JPH02278521A - Actuator protector - Google Patents

Abstract

PURPOSE:To prevent an over signal from being impressed to an actuator by providing a loop gain switching means to lower the loop gain of a servo system when a current detected by an impressed current detecting means, which detects a current impressed to the actuator, exceeds a prescribed reference value. CONSTITUTION:In the servo system, the impressed current detecting means composed of a resistor R5 for current detection is provided to detect a driving current impressed to an actuator 5 and the loop gain switching means is provided to supply a voltage corresponding to the detected impressed current through an amplifier 6 to a comparator 7, to compare the voltage with a reference, turn on a resistor R2, which is provided in the input side of a phase compensating circuit, and an analog switch 8 of a serial circuit and to lower the loop gain. When the current more than the reference value is applied to the actuator by disturbance, etc., in the servo system, the analog switch 8 of the loop gain switching means is turned on and the gain of the servo loop is lowered. Accordingly, it can be prevented that the over signal is impressed to the actuator 5.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an actuator protection device in a servo system of an optical information reading device.

[Conventional technology]

Conventionally, as an example of an actuator protection device in a servo system of an optical information reading device, Japanese Patent Publication No. 6333207 detects a DC component included in an error signal of a servo system, and the DC component becomes larger than a reference voltage. A tracking actuator protection device is disclosed that disables the displacement operation of a tracking actuator in the case of a tracking actuator. In this device, the means for disabling the displacement operation of the tracking actuator is to turn off an analog switch provided at a predetermined location of the servo loop, thereby cutting off the tracking servo loop.

[Problem to be solved by the invention]

However, in the technique described in Japanese Patent Publication No. 63-33207 mentioned above, if an abnormal state in which an excessive amplitude signal is applied to the actuator occurs continuously, the servo loop is interrupted each time, so data transfer is not possible. This poses a problem in that not only the rate drops significantly, but also other malfunctions may occur, requiring safety measures to be taken against them.

That is, if the servo loop is interrupted, the read data will be mixed with information from other tracks and become meaningless, so data decoding must be prohibited.

Further, even if the tracking servo is turned on after the abnormal state is no longer present, the target track will not be tracked, and the track search must be performed again, which poses the problem of taking time. Furthermore, since data transfer is prohibited during the waiting time for settling when the servo is turned on, there is also the problem that the transfer rate decreases. Further, when the protection of the actuator for focus control is applied, focus servo is also turned off, so there is a problem in that it is necessary to perform the entire sequence from focus search.

Furthermore, when the servo loop is turned on again, if a disturbance such as a scratch on the disk or external vibration occurs, the focus servo may perform an incorrect focus search, or the tracking servo may be blown toward the I/rack direction. There is also a problem in that it is necessary to create a new sequence when these abnormal operations occur.

An object of the present invention is to solve the above problems and provide an actuator protection device that can protect the actuator in the servo system of an optical information reading device without rendering the servo loop of the actuator inoperable. It is.

[Means and effects for solving the problem] The actuator protection device of the present invention is used in a servo system of an optical information reading device for controlling the relative position of an information reading beam with respect to an information track of an optical recording medium. an applied current detection means for detecting a current applied to the actuator in the applied current detection means; and a loop for lowering the loop gain of the servo system when the applied current to the actuator detected by the applied current detection means exceeds a predetermined reference value. The present invention is characterized by comprising a gain switching means.

In the above configuration, the applied current detection means detects the current applied to the actuator, and when the detected value exceeds a predetermined reference value, the analog switch for loop gain switching placed in the servo loop of the actuator is operated. By lowering the servo gain, it is possible to prevent the application of a current exceeding an allowable value to the actuator, thereby preventing damage to the actuator.

In addition, when a disturbance is applied, an excessive signal is applied to the actuator in order to try to follow it, but in the present invention, by lowering the loop gain, an excessive signal is applied to the actuator by the amount that the tracking error increases. Even in such a case, application of a current exceeding the allowable value of the actuator can be prevented. Furthermore, in addition to disturbances, even if an erroneous error signal is generated due to a scratch on the disk or the like and an excessive signal is applied to the actuator in an attempt to follow it, it is possible to similarly prevent the application of a current exceeding the allowable value of the actuator.

Further, in a general servo circuit, a low-frequency phase compensation circuit (phase delay circuit) is inserted in order to provide sufficient DC gain. Since the gain of the inverse transfer function is large in the low frequency band (mainly the low resonant frequency f of the actuator, the frequency band below), considering that this band operates to minimize the tracking error the most, the above-mentioned The frequency band of excessive signals applied to the actuator is concentrated in this band. Therefore, in a servo system with a low-frequency phase compensation circuit,
By switching the time constant of the low-frequency phase compensation circuit to lower the DC gain, the loop gain can be lowered more effectively, and it is possible to prevent an excessive signal exceeding a permissible value from being applied to the actuator.

〔Example〕

FIG. 1 is a block diagram showing the configuration of an example of an actuator protection device of the present invention. In FIG. 1, information on a track of an optical recording medium is read by a light receiving element 1, and the read light receiving element signal is supplied to a differential amplifier 2 to generate an error signal. The error signal is supplied to the phase compensation circuit 3 via the resistor R1 to compensate the phase. The error signal after phase compensation is further supplied as a drive signal to an actuator 5 for controlling the relative position of the information reading beam with respect to the information track of the optical recording medium via the drive amplifier 4, and is then supplied to the servo of the optical information reading device. It constitutes a system.

In the present invention, the servo system includes an applied current detection means consisting of a current detection resistor R5 that detects the drive current applied to the actuator 5, and a comparator that detects a voltage corresponding to the detected applied current via an amplifier 6. 7 and compares it with the reference voltage in the comparator 7, and if it exceeds the reference voltage,
A loop gain switching means is provided for turning on the analog switch 8 in a series circuit of the resistor R2 and the analog switch 8 provided on the input side of the phase compensation circuit to lower the loop gain.

In the above-described actuator protection device of the present invention, if a current exceeding the standard is applied to the actuator 5 in the servo system due to a disturbance or the like, the analog switch 8 of the loop gain switching means is turned on and the gain of the servo loop is lowered, so that the actuator Application of an excessive signal to 5 can be prevented.

FIG. 2 is a block diagram showing the configuration of another example of the actuator protection device of the present invention. In the embodiment shown in FIG. 2, the same members as those shown in FIG. 1 are given the same reference numerals, and their explanations will be omitted. The difference between the embodiment shown in FIG. 2 and the example shown in FIG. 1 is that the phase compensation circuit 3 is composed of a low-frequency phase compensation circuit 31 and a high-frequency phase compensation circuit 3-2.
When a current higher than the standard is applied to the actuator 5,
The point is that the time constant of the low-frequency phase compensation circuit 3-1 is changed to lower the loop gain of the servo system. That is, the third
The figure shows a specific example of the low-frequency phase compensation circuit 3-1, and FIG. 4 shows the amplitude versus frequency characteristics realized by the low-frequency phase compensation circuit 3-1 shown in FIG. By closing 8, the DC gain is (R3+R4)
/l? , to R*/R+. Therefore, in this embodiment as well, when a current higher than the standard is applied to the actuator 5, the loop gain in the low frequency region can be lowered, and application of an excessive signal to the actuator 5 can be prevented.

〔Effect of the invention〕

As is clear from the above description, the actuator protection device of the present invention includes an applied current detection means that detects the current applied to the actuator, and a servo system that detects the current applied to the actuator when the detected current exceeds a predetermined reference value. Since the actuator includes loop gain switching means for lowering the loop gain, application of an excessive signal to the actuator can be prevented. Therefore, there is no need to take safety measures to prevent a drop in data transfer rate or induction of malfunctions that would be expected if the servo loop were to be disconnected, and the servo loop would continue to follow without being disconnected even in the event of an abnormality, so There is no need to perform the entire sequence for tracking and forcing from the beginning.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of an example of the actuator protection device of the present invention, FIG. 2 is a block diagram showing the configuration of another example of the actuator protection device of the present invention, and FIG. 3 is the example shown in FIG. 2. FIG. 4 is a graph showing an amplitude versus frequency characteristic realized by the circuit shown in FIG. 3.

Claims (1)

[Claims] 1. In a servo system of an optical information reading device for controlling the relative position of an information reading beam with respect to an information track of an optical recording medium, an applied current detection means for detecting a current applied to an actuator in the servo system; An actuator protection device comprising: loop gain switching means for lowering the loop gain of the servo system when the current applied to the actuator detected by the current detection means exceeds a predetermined reference value.