JPS6331859B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical information recording and reproducing apparatus that uses optical means to record information on a recording medium or to reproduce information that has already been recorded.
It relates to a tracking position control device of said device.

Optical information that uses a laser beam as a light source and modulates this laser beam with a pulsed signal from an external information source to record binary information on a recording medium on a disk, or to read information that has already been recorded. In recording/reproducing devices, in order to accurately record or reproduce information, focus control is used to adjust the position of the condenser lens in the optical axis direction so that the surface of the recording medium is always at the focal point of the condenser lens. The track position control of the laser beam spot relative to the information track during information recording or reproduction is usually performed by determining the optimal width for the optical spot on the recording medium and the optimal depth for the wavelength of the laser beam used. The track position is controlled so that the beam spot follows the guide groove. Furthermore, the movement of the beam spot in the radial direction of the disk is usually carried out within a narrow area by moving only the condenser lens in the radial direction of the disk using a tracking actuator inside the optical head; The beam spot is moved by moving the entire optical head using an external actuator. In such a two-stage servo system, it is difficult to generate a signal that accurately represents the position of only the condensing lens inside the optical head, so a position sensor dedicated to the external actuator is usually used to detect the position inside the optical head. The position of the tracking actuator and the external actuator is controlled independently. However, this method requires an extra external position sensor, and furthermore, the movement of the internal actuator does not reflect the movement of the external actuator, making it difficult to detect track position errors due to deviation of the reflected optical axis when only the condensing lens is moved. , it is not possible to remove the negative effect on focus error detection. Using Figure 1 a and b,
This situation will be explained in detail. In FIG. 1A, incident light 15 passes through a polarizing beam splitter 10 and a quarter-wave plate 11, and is focused by a condensing lens 12 onto a beam spot on the recording medium surface of a disk 14. The reflected light from the disk 14 passes through the condensing lens 12 and the 1/4 wavelength plate 11, is reflected at the reflective surface 24 of the polarizing beam splitter 10, and is sent to two-split optical sensors 19 and 2 for detecting track position errors.
0. At this time, if the optical axis of the incident light 15 and the central axis of the condensing lens match,
At the same time that the reflected light is focused on the beam spot 21 on the recording medium, the reflected light enters the center of the two-split optical sensor as shown by the optical axis 17, and although not shown in the figure, the reflected light is directed to the tracking guide groove. The positional error of the spot 21 can be detected accurately. However, as shown in Figure b, the condenser lens 12
moves in the direction shown by the arrow 13, the incident light is focused on the beam spot 23 by the condensing lens 12, and at the same time the reflected light is focused on one side of the two-split optical sensor as shown by the optical axis 16. Even if a large amount of light is incident on the sensor 20 and the beam spot 23 is accurately positioned in the tracking guide groove, a tracking position error signal will be generated. Conversely, if the condensing lens moves to the left, a tracking position error signal with the opposite polarity will be generated. In this way, a tracking position error signal is generated depending only on the position of the condensing lens, regardless of the position of the tracking guide groove and the beam spot, and if the condensing lens position deviates significantly from the center, it is difficult to accurately Tracking position control becomes impossible, and at the same time, accurate recording and reproduction of information becomes impossible.

A further object of the present invention is to detect the position of the optical head of the condenser lens by reflecting the incident light by a beam splitter so that the central axis of the condenser lens coincides with the incident optical axis. An object of the present invention is to provide a tracking position control device that enables accurate position control of a light spot by controlling the position of an optical head using an external actuator.

Hereinafter, the present invention will be explained in detail using the drawings.

FIG. 2 is a block diagram showing a second embodiment of the tracking position control device according to the present invention. The laser beam emitted from the semiconductor laser 101 passes through a collimating lens 102, a polarizing beam splitter 104, a quarter wavelength plate 125, and a condensing lens 10.
5 and is focused on a beam spot 107 on the recording medium surface of the disk 106. At this time,
The beam from the semiconductor laser 101 that is incident on the polarizing beam splitter 104 is not completely linearly polarized, and the degree of separation of the polarizing beam splitter 104 is not ideal, so that the beam is reflected by the arrow 126 on the reflecting surface 128. It is reflected slightly in the direction shown by . This reflected light is incident on a two-split optical sensor 121, and the outputs of each are input into a differential amplifier 122, where the difference between the two optical sensors is calculated and output as an output 123. By doing so, as will be explained in detail later, the output 123 of the differential amplifier 122 is the same as the arrow 111 of the polarizing beam splitter 104 relative to the optical head 124.
Indicates the position in the direction indicated by . At this time, when the polarizing beam splitter 104 and the condensing lens light 105 are fixed in the direction shown by the arrow 111 on the tracking movable head 103, the polarizing beam splitter 104
04 and the condenser lens 105 will make the same movement in the disk radial direction, and the output 123 of the differential amplifier 122 will indicate the position of the condenser lens 105 in the disk radial direction with respect to the optical head 103. Position error signal 12 of this condensing lens 105
3 is input to the external actuator 127 via the optical head positioning circuit 126, and drives the optical head 124 in the direction shown by the arrow 129 so that the central axis of the condensing lens 105 and the optical axis of the incident light always coincide. The optical head 124 is positioned at. By doing this, the condenser lens 10 is always
5 and the optical axis of the incident light coincide with each other, and it is possible to eliminate the adverse effects caused by the deviation of the reflected optical axis described above.

On the other hand, the reflected light from the recording medium is collected by the condensing lens 10.
The light passes through the 5.1/4 wavelength plate 125, is separated from the incident light at the reflecting surface 128 of the polarizing beam splitter 104, is reflected in the direction shown by the arrow 127, and is incident on the half mirror 112. half mirror 11
2, the incident light is divided into two, one of which passes through a convex lens 113 and a knife edge 114 and enters a two-split optical sensor 115, where a focus error is detected. This focus error detection method is a well-known technique known as the knife edge method, and the output from the two-split optical sensor 115 is input to the focus control circuit 120 via the differential amplifier 116.
The output is sent to the focus control actuator 108 so that only the condenser lens 105 in the tracking movable section is moved as indicated by the arrow 10 so that the recording medium surface of the disk 106 is always the focal point of the condenser lens 105.
Drive in the direction shown by 9. Said half mirror 11
The other light divided by 2 is incident on the 2-split optical sensor 117, and although not shown in the figure, the tracking position error of the beam spot 107 with respect to the tracking guide groove provided on the surface of the disk 106 is detected. will be held. This tracking error detection method is conventionally well known as a push-pull method. The output from the two-split optical sensor 117 is calculated by a differential amplifier 118 to calculate the difference between the outputs of the two optical sensors, and a track position error signal is detected.
0, the tracking movable part is driven so that it is located at the center of the guide groove of the beam spot 107.

As explained in detail above, the position of the condensing lens 105 in the tracking direction with respect to the optical head 124 can be accurately detected by the two-split optical sensor 121, and based on this signal, the optical head is moved by the external actuator. By driving the
The condenser lens can always be positioned at the center of the incident light,
The position of the beam spot relative to the tracking guide groove can be controlled accurately, and information can be recorded and reproduced accurately.

FIG. 3 is an enlarged view of the tracking movable part in FIG. 2, and the gist of the present invention will be explained in more detail using this figure. Figure 3a shows the incident optical axis 2.
When the central axes of the polarizing beam splitter 104 and the condensing lens 105 are aligned with respect to 01,
FIG. 1B shows a case where the central axes of the polarizing beam splitter 104 and the condensing lens 105 are deviated from the incident optical axis 201 in the direction indicated by the arrow 203.

In FIG.
The light reflected there passes through a condensing lens 105 and a 1/4 wavelength plate 125 and is reflected by an arrow on the reflective surface 123 of the polarizing beam splitter recording 104. Focus error detection guided in the direction indicated by 127;
Tracking position error detection and signal detection are performed. At this time, the incident light 201 is as described above.
At the reflecting surface 123 of the polarizing beam splitter 104, it is slightly reflected in the direction shown by the arrow 126, and enters the two-split optical sensors 121a and 121b. When the incident optical axis and the central axes of the polarizing beam splitter and the condensing lens coincide, the axis of the incident light to the two-split optical sensor 121 is located on the dividing line of the two-split optical sensor 121. ,2
The amounts of light received by the two optical sensors 121a and 121b become equal, and their differential output 123 becomes zero.

On the other hand, as shown in FIG.
05 is shifted in the direction shown by the arrow 203, most of the light reflected by the reflective surface 123 of the incident light 201 will be incident on one of the two optical sensors 121a side of the two-split optical sensor 121. The differential output 123 of the optical sensor becomes a positive output. Conversely, although not shown in the figure, if the incident optical axis 201 and the central axes of the polarizing beam splitter 104 and the condensing lens 105 are shifted in the opposite direction to the direction indicated by the arrow 203, the two-split optical sensor 121 differential output 123
becomes a negative output, and the output 123 of the differential amplifier 122
indicates the position of the central axis of the condenser lens 105 with respect to the optical axis 201, or in other words, the optical head 124.

As explained above, by moving the condenser lens and the beam splitter simultaneously in the tracking direction and using the two-split optical sensor to detect the reflected light from the beam splitter, the position of the condenser lens relative to the optical head can be accurately determined. can be detected.

[Brief explanation of the drawing]

Figures 1a and b are conceptual diagrams illustrating the influence of condensing lens movement on tracking position error detection, Figure 2 is a block diagram showing a second embodiment of the tracking position control device according to the present invention, and Figure 3a , b are conceptual diagrams for explaining the principle of the tracking position control device shown in FIG. 2 in an easy-to-understand manner. In the figure, 101... semiconductor laser, 10
2... Collimating lens, 103... Tracking movable part, 104... Polarizing beam splitter, 1
25...1/4 wavelength plate, 105...Condensing lens, 1
06...Disc, 112...Half mirror, 1
15, 117, 121... 2-split optical sensor, 11
4...Knife edge, 113...Convex lens, 11
6,118,122... Differential amplifier, 108...
Focus control actuator, 110...tracking actuator, 127...external actuator, 120...focus control circuit, 119...tracking position control circuit, 126...optical head positioning circuit, 124...optical head, respectively.

Claims (1)

[Claims] 1 Recording of information on a recording medium using optical means,
Alternatively, in an optical information recording/reading device that reads information that has already been recorded, light is focused onto the surface of the recording medium by simultaneously driving a condensing lens and a beam splitter in the radial direction of the disk. The spot is moved in the disk radial direction, and the beam splitter splits the incident light from the light source to the beam splitter and the reflected light from the recording medium surface, and the reflected light from the recording medium surface is used. Then, a tracking position error of the optical spot is detected, and the tracking position is controlled based on the error, and the position of the condenser lens in the disk radial direction relative to the optical head is determined by the reflected light of the incident light on the beam splitter. 1. A tracking position control device for controlling the position of the optical head in the disk radial direction so that the central axis of the condensing lens coincides with the optical axis of the incident light.