JPH03134828A - Track tracing device correcting optical axis deviation - Google Patents

Abstract

PURPOSE:To exactly trace and control a light spot to a track on a medium by combining a means to synchronously detect the optical axis deviation of a track error signal and a means to always detect the optical axis deviation of the track error signal in a detection area on the surface of an optical disk and removing the direct current error component of the signal in the latter means. CONSTITUTION:By slightly moving an objective lens 9 to the directions of Z and Y axes, the light spot is formed in a target track 57 and positioned to be followed up. The optical head outputs a focus error signal and the track error signal from returning light 19 reflected on an optical disk 56. Difference between the output of the optical axis deviation detecting means for the synchronous track error signal in the detection area provided on the surface of the optical disk and the optical axis deviation detection signal of the track error signal to be detected just afterwards is detected and optical axis deviation can be detected. Based on the amount of this detection, the optical axis deviation amount of the track error signal to be always detected is corrected. Thus, the track error signal always is detected without fail.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for tracking and controlling 1 to 1 racks on a medium of an optical disk device using a guide groove type medium by means of a light spot.
The present invention relates to a track tracking device, and more particularly to a device for accurately tracking a track by correcting optical axis deviation.

[Conventional technology]

In an optical disc device, a plurality of tracks are provided at approximately equal intervals on the surface of an information recording medium. These tracks are grooves or pit rows with a certain width and depth, and are arranged in concentric circles or in a spiral shape. In order to accurately record and reproduce information, it is necessary for the light beam to accurately track one rack, and one method for such tracking control is a method using diffracted light. This method takes advantage of the fact that when a light beam is irradiated onto a track on a medium, a diffraction phenomenon occurs in the reflected light.If the center of the irradiated light and the center of the track deviate, there will be interference between the O-order light and the +1st-order diffracted light. Using the difference between the light intensity of the region and the light intensity of the interference region between the O-order pointing light and the 1st-order diffracted light, the differential output of the photodetector provided in the interference region is converted into a tracking error signal. It is something to do. However, in this method, if the recording medium is tilted or the incident beam position of the optical spot forming objective lens shifts from the center of the objective lens,
The light intensity distribution on the photodetector surface moves in parallel. The intensity of the light beam is symmetrical about the center axis, and the light intensity at the center has a large distribution, so even if the center of the optical slot 1- and the center of the track coincide, the photodetector surface will be affected as described above. If the second light intensity distribution deviates from the center, there is a problem that a difference (1 to easy detection optical axis deviation or offset) occurs in the amount of light detected by the pair of photodetectors provided in the interference region.

In order to solve this problem, one method has been proposed in which the track detection optical axis deviation is corrected by detecting the deviation of the zero-order light detector which is not affected by the diffracted light. The first example is a method in which the portion of the detector surface that is irradiated with only the zero-order light is divided, and the amount of movement of the first-order light is detected based on the difference in the light intensity of the divided rain detector sections (Unexamined Japanese Patent Publication No. Showa 64-6412
No. 7).

This method has the advantage of being able to constantly detect the amount of movement of the zero-order light, but in the case of the light beam reflected from the guide groove, the movement of the zero-order light is detected using the peripheral area where the light intensity is low, so the current of the photodetector is There is a problem that the electrical noise is small and the electrical noise is relatively large.

As a second example, a part of the medium surface has a mirror surface without guide grooves or recording pits, and since the reflected light from the mirror surface is only the 0th order light and does not include diffracted light, it is detected from the differential output of the detection light. vessel face”
This method detects the amount of movement of the second light beam. This method has the advantage that the output of the beam movement detection signal is large and the relative electrical noise is small, but since it can only detect a part of the time in one revolution, it is possible to detect partial tilts of the medium and There was a problem in that it could not cope with short-term deviations in incident light.

In order to solve these problems, a dedicated detector detects the amount of directional movement of the light beam incident on the photodetector, and a tilted glass plate is used to eliminate the lateral movement of the light boom on this detector. Method for adjusting the angle of
No. 32) have been proposed. However, this method requires an actuator to move the light beam laterally, and there is a problem that the device becomes larger and more complicated.

[Problem to be solved by the invention]

As described above, the above-mentioned conventional technology has the following advantages: the detected value of the track detection optical axis deviation is accurate, the track detection optical axis deviation can be constantly detected, the detection signal is highly reliable, and furthermore, 1.
- There was no means to satisfy the requirement that the rack detection optical axis deviation detection device has a simple configuration.

The present invention aims to accurately detect track detection optical axis deviation at all times, use this information to remove the optical axis deviation from the I/rack detection signal, and accurately track and control the optical spot to the track on the medium. There is.

Another purpose is to increase the reliability of the detection signal.

Another object of the present invention is to provide the track detection optical axis deviation detection means with a simple configuration.

[Means to solve the problem]

In order to achieve the above object, the optical axis misalignment correction track tracking device of the present invention has a means for synchronously and accurately detecting optical axis misalignment of 1 to rack error amount in a detection area provided on the optical disk surface. , a means for always detecting the optical axis deviation of the I/rack error signal, which contains an error, is combined to remove the DC-like error component of the latter signal.

In addition, optical axis deviation detection using synchronous tracking error signals has a limited detection time, so it is easily affected by slight defects on the disk. Abnormalities are detected by checking the magnitude of changes,
This is intended to increase the reliability of the detection signal.

[Effect]

The detection optical system detects the difference between the output of the optical axis deviation detection means of the synchronous tracking error signal in the detection area provided on the optical disk surface and the optical axis deviation detection signal of the tracking error signal detected immediately after that. Optical axis deviations due to individual system variations, optical head positional deviations, disk inclinations, etc. can be detected, and based on this detected amount, the optical axis deviation amount of the constantly detected track error signal is corrected.

The reliability of the optical axis deviation detection means for the synchronous 1-to-rack error signal is increased by providing a confirmation means.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS. 1 to 3.

FIG. 1 shows an outline of the case where the present invention is applied to a separate optical head. An optical head is arranged facing the rotating optical disk 56. On the recording surface of the optical disk 56, spiral racks 57 are arranged at intervals of about 1.6 μm, and there is a gap of about 0.1 μm between the trunk and the track.
A guide groove 58 is provided with a depth of m and a width of 0.4 to 0.5 μm.

The trunk is provided with mirror surface portions 59 without guide grooves 58 at a plurality of locations within one rotation. The mirror surface portion 59 has a radial shape, and no information is written thereon. This optical head forms a light spot of about 1-06 .mu.m on the recording surface of the optical disk 56 using the objective lens 9, and records or reads data on the recording surface. The optical slots 1 to 1 for transmitting the light from the objective lens 9 to the optical disk 56 are movable optical systems 12.
By coarsely moving in the Y-axis direction in the figure, that is, in a direction perpendicular to the track, the target I-rack 57 is moved. The mobile system 12 is also equipped with an AF actuator 11 that performs focusing and a TR actuator 10 that performs precise positioning or tracking in the Y-axis direction, and moves the objective lens 9 in the Z-axis and Y-axis directions. By making a slight movement, a light spot is formed on the target 1-rack 57 for tracking and positioning.

The optical head outputs from the return light 19 reflected by the optical disk 56 a focus error signal that is the amount of deviation of the optical spot in the direction of disk surface deflection, and a track error signal that is the amount of deviation in the radial direction from the target track. The movable optical system 12 and the objective lens 9 are driven so as to make the error signal zero. The recorded data on the optical disc 56 is read by changing the total amount of returned light.

The stationary optical system 17 is composed of a light source section and a detection section. The light source section includes a semiconductor laser 4 and a collimating lens 5.
It is composed of.

Further, the detection section includes a quarter wavelength plate 7. Polarizing beam splitter 6, convex lens 13. It consists of a half mirror 14 and a photodetector 15-1, 15-2.

In such a configuration, the light emitted by the semiconductor laser 4 is formed into a parallel light beam 18 by the collimating lens 5. This light beam 18 is transmitted to a polarizing beam splitter 6.
The light enters the movable optical system 12 via the quarter-wave plate 7, is reflected by the mirror 8, and is formed into a light spot by the objective lens 9. Return light 19 reflected on the recording surface of the optical disc 56
proceeds from the movable optical system 12 to the stationary optical system 17.

Since this light passes through the 174-wave plate twice, going forward and returning, the polarization direction changes from P polarized light to S polarized light, and is totally reflected at the next polarizing beam splitter 6 in a direction perpendicular to the forward path. The totally reflected return light 19 passes through the lens 13 and is separated into a reflection part and a transmission part by the next half mirror 14, and the transmission part enters the photodetector 15-1 and the reflection part enters the photodetector 15-2. do.

The returned light 19 is ideally detected by the photodetector 15 shown in FIG.
It has a circular cross section so as to be incident on each of the light receiving surfaces 32-1, 31-1, 31-1, 35-1 and 36-1, and corresponds to the light spot 55 on the photodetector 15. The cross section of the optical return light 19 is optically divided into three regions 1, 2.
In Figure 2, the center region 1 is the 0th order light, the right region 2 is the superimposed region of the 0th order light and the +1st order diffracted light, and the left region 3 is the superimposed region of the 0th order light and the 11th order diffracted light. be.

On the recording surface of the optical disc, the light spot is located in the guide groove 58.
This causes a diffraction phenomenon, forming stripes with uneven light intensity in the radial direction of the optical disc, which travels straight back without being diffracted, and the light in the center is called 0th order light, symmetrically around this, from the side closer to the center. They are called ±1st-order diffracted light and ±2nd-order diffracted light.

The photodetectors 15-1, 15-2 are positioned before and after the focal point of the convex lens, and each output value of the photodetector 15-1, 15-2 is detected when the light spot coincides with the recording surface of the optical disk. have been adjusted to match. Focus error signal 6
o calculates the difference between the focus error detection signal 161 from the detection unit 21 of the photodetector 15-1 and a similar signal 61-2 from the detection unit 20 of the photodetector 15-2 in the calculation unit 22, and reads it out. Part 2
It is configured to be read out at 3.

The photodetector 15-1, 15-
The size of the spot 55 on 2 changes. optical disc 5
6 and the objective lens 9 is the reference position M (the position where the focus of the light spot formed by the objective lens 9 coincides with the recording surface of the optical disc 56), the photodetector 15-1.1
．． The sizes of the second spora I to 55 of "52" are equal. When the distance between the optical disk 56 and the objective lens 9 is greater than the reference position, the diameter of the light spot on the photodetector 15-2 becomes large and the diameter of the light spot on the photodetector 15-1 becomes small. The opposite is true when the distance between the optical disc 56 and the objective lens 9 is shorter than the reference position.

The focus error detection signal 6''-1 is set to the light receiving surface 32-1.
1.34-1 and 35-1. In this case, if the light spot 55 becomes larger, the outputs E 32-1 and E 5s of each of the light receiving surfaces will increase.
-x, E34-1 and E311-1 become larger, and if the spoiler 1-55 becomes smaller, each of the above outputs becomes smaller. A focus error detection signal 611 is extracted as the sum of the respective outputs.

Next, the tracking error signal is transmitted to the photodetectors 15-1 and 15-1.
An equivalent signal can be obtained with -2.

In the following explanation, the photodetector 15-1 will be explained. The tracking error signal tr is the output E of each of the light receiving surface 36 that receives the +1st order light and the light receiving surface 37-1 that receives the 1st order light.
3e-x, E 37-1 is detected as the difference output El)1.

In this case, if the spot 55 is misaligned in the Y direction, the light intensity distribution in areas 2 and 3 is not uniform, causing an offset, that is, an optical axis deviation, in the tracking error signal tr(E5z). This offset is approximately proportional to the amount of deviation of the returned light 19 in the Y direction in a range where the positional deviation is small.

Next, when the returned light 19 moves in the ten direction of the Y axis, the light receiving area of the light receiving surface 32-1.35-1 increases, and the light receiving surface 33-1
．． Since the light receiving area of 34-1 decreases, these output signals E s2-+ , E 35-1 and their sum signal Eaa
-r increases and the output signal E 5s-1+ E 3a-s
and its sum signal E ae-+ decreases. Assuming that the difference output E41 between these sum signals E8B-1 and E39-1 is the offset detection signal to, this is similar to the trunk error signal tr in the second section, within a range where the amount of movement in the Y direction of the return light 19 is small, It is approximately proportional to the amount of movement in the Y direction. The gain is set so that the output E41 of the differential amplifier with respect to the amount of movement of the return light 19 in the Y direction is the same as the output E31 of the differential amplifier.

However, the light receiving surface 32-1.33-1, 341.35
-4 receives a small portion of the peripheral light of the returned light 19, so it is easily affected by the asymmetry of the light intensity distribution, and is a differential signal between them.

Furthermore, fluctuations are likely to occur due to the asymmetry of the light intensity distribution.

Therefore, even when the light spot on the recording surface of the optical disc 56 is located on the center of the track 57, the zero point of the track error signal tr and the zero point of the offset detection signal to do not coincide. It is considered that the amount of mismatch does not depend on the amount of movement in the Y-axis direction in a range where the amount of movement in the Y-axis direction of the returned light 19 on the photodetector 15 is small. Therefore, if the difference between the track error signal TR and the offset signal 1 to signal TO when the optical spot is on the center of the track 57 on the recording surface of the optical disc 56 is the correction amount TC, then trt c = t
r - T R + T O is the accurate tracking error signal 64
It is thought that it represents This tracking error signal 6
4 is read out by the reading unit 31.

It is difficult to determine with certainty that the light spot is on the center of the track 57. In the mirror surface portion 59, there is no influence of the diffracted light, which is equivalent to the fact that the intensities of the +1st-order and 11st-order diffracted lights are balanced. Therefore, the instantaneous track error signal of the mirror surface portion 59 is taken in as the rack error signal TR to 1 when the optical spots 1 to 1 are located on the center of the track 57. close to the guide groove 58
The offset signal at the position receiving the diffracted light from T
By taking in the optical axis deviation amount as o, the optical axis deviation amount correction amount can be obtained. When obtaining the offset signal TO, data is taken in between phase pits or data bits so that it is not easily influenced by phase pits formed in advance on the disk recording surface, such as sector marks, or data recorded by the device. This is desirable.

It is possible to repeatedly collect data from the offset signal To in a range close to the mirror surface portion 59. However, the mirror surface part 5
9 are provided within one rotation of the disk, for example, it is necessary to determine at each instant whether the results at each measurement point are reliable. Otherwise, if you move to a different radial position, you will not be able to obtain reliable data as the mirror track signal TR until you have obtained the signal TR of the mirror surface 59 in the vicinity several times, and you will not be able to start data processing. It will be too late to do so. Whether the mirror surface track signal is normal or abnormal can be determined based on several indicators.

The following can be considered as an example.

(1) The amount of total reflection light is within an appropriate range.

(2) Fluctuations in the amount of total reflected light at the mirror surface are sufficiently small.

(3) At the mirror surface (-rack error signal TR is sufficiently small U)
).

5-6 (4) Fluctuations in the tracking error signal TR at the mirror surface portion are sufficiently small.

(5) The instantaneous distance from the previous mirror surface is appropriate.

(6) The mirror surface track signal TR is within the allowable range for the disc.

By combining the above criteria, the reliability of the detected specular track signal TR can be made sufficiently high.

In the first embodiment, as shown in FIG.
At step 9 and 24, the gate 25 is turned on, and the first inspection section 26 checks whether there is an abnormality. After the gate 25 is turned on, the mirror surface track signal TR is set in the data holding section 28 after a time determined by the delay circuit 27. On the other hand, the fact that the surface is no longer a mirror surface is detected by the output of the mirror surface detection section 24, and the offset detection signal To at that time is set in the data holding section 29.

In addition to the outputs of the data holding units 28 and 29, the summing amplifier 30 is constantly inputted with a tracking error signal tr through a path 62 and an offset detection signal to through a path 63, and the amount of optical axis deviation is determined by tr-to-To+TR. The corrected track error signal can be detected at all times.

A more specific example of optical axis deviation correction is shown in FIG.

l.Rack error signal Signals from the light receiving surfaces 36-1 and 37-1 are input to an addition amplifier 43 and a differential amplifier 51, respectively. The output of the summing amplifier 43 becomes the input of a differentiator 44 and a comparator 48. The comparator 47 detects that the amount of light incident on the light-receiving surfaces 36-1 and 37-1 is greater than a predetermined value, and detects that the light spot has reached the mirror surface section 59, and the light spot reaches the mirror surface section 59. The mono-multivibrator 48 is turned ON for a period of time slightly shorter than the time it takes to pass through the section 59. On the other hand, the output of the differentiator 44 is compared with a predetermined value by a comparator 45, and if the variation in light quantity is small, the output of the comparator 45 is OFF, but if the variation in light quantity is large, the output of the comparator 45 is OFF. The output of becomes ON.

The output of the comparator 45 becomes the input of the AND circuit 46.

The other input of the AND circuit is the negative output of a flip-flop 49 which receives the output of the AND circuit 45. When the output of the comparator 45 turns ON while the mono multivibrator 48 is ON, the positive output of the flip-flop 49 becomes O.
If the comparator 45 remains OFF, it is OFF. The output of the mono multivibrator 48 is the clock signal of the flip-flop 49 and the output of the mono multivibrator 5
The input will be 0. Here, when the output of the mono multivibrator 48 changes from ON to OFF, the flip-flop
This clears the output. The mono multivibrator 50 can be operated by two people, and has the same function as, for example, Texas Instruments' TTL 5N74123. The above AND circuit 46. The timing chart of the signals of the flip-flop 49, mono multivibrator 5o, and mono multivibrator 48 is shown in the third diagram.
As shown in the figure.

When the mirror surface part 59 is normal, the signal of the mono multivibrator 50 outputs a short ○N pulse when the light spora 1 passes through the mirror surface part 59, but the amount of reflected light from the mirror surface part is within the appropriate range. The above O
N pulses are not output. Mono multi vibrator 50
The ON signal of is sufficiently shorter than the response time of the tracking servo system (usually about 0.05 m5ec).
The sample and hold circuit 42 is activated after a delay by the delay circuit 65 by the time necessary for the optical spoiler 1 to completely pass through the mirror surface portion 59, and the off camera 1 detection signal TO is detected.

The output of the mono multivibrator 50 is output from the differential amplifier 51.
The output obtained by passing the output through a signal smoothing low-pass filter 52 that does not affect the tracking servo system is used as a tracking error signal at a mirror surface section 59, that is, a photodetector ]-5
The sample and hold circuit 53 uses the most accurate signal TR of the amount of movement of the return light spot 55 in the Y direction on the surface.
Detection is performed differentially. As mentioned before, the delay circuit 65
Since the delay time of is sufficiently small, changes such as the inclination of the reflective surface of the disk are sufficiently small, and movements caused by vibrations of the optical head are also sufficiently small, so from the perspective of the track servo system, sample hole circuit 42, sample hold circuit 9 can be considered to be sampled at the same time.

As described above, since the offset and the detection signal shift TO-TR in the vicinity of the mirror surface part 59 can be detected, this value is used to transmit the offset signal 1 to the detection signal 0 until the next mirror surface part 59 is detected. and correct offset of the tracking error signal by the amount t.

TO+TR can be estimated.

Regarding the above, the accuracy can be further improved by averaging the deviations TO-TR of the offset detection signals detected at each mirror surface section or by excluding those outside the appropriate range. FIG. 4 shows the basic flow of this embodiment. In addition, by adding a low-pass filter for signal smoothing to each signal as necessary, or adding a hold circuit to interpolate the signal while excluding abnormal signals, more accurate tracking servo control can be achieved. can be realized.

〔Effect of the invention〕

According to the present invention, without particularly providing a new optical system,
Since it is possible to accurately detect the tracking error signal at all times,
When applied to a conventional optical head that is equipped with all the functions of an optical head, it has the effect of expanding the allowable range of adjustment deviation of the tracking error detection system.

The present invention uses a simple optical system in which only the objective lens section moves in the track direction, and the offset of the tracking error signal could not be suppressed without constructing a complicated optical system in the separation optical head. Moreover, it is effective in that it becomes possible to suppress the offset of the tracking error signal without making particularly complicated adjustments. As a result, the weight of the movable part can be reduced, and furthermore, an optical disk device with high-speed access can be realized.

[Brief explanation of the drawing]

FIG. 1 is an overall configuration diagram of an embodiment of the present invention, FIG. 2 is a configuration diagram of a photodetector and a tracking error signal processing system, and FIG. 3 is a diagram of a logic section for forming a sample and hold signal in the tracking error signal processing system. The time chart in FIG. 4 is an explanatory diagram of the recording surface of an optical disc according to the second embodiment of the present invention. 4. Laser, 9... Objective lens, 15... Detector,
17... Fixed optical system, 18... Incident light, 19... Return light, 62... Track error signal path, 63... Offset detection signal path, 64... Corrected tracking error signal.

Claims (1)

[Scope of Claims] 1. In an optical axis misalignment correction track tracking device including an optical head that has a light receiving surface that detects return light from an optical disk facing portion having a track and that detects a tracking error signal using a diffraction differential method. , at least one pair of light-receiving detectors that receive only the zero-order light at the reference position of the light spot are provided on the light-receiving surface symmetrically in the direction in which the diffracted light is generated, and the difference in the amount of light received by the light-receiving detectors is used to detect the return light. a first optical axis deviation detection means for detecting the amount of positional deviation; and a second optical axis deviation detection means for detecting the amount of positional deviation of the returned light on the light receiving surface in an optical axis deviation detection area provided on the optical disk. , an optical axis deviation amount correction amount is calculated from the difference between the detection amount of the first optical axis deviation detection means and the detection amount of the second optical axis deviation detection means in the optical axis deviation detection area, and the optical axis deviation detection area is A corrected optical axis deviation amount is calculated by subtracting the optical axis deviation amount correction amount from the detection amount of the first optical axis deviation detection means in the excluded area, and a tracking error signal obtained from the returned light is calculated as the corrected optical axis deviation amount. What is claimed is: 1. A track tracking device for correcting optical axis deviation, comprising means for correcting based on the above. 2. The optical axis deviation correction track tracking device according to claim 1, wherein the optical axis deviation detection area is a mirror surface portion provided on an optical disc. 3. As a means for confirming the amount detected by the second optical axis deviation detection means in the optical axis deviation detection area, the range of the magnitude of the received light amount, the range of time fluctuation of the amount of received light, or the detection amount of the optical axis deviation detection means 3. The optical axis deviation correction track tracking device according to claim 2, wherein a range or a range of time fluctuation of the amount detected by the optical axis deviation detection means is determined.