JPH0770071B2 - Tracking servo system - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tracking servo device which is preferably implemented in a device for reproducing an optical disc such as a compact disc.

2. Description of the Related Art For example, in a compact disc player, the light receiving element in the pickup is divided into two in the directions parallel and perpendicular to the track, that is, into four light receiving portions, and the sum output of the two light receiving portions on the diagonal line is obtained. The tracking error is detected by comparing these sum outputs with each other. The light receiving element is composed of, for example, a photodiode, and an error may be constantly generated due to variations in its characteristics. The same error may occur due to variations in the optical system. When such an error occurs, the track followability of the pick up deteriorates, and it becomes impossible to trace the track accurately. For this reason, in the typical prior art, in order to cancel such an error, a predetermined voltage corresponding to the error is applied and correction is performed.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention In the above-described prior art, the voltage for the correction is applied even when scratches or dust are attached to the compact disk and the reflected light is reduced, and therefore an accurate trace is obtained. However, in the extreme case, a track jump occurs and the track followability deteriorates.

It is an object of the present invention to provide a tracking servo device having improved track followability.

Means for Solving the Problems The present invention is to drive a recording medium to travel, and to read information recorded along a track of the recording medium by a reading means,
In a tracking servo device that corrects the vertical deviation of the track of the reading means based on the output of the reading means, the reading means is divided into at least two reading portions along at least the track direction, and each reading portion is divided. Phase control means for controlling the relative phase of the output from the portion corresponding to the difference in their characteristics, and waveform shaping for performing the waveform shaping of the output corresponding to each read portion from the phase control means. Means for detecting the time difference of the edge timing of the output of each reading portion from the output of each waveform shaping means, and deriving an error output corresponding to the time difference, and a reading means corresponding to the error output. And a drive means for displacing the drive in the vertical direction.

Operation According to the present invention, information such as an acoustic signal recorded on the recording medium along the track is read by the reading means and reproduced. In order to detect and correct the deviation of the reading means from the center of the track in the vertical direction of the track, the reading means is divided into two reading portions at least along the track direction.

The output from each reading portion is input to the phase control means. The phase control means relatively controls the phase of each output and outputs it in accordance with the difference in characteristics such as the detection sensitivity of each reading portion. The output corresponding to each read portion from the phase control means is given to the waveform shaping means to be shaped respectively, and then inputted to the time difference detecting means.

The time difference detecting means detects the time difference between the edge timings from the output of each waveform shaping means, and derives the error output corresponding to the time difference. This error output is given to driving means such as an actuator coil, and the reading means is displacement driven in the vertical direction.

Therefore, if the track shifts from the center of the reading means,
A level difference occurs in the output from each reading portion, and a phase difference corresponding to the amount of track deviation occurs in the waveform shaping output of that output, and by detecting this phase difference by the time difference detection means, The tracking servo corresponding to the amount of deviation can be performed.

Further, in detecting the phase difference in the time difference detecting means, the output of each reading means is corrected by the phase difference corresponding to the difference in the characteristics such as the sensitivity, whereby the difference in the characteristics can be obtained. When the output from each reading portion is small as compared with the case where a DC bias voltage corresponding to is applied, the offset that occurs when the DC component is applied does not occur, and thus each reading portion It is possible to improve the detection accuracy of the phase difference in the time difference detecting means by correcting the variation of the above.

Embodiment FIG. 1 is a block diagram of a compact disk player 50 according to an embodiment of the present invention. The information recorded on the compact disk 1, which is a recording medium, is read by the optical pickup 2. The light receiving element 3 in the optical pickup 2 is divided into four light receiving portions A to D which are reading means, and the output signals of the respective light receiving portions A to D are given to the amplifiers 4 to 7, respectively. Output signals a, c from amplifiers 4,6
Is given to the adder 8 and added, and the output signal (a +
It is derived as c). Similarly, output signals b and d of amplifiers 5 and 7
Is given to the adder 9 and added, and the output signal (b +
It is derived as d).

The output signals (a + c) and (b + d) from the adders 8 and 9 are
It is given to the adder 10 and given to the waveform shaping circuit 11 as an output signal (a + b + c + d). The waveform shaping circuit 11
Waveform the input signal (a + b + c + d), and
The value is converted and given to the decoder 12 and the clock reproduction circuit 15.
The clock reproduction circuit 15 reproduces the clock signal from the input signal and supplies it to the decoder 12 and the speed error detection circuit 17. The decoder 12 decodes the signal from the waveform shaping circuit 11 based on the reproduction clock signal from the clock reproduction circuit 15 and the reference clock signal from the oscillator 16 to create a digital signal. This digital signal is analog-converted by the digital / analog conversion circuit 13 and is derived from the output terminal 14 as an acoustic signal.

The speed error detection circuit 17 compares the reproduction clock signal from the clock reproduction circuit 15 with the reference clock signal from the oscillator 16 and applies a signal of a level corresponding to the error to the motor 19 via the drive circuit 18. . As a result, the motor 19 that rotationally drives the compact disk 1 can be rotationally driven at a rotational speed that is a signal reading speed that is synchronized with the reference clock.

The output signals a to d from the amplifiers 4 to 7 are also supplied to the focusing error detection circuit 20. Output signals b and c of the amplifiers 5 and 6 are given to the adder 21, and output signals a and a of the amplifiers 4 and 7,
d is provided to the adder 22. The output signals from the adders 21 and 22 are given to the low-pass filters 23 and 24, respectively, and the output signals of these low-pass filters 23 and 24 are given to the subtractor 25. The output signal from the subtractor 25 is a value corresponding to the amount of deviation of the optical pickup 2 from the focal point, and this output signal is given to the drive circuit 27 via the phase compensation circuit 26. As a result, the actuator coil 28 is driven, the objective lens (not shown) in the optical pickup 2 is moved in the vertical direction with respect to the compact disc 1, and the optical pickup 2 is brought into the in-focus state, thus focusing. Servo is realized.

The output signals (a + c) and (b + d) of the adders 8 and 9 are also
It is given to the phase control circuit 31 of the tracking error detection circuit 30. In the phase control circuit 31, the relative phases of the signals (a + c) and (b + d) are controlled as will be described later and led to the waveform shaping circuits 32 and 33, respectively. The output signals V1 and V2 from the waveform shaping circuits 32 and 33 are given to the time difference detection circuit 34, and the phase difference between these two signals V1 and V2 is detected. This phase difference corresponds to a tracking error, and the output of the time difference detection circuit 34 is given to the drive circuit 42 via the phase compensation circuit 40. As a result, the actuator coil 43 is driven, and the optical pickup 2 is displaced in parallel with the compact disc 1 and in the direction perpendicular to the track 70, which will be described later, thus realizing a tracking servo.

FIG. 2 is a block diagram showing a specific configuration of the phase control circuit 31. The output signal (a + c) of the adder 8 is input terminal
It is input from 52 to the inverting input terminal of the differential amplifier 53 via the resistor R1. The non-inverting input terminal of this differential amplifier 53 is grounded. The output of the differential amplifier 53 is led out to the output terminal 54 and also negatively fed back via the resistors R3 and R2.

The output signal (b + d) of the adder 9 is the resistance from the input terminal 55.
It is input to the inverting input terminal of the differential amplifier 56 via R11. The non-inverting input terminal of the differential amplifier 56 is grounded.
The output of the differential amplifier 56 is led to the output terminal 57, and is negatively fed back via the resistors R13 and R12.

The connection point 58 of the resistors R2 and R3 is connected to one terminal 59 of the variable resistor R via the capacitor C1, and the other terminal 60 of this variable resistor R is connected to the resistor R12 via the capacitor C11.
Is connected to a connection point 61 between the resistor R13 and the resistor R13. The movable piece 62 of the variable resistor R is grounded.

In the phase control circuit 31 thus configured, the terminal 59
When the resistance value r1 between the movable piece 62 and the movable piece 62 is equal to the resistance value r2 between the movable piece 62 and the terminal 60, the gain characteristics of the differential amplifiers 53 and 56 are shown in FIG. Equal as indicated by the reference sign l1. The phase difference between the input signal and the output signal at the cutoff frequency c at this time is, for example, −45 °, as indicated by the reference numeral l2.

For example, when the movable piece 62 is moved to the terminal 59 side to decrease the resistance value r1 and increase the resistance value r2, the gain curve of the comparator 53 has a cutoff frequency as shown by a virtual line l3 in FIG. The phase difference between the input signal and the output signal at the cutoff frequency c1 increases with the increase of the signal to c1. On the other hand, the gain curve of the differential amplifier 56 is
As indicated by a virtual line l4 in FIG. 3, the cutoff frequency drops to c2, and the phase difference between the input signal and the output signal becomes small. By adjusting the variable resistor R in this way, the cut-off frequency c of the differential amplifiers 53 and 56 can be changed, and the four light receiving portions A to D of the light receiving element 3 and the amplifier 4 can be changed.
It is possible to correct characteristic variations such as ~ 7.

FIGS. 4 and 5 are waveform diagrams for explaining the tracking servo operation when the track 70 indicated by the phantom line in FIG. 1 is shifted to the light receiving portions C and D sides of the light receiving element 3. When the track 70 travels in the direction of arrow 71, the reflected light of the track 70 is first detected by the light receiving portions A and D arranged on the upstream side of the travel direction 71. At this time, track 70
Is shifted to the light receiving area C, D side, the
When 2 reaches the light receiving portions A and D, the light receiving amount of the light receiving portion A is larger than the light receiving amount of the light receiving portion D, and the pit 72 passes through the light receiving portions A and D to receive the light receiving portions B and C. When this happens, the light receiving amount of the light receiving portion B is larger than the light receiving amount of the light receiving portion C. Therefore, the output signal (a +
c) is shown in FIG. 4 (1), and the output signal (b
+ D) is as shown in FIG. 4 (2). These output signals (a + c) and (b + d) are converted into waveform shaping circuits 32 and 33.
Signals V1 and V2 obtained by waveform shaping in FIG. 5 are shown in FIGS. 5 (1) and 5 (2), respectively.

FIGS. 6 and 7 are waveform diagrams for explaining the tracking servo operation when the track 70 is displaced toward the light receiving portions A and B of the light receiving element 3. Track 70 receives light A, B
If the pit 72 hits the light receiving portions A and D, the light receiving amount of the light receiving portion D is larger than the light receiving amount of the light receiving portion A, and the pit 72 shifts the light receiving portions A and D. When it passes and hits the light-receiving parts B and C, the light-receiving part B
The light receiving amount of the light receiving portion C is larger than the light receiving amount of. Therefore, the output signal (a + c) of the adder 8 is as shown in FIG. 6 (1), and the output signal (b + d) of the adder 9 is as shown in FIG. 6 (2). These output signals (a + c), (b
Signals V1 and V2 obtained by waveform shaping + d) by the waveform shaping circuits 32 and 33 are shown in FIGS. 7 (1) and 7 (2), respectively.

As is apparent from FIGS. 5 and 7 described above, the relative difference Δt between the signals V1 and V2 corresponding to the shift amount of the track 70 is increased.
Occurs. Therefore, the phase difference Δt is calculated by the time difference detection circuit.
Accurate tracking servo can be performed by detecting at 34 and driving the actuator coil 43 based on the detection result.

Further, when there are variations in the characteristics of the light receiving portions A to D of the light receiving element 3, for example, the output signal of the adder 8 becomes as indicated by the reference numeral l11 in FIG. 6 (1), which results in a waveform. The output signal V1 of the shaping circuit 32 changes as shown by a virtual line l12 in FIG. 7 (1). As a result, the phase difference between the signals V1 and V2 changes to Δt1, which makes it impossible to perform accurate tracking servo. Therefore, as described above, by adjusting the movable piece 62 of the variable resistor R, the cut-off frequencies c of the differential amplifiers 53 and 56 are changed in the opposite directions, whereby the input signal and the output signal are changed. The phase difference Δt2 caused by the variation in the characteristics of the light receiving portions A to D of the light receiving element 3 can be corrected.

Thus, the tracking error detection circuit according to the present invention
The reference numeral 30 denotes a differential signal, instead of applying a predetermined fixed correction voltage as described in the section of the prior art, in order to correct variations in characteristics of the light receiving portions A to D of the light receiving element 3. By changing the cutoff frequencies c of the amplifiers 53 and 56 in mutually opposite directions, the phase difference between the input signal and the output signal of these differential amplifiers 53 and 56 can be adjusted according to the outputs of the respective light receiving parts A to D. So that when the level of the reflected light is reduced due to scratches or dust on the surface of the compact disk 1, the output signals V of the waveform shaping circuits 32 and 33 are changed.
1, V2 becomes zero, and therefore the phase difference Δt detected by the time difference detecting circuit 34 becomes zero, so that the malfunction such as the jumping of the track as described in the section of the prior art is eliminated and the track difference is eliminated. Trackability is improved.

As described above, according to the present invention, the reading means is divided into at least two reading portions along at least the track direction of the recording medium, and the reading means is provided corresponding to the error output based on the phase difference of the output of each reading portion. In performing the tracking servo by displacing the reading means in the vertical direction of the track, the output of each reading portion is relatively adjusted by the phase control means in advance corresponding to the difference in the characteristics of the reading portion. Since the phase is controlled, it is possible to suppress the error when the output signal level is extremely small and to improve the track followability, as compared with the case where the difference in the characteristics is corrected by a constant correction voltage or the like.

[Brief description of drawings]

FIG. 1 is a block diagram of a compact disk player 50 according to an embodiment of the present invention, FIG. 2 is a block diagram showing a concrete configuration of the phase control circuit 31, and FIG. 3 is for explaining the operation of the phase control circuit 31. 4 and 7 are waveform charts for explaining the operation of the tracking error detection circuit 30. 1 ... Compact disk, 2 ... Optical pickup,
20 …… Focusing error detection circuit, 26, 40 …… Phase compensation circuit, 27, 42 …… Drive circuit, 28, 43 …… Actuator coil, 30 …… Tracking error detection circuit, 31 ……
Phase control circuit, 32, 33 …… Waveform shaping circuit, 34 …… Time difference detection circuit, 53, 56 …… Differential amplifier, 70 …… Truck, 72
...... Pits, A to D ...... Receiving part, R ...... Variable resistor

Claims (1)

[Claims] 1. A recording medium is driven to travel, information recorded along a track of the recording medium is read by a reading means, and based on an output of the reading means, the reading means moves in the vertical direction of the track. In the tracking servo device for correcting the deviation, the reading means is divided into at least two reading portions along the track direction, and the output from each reading portion is relative to the output corresponding to the difference in their characteristics. Phase control means for controlling the phase, waveform shaping means for respectively shaping the waveform of the output from the phase control means corresponding to each reading portion, and edge timing of the output of each reading portion from the output of each waveform shaping means Time difference detecting means for detecting the time difference between the two, and deriving an error output corresponding to the time difference, and a drive for displacing the reading means in the vertical direction in response to the error output. Tracking servo apparatus which comprises a stage.