JPH0682469B2 - Tracking controller - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention relates to a device for following a recording / reproducing optical head to an information track (hereinafter simply referred to as a track) of a disc-shaped optical information recording medium (hereinafter referred to as an optical disk). In particular, a device that controls the beam spot of a laser or the like to follow an information track of an optical disc or an information optical card (tracking servo,
Hereinafter simply referred to as servo system).

(Prior Art) FIG. 7 is a block diagram showing a configuration of a conventional servo system.

Reference numeral 1 denotes an optical disc, which has tracks called pregroups which are distinguished by concentric or spiral information pit rows or irregularities at a track pitch of about 1.5 μm to 2.5 μm. An optical disk motor 2 drives the optical disk 1 to rotate stably and accurately. Reference numeral 3 denotes an optical head (hereinafter, simply referred to as a head), which is an incident optical system that guides a laser beam spot onto the recording surface of the optical disc 1 by a laser or an optical component for recording / reproducing information, and a reflected light from the optical disc 1. And a reflection optical system leading to the information detector. The head 3 has an objective lens 5 for converging the laser light 4, a tracking coil 6 for moving the objective lens 5 in a direction orthogonal to the track, and a tracking detector (hereinafter, referred to as a tracking detector) for detecting a tracking signal from the reflected light. 7). Further, the head 3 is configured to be movable in the radial direction of the optical disc 1 by a linear motor 8 or other feeding mechanism. In addition, in general, a focus coil, a focus detector, and the like are provided, but the description thereof will be omitted.

Although the detector 7 has various detection methods,
In the following description, a detector used in the far field method, which is divided into at least two, will be described.

Now, the reflected light from the optical disk 1 applied on the detector 7 becomes a tracking signal having relative position information of the track and the laser spot by the differential amplifier 9,
The laser spot is supplied to the tracking coil 6 via the AGC circuit 10, the phase compensation circuit 11, the loop switch 12, and the tracking drive circuit 13 as required to make the laser spot follow a desired track.

Reference numeral 14 denotes an adder circuit for adding two output signals from the detector 7 which is divided into two and detecting the reflected light amount.
It is used as a control signal for the AGC circuit 10, and operates to keep the tracking loop gain constant even if a change in light amount or a change in the reflectance of the optical disc 1 occurs, thus achieving a stable operation of the servo system. The input point A shown in the tracking drive circuit 13 or the drive signal itself is applied to the linear motor 8 and the like through the phase compensation circuit 15 using a low-pass filter and the feed drive circuit 16, and the entire circumference of the optical disc 1 is applied. It forms a track-following servo system that operates stably over the entire length.

FIG. 8 is a diagram showing the detection principle of the tracking signal of the far field method. In the uppermost stage (a), the beam spot S of the optical laser is arranged on the track T in the order of FIG. 1 to FIG. It is a schematic diagram in the case of crossing, and the interruption (b) shows the light intensity distribution of the first-order diffracted light detected by the two-divided detector 7 (FIG. 7), and the beam spot S is correctly positioned on the track T. In the case, as shown in FIG. 3C, the light intensities of the left and right 7a, 7b are almost balanced, and the light intensities of the left and right 7a, 7b are broken as the beam spot S is separated from this. Note that the left and right light intensities are balanced even when the beam spot S is completely separated from the track T as shown in FIGS. After such a change in light intensity is converted into an electric signal by the detector 7, the electric signal is supplied to the differential amplifier 9 to obtain a sinusoidal tracking signal as shown in the lowermost stage (c).

The above tracking signal is observed when the loop switch 12 of the servo system in FIG. 7 is off, and when it is on and the servo system is operating stably, the tracking signal in the bottom row (c) of FIG. The DC signal fluctuates slightly around the point (3).

Although there are various detectors 7 other than those described above, the relationship between the track and the beam spot and the tracking signal are almost the same as those described above, and the operation is the same, so the description thereof is omitted.

(Problems to be Solved by the Invention) In an optical recording / reproducing apparatus having a servo system as described above, an optical disc or an optical information card used as an information recording medium is limited in its manufacturing accuracy or mounting accuracy of the apparatus itself. , Track pitch (1.5 μm to 2.5
μm), which is several tens to several hundred times the off-track phenomenon. The off-track amount is mainly due to the eccentricity of the center of the track with respect to the center of rotation of the optical disk, and the shape of the track. It is generated by being affected by the distortion of and the vibration from the outside.

Such eccentricity is corrected by a servo system that shifts the relative position between the objective lens and the target track. However, since the eccentricity is large as described above, the tracking signal until the servo system operates after the loop switch 12 is turned on has the waveform B as shown in FIG. The relatively low portion B'occurs at a half cycle of the rotation cycle of the optical disc. Therefore, in the vicinity of point B higher than the response frequency of the servo system, even if the loop switch 12 for operating the servo system is turned on, the servo system is turned on. Cannot respond immediately and therefore cannot be tracking retracted. Alternatively, there is a problem that the tracking drive circuit 13 is saturated by the tracking signal and a desired pull-in characteristic cannot be obtained, which makes the reading of recorded information on the optical disc 1 unstable.

Conventionally, for example, the following countermeasures have been proposed for such a problem, but each has a problem. That is, (1) The method described in Japanese Patent Laid-Open No. 56-7247, which keeps the relative positional relationship between the objective lens and the track constant by the eccentric memory even when the servo system loop is off.

(2) JP-A-62-16249 discloses that the relative positional relationship between the objective lens and the track is suppressed to a certain amount by using a signal that has a sine wave memory and digitally calculates the amplitude and phase close to the eccentricity of the optical disk. Other methods described.

(3) The phase of the envelope of the information signal is compared with that of the tracking signal, and when the polarity of the comparison output changes, the servo system loop is turned on and driven, so that the servo signal at the time when the frequency of the tracking signal becomes low. The method described in Japanese Examined Patent Publication No. 60-51173, which enables the retraction.

However, in the method of the above-mentioned proposal (1), tracking is inoperative at the time of start-up, and since the eccentricity memory is not set, the limit eccentricity amount for pulling is small, and the inner circumference of the disk (outer circumference of the center hole of rotation) Since the eccentricity is different from the outer circumference, a certain effect cannot be obtained. Further, the method (2) does not have the same effect when the difference between the inner and outer circumferences of the optical disc or the eccentric shape includes the second harmonic. Further, the method (3) has a drawback that a waiting time occurs until the tracking frequency becomes low, and access time and tracking accuracy are lowered. Further, the methods (1) and (2) have a problem that it is difficult to deal with the fluctuation of the eccentric phase due to the slip of the optical disk and the environmental change such as external vibration because the method is an open loop system.

The present invention is intended to eliminate the above-mentioned problems of the conventional servo system.

(Means for Solving Problems) The present invention solves the above problems by discriminating the direction of a track crossing component of a tracking signal into an F / V circuit, an objective lens, and a direction discriminating device that detects a crossing direction with respect to a track. Circuit, and add to the servo system after switching the output polarity of the F / V circuit by the output of the direction discrimination circuit,
The problem is solved by configuring the tracking servo system that activates it.

(Operation) With the device of the present invention having the above configuration, when the servo system is off, the relative moving speed between the objective lens and the track is kept substantially constant, and tracking pull-in is possible at any timing. If necessary, the output of the direction discriminating circuit is inverted and stabilized depending on the presence or absence of information pits to stabilize the characteristics depending on the type of information recording medium such as an optical disk and environmental changes such as external vibration. Therefore, stable tracking pull-in is always performed.

(Examples) Hereinafter, the present invention will be described with reference to Examples.

FIG. 1 is a block diagram showing a first embodiment of the present invention. In some embodiments described below,
7 is based on the configuration and operation of FIG. 7, and therefore, reference numerals and operation explanations not described below are based on the explanation of FIG. 7, and other reference numeral 17 is a direction discrimination circuit, which is the differential amplifier 9 and the addition circuit described above. The 14 AC components are phase-compared, and the transverse direction between the track and the objective lens 5 is determined by a flip-flop or the like. Reference numeral 18 denotes an F / V circuit, which converts the changing frequency of the tracking signal generated when the loop switch 12 of the servo system is off to a voltage.

Reference numeral 19 denotes a polarity switching circuit, which switches the output of the F / V circuit 18 by the output of the direction discriminating circuit 17 so that the output of the F / V circuit 18 becomes higher when the tracking signal frequency becomes higher. It has a switching function. 20 is an adder circuit, and F / V is added to the servo loop via the switch circuit 21.
The outputs of the circuit 18 are added and the drive control of the tracking coil 6 is performed.

With such a configuration, the output of the F / V circuit 18 is kept substantially constant, and therefore the tracking coil 6 operates stably, so that the relative moving speed of the objective lens 5 and the track becomes substantially constant, and therefore the tracking signal is As shown in FIGS. 2A to 2B, the frequency changes from a high frequency to a low frequency. The F / V circuit 18 is set so that the output frequency as shown in this figure (b) is made to substantially match the response frequency of the servo system.
If the constant of is set, the tracking pull-in of the servo system will be extremely stable.

FIG. 3 is a block diagram showing the second embodiment, which is suitable for an apparatus for performing phase change recording using a material such as TeOx,
The direction discriminating circuit 17 in the first embodiment described above and the information recording medium having a different structure and characteristics from those of the optical disc are to be implemented.

In such a configuration, since there is a difference in light reflectance between the recorded track and the unrecorded track, the discrimination output of the direction discrimination circuit 17 may be inverted. Therefore, an information recording detection circuit 22 and a polarity reversing circuit 23 are added to the configuration of FIG. 1 so that the polarity of the output of the above-mentioned F / V circuit 18 can be switched through them, and the recorded track and the unrecorded track can be changed. The output polarity of the direction discriminating circuit 17 is switched depending on the recording track.

FIG. 4 is a block diagram showing a third embodiment.

In the present embodiment, basically, the direction discriminating circuit 17 does not have to malfunction due to noise or the like on the optical disc 1 in view of the fact that the direction discriminating circuit 17 has only to operate within the half cycle of the rotation period of the optical disc 1 when the cross-track direction is reversed. Thus, the timer circuit 24 is provided to stabilize the output of the direction discriminating circuit 17 so that the output of the direction discriminating circuit 17 does not change in an excessively short period.

FIG. 5 is a diagram showing a fourth embodiment, which is an embodiment for coping with the case where the operation of the F / V circuit is unnecessary or impossible, and in the recording / reproducing apparatus embodying the present invention, generally, It has a random access function to detect any track that is largely off track. In that case, in the case of tracking for pulling in with respect to the eccentricity between the center of rotation of the optical disc and the center of the track, the object traverses at a speed several tens to several hundred times faster than the traverse speed of the track of the objective lens. The output of the / V circuit cannot be followed and has no meaning. Therefore, the F / V circuit should be disabled by a command from the microcomputer or the linear motor 8
Is provided with a speed detector 25, a level determination device 26 for determining whether or not the moving speed of the head 3 exceeds a certain level, and a switch control circuit 27 for controlling the switch circuit 21.
In order to save unnecessary power consumption during the random access operation as described above, the control operation of the track crossing frequency is limited.

FIG. 6 is a block diagram showing a fifth embodiment. For the same purpose and reason as the fourth embodiment, a level judgment circuit 28 for directly measuring the output level of the F / V circuit 18 is provided and The frequency of the tracking signal is measured to obtain the same effect as that of the fourth embodiment.

Although the present invention has been described above with reference to the embodiments, the present invention also has variations in the types of recording medium materials such as magneto-optical and organic dye-based materials, and in the shapes of information recording media such as optical disks and optical information cards. However, the effect can be sufficiently achieved,
Further, the components such as the F / V circuit and the direction discriminating circuit can obtain the same effect by either analog processing or digital processing.

(Effects of the Invention) As is apparent from the detailed description above, the present invention provides an F / V circuit for converting the tracking signal frequency into a voltage, a discriminating circuit in the cross-track direction, a polarity switching circuit for the F / V circuit, and a use thereof. It is possible to keep the relative movement speed between the objective lens and the track before the track pull-in almost constant with a simple structure that has peripheral circuits according to the characteristics of the information recording medium. A great effect can be obtained by implementing it as a tracking control device of an extremely stable optical information recording / reproducing device which is not affected by waiting or disturbance.

[Brief description of drawings]

FIG. 1 is an explanatory view of the first embodiment of the present invention, and FIG.
FIG. 3 is an auxiliary view for explaining the drawings, FIG. 3 is an explanatory view for the second embodiment, and FIG.
FIG. 7 is an explanatory view of the third embodiment, FIG. 5 is an explanatory view of the fourth embodiment, FIG. 6 is an explanatory view of the fifth embodiment, FIG. 7 is an explanatory view of a conventional example, and FIG. Is an explanatory diagram of the principle of tracking signal detection, and FIG. 9 is a diagram showing an example of a tracking signal. 1 ... Optical disk, 2 ... Optical disk motor, 3 ... Optical head (simply called head), 4 ... Laser light, 5 ...
... objective lens, 6 ... tracking coil, 7 ... tracking detector (simply called detector), 8 ...
Linear motor, 9 ... Differential amplifier, 10 ... AGC circuit, 11,
15 …… Phase compensation circuit, 12 …… Loop switch, 13 …… Tracking drive circuit, 14,20 …… Adding circuit, 16 …… Feed drive circuit, 17 …… Direction discrimination circuit, 18 …… F / V circuit, 19 ...
… Polarity switching circuit, 21 …… Switch circuit, 22 …… Information recording detection circuit, 23 …… Polarity inversion circuit, 24 …… Timer circuit,
25: speed detector, 26: level judgment device, 27: switch control circuit, 28: level judgment circuit.

Claims (5)

[Claims] 1. A tracking controller for an optical recording / reproducing apparatus for drawing a light beam spot onto an information track of an optical information recording medium, and a tracking detector for detecting the relative position of the information track and the light beam spot, and its output. Tracking control means for making the light beam spot follow an information track, a tracking drive circuit, a loop switch for inputting the tracking detector output to the tracking control means, and an F / V for converting the output signal frequency of the tracking detector into a voltage. A circuit, a direction discriminating circuit that detects the direction in which the light beam spot crosses the information track, and a polarity switching circuit that switches the polarity of the F / V circuit output, and when the loop switch is off, the F / V The circuit output is tracked via the polarity switching circuit. The polarity switching circuit is controlled by the output of the direction discriminating circuit while being applied to the driving input addition point of the driving circuit, and tracking is performed so that the relative crossing speed between the light beam spot and the information track becomes constant. A tracking control device characterized by controlling a control means. 2. A polarity detecting circuit for detecting an information pit of an information track, wherein the polarity switching circuit of the F / V circuit is controlled through an inverting circuit for inverting the output polarity of the direction discriminating circuit. The tracking control device according to claim (1). 3. When the information pit is recorded on the information track of the disc-shaped optical information recording medium, the direction discriminating circuit output is
The polarity switching circuit is controlled through a holding circuit such as a timer that holds a time shorter than 1/2 of the rotation cycle, and the polarity switching circuit is controlled. (1) or (2) Tracking control device. 4. An F / V circuit output is tracking-controlled by a moving speed detecting circuit for moving the light beam spot of the tracking control means in a direction orthogonal to the information track and a level judging circuit for judging its output level. Claims (1), (2) and (3), characterized in that when applying and adding to the means, addition is performed via a second switch circuit which is turned on and off by the output of the level determination circuit. ) The tracking control device according to any one of paragraphs. 5. An F / V for judging the magnitude of the output level of the F / V circuit
A level determination circuit is provided, which controls the addition of the F / V circuit output to the tracking control means input via a switch control circuit as a third switch which is turned on / off by the F / V circuit level determination circuit. The tracking control device according to any one of claims (1), (2) and (3), wherein the addition is performed via a second switch.