JPH0527172B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for adjusting an information reproducing device for optically reading information from a record carrier having information tracks.

Conventional Structures and Their Problems Optical data files, video disk players, compact disk players, and the like are already commercially available as information reproducing devices that optically read information from a record carrier having an information track. These information reproducing devices require accurate tracking control and focusing point control because of their high recording density. For example, in a compact disk player, tracking control must suppress a tracking error of 0.1 μm or less for an eccentricity of several hundred μm. In addition, focusing point control needs to keep the focusing error to less than 1 μm for surface runout of several hundred μm. If there is a scratch on the record carrier and a disturbance enters the tracking control system or focusing control system, the control system will be disturbed and the track will jump to a nearby track or move out of the depth of focus, making it impossible to read the information. Something happened. This tendency is particularly noticeable in compact disk players whose track linear speed is slow because the passage time through the defective portion is long. Therefore, the tracking control system and focusing point control system must be adjusted so that the control systems are not shaken by scratches on the record carrier. FIG. 1 is a block diagram showing an example of a focusing point control system of a conventional information reproducing apparatus, in which 1 is an information track, 2 is a record carrier, 3 is a light source, 4 is a beam splitter, 5 is a focus lens, and 6 is a photoelectric Converter, 7 is a balance adjustment means, 8 is a differential amplification means, 9 is an offset adjustment means, 10 is a gain adjustment means, 11 is an optical spot moving means, and 12 is a differential amplifier.

The operation of the focusing point control system configured as described above will be briefly explained below. The light beam generated from the light source 3 passes through a beam splitter 4 and a focus lens 5, connects a very small light spot to the information track 1 on the record carrier 2, and after being modulated according to the state of the information track 1, it is redirected. , enters the focus lens 5, is reflected by the beam splitter 4, and forms an image on the photoelectric converter 6. The photoelectric converter 6 outputs an information signal according to the state of the information track 1, and also outputs a pair of detection signals according to the relative position error between the focal position (minimum light spot position) and the information track. A method for obtaining a pair of detection signals is astigmatism, which uses two lenses with astigmatism in two different directions and takes advantage of the fact that the shape of the image on the photoelectric converter changes according to the relative position error. The aberration method, the critical angle method using the critical angle of a prism, the Foucault method using a knife edge, etc. are generally known. The pair of detection signals is adjusted by the balance adjustment means 7 so that their levels are equal when the relative position error is 0, and then the difference is taken by the differential amplifier 12 to generate an error that fluctuates plus or minus depending on the relative position error. It becomes a signal. The balance adjustment means 7 and the differential amplifier 12 constitute a differential amplification means 8. The error signal is amplified to a required amplitude by the gain adjustment means 10, and the optical spot moving means 11 moves the focus lens 5 to align the focal position with the information track. Offset adjustment means 9 is provided to cancel electrical and mechanical unbalanced components of the focusing point control system.
If the offset adjustment means 9 adjusts the focal point position and then the balance adjustment means 7 adjusts the levels of the detection signal pairs to be equal, a deviation from the previously adjusted focal point position occurs. For this reason, it is actually necessary to perform offset adjustment and balance adjustment alternately and repeat them. There are disadvantages such as it takes time to automatically perform offset adjustment and balance adjustment, and it does not match the optimum value. Furthermore, even if the balance has already been adjusted by some method, if the error rate of the signal read from the information track is used to detect the focal point position, there is a drawback that the offset adjustment takes time.

Purpose of the Invention The present invention has been made in view of the above-mentioned drawbacks.
The present invention provides a method for automatically and quickly adjusting an optical information reproducing device in response to scratches on a record carrier and changes in reflectance and transmittance.

Arrangement of the Invention The present invention includes a record carrier having an information track, a light source for generating a light beam, an optical convergence means for connecting a very small light spot to the information track, and a photodetector, which detects reflected or transmitted light from the information track. information reading means for reading information from the change and outputting at least one pair of detection signals that differentially changes depending on a relative position error between the information track and the optical spot; and one of the pair of detection signals. balance adjustment means for changing the gain for one signal relative to the gain for the other signal; differential amplification means for differentially amplifying the output of the balance adjustment means and outputting an error signal; A sub-differential amplification means that simply differentially amplifies and outputs a sub-error signal, a changeover switch that selects either the error signal or the sub-error signal, and a switch that controls the optical spot based on the selected error signal. a light spot moving means for moving the light spot; a light source modulating means for modulating the amount of light from the light source at a predetermined modulation frequency; the information reading means; the differential amplifying means;
comprising bias adjusting means for adjusting the DC bias voltage of the position control means comprising the optical spot moving means, and when the changeover switch is closed on the side where the sub-error signal is input to the optical spot moving means, Adjust the DC bias of the bias adjustment means so that the relative position error is minimized,
In this state, the light source modulation means modulates the amount of light at a predetermined modulation frequency, adjusts the balance adjustment means so that the modulation frequency component included in the error signal is minimized, and then the error signal moves the light spot. The changeover switch is closed on the input side to the means, and the DC bias of the bias adjustment means is readjusted so that the modulation frequency component included in the error signal is minimized. Therefore, it is possible to automatically and quickly perform strong adjustments against scratches on the record carrier and changes in reflectance and transmittance.

DESCRIPTION OF THE EMBODIMENTS FIG. 2 is a block diagram showing an embodiment of the present invention, in which 1 is an information track, 2 is a record carrier, 3 is a light source, 4 is a beam splitter, 5 is a focus lens, and 6 is a photoelectric converter. 7 is a balance adjustment means, 8
9 is a differential amplification means, 9 is an offset adjustment means, and 10 is a differential amplification means.
11 is a gain adjustment means; 11 is a light spot moving means;
12 is a differential amplifier. In addition, 1 to 12 mentioned above
1 corresponds to the conventional device shown in FIG. 20 is a sub-differential amplification means, 21 is a light source modulation means, 22 is a modulation component detection means, and 23 is a changeover switch.

The operation of the focusing point control system of the optical information reproducing apparatus in this embodiment configured as described above will be described below. The light beam generated from the light source 3 passes through a beam splitter 4 and a focus lens 5, connects a very small light spot to the information track 1 on the record carrier 2, and after being modulated according to the state of the information track 1, it is redirected. , enters the focus lens 5, is reflected by the beam splitter 4, and forms an image on the photoelectric converter 6. The photoelectric converter 6 of the information reading means 66 outputs an information signal to the information track 1 according to the state, and also determines the focal position (minimum light spot position).
A pair of output signals that differentially change depending on the relative position error between the information track and the information track are output. FIG. 3 is a detailed diagram of the information reading means 66. This example corresponds to the astigmatism method, and the shape of the image on the electroelectric transducer 6, which is divided into four parts using two lenses (not shown) with astigmatism in two different directions, is relative to each other. This takes advantage of the fact that it changes depending on the position error (in this case, the focus error), and 66B and 66C are two points on the diagonal.
This is a detection signal pair obtained by the sum of two detection planes. Further, 66A is a signal obtained by the sum of the four detection planes, that is, an information signal read from the record carrier 2. The pair of detection signals passes through the balance adjustment means 7, and the difference is taken by the differential amplifier 12, resulting in an error signal that fluctuates plus or minus depending on the relative position error. The balance adjustment means 7 and the differential amplifier 12 constitute a differential amplification means 8. Also, sub differential amplification means 2
0 simply takes the difference between the pair of detection signals to create a sub-error signal. After the sub error signal and the error signal are switched by the changeover switch 23, the gain adjustment means 10
The light spot is amplified to the required amplitude by the light spot moving means 1.
1, the focus lens 5 is moved to align the focal position with the information track. Offset adjustment means 9 is provided to cancel electrical and mechanical unbalanced components of the focusing point control system. Here, the error signal before adjustment includes a first offset component that fluctuates due to a change in light amount due to a positional shift of the photoelectric converter 6 or variations in each gain, etc.
A second offset component is included that does not vary due to changes in the amount of light caused by offset voltage of the circuit or misadjustment of the mechanical system. The first offset component may be adjusted to 0 by the balance adjustment means 7, and the second offset component may be adjusted to 0 by the bias adjustment means 9, but generally the respective offset components cannot be separated when there is no change in the amount of light. Therefore, first, the changeover switch 23 is switched to select the sub-error signal, and the offset adjustment means 9 adjusts the sum of the first offset component and the second offset component to 0, thereby minimizing the relative position error. In this state, the light intensity of the light source 3 is modulated at a predetermined frequency by the light source modulation means 21, the modulation component included in the error signal is detected by the modulation component detection means 22, and the balance adjustment means 7 adjusts the modulation component to zero. Adjust. The modulation component detection means 22 can use, for example, a synchronous detection circuit that uses the light source modulation frequency as a carrier wave. When the relative position error is minimum in the above adjustment, the error signal does not include the first offset component. Next, when the changeover switch 23 is switched to select the error signal, the focusing point control system is swayed by the second offset component, and a voltage corresponding to the relative position error generated at that time appears in the error signal. At this time, if the modulation component included in the error signal is detected by the modulation component detection means 22 and the bias adjustment means 9 is adjusted so that the modulation component becomes 0, the second offset component also becomes 0.
become. That is, with this configuration, balance adjustment is performed while the relative position error remains at a minimum, so there is no need to repeatedly perform balance adjustment and bias adjustment. In addition, if the balance has already been adjusted by some means, or if balance adjustment is not necessary, the modulation component included in the error signal is simply detected by the modulation component detection means 22, and the bias is set so that the modulation component becomes 0. It is only necessary to adjust the adjustment means 9. Although the focus point control system has been described here, it is obvious that the present invention is applicable not only to the focus point control system but also to tracking control systems.

Effects of the Invention As is clear from the above explanation, according to the adjustment method of the present invention, when the changeover switch is closed on the side where the sub error signal is input to the optical spot moving means, the relative position error is minimized. The DC bias of the bias adjustment means is adjusted so that the amount of light is modulated by the light source modulation means at a predetermined modulation frequency, and the balance adjustment means is adjusted so that the modulation frequency component included in the error signal is minimized. Then, the changeover switch is closed on the side where the error signal is input to the optical spot moving means, and the DC bias of the bias adjustment means is readjusted so that the modulation frequency component included in the error signal is minimized. Since there is no need to make adjustments for balance adjustment and bias adjustment, it is possible to automatically and quickly and accurately perform adjustments that are resistant to scratches on the record carrier and changes in reflectance and transmittance. can.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an example of a focusing point control system of a conventional information reproducing device, FIG. 2 is a block diagram showing an example of a focusing point control system of an optical information reproducing device of the present invention, and FIG. is the information reading means 6 in Fig. 2.
6 is a detailed explanatory diagram of FIG. 6...Photoelectric converter, 7...Balance adjustment means,
8... Differential amplifying means, 9... Offset adjusting means, 10... Gain adjusting means, 11... Optical spot moving means, 20... Sub-differential amplifying means, 21...
Light source modulation means, 22...Modulation component detection means, 23
...Toggle switch.

Claims (1)

[Claims] 1 A record carrier having an information track, a light source generating a luminous flux, an optical convergence means for connecting an extremely small light spot to the information track, and a photodetector, which detects changes in reflected or transmitted light from the information track. information reading means for reading information and outputting at least one pair of detection signals that differentially changes according to a relative position error between the information track and the optical spot; balance adjusting means for changing the gain relative to the gain for the other signal; differential amplifying means for differentially amplifying the output of the balance adjusting means and outputting an error signal; a sub-differential amplification means for dynamically amplifying and outputting a sub-error signal; a changeover switch for selecting either the error signal or the sub-error signal; and a switch for moving the optical spot based on the selected error signal. A DC bias voltage of a position control means consisting of a light spot moving means, a light source modulating means for modulating the amount of light from the light source at a predetermined modulation frequency, the information reading means, the differential amplification means, and the light spot moving means. bias adjustment means for adjusting the bias adjustment means, and when the changeover switch is closed on the side where the sub-error signal is input to the optical spot moving means, the DC current of the bias adjustment means is adjusted such that the relative position error is minimized. After adjusting the bias, the light source modulation means modulates the amount of light at a predetermined modulation frequency in this state, and the balance adjustment means is adjusted so that the modulation frequency component included in the error signal is minimized, and then the error signal is The changeover switch is closed on the side where the signal is input to the optical spot moving means, and the DC bias of the bias adjustment means is readjusted so that the modulation frequency component included in the error signal is minimized. A method for adjusting an optical information reproducing device, characterized in that: