JPS61177644A - Focus servo device - Google Patents

Abstract

PURPOSE:To prevent the heating of the coil of the actuator and to decrease the noise by limiting a focus error signal at the time of the access and limiting the electric current which flows at the actuator for the focus. CONSTITUTION:While the access is not executed, and access control circuit 7 sends the signal showing that the access is not executed to a limiter circuit 8, and the limiter 8 outputs the inputted signal without the limit, and therefore, the focus servo is normally operated. Namely, when the signal, which is not accessed, is inputted to a terminal F of the circuit 8, a switch 11 is turned off, a servo error signal inputted from a terminal D is not attenuated and outputted to a terminal E. On the other hand, the signal showing that the access if executed is inputted into the terminal F. and then, the switch 11 is turned on, and a servo error signal inputted into the terminal D is limited by the voltage determined by the forward direction voltage of the diode and outputted from the terminal E.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a focus servo device for an optical recording or reproducing device. There is an astigmatism method shown in the publication.

FIG. 3 shows the astigmatism method using a four-part detector. In Figure 3, 1 is a 4-split detector and 1-1
．． The detector is divided into 1-2.1-3.1-4.

When the light output from the pickup is focused on the disk, the disk reflected light is B on the 4-split detector 1.
When the pickup is close to the disk, an image as shown in A is formed, and when the pickup is far from the disk, an image as shown in C is formed. For this reason, 1-1
By performing servo control using the difference signal between the sum of 1-3 and the sum of 1-2 and 1-4, the position of the pickup can be controlled so as to focus on the disk. FIG. 4 is a block diagram showing the focus servo system. Reference numeral 1 denotes a four-part detector shown in FIG. 1, which receives reflected light from the disk. 2.3 is a current-voltage converter that converts the current output from the 4-split detector 1 into voltage, 4 is a differential amplifier, 6 is a drive circuit that drives a focusing actuator, 6 is a focusing actuator, and 7 is a An access control device is shown.

A detector 1-1.1-2.1-3 detects the reflected light from the disk.
Detected by 1-4, and detected by current-voltage converter 2゜3, 4
The output current of the divided detector 1 is converted into current and voltage, and the differential amplifier 4 outputs a difference signal. When the pickup is close to the disk, a positive voltage is generated at the output of the differential amplifier 4.

Further, if the pickup is far from the disk, a negative voltage is generated at the output of the differential amplifier 4. If the pickup is located at a distance where the light output from the pick amplifier focuses on the disk, the output of the differential amplifier 4 will be zero. The output of the differential amplifier 4 is input to the drive circuit 6, which drives the actuator 6 to control the output of the differential amplifier 4 to zero, which is the focus servo.

Problems to be Solved by the Invention By the way, with the above configuration, when access is performed by the access control device 7, the pickup is moved along the disk surface with the focus servo engaged, which causes the following problems. What happens? Figure 5 shows a cross section of the disk. Information is recorded on the disk surface by unevenness, and since the conditions are different between the concave and convex parts, the focus servo loop changes as the pickup moves. There are problems in that abnormal voltage gets mixed in and abnormal current flows through the focus actuator, causing the coil to heat up and burn out, and the accuracy of the focus servo to deteriorate.

In view of this, an object of the present invention is to provide a focus servo device in which the coil of the focus actuator does not generate heat during access.

Means for Solving the Problems The present invention provides an optical pickup, a focus control circuit for focusing the light from the optical pink-up on the disk surface, a moving means for moving the optical pickup, and an access control circuit for focusing the light from the optical pickup on the disk surface. The focus servo device is provided with a control means for controlling the movement of the pickup in the moving means, and the focus control circuit includes a limit circuit that limits the signal when the signal exceeds a predetermined voltage.

Operation The present invention has the above-described configuration, and when the optical pickup is moved by the moving means, when the signal of the focus control circuit exceeds a predetermined voltage, the signal is limited to prevent abnormal voltage from being applied to the optical pickup.

Embodiments Hereinafter, embodiments of the present invention will be described based on the drawings. In FIG. 1, components with the same numbers as in FIG. 4 indicate the same components.

In FIG. 1, 8 is a limiter circuit.

When no access is being made, the access control circuit 7 sends a signal to the limiter circuit 8 indicating that no access is being made, and the limiter circuit 8 outputs the input signal without limiting it. , the focus servo works normally.

On the other hand, during the access operation, the access control circuit 7 sends a signal indicating that the access operation is in progress to the limiter circuit 8, and the limiter circuit 8 limits the input signal so that it does not exceed a predetermined value. The mint circuit 8 can be easily constructed using diodes and switches. An example of this is shown in FIG. In Figure 2,
9°1o is a diode, and 11 is a switch. According to the access control circuit 7, when a signal indicating that access is not in progress is input to F, the switch 11 is turned off, and the servo error signal input from D is output to E without being attenuated or limited. . However, when a signal indicating that an access is in progress is input to F, the switch 11 is turned on and the servo error signal input from D is limited to a voltage determined by the forward voltage of the diode and output from E.

By performing the above control, it is possible to limit the current flowing to the focus actuator during access.

Effects of the Invention According to the present invention, by limiting the focus error signal and limiting the current flowing to the focusing actuator during access, it is possible to prevent heat generation in the coil of the actuator and reduce noise. be able to.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing one embodiment of the present invention.
Fig. 2 is a circuit diagram showing the limiter circuit in Fig. 1, Fig. 3 is an f-pattern diagram showing a 4-division detector and an image on the 4-division detector of disk reflected light, and Fig. 4 is a diagram showing a conventional focus servo system. The circuit diagram shown in FIG. 6 is an explanatory diagram showing the disk and focus noise. 8...Limiter circuit, 9.10...Diode, 11...Switch. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 2

Claims (1)

[Claims] an optical pickup, a focus control circuit for focusing light from the optical pickup on a disk surface, a moving means for moving the optical pickup, and a movement of the pickup controlled by the moving means during access. and a control means for controlling the focus control circuit, the focus control circuit having a limit circuit for limiting the focus control error signal to a predetermined voltage, and configured such that the control means limits the focus control error signal of the focus control circuit at the time of access. A focus servo device featuring: