JPH0221054B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention is directed to a recording medium such as a disk on which information such as video and audio signals is recorded at high density along spiral or concentric tracks. The present invention relates to a method for detecting track crossing of a light spot, which detects the direction in which the light spot crosses the track and counts the number of tracks crossed, in an apparatus for reproducing information using the reflected light or transmitted light.

[Background of the invention]

The optical detection type information reproducing device is well known from Philips Technical Review Vol. 33, 1973, No. 7. Figure 1 shows an outline of this playback device.
Laser light emitted from a laser light source 1 is divided into a zero-order beam and two first-order beams by a diffraction grating 2, passes through a lens 3, a half mirror 4, a mirror 5, an optical deflector 6, and an objective lens 7, and is directed to a disk. 8, 1μφ on the surface
It is narrowed down to three light spots 13, 14, and 15 of about The relationship between the three spots and the track 16 is as shown in FIG. 4 and enters the photodetector 9. The light-receiving surface of the photodetector 9 is also composed of three light-receiving surfaces 10, 11, and 12 corresponding to the three spots, and the signal on the light-receiving surface 11 corresponding to the central spot 14 is for a video signal. , the other two light spots 13,
Signals on the light receiving surfaces 10 and 12 corresponding to 15 are used for tracking servo. That is, by taking the difference between the outputs of the light receiving surfaces 10 and 12, the amount of deviation of the light spot from the track center can be detected.
Tracking can be performed by moving the optical deflector 6 by an amount corresponding to this differential signal. However, when the light spot 14 is completely removed from the track,
In other words, when you start the device, when you start playing from the middle of the disc, or when the light spot becomes unable to track the track due to some kind of disturbance, some special method must be used to prevent tracking. It is necessary to apply

In other words, when the light spot is not tracking the track, the light spot crosses the track due to eccentricity or precession, so by detecting the direction of traversal and the number of tracks crossed, the light spot can be positioned on the track ( This is called pulling in)
Next, when the light spot tends to shift from the center of the track due to disk eccentricity or precession, this shift is detected and the light spot is moved to cancel this shift. tracking) is necessary. By positioning the light spot on the track in this way and operating the tracking servo system, the light spot can accurately read out information along the track.

[Purpose of the invention]

An object of the present invention is to provide a method for accurately detecting track crossings caused by causes such as eccentricity or disturbance of a recording medium such as a disk.

[Summary of the invention]

In order to achieve this object, the present invention is characterized in that the direction in which the optical spot traverses the tracks and the number of tracks traversed are detected from the signal for reproducing information and the tracking servo signal.

[Embodiments of the invention]

First, an embodiment of the present invention will be described using FIGS. 3 and 4. Here, an example will be described in which the present invention detects eccentricity and performs tracking pull-in.

FIG. 3 shows the relationship between the movement of the optical spot 14 and the track 16 when the disk is eccentric.
In this figure, the track 16 is a spiral, but for the sake of simplicity, it is drawn as concentric circles, and shows a case where no tracking operation is being performed. FIG. 4 shows the output signal 11' of the light receiving surface 11 of the photodetector 9 corresponding to the light spot 14 and the output signal of the light receiving surface 10, 12 corresponding to the light spots 13, 15 when no tracking operation is performed. The output signal difference 20' is plotted, with the signal near point 17 in FIG. 3 being shown at A, and the signal near point 18 at B. The signal 20' is used for tracking servo, but when the eccentricity of the disk becomes about 100μ, the signal 20' becomes a frequency of about several KHz,
Since the tracking servo system hardly responds, tracking is not performed even if the tracking servo system is operating, resulting in almost the same signal as in FIG. 4. The present invention detects the cross-track direction and the number of cross-tracks of a light spot from a signal such as that shown in FIG. explain.

Now, the signal 11' in Fig. 4 is a signal for reproducing the recorded signal, and the point at which this signal 11' becomes minimum (maximum) is the point at which the center of the optical spot and the center of the track coincide. , the tracking servo signal 20' near this point has a positive slope at A,
In B, it is negative. That is, the tracking servo signal 2 is different when the light spot crosses the track from the inside to the outside and when it crosses the track from the outside to the inside.
When the phase of 0' is different, from inside to outside, signal 2
0' is ahead of the signal 11' in phase, and when it is from the outside to the inside, the phase is behind the signal 11'. Therefore, by comparing the phases of the signals 20' and 11', the direction in which the light spot crosses the track can be determined. For example, if the signal 11' is sliced into a pulse at a predetermined level and the slope of the signal 20' during the pulse time T is determined, the light spot crosses the track from the outside to the inside or from the inside to the outside. You can tell whether it crosses or not. This may also be done by checking whether the signal 23', which is the differentiated signal 20', is positive or negative during the period T.

Next, as for the amount of eccentricity, it is sufficient to calculate how many times the light spot crosses the track within a certain period of time. For example, assuming that the light spot crosses the track N times during one rotation of the disk, and assuming that the track pitch is aμ, the amount of eccentricity can be determined as N±1/4×a(μ).

As described above, the direction and magnitude of eccentricity of the disk can be determined by detecting the direction in which the light spot crosses the tracks and the number of tracks traversed.
This allows the light spot to move in the same way as the track. In this way, it is possible to make the time during which the light spot crosses the track more than a few milliseconds, and even in a servo system with poor frequency characteristics, it is possible to enter the servo control operating state, and tracking pull-in can be achieved. .

FIG. 5 is a block diagram of signal processing for tracking pull-in according to the present invention;
FIG. 4 shows waveforms obtained by processing these signals. In FIG. 5, three light receiving surfaces 10,
Among the output signals 11 and 12, the output signal 11' of the light receiving surface 11 corresponding to the central spot is reproduced as a video signal by the video signal demodulation circuit 19. In addition, the light receiving surface 1 corresponding to the left and right light spots is
The output signals of 0 and 12 pass through a tracking servo system, that is, a differential amplifier 20, a signal processing circuit 21, and an adder 22, and drive the optical deflector 6. The tracking pull-in circuit is the part C within the dotted line.
The output signal 20' of the differential amplifier 20 is sent to the differentiating circuit 23.
is differentiated by , resulting in a signal 23'. Further, the output of the gate signal generating circuit 24, which generates a gate pulse having the same pulse width as the period during which the signal 11' is at a certain level or more, is input to the gate circuit 25. In the gate circuit 25, the signal 23' is passed only during a certain period of the gate signal. Thus, each time a light spot passes through a track, a signal 2 indicating its direction of passage is generated.
5' is obtained. Since the pulse height and pulse width of the output signal 25' of the gate circuit 25 are not constant, the waveform shaping circuit 26 shapes the output signal 25' into a constant pulse. In this signal 26', the number of pulses represents the amount of eccentricity, and the positive and negative values of the pulses represent the direction of eccentricity. Therefore, by passing the signal 26' through the bandpass filter 27, a signal approximately corresponding to the movement of the track can be obtained. This signal is added to the tracking servo signal by the adder 22, and the optical deflector is When driven, the light spot moves almost in the same way as the track. At this time, the tracking/servo signal has a frequency of about several hundred Hz to several tens of Hz, and since the tracking servo system can respond sufficiently at such a frequency, tracking pull-in becomes possible.

Note that depending on the positive or negative of the output of the gate circuit 25,
A similar function can be achieved by accumulating positive and negative charges in a capacitor, passing a signal corresponding to this capacitance through a bandpass filter, and inputting it to the adder 22.

Furthermore, the present invention is not limited to the method of dividing the optical spot into three parts as shown in FIG. 1 and obtaining the tracking servo signal from the output signals from two of the spots. As disclosed in the above issue, one light spot is irradiated, the diffracted light is used to reproduce information using two information detection receivers, and another two tracking servo receivers are used to perform tracking and servo receivers. Even if it is a method of obtaining a servo signal, or detecting the diffracted light with two light receivers, obtaining a tracking servo signal from the difference in output, and obtaining a signal for reproducing information from the sum of the outputs. Since tracking servo signals similar to those shown in FIG. 4 can be obtained, the present invention can be applied. Also, JP-A-49-94340 or JP-A-49-
As disclosed in No. 103515, a light spot or track is made to vibrate minutely at a reference frequency, the reflected light is detected by one photodetector, and the reference frequency component of this output signal and the minute vibration signal are adjusted in phase. Even if the tracking servo signal is obtained by comparison, the same tracking servo signal as shown in FIG. 4 can be obtained, so the present invention can be applied.

Furthermore, according to the present invention, tracking pull-in can be realized by changing the band of the bandpass filter 27 even with respect to track movement due to deformation of the recording medium.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to optically accurately detect the direction and number of light spots crossing a track caused by eccentricity of a recording medium, etc.
This is highly effective in providing a method for easily detecting truck eccentricity.

[Brief explanation of drawings]

Fig. 1 is a schematic diagram of the optical information reproducing device, Fig. 2 is a diagram showing the positional relationship between the track and the optical spot, Fig. 3 is a diagram showing the movement of the optical disk and the optical spot, and Fig. 4 A and B. 5 is a signal waveform diagram for explaining the operation of the present invention, and FIG. 5 is a block diagram of signal processing for implementing the present invention. 10, 11, 12... Light receiving surface of photodetector, 19...
Video signal demodulation circuit, 20... differential amplifier, 21...
Signal processing circuit, 22...adder, 23...differentiation circuit,
24... Gate signal generation circuit, 25... Gate circuit,
26...Waveform shaping circuit, 27...Band filter.

Claims (1)

[Claims] 1. A light spot is irradiated onto a rotating recording medium having a track formed along the rotation direction, the light from the rotating recording medium is converted into an electrical signal, and the information recorded on the track is reproduced from this electrical signal. By generating a signal for tracking and a tracking servo signal, and comparing the phases of these two signals, the direction in which the optical spot crosses the track is detected, and the output of the phase comparison determines the direction in which the spot crosses. A method for detecting a light spot crossing a track, the method comprising detecting the number of tracks.