JPS59189306A - Focusing mechanism - Google Patents

Abstract

PURPOSE:To enable easy focusing without driving a large objective lens by constituting a titled mechanism of the objective lens, parallel lens and focusing lens and driving the focusing lens in the optical axis direction. CONSTITUTION:The laser beam past an objective lens 9 is focused on the plane of an optical tape 10 and the laser beam reflected therefrom returns in the same route. When the tape 10 fluctuates, a focusing lens 5 is moved in the same direction where the tape 10 fluctuates, thereby focusing the beam on the plane of the tape 10. The relation between the displacement Z of the tape 10 and the displacement x of the focusing lens is made equal and the focusing is accomplished by moving the displacement x by as much as the displacement Z at which the tape 10 moves. The focal depth of the objective lens is + or -3.5mum, which indicates that a + or -3.5mum error is permitted in moving the lens 5.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a focusing mechanism, and particularly relates to a focusing mechanism that uses a lens other than an objective lens, which is suitable when it is difficult to drive the objective lens greatly for focusing. It relates to a focusing mechanism that is driven and focused.

[Background of the invention]

In recent years, digital memory has been attracting attention as a new type of digital memory. One of the characteristics of optical memory is its low cost.

In the past, contactless recording and playback, semi-permanent storage life, etc. were mentioned. For example λ, an optical tape device can be considered as a specific example of an optical memory. The optical tape device is an optical tape device 110 in which the optical recording material shown in (1) is deposited on a tape-like material.
This is a device that uses a laser beam to record information as holes on the same surface, detects whether there are holes using the laser beam, and reproduces the recorded information. An optical mechanism for realizing an optical tape device requires a focusing mechanism for focusing on the optical tape 10 surface and a scanning mechanism for moving a light spot onto the optical tape 10 surface. The direction in which the light spot is moved on the optical tape 10 is the tracking direction D shown in FIG.
! and a scanning direction D2. ! In particular, the scanning mechanism needs to scan in the scanning direction about the width of the optical tape 10.

A laser printer is an example of a device that scans a light spot over a large distance, and an optical disk device is an example of a device that records and reproduces information on an optical recording material.

FIG. 2 is an explanatory diagram of the laser printer. A laser printer scans a light spot on a photosensitive paper by reflecting a laser beam by a polygon mirror 19 and passing it through a doublet spherical lens 18. Laser printers have very long focal lengths to increase scanning distance.

Therefore, since the diameter of the doublet spherical lens 18 is very rectangular compared to the focal length, the reflected light does not return. It can be seen that this optical mechanism cannot be applied to an optical tape device that reproduces recorded information using reflected light.

An optical disk device, like an optical tape device, is a device that records and reproduces information using a laser beam.

FIG. 3 is a diagram showing the principle of the optical disk device N. The laser beam is reflected by the galvanometer mirror 14 and is made incident on the objective lens 16 to move the light spot onto the surface of the optical disk 15. When the galvano mirror 14 is tilted by θ/2, the light spot changes to α
It moves by about tanθ. In order to focus on the surface of the optical disk 15, the objective lens 16 is moved in the direction normal to the surface of the optical disk 15.

The moving distance t of the light spot of the optical disk device is approximately several hundred μm. The scanning distance of the optical tape device is at least several ■
This degree is necessary! ,! It cannot be used with the optical mechanism of the optical disk device f. Travel distance t of light spot
The reason why it cannot be obtained for a long time is because of the objective lens 16 of the optical disk device.
This is because the angle of view is narrow. If the resolution is kept the same as that of the objective lens 16 of the optical disk device and both corners are widened, the size of the lens becomes larger. A mechanism for moving a large lens to focus on the surface of the optical tape 10 on the μm order is difficult.

As described above, the optical system of a laser printer cannot be used as an optical system for an optical memory because the reflected light does not return, and the optical system of an optical disk device cannot be used because the distance traveled by the light spot cannot be increased.

[Purpose of the invention]

An object of the present invention is to provide a focusing mechanism that can focus by driving a focusing lens other than the objective lens when it is difficult to drive the objective lens.

[Summary of the invention]

Since it is difficult to focus by driving a large objective lens, another small focusing lens is driven to facilitate focusing. FIG. 4 is a block diagram of the focusing mechanism of the present invention.

The present invention includes an optical member 20 for deflection that moves a light spot in the tracking direction, a lens 5 for focusing, a lens 7 for enlarging the light and making it almost parallel to the lens 9, and a light beam in the scanning direction. It consists of an optical member 21 for deflection to scan the spot and a lens 9 for focusing.

Lens 5, lens 7, and lens 9 will be referred to as focusing lens 5, parallel lens 7, and objective lens 9, respectively.
The focal length of each is f5 + f7 +
Let it be f9. It is assumed that the light from the light source side enters as almost parallel light, but here, to simplify the explanation, it will be assumed that the light enters as parallel light.

Furthermore, the optical members 20 and 21 that deflect the two optical axes can be omitted in the description of the present invention without causing any problems, so they will be omitted. FIG. 5 shows a diagram of the principle of operation of the present invention in which the optical member for deflecting the optical axis is omitted.

The distance is set so that the distance y between the optical tape 10 and the objective lens 9 becomes the focal length f9. When the incident light is parallel light, the distance is the sum of the focal lengths f5 and f7. However, the five focusing lenses can be driven as necessary.

The distance C between optical axes will be explained later. The reason why the objective lens 9 focuses at the focal length f9 is that the lens is designed based on the condition that the incident light is parallel light. A case in which the optical system is designed based on a state in which the distance y is f9 with the arrow direction in FIG. 5 as the positive focal direction will be described below.

If the position of the optical tape 10 does not change from the reference state,
The light that has entered the focusing lens 5 as parallel light is expanded by the parallel lens 7 and becomes parallel light. The reason for the expanded parallel light is the effective NA (numerical aperture) of the objective lens 9.
This is to ensure that The expanded parallel light is incident on the objective lens 9 and focused on the optical tape 10 surface.

The light reflected by the optical tape IOK returns along the same path.

If the position of the optical tape 10 has changed by a displacement Z from the reference state, the focusing lens 5 is moved by a displacement X to focus on the surface of the optical tape 10. From FIG. 5, the following relational expression is established.

1/(f9+Z)+1/a=1/f9 ・---・
(1)-1/(a-C)+1/(f7-X)=1/f7
・・・・・・・・・・・・(2) X<f7 ・・・・・・・・・・・・River・
・・・・・・(3) Z < f s
・・・・・・・・・・・・・・・・・・・・・(4)
Solving for X from equations (1) and (2), x = f”l
・Z/((f7+f9-C) -z+f: ) -(
5). If the distance C is the sum of f7 and f9, equation (5) is X = (f7/f9)2・Z...
...(6). From equations (3) and (6), Z〈(f9/f7)・f9...
...becomes a river (7). When the distance between optical axes is the sum of f7 and f9, the relationship between X and Z is directly proportional. Sensitivity f7 and f9
It can be the square of the ratio of f7 (when fg (4
), and when f7≧f9, the sensitivity can be changed by selecting f7 and f9 that satisfy the equation (7).

When the distance C between optical axes is different from the sum of f7 and f9, equation (5) is x=f/(fy+fe C) 10fLf:/II-((h+fs CLZ+f:)・
(fy+fe-C)) ・・・・・・・・・
...(8). When the distance C between optical axes is different from the sum of f7 and f9, the relationship between X and Z becomes nonlinear.

The principle of operation of the present invention shown in FIG. 6 shows a case where a focal length (9) of the focusing lens 5' is negative. The focal length of this focusing lens 5' is f
5, an equation is established based on the principle shown in FIG. In FIG. 6, equation α) and equation (2) in FIG.

Equation (4) is the same as Equation (3), but Equation (3) is different. The formula corresponding to formula (3) is f7)x−f5 ・・・・・・・・・・・・
・It becomes (9). When the distance C between optical axes is the sum of f7 and f9, from equations (6) and (9), Z<(fs/h)"・(fy+fs)...
・・・・・・αO. If the distance between optical axes C is the sum of f7 and f9, then Xl! :The relationship between Z is directly proportional. Sensitivity f
It can be the square of the ratio of 7 and f9. (4) Formula and 0
Sensitivity can be changed by selecting f5, f7, and f9 that satisfy both equations.

[Embodiments of the invention]

Next, a specific embodiment of the focusing mechanism of the present invention will be described using FIGS. 7 and 8. FIG. 7 is a front view, and FIG. 8 is a side view. optical tape 10
The optical tape device has a width of 8 m+ and uses a galvanometer mirror as an optical component to deflect the optical axis (10).

A laser beam is generated from laser 1 and collimated lens 2
is incident on the The laser beam, which has been made into parallel light by the collimating lens 2, is incident on the beam splitter 3. The laser beam that has passed through the beam splitter 3 is incident on a λ/4 plate 4, where the linearly polarized light is converted into elliptically polarized light. When the reflected light returns to the λ/4 plate 4, the reflected light changes from elliptically polarized light to linearly polarized light.

The incident laser beam is a P wave, and the reflected laser beam is an S wave. The reflected light is separated from the incident light by a beam splitter 3 which has the property of separating S waves and P waves, and is detected by an optical detector 3.

The optical mechanism at this size is the same as an optical disk device. λ
The parallel light that has passed through the /4 plate is incident on a galvanometer mirror 6 that moves in the tracking direction shown in FIG. The incident parallel light has a diameter of 4 mm. The reason why the laser beam is set to 4Wφ is to make the optical element smaller and reduce cost, and to facilitate position control. Since a laser beam having a diameter of 4 mm is incident, the mirror mirror 6 is a rectangular mirror with sides of 8W+ and 6ttvn. The laser beam, which is parallel light, is a galvanometer mirror.
6 and remains parallel to the focusing lens 5.
is incident on the Since it is sufficient to move the light spot by about 50 μm in the tracking direction shown in FIG. 1 using the galvanometer mirror 6, the focusing lens 5 should be equivalent to the objective lens of an optical disk device, with a focal length of 8 cm and a NA (numerical aperture).
is 0.45, weight is about 1g, diameter is 8mm, length is 1
Let it be a 0+o+ convex lens. The laser beam that has passed through the focusing lens 5 is incident on the parallel lens 7. The parallel lens 7 and the focusing lens 5 are set to approximately the sum of the focal lengths of the focusing lens 5 on the basis of the case where the optical tape 10 is at the focal position of the objective lens 9. The focusing lens 5 can be driven in the optical axis direction and its distance can be changed as required. Parallel lens 7 is objective lens 9
The parallel lens 7 will be explained using the objective lens 9, assuming that the same lens is used. The laser beam that has passed through the parallel lens 7 is incident on the galvanometer mirror 8. Galvano (12)
) The mirror 8 scans the light spot in the scanning direction shown in FIG. The focal length of the parallel lens 7, which will be explained later, is 2.
Since the power is 8.7W+, the laser beam has a diameter of 14.9 mm. Therefore, the galvanometer mirror 8 is a rectangle with each side having 30 power and 17 W+. The disadvantage is that the galvano mirror 8 becomes large. The laser beam reflected by the galvanometer mirror 8 is incident on the objective lens 9. Parallel lens 7 and objective lens 9
The distance between the optical axes of is set by the sum of the focal lengths of each lens. In this example, it is necessary to provide a distance between optical axes of 57.4 wR.

Parallel lens and 9 objective lenses, focal length 28.7m.

NA (numerical aperture) is 0.28, image size is 81WIIφ,
Effective diameter: 19mm, weight: 400g, diameter: 45mm
, 70 fins long. The laser beam passing through the objective lens 9 is focused on the surface of the optical tape 10, and the reflected laser beam returns along the same path. When the optical tape 10 moves, the focusing lens 5 is moved in the same direction as the direction in which the optical tape 10 moves to focus on the surface of the optical tape 10. (5
) From the equation (13), the relationship between the displacement Z of the optical tape 10 and the displacement X of the focusing lens is equal, and the displacement
You can focus by moving. Since the depth of focus of the objective lens is ±3.5 μm, there may be an error of ±3.5 μm in moving the focusing lens 5.

Note that if the focusing lens can be driven in two directions: the optical axis direction and the tracking direction shown in FIG. 1, the galvanometer mirror 6 for deflecting the optical axis can be omitted.

In the method of directly driving the objective lens of an optical disk device, the objective lens 9, which weighs 400 g, has a diameter of 45 mφ, and is 70 m long, must be driven by the displacement Z of the optical tape 10. Approximately 1g, diameter 8m+
Focusing can be easily achieved by simply moving the focusing lens 5 with a length of 10 m.

Further, in the description of the present invention, the case where the objective lens 9 is large is shown, but the present invention can be applied even when the objective lens 9 is small.

However, the parallel lens 7 becomes a lens as small as the objective lens 9, and the role of sending approximately (14) parallel light to the objective lens r9 remains the same.

〔Effect of the invention〕

According to the present invention, in an optical mechanism that scans a large light spot, when it is difficult to focus by directly driving the objective lens, it is possible to focus by driving a small focusing lens, which has the effect of increasing focusing accuracy. be.

[Brief explanation of drawings]

FIG. 1 is a conceptual diagram explaining an optical tape in an optical memory device, FIG. 2 is a principle diagram explaining an outline of a laser printer,
FIG. 3 is a principle diagram showing the method of focusing the optical disk device and moving the light spot, FIG. 4 is a diagram explaining the configuration of the focusing mechanism of the present invention, and FIGS. 5 and 6 are the focal points of the present invention. FIGS. 7 and 8 are diagrams showing the operating principle of the focusing mechanism, and are diagrams showing embodiments of the focusing mechanism of the present invention. 1...Laser, 2...Collimating lens, 3...
Beam splitter, 4... λ/4 plate, 5... Focusing lens, 6, 8.14... Galvano mirror 17.
...Parallel lens, 9.16...Objective lens, 10...
・Optical tape, (15) 11.12... Galvano mirror drive motor, 13.
...Optical detector, 15... Optical disc, 17...
Drum, 18-° doublet spherical lens, 1
9... Polygon mirror, 20.21... Optical member that deflects the optical axis. (16) %5 Figure 7 Figure 3

Claims (1)

[Claims] 1. An optical mechanism that makes parallel or nearly parallel light incident and focuses it on an object using a lens, which includes at least one
A focusing mechanism comprising two objective lenses, at least one parallel lens, and at least one focusing lens, the focusing mechanism being characterized in that the focusing lens is driven in an optical axis direction to focus. 2. The focus according to claim 1, characterized in that a focusing lens is set on the light source side, an objective lens is set on the object side, and a parallel lens is set between the focusing lens and the objective lens. Matching mechanism. 3. The focusing mechanism according to claim 2, further comprising an optical component inserted between the parallel lens and the objective lens to deflect the optical axis and scan the light spot. 4. The focusing mechanism according to claim 2 or 3, characterized in that the focusing lens is configured to be able to be driven in two directions: the optical axis direction and the tracking direction. 5. Set the focal length of the parallel lens and objective lens to f7.
and fs, the focusing mechanism according to any one of claims 2 to 4, wherein the distance between the optical axes is fixed to the sum of f7 and fs. . 6. When parallel light is incident from the light source side, the focal lengths of the focusing lens and the parallel lens are 'II + f, respectively.
7, the distance between the optical axes of the focusing lens and the parallel lens is set to approximately the sum of fs and f7.
Focusing mechanism as described in Section. 7. Let the displacement of the focusing lens be X with the variation of the object being 2.
When fs〉o, (f9/ft)・fs〉
Z and fs>Z, and when fs<O (f9
/f7)2・(h10f5)>Z and fs:>Z The focal point according to any one of claims 2 to 6, characterized in that it is configured to satisfy the following conditions: Matching mechanism.