JPS60209933A - Tracking servo device for optical information reader - Google Patents

Abstract

PURPOSE:To attain tracking control with high accuracy by using a detecting means for deviation amount (deflection amount) of a tangential mirror (mobile mirror) of a tangential servo device and correcting a tracking error signal in response to the output of said detecting means. CONSTITUTION:A difference [(a+b)-(c+d)] between the addition outputs of adders 15 and 16 is obtained by a subtractor 18. The difference output of the subtractor 18 is used as the comparison inputs of comparators 19 and 20 having reference levels +VTH and -VTH respectively. The comparison output of the comparator 19 is used as a control signal which turns on (closes) a switch S2. Thus a tangential mirror is deflected in response to a tangential error signal. When the amplitude of the tangential mirror exceeds a reference level, a control signal is produced from the comparator 19 or 20 according to the deflecting direction of the tangential mirror. Then a switch S2 or S1 is turned on in response to said control signal. Thus a tracking error signal is corrected in the positive or negative direction.

Description

DETAILED DESCRIPTION OF THE INVENTION Flame LLL The present invention relates to a tracking servo device, and more particularly to a tracking servo device in an optical information reading device having a tangential servo device using a movable mirror.

BACKGROUND ART In optical information reading devices, so-called tracking servo systems and tangential servo systems are essential. The tracking servo system controls the spot light for information reading so that it always accurately tracks on the recording track regardless of the eccentricity of the disk as a recording medium, and it controls the position deviation of the spot light in the direction orthogonal to the recording track. to do. On the other hand, the tangential servo system
This is to accurately control the time axis of the reproduced signal, and to control the positional deviation of the spot light in the tangential direction of the recording track.

The configuration of the optical system of these optical information reading devices having a servo system is shown in FIG. The light is focused on the recording surface of the disk 8 via the plate 4, the tracking mirror 5, the tangential mirror 6, and the objective lens 7. Second
As is clear from the figure and FIG. 3, three light beams are focused on the recording surface of the disk 8, resulting in two tracking servo spot lights A (A+).

Az>, B (B+, B2) and one RF signal detection spot light combination (C+, C2) are obtained. These three spot lights A, B, and C are reflected by the recording surface of the disk 8, travel in the opposite direction along the above-mentioned incident optical path, enter the beam splitter 3, further pass through the cylindrical lens 9, and enter the photodetector 1o. This photodetector 10 converts it into an electrical signal. The photodetector 10 receives three spot lights A, B,
The spot light A consists of three light-receiving elements that each receive light A.

The output difference between the two light receiving elements that receive B light is derived as a tracking error signal.

Next, the operation will be explained. In FIGS. 2 and 3, the focus servo system is closed and the light beam is directed to the disk 8.
, the tracking servo system is closed, and the RF multiplied signal recorded on the disk 8 is detected by the spot light C. In this state, the rotational speed of the disk 8 is When the spindle servo system and the tangential robot group which control the tangential mirror 6 are closed, the tangential mirror 6 swings in the direction of the arrow in response to a genial error signal outputted from means (not shown). As a result, three spot lights A and B
, C move in the tangential direction P without changing their relative positions, and the RF multiplied signal is detected from the recording track T by the spot light C.

In the conventional device configured in this way, when the tangential mirror 6 swings, either the spot light A or the spot light B approaches the end of the objective lens 7 depending on the direction of the swing of the tangential mirror 6, so that Since there will be a difference in the amount of light spots A and B on the recording surface of the disk 8, a tracking error signal will be generated even though the spot light C is located on the recording track T, and the spot light There was a drawback that the light C was controlled in a direction that deviated from above the recording track 1-.

(1) The present invention is a tracking servo device in an optical information reading device, which has been made to eliminate the drawbacks of the conventional device as described above, and is capable of performing accurate tracking control regardless of the operation of the tangential mirror. The purpose is to provide

The tracking servo device in the optical information reading device according to the present invention includes a detection means for detecting the amount of deviation (oscillation amplitude) of the tangential mirror (movable mirror) in the tangential mirror device, and the output of the detection means The configuration is such that the tracking error signal is corrected accordingly.

Example Hereinafter, embodiments of the present invention will be described in detail based on the drawings.

In FIG. 4, a photodetector 10 that receives a light beam reflected on a disk recording surface includes two light receiving elements 11 that receive spot lights A and B for t-racking servo, respectively.
．． 12, and a photodetector 13 that combines and receives spot light for RF signal detection. Two light receiving elements 11.12
If the subtracter 14 detects the difference in the output of It is derived as a tracking error signal. The subtracter 14 is composed of an operational amplifier OP and resistors R1 to R4. A resistor R5 and a switch S1 connected in series are connected in parallel to the resistor R1 of the subtracter 14, and a resistor R6 and a switch S1 connected in series are connected to the resistor R3.
2 are connected in parallel.

As the light detector 13, a so-called four-split photodetector is used. As shown in the figure, this photodetector 13 has four light-receiving surfaces divided by two dividing lines X and Y that are orthogonal to each other, and these surfaces are each light-receiving surface of four independent photoelectric conversion elements. It is made up of. The dividing lines X are arranged so as to be perpendicular to the track tangential direction, and the dividing lines Y are arranged parallel to each other. Same as the output sum (a + b) of the light receiving surfaces a and b, which are symmetrical with respect to the dividing line Y, the light receiving surfaces c and d
The output sum (c + d ) of is derived by adders 15 and 16, respectively. The respective outputs of adders 15 and 16 are further added by adder 17, and the output ((a + b)
+ (c+d)) or 4 at the photodetector 14
The sum of the outputs of the light receiving surfaces is derived as an RF signal.

The difference between the addition outputs of adders 15 and 16 [(a+b)-(
c+d)) is obtained in the subtractor 18. The spot light C incident on the light-receiving surface of the photodetector 14 moves along the dividing line Y within the light-receiving surface in response to the deflection of the tangential mirror 6 (see FIG. 2).
Therefore, by deriving the difference ((a+b)-(c+d)) between the outputs of the adders 15 and 16, the direction and amount of deflection of the tangential mirror 6 can be detected. This difference output ((a + b) − (
c + d)) corresponds to the degree of unbalance in the amount of light of the tracking servo spot lights A and B due to the deflection of the tangential mirror 6, that is, the difference in the amount of light between the two. The difference output of the subtractor 18 is at the reference level +VTI-1°-
It becomes the comparison input of comparator 19.20 with Vv day. The comparison output of the comparator 19 becomes a control signal for turning on (opening) the switch S2, and the comparison output of the comparator 20 becomes a control signal for turning on the switch S1.

According to this configuration, when the tangential mirror 6 swings in response to the tangential mirror signal and the swing width becomes larger than the reference width, a control signal is generated from the comparator 19 or 20 corresponding to the swing direction. , the switch $2 or Sl is turned on in response to this control signal, so that the tracking error signal is corrected in the positive or negative direction. That is, in FIG. 5 showing the basic form of a subtracter, if the two inputs corresponding to the respective outputs of the two light receiving elements 11 and 12 are V8 and Vs, and the output corresponding to the tracking error signal is Vo, then the input ■A , VB and output Vo
The relationship with is expressed by the following equation.

In the above equation, if ZB is made small, the output V.

can be increased, and by decreasing Zg, the output ■0 can be decreased. Therefore, in FIG. 4, by turning on the switch S1 and connecting the resistor R5 in parallel with the resistor R+, the tracking error signal is made to go in the positive direction. Further, by turning on the switch S2 and connecting the resistor R6 in parallel to the resistor R3, the tracking error signal can be corrected in the negative direction. The amount of correction is determined by the resistance value of each resistor.

Note that in the above embodiment, two comparators 19
．． Using 20, the swing width of the tangential mirror 〇 is 2
Although the tracking error signal is corrected when the two reference widths are exceeded, the tracking error signal may be corrected more finely by increasing the number of comparators. It is also possible to continuously correct the tracking error signal by using a subtracter 18 and changing its impedance based on the output of the subtracter 18.

Further, as a means for detecting the deviation of the tangential mirror, a four-split photodetector 13 and a four-part photodetector 13 are used.
A circuit for screening each output of the two light receiving surfaces (15, 16, 18
), but for example, a potentiometer may be connected to the rotary wheel of the tangential mirror to directly detect the displacement m of the tangential mirror. Furthermore, when the tangential mirror rotates, an optical sensor consisting of a combination of a light emitting element that emits light toward the reflective surface of the tangential mirror and a light receiving element that receives the light reflected from the reflective surface is used. It may be configured such that the amount of light received by the light receiving element is changed and the amount of displacement of the tangential mirror is detected based on the output of this light receiving element.

--1 As explained above, according to the present invention, the deflection amount of the tangential mirror is detected and the tracking error signal is corrected according to the detected output, so that the viewing angle of the tracking servo can be adjusted. As the width becomes wider, a tracking servo device for an optical information reading device is obtained, in which tracking servo is properly performed and a water pot for detecting an RF signal can be positioned on a recording track with high precision.

[Brief explanation of drawings]

Fig. 1 is a configuration diagram showing the optical system of an optical information reading device, Fig. 2 is an enlarged view showing the state of the light beam at the tangential mirror and objective lens in Fig. 1, and Fig. 3 is a diagram showing the state of the light beam in relation to the recording track. A diagram showing the positional relationship of three optical pots,
FIG. 4 is a circuit diagram showing an embodiment of the present invention, and FIG. 5 is a circuit diagram showing an embodiment of the present invention.
FIG. 2 is a circuit diagram showing the basic form of the subtracter in the figure. Explanation of symbols of main parts 1... Light source 3... Beam splitter 5... Tracking mirror 6... Tangential mirror 7...
Objective lens 8...Disk 10...Photodetector 14...Subtractor 19.20...Comparator Applicant Pioneer Corporation Agent Patent attorney Motohiko Fujimura #1 Figure tail 2 Figure 3 Map 5

Claims (3)

[Claims] (1) A tracking servo device in an optical information reading device having a tangential V servo device that uses a movable mirror to control the movement of information reading spora I/light in the tangential direction of a recording track of a recording medium, wherein the movable mirror Biased (I
1. A tracking servo device for use in an optical information reading device, characterized in that the tracking servo device is equipped with a detection device for detecting a signal II, and corrects a tracking error signal according to an output of the detection device. (2) The detection means has a light-receiving surface that receives the spot light that has passed through the recording surface of the recording medium, and generates a signal corresponding to the deviation of the center of the received spot light with respect to a reference position on the light-receiving surface. A tracking servo device in an optical information reading station according to claim 1, characterized in that the tracking servo device includes a photodetector. (3) The light-receiving surface of the photodetector is composed of four surfaces divided by two lines perpendicular to each other, and these surfaces are composed of the light-receiving surfaces of four independent photoelectric conversion elements. A tracking servo device in an optical information reading device according to claim 2, characterized in that: