JPH01258232A - Control circuit for position of optical system - Google Patents

Abstract

PURPOSE:To correct the conversion of an error signal due to the change of reproducing light quantity and to stabilize position control by detecting a reproducing light quantity change level from a recording medium and adding a direct current signal, which corresponds to this level, to the error signal. CONSTITUTION:An HF signal to be obtained from an optical pick-up 3 is supplied through an HF signal detecting circuit 11 to a pre-amplifier 12 and amplified. After that, the signal is inputted to a signal processing circuit 14. This HF signal is branched and the direct current component of the signal is fetched by an LPF13 and adjusted to a suitable level by a variable resistor VR1 for level adjustment. Then, the component is added to a tracking error signal by an adding circuit 6. In a variable resistor VR2 for fixed off-set adjustment, the adjustment of off-set quantity is executed without depending on the light quantity change of an optical beam spot, by which an optical disk is irradiated, to be caused by the off-set of an operational amplifier, an adding and subtracting error and the dark and hot current of the detector of a photodetecting element, etc. Thus, the conversion of the error signal is automatically corrected and the position control can be stabilized.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical system position control circuit suitable for use, for example, in tracking or focus control of a write-once optical disc.

[Conventional technology]

Conventionally, optical system position control such as tracking control and focus control has been performed to three-dimensionally control the position of a light beam spot in order to track a specific track with a light beam spot when reproducing an optical disc. FIG. 4 shows a system diagram of a conventional tracking control circuit. In FIG. 4, the optical disc (1) is rotationally driven by a drive motor (2), and the optical pickup (3) moves in the radial direction of the optical disc (1).

The optical pickup (3) includes an optical system such as a detector consisting of a light receiving element, and an actuator such as a tracking coil (10). The tracking error detected by the light receiving element passes through a tracking error detection circuit (4), is amplified by an amplifier circuit (5), and is supplied to an adder circuit (6). A DC voltage E is applied to the adder circuit (6) via a variable resistor VR. The reason for applying the DC voltage l is that the tracking error signal obtained from the tracking error detection circuit [4] may not match the true track position due to the tilt of the optical disk, adjustment error of the optical system of the optical pickup (3), or beam asymmetry. If the laser beam does not hit, the reflected beam spot does not focus on the center position of the split light receiving element, for example, but focuses on a shifted position, so that the zero crossing point on the S curve of the tracking error signal is the true This is to correct deviation from the position.

In this way, after the tracking error signal is corrected in the adder circuit (6), compensation for eccentricity of the turntable is performed in the phase compensation circuit (8) via the gain adjustment amplifier (7), and the tracking error signal is compensated for. A tracking coil (10) is driven via a drive circuit (9) to perform tracking control of the optical pickup (3) in the direction shown by arrow A-A.

[Problem to be solved by the invention]

According to the conventional configuration shown in FIG. 4, for example, if the optical disc is a write-once type, there are parts on the track where data has already been recorded and parts where no data has been recorded yet. The reflected light intensity changes in both cases, resulting in an error in the tracking offset. If this error is large, the tracking servo may become erroneous.

The present invention was created in view of the above-mentioned drawbacks, and its purpose is to automatically adjust the amount of offset so that the optical system position servo is applied stably even if the light intensity changes due to the presence or absence of pits. This provides an optical system position control circuit.

[Means to solve the problem]

An example of the optical system position control circuit of the present invention is shown in FIG. 1
), a reproduction light amount detection means (11) for detecting the level of change in the reproduction light amount from the DC output signal (13), a DC output means (13) for obtaining a DC output signal corresponding to this level, and an addition means (11) for adding this DC output signal to an error signal. 6), and automatically corrects the conversion of error signals caused by changes in the amount of reproduction light.

[Effect]

The optical system position control circuit of the present invention generates an optical system position error signal (for example, a tracking or focus error signal) when a spot is irradiated on an unrecorded area and a recorded area on a track.
By utilizing the fact that the error voltage of the S-curve characteristic curve obtained as is proportional to offset voltage l, the optical system position servo can be stabilized by automatically adjusting the offset voltage so that it is proportional to the amount of reproduced light. This is what I did.

〔Example〕

Hereinafter, as an embodiment of the optical system position control circuit of the present invention,
The tracking servo circuit will be explained with reference to FIGS. 1 to 3. In FIG. 1, parts corresponding to those in FIG. 4 are given the same reference numerals, and redundant explanation will be omitted.

In Fig. 1, the HF signal obtained from the light receiving element included in the optical pickup (3) is supplied to the preamplifier (12) through the HF signal detection circuit (11), and after preamplification, the signal processing circuit (14) is manually powered. This HF signal is branched, the DC component is taken out by L P F (13), adjusted to an appropriate level by a variable resistor VR for level adjustment, and added to the tracking error signal by an adder circuit (6). be done. The variable resistor VR2 for fixed offset adjustment does not depend on changes in the light intensity of the light beam spot irradiated onto the optical disc, which occurs due to operational amplifier offset, adjustment error, dark current of detectors such as light receiving elements, etc. adjustments will be made. Note that symbols (1) to (10) are completely the same as in the first configuration.

The operation of the above configuration will be explained using the waveform diagrams of FIGS. 2 and 3.

In FIG. 2, the vertical axis represents the amount of reflected light from the light beam irradiated onto the optical disc (1) from the optical pickup (3), and the horizontal axis represents the track direction. Optical disc (1)
When the unrecorded part (17) and the recorded part (18) coexist in the disc, the HF signal (16) obtained from the detector of the optical pickup (3) in the recording part (18) is not the same as that of the optical disc (1). Is it possible to obtain a signal in which the amount of reflected light changes between the pit position and the land position?In the unrecorded portion (17), the amount of reflected light is the same as that at the land position. Therefore, the S-curve characteristics showing the relationship between the spot position and the tracking error signal voltage when crossing a track on the disk are as shown in FIGS. 3A and 3B. That is, FIG. 3A shows the S-curve characteristic in the unrecorded area of the optical disc (1), and FIG. 3B shows the S-curve characteristic in the recorded area. (
The true track center point of the light beam irradiated on the track 1) (21) is caused by various causes such as optical adjustment errors, variations in the sensitivity of the error detector caused by warping of the disk, and gain errors in the preamplifier. Due to the offset, the zero cross point (21) on the detection signal of the S curve (19a), (19b) is moved from the true track center point (21) in FIG. 3A.

As shown in the figure, the offset is offset by lΔX. The offset voltage to be corrected at that time is ΔV.

In the conventional configuration, the variable resistor VR supplies only the offset voltage ΔV to the adder circuit (6) as a DC voltage, and the S curve (19a) is translated in parallel to become the S curve (19C) shown by the broken line, which allows true tracking. Center point (21) and S
It was adjusted so that the zero cross point of the curve (19C) matched.

Next, if the light beam is irradiated onto the recording area (18) shown in FIG. 2, the total amount of light obtained by the detector will increase compared to when it is at the unrecorded area (17). In accordance with this increase, the tracking error signal voltage increases as shown in FIG. 3B, and becomes like an S curve (19b).

Now, if the total amount of light has increased by a times, the offset voltage to be corrected will be a·ΔV. In other words, the overall change in the amount of reproduction light and the offset (offset) caused thereby are proportional to each other. By utilizing this fact and changing the offset voltage ΔV added to the tracking error signal so as to be proportional to the amount of reproduced light, stable servo operation can be obtained. In this example, since the DC component of the HF signal is used, the offset voltage proportional to the amount of reproduced light is applied to the HF signal obtained by the detector.
It is pre-amplified through the signal detection circuit (11) and LPE (1
3), the HF signal obtained in the recording section (18) as shown in FIG. 2 is converted to DC as shown in the LPF output waveform (15). Since this DC component has a value that changes depending on the amount of offset, stable tracking control can be performed even if recorded areas and unrecorded areas exist alternately in the optical disc.

In the above embodiment, a tracking servo circuit has been described, but since the error output of the detector exhibits an S-curve characteristic, for example, like a focus servo circuit, focus control can be performed in the same way as in the present invention.

Note that the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the gist of the present invention.

〔Effect of the invention〕

If the optical system position control circuit of the present invention is used, even if recorded areas and unrecorded areas are alternately present on a track, fluctuation components of offset 1 caused by this, such as optical adjustment errors and constant skids of the disc, can be eliminated. Errors caused by this, variations in detector sensitivity, preamplifier gain errors, etc. can be corrected, and the optical system position can be controlled stably.

[Brief explanation of the drawing]

Fig. 1 is a system diagram of a tracking control circuit showing an embodiment of the present invention, Fig. 2 is a waveform diagram showing the amount of reflected light from the disk, and Fig. 3 is a tracking error signal when a reproduction light beam crosses a track. The waveform diagram in FIG. 4 is a system diagram of a conventional tracking servo circuit. (1) is an optical disk, (3) is an optical pickup, (11
) is the HF signal detection circuit, (12) is the preamplifier, (13
) is an LPF, and VR is a variable resistor.

Claims (1)

[Scope of Claims] In an optical system position control circuit that performs optical recording and reproduction by irradiating a laser beam onto a recording medium, a reproduction light amount detection means for detecting a change level of reproduction light amount from the recording medium; It is characterized by comprising a DC output means for obtaining a DC output signal according to the level, and an addition means for adding the DC output signal to an error signal, and automatically correcting changes in the error signal caused by changes in the amount of reproduced light. optical system position control circuit.