JPH0328759B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a disc playback device. Systems called so-called video disks and digital audio disks, in which video signals and digital audio signals are recorded at high density, are about to be put into practical use. With such high-density recording discs, it is extremely difficult to perform manual searches, such as visually searching for the feed groove and lowering the stylus, as with conventional LP records, and it is usually difficult to manually search by specifying an arbitrary position on the disc surface. It is necessary to have a so-called random access function that automatically searches for that part. This random access function is normally configured to detect an index signal recorded on the disk along with an information signal, scan the pickup while comparing the commanded position and the current position, and stop at the target position. Ru. If the disc is recorded using the constant angular velocity (CAV) method, sufficiently high-speed random access is possible with the above method, but if the disc is recorded using the constant linear velocity (CLV) method, The rotational angular velocity of the disk must be changed in response to the movement of the pick-up, and due to time delay factors such as the influence of the inertia of the rotation system and the time constant of the PLL circuit included in the servo system, each access operation If the index signal is detected, the operation speed will be limited by the above-mentioned time delay element, making it difficult to perform high-speed access operations. Therefore, for CLV type disks, when the disk is inserted into a playback device, the index signal is read over the entire surface of the disk by high-speed pick-up scanning, and is stored in a semiconductor memory or the like along with the pick-up position data. A method has been proposed in which the movement of the pick-up is controlled by comparing target position data converted into a pick-up position with current position data. In order to perform high-speed pickup scanning in this method, it is necessary to perform a so-called sampling method reading in which the tracking servo is activated intermittently and the index signal is read only during that period. However, if the pickup scanning speed is constant and the sampling period (interval when the tracking servo is turned on) is constant, then the actual performance time axis of the information signal on the disc recorded using the CLV method will be In this case, the sampling will not be at equal intervals, and the sampling will be dense on the inner circumference of the disk and sparse on the outer circumference, and if a short song is recorded on the outer circumference, that song will not be sampled even once. The disadvantage is that cases may occur. The situation will be explained using drawings. In other words, Figure 1b shows 12 pieces of music recorded using the CLV method on a small high-density recording disk with a diameter of 120 mm (assuming that the playing time is approximately equal to 5 minutes). The numbers are recorded from the innermost circumference (diameter 50mm) to the outermost circumference (diameter 116mm). Track pitch 1.6μm,
If the linear velocity is 1.25 m/s, the position (radius) of the beginning of each song corresponds as shown in the following table (Figure 1 a).
is the disk radius value).

[Table] As is clear from this table, the same length (5 minutes)
It can be seen that even for a song, the first song at the innermost circumference has a width of 3.56 mm in the radial direction, while the 11th song at the outermost circumference has a width of only 1.87 mm. Figure 1c shows the sampling points (positions of arrows) when the pickup is scanned at a constant speed and sampled at a constant cycle.Compared with Figure 1b, it shows that the number of samples is sufficient at the inner circumference of the disk. Also, in the outer periphery, for example, in the 11th song, it is shown to be insufficient. On the other hand, reducing the sampling interval has the disadvantage that the scanning time becomes longer. Therefore, an object of the present invention is to perform a pick-up within the recording range of the disk prior to playing a disk on which index signals such as music track numbers and elapsed time are recorded in a time-division multiplex manner at a constant linear velocity in addition to information signals. The contents of the disk are searched in a short time and recorded in a semiconductor memory, etc., by scanning and reading the index signal at intervals, automatically searching from any part of the disk surface (so-called random access). ), it is an object of the present invention to provide a disc reproducing device capable of performing high-speed sampling scanning and eliminating omissions in information retrieval. An embodiment of the invention is shown in FIGS. 1 to 3. That is, this disc playback device is shown in Fig. 1d.
As shown in the figure, the sampling interval (cycle of turning the tracking servo on and off) during the period when the pickup is scanning at high speed is changed continuously or stepwise so that it is longer on the inner circumference of the disk and gradually becomes shorter on the outer circumference. . As a result, while ensuring a sufficient number of samplings on the outer periphery of the disk, it is also possible to prevent the scanning time from increasing due to an excessive number of samplings on the inner periphery. FIGS. 2 and 3 show means for varying the on/off repetition frequency of the tracking servo to be low at the inner circumference of the disk and high at the outer circumference. That is, the disk 4 is placed on a turntable 5 and is rotationally driven by a motor 6. The rotational speed of the motor 6 is controlled by the known CLV servo technology so that the linear speed is constant. An optical pickup 7 faces the lower surface of the disk 4 and is supported by a rail 8 and a feed screw 9. The feed screw 9 is rotationally driven by a motor 11 via a belt 10, and moves the optical pickup 7 in parallel. Further, the position of the slider of the linear potentiometer 12 is coupled to the optical pickup 7 so as to move in synchronization with the movement of the optical pickup 7. Third
The figure shows the connection state when the optical pickup is scanned at high speed prior to playback and the index signal contained in the signal on the disk is read by intermittent sampling. A DC voltage 13 is applied to both ends of the linear potentiometer 12, and the DC voltage generated in the slider (which changes in synchronization with the movement of the optical pickup) is applied as a control voltage to the voltage controlled oscillator 14, 7 oscillates a low frequency pulse signal when it is located on the inner circumference of the disk 4, and a high frequency pulse signal when it is located on the outer circumference. This pulse signal is frequency-divided by a frequency divider 15, and after adjusting the duty by a monostable multivibrator 16, it is supplied as an on/off signal for the tracking servo. The tracking servo circuit 17 inputs the output signal 18 of the optical pickup 7, and supplies a current to the tracking actuator 19 so that the laser spot correctly follows the track of the disk, thereby moving the objective lens of the optical pickup 7 toward the disk. The function is to move it in the radial direction. loop switch 20
is used to turn on and off the tracking action. During the on period, the laser spot follows the track due to the action of the tracking servo. During this time, the index signal is read and the semiconductor memory (not shown) that holds the data for random access is read. ).
Monostable multivibrator 1 during fast scanning
The loop switch 20 is turned on and off by the output of 6, and the operation of reading and storing the index signal every time it is on is repeated, thereby accumulating discrete data about the correlation between the index signal and the position of the pickup. . Then, during random access operation, this accumulated data is used to calculate the position of the beginning of each song by converting the index signal data into pick-up position data, and moves the pick-up to the target position. The timing of turning on and off the loop switch 20 of the tracking servo has a contradictory effect on the number of data that can be collected by sampling during index reading and the time required for high-speed pick-up scanning. However, according to the results of experiments, it is possible to scan the entire disk at high speed in 10 seconds (on which 12 5-minute songs are recorded). In this case, good results have been obtained if the following timing is used:
In other words, the on-off cycle is 5Hz at the innermost circumference,
The outermost circumference is 10Hz and the on time is 60ms. In this way, by keeping the on-time of the tracking servo constant and setting the on-off cycle at a high frequency on the outer periphery, sampling is performed at equal intervals on the time axis during actual performance of the disc, and the high-speed scanning time is It has great industrial effects, such as being able to detect short songs without missing them, and not increasing the required memory size due to excessive sampling even in the inner periphery. . As described above, in the disk playback device of the present invention, during reading by scanning the pick-up prior to playback, the scanning speed of the pick-up is kept constant, and the time interval between sampling points is large on the inner circumference side of the disk and gradually becomes smaller on the outer circumference side. Because I did it like this,
This has the effect of ensuring a sufficient number of samples even in the outer periphery without increasing the scanning time, and detecting all short pieces of music, thereby increasing the reliability of automatic search operations.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing sampling positions for high-speed scanning on a disk, FIG. 2 is a partial perspective view of an embodiment of the present invention, and FIG. 3 is a block diagram of the main part of its control circuit. 4...disc, 7...pickup, 17...tracking servo.

Claims (1)

[Claims] 1. A disk on which information signals and index signals are recorded at a constant linear velocity, an optical pickup for reading information on this disk, and an optical pickup that scans at a constant speed. The index signal is provided with a sampling means for sampling the index signal at each short time period, and a storage means for storing the sampled signal, and a random access operation is performed using the index signal stored in the storage means. A distinctive disc playback device.