JPH0344826A - Eccentricity measuring instrument for recording or reproducing disk - Google Patents

Abstract

PURPOSE:To exactly measure the eccentricity of a disk by measuring the fluctuating state of the disk in a moving direction caused by the eccentricity in a state of a tracking control loop is closed, and counting the number of tracks crossing a pickup due to the eccentricity in a state of the tracking control loop is opened. CONSTITUTION:A tracking error signal (h) of a pickup 30 is applied through a switch 8 and a resistor 12 to an actuator driving coil 33 of the pickup 30, applies tracking control to an objective lens 35 and is compared with a reference level by a comparator 10. The output of the comparator 10 is supplied through a switch 17 to an up/down counter 18 and the output of the up/down counter 18 is supplied to a maximum value holding circuit 19 and a minimum value holding circuit 20. Then, the outputs of the respective holding circuits 19 and 10 are subtracted by a subtracting circuit 21 and a subtracted result is led out to an output terminal 22. Thus, the number of cross of tracks can be accumulated without fail corresponding to the direction of cross of the track and the eccentricity of the disk can be exactly measured.

Description

DETAILED DESCRIPTION OF THE INVENTION [Prior Art] Conventionally, for example, in order to measure the eccentricity of an optical disc, the optical disc is placed in a playback state with the pink-up fixed, and track cross signals are counted. In this case, when the pickup crosses the track from the inside to the outside, it counts up, and when it crosses the track from the outside to the inside, it counts down, monitors the fluctuation of the count value during one rotation of the disk, and then checks the maximum fit! Eccentricity A is calculated by Tmax and minimum value Twin: A= (Tmax −Twin)X
(P/2). Here, P is the track pitch.

[Problem to be solved by the invention]

In this case, it was difficult to sense the direction across the trunk, making it difficult to put it into practical use.

The present invention has been made with the aim of improving these drawbacks.

Means for alternately setting a tracking control loop to an open state and a closed state in synchronization with the rotation of the disk, and obtaining a momentary disk movement direction signal obtained by differentiating a tracking error signal in the closed state of the tracking control loop. means for obtaining a delayed signal by delaying the disk movement direction signal until the tracking control loop is open; and obtaining a track crossing signal by detecting a tracking error signal when the tracking control loop is open. and means for adding or subtracting the track cross signal according to the polarity of the delayed signal.

[Effect]

Therefore, when the tracking control loop is closed, fluctuations in the moving direction of the disk due to eccentricity are measured, and when the tracking control loop is open, the eccentricity causes a track to cross the pickup.

〔Example〕

Embodiments of the present invention will be described below with reference to FIG.

The disk l is rotated by a motor 2 at 200 rpm, and the motor 2 is provided with a rotation pulse generator 3 that generates one rotation pulse a for each rotation.
enters the flip-flop (FF) 4 which performs a toggle operation, and the duty is 50, where one cycle is two rotations of the disk 1:
50 mode signals are used, RAM? and switch 8
control.

The rotation pulse a is also applied to the address counter 5 and the up-down counter 1 day clear terminal. The pickup 30 irradiates the disk 11 with a laser beam from a laser oscillator 31, applies the reflected light to a two-split photodetector 34 via a prism 32, and obtains the output difference between them using a differential amplifier 36 to generate a well-known tracking error signal. get the benefits.

The tracking error signal of the pickup 30 is applied to the actuator drive coil 33 of the pickup 30 via the switch 8 and the resistor 12 to control the tracking of the objective lens 35, and is compared with a reference level by the comparator 10. The voltage drop across resistor 12 is applied to differential amplifier 13.
and is amplified by a low pass filter 14. Differential circuit 15
The output of the oscillator 6 is applied to the address counter 5, and its address output is applied to the address terminal of the RAM 7. The output g of RAM 7 controls switch 17. The output of comparator IO is applied to up/down counter 18 via switch 17. Amplifier down counter 1
The output of 8 is the maximum value holding circuit 19 and the minimum value holding circuit 2.
0, and the output of each holding circuit 19, 20 is subtracted by a subtraction circuit 21, and the result is delivered to an output terminal 22.

The operation of the above configuration will be described in detail below with reference to the waveform diagram of each part in FIG. The waveform diagrams a''-h in the figure show waveforms appearing at the portions with the same reference numerals in FIG.

Now, when the disk 1 is rotated with the pickup 30 fixed, the address counter 5 and up/down counter 18 are cleared by the first rotation pulse al in FIG. 2, and the mode signal from the flip-flop 4 is cleared. However, it becomes L level and enters the track cross direction detection mode as shown below.

That is, when the mode signal from the flip-flop 4 becomes L level, the loop switch 8 is turned on.
As a result, the tracking error signal detected by the photodiode 34 and the differential amplifier 35 is transferred to the loop switch 8.
The signal is applied to the objective lens driving coil 33 via the 400° C. to perform well-known tracking control, and the objective lens 35 is controlled to follow the track. The tire knocking error signal thus obtained varies in accordance with the movement of the disk l due to eccentricity.

Since the level of such a tracking error signal manually inputted to the actuator drive coil 33 is extremely low in the tracking control state, it is converted into a voltage by the current detection resistor 12, and is amplified to a large level by the differential amplifier 13 to be biased. The core detection output becomes C. The output C is input to a low-pass filter 14 to remove noise components. The output d of the low-pass filter 14 is position data of the objective lens 35 that follows the eccentricity of the disk l, and is input to the differentiating circuit 15 in order to convert this into movement direction data. Since the output e of the differentiating circuit 15 has a polarity that corresponds to the driving direction of the objective lens 35, it is converted by the comparator 16 into a square wave lens movement direction signal f that has a polarity that corresponds to the direction.

Further, as mentioned above, when the mode signal becomes L level, the RAM 7 is put into the writing state, and the address counter 5 is cleared, so that the oscillation frequency I
The address counter 5 starts a count amplifier by the MHz oscillator 6, and its output is R as an address signal.
It is input to the address of AM7. Therefore, the lens movement direction signal f that is manually input from time to time in accordance with the rotation of the disk 1
The track cross direction data indicated by is written to the address specified by the address counter 5.

Writing of data indicating the track crossing direction is continued until the next rotation pulse a2 arrives, and when the next rotation pulse a2 is output, the address counter 5 and up/down counter 18 are cleared again. Further, the mode signal from the flip-flop 4 becomes H level, and the mode shifts to the track cross counting mode.

In this mode, the loop switch 8 is turned off, so the objective lens 35 is fixed together with the pickup 30 without any control over the eccentricity of the disk. As a result, the objective lens 35 crosses the track according to the eccentricity, and the tracking error signal obtained from the differential amplifier 36 becomes an AC signal whose polarity changes greatly between positive and negative at each track crossing. Converts the error signal to a square wave track cross signal.

On the other hand, the RAM 7 is set to a read state by the mode signal S, and immediately after the rotation pulse a2, the address counter 5 starts reading data in the same order and at the same cycle as the write address generation in the track cross direction detection mode. The address will be output. Therefore, from the RAM 7, a lens movement direction signal g obtained by delaying the lens movement direction signal f by one revolution of the disk 1 can be obtained. The switch 17 is controlled so that when the lens movement direction signal g obtained in this way is at H level, it becomes a count up signal, and when it is at L level, it becomes a count down signal, and the track cross signal from the comparator 10 goes up. It is input to the down counter 18. up/down counter 1
8 repeats the above-mentioned count amplifier and countdown while the mode signal from the flip-flop 4 is at H level and outputs the instantaneous counting results. The maximum value and minimum value of the count output thus obtained are held by the maximum value holding circuit 19 and the minimum value holding circuit 20, and the values are transferred to the subtracter 21.
By inputting , the maximum eccentricity value A can be detected using the front part.

〔Effect of the invention〕

As described above, according to the present invention, with a simple configuration, the number of track crosses can be reliably integrated according to the direction of track crosses, and the eccentricity of the disk can be accurately measured.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing one embodiment of the present invention, and FIG. 2 is a waveform diagram of each part to explain its operation. 3...1 revolution pulse generator 5...address counter 7...RAM 8...loop switch 15...differentiation circuit 17...switch 18...up/down counter note 20

Claims (1)

[Claims] Means for alternately setting a tracking control loop to an open state and a closed state in synchronization with the rotation of the disk, and obtaining a momentary disk movement direction signal obtained by differentiating a tracking error signal in the closed state of the tracking control loop. means and
means for obtaining a delayed signal by delaying the disk movement direction signal until the tracking control loop is open; and means for obtaining a track cross signal by detecting a tracking error signal in the open state of the tracking control loop; An apparatus for measuring eccentricity of a recording or reproducing disk, characterized in that the track cross signal is added or subtracted according to the polarity of the delayed signal.