JP2625671B2 - Focus position control device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a focus position control device (focusing servo) used in an optical disk device for recording or reproducing an optical disk (hereinafter abbreviated as a disk).

2. Description of the Related Art In a conventional focusing servo used for an optical disk player, when the focusing servo is turned on at the start of the operation of the player, as shown in FIG. Due to the fact that the focal position 25a does not always coincide with the average position of the signal surface of the rotating disk 1, and the detection resolution and the detection dynamic range of the focus position of the photodetector described later, the disk surface detection signal shown in FIG. Since the range 28 in which 27 can be obtained is very narrow, the disk surface detection signal 27 may not be obtained depending on the average height and the amount of surface runout of the disk.

Therefore, first, the focusing lens is strongly moved up and down to obtain a detection signal 27, and 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.

The signal surface of the disk 1 is irradiated with the laser beam 2 emitted from the pickup 9 to record a signal on the disk or read the recorded signal.

In the pickup 9, light emitted from a semiconductor laser (not shown) passes through the optical block 7, is focused on the beam 2 by the condenser lens 4, and is irradiated on the disk 1. The light reflected by the disk 1 passes through the condenser lens 4 and the optical block 7 again, and then travels to the photodetector 8. Focusing control and tracking control are required to record and reproduce signals on the optical disk. Here, focusing control relating to the present invention will be described.

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

Further, the detection signal of the disk surface obtained by the photodetector 8 is input to the focusing 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, and a current is caused to flow through the focusing coil 6. Excite.

The detection output from the zero-cross detection circuit 10 is latched.
It is held at 29 and the control circuit from the shaker 19 by the switch circuit 18.
Switch to 16 to activate focusing control.

However, in the above configuration, the focal position 25a of the laser 2a emitted from the condenser lens 4a does not always match the average position of the disk surface as described above. The error signal includes a DC component of an AC component.
Further, if the warp of the disk itself is added, the DC component is further increased.

Now, assuming that the error obtained by adding the initial focus position difference and the disk warpage is 1000 μm, and that the gain of the DC component is 70 dB, the residual error after applying the focusing servo is
1000/3000 (≒ 70 dB) = 0.33 μm.

Although the focus depth of the pickup is about ± 1 μm, it is needless to say that the C / N of the reproduced signal is best when the focal point coincides with the signal surface of the disk.

However, a defocus of 0.33 μm has already occurred due to the relationship between the condenser lens and the disk. There has been a problem that the error is further widened due to temperature changes and assembly variations.

The present invention has been made in view of the above problems, and provides a focus position control apparatus that minimizes a residual error of a DC component.

FIG. 6 shows this state. The configuration is such that the gain of the DC component is increased with respect to the frequency characteristic 30 of the element for driving the condenser lens, and the open-loop characteristic as shown at 31 is obtained.

Means for Solving the Problems In order to solve the above problems, the focus position control device of the present invention provides a DC voltage corresponding to the difference between the warpage of the disk, the initial focus position and the average position of the signal surface of the disk. Then, a bias is applied to the condenser lens in advance.

Operation The present invention makes it possible to minimize the apparent DC deviation by the above-described configuration. According to the configuration of the present invention, it is assumed that the DC component is 950.
If it is detected as μm, a bias is applied to the condenser lens, so that an apparent residual error of the DC component becomes 50 μm. If you turn on the focusing servo in this state, the residual error will be
50/3000 (≒ 70dB) = 0.017 [μm], with a depth of focus of 1
For the conventional DC component residual error of 0.33 μm in μm,
The error of about 0.31 μm is reduced, and the effect is very large.

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

FIG. 1A shows a circuit configuration of a focus position control in an embodiment of the present invention, and FIG. 1B shows a waveform obtained therein.

In FIG. 1, 1 is a disk, 3 to 8 are components included in the pickup 9, 2 is a laser beam emitted from the pickup 9, and 10 to 21 are circuits according to the present invention.
FIG. 6B shows waveforms corresponding to points A to D in FIG.

Initial setting circuit 20 before turning on the focusing servo
Then, the switch circuit 18 is set to the vibration circuit 19 side, and the drive circuit 21 forcibly vibrates the condenser lens 4 in the pickup 9 in a substantially sine wave shape or a triangular wave shape in the vertical direction of the disk 1. As a result of exciting the condenser lens 4, the first
The waveform shown in FIG. 2B is obtained and sent to the focusing control circuit 16 and simultaneously to the bias setting blocks 10 to 15.

In the bias setting block, the zero-cross point is obtained by the zero-cross detection circuit 10 from the disk surface detection signal obtained by the photodetector 8, and the position of the condenser lens is detected by the position detection circuit 11. Here, the position detection circuit 11 falls by the output of the zero-cross detection circuit 10 by the first zero-cross detection signal detected by the disk surface detection signal that appears after the converging lens is vibrated, and then by the second zero-cross detection signal that appears subsequently , A signal which falls again by the third zero-crossing detection signal which appears subsequently, is output, and a waveform as shown by C in FIG. 1 (b) is obtained. The period during which the C waveform has a low potential means a period when the condenser lens is too close to the disk surface from the optimum position, and the period when the C waveform has a high potential means a period when the condenser lens is farther from the disk surface than the optimum position. I have. When the period of low potential and the period of high potential are almost equal, the condenser lens is almost at the optimal position, and the longer the period of high potential, the farther from the disk surface the optimal position. However, the time difference between the high potential period and the low potential period is a signal that is substantially proportional to the amount of distance. Thereafter integrator circuit 2 using the output of the position detecting circuit, the positional deviation amount V ₁ obtained in one rotation of the disc determined, after A / D conversion by the A / D converter 13, the value in the memory circuit 14 The data is stored in a memory, D / A converted by a D / A converter at 15, and added to a summing circuit 17 in a control circuit as a bias value of a condenser lens.

As described above, in the first embodiment shown in FIG. 1, the vibrating device falls by the first zero-cross detection signal detected from the disk surface detection signal which appears after the converging lens is vibrated by the vibrating device, and the second zero-crossing signal which subsequently appears The time difference between the zero crosses is determined by the time difference between the low potential time and the high potential time of the output of the position detecting device which outputs a signal which rises by the zero cross detection signal of No. 2 and falls again by the third zero cross detection signal which appears subsequently. Although the bias voltage is exchanged by the waveform shaping and integration circuit, the second embodiment shown in FIG. 2 shows a simple method of using a counter in the bias setting block, and the waveform C of FIG. A constant clock 24 is input to the up / down counter 22, and when the signal C in FIG. 1 is "L", the count is down, and when the signal C is "H", the count is up. And und, by latching the counter output after the rotary disk 1 at the latch circuit 23, in which determining the bias value and the output to D / A conversion by the D / A converter 15.

As another method, processing by a microcomputer and setting a bias value can of course be considered.

As described above, according to the present invention, before the operation of the focusing control is started, the interval of the disk surface detection signal generated in the temple where the condenser lens is vibrated in the direction perpendicular to the disk surface is obtained and fixed from the interval. By applying a bias voltage to the condenser lens in the pickup, it is possible to greatly reduce the DC residual error, and in practice, there is no DC problem, that is, there is no problem that the focal position is always shifted. Stability is improved even when using a disk with a large sled.

[Brief description of the drawings]

FIG. 1A is a configuration diagram of a focus position control device according to a first embodiment of the present invention, FIG. 1B is a waveform diagram of each point in FIG. 1, FIG.
FIG. 3 is a block diagram showing a bias setting block according to a second embodiment of the present invention, FIG. 3 is a diagram showing the relationship between a disk and a condenser lens, FIG. 4 is a waveform diagram showing a disk surface detection signal, and FIG. FIG. 1 is a configuration diagram of a conventional focus position control device, and FIG. 6 is a diagram illustrating frequency characteristics of the control device. DESCRIPTION OF SYMBOLS 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 Vibration circuit.

Claims (1)

(57) [Claims] 1. A rotating optical disc, a pickup for reading a signal recorded on the optical disc or recording a signal on the optical disc, and a condenser lens included in the pickup at a substantially constant period. A vibration device that vibrates up and down, a focus error detection device that detects a focus error between the laser beam focused by the focusing lens and the signal surface of the optical disc, and the focusing lens before the operation of a focusing servo. A zero-cross detection device that detects a zero-cross point of a disk surface detection signal obtained from an output of the focus error detection device when the vibration device vibrates, and outputs a zero-cross detection signal; and receives an output of the zero-cross detection device. Then, the condensing lens falls by the first zero-cross detection signal which appears first after the converging lens is vibrated by the vibrating device. A position detecting device that outputs a signal that rises by a second zero-crossing detection signal that appears and then falls again by a third zero-crossing detection signal that appears subsequently; a time when the output of the position detecting device is a low potential; and a high potential. An initial position setting device for setting a bias voltage corresponding to an initial setting position to be given to the condenser lens based on a time difference between the times, and an adding device for adding the bias voltage to an output of a focusing control circuit during a focusing servo operation. A focus position control device, characterized in that: