JPH06267085A - Optical disc apparatus - Google Patents

Abstract

PURPOSE:To improve the detecting accuracy of the moving speed of an optical pickup when an optical disc apparatus makes access. CONSTITUTION:During accessing, a controller 5 outputs a filter constant switching signal 26 to a speed detecting circuit 2 in accordance with a target speed value 13 set for an optical pickup. In consequence, a cut-off frequency of a cut-off frequency variable filter in the speed detecting circuit 2 is selected, thereby to attenuate noises of a track traversing signal 8. Accordingly, the speed is detected with high accuracy while hardly influenced by noises or the like.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disk device which is connected to a computer or the like to record / reproduce data.

[0002]

2. Description of the Related Art Optical disks can record a large amount of information,
Further, it is a recording medium that can be repeatedly erased and reproduced. The optical disk device uses a laser beam to record and reproduce a signal on a track provided at a pitch of about 1 μm on the disk surface, and is highly accurate for accurately causing a laser spot to follow a target track on the disk surface. It requires a servo mechanism and a highly accurate access mechanism to move between tracks at high speed and stably. Since an optical pickup generally has an order of magnitude larger mass than a magnetic head of a hard disk, it is difficult to shorten the track access time for moving the optical pickup to move an optical spot from one track to another track. However, in recent years, with the downsizing of optical pickups and the development of control technology, the track access time, which has been a drawback of optical disk devices, is remarkably shortened.

In an optical disk device, a tracking servo operation for moving a light spot onto a target track and following the target track so as not to cause off-track and reproducing / recording a signal is rough for a rough movement. A two-stage servo system in which a linear motor or the like is used as an actuator and a minute movement is performed by a coil actuator or the like is common. In this case, an optical pickup equipped with a light emitting element, a light receiving element, and a beam splitter objective lens is moved by a coarse actuator such as a linear motor, and only the objective lens is displaced within the optical unit by a fine actuator such as a coil actuator. The configuration is general. A sensor in the optical pickup detects a signal proportional to the amount of deviation of the light spot on the recording surface of the disc from the track center, that is, the coarse and fine actuators are set so that the signal becomes zero. Have control.

Further, during data recording / reproduction, it becomes necessary to perform an access operation for moving the optical pickup from one track to another at high speed. If the number of tracks to move to the target track is large, the target speed is set according to the number of tracks to the target track by a command, and the target of the speed servo mechanism that moves the optical pickup unit in the radial direction of the disk for this set value. It is given as a speed to control the moving speed of the optical pickup, and the moving speed is slowed down as the target track approaches, and when the number of remaining tracks becomes zero, the mode is switched to the tracking servo mode to complete the access operation to the target track.

The access control system of the optical pickup used in the conventional optical disk device as described above has a configuration as shown in FIG. In FIG. 8, 1 is an optical pickup, 2 is a speed detection circuit, 3 is a differential operation circuit, 4 is a pickup drive circuit, 5 is a controller, 6 is a remaining track number detection circuit, 7 is a speed target value output circuit, and 8 is Track crossing signal, 9 movement direction signal, 10 edge pulse, 11 speed detection value, 12 remaining number of tracks, 13 target speed value, 14
Is the speed deviation and 15 is the number of moving tracks.

The operation of the conventional optical pickup control device configured as described above will be described. At the start of access, the number of moving tracks 15 from the controller 5 to the target track is initialized in the remaining track number detecting circuit 6. The speed detection circuit 2 outputs an edge pulse 10 at the zero cross point of the track crossing signal 8, and
The moving speed of the optical pickup 1 is detected from the cycle of the track crossing signal 8 and the moving direction signal 9 to output a speed detection value 11. Further, the remaining track number detection circuit 6 performs a calculation process of adding or subtracting the number of track crossing signals based on the moving direction signal 9 of the optical pickup 1 from the initially set moving track number 15, and the remaining track number 12 Is output. The target speed data corresponding to the input remaining track number 12 is stored in the ROM (read only memory) in the target speed value output circuit 7, and the target speed value 13 is output. Target speed value
The difference between 13 and the speed detection value 11 is set as the speed deviation 14, which is input to the pickup drive circuit 4 so that the moving speed of the optical pickup 1 follows the target speed. When switching to the tracking servo operation, the target speed is generally set slower as the number of remaining tracks decreases so that the tracking servo can be stably pulled into the target track.

FIG. 9 shows an operation block diagram of a conventional speed detecting circuit. In FIG. 9, 8 is a track crossing signal, 9 is a movement direction signal, 10 is an edge pulse, 11 is a speed detection value, 16 is a low pass filter, 17 is a comparator, 18 is an edge pulse generation circuit, 19 is a reference clock generation circuit. , 20 is a counter circuit, 21 is a ROM, 22 is a D / A converter, 23 is a track crossing pulse, 24 is a clock signal, and 25 is periodic data.

The operation of the conventional speed detecting device constructed as above will be described. The track crossing signal 8 is input to the comparator 17 after the unnecessary high frequency noise is attenuated by the low pass filter 16. Comparator 17
Binarizes the track crossing signal 8 at the zero cross point and outputs a pulse signal to the edge pulse generating circuit 18. The edge pulse generation circuit 18 generates a short edge pulse 10 at the rising and falling timings of the input pulse, and the counter circuit 20 determines the cycle in which the edge pulse 10 is generated based on the movement direction signal 9. Counting is performed based on the 19 clock signal 24, and it is output to the address of the ROM 21 as cycle data 25 including the moving direction. ROM
The data of each address is written in 21 as a value proportional to the reciprocal of the address, and the speed data is converted into a D / A converter.
Output sequentially to. In this way, each time the edge pulse 10 is generated, the speed detection value 11 is updated and output.

Further, FIG. 10 shows an operation of the speed detecting circuit shown in FIG. 9 when the optical pickup is decelerating. In FIG. 10, (a) shows a track crossing signal, (b) shows a binarized signal of the track crossing signal, (c) shows an edge pulse, and (d) shows how the speed detection value changes at that time. . An edge pulse is generated at each zero cross of the track crossing signal, and the detected speed value obtained by measuring the period is output. Note that FIG. 11 shows a state of a track crossing signal when the optical pickup in the conventional example moves at a low speed (immediately before the end of the access operation).

[0010]

However, the above conventional structure has the following problems. The frequency of the track crossing signal that occurs when a high-speed access operation, that is, when the optical pickup is moved at a high speed and when the target track is pulled in stably, is from several kHz just before reaching the target track to several hundred kHz at the maximum speed. It becomes a wide area. Therefore, the cutoff frequency of the low-pass filter that can be applied in order to avoid malfunction due to the influence of noise is at least several hundreds of kHz or more, and when the track crossing signal is binarized by the comparator, noise components below the cutoff frequency are not affected. Inevitable.

Further, when the light spot passes through the preformatted area of the disc, the signal of the preformatted portion appears in the track crossing signal (see FIG. 11 when the conventional optical pickup moves at a low speed (immediately before the end of the access operation). Shows the state of the cross-track signal.) Conventionally, a comparator is provided with a hysteresis characteristic in order to prevent malfunction due to noise or the like, and a configuration is used to prevent malfunction with respect to noise amplitude below the hysteresis width, but as can be seen from FIG. Since the hysteresis width that can be set for the signal of the preformat section is limited, there is a possibility that binarization will be performed at points other than the zero cross point of the track crossing signal when noise or offset fluctuation of the track crossing signal occurs. Is high and malfunctions are likely to occur. Particularly, if the comparator malfunctions when the optical pickup moves at a low speed immediately before the pulling of the tracking servo to the target track, the speed control system becomes unstable and the pulling of the tracking servo to the target track tends to fail. SUMMARY OF THE INVENTION It is an object of the present invention to solve the above conventional problems and to provide an optical disk device capable of performing stable and accurate speed control when moving to a target track during access.

[0012]

In order to achieve the above object, an optical disk apparatus of the present invention scans a track on an optical disk with an optical spot to reproduce a signal, and when the optical spot crosses the track. An optical pickup that generates a sinusoidal cross-track signal, a cut-off frequency variable low-pass filter that is provided to attenuate the noise of the cross-track signal, and a controller that outputs a cut-off frequency switching signal for switching the cut-off frequency. A track crossing pulse generating means for binarizing an output from the cutoff frequency variable low pass filter to generate a track crossing pulse; and a speed detection for measuring a moving speed of the optical pickup by measuring a cycle of the track crossing pulse. Means and counting means for counting the cross-track pulses, A target speed generating means for outputting a speed target value of the moving speed of the optical pickup in response to the output of the counting means and a driving means for moving the optical pickup in the radial direction of the optical disc are provided. At this time, an optical disk device for controlling the moving speed of the optical pickup to follow the speed target value, wherein the controller is configured to perform the cutoff frequency switching signal according to the moving speed of the optical pickup during an access operation. Is output to switch the cutoff frequency of the cutoff frequency variable low-pass filter.

[0013]

According to the present invention having the above structure, when the moving speed of the optical pickup is detected, the cutoff frequency of the low-pass filter for passing the track crossing signal input to the comparator is selected according to the moving speed of the optical pickup. Binary operation with less malfunction due to noise at low speed movement is possible,
The speed detector accuracy can be improved.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a circuit operation block diagram of an access control system in the first embodiment of the present invention.
In FIG. 1, 1 is an optical pickup, 2 is a speed detection circuit, 3 is a differential arithmetic circuit, 4 is a pickup drive circuit, 5
Is a controller, 6 is a remaining track number detection circuit, 7 is a speed target value output circuit, 8 is a track crossing signal, 9 is a movement direction signal, 10 is an edge pulse, 11 is a speed detection value, 12 is the number of remaining tracks, and 13 is A target speed value, 14 is a speed deviation, 15 is the number of moving tracks, and 26 is a filter constant switching signal.

The operation of the circuit operation block diagram of the access control system in the first embodiment of the present invention configured as above will be described. At the start of access, the number of moving tracks 15 from the controller 5 to the target track is initialized in the remaining track number detecting circuit 6. Speed detection circuit 2
Outputs an edge pulse 10 at the zero cross point of the track crossing signal 8, detects the moving speed of the optical pickup 1 from the cycle of the track crossing signal 8 and the moving direction signal 9, and outputs a speed detection value 11. Further, the remaining track number detection circuit 6 performs a calculation process of adding or subtracting the number of track crossing signals based on the moving direction signal 9 of the optical pickup 1 from the initially set moving track number 15, and the remaining track number 12 Is output. The controller 5 monitors the remaining track number 12 and outputs a filter constant switching signal 26 corresponding to the remaining track number 12 to the speed detection circuit 2. The target speed data corresponding to the input remaining track number 12 is stored in the ROM of the target speed value output circuit 7, and the target speed value 13 is output. The difference between the target speed value 13 and the detected speed value 11 is set as a speed deviation 14, which is input to the pickup driving circuit 4 so that the moving speed of the optical pickup 1 follows the target speed.

FIG. 2 shows a circuit operation block of the speed detecting device of the optical disk device according to the first embodiment of the present invention. In FIG. 2, 8 is a track crossing signal, 9 is a moving direction signal, 10 is an edge pulse, 11 is a speed detection value, 17
Is a comparator, 18 is an edge pulse generation circuit, 19 is a reference clock generation circuit, 20 is a counter circuit, 21 is ROM, 22 is D /
A converter, 23 is a track crossing pulse, 24 is a clock signal, 25 is periodic data, 26 is a filter constant switching signal,
27 is a cutoff frequency variable low-pass filter.

The operation of the speed detecting device of the present invention constructed as above will be described. The track crossing signal 8 is input to the comparator 17 after the unnecessary high frequency noise is attenuated by the cutoff frequency variable low pass filter 27. The cutoff frequency of the cutoff frequency variable low pass filter 27 is selected according to the moving speed of the optical pickup by the filter constant switching signal 26 from the controller 5. The comparator 17 is 2 at the zero cross point of the track crossing signal 8.
The value is converted and the pulse signal is output to the edge pulse generation circuit 18. The edge pulse generation circuit 18 generates a short edge pulse 10 at the rising and falling timings of the input track crossing pulse 23, and the counter circuit 20 uses the movement direction signal 9 as a reference to generate the edge pulse 10. Counting is performed based on the clock signal 24 of the clock generating circuit 19, and the period data 25 including the moving direction is output to the address of the ROM 21. In the ROM 21, data of each address is written with a value proportional to the reciprocal of the address,
The speed data is sequentially output to the D / A converter 22. In this way, each time the edge pulse 10 is generated, the speed detection value 11 is updated and output.

FIG. 3 shows an example of the target speed value output with respect to the number of remaining tracks of the target speed value output circuit and the frequency of the track crossing signal corresponding to the speed. When performing speed control in which the moving speed of the optical pickup is linearly reduced as the target track is approached, the target speed value is set to be proportional to the square root of 2 for the remaining tracks as shown in FIG. Further, in order to prevent the speed control system from becoming unstable, it is necessary to give a certain speed target value (here, V _MIN ) when the number of remaining tracks is zero. In FIG. 3, the maximum value of the speed target value to be set is V _MAX , and the frequency of the track crossing signal generated at that time is f _MAX . The minimum value is V _MIN which is the speed immediately before the target track is _{pulled in} , and the frequency of the track crossing signal at that time is f _MIN . The controller sets N _C in advance as a threshold of the number of remaining tracks for switching the cutoff frequency of the filter (the target speed value at this time is V _C , the frequency of the cross-track signal is f _C ) and the number of remaining tracks is N _C. A cut-off frequency switching signal is output so that the cut-off frequency is set higher when the value is larger than the above, and set lower when the number of remaining tracks is smaller than N _C.

FIG. 4 shows an example of a circuit configuration of a cutoff frequency variable low-pass filter (second-order Butterworth type) in the first embodiment of the present invention. In FIG. 4, A is an operational amplifier, B is an inverter, C is a capacitor, R ₁ ,
R ₂ is a resistor (here, R ₁ > R ₂ ), SW ₁ , SW
₂ , SW ₃ , SW ₄ are analog switches. In this circuit example, the cutoff frequency can be switched in two steps.

The operation of the circuit of the cut-off frequency variable low-pass filter configured as described above will be described.
A track crossing signal is input to the input terminal in the figure. When the filter constant switching signal from the controller is L, SW ₁ and SW ₃ of the analog switch are selected, and the first cutoff frequency f _C1 of this low-pass filter is given by Formula 1.

[0021]

## EQU1 ## 1 / (2√2πR ₁ C) (Hz) When the filter constant switching signal is H, the analog switches SW ₂ and SW ₄ are selected, and the second cutoff frequency f _{C2 of} this low-pass filter is selected. Becomes Equation 2.

[0022]

[Expression 2] 1 / (2√2πR ₂ C) (Hz) Of the track crossing signals generated during the access operation, the frequency at which the optical pickup is moving at the maximum speed is f _MAX , and the controller switches the cutoff frequency. If the frequency is f _C and the frequency immediately before the entry into the target track is f _MIN , each constant may be selected so that f _MIN <f _C1 <f _MAX <f _C2 .

FIG. 5 shows a circuit operation block diagram of the access control system in the second embodiment of the present invention. In FIG. 5, each symbol is common to FIG. The operation of the circuit operation block diagram of the access control system in the second embodiment of the present invention configured as above will be described. At the start of access, the number of moving tracks 15 from the controller 5 to the target track is initialized in the remaining track number detecting circuit 6. The speed detection circuit 2 outputs an edge pulse 10 at the zero cross point of the track crossing signal 8 and detects the moving speed of the optical pickup 1 from the cycle of the track crossing signal 8 and the moving direction signal 9 to output a speed detection value 11. To do. Further, the remaining track number detection circuit 6 performs a calculation process of adding or subtracting the number of track crossing signals based on the moving direction signal 9 of the optical pickup 1 from the initially set moving track number 15, and the remaining track number 12 Is output.
The number of remaining tracks input to the speed target value output circuit 7 is 12
The target speed data corresponding to is stored in the ROM, and the target speed value 13 is output. Controller 5 has a target speed value of 13
Is monitored and the filter constant switching signal 26 corresponding to the target speed value 13 is output to the speed detection circuit 2. Target speed value 13
And the speed detection value 11 is set as a speed deviation 14, which is input to the pickup drive circuit 4 so that the moving speed of the optical pickup 1 follows the target speed.

FIG. 6 shows an example of the target speed value output during the access operation and the frequency of the track crossing signal corresponding to the speed. In FIG. 6, the optical pickup is accelerated from the start of access to the maximum speed V _MAX . The frequency of the cross-track signal generated at that time is f _MAX .
After that, after moving at a constant speed, as the number of remaining tracks decreases, the speed is reduced to V _MIN , which is the speed immediately before the target track is pulled. The frequency of the cross-track signal generated at that time is f _MIN . The controller sets V _C in advance as the threshold value of the speed target value for switching the cutoff frequency of the filter (the frequency of the track crossing signal at this time is f _C ), and when the speed target value is larger than V _{C, the} cutoff frequency is increased. When the speed target value is smaller than V _C , the cutoff frequency switching signal is output so as to set the cutoff frequency low.

FIG. 7 shows the state of the track crossing signal when the optical pickup according to the embodiment of the present invention moves at a low speed (immediately before the end of the access operation). Compared with the conventional waveform of Fig. 11, the cutoff frequency of the low-pass filter is set lower,
It can be seen that the noise component when passing through the preformatted area is reduced, and binarization by the comparator is extremely easy.

[0026]

As is apparent from the above embodiments, the present invention provides a cutoff frequency variable low-pass filter in the speed detection circuit for detecting the moving speed of the optical pickup, and the controller controls the cutoff frequency according to the moving speed of the optical pickup. By switching the cutoff frequency of the cutoff frequency variable low-pass filter, in any case when the pickup moves from low speed to high speed during access operation,
It becomes possible to stably binarize by the comparator without attenuating the amplitude of the track crossing signal and to accurately detect the speed when moving to the target track, and as a result, stable and high speed access operation is possible. It has an effect that an excellent optical disk device can be realized.

[Brief description of drawings]

FIG. 1 is a circuit operation block diagram of an access control system in a first embodiment of the present invention.

FIG. 2 is a circuit operation block diagram of a speed detecting device of the optical disk device in the first embodiment of the present invention.

FIG. 3 is a diagram showing an example of speed target value output with respect to the number of remaining tracks of the speed target value output circuit and the frequency of a track crossing signal corresponding to the speed in the first embodiment of the invention.

FIG. 4 is a diagram showing an example of a circuit configuration of a cutoff frequency variable low-pass filter (second-order Butterworth type) in the first embodiment of the present invention.

FIG. 5 is a circuit operation block diagram of an access control system according to a second embodiment of the present invention.

FIG. 6 is a diagram showing an example of a velocity target value output during an access operation and a frequency of a track crossing signal corresponding to the velocity in the second embodiment of the present invention.

FIG. 7 is a diagram showing a state of a track crossing signal when the optical pickup according to the embodiment of the present invention moves at a low speed (immediately before the end of the access operation).

FIG. 8 is an operation block diagram of a control system of a conventional optical pickup.

FIG. 9 is an operation block diagram of a conventional speed detection circuit.

FIG. 10 is a diagram showing the operation of the speed detection circuit shown in FIG. 9, in which the optical pickup is decelerated, and a track crossing signal, a signal obtained by binarizing the track crossing signal, an edge pulse, and a change in the speed detection value. It is a figure which shows the mode.

FIG. 11 is a diagram showing a state of a track crossing signal when the optical pickup of the conventional example moves at a low speed (immediately before the end of the access operation).

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Optical pickup, 2 ... Speed detection circuit, 3 ... Differential calculation circuit, 4 ... Pickup drive circuit, 5 ... Controller, 6 ... Remaining track number detection circuit, 7 ... Target speed value output circuit, 8 ... Track crossing signal, 9 ... Movement direction signal, 10 ... Edge pulse, 11 ... Speed detection value, 12
… Number of remaining tracks, 13… Target speed value, 14… Speed deviation,
15… Number of moving tracks, 16… Low-pass filter, 17
Comparator, 18 ... Edge pulse generation circuit, 19 ... Reference clock generation circuit, 20 ... Counter circuit, 21 ... ROM,
22 ... D / A converter, 23 ... Track crossing pulse, 24
… Clock signal, 25… Period data, 26… Filter constant switching signal, 27… Cutoff frequency variable low-pass filter.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Takamune Hisagi, 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (1)

[Claims] 1. An optical pickup that scans a track on an optical disk with a light spot to reproduce a signal and generates a sinusoidal track crossing signal when the light spot crosses the track, and noise of the track crossing signal. Cut-off frequency variable low-pass filter provided for attenuating the cut-off frequency, a controller outputting a cut-off frequency switching signal for switching the cut-off frequency, and binarizing the output from the cut-off frequency variable low-pass filter to generate a track crossing pulse. Track crossing pulse generation means for generating, speed detection means for measuring the movement speed of the optical pickup by measuring the cycle of the track crossing pulse,
Counting means for counting the track crossing pulses, target speed generating means for outputting a speed target value of the moving speed of the optical pickup according to the output of the counting means, and moving the optical pickup in the radial direction of the optical disc. An optical disc device for controlling the moving speed of the optical pickup to follow the speed target value during an access operation, the controller including: The optical disk device, wherein the cutoff frequency switching signal is output according to the moving speed of the switch, and the cutoff frequency of the cutoff frequency variable low-pass filter is switched.