JPH04205819A - Optical disk device - Google Patents

Abstract

PURPOSE:To prevent deterioration of recording/erasure of a data by judging a size of a focus error signal and then inhibiting recording/erasure of the data when defocusing occurs due to focus shift. CONSTITUTION:A focus error signal which is input to a discrimination circuit 8 gradually approaches a discrimination value signal and a focus error signal exceeds a preset discrimination value signal immediately before an objective lens 2 moves to a focusing position of recording/erasure mode of data. Then, the discrimination circuit 8 stops the recording/erasure inhibition signal which is output to a CPU 11 up to this point, permits recording/erasure of data for the CPU 11, discriminates a size of focus error signal, and then controls recording/erasure of data. In this manner, when defocusing occurs due to focus shift, a recording/erasure inhibition signal is output from the discrimination circuit 8, thus preventing data from being recorded and erased actually.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical disc device that performs focus control.

[Prior Art] Generally, when data is optically reproduced and recorded/erased by condensing semiconductor laser (hereinafter referred to as LD) light onto an information recording medium, data recording/erasing is faster. A larger LD output is required than when reproducing data.

However, when the LD output is slightly increased during data recording/erasing, the wavelength of the LD light shifts to the longer wavelength side, which lowers the refractive index of the lens and increases the focal length.

As a result, the focal position shifts in the direction away from the lens, causing a phenomenon called defocusing in which the light spot deviates from the focal position.

The relationship between this defocus, the focus shift caused by wavelength fluctuation, and the operation of the focus control system will be explained using FIG. 4.

In the figure, 1 is a disk medium, and 2 is an objective lens.

(1) shows the state of the data playback mode in which the LD performs focus control in a low output power state. Since there is no focus shift in this data playback mode, focus control by the focus control system is necessary for data playback. This is done in a focused position.

(2) shows the state in which the optical disc device has entered the recording/erasing mode, but before D emits light in a high output power state. In this state, there is no focal shift as in (1), so
Focus control by the focus control system is performed at a focus position for data reproduction.

(3) shows a state in which recording/erasing of data in the recording/erasing mode is started and the LD emits light in a high output power state. In this state, a focus shift occurs due to the wavelength fluctuation of the LD, so the optical spot 3 is defocused. Note that the focus control system controls the objective lens 2 to eliminate defocus, but immediately after the focus shift occurs, the focus control system cannot control the objective lens 2, resulting in a defocus state. (4) shows a state in which data is being recorded/erased after a predetermined time has elapsed, and in this state, the focus is shifted to the in-focus position again under control by the focus control system.

In this way, in the conventional optical disc game device, the focus shift caused by the difference in the output of the LD depending on the data reproduction mode and recording/erasing mode is eliminated by tracking the focus control system.

[Problem to be solved by the invention] However, in the conventional optical disk device, from the state (3) to the state (4) in FIG. 4, data is recorded in a defocused state due to a focus shift. /erasing is performed, and data recording/erasing becomes incomplete, resulting in a problem that the reliability of the data decreases.

One way to solve this problem is to use a special lens such as an aspherical single lens.
Even if such a special lens is used, it is not possible to completely eliminate the focal shift, and since such a special lens is expensive, there is also a problem in terms of cost.

The present invention provides low-cost data recording/recording by focus shift.
It is an object of the present invention to provide an optical disc device that prevents deterioration of erasing characteristics and improves data reliability.

[Means for Solving the Problems] The present invention includes means for detecting a focus error signal, means for generating an electrical offset signal, and subtraction means for subtracting the electrical offset signal and the focus error signal. , means for servo-controlling an objective lens to a focused position based on the output from the subtracting means; means for inputting an offset signal to the subtracting means when a data recording/erasing mode is entered; means for generating a preset discriminant value signal, discriminating means for discriminating whether or not the focus error signal exceeds the discriminant value signal, and recording/recording of data according to the discriminating result of the discriminating means.
It is equipped with means for starting an erasing operation.

[Effects] As a result, if it is determined from the magnitude of the focus error signal that defocus has occurred due to a focus shift, data recording/erasing can be prohibited, and data recording/erasing characteristics may deteriorate. can be prevented.

[Embodiments] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 shows a configuration diagram of an optical disc device according to an embodiment of the present invention.

In the figure, the optical head 4 is L relative to the disk medium L.
Data is recorded/erased by irradiating the spot light from D, and data is reproduced by receiving reflected light from the disk medium l. The optical head 4 has an objective lens 2 for focusing the LD light onto the disk medium 1, and a focus actuator 5 for driving the objective lens 2 in the focusing direction. The focus signal detector 6 receives a part of the reflected light from the disk medium l, detects a focus error signal indicating a deviation from the in-focus position in the focus direction, and outputs it to a subtraction amplifier 7 and a discrimination circuit 8, which will be described later. It is provided inside the optical head 4.

On the other hand, the offset detection circuit 9 generates an electrical offset signal that is set so that the objective lens 2 is precisely in focus when the LD emits light in a high output power state and a focus shift occurs due to wavelength fluctuation. do. The analog switch 10 performs ○N/○FF in response to a recording/erase mode signal from the CPU 1l, which will be described later, and outputs an offset signal to the subtraction amplifier 7. The subtracting amplifier 7 subtracts the focus error signal from the offset signal in the recording/erasing mode, and outputs the subtraction result to the focus control system 12.

The focus control system 12 outputs a focus control signal to the power amplifier 13 based on the subtraction result from the subtraction amplifier 7. The power amplifier 13 generates a focus drive signal based on the focus control signal from the focus control system 12, and servo-controls the focus actuator 5 to a focus position.

Further, the discrimination value setting circuit 14 generates a discrimination value signal that serves as a reference for the magnitude of the focus error signal.

Here, this discrimination value signal is a signal that is slightly larger than the focus error signal detected when the objective lens 2 is moved to the in-focus position for recording/erasing data. The discrimination value signal output from the discrimination value setting circuit 14 is output to the discrimination circuit 8.

The discrimination circuit 8 subtracts the focus error signal from the discrimination value signal when the LD emits light in a high output power state and a focus shift occurs due to wavelength fluctuation, and when the focus error signal is smaller than the discrimination value signal, that is, the objective lens 2 However, if the focus position is not yet set for data recording/erasing, a recording/erasing prohibition signal for inhibiting data recording/erasing is output to CPULL. The CPU II triggers the analog switch 1 by generating a record/erase mode signal.
0N10FF is performed, and if the objective lens 2 is not controlled to the focusing position for recording/erasing data by the recording/erasing prohibition signal from the discrimination circuit 8, the LD
Prohibits high output power light emission.

Next, the focus control operation of the optical disc device configured as described above will be explained with reference to FIG.

In the figure, (1) is a state during data reproduction in which the LD performs focus control in a low output power state, and there is no focus shift. Further, in this state, the recording/erase mode signal is not output from CPtJll and the offset signal is not output to the subtraction amplifier 7, so focus control is performed at the focal position for data reproduction.

(2) is a state in which the optical disc device has entered the recording/erasing mode, but before the LD emits light in a high output power state.

In this state, a record/erase mode signal is output from the CPU II and an offset signal is output to the subtracting amplifier 7, which adds an offset to the focus system. Focus control is being performed.

In addition, to transition from state (1) to state (2),
Data recording/recording of objective lens 2 from the data playback focus position
It must be moved to the focus position for erasure. This movement of the objective lens 2 requires approximately several m5EC of time. The determination circuit 8 outputs a recording/erasing prohibition signal so that data is not recorded/erasing during the period of movement of the objective lens 2, and also outputs a recording/erasing prohibition signal when the movement of the objective lens 2 is completed. Stop outputting.

Here, the operation of this discrimination circuit 8 will be explained using timing charts 1 to 1 shown in FIG.

(a) shows the mode signal, and now the record/erase mode signal is output from the CPU 11 and the analog switch 10
When turned on, an offset signal from the offset detection circuit 9 is input to the focus control system. On the other hand, the focus error signal is
As shown in (b), focus control is performed so that the level is approximately zero. Therefore, in this case, since the focus error signal input to the discrimination circuit 8 as shown in (b) is smaller than the discrimination value signal output from the discrimination value setting circuit 15, the recording/erasure prohibition signal shown in (c) is is the CPU
It is output to II.

However, when the offset signal from the offset detection circuit 9 is input to the focus control system 12 via the subtraction amplifier 7 after a predetermined time has elapsed, the focus control system 12 outputs a focus control signal to the power amplifier 13. A focus drive signal is output from the power amplifier 13 to the focus actuator 5, and the operation of the focus actuator 5 causes the objective lens 2 to gradually move away from the in-focus position for data reproduction.

Here, a focus error signal is generated as the objective lens 2 moves, and this focus error signal is transmitted to the subtraction amplifier 7.
and is input to the discrimination circuit 8. The focus error signal input to the subtracting amplifier 7 gradually reduces the offset signal, and when the objective lens 2 moves to the in-focus position in the data recording/erasing mode, the output of the subtracting amplifier 7 is set to O, and the offset signal of the objective lens 2 is changed to O. stop movement.

Further, the focus error signal input to the discrimination circuit 8 gradually approaches the discrimination value signal, and just before the objective lens 2 moves to the focus position in the data recording/erasing mode, (
As shown in b), the focus error signal exceeds the preset discrimination value signal. At this time, the discrimination circuit 8 (
As shown in c), the recording/erasing prohibition signal that had been output to the CPU II is stopped, and data recording/erasing is permitted for cpt, ;z.

In this manner, the discrimination circuit 8 controls recording/erasing of data by determining the magnitude of the focus error signal.

(3) After entering the state of (2), the CPU II 1 detects that the recording/erasing prohibition signal from the discrimination circuit 8 has been stopped, and the optical head 4 is at the desired position to start recording/erasing data. This is the state in which data recording/erasing has actually started. In this case, since the LD emits light in a high output power state, a focus shift occurs due to wavelength fluctuations of the LD, but since focus control is performed in advance at the focal position for recording/erasing data, the light spot is It never defocuses.

Note that if the output of the recording/erasing prohibition signal is not stopped when the optical head 4 reaches the target position, the CPU
], 1 causes the optical head 4 to wait in the vicinity of the target position until the output of the recording/erasing prohibition signal is stopped in order to prevent recording/erasing of data in this state. This can prevent data from being erroneously recorded/erased when the objective lens 2 is not at the in-focus position for data recording/erasing.

When defocus occurs due to focus shift in this way, a recording/erasing prohibition signal is output from the determination circuit 8 to the CPU 11, so that data can be prevented from being actually recorded/erased.

Additionally, it is possible to always maintain focus during data recording/erasing.

[Effects of the Invention] As explained above, according to the present invention, by determining the magnitude of the focus error signal, if defocus occurs due to focus shift, recording/erasing of data is prohibited. Deterioration of data recording/erasing characteristics can be prevented. Moreover, since expensive parts such as special lenses are not used, cost problems can also be solved.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an embodiment of an optical disc device according to the present invention, FIG. 2 is a diagram showing the relationship between defocus, focus shift, and operation of the focus control system in the optical disc device according to the present invention, and FIG. 3 is a diagram showing the relationship between the operation of the focus control system and the discrimination FIG. 4 is a timing chart showing the operation of the circuit, and is a diagram showing the relationship between defocus, focus shift, and operation of the focus control system in a conventional optical disc device. ■...Disk medium, 2...Objective lens, 4...Optical head, 5...Focus actuator, 6...
・Focus signal detector, 7... Subtraction amplifier, 8...
- Discrimination circuit, 9... Offset detection circuit, 10...
Analog switch, 11...CPU, 12...Focus control system, 13...Power amplifier, 14...Discrimination value setting circuit.

Claims (1)

[Claims] means for detecting a focus error signal, means for generating an electrical offset signal, subtraction means for subtracting the electrical offset signal and the focus error signal, and focusing the objective lens using the output from the subtraction means. In an optical disk device, the optical disc device includes means for servo-controlling a position, means for inputting the offset signal to the subtracting means when entering a data recording/erasing mode, and means for generating a preset discrimination value signal. , a determining means for determining whether or not the focus error signal exceeds the discriminant value signal;
An optical disc device characterized by comprising means for starting a data recording/erasing operation according to the determination result of the determining means.