JPS62143234A - Control device for focus servo of optical pickup - Google Patents

Abstract

PURPOSE:To change the characteristic such as search speed in matching with the characteristic of a control system without modifying the control circuit and to surely attain the initial lock without being affected by the characteristic change in the control system by providing a drive limit detection means detecting that a drive signal fed to an actuator of a focus adjusting means reaches a setting value. CONSTITUTION:A voltage comparator circuit 12 compares a drive voltage outputted from a drive circuit 2 and fed to the actuator 3 with a reference voltage set optionally and inverts the output by the comparison of quantity. That is, a changeover switch 11 is switched to input a search voltage to the drive circuit 2, an objective lens 5 is directed from the home position to the end position and approaches gradually an optical disc 4. When a focus detection signal is caused from the circuit 9 in this process, the changeover switch 11 is switched to input a focus error signal to the drive circuit 2. When the objective lens 5 is displaced up to the end position while no focus detection signal is produced, the output of the voltage comparator 12 is inverted and the control circuit 10 stops the searching.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical pickup in an optical information reproducing device typified by an optical disc player, and particularly relates to an improvement of a servo control device for the optical pickup.

[Prior art] In the optical pickup of an optical disc player, the second
A focus servo control device having a configuration as shown in the figure is known.

In the conventional example shown in Fig. 2, the objective lens (5
) and the surface of the optical disk (4), two photodiodes (6) and (7) using the Knife-J method or the eccentric auxiliary beam method are used as focus error detection means for obtaining a focus error signal corresponding to the difference between the focus position of the optical disc (4) and the surface of the optical disk (4). , and a differential amplifier (8) that outputs the difference between the output points thereof as a focus error signal.

An objective lens (5) serves as a focus adjustment means for changing the focus position in the vertical direction of the optical disc (4).
The mechanism is such that the actuator (3) displaces the lens in the optical axis direction.

In the steady operation state of the focus servo, the differential amplifier (8
) is input to the drive circuit (2) via the changeover switch (11), and this drive circuit (2)
The actuator (3) is driven by the output. This will cause servo control to work in the direction of zeroing out the focus error signal.

When the player is in a non-operating state, the objective lens (5) is returned to its origin (one limit point of its movable range) by the force of a spring or the like. When the player is started, the following focus search function operates to create an in-focus state (referred to as initial pull-in), and then the above-mentioned focus servo operates.

When the control circuit (10) using a microcomputer is given a start signal, it prevents the υ-di voltage generation circuit (1) from operating and at the same time switches the changeover switch (11) to turn on the search voltage generation circuit (1). The output is input to the drive circuit (2). At this time, the search voltage generating circuit (1) outputs a search voltage whose upper limit gradually increases. Therefore, the objective lens (5) gradually approaches the optical disk (4). When a focused state is reached during this process, the focus error signal becomes almost zero (less than a small set value), and at that time a detection signal is generated from the focused point detection circuit (9).

When this focused point detection signal is generated, the control circuit (10) returns the changeover switch (11>), inputs the focus error signal to the drive circuit (2), and shifts to focus servo.

If the optical disc (4) is not set, if the disc surface is set upside down, or if there is some abnormality in operation, the focus state may not be detected in the focus search operation described above.

The control circuit (10) monitors the focus surge time after startup, and when a focused point detection signal is not generated even after a certain period of time, stops the output of the search voltage generation circuit (1),
Stop focus search operation. Alternatively, perform the same Force Snatch motion again, and if that doesn't work, stop the search.

[Problems to be Solved by the Invention] As described above, in the conventional method, the operation period of focus search is defined in terms of time. Specifically, the control circuit (
10) The time monitoring function by the microcomputer limits the time to a certain period.

The set value of the search time is determined to be an appropriate value that is neither too long nor too short, depending on the movable range of the objective lens (5) and its displacement speed during the search.

However, the search voltage generation circuit (1) and the drive circuit (2)
) If there are large variations or changes over time in the characteristics of a device, the search time of a properly designed device may become too short. If the search time is too short, the search operation will stop before the objective lens (5) is displaced to the limit position, making it impossible to detect the focused state that should be detected.

Further, when changing the characteristics of the filter adjustment means, its drive system, search speed, etc., the search time must be changed accordingly.

This means that the form 1 square control device (10)
This means that it cannot be used universally for things with different characteristics.

This invention was made in view of the above-mentioned conventional problems, and its purpose is to ensure initial pull-in without being affected by changes in control system characteristics, and to improve search speed etc. without changing the control circuit at all. An object of the present invention is to provide a focus servo control device for an optical pickup that can be changed according to the characteristics of a control system.

[Means for Solving the Problems] Therefore, in the present invention, the search period is no longer limited to a fixed time period, and instead a drive signal that detects when the drive signal applied to the actuator of the focus adjustment means reaches a set value is adopted. A limit detection means is provided, and the search is stopped when a drive limit detection signal is generated without a focused point detection signal being obtained during a search.

[Operation] The drive limit detection signal is generated when the focus adjustment means reaches the end point of its movable range. If no in-focus point detection signal is obtained until this signal is generated, the four notches will stop.

[Embodiment] FIG. 1 shows the configuration of an embodiment of the present invention. Reach voltage generation circuit (1), drive circuit (2), actuator (3), optical disk (4), objective lens (5), photodiode (6), (7), differential amplifier (8), focal point detection The configuration and function of the circuit (9) and changeover switch (11) are the same as those of the conventional example shown in FIG. 2, so the previous explanation will be used and no redundant explanation will be given.

In this invention, the operation of the control device (10) using a microcomputer is different from the conventional one as described below, and a voltage comparison circuit (12) is added.

The voltage comparison circuit (12) compares the drive voltage outputted from the drive circuit (2) and applied to the actuator (3) with an arbitrarily settable reference voltage, and inverts the output based on the magnitude comparison. . This reference voltage is set equal to the drive voltage of the actuator (3) required to position the objective lens (5) at the end point of the movable range (adjustment range).

Upon receiving the activation signal, the control circuit (10) operates the reach voltage generation circuit (1) and also operates the changeover switch (11).
and apply the search voltage to the drive circuit (2).
/, The objective lens (5) is gradually brought closer to the optical disk (4) from the origin position toward the end position. In this process, the circuit (
When the focused point detection signal is generated from 9), the selector switch (1
1) and inputs the focus error signal to the drive circuit (2). The objective lens (
5) is displaced to the end point position, the output J of the voltage comparator (12) is inverted, and in response to this, the control circuit (10) stops the search operation. Of course, it is also possible to repeat the same search operation and completely stop the search when the in-focus state cannot be detected.

In the above configuration, the search speed can be adjusted by changing the characteristics of the reach voltage generation circuit (1), and even if this adjustment is made, there is no need to change the control circuit (10) at all. In addition, by adjusting the reference voltage of the voltage comparator (12), it is possible to respond to changes in the characteristics of the focus adjustment means and drive system.
There is no need to make any changes to the control circuit (10).

[Effects of the Invention] As described in detail above, according to the present invention, the initial pull-in of the focus servo can be performed reliably, and high reliability that is not affected by variations in circuit characteristics or changes over time can be achieved. In addition, it can easily respond to changes in the characteristics of each part.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention, and FIG. 2 is a block diagram of a conventional example. In the figure, (1) is a search voltage generation circuit, (2) is a drive circuit, (3) is an actuator, (4) is an optical disk, (5) is an objective lens, (8) is a differential amplifier, and (9) is a A focused point detection circuit, (10) a control circuit, (11) a changeover switch, and (12) a voltage comparison circuit (driving limit detection means). Note that the same reference numerals in each figure indicate the same or corresponding parts. Agent: Masuo Oiwa, patent attorney (2 others)

Claims (1)

[Claims] (1)) A focus error detection means for obtaining a focus error signal corresponding to the difference between the focus position of the objective lens of the optical pickup and the surface of the information recording carrier, and changing the focus position in a direction perpendicular to the surface of the information recording carrier. a focus adjustment means; a servo drive means for driving an actuator of the focus adjustment means in a direction to make the focus error signal zero; and a focused point detection means for detecting when the focus error signal becomes a minute setting value or less. a search signal generating means for generating a predetermined search signal in response to the start signal; and a search signal generating means for generating a predetermined search signal in response to the start signal; signal switching means for inputting the search signal to the servo drive means; drive limit detection means for detecting when the drive signal applied to the actuator reaches a set value; A focus servo control device for an optical pickup, comprising: control means for stopping control based on the search signal when a detection signal from the drive limit detection means is generated before a detection signal from the focused point detection means is generated.