JPH0750415B2 - Servo loop circuit of optical recording / reproducing device - Google Patents

Description

TECHNICAL FIELD The present invention relates to a servo loop circuit suitable for drive control of an optical system of an optical information recording / reproducing apparatus.

(Prior Art) An optical information recording / reproducing apparatus projects a light beam converged in a minute spot shape onto a recording medium from a pickup equipped with an optical system, and records / reproduces optical information using reflected light or transmitted light thereof. Is configured. In this optical information recording / reproducing apparatus, a light beam is accurately projected in the focusing direction and the tracking direction of the pit surface on the optical disk even if disturbances due to surface wobbling or eccentricity of the optical disk as an optical recording medium occur. There must be. For this reason, a focusing servo mechanism and a tracking servo mechanism are provided in an actuator that is an optical system driving device so that the light beam accurately follows the pit surface on which information is recorded.

FIG. 1 is a block diagram showing the configuration of a conventional servo circuit that controls driving of an actuator. Actuator 1
And the disturbance shift signal are optically added, detected by the detector 2 as an electric signal, and input to the adder / subtractor 3. A target value is input to the adder / subtractor 3, an error signal is detected from the detected shift amount and the target value, the phase is compensated by the phase compensating circuit 4, and the signal is passed through the drive amplifier 5 to the actuator 1 as a drive signal. input. The displacement signal of the actuator 1 is fed back to the detector 2 via a feedback loop so that the follow-up operation can be accurately performed even if a disturbance occurs. In this conventional servo circuit, a target value that serves as a reference for control is set in advance, and the target value is used as a center for driving based on the amount of deviation from the target value for ordinary minute disturbances due to surface wobbling or eccentricity of the optical disk. The signal is supplied to the servo loop so that the follow-up operation can be performed accurately. However, the optical disc has a structure in which a transparent protective layer is formed on a reflective film having pits formed therein, and a light beam incident on the optical disc is transmitted through the transparent protective layer and reflected by the reflective film. Therefore, if the optical disc surface has irregularities, or if the thickness of the transparent protective layer is different for each disc, these irregularities on the surface and unevenness of the protective layer thickness act as a lens, so a cycle different from normal minute disturbances Is a long disturbance (a disturbance caused by non-uniform optical performance of the optical disc), which causes a large deviation from the target value set for each disc or each part of the disc, and there is the inconvenience of drive control at a position deviating from the optimum setting position. It was happening. That is, when a disturbance with a long period occurs due to the optical nonuniformity of such an optical disc,
The evaluation value that indicates the tracking capability of the optical beam such as the amplitude and jitter amount of the reproduced RF signal deteriorates, and the tracking control is performed at a position that greatly deviates from the set best position, and accurate tracking control can be performed. However, there is an inconvenience that a focusing error and a tracking error are likely to occur. On the other hand, it is extremely difficult to manufacture an optical disc that has no unevenness on the surface and that the thickness of the transparent protective layer is uniform.

(Object of the Invention) An object of the present invention is to eliminate the above-mentioned drawbacks and to perform servo control of an optical recording / reproducing apparatus that can always control at the best drive control position even if a disturbance having a long period due to optical nonuniformity occurs. To provide a loop.

(Summary of the Invention) The present invention provides an actuator for causing a light beam to follow an optical recording medium and a feedback signal from the actuator.
A servo loop for driving and controlling this actuator to a target value, a signal generating means for supplying a periodic signal that periodically changes to this servo loop, a drive control amount applied to the actuator by the servo valve, and a target of the actuator. An evaluation value detecting means for detecting an evaluation value that changes corresponding to the amount of deviation from the value; a means for multiplying the periodic signal by the detected evaluation value; and an output signal of the multiplying means. It is characterized in that it has a band limiting means for band limiting, and means for adding the output of the band limiting means to the servo loop as a new target value, and performs drive control while updating the target value.

(Embodiment) FIG. 2 is a block diagram showing a configuration of an example of a servo loop circuit according to the present invention. The deviation signal and the disturbance deviation signal of the actuator 10 are optically added / subtracted and input to the detector 11 to be detected as a deviation signal. The detected shift signal is input to the adder / subtractor 12 with the sine wave signal output from the sine wave generator 13 superimposed on the input. Further, in parallel, an evaluation value signal for evaluating the deviation amount from the control target value of the actuator 10 is input to the evaluation value detection circuit 15. The evaluation value of the deviation amount of the actuator 10 includes the jitter amount of the RF signal obtained by photoelectrically converting the read light from the optical disk, the amplitude value of the RF signal, the noise in the tracking error signal, etc. The amount of signal jitter is used. The evaluation value detection circuit 15 is a signal processing circuit that detects the evaluation value as a DC voltage from the evaluation value signal. The evaluation value detected by the evaluation value detection circuit is supplied to the multiplier 16 and multiplied by the sine wave signal output from the sine wave generation circuit 13, which is input to the reduction filter 17 to extract the DC component and amplified by the amplifier 18. Then, it is input to the adder / subtractor 14 as an offset signal for correcting the deviation amount from the target value. Then, the shift signal to which the sine wave signal is added is added / subtracted by this offset signal, the phase is compensated by the phase compensation circuit 19, and is supplied to the actuator 10 via the drive amplifier 20.

Next, the operation of the servo loop circuit according to the present invention will be described. 3A to 3C are graphs of the evaluation value function showing the relationship between the control voltage of the actuator 10 and the jitter amount of the RF signal which is the evaluation value. FIG. 3B shows the case where the deviation amount from the target value when the actuator is following is zero, and in FIGS. 3A and 3B, the deviation amounts corresponding to the driving voltages of −V ₀ and + V ₀ are generated. The case is shown. Comparing each figure, FIG. 3B
In the case, the shift amount is zero, that is, the state is controlled to the best position, that is, the jitter amount is the smallest. FIG. 3A shows a state in which the displacement amount of the actuator 10 is displaced by an amount corresponding to the drive voltage −V ₀ , and FIG. 3C is displaced by an amount equivalent to the drive voltage + V ₀ . The case is shown. In the present invention, since the sine wave signal shown in FIG. 4A is superposed on the servo loop from the sine wave generator 13 via the adder / subtractor 12, the evaluation value functions shown in FIGS. The value (jitter amount) changes sinusoidally with time as shown in FIGS. 4B to 4D with the servo loop closed. Now, when the output signal of the sine wave generator 13 is expressed by the equation (1), V (t) = a · cosωt (1) where ω: angular frequency a: constant The evaluation value shown in FIG. 3A is Approximately expressed by equation (2), b ₁ + c ₁ · cosωt (2) However, b ₁ and c ₁ are constants. The evaluation values shown in FIG. 3B are approximately expressed by equation (3). , B ₂ + c ₂ · cos 2ωt (3) The evaluation value shown in FIG. 3C is approximately represented by the equation (4).

b ₁ + c ₁ · cos ωt (4) When the signals represented by these equations (2) to (4) are multiplied by the sine wave signal output from the sine wave generator 13 by the multiplier 16, the following signals are obtained. can get.

i) In the case of having the evaluation value function shown in FIG. 3A ii) In case of having the evaluation value function shown in FIG. 3B iii) In the case of having the evaluation value function shown in FIG. 3C As can be understood from the equations (5) to (7), the output signal of the multiplier 16 has no DC component when the deviation amount of the actuator 10 is zero, but the actuator 10 moves in the positive or negative direction. If there is a deviation, there is a DC component whose sign is preserved. Therefore, if the output signal of the multiplier 16 extracts the DC component by the reduction filter 17, the extracted DC component is amplified by the amplifier 18 by a predetermined multiplication factor, and is supplied to the servo loop via the adder / subtractor 14 as an offset signal, The actuator can be controlled to follow the target at the best position. That is, since the target value is updated according to the disturbance, it is possible to drive and control the actuator in the best condition.

The present invention is not limited to the above-mentioned embodiments, but various modifications and variations are possible. For example, in the embodiment described above
The case where the RF signal is a digital signal has been described. In this case, the clock generator circuit for reading the RF signal is
Although it is composed of (phased Locked Loop), the jitter amount can be obtained by converting the error signal of this PLL (the signal after the phase comparison between the output signal from the VCO and the reproduction signal) to the effective value.

In addition, the evaluation value is only the amount of jitter of the RF signal.
It is also possible to use the amplitude value of the signal, and further characteristic values such as noise in the tracking error signal and its S / N value. In this case, when using the amplitude value of the RF signal as the evaluation value, the evaluation value signal becomes the RF signal, and the evaluation value detection circuit 15 acts as an amplitude detection circuit that detects the amplitude value of the RF signal and outputs it as a DC voltage signal. , The evaluation value function shown in FIGS. 3A to 3C has a convex shape.

(Effect of the Invention) As described above, according to the present invention, an evaluation value representing a tracking characteristic of a light beam with respect to an optical recording medium is obtained, an offset amount due to disturbance is obtained from the obtained evaluation value, and the obtained offset amount is obtained. Is supplied to the servo loop as a new target value, the drive control is performed while the target value is being updated, and the actuator can always be drive-controlled in the best state even when a disturbance having a long cycle occurs.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of a conventional servo circuit, FIG. 2 is a block diagram showing the configuration of an example of the servo circuit according to the present invention, and FIGS. 3A to 3C are the relations between the control voltage of the actuator and the evaluation value. 4A is a graph showing the output signal of the sine wave generator, and FIGS. 4B to 4D are graphs showing the output signal of the evaluation value detection circuit. 10 …… actuator, 11 …… deviation signal detector 12 …… adder / subtractor, 13 …… sine wave generator 14 …… adder / subtractor, 15 …… evaluation value detection circuit 16 …… multiplier, 17 …… reduction filter 18 …… Amplifier, 19 …… Phase compensation circuit 20 …… Drive amplifier

Claims (1)

[Claims] 1. An actuator for causing a light beam to follow an optical recording medium, and a feedback signal from the actuator,
A servo loop for driving and controlling this actuator to a target value, a signal generating means for supplying a periodic signal that periodically changes to this servo loop, a drive control amount applied to the actuator by the servo loop and the actuator Evaluation value detecting means for detecting an evaluation value that changes corresponding to the amount of deviation from the target value, means for multiplying the periodic signal by the detected evaluation value, and an output signal of the multiplying means An optical recording / reproducing apparatus characterized in that it has a band limiting means for band limiting, and means for adding the output of the band limiting means to the servo loop as a new target value, and drive control while updating the target value. Servo loop circuit.