JPS59157877A - Servo system for information recording and/or reproducing device - Google Patents

Abstract

PURPOSE:To fix the loop gain of a servo system and to stabilize a servo operation by sampling an error signal with a signal synchronized with the information signal. CONSTITUTION:Input signals (a) and (b) are supplied to an input terminal 22 of a waveform shaping circuit 20 as well as to the negative and positive input terminals of operational amplifiers IC1 and IC2, respectively. Then these signals (a) and (b) are compared with reference voltages Vth(W) and Vth(R). If the input voltage is higher than Vth(W), the outputs of IC1 and IC2 are set at +15V and -15V respectively. The error signal supplied to the terminal 22 is delivered as it is from an output terminal 26 in the form of a sample holding error signal. In such a way, an error signal is sampled with a signal synchronized with an information signal. As a result, the loop gain of a servo system is fixed and the servo operation is more stabilized. In addition, the more accurate and more stable record and reproduction are possible to a recording medium.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a servo system for an information recording and/or reproducing apparatus, and is intended to make the servo operation more stable by sampling an error signal using an information signal.

FIG. 1 is an example of a tracking servo system for a conventional disc-shaped recording medium recording and reproducing apparatus. In the figure, 1 is a light source made of, for example, a semiconductor laser, 2 is a collimator lens for converting the light from the semiconductor laser 1 into a parallel beam, and 3 is because the expansion angles of the semiconductor laser in the vertical and horizontal directions with respect to the junction surface are different. A prism corrects this; 4 is an objective lens that condenses parallel light; 5 is a disk-shaped recording medium (hereinafter referred to as a disk); 6 is a guide track made in advance on the disk 5; 7 is for rotating the disk 5. Disk motor, 8 is a guide track 6 in the rotating disk 5
An objective lens that drives the objective lens 4 in a direction perpendicular to the groove of the guide track 6, for example, is constructed of something like a voice coil of a speaker so that a minute spot focused by the objective lens 4 is maintained at the center of the A driving device 9 is a quarter-wave plate for shifting the phase of the light from the semiconductor laser l by a quarter wavelength in total on the way back and forth from the disk 5; 90° optical path of shifted light
Bending beam printer, work 1 is beam splitter 1
12 is an arithmetic circuit that produces a difference between the respective outputs of the 2-split photodetector 11, and 13 is an amplifier circuit that amplifies this difference. ,1
4 is a compensation circuit that compensates for phase delays, etc.; 15 is a drive circuit that moves the objective lens driving device 8; 16 is an arithmetic circuit that produces the sum of the respective outputs of the two-split photodetector 11; and 17 is a amplification of this sum. 18 is a division circuit that divides the output of the amplifier circuit 3 by the output of the amplifier circuit 17; 19 is a drive circuit for modulating the semiconductor laser 1;

Next, the operation of the above method will be explained. The light emitted from the semiconductor laser 1 is collimated by a collimator lens 2, shaped by a triangular prism 3, passes through a beam sinter 10, and is shifted in phase by a quarter wavelength by a quarter wavelength plate 9. is,
The light is focused by an objective lens 4 onto a guide track 6 in a disk 5 .

In the case of recording, the information signal to be recorded causes the semiconductor laser to
A drive circuit 19 that directly modulates the laser beam 1 operates so that the energy density of this focused spot repeatedly rises above a level capable of changing the reflectance of the recording medium in the groove of the guide track 6 and falls below it.

For reading, it is maintained below the above level.

For example, when there is an information signal to be recorded or recorded as shown in FIG. evaporates, significantly reducing the reflectance of the area. Thereby, information signals of 0 and 1 can be recorded in the guide trunk 6. Conversely, the reflected light is collected by the objective lens 4, and further divided into quarters by the quarter-wave plate 9.
After the wavelength phase is shifted, it enters the beam stabilizer 10, bends 90'', and enters the two-split photodetector 11.The guide track 6 has a convex or concave structure by 1/98 wavelength compared to the surroundings, so that the reflected light is not reflected. undergoes diffraction. Therefore, the positional deviation between the focused spot and the guide trunk 6 causes anisotropy in the reflected light. Therefore, if the difference between the two-split photodetector 11 is taken, it can be used for tracking control. An error signal can be obtained.If you take the sum of this two-split photodetector 11, then if recording is done in a direction that reduces the reflectance, then in the case of recording ) for the information signal shown in Figure 2 (b) (the output of the amplifier circuit 17 during recording), and in the case of reproduction, the information signal shown in Figure 2 pin is recorded on the disk 5. On the other hand, the information signal (
output of the amplifier 17 during reproduction) can be obtained respectively.

The above error signal is amplified by the amplifier circuit 13, and divided by the information signal also amplified by the amplifier circuit 17.
divided by The output of this division circuit 18 is further compensated for its phase etc. by a compensation circuit 14, and then enters the drive circuit 15 of the objective lens drive device 8, so that the spot focused by the objective lens 4 is placed in the center of the guide track 6. Move the objective lens 4 in the coming direction. The spot is therefore always located in the center of the guide trunk 6.

However, in the above conventional method, the tracking servo lube changes due to a 5 to 10 times change in the amount of reflected light between recording and playback, and a change of about twice the amount of reflected light due to a change in the reflectance of the recording medium during playback. In order to compensate for the change in key, it was necessary to have a divider circuit 18 with a wide range and high reliability. That is, changes in the tracking servo loop key must be avoided because they may deteriorate tracking accuracy or, in severe cases, may make tracking impossible. Since the detection signal of No. 4g and the information signal are not in a perfect proportional relationship, there have been drawbacks such as the fact that the correction may not be sufficient just by performing division. This also applies to focus servo and time axis servo which have exactly the same configuration.

The present invention has been made in order to eliminate the above-mentioned drawbacks of the conventional art, and by sampling the error signal with a signal synchronized with the information signal using the information signal, it is possible to eliminate the conventional division problem. It is an object of the present invention to provide a servo system for an information recording and/or reproducing device that can keep the servo loop gain constant without using an arithmetic circuit 18.

Embodiments of the present invention will be described below with reference to the drawings.

In FIG. 3, 20 is a waveform shaping circuit that receives the output of the amplifier circuit 17 as an input, and 21 is a sample hold circuit that receives the output of the amplifier circuit 13 as an input and receives the output of the waveform shaping circuit 20 as a gate input.

In the above configuration, the light emitted from the semiconductor laser 1 is condensed by the objective lens 4 and the disk 5 as in the conventional case.
The reflected light from 2 is also collected by the objective lens 4.
The light is guided to a split photodetector 11. This two-division - photodetector 1
The difference between the respective outputs of 1 is created by the arithmetic circuit 12 and becomes a tracking error signal. The signal is amplified by the amplifier circuit 13 and input to the sample hold circuit 21. In the case of playback, the sample hold circuit is used only when tracking an area where the reflected light does not change, for example, an area where no holes are made, and in the case of recording, it tracks an area where the reflected light does not change, for example, an area where no holes are made. The tracking error signal of the output of the amplifier circuit 13 is passed only when tracking the
In other cases, the immediately preceding tracking error signal is held.

A waveform shaping circuit outputs a sample pulse for screening and passing this error signal. That is,
The waveform shaping circuit 20 uses the arithmetic circuit 16 to sum the respective outputs of the two-split photodetector 11 to convert the output from (o) or 0→ in FIG.
The information signal extracted in the form of
In comparison with a), a pulse corresponding to the case where vthw'i exceeds or falls below vth@) is generated, and the output is as shown in Fig. 2).

Therefore, the output of the sample hold circuit 21 at this time is as shown in FIG. 2 (E). After passing through a compensation circuit 14 that compensates for phase lag, etc., such an output is sent to a drive circuit 15.
input, and the objective lens 4 is driven in the direction where the tracking error becomes smaller.

A concrete example of the waveform shaping circuit 20 and two sample and hold circuits is shown in FIG. In FIG. 4, the waveform shaping circuit 2
2 (b) to the input terminal 22 of 0, that is, the non-inverting terminal of the operational amplifier ICI and the inverting terminal of the operational amplifier IC2.

An input signal a or b as shown in C'9 is input, and this is compared with the reference voltages vth and vthw given to the other terminals of the operational amplifiers ICI and IC2.If the input voltage is higher than vthw, the operational amplifier ICI The output is +15V, and the output of the operational amplifier IC2 is -15V. Also, if the input voltage is lower than vthw, the operational amplifier I
The output of CI is -15V and the output of operational amplifier IC2 is +1
If it is lower than vthw (vth W) and higher than vthw, both outputs will be -15V. operational amplifier IC
1. When either of the outputs of IC2 reaches +15V, current flows to the transistor TRI through the resistor R1 and the diode DI (or the resistor R2>, 1: and the diode D2), so the transistor TRI becomes conductive. A voltage drop occurs across the resistor R3, and the voltage at the output terminal 23 becomes 115V. Also, Abeamp ICI.

When both outputs of IC2 reach ~15V, transistor T
RI becomes non-conductive, the voltage drop across the resistor R3 disappears, and the voltage at the output terminal 23 becomes +15V.

Therefore, in Figure 2, +1 corresponds to 1.
5V corresponds to 0, and 115V corresponds to 0. The output of the waveform shaping circuit 2o is sent as a sample pulse to the sample pulse input terminal 24 of the sample hold circuit 21.
That is, it is input to the field effect transistor TR2 (P-) via the diode D3. When the sample pulse input is 1 J+15V, the output of the operational amplifier IC3 is input to the r-) of the transistor TR2 via the resistor R4, so the transistor TR2 becomes conductive, and the output of the operational amplifier IC3 is input to the it operational amplifier IC4. The fC error signal inputted to the input terminal 25 is outputted as it is from the output terminal 26 as a sampled and held error signal.

This state is the sample period in FIG. 2(E).

Also, when the sample pulse input is 0 to 15, this voltage is applied to the r-) of the transistor TR2 via the diode D3, so the output of the operational amplifier IC3 and the input of the operational amplifier IC4 are disconnected, and the capacitor CIK The stored voltage immediately before disconnection is input to the operational amplifier IC4. Therefore, the immediately preceding error signal is held and becomes the output of the sample and hold circuit 21. This state is shown in Figure 2←
This is the hold period in F. In this way, the error signal can be sampled using the information signal.

In the above embodiment, the information signal is extracted from the reflected light even in the case of recording, but the signal for modulating the semiconductor laser may be branched and extracted from the drive circuit 19. In this case, the output of the amplifier 17 and the drive circuit The output taken from 19 is sent to the waveform shaping circuit 2 by switching a switch during playback and recording.
It is input to 0. Further, although the case where the present invention is applied to a tracking servo in a recording system or a reproduction system has been described, it goes without saying that the present invention can also be applied to a focus servo or a time axis servo in a recording system or a reproduction system. Further, the signal conversion element for recording and/or reproducing information signals on the disk of the recording and/or reproducing device may be a light beam, a scanning needle, a magnetic head, etc., and the information signal may also be a video signal, an audio signal, or a facsimile. Any signal that can be converted into a binary signal can be used. Further, the recording medium is not limited to a disc-shaped one, and may be any recording medium such as a tape-shaped or a drum-shaped one.

As described above, in the servo system of the information recording and/or reproducing apparatus according to the present invention, the error signal is sampled with a signal synchronized with the information signal, and the loop dyne of the servo system is kept constant. This makes it possible to further stabilize the servo operation, and to perform more accurate and stable recording and/or reproduction on the recording medium.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of a tracking servo system of a conventional recording and reproducing device, and FIGS. FIG. 3 is a specific configuration diagram of some waveform shaping circuits and sample-hold circuits. DESCRIPTION OF SYMBOLS 1... Light source, 2... Collimator lens, 3... Prism, 4... Objective lens, 5... Disc-shaped recording medium (disk), 6... Guide track, 7... Disk Motor, 8... Objective lens drive device, 9... Quarter wavelength plate, 10... Beam splitter, 11...
Two-split photodetector, 12.16 --- Arithmetic circuit, 15.1
9... Drive circuit, 20... Waveform shaping circuit, 21
...Sample and hold circuit. Note that the same reference numerals in the figures indicate the same or similar parts. Agent Makoto Kuzuno - Figure 2 LVJ Procedural Amendment (Voluntary) Commissioner of the Japan Patent Office 1, Indication of Case Patent Application 1987-3209392, Name of Invention Servo System for Information Recording and/or Reproducing Device 3, Make Amendment User 5, Target of correction 6, Contents of correction (1) Correct "read" to "playback" in the 19th line of page 3. (2) “Input” on page 6, line 20 “Input”
and correct it. (3) Correct "S7 Allen voltage" on page 8, line 17 to "threshold voltage". (4) Correct "sample held" in line 5 of page 10 to "sampled". that's all

Claims (1)

[Claims] (1) In a closed loop servo system that controls a recording and/or reproduction signal conversion element in a device that records information signals on a recording medium and/or reproduces information signals from a recording medium, an error signal is converted into an information signal. A servo method for an information recording and/or reproducing device characterized by sampling using synchronized signals.