JPH0736229B2 - Focus control device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a focus control device for an optical recording / reproducing apparatus that records or reproduces a signal on the surface of a recording medium using a converged light beam.

2. Description of the Related Art A conventional focus control device for an optical recording / reproducing apparatus is disclosed in Japanese Patent Laid-Open No. 121537/1985.

In order to perform high-density recording as an optical recording / reproducing device and obtain a high-quality reproduction signal, a light beam output from a light source such as a semiconductor laser is minutely recorded on a recording medium (hereinafter referred to as an optical disk) to be about 1 μmφ. Converge and accurately measure, for example ± 0.5
It is necessary to perform focus control that follows with an error of about μm.

A focus pull-in operation is performed to change the focus control from the inoperative state to the operating state on the recording medium surface of the optical disc.

The focus pulling-in operation is performed by moving the focus point of the light beam by the focus moving means and closing the control loop when it comes near the recording medium surface.

FIG. 2 shows the positional relationship between the output of the focus shift detecting means and the focal point of the light beam on the optical disk for explaining the focus pull-in operation.

The horizontal axis shows the position of the focal point of the light beam, and the vertical axis shows the output of the focus shift detecting means.

When the focus of the light beam is brought closer to the optical disc, a focus shift detection signal appears on the protective layer surface of the optical disc surface, and when it is further brought closer, a focus shift detection signal appears on the recording medium surface.

Conventionally, the comparison level V1 is set for the focus pull-in operation, and the focus point of the light beam is moved in the direction of approaching from the position a away from the optical disc, and when the focus deviation detection signal reaches the comparison level V1, the focus control loop. In order to avoid the focus control on the surface of the protective layer and to set the focus control operation state on the surface of the recording medium.

Further, in order to deal with the case where the amount of reflected light on the surface of the recording medium is smaller than the amount of reflected light on the surface of the protective layer and the focus shift detection signal on the surface of the recording medium is smaller than the surface of the protective layer, the light beam converging point is once brought close to b to the optical disc. After that, the focus control loop is closed when the focus shift detection signal reaches the comparison level V2 after the distance, and the focus point of the light beam is drawn so as to follow the recording medium surface.

Problems to be Solved by the Invention However, in the above-described configuration, the following problems occur when optical disks 7 having different reflectances are used or when the optical disk 7 is recorded and the reflectance changes.

For example, if the reflectance becomes low and the comparison level V2 exceeds the peak value c of the focus shift detection signal as shown in FIG. 3A, the focus control loop cannot be closed on the recording medium surface. In addition, the reflectance is high and the comparison level
If the parasitic peak value d near the surface of the recording medium, which is generated by vignetting of the optical system before V2 reaches the position of the recording medium surface, is exceeded, the focus control loop is closed at this position and the focus point of the light beam is converged. Cannot be controlled to follow the recording medium surface of the optical disc.

In view of the above problems, the present invention provides a focus control device in which stable focus control is pulled in at a recording medium surface position even if optical discs having different reflectivities are used or if the reflectivity changes due to recording. To do.

Means for Solving the Problems In order to solve the above problems, a focus control device of the present invention is a peak value detecting means for detecting a peak value of a focus shift detecting means, and a calculation for calculating a focus control start level from the peak value. Means for driving the focus moving means, the peak value detecting means stores the peak value of the detection signal of the focus deviation detecting means, and the calculating means for the focus control start level or the amplification factor of the focus deviation detecting means. Is calculated and set, the focus moving means is driven again, the focus control start level is compared with the detection signal of the focus shift detection means, and the operation of the focus control means is started.

Operation The present invention has the above-described configuration, and detects the peak value of the detection signal of the focus shift detection means even if the optical disk 7 having a different reflectance is used or the reflectance is changed due to recording. And a calculation means for calculating the focus control start level or the amplification factor of the focus shift detection means from the peak value, when the focus moving means is driven once and the operation of the focus control means is started by the calculation means. Since the comparison value to be compared with the detection signal of the focus shift detecting means is calculated every time the focus control is started, the focus pull-in operation can be stably performed.

Example A focus control device according to an example of the present invention will be described below.
A description will be given with reference to the drawings.

FIG. 1 shows a block diagram of a focus control device in an embodiment of the present invention.

The light beam 2 emitted from the semiconductor laser 1 is converted into parallel light by the collimator lens 3 and the polarization beam splitter 4 and 1/4.
The light is focused on a recording medium 7 (hereinafter referred to as an optical disk) via the wave plate 5 and the diaphragm lens 6.

For recording and reproducing signals, the optical disk 7 is driven by a motor 12 to rotate, and the focal point of the light beam is track-controlled to the information track 8.

Next, the light reflected from the surface of the recording medium passes through the aperture lens 6 again to become parallel light, which passes through the quarter-wave plate 5 and the polarization beam splitter 4 and is partially shielded by the shielding plate 9 and partially condensed. A focus shift detector 11 is passed through the lens 10 to form a knife edge type detector.

The focus shift detector 11 is made up of two-divided PIN diodes, and is set so that the same amount of light is incident on each PIN diode when the recording medium surface of the optical disk 7 and the light beam converging point are aligned in the vertical direction. Has been done.

When the light beam condensing point and the recording medium surface of the optical disk 7 are displaced, the amount of light incident on the PIN diode is unbalanced, and the unbalanced amount of light is converted into a current, and an amplifier circuit 14 is provided for each. It is converted to a voltage at 15 and 15. The differential amplifier circuit 16 differentially amplifies and outputs a focus shift signal 17.

The focus shift signal 17 is converted into digital data by an analog-digital conversion circuit 18 (hereinafter referred to as an AD conversion circuit), is subjected to phase compensation calculation processing of a focus control loop by a digital signal processing circuit 19, and is passed through a drive circuit 20 to a focus coil. Apply current to 13.

This current drives the position of the diaphragm lens 6 in the direction perpendicular to the optical disc to control the focal point of the light beam to follow the recording medium surface of the optical disc.

In order to perform this focus control, first the light beam 2
The focus point is moved to the vicinity of the recording medium surface of the optical disk, and the focus pull-in operation that closes the control loop is performed.

Focus start signal 21 is digital signal processing circuit 19
When it enters, the control section 24 formed inside the digital signal processing circuit 19 operates the drive signal generating section 25 to supply a current to the focus coil 13 via the drive circuit 20 to bring the diaphragm lens 6 close to the optical disk 7 once.

At this time, the focus shift signal 17 is stored in the memory unit 26,
Based on the stored data, the control section 24 performs arithmetic processing to obtain the peak value Va shown in FIG. 4 (a). Then the peak value
Divide Va by a predetermined value to obtain a comparison level Vb.

Here, the focus shift signal 17 is thinned out and stored in the memory unit 26, or the focus shift signal is sequentially compared by the control unit to store the maximum or minimum value so that the peak value Va is left in the memory unit 26. Even if the peak value Va is divided by a predetermined value, the comparison level Vb can be obtained.

Next, an electric current is passed from the drive signal generator 25 to the focus coil 13 so as to move the diaphragm lens 6 away from the optical disk.

At this time, the comparison unit 27 in the digital signal processing circuit 19 compares the digital signal of the focus shift signal with the comparison level Vb obtained by calculation.

The focus shift signal 17 is in the opposite direction to the case where the light beam converging point approaches the optical disk shown in FIG. 4 (a), and when the positive peak value is Va, the negative peak value is exceeded and the recording medium surface is reached. Pass through.

The focus shift signal 17 reaches the comparison level Vb when the focus point is further moved away.

Digital data of defocus signal 17 is comparison level
When the control unit 24 detects that Vb has been reached, the switch unit 23 is operated to close the focus control loop.

In this way, the focal point of the light beam is controlled to follow the recording medium surface of the optical disk 7.

As another embodiment, in the process of obtaining the comparison level Vb from the positive peak value Va described above, FIG. 4 (b) is used instead of Va and Vb.
The comparison level Vd is obtained from the negative peak value Vc shown in
Switch when the control unit 24 detects that the digital data of the defocus signal 17 has reached the comparison level Vb after the control unit 24 detects that the light passes through the vicinity of the negative peak value Vc when the focus point is moved away. The focusing point of the light beam can also be stably controlled to follow the recording medium surface of the optical disk 7 by operating the unit 23 and closing the focus control loop.

As another embodiment, in the process of fixing the comparison level at the time of pulling in the focus control to Ve as shown in FIG. 5 and obtaining the comparison level Vb from the positive peak value Va, further Ve / Vb Calculate and differential amplifier circuit 16 or AD
Ve in the conversion circuit 18 or the digital signal processing circuit 19
Ve / V in the processing part of the focus shift signal until it is compared with
The control section indicates that the digital data of the defocus signal amplified by b amplification has reached the comparison level Ve.
Even when the switch unit 23 is operated and the focus control loop is closed when 24 detects, the focusing point of the light beam can be stably controlled to follow the recording medium surface of the optical disk 7.

EFFECTS OF THE INVENTION As described above, according to the present invention, even if the optical disk having different reflectance is used or the reflectance is changed due to recording, the focus control unit starts focusing operation. Since the amplification factor of the detection signal of the deviation detecting means is calculated and changed before the focus control is started and compared with the focus start level, the loop gain can be made constant and the stable pull-in operation of the focus control can be performed.

[Brief description of drawings]

FIG. 1 is a block diagram of a focus control device according to an embodiment of the present invention, FIGS. 2 and 3 are waveform diagrams of a focus shift signal for explaining a focus control pull-in operation in a conventional example, FIG. 4 and FIG. FIG. 5 is a waveform diagram of the focus shift signal for explaining the pull-in operation of the focus control device of the present invention. 1 ... Semiconductor laser, 6 ... Aperture lens, 7 ... Optical disk, 11 ... Focus deviation detector, 13 ... Focus coil, 17 ... Focus deviation signal, 18 ... AD conversion circuit, 19 ... Digital signal Processing circuit, 20 …… Drive circuit.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Katsuya Watanabe 1006, Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (56) References JP 61-158036 (JP, A)

Claims (1)

[Claims] 1. Converging means for converging a light beam emitted from a light source and irradiating the recording medium surface, focus deviation detecting means for detecting a converging state from light reflected from the recording medium surface, A focus moving means for moving the converging means in a direction substantially perpendicular to the recording medium surface, and a drive means for driving the focus moving means in accordance with the output of the focus shift detecting means to converge the light beam on the recording medium surface in a substantially constant manner. Focus control means for controlling so as to be in a state,
Peak value detecting means for detecting a peak value from the detection signal of the focus shift detecting means, calculating means for calculating an amplification factor of the focus shift detecting means from the peak value, detection signal of the focus shift detecting means and focus start A comparison means for operating the focus control means by comparing with a level, the focus moving means moves the converging means, and the peak value detecting means detects the peak value of the detection signal of the focus shift detecting means. A focus control device characterized in that, after changing the amplification factor of the focus shift detection means by the calculation means, the focus control means is operated by the comparison means.