third embodiment for the device according to the invention, the linear velocity is set in dependence on the distance r. Control unit 4 is supplied with a signal that is indicative of the real angular velocity i.e. clock signal 13 or signal 15 from switch 10, as is shown in FIG. 1. The sensor and the sensing signal 14 are not necessary now, but may be supplied, as required, for controlling the velocity if the read signal is unreliable, for example, during a rapid displacement. With an increasing distance r a larger linear velocity is set, while the linear velocity increases less than proportionally to increasing r. In the control loop the control means 4 compare the set linear velocity with the signal 16 that indicates the real angular velocity. The driving signal for drive means 3 is derived in dependent on this comparison. The distance r can be sensed by position sensor 20 and presented by means of signal 21, as is shown in FIG. 2.
A fourth embodiment for a device according to the invention is similar to the third embodiment, with the exception that r is derived now from address information of signal 22 or signal 15, as shown in FIG. 3. Position sensor 20 and signal 21 are lacking here.
A fifth embodiment for a device according to the invention is similar to the previous embodiment, except that the angular velocity in the CLV system is controlled while information is being recorded. The recording parameters such as the recording power and the recording pulse may then have fixed settings.
A sixth embodiment for the device according to the invention is similar to the previous embodiment with the exception that the angular velocity in the CAV system is controlled during the information recording. The clock rate is varied inversely proportionally to r, for example, by coupling a signal 21 or 22 indicative of the distance r to a VCO (Voltage-Controlled Oscillator). Then, r may be determined by a sensor 20 or read from a signal 15 or 22 from the information carrier 1. As a result, there will arise a high, constant information density combined with the constant angular velocity. After a rapid displacement it is then possible to record forthwith, because the angular velocity need not be adapted and there is thus no danger of recording too fast or too slowly, so that information would end up in a wrong area of the information carrier 1.
In a first embodiment for the control means 4, the CLV curve 32 is followed from the outer edge at rmax to a specific distance r1. Consequently, the information track having the larger diameters is read and recorded with optimum velocity. From this distance r1 the angular velocity is maintained constant at ωmax, as is shown by curve 34. Mechanical restrictions or restrictions as to high angular velocity servotracking are thus taken into account.
In a second embodiment for the control means 4, the maximum information processing rate is taken into account and the access time is maintained at a minimum level. In the case of a rapid displacement to the centre, the information carrier 1 will have to be accelerated until the angular velocity corresponds to the new distance r. The information rate will thus be temporarily lower and the (recovered) clock will follow this lower rate. To this end, the system control may temporarily adjust, as required, the modulator 5 or demodulator 7, respectively. In the case of a rapid displacement from the centre outwards, the information carrier 1 will have to be decelerated. Since the maximum rate of the information processing circuit is limited, the angular velocity must not be too high when the read/write head 2 arrives at the desired part of the information track. A minimum access time prescribes that the time required for decelerating the information carrier is always smaller than or equal to the time necessary for displacing the read/write head 2. The minimum access time is obtained by selecting the velocity curve in such a way that for each distance r the rapid displacement time is, substantially, at least equal to the deceleration time for each rapid displacement from all other operational distances r. The variation for a specific device is given in curve 33. Under the conditions of the minimum access time, there will then also arise the maximum average information rate.
The variation of the rapid displacement time for a device will have to be determined to attune the velocity curve thereto. If the rapid displacement time is proportional to the radial displacement, the rapid displacement time can easily be determined. In general, however, the displacement of the read/write head 2 will be effected by first strongly accelerating and then decelerating again. The period of time necessary for adapting the angular velocity will have to be determined from the difference of distance to be covered and the motor parameters. For the CLV curve 32 the difference of angular velocity after a rapid displacement is proportional to the radial displacement added to the distance r. As the rapid displacement takes place over a specific distance closer to the outer edge, so the difference of angular velocity will be smaller and so the necessary deceleration time will be shorter.
For a specific distance rclv it will hold that the rapid displacement time is, substantially, equal to the deceleration time. Without a detrimental effect on the access time, the CLV curve 32 can be followed from distance rmax to rclv. In this part of the curve 33 the angular velocity is thus totally determined by the maximum rate of the information processing circuit, whereas in the part from rmin to rclv, the curve 33 is determined by the properties of the motor. Depending on the physical properties of the system, the calculated rclv may also be smaller than rmin (in that case the curve will decrease to the known CLV curve) or larger than rmax (in that case curve 33 lies completely in the area 30). To be certain that the information can always be processed after a rapid displacement, the point rclv can be selected slightly more towards the outer edge. This creates then a slight margin for physical property tolerance of the device.
In a third embodiment for the control means 4, a higher average information rate is obtained than in the previous embodiment if a minimum access time is not required in all situations, so that, for example, some extra time is allowed for rate adaptation in the case of a rapid displacement over more than ⅔ of the operational area. The maximum velocity upon arrival is then to fall within the clock recovery capture range in the demodulator 7, so that the correct linear velocity is sensed. The decoder 8 starts decoding if the linear velocity has come to within the lock range. The curve then shows a variation partly in the area 30 between the CLV curve 32 and the optimum curve 33.
In a fourth embodiment for the control means 4, the minimum access time is obtained by a velocity variation mainly found in curve 33 and, as required, in curve 34. The desired curve may be approximated, for example, by several fixed setting points. The control means 4 then comprise a simple selection mechanism and the sensor and sensing signal 14 may be omitted. The result is then, it is true, a slightly lower average information rate.
For the above embodiments it holds that a simple balancing between average access time and average information rate may be made by suitably selecting a curve in the area 30 between the CLV curve 32 and the CAV curve 31.
In a further embodiment for a device according to the invention, an information carrier 1 is used on which the information density decreases as r increases. For example, the distance r can be divided into zones of constant angular velocity, for example, in accordance with curve 42 in FIG. 5. With a constant clock rate the density within a zone will then decrease with increasing r; the clock is adjusted per zone, so that, substantially, the density in the inner zone is greater than the density in the outer zone. Also the clock rate may be varied inversely proportionally to r, for example, by coupling a signal 21 or 22 indicative of the distance r to a VCO (Voltage-Controlled Oscillator). This causes a constant density to develop, for example, per zone. During recording, such a coupling can be used over the entire distance r in combination, for example, with a constant angular velocity. r may then be determined by a sensor 20 or from a signal 15 or 22 read from the information carrier 1. After a rapid displacement, recording is possible forthwith, because the angular velocity need not be adapted, whereas still a high, constant, information density is obtained.
Combinations of variable density, angular velocity and linear velocity make an optimum tuning possible of the average information rate, the access time and the total storage capacity of the information carrier 1. There should be observed that combinations essentially copying the CAV or CLV variation, for example, by approximating the CLV curve by zones of constant angular velocity, are already known. In that case, however, the angular velocity or linear velocity shows a variation, however, only within a zone different from that of the known CAV or CLV systems, and the angular velocity or lines velocity continues to be constant, substantially.
Bakx, Johannus L., Stan, Gheorghe S.
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