JPH05197989A - Beam alignment measurement mechanism for multi-beam optical disk device - Google Patents

Abstract

PURPOSE:To improve the accuracy of tracking at the time of recording and reproducing on multi-track by multi-beam and to secure the interchangeability of an optical disk. CONSTITUTION:A tracking actuator is vibrated in the direction vertical to the groove P on the optical disk D over plural pieces of the grooves P by a sine wave phase-synchronizing with the rotation of the optical disk D, and intervals P1, P2, P3, P4 between the zero cross points of an obtained tracking error signal are obtained and beam alignment is measured.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a beam alignment measuring mechanism for a multi-beam optical disc device such as a magneto-optical disc, a phase change type optical disc and a write-once type optical disc.

[0002]

2. Description of the Related Art As a method for increasing the recording / reproducing speed of an optical disk such as a magneto-optical disk, a multi-beam method has been conventionally used in which a plurality of optical beam spots are used to simultaneously record / reproduce a plurality of tracks on a disk in parallel. Are known.

FIG. 7 is a perspective view showing the relationship between the disc and the light beam spot in this multi-beam system. Only the spiral groove P used for tracking and information recording on the disc D and the information recording between the grooves P are shown. Land L used
And are provided. The plurality of light beam spots B1 to B4 from the multi-beam laser light source are, for example, at intervals of several tens of μm in the rotation direction of the disc D and at intervals of 1 to 2 μm in the radial direction, along a line forming a minute angle with respect to the groove P. D
It is arranged so that the groove P is irradiated with the light from above and one of the light beam spots B1 to B4, for example, the light beam spot B2 in FIG. Although a plurality of tracks T are formed on the land L in parallel with the groove P at the time of recording, they are not particularly shown on the disk D.

FIG. 8 is a block diagram of a tracking detector when reproducing is performed by using the reflected light on the disk D.
The elements 1a and 1b of the split photodiode 1 are connected to the differential amplifier 2, respectively. The light beam spots B1 to B4 are reflected on the disk D, and a part thereof is incident on the elements 1a and 1b via the light receiving optical system. Of the reflection spots R1 to R4 corresponding to the light beam spots B1 to B4, the land L
The spots R1, R3, and R4 reflected by are incident on the elements 1a and 1b with the same light intensity regardless of whether the tracking is correct or not by optical adjustment in advance. On the other hand, the groove P
Since the spot R2 reflected by is diffracted at the left and right ends of the groove P during reflection, strong reflected light is generated on the left and right sides of the groove P.

Therefore, when the intensities of the light beam spot B2 incident on the groove P are different at the left and right ends of the groove P, that is, the light beam spot B2 is irradiated off the center of the groove P and the tracking is matched. If not, the reflection spot R2
Since the intensities of are different between the left and right, the amounts of light incident on the elements 1a and 1b also differ. That is, the incident light amounts of the reflected spot R2 on the elements 1a and 1b become equal only when the tracking is correct. The difference in the amount of incident light between the two-divided photodiodes 1a and 1b is detected by the differential amplifier 2. Therefore, if adjustment is made by a control device (not shown) so that this differential output becomes zero, the light beam spot B2 on the groove P is adjusted. You will be able to track accurately.

[0006]

However, in such a tracking method, among the plurality of light beams,
Tracking control is performed only on the light beam tracing the groove P, and tracking control is not performed on other light beams tracing the track T on the land L. Therefore, when the disc D is exchanged, that is, when a disc recorded by using another disc drive device is reproduced, or when the disc drive device is exchanged, or due to temperature change or the like, the multi-beam spot row and the groove P If the mutual relationship between the recording track T of the disc D to be reproduced and the drive device of the disc D is slightly deviated from the normal state, such as when the angle formed is changed, tracking control is not performed. There is a disadvantage in that tracking of a plurality of light beam spots on the land L is deviated, and information recording / reproduction cannot be performed well.

On the other hand, conventionally, the angle of the light beam is adjusted by observing the light beam spot on the disk using a microscope, but it is difficult to perform the accurate adjustment. ..

The object of the present invention is to solve the above-mentioned problems,
It is an object of the present invention to provide a beam alignment measuring mechanism of a multi-beam optical disk device capable of adjusting a light beam with high accuracy.

[0009]

A beam alignment measuring mechanism of a multi-beam optical disk device according to the present invention for achieving the above-mentioned object comprises a set of n recording tracks spirally equidistantly on an optical disk. Place multiple sets,
One of the recording tracks is used as a groove, and n light beam spots linearly arranged on the optical disc are provided by the multi-beam optical head, and the arrangement direction of these light beam spots is tilted with respect to the groove. , N signals are simultaneously recorded / reproduced, the tracking actuator is vibrated across a plurality of the grooves in a direction orthogonal to the grooves by a sine wave that is phase-locked with the rotation of the optical disk. It is characterized in that the time interval between the zero cross points of the tracking error signal obtained by the vibration is measured.

[0010]

In the beam alignment measuring mechanism of the multi-beam optical disk device having the above-described structure, the tracking actuator vibrates across a plurality of grooves in a direction orthogonal to the grooves on the optical disk by a sine wave phase-synchronized with the rotation of the optical disk, When the tracking actuator has a constant linear velocity at the center of sinusoidal vibration, the time interval between the zero-cross points of the tracking error signal is measured to measure the beam alignment.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail with reference to the embodiments shown in FIGS. FIG. 1 is a general configuration diagram in which tracking control and focusing control are combined to explain the present invention. Element 1 of 2-split photodiode 1
The outputs of a and 1b are connected to the comparator 3, the switch 4 and the switch 5 via the differential amplifier 2, and the binarized output of the comparator 3 is connected to the CPU 7 via the counter 6. Four
Elements 8a, 8b, 8 constituting the split photodiode 8
Of c and 8d, the current output Ia of the element 8a is the adder 9, 1
0, and the current output Ib of the element 8b is the adder 11, 1
0, the current output Ic of the element 8c is the adder 11, 1
2 and the current output Id of the element 8d is added to the adders 9 and 12
It is connected to the. The outputs of the adders 9 and 11 are connected to the coil 17f of the lens drive mechanism 16 in the optical head 15 via the differential amplifier 13 and the drive amplifier 14a. The outputs of the adders 10 and 12 are connected to the CPU 7 via the differential amplifier 18 and the comparator 19. Further, the output of the comparator 19 is connected to the counter 6. The output of the CPU 7 is connected to the display 20 and the low frequency oscillator 21.

The switch 4 selects the output of the comparator 2 and the output of the low frequency oscillator 21 and connects it to the tracking coil 17t of the lens driving mechanism 16 which serves as a tracking actuator via the driving amplifier 14b. Further, the switch 5 selects the output of the comparator 2 and the output of the slider signal J1 for search and connects it to the coil 22 via the drive amplifier 14c. The roller 23 moves the optical head 15 in the radial direction of the optical disc D. I am trying to do it. Further, the lens driving mechanism 16 is provided with the objective lens 24 driven by the coils 17f and 11f so as to face the optical disc D.

In the focusing control system including the four-division photodiode 8 including the elements 8a to 8d, the adders 9 and 11, and the differential amplifier 13, the light beam spot B1
When B2, B3, and B4 are incident, the currents Ia to Id from the outputs of the elements 8a to 8d are obtained as signals (Ia + Id)-(Ib + Ic) by the adders 9 and 11 and the differential amplifier 13, and this signal Passes through the drive amplifier 14a as the focus error signal F, and drives the objective lens 24 by the coil 17f of the lens drive mechanism 16.

Further, the element 8 of the four-division photodiode 8
From the outputs a to 8d, adders 10 and 12 and a differential amplifier 1
After going through 8, (Ia + Ib) − (Ic + Id) is obtained. This is the tracking control signal TC for the light beam spot B2.
However, the control signal TC is applied to the comparator 19 to
It becomes a digitized pulse and is added to the CPU 7 and the counter 6.

The tracking error signal TE obtained by passing the output of the two-divided diode 1 composed of the elements 1a and 1b through the differential amplifier 2 passes through the switch 4 and the drive amplifier 14b and is composed of the tracking coil 17t of the lens drive mechanism 16. Objective lens 2 by actuator
Drive 4 The slider signal J1 for searching is used for the switch 5 and the driving amplifier 14 when the desired track is accessed.
The optical head 15 is moved by the roller 23 in the radial direction of the optical disc D by using the coil 22 through c.

The drive amplifier 14b has a bandwidth of 10 k.
It is for fine tracking control at Hz. The bandwidth of the drive amplifier 14c is several kHz, and the coil 22
Therefore, coarse tracking control is performed.

Further, a control signal from the CPU 7 is applied to the low frequency oscillator 21 to generate a sine wave having the same frequency as the rotation frequency of the optical disc D and phase-locked with the rotation of the optical disc D. This sine wave is generated by the switch 4 and drive amplifier 14b.
Via the tracking coil 17 of the lens drive mechanism 16
The tracking actuator based on t is vibrated in the direction perpendicular to the grooves over ten grooves, for example, about 80 grooves on the optical disk D.

FIG. 2 is an explanatory diagram for the case of four beams. FIG. 2A shows the positional relationship of the light beam spots B1, B2, B3, and B4 with respect to the groove of the optical disc D, and shows that the light beam spot row is inclined with respect to the track on the optical disc D. There is. FIG. 2B shows that when the tracking coil 17t is sine-wave oscillated in a direction orthogonal to the groove P on the optical disc D, the light beam spot B1 causes 2
This is a tracking error signal obtained by the split diode 1.

Similarly, FIGS. 2 (c), 2 (d) and 2 (e) are tracking error signals obtained from the light beam spots B2, B3 and B4, respectively. Figure 2 (f) shows these (b), (c),
The waveforms of (d) and (e) are superimposed. As a result, the tracking error signal for four-beam synthesis is as shown in FIG. Waveforms (b), (c), (d),
The intervals between the zero-cross points in (e) are P1, P2, P3, and P, respectively.
4, assuming that the velocity v of the light beam spots B1 to B4 oscillating in a sine wave in the direction perpendicular to the groove P of the optical disc D is constant, the times t1, t2, t3, and t4 are set to the respective beams B1 to B4.
Let B4 be the time it takes to pass between intervals P1 and P4, the interval P1 = v
・ Since t1, P2 = v ・ t2, P3 = v ・ t3, P4 = v ・ t4, the time t1 to t4 is measured by the counter 6, and then CP
The intervals P1 to P4 can be obtained by performing the calculation of v · t1, v · t2, v · t3, and v · t4 in U7.

In this case, four light beam spots B1 ...
It is necessary to match the light intensity of B4. First, only the light beam spots B1 and B3 are turned on, and matching is performed so that the tracking error signals of B1 and B3 have the same amplitude. Next, all the four light beam spots B1 to B4 are turned on, and with the waveform shown in FIG. 2 (g), the zero crossing point h of the light beam spot B1 and one zero crossing point i of the light beam spot B2 are exactly in the middle. , The light intensity of the light beam spot B2 is selected so that the other zero-cross point j of the light beam spot B2 comes.

Similarly, regarding the light intensity of the light beam spot B4, the zero cross point k of the light beam spot B3 and the zero cross point 1 of one of the light beam spots B4 are located exactly in the middle of the other zero cross point of the light beam spot B4. The light intensity of the light beam spot B4 is selected so that m comes. Similarly, it is confirmed that the middle n between the zero-cross points i and k comes to the exact middle position between the zero-cross points i and k, and if they are deviated, the beam powers of the light beam spots B3 and B4 are readjusted. ..

FIGS. 3, 4, and 5 are views of FIG. 2 drawn from different viewpoints. In FIG. 3, (a) is a sine wave phase-synchronized with the rotation of the optical disc D input to the switch 4 of FIG. Level A indicates the center position of the vibration of the tracking coil 17t that vibrates in a sine wave. The waveform of (b) is the output of the differential amplifier 2 in this case, that is, the tracking error signal TE, but in the present embodiment, since it is the case of 4 beams, the tracking error signal TE for 4 beams appears. The waveform in (c) is the measurement timing signal.
It shows the zero-crossing point of the sine wave in (a). Figure 4
Shows the time axis of FIG. 3 magnified 20 times.

FIG. 5 is for further explaining FIG. The waveform shown in (a) is the tracking error signal TE of the light beam spot B3, and the waveform shown in (b) is the total of the tracking error signals TE of the four light beams. The waveform of (c) is the output of the counter 6 or the comparator 3, and this is a rectangular wave whose rising and falling are the zero cross points of the waveform of (b). The waveform of (d) is shown in Fig. 4.
This is the measurement timing signal shown by the waveform in (c).

Next, the case where the optical disc D is eccentric will be considered. When the center of rotation K of the optical disc D is separated from the center M of the groove by d as shown in FIG. 6 (a), the center M draws a circle as shown by the locus L with the rotation of the optical disc D, and is eccentric. The movement of the center M in the y direction due to is given by the following equation. y = d · sin θ = d · sin ωt

Further, the movement in the x direction, that is, what is normally detected as the eccentricity of the disk D is given by x = d · cos θ = d · cos ωt, and the movement in the x direction is caused by the tracking servo and Since the beam is compensated by the slider servo, the beam is fixed at the same radial position regardless of the eccentricity.

Since the beam alignment is determined by the angle formed by the multi-beam spot array and the groove P, the center of the groove P moves in the y direction due to the eccentricity of the disk D, and the angle of the groove P with respect to the light beam spot array. When changes in, the measurement phase causes a measurement error.

Therefore, it is necessary to set the measurement phase so that the influence of eccentricity is minimized during measurement. Figure 6
It can be seen that the phases in which the movement in the y direction becomes small are (a) and (c). That is, since the movement in the y direction has a phase difference of 90 degrees from the movement in the x direction, if the movement in the x direction is measured at the maximum phase, the influence of eccentricity can be minimized. ..

When the time t1 to t4 is measured at two points which are 180 degrees out of phase in synchronization with the rotation of the optical disc D, and when the vibration center of the tracking actuator composed of the tracking coil 17t faces the outer peripheral portion of the optical disc D, By taking the addition average of each of the times t1 to t4 when going to the inner peripheral portion, it is possible to reduce an error that occurs in measurement due to eccentricity or other causes.

The tracking alignment according to this embodiment is performed under the control of the CPU 7, and the outline of the procedure is as follows. (1) Turn off tracking control. (2) If an eccentricity correction mechanism is added, turn it off. (3) The tracking actuator is driven with a sine wave synchronized with the rotation so that its vibration amplitude becomes 120 μm pp. The vibration amplitude is measured by counting the number of times the beam spot crosses the track using the track pitch as a scale. (4) The moving direction of the tracking actuator is detected by the sensor, and the tracking error signal TE is used to find the point where the light beam spot B2 crosses the track. (5) When the light beam spot B2 is detected, the beam intervals P1 to P4 are measured by the counter 6 from the zero cross point of the tracking error signal TE with reference to this. (6) Perform (4) and (5) above for both the forward and reverse directions of the tracking actuator movement. (7) The measurements from (4) to (6) above are performed, for example, 100 times, and this is averaged.

As a result, the influence of noise or the like is removed, and the addition and averaging result is displayed on the display 20, but it can be printed out by a printer.
Table 1 shows an example of the display result.

[0031]

[Table 1]

Here, BEAM B1-B2, B2-B3, B3-B4,
B4-B1 indicates the pitches of beams B1, B2, B3, and B4.
t and rear represent the pitch determined by the power of both beams from each beam to the midpoint of the beam, and similarly total represents the sum of front and rear, which corresponds to the pitch between the beams. Also, the ratio is B2-B3
It shows the pitch between other beams in the case of using as a reference, and the + sign shows the case where it is wider than the B2-B3 standard, and the-sign shows the case where it is narrower than the B2-B3 standard. In an ideal state, this ratio is 0%.

[0033]

As described above, the beam alignment measuring mechanism of the multi-beam optical disc apparatus according to the present invention can accurately adjust the beam spot interval according to the reference disc, and the tracking precision during recording / reproducing. And the compatibility of optical discs can be secured.

[Brief description of drawings]

FIG. 1 is a configuration diagram.

FIG. 2 is an explanatory diagram based on a time chart.

FIG. 3 is an explanatory diagram based on a time chart.

FIG. 4 is an explanatory diagram based on a time chart.

FIG. 5 is an explanatory diagram based on a time chart.

FIG. 6 is an explanatory diagram when a disc has an eccentricity.

FIG. 7 is a partial perspective view of a disc.

FIG. 8 is a configuration diagram of a tracking detector.

[Explanation of symbols]

 1 2-division photodiode 2, 10, 18 Differential amplifier 3, 19 Comparator 4, 5 switch 7 CPU 8 4-division photodiode 15 Optical head 16 Lens drive mechanism 17, 22 Coil 23 Roll 24 Objective lens D Optical disk

Claims (2)

[Claims] 1. A plurality of sets of n recording tracks are spirally arranged at equal intervals on the optical disc, and one of the recording tracks is used as a groove, and n is recorded on the optical disc by a multi-beam optical head. In an optical disk device which gives a plurality of linearly arranged light beam spots, tilts the arrangement direction of these light beam spots with respect to the groove, and simultaneously records / reproduces n signals, a tracking actuator is used to rotate the optical disk. The phase-synchronized sine wave is oscillated over a plurality of the grooves in the direction orthogonal to the groove, and the time interval of the zero cross points of the tracking error signal obtained by the vibration of the tracking actuator is measured. Beam alignment measuring mechanism for multi-beam optical disk device. 2. The multi-beam optical disk according to claim 1, wherein an average of time intervals of the zero-cross points when the vibration center of the tracking actuator faces the outer peripheral portion and the inner peripheral portion of the optical disk is obtained. Beam alignment measurement mechanism of the device.