JP2000195064A - Optical disk-reproducing apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To surely reproduce an optical disk even when the optical disk is brought in a reproduction impossible state by moving an optical unit to a reference position when an address data read abnormal state of the optical unit is detected and starting a characteristic-adjusting means. SOLUTION: Offset adjustment, initial adjustment such as focus search or the like are automatically carried out when a magneto-optic disk is loaded. The process is executed even when a position or a focus of an optical unit becomes uncontrollable in the middle of the reproduction. When a reproduction abnormality is brought about during the reproduction, if the position of the optical unit is feared to deviate from address data or if the address data is missing, it is so judged that there is a fear of the optical unit's being out of a groove area to move to a pit area or read-out area. The optical unit is immediately returned to an innermost circumferential position (reference position). Then, the initial adjustment is automatically carried out at a predetermined position, and the focus search is conducted to return the optical unit to a state in which the focus servo is possible.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disk reproducing apparatus, and more particularly to an optical disk reproducing apparatus capable of quickly returning to a state where data can be read even when data cannot be read.

[0002]

2. Description of the Related Art FIG. 2 is a block diagram showing a configuration of a magneto-optical disk reproducing apparatus. Hereinafter, description will be made with reference to the drawings.

[0003] Reference numeral 1 denotes information recording by irradiating a laser beam to a magneto-optical disk (MD) 2, and a difference in the amount of light reflected from pits or a difference in polarization plane from a magnetic film by irradiating the laser beam. The position is adjusted by a sled motor 41 that moves the magneto-optical disk 2 in the radial direction with an optical unit that reads information recorded based on the information. Reference numeral 2 denotes a recordable and reproducible magneto-optical disk (MD) in which data is spirally recorded on a disk, and is provided at an innermost periphery and is a read-only pit area for reading out TOC information recorded in a pit shape. A read / write groove area formed of a magnetic film on which a user can write and read information by a user, and a read-out area provided on the outermost periphery where a signal indicating the end of data is recorded. ing. Reference numeral 31 denotes an RF amplifier for amplifying a signal output from the optical unit 1, which separates a focus signal and a tracking signal for realizing a servo, and converts an audio signal into a digital signal processing unit 32.
Output to Reference numeral 32 denotes a digital signal processing unit which performs signal processing of a digital signal, converts an audio signal into an analog signal, outputs the analog signal to the audio output unit 6, and detects an address abnormality. 33
Is a thread servo circuit for controlling the movement of the optical unit 1 in the radial direction. A spindle servo circuit 34 controls the rotation of the magneto-optical disk 2 at a predetermined linear velocity. 35
Reference numeral denotes a focus servo circuit which performs control based on a focus error signal in order to move the objective lens back and forth so that the light beam is always focused on the magneto-optical disk 2.
Reference numeral 36 denotes a tracking servo circuit that drives an actuator (not shown) to perform control based on a tracking signal so as to track a predetermined track. Reference numeral 41 denotes a sled motor for moving the optical unit 1 in the radial direction of the magneto-optical disk 2. Reference numeral 42 denotes a spindle motor that drives the magneto-optical disk 2 to rotate at a predetermined linear speed. A control unit 5 includes a microcomputer for performing servo control, control of the entire system, and various signal processing. 6
Is an audio output unit for amplifying an audio signal and converting it into audio by a speaker. Reference numeral 7 denotes a detection switch which is provided at a position corresponding to the pit area which is the innermost circumference of the magneto-optical disk 2 and detects that the optical unit 1 is in the pit area.

FIG. 3 is a flowchart of a process performed by the control unit 5 of the conventional magneto-optical disk reproducing apparatus. Hereinafter, description will be made with reference to the drawings. This process starts from the time when the magneto-optical disk 2 is set in the magneto-optical disk reproducing device.

In step S21, the optical unit is moved to the innermost circumference of the magneto-optical disk, and the flow advances to step S22.
That is, when the magneto-optical disk 2 is mounted on the magneto-optical disk reproducing device, the optical unit 1 and the magneto-optical disk 2
The relative position of fluctuates. For this purpose, for example, the centers of the pits of the optical unit 1 and the magneto-optical disk 2 are made to coincide with each other, or initial adjustment is performed so that the signal gain is optimized. However, the entire surface of the recording / reproducing magneto-optical disc 2 is not the same area, and the state of the detection signal is different between the pit area and the groove area, and the initial adjustment must be made in accordance with each area. For this purpose, it is necessary to determine in which area (position) the optical unit 1 is located on the magneto-optical disk 2. Therefore, first, when the optical unit 1 is moved in the inner circumferential direction of the magneto-optical disk 2 and the detection switch 7 is turned on, it is assumed that the optical unit 1 is at a position corresponding to the innermost pit area of the magneto-optical disk 2. to decide.

In step S22, automatic adjustment is performed, and the flow advances to step S23. That is, the gain is adjusted so that the detection signal from each detection unit (photodiode) has an appropriate value. This is performed for both the pit area and the groove area. The initial adjustment includes offset adjustment, focus search, trekking gain adjustment, track cross gain adjustment, focus gain adjustment, and the like. Will be implemented. This process is also performed when the position or the focus of the optical unit 1 cannot be controlled during the performance (reproduction).

In step S23, a focus search is performed, and the flow advances to step S24. That is, since the focal depth of the lens system is very shallow, when the magneto-optical disk 2 is set in the magneto-optical disk reproducing device, it is far away from the focus position, and the reflected light from the magneto-optical disk 2 is hardly reflected. It does not enter a quadrant photodiode (not shown). As a result, the focus error signal for detecting the focus state is a difference signal of the output sum of the two pairs of diagonal diodes of the four-division photodiode, but since the output sums of the two pairs of diagonal diodes are both small, The value becomes 0 in spite of a large deviation from the in-focus position, the focus is determined and the focus servo cannot be performed. Therefore, a focus search signal is output and added to the focus servo signal to largely move the objective lens. In the process, a focus error signal is detected and pulled in the vicinity of the focal point.

In step S24, reproduction is performed, and the process proceeds to step S25. That is, since the initial adjustment and the focus search are completed and the adjustment is performed so that an appropriate reproduction signal can be obtained, the audio reproduction is performed. For reproduction, data is read based on the difference in the plane of polarization of the reflected light from the magneto-optical disk 2.

In step S25, it is determined whether or not abnormal reproduction is detected.
Returning to step S22, if no abnormal reproduction is detected, step S2
Return to Step 4 and continue the reproduction. Playback abnormalities include focus abnormalities and address input abnormalities.For example, a state in which focus servo cannot be applied is called out of focus.
Since a focus error signal sufficient for performing the focus servo cannot be obtained, it is not possible to bring the focus to the focal point.
An address input error refers to a state in which data cannot be read due to a rotation error of the spindle motor 42 for rotating the disk, and is detected by the digital signal processing unit 32. That is, address data indicating the recording position of data on the magneto-optical disk is recorded on the magneto-optical disk 2. Since the address data indicates a recording position, the address data has a continuous value. Therefore, in a normal data reading state, the read address data has a continuous value. An address input error can be detected from the continuity of the read address data.

As described above, when a reproduction error occurs during reproduction, it is determined that the initial adjustment is incomplete, and the process immediately returns to step S22 to automatically perform the initial adjustment, and then performs a focus search. By returning to the state where the focus servo can be performed, sound reproduction becomes possible.

[0011]

When the focus servo is deviated or an address input error occurs during reproduction of the magneto-optical disk, the optical unit is usually in the groove area, and the position is determined from the read address data. it can. However, if the address input becomes abnormal due to vibration or the like, the position of the optical unit cannot be determined. Further, during the search or movement of the designated position, the optical unit is moving at a high speed by the sled motor, so that the optical unit cannot be stopped immediately due to inertia. In such a case, if the reproduction is interrupted due to defocus or a voltage drop or an overcurrent, the address data read immediately before the reproduction becomes impossible and the actual position of the optical unit do not always coincide with each other. May be out of place.

In the conventional initial adjustment method of the magneto-optical disk reproducing apparatus, the optical unit 1 is moved to the innermost TOC area (pit area) or the outermost lead-out area due to a positional shift. However, since the initial adjustment is performed assuming that it is in the groove area, the initial adjustment conditions are different. Incidentally, such a problem is caused not only in a magneto-optical disk but also in an optical disk in which a plurality of types of signal storage systems (a plurality of types of bits) exist in the disk.
For example, it also occurs in a compact disk (CD-R) or the like.

An object of the present invention is to provide an optical disk reproducing apparatus which can return to a state in which reproduction can be reliably performed in a short time even if the reproduction becomes impossible during reproduction of the optical disk.

[0014]

In order to achieve the above object, the present invention provides an optical unit for irradiating an optical disk on which data is recorded with a light beam and outputting a detection signal based on light reflected from the optical disk; An optical disc reproducing apparatus comprising: a servo unit that performs feedback control of the operation of the optical unit based on a detection signal of the optical unit; and a characteristic adjustment unit that adjusts an operation characteristic of the servo unit to be optimal. Reference position moving means for moving the optical unit to a reference position corresponding to a predetermined position on the optical disc; and characteristic adjustment activation means for operating the characteristic adjustment means when the optical unit is in a data readable state, The read value of the address data indicating the data recording position on the optical disc by the optical unit is continuous. The address data abnormality detecting means for detecting an abnormal state of address data reading, and the address data abnormality detecting means for detecting an abnormal state of address data reading of the optical unit by the reference position moving means. After the optical unit is moved to the reference position, the characteristic adjustment activation unit activates the characteristic adjustment unit.

An optical unit for irradiating an optical disk on which data is recorded with a light beam and outputting a detection signal based on the reflected light from the optical disk, and operating the optical unit based on the detection signal of the optical unit. In an optical disc reproducing apparatus including a servo unit for performing feedback control and a characteristic adjusting unit for adjusting an operation characteristic of the servo unit to be an optimum one, the optical unit is moved to a reference position corresponding to a predetermined position of the optical disk. Reference position moving means for moving, high-speed movement detecting means for detecting that the optical unit is moving at a higher speed than during normal recording and reproduction, and when the optical unit is in a data reading disabled state, A characteristic adjustment activation unit for operating the characteristic adjustment unit and a state in which the focus control of the optical unit cannot be controlled are detected. A focus uncontrollable detecting means for, detects that the high-speed movement detecting means said optical unit is moved at a speed higher than that during normal recording and reproduction,
When the focus control inability detecting means detects the inability to control the focus control of the optical unit, the reference position moving means moves the optical unit to a reference position, and then the characteristic adjustment activation means causes It is characterized by including a starting means for starting the characteristic adjusting means.

An optical unit for irradiating an optical disk on which data is recorded with a light beam and outputting a detection signal based on light reflected from the optical disk, and operating the optical unit based on the detection signal of the optical unit. In an optical disc reproducing apparatus including a servo unit for performing feedback control and a characteristic adjusting unit for adjusting an operation characteristic of the servo unit to be an optimum one, the optical unit is moved to a reference position corresponding to a predetermined position of the optical disk. A reference position moving means for moving, a characteristic adjustment starting means for operating the characteristic adjusting means when the optical unit becomes incapable of reading data, and a focus control for detecting an uncontrollable state of the focus control of the optical unit The optical unit by the optical disc by the inability detection means and the reference position moving means. When the stop of the optical disc and the reproduction following the stop are instructed while moving to the reference position corresponding to the predetermined position, after moving the optical unit to the reference position by the reference position moving means, the characteristic The apparatus further comprises a starting unit for starting the characteristic adjusting unit by the adjusting starting unit.

Also, an optical unit for irradiating a light beam on an optical disk on which data is recorded and outputting a detection signal based on the reflected light from the optical disk, and operating the optical unit based on the detection signal of the optical unit. In an optical disc reproducing apparatus including a servo unit for performing feedback control and a characteristic adjusting unit for adjusting an operation characteristic of the servo unit to be an optimum one, the optical unit is moved to a reference position corresponding to a predetermined position of the optical disk. Reference position moving means for moving, high-speed movement detecting means for detecting that the optical unit is moving at a higher speed than during normal recording / reproducing, and a power supply for detecting an abnormality of a power supply for driving the optical disc reproducing apparatus Abnormality detecting means, and operating the characteristic adjusting means when the optical unit becomes incapable of reading data. The characteristic adjustment activation unit and the high-speed movement detection unit detect that the optical unit is moving at a higher speed than during normal recording / reproducing, and that the power supply abnormality detection unit has an abnormality in the power supply. When the detection is detected, after the optical unit is moved to the reference position by the reference position moving means, a starting means for starting the characteristic adjusting means by the characteristic adjustment starting means is provided.

Further, the predetermined position of the optical disk is a data recording area at an innermost circumference of the optical disk.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, an embodiment of the present invention will be described with reference to a magneto-optical disk reproducing apparatus as an example.
Since the configuration is the same as that described above, the description of the hardware configuration will be omitted, and the characteristic processing performed by the control unit 5 will be described.

FIG. 1 is a flowchart of a process performed by the control unit 5 of the magneto-optical disk reproducing apparatus according to the first embodiment of the present invention. Hereinafter, description will be made with reference to the drawings. This process starts from the time when the magneto-optical disk 2 is set in the magneto-optical disk reproducing device.

In step S11, the optical unit is moved to the innermost circumference of the magneto-optical disk, and the flow advances to step S12.
That is, when the magneto-optical disk 2 is mounted on the magneto-optical disk reproducing device, the optical unit 1 and the magneto-optical disk 2
The relative position of fluctuates. For this purpose, for example, the centers of the pits of the optical unit 1 and the magneto-optical disk 2 are made to coincide with each other, or initial adjustment is performed so that the signal gain is optimized. However, the entire surface of the recording / reproducing magneto-optical disc 2 is not the same area, and the state of the detection signal is different between the pit area and the groove area, and the initial adjustment must be made in accordance with each area. For this purpose, it is necessary to determine in which area (position) the optical unit 1 is located on the magneto-optical disk 2. Therefore, first, when the optical unit 1 is moved in the inner circumferential direction of the magneto-optical disk 2 and the detection switch 7 is turned on, it is assumed that the optical unit 1 is at a position corresponding to the innermost pit area of the magneto-optical disk 2. to decide.

In step S12, automatic adjustment is performed, and the flow advances to step S13. That is, the gain is adjusted so that the detection signal from each detection unit (photodiode) has an appropriate value. This is performed for both the pit area and the groove area. The initial adjustment includes offset adjustment, focus search, trekking gain adjustment, track cross gain adjustment, focus gain adjustment, and the like. Will be implemented. This process is also performed when the position or the focus of the optical unit 1 cannot be controlled during the performance (reproduction).

In step S13, a focus search is performed, and the flow advances to step S14. That is, since the focal depth of the lens system is very shallow, when the magneto-optical disk 2 is set in the magneto-optical disk reproducing device, it is far away from the focus position, and the reflected light from the magneto-optical disk 2 is hardly reflected. It does not enter a quadrant photodiode (not shown). As a result, the focus error signal for detecting the focus state is a difference signal of the output sum of the two pairs of diagonal diodes of the four-division photodiode, but since the output sums of the two pairs of diagonal diodes are both small, The value becomes 0 in spite of a large deviation from the in-focus position, the focus is determined and the focus servo cannot be performed. Therefore, a focus search signal is output and added to the focus servo signal to largely move the objective lens. In the process, a focus error signal is detected and pulled in the vicinity of the focal point.

In step S14, reproduction is performed, and the flow advances to step S15. That is, since the initial adjustment and the focus search are completed and the adjustment is performed so that an appropriate reproduction signal can be obtained, the audio reproduction is performed. For reproduction, data is read based on the difference in the plane of polarization of the reflected light from the magneto-optical disk 2.

In step S15, it is determined whether an address input error is detected. If an address input error is detected, the process returns to step S11. If no address input error is detected, the process proceeds to step S16. An address input error refers to a state in which data cannot be read due to a rotation error of the spindle motor 42 that rotates the disk, and is detected by the digital signal processing unit 32. That is, address data indicating the recording position of data on the magneto-optical disk is recorded on the magneto-optical disk 2. Since the address data indicates a recording position, the address data has a continuous value. Therefore, in a normal data reading state, the read address data has a continuous value. An address input error can be detected from the continuity of the read address data. If an address input error occurs, the exact position of the optical unit 1 cannot be determined. When the optical unit 1 is in the pit area, data cannot be read because tracking cannot be performed. It should be noted that instead of immediately returning to step S11 when an address input abnormality is detected, the process may return to step S11 if it is not possible to repeat the process several times.

In step S16, it is determined whether or not the search is being performed. If the search is being performed, the process proceeds to step S17. If the search is not being performed, the process returns to step S14. That is, it is determined whether or not the optical unit 1 is moving to the position specified by the thread motor 41 at a high speed. When the focus is lost due to vibration during the search, the optical unit 1 is easy to move.

In step S17, it is determined whether or not the out-of-focus state is detected. If the out-of-focus state is detected, the process returns to step S11. If the out-of-focus state is not detected, the process proceeds to step S18. In other words, it is impossible to bring the focus to the focus point in a state where a sufficient focus error signal for performing the focus servo cannot be obtained. Since the optical unit 1 is moving at a high speed by the thread motor 41, the optical unit 1 may be deviated from the groove area due to the vibration. Instead of returning to step S11 immediately when out-of-focus is detected, the process may return to step S11 if focus servo (or focus search) cannot be repeated several times.

In step S18, it is determined whether or not a power supply abnormality is detected.
Returning to step S11, if no power failure is detected, step S1
Move to 9. That is, when a drop in the backup voltage or overcurrent is detected. In such a case, the power supply is cut off and the reproduction is interrupted.
Because it is moving at high speed, it cannot stop immediately due to inertia. As a result, a deviation occurs between the address data read immediately before the reproduction becomes impossible and the actual position of the optical unit 1, and even when the globe area is being searched, the optical unit 1 deviates from the groove area and is located in the pit area. , There is a possibility that the outer periphery is protruding.

In step S19, it is determined whether or not the vehicle is moving to the innermost periphery. If the vehicle is moving to the innermost periphery, the process proceeds to step S20. If not, the process proceeds to step S14. Return to That is, the optical unit 1 is moving at a high speed by the sled motor 41 during the movement to the innermost circumference, and may move by inertia even if a stop instruction is issued.

In step S20, it is determined whether or not a reproduction instruction has been received following the stop instruction. If a reproduction instruction has been received following the stop instruction, the flow returns to step S11. If no reproduction instruction has been received following the stop instruction, the flow returns to step S19. . Since the optical unit 1 is moving at high speed by the thread motor 41, it cannot be stopped immediately due to inertia. When reproduction is instructed in such a state, there is a possibility that the optical unit 1 moves out of the groove area and moves to the pit area.

As described above, when there is a possibility that the position of the optical unit 1 is deviated from the address data when a reproduction error occurs during the reproduction, or when there is no address data, the optical unit 1 moves out of the groove area. It is determined that there is a possibility that the optical unit 1 has deviated and moved to the pit area or the lead-out area, and immediately returns to step S11 to return the optical unit 1 to the innermost peripheral position (reference position) and then perform initial adjustment at a predetermined position. Is automatically performed, and then a focus search is performed to return to a state in which the focus servo can be performed.

As described above, in this embodiment, when there is a possibility that an address input is abnormal or the position of the optical unit is deviated from the address, the optical unit is immediately returned to the reference position and the initial adjustment is performed at the predetermined position. Since the optical unit is always in the groove area, the initial adjustment can be performed reliably and quickly, and the optical unit can be made ready for reproduction.

[0033]

As described above, according to the present invention, it is possible to provide an optical disk reproducing apparatus capable of returning to a state in which reproduction can be reliably performed in a short time even if the reproduction becomes impossible during reproduction of the optical disk.

[Brief description of the drawings]

FIG. 1 is a processing flowchart of a magneto-optical disk reproducing apparatus according to an embodiment of the present invention.

FIG. 2 is a block diagram illustrating a configuration of a magneto-optical disk reproducing device.

FIG. 3 is a processing flowchart of a conventional magneto-optical disk reproducing device.

[Explanation of symbols]

1 ··· optical unit, 36 ··· tracking servo circuit, 2 ··· magneto-optical disk,
41: Thread motor, 31: RF amplifier, 42: Spindle motor, 32
... Digital signal processing unit, 5 ... Control unit,
33: a thread servo circuit, 6: an audio output unit, 34: a spindle servo circuit. 7 ...
..Detection switch, 35 ... focus servo circuit.

Claims (5)

[Claims] 1. An optical unit for irradiating an optical disk on which data is recorded with a light beam and outputting a detection signal based on light reflected from the optical disk, and operating the optical unit based on the detection signal of the optical unit. In an optical disc reproducing apparatus including a servo unit for performing feedback control and a characteristic adjustment unit for adjusting an operation characteristic of the servo unit to be an optimum one, the optical unit is moved to a reference position corresponding to a predetermined position of the optical disk. A reference position moving means for moving; a characteristic adjustment starting means for operating the characteristic adjusting means when the optical unit becomes incapable of reading data; and an optical element of the address data indicating a recording position of data on the optical disk. Abnormal address data reading when unit readings are not continuous And address data abnormality detecting means for detecting, when the address data read abnormal state of the optical unit is detected by the address data abnormality detecting means,
An optical disc reproducing apparatus, comprising: starting means for starting the characteristic adjusting means by the characteristic adjustment starting means after moving the optical unit to the reference position by the reference position moving means. 2. An optical unit for irradiating an optical disk on which data is recorded with a light beam and outputting a detection signal based on reflected light from the optical disk, and operating the optical unit based on the detection signal of the optical unit. In an optical disc reproducing apparatus including a servo unit for performing feedback control and a characteristic adjustment unit for adjusting an operation characteristic of the servo unit to be an optimum one, the optical unit is moved to a reference position corresponding to a predetermined position of the optical disk. Reference position moving means for moving, high-speed movement detecting means for detecting that the optical unit is moving at a higher speed than during normal recording / reproduction, and when the optical unit is in a data reading disabled state, A characteristic adjustment activation unit that operates the characteristic adjustment unit; and detects an uncontrollable state of focus control of the optical unit. Focus control disable detecting means, and the high-speed movement detecting means detects that the optical unit is moving at a higher speed than during normal recording / reproducing, and the focus control disable detecting means detects the optical unit. When an uncontrollable state of the focus control is detected, after the optical unit is moved to the reference position by the reference position moving means, the characteristic adjustment starting means activates the characteristic adjusting means. An optical disc reproducing apparatus characterized by the following. 3. An optical unit for irradiating a light beam on an optical disk on which data is recorded and outputting a detection signal based on light reflected from the optical disk, and operating the optical unit based on the detection signal of the optical unit. In an optical disc reproducing apparatus including a servo unit for performing feedback control and a characteristic adjustment unit for adjusting an operation characteristic of the servo unit to be an optimum one, the optical unit is moved to a reference position corresponding to a predetermined position of the optical disk. A reference position moving means for moving; a characteristic adjustment starting means for operating the characteristic adjusting means when the optical unit becomes incapable of reading data; and a focus control for detecting an uncontrollable state of the focus control of the optical unit. The optical unit by the inability detecting means and the reference position moving means. When the stop of the optical disc and the reproduction following the stop are instructed while moving to the reference position corresponding to the predetermined position, after moving the optical unit to the reference position by the reference position moving means, the characteristic An optical disc reproducing apparatus comprising: a start-up unit for starting the characteristic adjustment unit by the adjustment start-up unit. 4. An optical unit that irradiates a light beam onto an optical disk on which data is recorded and outputs a detection signal based on reflected light from the optical disk, and controls the operation of the optical unit based on the detection signal of the optical unit. In an optical disc reproducing apparatus including a servo unit for performing feedback control and a characteristic adjustment unit for adjusting an operation characteristic of the servo unit to be an optimum one, the optical unit is moved to a reference position corresponding to a predetermined position of the optical disk. Reference position moving means for moving; high-speed movement detecting means for detecting that the optical unit is moving at a higher speed than during normal recording / reproducing; and power supply for detecting an abnormality in a power supply for driving the optical disc reproducing apparatus Abnormality detecting means, and operating the characteristic adjusting means when the optical unit becomes incapable of reading data. The characteristic adjustment activation unit and the high-speed movement detection unit detect that the optical unit is moving at a higher speed than during normal recording / reproducing, and that the power supply abnormality detection unit has an abnormality in the power supply. An optical disc reproducing apparatus, comprising: a starting means for, when detected, moving the optical unit to a reference position by the reference position moving means and then starting the characteristic adjusting means by the characteristic adjustment starting means. 5. The optical disk reproducing apparatus according to claim 1, wherein the predetermined position of the optical disk is a data recording area on an innermost circumference of the optical disk.