JPH033311B2 - - 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 a so-called manual search, which involves visually finding the feed groove and lowering the stylus, as with conventional LP records, and it is usually not possible to specify an arbitrary position on the disc surface. , a so-called random access function that automatically searches for that part is required. 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. However, if the disc is recorded using the constant angular velocity (CAV) method, this method also allows for sufficiently high-speed random access, 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, If the index signal is detected at the same time, the operation speed will be limited by the above-mentioned time delay, making it difficult to perform high-speed access operations. Therefore, regarding this CLV type disk,
The index signal is read over the entire surface of the disk by high-speed scanning of a pick-up mounted on a playback device, and the index signal is stored in a semiconductor memory or the like along with the pick-up position data, and when an access operation is performed, the target position data is converted to the pick-up position. A method has been proposed in which the movement of the pick-up is controlled by comparing the current position data with the current position data. In order to perform high-speed pickup scanning in this system, it is necessary to operate the tracking servo intermittently and read the index signal only during that period, which is a so-called sampling method. However, if the pickup scanning speed is constant and the sampling period (trunking servo on interval) is constant,
Information signals on discs recorded using the CLV method are not sampled at equal intervals on the actual performance time axis, and sampling is dense on the inner periphery and sparse on the outer periphery, resulting in short pieces of music being recorded on the outer periphery. There is a drawback that if the song is sampled even once, the song may not be sampled even once. The situation will be explained using drawings. In other words, Figure 1b shows a compact high-density recording disk with a diameter of 120 mm using the CLV method.
It shows recordings of 12 songs (assuming the playing time is approximately equal for each, approximately 5 minutes) (~ is the song number), ranging from the innermost circumference (diameter 50 mm) to the outermost circumference (diameter 116 mm). It has been recorded before.
If the track pitch is 1.6 μm and the linear velocity is 1.25 m/s, the positions (radii) of the beginnings of each song correspond as shown in the table below (Figure 1 a shows the radius values of the discs).

[Table] As is clear from this table, the same length (5 minutes)
It can be seen that even in the case of 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. This indicates that the outer periphery may 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 scan the recording range of a pick-up prior to playing a disk on which index signals such as song numbers and elapsed times are recorded in addition to information signals in a time-division multiplexed manner at a constant linear velocity. By reading the index signal intermittently and searching the contents of the disk in a short time and storing it in a semiconductor memory etc., it is possible to automatically search from any part of the disk surface (so-called random access).
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 and 2. In other words, as shown in Figure 1(d), this disc playback device performs sampling at a constant cycle while varying the pick-up scanning speed to be faster on the inner periphery of the disc and slower on the outer periphery (arrows indicate sampling points). ). 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. FIG. 2 shows the configuration of the control system of the disc playback device of the present invention, in which the optical pickup is scanned at high speed prior to playback.
This figure shows the connection state when an index signal included in a disk signal is read by intermittent sampling. The disk 4 is placed on a turntable 5 and rotated by a motor 6. A frequency generator 7 is coaxially attached to the motor 6 and generates a signal with a frequency proportional to the rotational angular velocity of the motor 6. The optical pickup 8 is of a well-known non-contact detection type that combines a semiconductor laser, an optical sensor, etc., and is driven by a motor 10 via a feed screw 9 to move parallel to the radial direction of the disk 4. The motor 10 has a frequency generator 1
1 is coaxially mounted and generates a signal with a frequency proportional to the rotational angular velocity of the motor 10. Also, a linear potentiometer 1 is installed near the feed screw 9.
2, which generates a high DC voltage at the inner circumference of the disk 4 and a low DC voltage at the outer circumference, corresponding to the position of the optical pickup 8, and is applied as a reference voltage to the two servo circuits 13 and 16. Ru. The servo circuit 13 controls the rotational angular velocity of the motor 6 that drives the turntable 5.
Converter (frequency-voltage converter) 14 and amplifier 15
The circuit speed of the motor 6 is controlled in accordance with the output voltage of the linear potentiometer 12. Since disk 4 is recorded at a constant linear velocity, this causes the inner circumference of the disk to be faster;
The outer peripheral portion is rotated slowly to keep the linear velocity relative to the pick-up 8 constant. Also, servo circuit 1
Reference numeral 6 controls the rotational angular velocity of the motor 10 that drives the feed screw 9, and is composed of an F-V converter 17 and an amplifier 18. Control the rotational angular velocity. That is, when high-speed scanning is performed prior to reproduction, the rotational speed of the motor 10 is controlled by the output voltage of the linear potentiometer 12 as shown in the figure, so the rotation speed of the motor 10 is controlled by the output voltage of the linear potentiometer 12 as shown in the figure. The scanning speed of the optical pickup 8 changes continuously, being fast at the inner circumference and slow at the outer circumference. A tracking servo circuit (not shown) for reading the index signal is activated to read the disk signal by intermittent sampling by repeatedly turning on and off at fixed time intervals during the high-speed scanning period. Therefore, in conjunction with the changing scanning speed described above, sampling is performed at equal intervals on the time axis during actual performance of the disc. It is well known that when performing normal reproduction, the error voltage of a tracking servo circuit (not shown) is used as the reference voltage of the servo circuit 16. As described above, the disk playback device of the present invention increases the pick-up scanning speed at the inner circumference of the disk during reading by scanning prior to playback.
Since the speed is slowed down at the outer periphery, it is possible to secure a sufficient number of samples even at the outer periphery of the disk without increasing the scanning time, and it is possible to detect short songs without exception, increasing the reliability of the automatic search operation. effective.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing sampling positions for high-speed scanning on a disc, and FIG. 2 is a block diagram of a control system of a disc reproducing apparatus according to an embodiment of the present invention. 4...Disk, 8...Optical pick-up, 9
...Feed screw, 12...Linear potentiometer, 13, 16...Servo circuit.

Claims (1)

[Claims] 1. A disk on which information signals and index signals are recorded at a constant linear velocity, an optical pick-up for reading the signals of this disk, and a high-speed scanning of this pick-up, which starts at the inner circumference of the disk and gradually slows down at the outer circumference, and at a constant speed during the scanning. A disc playback device comprising sampling means for sampling the index signal at each time interval, and random access storage means for storing the sampled signal.