JPH0423231A - Light spot controller - Google Patents

Abstract

PURPOSE:To prevent rocking when performing fast tracking access by providing a wedge type prism at the front stage of an objective lens, and varying an inclination of incident light on the lens by turning the prism and the lens integrally. CONSTITUTION:The center 105a of an incident beam of light from the lower plane of the wedge type prism 15 is inclined and emitted by refraction. When the prism 15 is turned by a micro amount from a state of neutral point where the center 105a of the beam of light from the prism 15 aligns with the optical axis of the objective lens 13, the inclination of the center of an emitted beam of light is varied, which varies the inclination for the lens 13. Since the prism 15 and the lens 13 are turned integrally, a spot irradiating position on a disk 17 is moved in a diameter direction, which enables a recording track to be accurately irradiated with a spot. Thereby, it is possible to prevent the occurrence of rocking in fast tracking and to attain the acceleration and light weight of a device.

Description

[Detailed Description of the Invention] The present invention optically reads and writes information by irradiating a light spot onto an optical recording medium such as an optical disk, magneto-optical disk, or optical cart. The present invention relates to a method and device (actuator) for controlling the irradiation position of a light spot in an optical recording system.

In the J1 optical recording system, it is necessary to converge and image a light beam using an objective lens, and to irradiate the recording track of the recording medium with light as a microscopic optical spot. For example, in the case of a disc-shaped recording medium such as an optical disc or a magneto-optical disc, the disc is rotated and an objective lens is moved in the radial direction of the disc to irradiate a target recording track with light. In random access,
After coarse access driving is performed at high speed to near the target recording track, the address is read and fine access is performed, and a light beam is spot-irradiated onto the recording track.

However, the width of the recording track is minute, and there are limits to the accuracy of forming the recording track, the positional accuracy when mounting the recording medium, and the driving accuracy of the objective lens. Therefore, it is not possible to simply drive the objective lens mechanically. , it is not possible to accurately spot the light beam onto the recording trunk.

Therefore, the positional deviation between the spot light and the recording track is detected as an error signal, and the light spot is finely adjusted in the tracking direction so that it is irradiated on the recording track, and the focus direction is adjusted so that the light spot is focused on the recording track. It will be necessary to make some fine adjustments. As such a tracking control system, various systems have been proposed, such as the objective lens driving device described in Japanese Patent Publication No. 61-2058.

FIG. 8 is a perspective view for explaining the movable part of the conventional optical spot control device, and FIG. 9 shows the movable part connected to the fitting shaft 67.
It is a sectional view showing a state where it is fitted.

The objective lens 13 is supported by a holder 61 called a bobbin, and a focus coil 25 is wound around the circumferential surface of the holder 6, and a wound tracking coil 27 is attached thereto. By applying a signal current to these coils 25 and 27, a force is exerted between them and a separate magnetic circuit (not shown), and the holder 61, which is fitted onto the fitting shaft 67 through the fitting hole 65, is By rotating around the fitting axis 67, the objective lens 13 is driven in the tracking direction Tr, and by sliding the holder 61 up and down along the fitting axis 67, the objective lens 13 is driven in the focusing direction Fo. driven by

In such a light spot control device, a balancer 63 of the same weight is provided on the opposite side of the objective lens 13 in order to balance the weight, but due to manufacturing, a weight imbalance occurs around the fitting shaft 67. That is inevitable.

Therefore, the holder 61 is rotationally displaced in the tracking direction by the acceleration applied during coarse access driven at high speed, and enters a tracking operation while inducing vibration during fine access, causing a delay in access time. In particular, since the objective lens 13 and balancer 63, which are heavy, are located away from the fitting shaft 67, which is the center of rotation, the moment of inertia becomes large, and even a small weight imbalance tends to cause the objective lens 13 to swing. Further, since the balancer 63 is essentially unnecessary, it is desirable to not use it or to make it lightweight from the viewpoint of reducing the weight of the actuator.

Furthermore, when tracking is controlled by moving the objective lens 13 horizontally as shown in FIG. 8, the reflected light from the recording medium is displaced in parallel even when tracking is achieved, and the apparent tracking error above is There was a problem that occurred. FIGS. 10A and 10B are explanatory diagrams showing this situation.

FIG. 10A shows a state in which the objective lenses O and L are at neutral points, and the center of the intensity distribution of the incident light 101 coincides with the optical axis of the objective lens O1L.

Since the center of the intensity distribution of a luminous flux is generally the center of the luminous flux, the center of the intensity distribution of the luminous flux will hereinafter be referred to simply as the center of the luminous flux or the center of incident light.

In the state shown in FIG. 10A, the center of the incident light 101 from the laser light source coincides with the center of the reflected light 103 that is converged by the objective lenses ◯ and L and reflected by the disk surface. The reflected light 103 is reflected by the mirror M, passes through the beam splitters B and S, and is sent to the four-split photodiode P.
D, and the error signal and data signal are detected. The reflected light 103 is incident on the center of the 4-split photodiodes P and D, and if tracking is achieved, the light intensity distribution from the center of the beam is equal, so the polarization of the light amount on the 4-split photodiodes P and D is equal. It does not occur more than that. When tracking deviates from the center of 1 to rank, a deviation occurs in the light amount distribution from the center of the light beam, and the amount of deviation is detected as an error signal. Now, following the disk eccentricity etc.,
Objective lens 0. Suppose that L is displaced by ΔX and the incident position on the disk (imaging position) is moved by ΔX. At this time, the center 101 of the incident light is the objective lens ○, L,
The center of the incident light is 10
1 and the center 103 of the reflected light are shifted in parallel by ΔL2=2·ΔX. Therefore, the center 103 of the reflected light enters the four-split photodiodes P and D of the detection system with a deviation from the center by that amount, and the light intensity distribution from the center of the reflected light beam is equal and actually accurate. Even though tracking is achieved and the image is formed on the recording track, it is detected as if there is a tracking error, and if control is performed in this state, the light spot will be placed at a position shifted from the center of the recording track of the disc. becomes an image. Therefore, unless this apparent amount of tracking error is offset, the quality of recording and reproducing information will deteriorate.

As a method for offsetting this apparent amount of tracking error, Japanese Patent Laid-Open No. 58-9228 discloses that the reflective surface of a galvanometer mirror that guides the light flux to the objective lens and guides the reflected light to the tracking error detection system is It has been proposed to match the back focus. however,
Since the back focal length of the objective lens is very short, for example, about 2 to 51 degrees, it is almost impossible to arrange the galvanometer mirror at this position in terms of design.

Furthermore, Japanese Patent Application Laid-Open No. 61-160841 discloses that the light beam always passes through the back focal point of the objective lens.

It has been reported to eccentrically drive a rotating prism that acts as a mirror. However, this method inevitably increases the size of the device. Furthermore, in the above two methods, there is a problem in that it is difficult to precisely maintain the posture of the mirror when the optical head accesses the disk at high speed.

Regarding scanning a light beam or changing the direction of a light beam by utilizing the property of a wedge-shaped prism that the inclination of the emitted light changes with rotation, U.S. Pat. , 297,395, 3,378,687, 3.736
Specification No. 848, Specification No. 3,827,787, Specification No. 4
, 118, 109, etc.

However, these do not suggest use in a light spot irradiation device.

The present invention is intended to provide a light spot control device that can improve the swinging of an objective lens during high-speed access due to weight imbalance.

The present invention also provides a light spot control device that can prevent the occurrence of apparent tracking errors.

The optical spot control device of the present invention includes an objective lens for irradiating light onto a recording medium, and a rotatably provided front stage of the objective lens, which imparts an inclination to the incident light beam and outputs it to the objective lens. a wedge-shaped prism that changes the inclination of the incident light beam with respect to the optical axis of the objective lens, a wedge-shaped prism that holds the objective lens and the wedge-shaped prism, is movable back and forth in the focus direction of the objective lens, and emits light from the wedge-shaped prism. The optical system holder is rotatably arranged to change the inclination of the optical axis of the optical system.

FIG. 1 is a conceptual diagram showing the principle of the optical system used in the present invention. The center 105a of the light beam that has entered the lower surface of the wedge-shaped prism 15 at right angles is tilted by refraction and exits from the wedge-shaped prism 15. The magnitude of this inclination is determined by the inclination α (third
(see figure), that is, determined by the wedge angle and the refractive index of the wedge-shaped prism 15. When the wedge-shaped prism 15 is rotated, the direction of inclination of the emitted light from the wedge-shaped prism 15 changes, and the center of the emitted light rotates as shown as a locus 111. 105a' is the wedge-shaped prism 15 when the wedge-shaped prism has rotated half a turn and is in the state 15'.
It shows the direction of inclination of the luminous flux emitted from '.

In the present invention, instead of rotating the wedge-shaped prism 15 once, the wedge-shaped prism 15 is rotated by a small amount to change the inclination direction of the wedge-shaped prism 15 by a small amount, and this light beam is transferred to the objective lens 13.
lead to. Now, assuming that the center 105a of the light beam emitted from the wedge-shaped prism 15 coincides with the optical axis of the objective lens 13, the light beam is converged by the objective lens 13 and reaches a point 71a on the disk 71 where a recording track is formed. It is assumed that spot irradiation is being performed, and this state is defined as a neutral point. If the wedge-shaped prism 15 is rotated by a small amount in this state, the direction of inclination of the center of the light beam emitted from the wedge-shaped prism 15 will change]
, 05a#;'105a;;105a'#, and the objective lens 1 with the center of the light beam incident on the objective lens 13
The slope relative to 3 changes. Therefore, the spot irradiation position on the disk 71 by the objective lens 13 is 71b;
It moves in the tracking direction, that is, in the diametrical direction of the disk 71 as shown in l:j71a;71c, and can accurately irradiate a light spot onto a target recording track.

FIG. 2 is an explanatory diagram showing tracking control by obliquely entering the objective lens 13. Incident light 1
05 is the optical axis 107 of the objective lens 13.
The neutral point position is when it matches. Due to the rotation of the wedge-shaped prism 15, the center of the light flux of the incident light is tilted by θ with respect to the optical axis 107 of the objective lens 13 and becomes 105a'. If the focal length of the lens 13 is f, Δx
Move by j+=fXtanθ.

FIG. 3 is an explanatory diagram showing an example of an optical system used in the control device of the present invention. In order to make it easier to understand the principle of the present invention, in FIG. 1, the light beam is incident from the surface of the wedge-shaped prism 15 that is perpendicular to the rotation axis of the wedge-shaped prism 15, but in the optical system of FIG. , wedge prism 1
In order to make the rotational axis of the lens 5 parallel to the optical axis of the objective lens 13, a light beam is made to enter from the inclined surface 15a of the wedge-shaped prism 15. The recording disk 71 has recording tracks spirally or concentrically provided in its radial direction, and the radial direction is the tracking direction Tr. A light beam 105 from the light source is reflected by the upright mirror 11 and is tilted with respect to the optical axis 107 of the objective lens 13.
The light is incident on the wedge-shaped prism 15. 105a indicates the center of the luminous flux. FIG. 3 shows a case where the wedge-shaped prism 15 is at a neutral point, and the light beam incident on the wedge-shaped prism 15 has its output direction changed by its refractive power, and the center 105a of the light beam is the optical axis of the objective lens 13. 107. Here, when the wedge-shaped prism 15 is rotated, the direction in which the light beam 105 is tilted by the wedge-shaped prism 15 changes by a minute amount, and accordingly, the objective lens 13
The angle of inclination of the light beam 105 incident on the light beam 105 changes by a minute amount.

As shown in FIG. 2, when the optical axis of the objective lens 13 and the center 105a of the incident light 105 coincide, the incident light 10
5 is spot irradiated onto the disk 71 on the optical axis of the objective lens 13. When the incident light enters the objective lens 13 at an angle of θ with respect to the optical axis as indicated by 105', the spot imaging position on the disk 71 moves by ΔX in the tracking direction. In this way, the spot imaging position can be moved according to the inclination of the incident light 105. Therefore, by controlling the amount of rotation of the wedge-shaped prism 15, the irradiation position of the spot light from the objective lens 13 can be moved in the tracking direction (Tr) to follow the recording track. In this way, tracking drive is performed only by rotating the wedge-shaped prism 15, and the objective lens 1
There is no need to move 3 horizontally.

Further, as shown in FIG. 3, the center 105a of the light beam 105 incident on the rotating wedge-shaped prism 15 is tilted at a point P (hereinafter referred to as the tilt angle generation point), that is, the rotating first The incident position of the center of the light beam 105a onto the inclined surface 15a of the wedge-shaped prism I5 is made to coincide with the back focal point Fb of the objective lens 13. FIG. 4 is an explanatory diagram showing the behavior of reflected light from the disk in this state. Assume that the center +05a of the light beam is incident on the recording disk through the centers of the objective lenses O, L, and that the imaging position is moved by ΔX due to tracking control to follow the recording track. Then, when the tilt angle generation point P and the back focal point Fb coincide, the center of the incident light 101 and the reflected light 1
The center of 03 matches. Therefore, one reflected light 103 is incident on the center of the divided photodiodes P and D without any shift in the intensity distribution, and the apparent tracking error as explained in FIGS. 10A and 10B does not occur.Furthermore, According to the method of moving the imaging position in the tracking direction by making the objective lens enter the objective lens obliquely without moving the objective lens horizontally, even when the tilt angle generation point P and the back focal point Fb of the objective lens do not exactly match, , 10A and 10B, it is possible to reduce the apparent tracking error caused by the movement of the center of intensity of the incident light and the reflected light, compared to the horizontal movement method of the objective lens shown in FIGS. 10A and 10B. FIG. 5 is an explanatory diagram showing the amount of apparent tracking error. If the back focal point Fb and the tilt angle generation point P do not match, if the imaging position on the disk is moved by ΔX from the center point, the center of the reflected light 103 will be shifted from the center of the incident light 101 by ΔL□. This amount is determined by α, the distance between the back focal point Fb and the point of inclination P, and the objective lens 0. If the angle of incidence on L is θ, then ΔL□=2Q
-tanθ. ΔL2 in Figure 10B is 2
- Since ΔX, if the amount of movement ΔX of the imaging position is 30 μm, then ΔL2=60 μm. On the other hand, in FIG. 5, it is assumed that Q=1 mm and the focal length of the objective lens is 3+am.

θ=0.57', ΔL□=22 μm, and the apparent tracking error can be kept small.

Of course, 12=o is desirable, but within the required accuracy range, a large degree of freedom in design can be achieved.

FIG. 6 and FIG. 7 are drawings showing an embodiment of the optical spot control device of the present invention.

FIG. 6 is a plan view of FIG. 7 with the housing 21 removed.

FIG. 7 is a vertical sectional view taken along the line 0)gA-center o-B in FIG. 6 and expanded.

A hollow shaft body having a cylindrical rising portion 31a and a peripheral wall portion 31b is fixed to the housing 21. A permanent magnet 33 is attached to the peripheral wall portion 31b of the hollow shaft body 31, forming a magnetic circuit. That is, the hollow shaft body 31 having the cylindrical rising portion 31a and the peripheral wall portion 31b that face each other also functions as a yoke. In the cylindrical rising portion 31a of the hollow shaft body 31.

A cylindrical optical system holder 23 is fitted. An objective lens 13 and a wedge-shaped prism 15 are fixed to the optical system holder 23. The wedge-shaped prism 15 is arranged such that its inclination angle generation point P is located at the back focal point Fb of the objective lens 13.

The optical system holder 23 can move back and forth in the focus direction FO of the objective lens 13 by sliding the five cylindrical rising portions 31a in the vertical direction. Further, as shown by arrow R in FIG. 7, the optical system holder 23 has a cylindrical rising portion 31a.
It can be rotated around the axis. That is, the cylindrical rising portion 31a functions as a rotating and sliding axis of the optical system holder 23. A focusing coil 25 is wound around the outer peripheral surface of the cylindrical optical system holder 23, and a wound tracking coil 27 is fixed thereto (see also FIG. 8). When a signal current is supplied to the focus coil 25, a near motor is formed with a magnetic circuit consisting of a permanent magnet 33 and a hollow shaft body 31, and according to the signal current,
The optical system holder 23 is driven in the focus direction Fo, and the imaging position (focal position) of the objective lens 13 can be controlled so as to always be on the optical disk 71.

Further, a tracking coil 27 wound twice is fixed to the outer peripheral surface of the optical system holder 23 so that one coil flux running vertically intersects the magnetic flux from the permanent magnet 33. When a signal current is supplied to this tracking coil 27, a magnetic circuit consisting of a permanent magnet 33 and a hollow shaft body 31 forms a rotating motor, and the optical system holder 23 rotates in response to the signal current. do. In addition, focus coil 2
5 and the tracking coil 27 and the driving principle are basically the same as those of conventional actuators (No. 8
(see figure).

As shown in the optical system in Fig. 3, the luminous flux 105 from the light source
is reflected by the upright mirror 11 and tilted with respect to the optical axis 107 of the objective lens 13.

The light is incident on the wedge-shaped prism 15. 105a indicates the center of the luminous flux. 3 and 7 show the case where the wedge-shaped prism 15 is at a neutral point, and the direction of the light beam incident on the wedge-shaped prism 15 is changed by its refractive power, so that the optical axis 105a becomes the optical axis 107. Match. Here, when the wedge-shaped prism 15 is rotated, the direction of the light beam 105 changes by *lJ\ amount due to the wedge-shaped prism 15, and accordingly, the light beam 105 incident on the objective lens 13
The angle of inclination changes by a minute amount. Therefore, by controlling the rotation angle of the wedge-shaped prism 15, the irradiation position of the spot light from the objective lens 13 can be moved in the tracking direction (Tr) to follow the recording track. In this way, the tracking drive is performed only by rotating the wedge-shaped prism 15, and there is no need to move the objective lens 13 in the horizontal direction. Generation point P
, the occurrence of apparent tracking errors is prevented.

The objective lens 13 is driven back and forth in the focus direction Fo to adjust the imaging position, but since the objective lens 13 and the wedge-shaped prism 15 are held integrally, the positional relationship (distance) between them does not change. . Therefore, even when the focus is driven, the inclination angle generation point P of the wedge-shaped prism 15 does not deviate from the back focal point Fb of the objective lens 13.

Further, the displacement of the spot light irradiation from the objective lens 13 is linked to the rotation of the wedge-shaped prism 15, but its magnitude can be made smaller than the amount of rotation of the wedge-shaped prism I5. Therefore, even if the optical spot control device were to swing in the tracking direction during high-speed access and the wedge-shaped prism 15 would be rotated by this force, the effect would be alleviated.

Furthermore, by rotating and controlling the tracking of the wedge-shaped prism 15 provided at the front stage on the optical axis of the objective lens 13, the structure is such that weight imbalance with respect to the rotation axis is less likely to occur.

Therefore, compared to the conventional examples shown in FIGS. 8 and 9, it is possible to prevent swinging due to weight imbalance caused by acceleration applied during high-speed access, and since a large balancer is not required, the movable part of the actuator is This also leads to overall weight reduction. In addition, the reality is that it is impossible to completely eliminate weight imbalance due to variations in parts and manufacturing processes, but in this case as well, the mass point is mostly concentrated on the rotation axis, so the moment of inertia is small. Even if there is some weight imbalance, it is unlikely to cause rocking during high-speed access.

Further, since the objective lens 13 and the first wedge-shaped prism 15 are driven integrally, the configuration is simple and the weight of the entire device can be reduced.

According to the present invention, a wedge-shaped prism is provided in front of the objective lens, and the wedge-shaped prism allows a beam of light to enter the objective lens obliquely, thereby integrating the wedge-shaped prism and the objective lens. By rotating and changing the inclination of the incident light to the objective lens to control the imaging position in the tracking direction, swinging during high-speed tracking access is prevented.
The device can be made faster and lighter.

[Brief explanation of the drawing]

1 and 2 are drawings showing the principle of the tracking control method used in the present invention. FIG. 3 is an explanatory diagram showing the optical system used in the present invention. FIGS. 4 and 5 are explanatory diagrams illustrating apparent tracking errors. FIG. 6 is a plan view showing an embodiment of the optical spot control device of the present invention, and FIG. 7 is a longitudinal sectional view. FIG. 8 is a perspective view showing a conventional example, and FIG. 9 is a sectional view showing a state in which it is fitted onto a rotation shaft. FIGS. 10A and 10B are explanatory diagrams showing apparent tracking errors in the conventional example. 11... Raising mirror ]3... Objective lens 15
... Wedge-shaped prism 21 ... Housing 23 ...
・Optical system holder 25...Focus coil 27・
・Tracking coil 3】・・・Hollow shaft body 33・Magnet 61・Holding body 63・Balancer 65・・Fitting hole
67...Mating shaft (Figure 3, Figure 4, Figure 6, Figure〉B, Figure 7, Figure 8, Figure 10A, Figure 11, 11]) λsc0, L. Figure 10B

Claims (1)

[Scope of Claims] 1. An objective lens for irradiating light onto a recording medium; and an objective lens rotatably provided in front of the objective lens, which imparts an inclination to the incident light beam and outputs it, and directs the incident light beam to the objective lens. It holds a wedge-shaped prism that changes the inclination of the lens with respect to the optical axis, an objective lens, and a wedge-shaped prism, and is movable back and forth in the focus direction of the objective lens. 1. A light spot control device comprising: an optical system holder rotatably arranged to change the light spot. 2. The light spot according to claim 1, wherein the wedge-shaped prism is arranged so that the part of the wedge-shaped prism that gives the inclination to the center of intensity of the incident light beam is located at or near the back focal point of the objective lens. Control device.