JPH038125A - Focus servo controller - Google Patents

Abstract

PURPOSE:To surely focus an objective lens to the recording surface of an information recording medium by providing a blanking pulse generating circuit for generating a blanking pulse synchronizing with a search signal. CONSTITUTION:A blanking pulse generating circuit 12 sends out a blanking pulse to a zero crossing detector 10, while the blanking pulse synchronizing with a search signal, that is, an objective lens is driven in the direction being adjacent to an information recording medium 1. While this blanking pulse is going sent out, an operation of the detector 10 is stopped. Accordingly, the detector 10 is operated in the case the objective lens is driven in the direction going away from the recording medium 1, and also, when a first signal is inputted. This first signal always becomes a focus error signal, therefore, it can be prevented that the objective lens is focused erroneously to the reverse side 3 by a signal being similar to a focus error signal generated by a reflection from the reverse side 3 of the recording medium 1 as in a conventional device.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a focus servo control device for focusing an objective lens on the recording surface of an information recording medium in an optical information recording/reproducing apparatus.

[Prior Art] A conventional device of this type is shown in FIG. FIG. 5 is a block diagram showing the configuration of a conventional focus servo control device, in which (1) is an information recording medium, 2) is the recording surface of the information recording medium (1), and (3) is the information recording medium ( On the back side of 1), (4) is a pickup, which has a built-in objective lens (not shown) and focuses parallel light from a light source (not shown) onto the recording surface 2). It plays the role of making the reflected light of the light incident on a photodetector (not shown).

(5) is a focus actuator that drives the objective lens in the focus direction, (6) is a focus actuator drive circuit that supplies a drive current to the actuator (5), (7B) is a focus search circuit that outputs a focus search signal, (8) ) is a focus error detection circuit that outputs a focus error signal from the output of the photodetector, (9
) is the focus servo pull-in circuit, and the focus actuator drive circuit (6) is connected to the focus search circuit (
(10) is a zero cross detector that automatically switches between inputting the output of 7B) to perform a focus search operation and inputting the output of the focus error detection circuit (8) to perform a focus servo operation. It is provided in the focus servo pull-in circuit (9) and detects the point where the polarity of the focus error signal from the focus error detection circuit (8) is reversed. (11) is a switch which opens and closes according to the output from the zero cross detector (10).

Further, FIG. 6 is a timing chart showing the relationship between the temporal movement position of the objective lens based on the focus search signal and the focus error signal in the apparatus shown in FIG. 5.

Next, the operation will be explained. In order to drive the objective lens from a stationary state of the device, focus the objective lens on the recording surface 2) of the information recording medium (1), and keep the objective lens at the in-focus position, first set the focus direction in a predetermined position. A focus search operation that drives the objective lens within the range and detects the in-focus position, and a focus servo operation that holds the objective lens at the in-focus position and automatically corrects the shift if this position shifts. be exposed.

The focus search operation is performed using the focus search circuit (7B
), the actuator (5) is driven via the drive circuit (6), and while the objective lens is moved within a predetermined range in the focus direction, a focus error signal is detected from the focus error detection circuit (8). wait until

As shown in Figure 6, the focus error signal is zero voltage if the objective lens position is a considerable distance away from the in-focus position, and if there is a slight deviation from the in-focus position, the voltage is zero. “Positive” (or “Negative”) for the front side
), the voltage is zero when it is exactly at the in-focus position, and is ``negative'' (or ``positive'') when it is behind the in-focus position.

When a focus error signal is output from the focus error detection circuit (8), this error signal is sent to the zero cross detector (10) of the focus servo pull-in circuit (9).
It is detected by the output from the zero cross detector (10) that the objective lens is in the in-focus position.

The output of this zero cross detector (10) stops the operation of the focus search circuit (7A), and
The switch (11) is operated to connect the circuit, and the error signal detected from the focus error detection circuit (8) is inputted to the drive circuit (6), and the focus servo operation is started. If the objective lens position is misaligned, the drive circuit (6) drives the actuator (5) using the focus error signal from the detection circuit (8).
This is corrected automatically.

[Problems to be Solved by the Invention] Since the conventional focus servo control device as described above is configured as described above, when a search operation is performed while the objective lens moves in a direction approaching the information recording medium. As shown in FIG. 6, before the focus error signal from the recording surface of the information recording medium is input, a signal similar to the focus error signal due to reflection from the back surface of the information recording medium is input.

This signal from the back surface is an erroneous signal that focuses on the back surface position, and its level varies depending on variations in the light source and reflection efficiency, but in some cases it may reach the threshold of the zero cross detector.
There is a problem that the signal from the back side ends the search operation and shifts to the focus servo operation.

The present invention was made to solve this problem, and an object of the present invention is to provide a focus servo control device that can reliably focus an objective lens on the recording surface of an information recording medium.

[Means for Solving the Problems] The focus servo control device according to the present invention is provided with a blanking pulse generation circuit that generates a blanking pulse synchronized with a search signal in the first invention of the present application, and In the invention, in the focus search operation, the objective lens is once rapidly brought close to the information recording medium, and then the search operation is performed while moving backward from this position at a normal speed.

[Operation] In this invention, the signal for focus search is detected only when the objective lens is moving away from the information recording medium, so the signal detected first is always recorded. This is a focus error signal from the front.

[Example] Hereinafter, an example of the present invention will be described with reference to the drawings. 1st
The figure is a block diagram showing an embodiment of the first invention of the present application. In the figure, the same reference numerals as in FIG. 5 indicate the same or corresponding parts,
(7) is the focus search circuit in this embodiment, (
12) is a blanking pulse generation circuit that generates a blanking pulse synchronized with the search signal from the focus search circuit (7).

FIG. 2 is a timing chart showing the relationship between the position of the objective lens, the focus error signal, and the blanking pulse according to the first invention.

Next, the operation of the first invention will be explained. When the search operation is started, a search signal from the focus search circuit causes the actuator (5) to be activated via the drive circuit (6).
is driven, and the objective lens is driven within a predetermined range in the focus direction.

The direction in which the objective lens is first driven is either toward or away from the information recording medium (1) depending on its resting position, but here, as shown in Figure 2, , it is assumed that the direction in which the objective lens is driven is a direction approaching the information recording medium (1).

When the objective lens is driven, a signal similar to the focus error signal due to reflection from the back surface (3) of the information recording medium (1) is output from the detection circuit (8), and when the objective lens approaches (approximately 700 to 800 μm) , focus error signals from the recording surface (2) are output, and input to the zero cross detector (10) of the focus servo pull-in circuit (9).

When the objective lens moves further and reaches a predetermined position, the focus search circuit (7) drives it in the opposite direction away from the information recording medium (1). , first the recording surface (2)
A focus error signal is output from the detection circuit (8), and then a signal similar to the focus error signal due to reflection from the back surface (3) of the information recording medium (1) is output.

On the other hand, the blanking pulse generation circuit (12) generates a blanking pulse synchronized with the search signal of the focus search circuit <7), that is, as shown in FIG. While driving, a blanking pulse is sent to the zero cross detector (10), and while this blanking pulse is being sent, the operation of the zero cross detector (10) is stopped. Therefore, the zero cross detector (10) operates when the objective lens is being driven away from the information recording medium (1) and when the first signal is input, and this first signal is always in focus. Since this is an error signal, unlike conventional devices, the objective lens may be erroneously focused on the back surface (3) by a signal similar to a focus error signal caused by reflection from the back surface (3) of the information recording medium (1). You can prevent it from getting stuck.

FIG. 3 is a block diagram showing an embodiment of the invention of the present invention cylinder 2. In the figure, the same reference numerals as in FIGS. 1 and 5 indicate the same or corresponding parts, and (7A) is the focus search in this embodiment. It is a circuit.

Further, FIG. 4 is a diagram showing the relationship between the search signal, the position of the objective lens, and the focus error signal according to the second invention.

Next, the operation of this second invention will be explained.

The focus search circuit (7A) is as shown in FIG.
When the search operation starts, a high voltage search signal is output, and the output voltage is gradually weakened.Then, in synchronization with this search signal, the objective lens rapidly approaches the information recording medium (1). After that, the moving direction is changed and the drive is gradually moved away from the information recording medium (1) at a normal speed. Furthermore, while the objective lens is rapidly approaching the information recording medium (1), the output from the detection circuit (8) is not input to the focus servo pull-in circuit (9), and the objective lens From the time when the focus servo pull-in circuit (9) starts driving in the direction away from the information recording medium (1), the focus servo pull-in circuit (9) waits for a focus error signal from the detection circuit (8). Therefore, the first signal input to the focus servo pull-in circuit (9) is the information recording medium (
This is a focus error signal due to reflection from the recording surface (2) in 1), and then a signal similar to the focus error signal due to reflection from the back surface (3) is input, and the first focus error signal causes the zero cross detector to The switch (11) is actuated by the output from (10), and from this point on, the focus servo operation is started. Therefore, unlike conventional devices, it is possible to prevent the objective lens from being erroneously focused on the back surface (3).

[Effects of the Invention] As explained above, in this invention, the signal for focus search is detected only when the objective lens is being driven in the direction away from the information recording medium, so that information can be reliably detected. This has the effect that the objective lens can be focused on the recording surface of the recording medium.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the invention of the present invention cylinder 1,
FIG. 2 is a timing chart in the invention of the present cylinder 1,
FIG. 3 is a block diagram showing an embodiment of the invention of the present invention cylinder 2,
FIG. 4 is a timing chart in the invention of the present cylinder 2,
FIG. 5 is a block diagram showing a conventional device, and FIG. 6 is a timing chart of the conventional device. 1) is an information recording medium, (2) is a recording surface, <3) is a back surface, (4) is a pickup, (5) is a focus actuator, (6) is a focus actuator drive circuit,
(7) and (7A) are respectively focus search circuits, (8) are focus error detection circuits, (9) are focus servo pull-in circuits, (10) are zero cross detectors, (11) are switches, and (12) are blanking circuits. Pulse generation circuit. Note that the same reference numerals in each figure indicate the same or corresponding parts.

Claims (2)

[Claims] (1) Focus search, a focus search means for driving an objective lens within a predetermined range in the focus direction using a search signal from a circuit to perform a focus search while moving close to or away from an information recording medium, the objective lens recording information. A focus system consisting of a focus error detection circuit that outputs a focus error signal indicating whether or not the medium is in focus, a zero cross detector that detects the point where the polarity of the focus error signal is reversed and determines the focus position, and a changeover switch. a servo retracting circuit, a focus servo means for performing a focus servo operation for holding the objective lens at a focused position and correcting the shift by driving the objective lens using the focus error signal when the position shifts; Focus servo control that performs a focus search operation by the means, stops the operation of the focus search circuit by the output from the zero cross detector to complete the focus search operation, and at the same time switches the switch to perform the focus servo operation by the focus servo means. The apparatus includes a blanking pulse generation circuit that generates a blanking pulse synchronized with the focus search signal, and drives the objective lens in a direction close to the information recording medium when a focus search operation is performed. The focus servo control device is characterized in that the blanking pulse generating circuit sends a blanking pulse to the zero cross detector and stops the operation of the zero cross detector. (2) A focus search means for driving an objective lens within a predetermined range in the focus direction using a search signal from a focus search circuit to perform a focus search while approaching or separating from an information recording medium, the objective lens being an information recording medium. A focus servo consisting of a focus error detection circuit that outputs a focus error signal indicating whether or not the focus is focused upward, a zero cross detector that detects the point where the polarity of the focus error signal is reversed and determines the focus position, and a changeover switch. a retracting circuit, a focus servo means for holding the objective lens at a focus position and performing a focus servo operation to correct the shift by driving the objective lens with the focus error signal when the position shifts, and the focus search means a focus servo control device that performs a focus search operation using the zero cross detector, stops the operation of the focus search circuit based on the output from the zero cross detector to complete the focus search operation, and switches the switch to perform a focus servo operation using the focus servo means; In response to the search signal from the focus search circuit, the objective lens is once rapidly driven to a position close to the information recording medium, and from this position it is reversed at a normal speed to perform a focus search operation. A focus servo control device characterized in that the zero cross detector is controlled to operate only while the lens is moving backward.