JPS5944699B2 - Eccentricity detection method - Google Patents

Description

Detailed Description of the Invention The present invention irradiates a light beam onto an information groove on a recording medium such as a disk in which information such as video and audio signals is recorded at high density in a spiral or circular manner. The present invention relates to an eccentricity detection method for detecting the eccentricity of a recording medium in order to draw a light beam into an information groove recorded on a moving recording medium in a device that reproduces information using reflected light or transmitted light.

Recently, for example, a TV signal is converted into a light intensity signal, and this modulated light is focused with an optical lens to a diameter of about 1μφ.
Optical recording is performed in a spiral on a 30 (1V7!φ) disk rotating at a
A so-called video disc is being developed to optically reproduce the television signal recorded on this duplicate disc.

Here, an example of a duplicate disk is shown in FIG. In Fig. 1a, there is a hole in the center of the disc 1 like a normal record, and information 21, 22, 23 is recorded on spiral information grooves (hereinafter referred to as tracks) 2, 3, 4, 5, 6. has been done. Here, the track interval is about 2μ. Information 21, 22, and 23 are recorded in a concave and convex shape as shown in FIG. 1b. Rotating such a duplicate disk,
When attempting to reproduce information by irradiating the rotating disk with a light beam, there is usually a deviation between the rotation center of the disk in the recording device and the rotation center of the reproduction disk in the reproduction device, that is, eccentricity.

This shift in the center of rotation, that is, eccentricity, causes the information groove to appear to be moving when viewed from a simply stationary light beam when the disk is rotated.

Another cause of the blurring described above is differential movement caused by movement of the center of rotation of the reproduction disk in the reproduction apparatus.
If the light beam does not track the information groove accurately (this is the case when the playback device starts operating or when mechanical disturbance is applied to the playback device), the light beam may On the other hand, the information gap is blurred. In order for the light beam to accurately track the track from this state, the light beam spot must first be positioned on the track (this is called pulling), and then the light beam must move from the center of the track to the eccentric or precessional movement of the disk. It is necessary to detect the deviation and deflect the light beam so as to cancel the deviation (this is called tracking).

By performing the pull-in and operating the tracking servo system, the light beam can accurately read out information without deviating from the track. The fact that attraction is necessary for tracking is
This is due to the reasons stated below.

That is, the frequency characteristics of the tracking servo system are determined by the frequency characteristics of the main optical deflector. for example,
When the duplicate disk 1 shown in Fig. 1 is rotated at 30 Hz, the center hole of the disk 1 has a fitting error of about 500μ, so if one fixed point on the rotating disk is observed, the track spacing is 2μ. That's about 1 second? X3O
= 7,500 tracks can be seen crossing.

Further, the disk 1 is rotated at 30 Hz, and a light spot of about 1 μm is irradiated onto the disk 1 using an optical lens.
23, if there is a disk eccentricity of about 500 .mu., the time it takes to cross track 4 will be about 1 msec, for example. Therefore, in order to perform tracking along the track while the light beam crosses the track, the servo system must have a flat frequency characteristic up to at least 1 KHz and a polarizer with good phase characteristics. The direction of the light spot 13 must be changed using, for example, the moment the light spot 13 crosses the track 4. However, most of the inexpensive commercially available galvanic mirrors for changing the position of the optical spot have a response of 100Hz, so they cannot be used for that purpose.
It is necessary to develop a galvanic mirror to respond at EC, that is, 1 KHz, which increases the price.

However, since the above-mentioned information reproducing apparatus is desired to be low in price, tracking must be possible even with an optical deflector having poor frequency characteristics.

To do this, the time the light beam traverses the information groove may be lengthened, that is, the light beam may be pulled in. If such pull-in is possible with a galvanic mirror that has a response of about 100 Hz, then various tracking methods for the optical spot 13 to follow on the track 4 have been put into practical use, so the frequency characteristics should be relatively low. Good tracking is possible even with a poor tracking servo system, and the light beam follows the information groove without straying.

In addition, as a tracking method, Japanese Patent Application Laid-Open No. 49-509
The method using three optical spots disclosed in No. 54,
A method using diffracted light from a single light spot disclosed in Japanese Patent Application Laid-Open No. 4960702 is well known.

For example, in a three-spot type information reproducing apparatus, a light beam is separated into three by a diffraction grating, and three light spots are irradiated onto the disk surface.

Among these three light spots, one spot is placed in the middle of the track, and the remaining two spots are placed symmetrically by a slight deviation from the center of the track. The reflected light or transmitted light from the disk is received by three independent photodetectors corresponding to the three spots mentioned above, and the output from the middle photodetector becomes a signal for reproducing information, and the output from the remaining two The output from the photodetector becomes a signal for detecting the deviation between the track and the optical spot, and these two signals are converted into a tracking servo signal by a differential amplifier. In addition, in a method using diffracted light from one optical spot, the photoelectric conversion means is composed of a photodetector divided into two, and the tracking servo signal is generated by converting the difference in output from these photodetectors into a differential amplifier. The signal for reproducing information can be obtained by adding the outputs of these photodetectors using an adder, etc., but in the electrical signals obtained from these, regardless of the method, It's the same. Therefore, an object of the present invention is to optically detect the eccentricity of a recording medium such as a disk, thereby making it possible to quickly draw a light spot into a certain track even if an inexpensive galvanic mirror is used. An object of the present invention is to provide an eccentricity detection method.

In other words, in the present invention, a light spot is irradiated onto an information groove formed on a recording medium, the light modulated by the information groove is received by at least two photoelectric conversion elements U2, and the output of the two photoelectric conversion elements is In a device that reproduces information while performing tracking using a signal difference, by detecting the direction and speed at which the optical spot crosses the information groove from the output signal of the photoelectric conversion element for performing the tracking, The present invention is characterized in that eccentricity of the recording medium is detected.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

As mentioned above, FIG. 1 shows a rotating disk on which the modulated information used in the present invention is recorded in a spiral or concentric manner.

FIG. 2 is a block diagram of the present invention for optically detecting the amount of eccentricity of the rotary disk shown in FIG. 1, and shows a three-spot method. In Figure 1, 1 is a rotating disk, 2,
3, 4, 5, 6 are video signals 20, 21, 22, 23,
24 and 25 are tracks recorded electrochemically in the form of irregularities or shading. The track spacing is about 2μ. The take shown in FIG. 1 is used for reproduction in FIG. In Fig. 2, 7 is a light source, for example, a helium neon laser, and 8 is a laser beam from the laser light source 7 of O order.
A diffraction grating for ±1st order diffraction, 9 a first converging lens for converging the laser beam, 12 a 1μ
The second converging lenses 13, 13', and 13I are used to create very small light spots, and the O-th, -1st, and +1st-order laser beams diffracted by the diffraction gratings are connected to the lenses 9, 13, and 13I.
This is a light spot imaged on the disk by 12 (not shown accurately because it is minute). 14
, 14', 14I are light spots 13, 13! , 13'' are spots that are reflected onto the disk surface 1 and imaged again by the lens 12 at a position conjugate with the disk surface 1 (the same applies to this case as well).

). 10 is prism or half mirror 11 is disk 1
This is a galvanic mirror for changing the position of the light spots 13, 13'', 13'' condensed on the surface in the radial direction of the disk.

15, 157, 15I are light spots 14, 141, 14
This is a photodetector that converts the amount of light of '' into an electrical signal.

16 is a low-pass filter, 17 is a phase comparator, 19 is a pulse counter, and 18 is a drive circuit for driving the galvanic mirror 11.

In FIG. 2, the light from the light source 7 is passed through the diffraction grating 8 to
The light is diffracted in three directions: second order, +1st order, and -1st order, and each of these lights is reflected onto the disk 1 by a first converging lens 9, a prism 10, a galvanic mirror 11, and a second converging lens 12. Two light spots 13, 13'', 13'' are formed.

These light spots 13, 13', 13'' are modulated by information recorded on a disk as shown in FIG.
Through the prism 10, minute light spot openings 4, 14', and 51C are formed on a surface conjugate with the disk surface 1 (at this time,
The diameter of the light spot is approximately 100 μm. ). The intensity of the light spot is converted into an electrical signal by photodetectors 15, 15'', 15'', respectively. Disc 1 at 30Hz
When rotating at , the frequency component of the eccentricity of the disk is 3
Since most of the frequencies are 0Hz and 60Hz, the photodetector 15' is used to detect the magnitude and sign of the eccentricity of the disk 1.
, 1SI are passed through a low-pass filter 16 of approximately 50 KHz. By passing the signals from the photodetectors 15/1 and 1 through the low-pass filter 16 and processing these two signals, it is possible to optically detect the magnitude and sign of the eccentricity of the rotating disk 1. becomes. Next, the operation of the apparatus of this embodiment will be explained using FIG.

By adjusting the angle of the diffraction grating 8 shown in FIG.
Next, it is technically possible to set the optical spots 137, 13'' due to the +1st-order diffracted wave so that they are on both sides of the track 4, for example, as shown in FIG. 3a. As shown in FIG. 3a, when the disk 1 moves in a positive direction or a negative direction in a direction substantially perpendicular to the track due to eccentricity with the disk 1 hanging on both sides of the track, the light spots 13', The optical signal from the disk surface 1 of 137 is converted into an electrical signal by the photodetectors 15' and 15'', and the output from the low-pass filter 16 at a frequency lower than the video signal frequency range, for example, up to 50 KHz is shown in the figure. 3b and 3c. FIG. 3b shows the photodetector 15' when the disk is eccentric in the positive direction.
15'', and Figure 3c is the output signal when the disk is eccentric in the negative direction.As is clear from Figures 3b and 3c, when the disk is eccentric in the positive direction and When the photodetector 1 is eccentric in the negative direction,
It can be seen from the difference in the phase of the output signals from 5' and 15''.In other words, in order to know in which direction the disk 1 is eccentric, it is necessary to use the photodetector 15.
15'' are independently passed through a low-pass filter 16 to remove video domain signals, and the output signals thereof are passed through a phase comparator 17 as shown in FIG. The sign of the eccentricity of can be detected. For example, by slicing the output signal from the low-pass filter 16 at a predetermined level and making it into pulses, and determining the level of the other based on the rising edge (or falling edge) of one of these pulse outputs, it is possible to At the same time as detecting the direction in which the spot passes through the track, it outputs a pulse corresponding to the polarity of the detected phase each time the optical spot passes through the track. Such a phase comparator is known as a digital phase comparator. Therefore, the magnitude (velocity) of the eccentricity of the rotating disk is determined by counting how many pulses with the same phase polarity are output from the phase comparator 17 each time the optical spot passes the track. This can be detected by counting the number of tracks that the light spot has passed through.

Therefore, the phase comparator 17 and the pulse counter 1
9 makes it possible to easily detect the magnitude and sign of the eccentricity of the rotating disk at the same time. Then, a signal including the output voltage and its sign in proportion to the number of pulses from the phase comparator 17 and the pulse counter 19 is inputted to the galvanic mirror drive circuit 18.
When driven, the optical spots 13, 13', 13'' exhibit the same movement as the eccentric movement of the rotating disk 1, and it becomes possible to easily realize the drawing into the track recorded on the disk. However, the tracking servo signal is also input to the galvan mirror drive circuit 18 from the tracking deviation detection circuit.However, since the tracking servo signal has a frequency of about several KHz, the resonance frequency is low. Galver mirror 11 hardly moves with the tracking servo signal,
It moves based on the tracking pull-in signal, and the light spot moves almost in the same way as the truck. As a result, the time during which the optical spot is located on the track becomes very long, and when the optical spot is pulled in, the tracking servo signal at that time ranges from several hundred Hz to several + Hz. At such a frequency, even a tracking servo system with poor frequency characteristics can respond sufficiently, and tracking is performed. Regarding the tracking servo system,
This is detailed in the aforementioned Japanese Patent Application Laid-open No. 49-50954. FIG. 4 shows another embodiment according to the invention.

In Fig. 2, the third
As shown in figure a, the number of pulses crossing tracks 2, 3, 4, and 5 was counted, but when a light spot crosses a particular track groove, for example track 4, a television signal is generated on the track. Since it is recorded, for example, 4M
Pulses on the order of Hz are detected. The smaller the number of information signals of about 4 MHz counted when crossing a track, the larger the eccentricity, and the larger the number of pulses, the smaller the eccentricity.
That is, as shown in FIG. 4, the direction of eccentricity is determined by the phase comparator 1.
7 and the speed of eccentricity can be detected by inputting the output of a photodetector, e.g. 15, directly to a pulse counter 19 and counting the pulses in the video area detected as it traverses the track. Therefore, when these two signals are input to the galvanic mirror drive circuit 18 to drive the galvanic mirror 11, the optical spots 13, 13', 13''
shows the same movement as the eccentric movement of the rotary disk 1, and it becomes possible to easily realize the pull-in to the track recorded on the disk. In the above explanation, we have taken as an example a disk on which information is recorded concentrically or spirally, but the invention is not limited to these in any way; for example, information may be recorded linearly. It is clear that the present invention can be applied to sheet disks of different types.

As detailed above, according to the present invention, it is possible to optically easily detect the eccentricity of a rotating disk, and it provides a method for easily pulling into a track where information is recorded. The effect is large.

[Brief explanation of the drawing]

Fig. 1 is a conceptual diagram of a video disk, Fig. 2 is an illustration of one embodiment of the present invention, Fig. 3 is a diagram for explaining the operation of Fig. 2, and Fig. 4 is another embodiment of the invention. It is a diagram. In the same figure, 1: rotating disk, 2, 3, 4, 5, 6
Track groove, 7; Light source, 8; Diffraction grating, 9; First converging lens, 10: Prism, 11; Galver mirror 12;
Second converging lens, 13, 13″, 13″, 14, 14′
, 14I; Light spot, 15, 15', 15''; Photodetector, 16: Low-pass filter 1, 17; Phase comparator, 18;
Drive circuit, 19; pulse counter 20, 21, 22,
23, 24, 25; pulse signal.

Claims (1)

[Claims] 1. A light spot is irradiated onto an information groove formed on a recording medium, the light modulated by the information groove is received by at least two photoelectric conversion elements, and the difference between the output signals of the two photoelectric conversion elements is calculated. In a device that reproduces information while performing tracking, the direction in which the optical spot crosses the information groove is detected by comparing the phases of the low-frequency components of the output signal, and the pulse of the output whose phase has been compared is detected. An eccentricity detection method characterized in that the number of the light spots crossing the information groove is detected by counting the number.