JPS62148803A - Detecting method for center position of optical disk substrate - Google Patents

Abstract

PURPOSE:To facilitate high-accuracy detecting by moving an optical disk substrate in an X-axial and a Y-axial direction while placing an optical pickup in a focus servo state on the optical disk substrate, detecting the innermost peripheral groove from the difference between a focus RF signal and a flat part level, and detecting the rotational center position of the innermost peripheral groove. CONSTITUTION:The optical disk substrate 18 with grooves are mounted on a table 2 and the position of the optical disk substrate is set to the just focus point of the optical pickup by a motor M1 for Z-axial driving and a focus servo circuit 12. The table 2 is moved in the X-axial and Y-axis directions in said state. At this time, when the focus RF signal of the optical pickup 10 is considered, there is a difference in signal level generated between the flat part and groove part of the optical disk substrate. This is utilized to detect the innermost peripheral groove part by a groove detecting circuit 14.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to a method for detecting the center position of an optical disc substrate.

(Prior Art) In the manufacturing process of an optical disk substrate, grooves are formed concentrically, for example, in a spiral shape, on a flat optical disk substrate transferred from a stamper, but the rotational position of the grooves is unknown.

However, it is necessary to find the rotation center and drill a hole at that position in order to use it as a reference for subsequent processing or for mounting it as an optical disc in an information reproducing device.

Conventionally, in order to find this center of rotation, for example, an optical disc board was mounted on a turntable, and the innermost (or outermost)
The method used is to place a microscope near the groove and observe the groove. That is, the turntable is rotated, and the transfer disk is moved in one direction and in a direction orthogonal thereto so that the locus of the innermost groove due to rotation does not deviate at the combined m''AIQ point, and the center of rotation of the groove and the turntable are aligned. The center position is determined by aligning the centers of rotation.

However, this method cannot require high accuracy because it requires human intervention. Further, there is a problem that the workability is low and it is not suitable for processing in large quantities.

(Objective) Therefore, an object of the present invention is to provide an improved method for detecting the center position of an optical disc substrate, which allows easy and highly accurate detection.

(Structure) In order to achieve the above object, the present invention moves the optical disc substrate together with a table in the X and Y axis directions while the optical pickup is in focus servo with respect to the optical disc substrate. This method is characterized in that the groove is detected based on the difference between the level of the flat part of the focus RF signal and the rotational center position of the detected innermost groove is detected.

Hereinafter, a detailed explanation will be given based on one embodiment of the present invention.

In FIG. 1 schematically showing the center position detection device according to the present invention, reference numeral 2 indicates a table on which an optical disc substrate is mounted. This table 2 can be driven by a motor Ml in the Y-axis direction perpendicular to the table surface. This table 2 is also joined with xy child table, table 2
It is linearly movable in the X direction and Y direction, which are two axes that are parallel to the plane and orthogonal to each other. Here, the X direction refers to the left and right direction, and is driven by the motor M2. Further, the Y direction is a direction that passes through the plane of the paper, and is driven by a motor M3. Therefore, in the end, table 2 has X, Y, Z
It can be moved freely in each axis direction. In the figure, reference numeral 6 indicates a linear scale that detects movement in the X-axis direction, and reference numeral 8 indicates a linear scale that detects movement in the Y-axis direction.

An optical pickup 10 is placed below the table 2.

This optical pickup 10 is set so that its optical axis is perpendicular to the surface of the table 2, and is connected to a focus servo circuit 12 so that focus servo can be performed on the optical disk substrate mounted on the table 2. . Also provided are a groove detection circuit 14 that detects grooves from changes in the RF multiplied signal, and a system controller 16 that controls the entire system such as motor control, linear scale measurement control, and timing of groove detection.

In this example, after the optical disc substrate 18 is mounted on the table 2, the innermost circumferential groove is detected by the optical pickup while the optical pickup 10 is focus servoed to the optical disc substrate 18, and the rotation center of the spiral groove is detected. Detect.

Specifically, the detection is performed as follows.

Mount the grooved optical disc board 18 on the table 2, and
A shaft driving motor Ml and a focus servo circuit 12 position the optical disk substrate at just the focus point with respect to the optical pickup. Then, in this state, the table 2 is moved in the X-axis direction and the Y-axis direction as shown in FIG.

At this time, when paying attention to the focus RF signal of the optical pickup 10, there is a difference in signal level between the flat part and the groove part of the optical disc substrate. Utilizing this, the innermost circumferential groove portion is detected by the groove detection circuit 14.

For example, in FIG. 2, by moving in the Y-axis direction, the groove 20
The relative positions of points a and S above are detected, and the relative positions of points C and d are similarly detected by movement in the X-axis direction. In other words, points a and b are assumed to be the virtual origin as the starting point of table movement.
, c, and d are measured using a linear scale 6.8 in synchronization with the groove detection signal.

If the relative positions of these points can be detected, the spiral groove 20 can be rotated with respect to the virtual origin.

A series of these controls, motor driver control, and linear scale measurement calculation processing using groove detection are all performed by the system controller 16.

(Effects) According to the present invention, the rotation center position of the optical disk substrate can be easily and accurately determined by highly accurate mechanical control.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a center position detecting device suitable for an embodiment of the present invention, and FIG. 2 is a plan view of an optical disc substrate during the detection process. 18... Optical disk substrate, 20... Groove.

Claims (1)

[Claims] A table on which an optical disk substrate is mounted, a Z-axis perpendicular to the table surface, an X-axis, a Y-axis parallel to the table surface and perpendicular to each other, and a table driven about these X-, Y-, and Z-axes. In a center position detection device having a drive device and an optical pickup set in such a manner that its optical axis is perpendicular to the table surface, the optical disk substrate is moved in XY direction along with the table while the optical pickup is in focus servo with respect to the optical disk substrate.
The innermost groove of the optical disc substrate is detected by moving it in the axial direction based on the difference between the level of the flat part of the focus RF signal, and the innermost groove is detected from the midpoint of the distance between two points of the detected innermost groove. A method for detecting the center position of an optical disk substrate, the method comprising detecting the rotation center position.