JPS61113138A - Focus position control device - Google Patents

Abstract

PURPOSE:To minimize a residual error of a direct current component by obtaining an interval of a disk surface detecting signal generated when a condenser lens is excited in the vertical direction on the disk surface before the focusing control starts to operate, and giving the bias voltage fixed from the interval to the condenser lens in the pick-up. CONSTITUTION:Before the focusing servo is turned on, a switching circuit 18 is set to an exciting circuit 19 side at an initial setting circuit 20, and a condenser lens 4 in a pick-up 9 at a driving circuit 21 is forcibly excited almost at the sine wave shape or in the triangular wave shape in the vertical direction of a disk 1. A zero cross point is obtained at a zero cross detecting circuit 10 from a disk surface detecting signal B obtained by a light detecting device 8 at the bias setting block, the position detection of the condenser lens is executed by a position detecting circuit 11 and a position dislocating quantity V1 obtained by one rotation of the disk is obtained at an integrating circuit 12. After A/D conversion is executed at an A/D converting device 13,the value is stored in a memory circuit 14, D/A conversion is executed at a D/A converting device 15 and an adder circuit 17 in the control circuit is added as a bias value of the condenser lens.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a focus position control device (focusing servo) used in optical disc players and the like.

2. Description of the Related Art In a focusing servo used in a conventional optical disc player, when the focusing servo is turned on at the start of the player's operation, as shown in FIG. ! Since the focal position 26& of L does not necessarily match the average position of the signal surface of the rotating disk 1, and the range 28 in which the disk surface detection voltage shown in FIG. Depending on the average height and amount of surface runout, the disk surface detection signal 27 may not be obtained.

Therefore, the detection signal 27 is generated by forcefully moving the condensing lens up and down.
After detecting the zero cross point 26 of the signal, the focusing servo is turned on.

FIG. 5 shows a block diagram of this conventional focusing control circuit.

A laser beam 2 emitted from a pickup 9 is irradiated onto the signal surface of the disc 1 to record a signal on the disc or read the recorded signal.

In the pickup 9, light emitted from a semiconductor laser (not shown) passes through an optical block 7, is condensed into a beam 2 by a condenser lens 4, and is irradiated onto the disk 1. The light reflected by the disk 1 passes through the condenser lens 4° and the optical block 7 again, and then heads toward the photodetector 8. Focusing control and tracking control are required to record and reproduce signals on an optical disc, and here, focusing control related to this case will be explained.

After being reflected by the disk, the light passes through the optical block 7 and is detected by a focusing control photodetector 8 using conventionally known means to detect the position of the disk surface. The detection signal has a waveform as shown in FIG. A zero-crossing point 26 is detected by the zero-crossing detection circuit 10 from this detection signal. The zero cross point is the condenser lens 4
This indicates that the distance between and the disk surface is the optimal position. By detecting this zero-crossing point, the operation of the sh7 orcasing control circuit is started.

Further, a detection signal of the disk surface obtained by the photodetector 8 is inputted to the focuser control circuit 16 .

Before detecting the zero cross signal, the signal from the vibrator 19 is applied to the drive circuit 20 via the switch circuit, NR is applied to the focusing coil 6, and the condenser lens 4 is moved in the direction perpendicular to the disk 1. Excite.

The detection output from the zero-cross detection circuit 10 is held in the latch circuit 29, and the switch circuit 18 switches from the vibrator 19 to the control circuit 16 to operate focusing control.

Problems to be Solved by the Invention However, in the above configuration, the focal position 25& of the laser 2a emitted from the condensing lens 4a does not necessarily match the average position of the disk surface.
The surface runout error signal includes an AC component and a DC component. Furthermore, if the disc's own glue is added, the DC component will increase further.

Now, suppose that there is an error of 1000 μm, including the difference in the initial focus position and the warpage of the disk, and the gain of the DC component is To(i
B If there is, the residual error after applying the focusing servo is 1000/3000 (70dB) = 0.
It will be 33pm.

The depth of focus of the pickup is approximately ±1 μm, but it goes without saying that the C/N of the reproduced signal is best when the focus coincides with the signal surface of the disk.

However, due to the relationship between the condenser lens and the disk, a focal shift of 0.33 μm has already occurred.

There was a problem in that the error would further increase due to temperature changes and assembly variations.

The present invention overcomes the above problems and provides a focal position control device that minimizes the residual error of the DC component.

Figure 6 shows this situation, and is configured to increase the gain of the value flow component with respect to the frequency characteristic 30 of the element that drives the condenser lens, creating an open loop characteristic as shown in 31. .

Means for Solving the Problems In order to solve the above problems, the focal position control device of the present invention applies a DC voltage corresponding to the warpage of the disc and the difference between the initial focal position and the average position of the signal surface of the disc. The structure is such that a bias is applied to the condensing lens in advance.

Operation The present invention makes it possible to minimize the apparent DC deviation by the above-described configuration. For example, in the above example, the deviation of 1000 μm and the gain of the DC component can be
In the case of dB, if a DC component of 950 μm is detected on the metal plate using the configuration of the present invention, the apparent residual error of the DC component will be 50 μm since a bias is applied to the condenser lens.

If you turn on the focusing servo in this state, the residual error will be 50/3000 ('; 70 dB) = 0
．． 017 [μm], which is approximately 0.31 μm compared to the conventional residual error of DC component of 0.33 μm within a depth of focus of 1 μm.
The error in m is reduced, and the effect is very large.

Embodiment Hereinafter, a focus position control device according to an embodiment of the present invention will be described with reference to the drawings.

FIG. 1A shows a four-way configuration for focal position control in an embodiment of the present invention, and FIG. 1A shows waveforms obtained therein.

In FIG. 1, 1 is a disk, 3 to 8 are components included in the pink-up 9, 2 is a laser beam emitted from the pink-up 9, and 10 to 21 are circuits according to the present invention. The figure shows waveforms corresponding to points B to D in the same figure.

Initial setting port 2o before turning on the focusing servo
, set the switch circuit 18 to the excitation circuit 19 side, and connect the drive circuit 2 to the excitation circuit 19 side.
1, the condenser lens 4 in the pickup 9 is forcibly vibrated in a direction perpendicular to the disk 1 in a substantially sinusoidal or triangular waveform. As a result of excitation of the condensing lens 4, a waveform shown in FIG.
send to

In the bias setting block, a zero-cross detection circuit 10 determines the zero-cross point from the disk surface detection signal obtained by the photodetector 8, a position detection circuit 11 detects the position of the condenser lens, and an integration circuit 12 detects one revolution of the disk. The amount of positional deviation v1 obtained by
6, it is D/A converted and added to the addition circuit 1 in the control circuit as a bias value for the condensing lens.

The second embodiment shown in FIG. 2 shows a method that can be easily realized by using a counter in the bias setting block.A waveform corresponding to waveform C in FIG. Input the clock 24 of 1. When the first symbol C is L, it counts down, and when it is H, it counts up. By latching the counter output after one rotation of the disk in the launch circuit 23, the output is transferred to the D/M converter 16. The bias value is determined by converting D/person.

As another method, it is of course conceivable to process it with a microcomputer and set the bias value.

Effects of the Invention As described above, according to the present invention, the interval between the disc surface detection signals generated when the condenser lens is vibrated in a direction perpendicular to the disc surface is determined before the start of the focusing control operation, and the fixed bias is determined from the interval. By applying a voltage to the condensing lens in the pickup, it is possible to significantly reduce the DC residual error, and in practice, the problem of DC, that is, the focus position always being shifted, is eliminated, and the Stability is also improved when using large disks.

[Brief explanation of the drawing]

FIG. 1 & is a block diagram of the focal position control device in the first embodiment of the present invention, FIG. 1 is a waveform diagram of each point in FIG. 1, and FIG.
The figure is a block diagram showing a second embodiment of the bias setting block in Fig. 1, Fig. 3 is a diagram showing the relationship between the disk and the condenser lens, Fig. 4 is a waveform diagram showing the disk surface detection signal, and Fig. 4 is a waveform diagram showing the disk surface detection signal. The figure is a block diagram of a conventional focal position control device, and FIG. 6 is a diagram showing the frequency characteristics of the control device. 1...-Disc, 2...Laser beam, 4...Condensing lens, 8...Photodetector, 9...Pickup, 10... Zero cross detection circuit, 11... Position detection circuit, 12
... Integration circuit, 13 ... A/D converter, 14 ... Memory circuit, 15 ... D/
A converter, 16... Control circuit, 17...
・Addition circuit, 18...Switch circuit, 19...
...Excitation circuit. Name of agent: Patent attorney Toshio Nakao and 1 other person
1 Figure (α) Figure 1 tb+ Figure 2 Figure 3! Figure 5

Claims (1)

[Claims] a pickup for reading signals recorded on an optical disk or for recording signals on an optical disk; an excitation device for vertically vibrating a condensing lens included in the pickup; and a detection signal of the disk surface obtained when the condenser lens is vibrated by the vibrating means before the focusing servo starts operating, and the average position of the condenser lens is determined from A device that detects the magnitude of the distance to the disk surface relative to the optimal distance, a device that sets the bias voltage to be applied to the condensing lens based on the time when the distance is large and small, and the bias voltage is sent to the focusing control circuit. A focal position control device characterized by comprising an adding device.