JPS622375B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION It is an object of the present invention to provide a method for reducing time axis fluctuations based on disc eccentricity contained in a reproduction signal of a disc player.

In a disc player, a playback signal is obtained by rotating a disc fixed on a rotary table mounted on a rotating shaft and bringing a pick _- up into contact with it _. It is impossible to avoid so-called eccentricity, which is different from the original signal, and based on this, the reproduced signal fluctuates in the time axis, resulting in time axis distortion (wow, jitter) of the original signal. That is, as shown in FIG. 1, the speed of the pickup tracing on a track with radius r (circumferential speed of the disk at radius r) v is δr·ω ₀ (ω ₀ =2πn) as shown in FIG.
As a result, the signal recorded at _{a constant speed r・ω 0 becomes} δ when played back.
This is because the signal is frequency modulated by r·ω ₀ and then reproduced. Here, δr is the amount of eccentricity, and n is the number of rotations per second.

The cause of the eccentricity mentioned above is that the center of the rotary table
There is a positional deviation δr 1 between O ₁ and _the center O ₃ of the pressing body that clamps the disk to this rotary table, and a deviation δr ₂ between the track center O ₂ and the center O ₃ of the center hole of the disk itself. , a deviation between the center of the pressing body and the center of the center hole of the disk may also be considered, but this will be omitted to simplify the explanation). The combination of δr ₁ and δr ₂ corresponds to the amount of eccentricity mentioned above, as shown in FIG. Furthermore, these δ
r ₁ and δr ₂ are necessary to ensure smooth engagement of the pressing body with the rotary table and due to problems with machining accuracy of the disk center hole, and it is impossible to reduce them to zero. It is. However, if the angle between the directions of δr ₁ and δr ₂ is changed (see FIG. 2), the magnitude of δr, which is the sum of these vectors, can be changed as shown in FIG. 3. Therefore, by controlling the angle, it is possible to reduce the time axis variation included in the reproduced signal due to the eccentricity.

Taking this point into consideration, the present invention selects the directional arrangement of δr ₁ and δr ₂ , which are the components of the eccentricity, so that their combined eccentricity δr becomes small, and thereby calculates the time axis fluctuation based on this eccentricity. The aim is to reduce this. In other words, the disc is fixed more loosely than the regular one so that it can slide a little against the rotary table, and the playback signal is extracted in that state, and the timing when the time axis fluctuation included in the playback signal reaches a predetermined level. It is an object of the present invention to provide a method for reducing time axis fluctuations of a disk player, which makes the above-mentioned fixation regular.

The disk is loosely fixed to a rotary table that rotates at a slightly slower speed than the normal rotation speed n (rps), for example, and the disk is rotated at n−δn with a slight slippage between the two. In this case, as shown in Fig. 4, δr, which is the composite vector of δr ₁ and δr ₂ , is because δr ₂ rotates at a rotation speed of δn around the center of the disk center hole, that is, the center O ₃ of the pressing body. , changes as shown in Figure 3 (which can be viewed as a change over time). Therefore, the first
The pick-up trace speed v described in connection with the figure varies as shown in FIG. Here, the envelope of the waveform of the speed change becomes an amplitude modulated wave that shows a change in δnHz. The eccentricity δr is the smallest in the fifth
Since this is the trough of the envelope of the waveform shown in the figure, it is understood that it is sufficient to detect this vicinity and fix the disk to the rotary table so that the disk does not slip.

Next, an embodiment in which the present invention is applied to a video disc player will be described. FIGS. 6A and 6B show main part configuration diagrams of an embodiment of the clamp device applied to this in different operating states.
A rotary table 2 provided on a rotary shaft 1 is rotated at a regular rotation speed n (rps) by a motor (not shown), and a disk 3 is mounted on a pressing body 4.
is being pressed by. The pressing force is obtained from its own weight and the repulsive force between it and the magnet 5 placed above it, but in the case of Fig. 6A, the solenoid 6 is not activated, and its activation is Since the magnet 5 is positioned further away from the pressing body 4 than in the case shown in FIG. It is designed to rotate at δn (rps). On the other hand, in the case shown in FIG. 3B, this slippage can be eliminated and the disk can be rotated at the normal rotation speed. 7 is a switch that controls the solenoid, 8 is a plunger of the solenoid, and 9 is a lever that is controlled by the plunger and supports the magnet.

FIG. 7 is a block diagram for controlling the above-mentioned solenoid, and FIG. 8 is an explanatory diagram of its operation. The signal recorded on disk 3 is picked up 1.
0 from the rotating disk and demodulated by the demodulator 11. The output video signal is applied to a sync separation circuit 12 to obtain a horizontal sync signal.
If the tracking speed of the pickup is subject to variation, this synchronization signal is also subject to time axis variation (jitter). Therefore, speed fluctuations can be detected by converting the time axis fluctuations of this synchronization signal into voltage. 13 is a jitter detector that performs this operation. The fluctuation signal detected by this detector includes fluctuations due to various causes in addition to fluctuations due to eccentricity, but the fluctuation frequency due to eccentricity is nHz when the disk is rotating n (rps). Taking this into consideration, the signal is added to the nHz band filter 14, from which only the nHz component is extracted. It will be clear from the above description of FIG. 5 that if the disk has slipped by .delta.n, the output from the bandpass filter 14 will have a waveform as shown in FIG. 8A. This signal is transmitted to the rectifier circuit 15
The envelope waveform (b) of the same figure is extracted. The signal is applied to the next Schmitt circuit 16, which detects a predetermined level 17 and presents as its output a signal as shown in FIG. This signal is input to the set terminal of the RS flip-flop 18, and its output drives the switch 7, which in turn drives the solenoid 6. Reference numeral 19 generates a reset signal to the flip-flop 18, and is configured to generate a reset signal when the pressing body 4 is removed from the rotary table 2, for example. The waveform diagram in FIG. 8 shows the case where the solenoid 6 is not driven.
The corresponding waveform when this is driven is as shown in FIG. Initially, when the solenoid is off (a reset signal has been input to the flip-flop in advance), the disk is in the state shown in Figure 6A, and the repulsive force between the pusher 4 and the magnet 5 is small and the disk is weakly pressed by the pusher. It is sliding against the rotary table. Note that this slippage is caused by friction and wind damage between the disk and the fixed table that supports it via an air flow. Therefore, the output of the bandpass filter 14 (FIG. 9A) and the output of the rectifier circuit (FIG. 9B) are as shown in the figure. The rectified output gradually decreases from its maximum value as shown in the figure, and when it reaches the trigger level 17 of the Schmitt circuit 16, the output is inverted as shown in C of the figure. In response, the flip-flop 18 is reversed, and the switch 7 is turned on (see d in the same figure), and the solenoid 6 is operated from then on, and the pressing body 4 and the disk 3 are turned on.
is strongly pressed against the rotary table as shown in Figure 6B, and its slippage is eliminated. For this reason, the eccentricity thereafter maintains the level at the time of inversion of the Schmitt circuit, and the waveform becomes as shown in the figure. Incidentally, the flip-flop 18 is used to prevent chattering that occurs during the inversion transition of the Schmitt circuit. Regarding the setting of the trigger level mentioned above, since the amount of eccentricity varies depending on the player and disc, it is difficult to set it to the minimum value.
Practically speaking, the range of the minimum value can be determined through experiments, and by setting the minimum value to the upper limit, it is possible to reduce the time axis fluctuations due to eccentricity.

FIG. 10 shows another embodiment of the clamp mechanism that can be used in the present invention. A member 2 facing the pressing body 4
0 is a non-magnetic magnetic core, a coil 21 is wound around it, and a current is passed through it to operate it as an electromagnet, thereby creating a repulsive force between the two, and the strength of this repulsive force is determined by the coil. This can be obtained by controlling the amount of current flowing.

[Brief explanation of the drawing]

Figure 1 is a waveform diagram showing changes in circumferential velocity due to eccentricity, Figure 2 is a vector diagram showing the components of eccentricity,
Fig. 3 is a diagram showing the amount of eccentricity when one eccentric element is rotated, Fig. 4 is a diagram showing the state of the rotation,
FIG. 5 is a diagram showing changes in circumferential speed due to the rotation. Figures 6A and 6B show a model of one embodiment of the clamping device that can be applied to the present invention, with Figure 6A showing the solenoid not operating, and Figure 6B showing the solenoid operating state. It is. FIG. 7 is a block diagram of a device for controlling this solenoid, and FIGS. 8 and 9 are explanatory diagrams of its operation. 10th
The figure shows another embodiment of the clamp device. O ₁ ... Center of rotation of the disk, O ₂ ... Center of the trace circle, O ₃ ... Center of the disk center hole (center of the pressing body), 2... Rotating table, 3... Disk, 4... Pressing body, 5... Magnet, 6 …solenoid.

Claims (1)

[Claims] 1. The disk is fixed loosely compared to the regular one so that it can slide a little against the rotary table, and in that state the playback signal is extracted, and the time axis fluctuation based on the eccentricity of the disk included in the playback signal is determined to be a predetermined value. A time axis fluctuation reduction method for a disk player in which the above fixation is made normal at the timing when the level falls below the level.