Abstract:
Recorded on the so-called lead-in track of a compact disc is the contents list of the disc. The data stored in the contents list are divided into several blocks. Several blocks containing the same data are recorded in series on the CD for redundancy purposes. A CD player reads the whole contents list, reading all the blocks, even the redundant ones, one after the other, by moving a scanning device along the spiral data track. In order to reduce the time taken to read the contents list, the invention calls for the scanning device, when reading the data making up the contents list, to jump one track outwards or inwards when it has read a block. This means that the scanning device no longer reads all the redundant blocks, but only a small proportion of them, thus considerably reducing the time taken to read and store the data making up the contents list.
Abstract:
In order to obtain perfect scanning of audio and/or video disks through application of contactless scanning with a coarse and fine drive combination for radial servo readjustment, the fine drive optimal working point (A) is reached through a correct interaction of coarse and fine drive, even in the case of different large radial excentricity amplitudes. This is done through adjustment of the coarse drive, using a comparator (10), as a threshold value detector, and through an evaluation of the impulse sequences occurring at the comparator exit.
Abstract:
A method of reducing the time to access a given point on a data track on a rotating disc. When the scanning device of a reproduction device jumps rapidly over many tracks on a disc, the scanning device can jump accurately only onto a particular track, but not onto a particular point on that track. In the worst case, the disc (CD) must then carry out a whole revolution before the designated point is detected by the light beam of the scanning device. In a compact-disc player, which is a constant-linear-velocity system, this waiting time is between 120 and 330 ms. In order to reduce the access time, the invention calls for the rotational speed of the disc which is necessary for the designated point (P2) to be detected on arrival at the designed track (S2) to be calculated from the number A of tracks lying between the last track to be scanned (S1) and the designed track (S2), the angular position of the last point to be scanned (P1) on the last track scanned (S1) and the angular position of the designed point (P2) on the designed track (S2), and the length of time taken for the jump. The invention is of use in reproduction and/or recording devices in which a rotating disc is scanned by a non-contact means, such as CD players, video disc players, DRAW disc players and magneto-optical devices.
Abstract:
In playing devices which scan a rotating disc at a constant track speed, when shifting from one track to a target track the rotation speed control circuit is broken and the speed of the disc is adjusted to the value required for the target track by a second control circuit. As soon as the scanner has reached the target track the rotation speed control circuit is made once more. In order to do away with the second control circuit, before playing the pulse width ratio of the control signal for the disc concerned is found and stored which is needed for the electric motor to spin the disc at the prescribed speed for a given track. When changing tracks, the pulse width ratio needed for the target track is calculated from the stored figure. A control signal with the calculated pulse width ratio is applied to the electric motor so that the speed of the disc is set to the value needed for the target track. As soon as the target track has been reached the speed control circuit is once more made. CD players, video disc players, DRAW disc players and magneto-optical devices.
Abstract:
When data is being read off a optical disc, the light beam can lose the data track if it encounters a dirty or damaged spot on the disc. A tracking circuit steers it back on to the correct track some distance after passing the dirty or damaged spot. In order that the light beam (L) is steered back on to the correct track (B) as soon as possible after passing a dirty spot (SK), the invention calls first for the address of the point (1) at which the light beam (L) leaves the track (B) to be stored. From the control signal necessary to bring the light beam back on to the correct track, a first modified control signal is then calculated and also stored. When, during subsequent plays, the light beam (L) comes to the point (1) on the disc, now stored in the memory, the first modified control signal is fed to the tracking circuit. In order to produce an optimum modified control signal, the light beam (L) is taken several times past the point (1) stored in the memory, and each time a new modified control signal is calculated and stored. The invention is of use in CD players, video disc players, DRAW disc players and magneto-optical recording and replaying devices.
Abstract:
A writing and/or reading head can write and/or read data on the tracks of an information support. The writing and/or reading head can be positioned over each track of the information support by means of a coarse-feed drive (S, G) and by a fine-feed drive (S, F) which is mechanically linked with the coarse-feed drive. When searching for a track, the coarse-feed drive travels fast over the tracks until it stops at the target track. The braking phase of the coarse-feed drive is kept short by a large time-log. At the latest at the beginning of the braking phase of the coarse-feed drive the regulating circuit of the fine-feed drive is disconnected. During the braking phase a control signal is applied to the fine-feed drive which clamps the mechanical oscillations of the fine-feed drive as a result of the inertial forces which arise when the coarse-feed drive is braked. Consequently, after braking of the coarse-feed drive, the regulating circuit of the fine-feed drive can again be connected. The fine-feed drive is then brought precisely over the track sought.
Abstract:
A tracking circuit is disclosed for a recording and/or playback machine that scans a recording medium without contact. The tracking circuit of a CD-player is provided for example with a coarse drive (M2, SP) on which is mounted a fine drive. In order to be able to guide the data-scanning light beam (L) along the data tracks of the disk (CD), the coarse drive (M2) is switched on from time to time. The coarse drive generates mechanical vibrations, however, which can cause track loss or even focus loss, if at the same time defects are found on the CD, for example scratches or fingerprints. In order to increase the scanning reliability, the track error signal (TE) or the focus error signal (FE) is checked for errors by a detector (H1), for example. As long as the detector (H1) indicates an error, the coarse drive (M2) remains switched off.
Abstract:
In order to adjust the scanning device of a positioning device, the unit to be positioned is taken manually to a given place. The sensor of the scanning device is then adjusted so that ist output signal is at its maximum. To shorten and simplify this time-consuming and laborious operation, the unit (AS) to be positioned is first taken manually to a defined initial position. The unit (AS) is then, in a second step, automatically moved to a second position until the output signal of the scanning device sensor (E) is at its maximum. The difference between the first and second positions is stored as an offset. In operation, with each positioning procedure the unit (AS) is positioned in a first step until the output signal of the sensor (E) is at its maximum. In a second step the unit (AS) is then moved further into the final position by the stored offset. Positioning device, e.g. in record changers, in order to be able to position the playing device in front of the individual compartments of a magazine in which the records are held.
Abstract:
The light beam is focussed with the aid of an optical system on to an optical recording medium. The optical system consists of a light source and a movable lens (20) which can be moved by means of servo-element (SG). The recording medium reflects the light beam on to a number of photoelectric cells (A, B, C and D). From their output voltages an initial control voltage is obtained by subtraction and addition of the differences thus obtained, and this is transferred by a servo-amplifier (RV) to the servo-element (SG) so that a closed loop system is formed. When the closed loop system is opened a second control voltage Us is fed to the servo-element (SG) and is modified. If the light beam is focussed on to the recording medium, the control loop system is again closed. The value of the second control voltage Us received at that moment is maintained and is available at the servo-element (SG) as a pre-voltage.
Abstract:
The invention relates to a method for reproducing data, especially digital audio and/or video data, which is stored on a storage medium (1, 5, 10), especially an optical storage plate, in a playback device (15). Accelerated selection of storage mediums that have to be reproduced or ejected from the playback device (15) is possible. In a first operating mode, data is stored in a, preferably non-volatile, memory (20) during playback of the storage medium (1, 5, 10). In a second operating mode, the storage medium (1, 5, 10) is selected, especially for playback and reproduction. At least a portion of the data which is stored in the memory (20) is replayed and reproduced within a period of time, wherein the selected storage medium (1, 5, 10) is brought into a playback position, wherein the data stored on the storage medium (1, 5, 10) can be read out by a reading device, or into an ejection position, wherein the selected storage medium (1, 5, 10) can be taken out, by means of a reserve memory (25).