JPS5925287B2 - information reproducing device - Google Patents

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention is directed to recording information on a recording medium such as a disk in which information such as video and audio signals is recorded at high density along spiral or concentric tracks. It relates to a device that irradiates a light beam and reproduces information using the reflected light or transmitted light, and in particular, reproduces information on tracks recorded on a moving recording medium by detecting the deviation between the light beam and the track. It relates to a device for drawing in a light beam.

[Background of the invention]

A light detection type information reproducing device is well known from Philips Technical Review Vol. 33, 1973, Mashi, 7.

FIG. 1 is a schematic diagram of this reproducing device. Laser light emitted from a laser light source 1 is divided by a diffraction grating 2 into a primary beam and two primary beams.
, an optical deflector 6, and an objective lens T), and three optical spots 13, 14, 15 of about 1 μφ are formed on the surface of the disk 8.
Squeezed. 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 also consists 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. , signals from the light receiving surfaces 10 and 12 corresponding to the other two light spots 13 and 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 optical spot from the track center can be detected, and by moving the optical deflector 6 by an amount corresponding to this differential signal, tracking can be detected. I can do it. However, if the optical sub-bot 14 is completely removed from the track, that is, when the device is started, when playing is performed from the middle of the disc, or when some disturbance makes it impossible for the optical sub-bot to follow the track. In some cases, it is necessary to take some special measures to prevent tracking. That is, for a light beam to accurately track information along a track, the light beam spot must first be positioned on the track (this is called pulling).
Next, when the light beam tends to deviate from the center of the track due to causes such as eccentricity or precession of the disk, this deviation is detected and the light beam is moved to cancel this deviation ( This is called tracking).

The retraction is performed and the tracking servo system is activated so that the light beam can accurately read out information along the track. The reason why pull-in is necessary for tracking is as follows.

That is, the frequency characteristics of the tracking servo system are mainly determined by the frequency characteristics of an optical scanning means such as an optical deflector. For example, when the eccentricity of the disk is 1001 tm, the rotational speed is 1800 rpm, the diameter of the light beam on the disk is 1 μmφ, and the width of the spiral or concentric track is 1 μm, the time for the light beam to cross the track is the shortest. 0.05ms, and the longest is about 1ms.

Therefore, in order for tracking to occur along a track while the light beam traverses the track in the radial direction of the disk, the frequency response of the servo system must be at least 1 KHz.
It must be flat and have good phase characteristics. For this purpose, it is necessary to use an optical deflector with good frequency characteristics, which is therefore expensive. However, since the above-mentioned information reproducing apparatus is desired to be low in price, it must be possible to perform tracking even with a tracking servo system having poor frequency characteristics.

To achieve this, the time the light beam traverses the track can be lengthened, that is, the light beam can be pulled in. In this way, good tracking is possible even with a tracking servo system having relatively poor frequency characteristics, and the light beam can be tracked without deviating from the track. [
OBJECT OF THE INVENTION] An object of the present invention is to perform retraction by detecting the deviation when a track deviates from the light beam due to eccentricity of a recording medium such as a disk or disturbance, etc.
An object of the present invention is to provide an information reproducing device equipped with a tracking pull-in device that enables tracking.

[Summary of the invention]

In order to achieve this object, the present invention provides a circuit that compares the phase of a signal for reproducing recorded information and a tracking servo signal and generates a signal indicating the direction of passage of a light beam each time it crosses a track; The present invention is characterized in that a circuit is provided which uses the output thereof to generate a signal indicating the deviation of the track with respect to the light beam, and the tracking servo system is controlled by the output of this circuit.

[Embodiments of the invention]

First, the principle of the present invention will be explained using FIGS. 3 and 4.

Figure 3 shows the optical spot 14 when the disk is eccentric.
The relationship between the movement of the track 16 and the track 16 is shown.

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 optical spot 14 when no tracking operation is performed.
', and the light receiving surfaces 10, 1 corresponding to the light spots 13, 15
The difference 20/ between the two output signals is shown, and the signal near point 17 in FIG. 3 is shown in A, and the signal near point 18 in FIG. 3 is shown in 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, and the tracking servo
The servo system hardly responds. Now, signal 1 in Figure 4
V is a signal for reproducing the recorded signal, and the point where this signal 1V becomes minimum (maximum) is the point where the center of the optical spot and the center of the track coincide, and the signal 20' near this point The slope is positive at A and negative at B. That is, the phase of the tracking servo signal 20' is different when the light spot crosses the track from inside to outside and when it crosses the track from outside to inside, and when the light spot crosses the track from inside to outside, the phase of the tracking servo signal 20' is different.
0' is ahead of the signal 1V in phase, and when it is from the outside to the inside, the phase is behind the signal 1V. Therefore, by comparing the phases of signal 20' and signal 11', the direction in which the light spot crosses the track can be determined. For example, if a signal 1V is sliced at a predetermined level and made into a pulse, then from the slope of the signal 20' during the pulse time T, the light spot crosses the track from the outside to the inside or from the inside to the outside. It is possible to distinguish between This is also
It is also possible to check whether the signal 23', which is obtained by differentiating the signal 20', is positive or negative during the period T. Next, as for the amount of eccentricity, it is sufficient to count 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 revolution of the disk, and assuming that the track pitch is aμ, the amount of eccentricity can be determined as follows.

As described above, if the direction and size of the eccentricity of the disk can be determined, it becomes possible to move the light spot in the same way as the movement of the track, and therefore the time it takes for the light spot to cross the track can be set to several MS or more. Even if the servo system has poor frequency characteristics, it becomes possible to enter the servo control operating state, and tracking pull-in can be achieved.

Next, embodiments of the present invention will be described in detail.

FIG. 5 is a block diagram of signal processing for tracking pull-in, and FIG. 4 shows the waveforms of the processed signals. In FIG. 5, among the output signals of the three light-receiving surfaces 10, 11, and 12 of the photodetector 9, the output signal 1V of the light-receiving surface 11 corresponding to the central spot is converted into a video signal by the video signal demodulation circuit 19. is played. Further, the output signals of the light receiving surfaces 10 and 12 corresponding to the left and right optical spots are transmitted by a tracking servo system, that is, a differential amplifier 20,
The light passes through a signal processing circuit 21 and an adder 22, and drives 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 2.
3, resulting in signal 23'. Also, the signal 1V
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 is equal to or higher than a certain level, is input to the gate circuit 25. The gate circuit 25 allows the signal 23' to pass only during a certain period of the gate signal. Thus, each time a light spot passes through a track, a signal 25' is obtained indicating its direction of passage. 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 sides of the pulses represent the direction of eccentricity. Therefore, by passing the signal 26' through the bandpass filter 27,
Since a signal that approximately corresponds to the movement of the track is obtained, this signal is added to the tracking servo signal by the adder 22, and if the optical deflector is driven, the optical spot will move approximately in the same manner as the track. At this time, the tracking servo signal has a frequency of about several hundred Hz to several + Hz, and since the tracking servo system can respond sufficiently at such a frequency, tracking pull-in becomes possible. Note that the same function can be achieved by accumulating positive and negative charges in a capacitor depending on whether the output of the gate circuit 25 is positive or negative, passing a signal corresponding to this capacitance through a bandpass filter, and inputting it to the adder 22. I can do it.

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 servo signal from the output signals from two of the spots.
As disclosed in No. 2, one light spot is irradiated, the diffracted light is used to reproduce information using two information detection receivers, and is tracked by two other tracking/servo receivers. - Obtain a servo signal, or detect the diffracted light with two light receivers, obtain a tracking servo signal from the difference in output, and obtain a signal for reproducing information from the sum of the outputs. Since the same tracking servo signal as in FIG. 4 can also be obtained, the present invention can be applied to this case.

Furthermore, as disclosed in JP-A-49-94304 or JP-A-49-103515, a light spot or track is slightly vibrated at a reference frequency to reduce the reflected light to 1.
Tracking is performed by comparing the phase of the reference frequency component of this output signal and the minute vibration signal.
Even if the system uses a method for obtaining a servo signal, 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 can be achieved by changing the band of the bandpass filter 27 even when the track movement is caused by deformation of the recording medium.

〔Effect of the invention〕

As described above, according to the present invention, by adding only a few electric circuits, it is possible to draw a light spot into a track even if a tracking servo system with poor frequency characteristics is used.

[Brief explanation of the drawing]

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 disk and the optical spot, and Fig. 4 A and B are diagrams. , 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...
bandpass filter.

Claims (1)

[Scope of Claims] 1. means for irradiating a light spot onto information formed along a track on a rotating recording medium; a light detection means for converting light modulated by the information into an electrical signal; means for producing a signal for reproducing the information from the output of the light detection means and a tracking servo signal; and in response to the tracking servo signal, the light spot is scanned so that the information is scanned along the track. In an information reproducing apparatus comprising a moving tracking means, the signal for reproducing the information and the tracking servo signal are input, and the phases of these signals are compared and the passage of the optical spot is determined each time the optical spot crosses the track. A first circuit that generates a pulse whose direction can be discriminated; and a second circuit that uses the output of the first circuit to generate a signal indicating a deviation of the track with respect to the optical spot; An information reproducing device characterized in that the tracking means is driven by the output of the information reproducing device. 2. In the information reproducing device according to claim 1, the first circuit determines the passing direction from a pulsed signal for reproducing the information and a signal obtained by differentiating the tracking servo signal. An information reproducing device characterized in that it is configured to produce distinguishable pulses.