JPH0481809B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an optical pickup for determining whether the mounting angle of a diffraction grating used in an optical pickup for detecting a tracking error signal by a three-beam method is appropriate. The present invention relates to a device for determining whether or not the mounting angle of a diffraction grating is appropriate.

[Prior Art] In this type of optical pickup, a diffraction grating is disposed between a laser diode and a beam splitter with its surface parallel to the objective lens. When this diffraction grating is rotated in its plane, i.e.
When the mounting angle of the diffraction grating is changed, as shown in Figure 3, the main beam spot MB is
Also, the angle θ between the track and the beam spot row consisting of sub-beam spots SB1 and SB2 changes.

The tracking servo mechanism uses the difference in intensity of the return light of the two sub-beams as a tracking error signal.
As TE1, it is designed to perform correction operations.
The level of the tracking error signal TE1 becomes the same when the beam spot rows are line-symmetrical with respect to the track as shown in FIGS. 3A and 3B.
Therefore, if a correction operation is performed in the state shown in FIG. 3A using this tracking error signal TE1 (the tracking servo is closed), then the third
In the state shown in Figure B, feedback is applied in the direction of the main beam moving away from the track, and no corrective action is performed (the servo does not close).

Conventionally, therefore, it has been determined whether the mounting angle of the diffraction grating is appropriate by testing whether the tracking servo closes or not, and then adjusting this mounting angle.

[Problems to be Solved by the Invention] However, it takes time to determine whether the tracking servo is closed. In particular, if it is determined that the tracking servo does not close, it is necessary to change the mounting angle of the diffraction grating and try again to see if the tracking servo closes, which takes a long time to adjust the mounting angle of the diffraction grating. It's time.

In view of the above-mentioned problems, an object of the present invention is to provide an optical system that can quickly determine whether or not the mounting angle of a diffraction grating is appropriate, thereby making it possible to adjust the mounting angle in a short time. An object of the present invention is to provide a device for determining whether or not the mounting angle of a pick-up diffraction grating is appropriate.

[Means for Solving the Problems] In the present invention, the returned light of the main beam, which is the 0th order diffracted light of the laser light that has passed through the diffraction grating, is received by photodetectors A, B, C, and D divided into four, Photodetector A,
The sum of the outputs of B, C, and D is used as an RF signal, and the return lights of the two sub-beams, which are the first-order diffracted lights of the laser light that passed through the diffraction grating, are received by photodetectors E and F, respectively. In an optical disk player using the three-beam method, in which the difference between the output and the output of photodetector F is used as the tracking error signal TE1, the main beam spot is means P for determining that the main beam spot is approximately on the track of the optical disk; and means Q for outputting the tracking error signal TE1 as the tracking error signal TE2 only when it is determined that the main beam spot is approximately on the track of the optical disk. and means R for outputting the sum of the outputs of photodetector A and photodetector C as diagonal sum signal X, and the sum of the outputs of photodetector B and photodetector D as diagonal sum signal Y; It has a means S for outputting a signal PD corresponding to the phase difference between the angle sum signal It is characterized by the fact that

[Function] The optical disk is rotated without operating the tracking servo mechanism. As shown in FIG. 4, when the main beam spot draws a trajectory K across tracks T1, T2, and T3 during one rotation of the optical disk, for example, a point M1 before and after crossing track T2
It is determined that the main beam spot is approximately on the track of the optical disk between the point M2 and the point M2. The distance from point M1 to point M2 is approximately 1/1 of the optical disk.
This corresponds to 8 rotations, and the time the light beam passes through this period is as short as 38 msec at most. Observe the waveforms of tracking error signal TE2 and phase difference signal PD within this short time, and
By checking the relationship between the waveform of the tracking error signal TE2 and the PD waveform, it is possible to determine whether the tracking servo is in a closed state, that is, whether the mounting angle of the diffraction grating is appropriate. can be determined.

Therefore, it is possible to instantly determine whether or not the mounting angle is appropriate, and the mounting angle of the diffraction grating can be adjusted in a short time.

[Example] A preferred example of the present invention will be described based on the drawings.

FIG. 1 shows the circuit configuration of a device for determining the suitability of the mounting angle of a diffraction grating for optical pickup. , D, and photodetectors E and F that detect the return light of the sub-beams. The photodetectors A, B, C, and D are arranged so that the direction of the arrow z in FIG. 1 is the track direction, and the center of the four divisions corresponds to the center of the spot of the returned light. A reverse voltage is applied to these photodetectors A to F,
A current is output according to the amount of light received.

The output currents of photodetectors E and F are I-V, respectively.
The current is converted into a voltage proportional to the current by the converters 10 and 12, and the difference between the two voltages is outputted to the terminal 16 by the differential amplifier as the tracking error signal TE1.

Circuit R is an I-V circuit that converts the sum of the output currents of photodetector A and photodetector C into a voltage proportional to the sum of the output currents of photodetector A and photodetector C.
converter 18 followed by an inverting amplifier 22
and the sum of the output currents of photodetector B and photodetector D,
I-V converter 20 converts it into a voltage proportional to this
and an inverting amplifier 24 following it,
Diagonal sum signals X and Y are output from inverting amplifiers 22 and 24, respectively.

The output voltages of the I-V converters 18 and 20 are output to the adder 2.
6 and taken out to the terminal 28 as an RF signal.

The circuit P includes a voltage follower 30 as a buffer to which the output voltage of the adder 26 is supplied, and is followed by the voltage follower 30, and converts the modulation side envelope of the RF signal.
An envelope detector 32 removes the DC component and extracts it as a signal EN, and an envelope detector 32 that binarizes the signal EN with a discrimination level of 0V and generates an on-track signal OT.
and a comparator 34 that outputs .

Circuit Q includes a FET 36 as an analog switch to which the on-track signal OT is applied;
and a voltage follower 38 that supplies the tracking error signal TE1 to the source of the FET 36.
A tracking error signal TE2 is taken out from the drain of 36 to a terminal 40.

Therefore, when the on-track signal OT is at a high level, the gate of FET 36 is opened and
The tracking error signal TE1 is the voltage follower 38,
It passes through FET 36 and appears at terminal 40 as tracking error signal TE2. In addition, Ontrack signal
When OT is low level, the gate of FET36 is closed and 0V is the tracking error signal.
Appears at terminal 40 as TE2.

The circuit S includes a coupling capacitor 42 that removes the alternating current component of the output voltage of the inverting amplifier 22, an inverting amplifier 44, an inverter 46 that shapes the wave into a square wave, and an inverter 48 that inverts the wave. . Similarly, a coupling capacitor 50 that removes the alternating current component of the output voltage of the inverting amplifier 24, an inverting amplifier 52, and an inverter 5 that shapes the output voltage into a square wave.
4 and an inverter 56 that inverts this are connected in cascade. Furthermore, the circuit S includes an inverter 4
D flip-flop 58 is set by the rise of the output voltage of inverter 54 and reset by the fall of the output voltage of inverter 54; A D flip-flop 60 and a D flip-flop 62 which are set by the rise of the output voltage of the inverter 48 and reset by the fall of the output voltage of the inverter 54.
, the D flip-flop 64 which is set by the rise of the output voltage of the inverter 56 and reset by the fall of the output voltage of the inverter 46, the Q output terminals of the D flip-flop 58 and the D flip-flop 62, and the Q output terminals of the D flip-flop 62.
Resistors r ₁ , each having the same resistance value are connected at one end to the output terminals of the 0 and D flip-flops 64, respectively.
r ₃ , r ₂ , r ₄ and a bandpass filter 66 connected via a signal line L to the other ends of the resistors r ₁ to _{r 4} .

Therefore, the Q output terminal of D flip-flop 58 and the output terminal of D flip-flop 60 are
The output voltage of the inverter 46 (the shaped wave of the diagonal sum signal X) rises to a high level during the period from when the output voltage of the inverter 54 (the shaped wave of the diagonal sum signal Y) rises. Further, the Q output terminal of the D flip-flop 62 and the Q output terminal of the D flip-flop 64 are at a high level from the time when the output voltage of the inverter 46 falls until the output voltage of the inverter 54 falls.

Here, the potential of the signal line L is the same as that of the D flip-flops 58 to 64 whose output voltage is at a high level.
increases in proportion to the number of Furthermore, the bandpass filter 66 removes DC components and high frequency components.

Therefore, from the bandpass filter 66 to the terminal 68
When the center of the main beam spot MB is on the center line of the track, the phase difference signal PD extracted to the
The sum of the outputs of will have the same phase and will be 0V. In addition, the phase difference signal PD is
When the center of MB deviates from the center line of the track, a difference occurs between the phase of the sum of the outputs of photodetectors A and C and the phase of the sum of the outputs of photodetectors B and D, depending on the amount of deviation. , the voltage increases in proportion to the amount of phase difference.

Next, the operation of this embodiment configured as described above will be explained.

To rotate an optical disk without operating a tracking servo mechanism. As a result, as shown in FIG. 4, for example, the main beam spot crosses track T2 from track T1 to track T3 in half a rotation of the optical disk, and crosses track T2 again in a half rotation (not shown) to land on track T1. return. This is due to the fact that the center axis of the spindle motor does not perfectly match the center of the track, the accuracy of the position of the center hole of the optical disk, the error when checking the optical disk to the spindle motor, etc.

In this case, the RF signal appearing at terminal 28 is
As shown in the figure, the lower envelope EL1 is wavy. This means that when the center of the main beam spot is at the center of the pit (times t ₁ , t ₅ , t ₉ ), the level of the RF signal is at its minimum, and when the center of the main beam spot is at the center of the adjacent track ( time t ₃ , t ₇ ),
This is because the level of the RF signal becomes maximum. The reason why the upper envelope EL2 is at a constant level is because the intensity of the returned light when the main beam is reflected by the mirror surface section is constant.

When the main beam spot is approximately on the track (from time t ₀ to time t ₂ , from time t ₄ to time t ₆ , from time t ₈ to time ₁₀ ), the signal
EN becomes a negative level, and the on-track signal OT becomes a high level.

The tracking error signal TE1 is generated when the center of the main beam spot is on the center line of the track (times _t1 , _t5 , _t9 ) and at the center position between adjacent tracks (times _t3 , _t7) . ), the level is 0, regardless of the sign of the angle θ of the spot row with respect to the center line of the track (see FIG. 3). but,
Between these points in time, if the sign of the angle θ is opposite, the tracking error signal TE1A (corresponding to FIG. 3A) and the tracking error signal TE1B (corresponding to the third (corresponding to Figure B) have opposite signs.

Therefore, if the tracking servo closes when the tracking servo mechanism is operated using the tracking error signal TE1A, the tracking servo does not close when the tracking error signal TE1B is used.

Even by observing the waveform of this tracking error signal TE1, it is not possible to determine whether the tracking servo is closed or not. However, the phase difference signal
The sign of PD depends on whether the main beam spot is shifted to the right or left side of the track, so the waveform of the tracking error signal TE1 when the main beam spot is approximately on the track (the waveform of the tracking error signal TE2) It is possible to determine whether the tracking servo is in the closed state when the tracking servo mechanism is activated by taking out the waveform) and checking whether the sign of the phase difference signal PD and the sign of the tracking error signal TE2 are the same. can. For example, if the tracking servo is in a closed state when the sign of the phase difference signal PD and the sign of the tracking error signal TE2 are opposite, then in the case of the tracking error signal TE2A, the tracking servo is closed and a tracking error occurs. signal
In the case of TE2B, the tracking servo does not close.

In this way, by simultaneously observing the waveforms of the tracking error signal TE2 and the phase difference signal PD between time _t0 and time _t2 , it is possible to determine whether the tracking servo is in the closed state. can. In this example, the time from time t ₀ to time t ₂ corresponds to 1/8 revolution of the optical disc, and since the rotation speed of the optical disc is 200 rpm even on the outer circumferential side, the time from time t 0 to time t 2 is 38 msec or less at most. By observing the waveform for a short period of time, it is possible to determine whether the servo is in the closed state. If the tracking servo does not close, the tracking error signal TE2
While observing the waveform of the phase difference signal PD, rotate the diffraction grating within that plane, and fix the diffraction grating when the waveform reaches the state where the servo is closed.

FIG. 5A shows a waveform diagram when the tracking error signal TE2A is applied to the horizontal deflection plate of the oscilloscope, and the phase difference signal PD is applied to the vertical deflection plate. Figure 5B also shows a tracking error signal on the horizontal deflection plate of the oscilloscope.
Apply TE2A and output a phase difference signal to its vertical deflection plate.
A waveform diagram is shown when PD is applied. In this example, it is possible to determine whether the tracking servo is closed by simply observing whether the single waveform is upward to the right or upward to the left.

Note that, although the means P described in the claims uses an RF signal that is the sum of the outputs of the photodetectors A, B, C, and D in the above embodiment, it is important that the main beam spot is substantially on the track. It is sufficient if the absolute value of the phase difference signal PD representing the difference between the diagonal sums of the photodetectors A, B, C, and D is less than or equal to a predetermined value.

Further, to determine whether or not the mounting angle of the diffraction grating is appropriate, the product of the tracking error signal TE2 and the phase difference signal PD may be displayed, or different sounds may be generated depending on the sign of the product.

[Effects of the Invention] The device for determining whether or not the installation angle of a diffraction grating for optical pickup according to the present invention is appropriate outputs the tracking error signal TE1 when the main beam spot is approximately on the track of the optical disk as the tracking error signal TE2. , outputs a signal PD according to the phase difference between the diagonal sum signals X and Y, and outputs a tracking error signal TE2.
It is possible to determine whether the tracking servo is in the closed state from the relationship between the position and the signal PD, and it is possible to determine whether the mounting angle of the diffraction grating is appropriate in an extremely short time. This has the excellent effect of making it possible to adjust the mounting angle in a short time.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing the configuration of an embodiment of the present invention;
Figure 2 shows RF signal and tracking error signal
TE1A, TE1B, tracking error signal TE2A,
A waveform diagram showing a comparison of TE2B and phase difference signal PD,
Figure 3 is a diagram explaining that it is not possible to determine whether the tracking servo is closed or not using only the tracking error signal TE1, and Figure 4 is a diagram showing how the optical disk is rotated without the tracking servo mechanism working. Fig. 5 is a waveform diagram displayed on a cathode ray tube when a tracking error signal TE2 is applied to the horizontal deflection plate and a phase difference signal is applied to the vertical deflection plate. It is. A to F...photodetector, 10, 12, 18, 20
...IV converter, 22, 24, 44, 52...
Inverting amplifier, 30, 38... Voltage follower, 32...
...Envelope detector, 34...Comparator, 58-
64...D flip-flop, 66...band pass filter.

Claims (1)

[Claims] 1. The return light of the main beam, which is the 0th order diffracted light of the laser light that has passed through the diffraction grating, is received by the photodetectors A, B, C, and D, which are divided into four. C,D
The sum of the outputs of the two sub-beams, which are the first-order diffracted lights of the laser beam that passed through the diffraction grating, are received by photodetectors E and F, respectively, and the output of photodetector E and the photodetector In an optical disc player using the three-beam method, in which the difference in the outputs of F is used as the tracking error signal TE1, the main beam spot is positioned approximately on the track of the optical disc by the signals from photodetectors A, B, C, and D. means P for determining that the main beam spot is substantially on the track of the optical disk; means Q for outputting the tracking error signal TE1 as the tracking error signal TE2 only when it is determined that the main beam spot is substantially on the track of the optical disk; and a photodetector. means R for outputting the sum of the outputs of photodetector A and photodetector C as diagonal sum signal X, and outputting the sum of the outputs of photodetector B and photodetector D as diagonal sum signal Y; It has a means S for outputting a signal PD corresponding to the phase difference of the diagonal sum signal Y, and the tracking error signal TE2 and the signal PD are used to determine whether or not the mounting angle of the diffraction grating is appropriate. A device for determining the suitability of the mounting angle of a diffraction grating for optical pickup.