JPH0415549B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a tracking control device for a VHD video disk player, and an object of the present invention is to provide an apparatus that can accurately track the main track during special playback even if the surface condition of the disk is not good. be.

In the VHD system, there are no grooves on the disk surface, and video signals, audio signals, etc. are modulated and recorded in a series of small holes called pits in a spiral pattern from the outer circumference to the inner circumference. This method detects changes in capacitance between the electrode to which the needle is attached and the row of pits and demodulates information, and is called a grooveless capacitance method.

In the VHD system, if the track containing the video signal is called the main track, two types of signals are alternately transmitted between this main track and the adjacent main track as control signals for tracking control. is recorded. If we call these two types of signals FP1 and FP2, FP1 and FP2 are approximately 511KHz and 716KHz, respectively.
The horizontal synchronizing signal is stored in burst form at the recorded position, and the tip of the pick-up is moved in the radial direction on the disk surface according to the detection level difference between FP1 and FP2, and the electrode part at the tip of the pick-up is moved to the main track. is controlled to follow.

FIG. 1 shows the state of the disk surface. On main track 1, a video signal and an audio signal are modulated and recorded, and between main track 1 and the adjacent main track 1, FP1, 2, FP2, and 3 are the parts where the horizontal synchronization signal of main track 1 is recorded. A switching signal for switching the polarity of the tracking control loop is recorded at one point per rotation, superimposed on the vertical synchronizing signal. This switching signal will be referred to as FP3.

Since FP1 and FP2 are recorded in burst form as described above, the outputs obtained by detecting both are obtained as 4 and 5, respectively, in FIG. 2. FP1, FP2
A differential amplifier 6 serving as an error signal detection circuit compares the detected outputs 4 and 5 of the differential error signal 7 to obtain a differential error signal 7. If this differential error signal 7 is amplified and averaged, a signal 8 shown by a broken line is obtained. Then, this signal 8 is passed through a phase compensation circuit to form an optimal control loop, and the pickup is controlled.

When special reproduction is performed, a pulse called a kick pulse as shown in FIG. 3 is added to the tracking control loop to move the pickup to another track. In addition, in FIGS. 3a and 3b, the polarity is reversed depending on the direction in which the pickup is moved. Figure 4 shows the positions where kick pulses are added when performing special playback, where 9 and 10 are the outermost periphery of the signal recorded on the disk, respectively.
At the innermost position, vertical synchronization signals of the video signal are recorded at positions AA', BB', CC', and DD'.

Assuming that the above-mentioned FP3 is now recorded in the AA' portion, the timing at which the kick pulse is generated is as shown in FIG. a, b, c, d, e
are forward triple-speed reproduction, backward triple-speed reproduction, forward low-speed reproduction, and 11 is the kick pulse explained in FIG. 3, respectively. This is the case for reverse low-speed playback and stationary playback. If the surface of the disk is in good condition, there will be no problem, but if there are scratches on the disk, FP1,
Noise is superimposed on the FP2 detection signal, making tracking control unstable. In particular, during special playback, a kick pulse is applied to the pickup, forcing a disturbance to the control loop, which increases instability. It is almost impossible to eliminate scratches on the disk surface, adhering dust, etc. even during use, and they often occur.

The present invention provides a VHD video disc player that has no grooves on the disc surface and detects signals on the disc by changes in capacitance, in which two types of tracking control signals are recorded on both sides of a main track for recording video signals on the disc. , and a tracking control loop that reads a switching control signal recorded at one point per rotation of the disk and controls the pickup driving means to follow the pickup or the main track, and moves the pickup by a predetermined track in the radius of the disk. The present invention is characterized in that, during special reproduction in which a kick pulse for forcibly moving the disk in the direction of Even when the condition is not good, the effect of stably performing special playback can be obtained.

Hereinafter, embodiments of the present invention will be described in comparison with conventional examples.

First, the cause of instability in the conventional method described above will be explained with reference to FIG. 12 is the kick pulse to be added, 13 is the pickup drive waveform after addition in a good tracking state, and 14 is the drive waveform when there is noise such as scratches on the disk surface.
As can be understood by comparing 4, the amount of movement of the pick-up is constant in good conditions, but in a state like 14, the amount of movement of the pick-up is difficult to determine.

The present invention attempts to significantly improve the conventional unstable reproduction state described above with a simple device. That is, the tracking control loop is cut off or the gain is reduced during approximately the width of the kick pulse to prevent electrical noise generated from the disk (FIG. 6, 14) from being added to the pickup drive means. An example of this situation is shown in FIG. In this example, during special playback in which a kick pulse 16 is added to the pick-up drive waveform 15 before the addition of the kick pulse, the control loop is cut at a pulse 17 (hereinafter referred to as a mut pulse) that cuts the control loop over the period of the kick pulse, and this state is If a kick pulse is added at , the waveform 18 after the addition will not be affected by noise, and the pickup will always have a constant amount of movement, allowing stable special playback.

FIG. 8 shows a specific embodiment of FIG. 7. An error signal is obtained by an error signal detection circuit 20 from the signal detected from the disk 19, passed through a phase compensation circuit 21 necessary for the control loop, the circuit is cut off by a mute circuit 22, and a kick pulse is added by an adder circuit 23. The signal to which the kick pulses have been added causes a drive circuit 24 to cause a current to flow through a drive coil 25 serving as a pickup drive means to move the pickup. On the other hand, for the kick pulse, a circuit 31 inverts and adds one of the consecutive pulses, and the polarity is determined by an inverting/non-inverting circuit 32 depending on whether the vehicle is moving forward or backward.
In addition, the Miyuto pulse consists of two pulses 26 and 27.
The rising edge of the front pulse 26 is detected 28, the falling edge of the rear pulse 27 is detected 29, and both are input to the latch circuit 30 to generate a pulse, which is applied to the mute circuit 22. In addition,
A similar mute pulse can be obtained by simply adding these two pulses 26 and 27, and a similar mute pulse can also be obtained by a microcomputer.

Further, in the embodiments shown in FIGS. 7 and 8, the control loop is completely cut off by the mute circuit 22, but instead of the mute circuit 22, the loop of the control loop is cut off over the period of the kick pulse. It may be configured to lower the gain, and in this case, the effect will be slightly lower than in the cases of FIGS. 7 and 8, but the loop pull-in characteristic will be improved.

As explained above, according to the present invention, the tracking control loop is cut off or the loop gain is reduced during the period in which the kick pulse is applied, so that even if the disk surface condition is not very good, the pickup can be performed by the necessary amount. This allows for stable special playback.
Further, since the configuration of the present invention can be easily realized with a simple device, it can contribute to cost reduction.

[Brief explanation of drawings]

Figure 1 is an explanatory diagram of the disk surface of the VHD system.
Fig. 2 is an explanatory diagram of the tracking principle, Fig. 3 is a diagram of the kick pulse waveform, Fig. 4 is an explanatory diagram of the addition position of the kick pulse during special playback, Fig. 5 is a diagram of the addition timing of the kick pulse in various special playback states, and Fig. 6 7 is a waveform diagram of a main part of a tracking control loop during special playback in a conventional special playback mode. FIG. 7 is a waveform diagram of a main part of a tracking control loop during special playback according to an embodiment of the present invention. FIG. FIG.
1... Main track, 2, 3... Tracking control signal, 11... Kick pulse, 20... Error detection circuit, 21... Phase compensation circuit, 22... Mute circuit, 23... Addition circuit, 24... Drive Circuit, 25... Drive coil [pickup drive means].

Claims (1)

[Claims] 1. In a VHD video disk player that has no grooves on the disk surface and detects signals on the disk by changes in capacitance, two types of tracking control signals are recorded on both sides of the main track for recording video signals on the disk, and A tracking control loop is provided for reading a switching control signal recorded at one point per rotation of the disk and controlling a pickup driving means so that the pickup follows the main track, and forcing the pickup in the radial direction of the disk by a predetermined track. A tracking control device configured to cut off the control loop or reduce the gain during special reproduction in which a kick pulse for moving the pick-up is applied to the pickup drive means over the period of the kick pulse.