JPH10247215A - Optical path length variable element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To vary an optical path length in an image-forming optical system and to easily control focusing. SOLUTION: Bellows 13 which can be extended/contracted in an axial direction forming a water tight space are provided between two transparent glass plates 11 and 12 which are oppositely arranged. Optical refraction liquid 16 is filled in the water tight space. The two glass plates 11 and 12 are relatively moved in parallel by a driving mechanism constituted of a yoke 19, coils 20 and 21 and a permanent magnet 22. The length (thickness) of the optical axis direction of optical refraction liquid 16 is changed by extending/contracting the bellows 13 and moving the two glass plates 11 and 12 in parallel. When an automatic focus mechanism is constituted by using the optical path variable element, the mechanism for driving the lens of the image-forming optical system is not required and the automatic focus mechanism of simple constitution can inexpensively be constituted.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an element for changing an optical path length, and more particularly to an optical path length variable element suitable for controlling a focal position in an imaging optical system.

[0002]

2. Description of the Related Art In recent years, optical apparatuses having an image forming optical system are often provided with an automatic focusing mechanism for automatically focusing an image forming position. However, in this automatic focusing mechanism, the lens constituting the imaging optical system is moved in the direction of the optical axis to perform focusing, so that the mechanism is complicated, and it is difficult to adopt the simple configuration and low-cost optical equipment. For this reason, a configuration is adopted in which focusing is performed by narrowing the imaging optical system to increase the depth of field. For example,
In non-contact two-dimensional code readers, the range of focusing with the required resolution is expanded by designing the aperture of the optical system for imaging the bar code to be the subject to be a small aperture, and within this range If the bar code is located at the position, it can be read. For this reason, an automatic focusing mechanism becomes unnecessary, and cost reduction can be realized.

[0003]

However, when the aperture is set to a small aperture, the formed image naturally becomes dark,
The light receiving output of a light receiving element such as a CCD is reduced. For this reason, lighting for illuminating the barcode side brightly is required, which leads to an increase in power consumption.
In addition, a light-receiving element that requires high sensitivity or a high-gain amplifier circuit is required, which eventually increases the component cost, which is an obstacle to reducing the price.

An object of the present invention is to make it possible to adjust an image forming position by making an optical path length in an image forming optical system variable, thereby realizing substantial focusing control without providing an automatic focusing mechanism. It is an object of the present invention to provide an optical path variable element having a simple configuration capable of performing the following.

[0005]

According to the present invention, there are provided two light-transmitting transparent plates which are arranged on the optical path in the direction of the optical axis, and a liquid-tight transparent plate interposed between the transparent plates. An axially expandable bellows defining a space, a photorefractive liquid filled in the liquid-tight space, and a drive mechanism for relatively translating the two transparent plates are provided. The drive mechanism includes a coil provided on one of the transparent plates,
A permanent magnet provided on the other transparent plate side, wherein the transparent plate is relatively moved by a force generated when a coil is energized in the magnetic field of the permanent magnet. In this case, the coil and the permanent magnet are disposed around the bellows and formed at a position surrounding the bellows, preferably in a concentric annular shape, and the coil is formed by a winding arranged in the axial direction. Preferably, the permanent magnet is configured to be magnetized in the axial direction. In this case, it is preferable that the coil is divided into two in the axial direction corresponding to the N pole and the S pole in the axial direction of the permanent magnet, and wound in opposite directions in each divided region. In addition, an elastic member for absorbing a volume change of the liquid accompanying the expansion and contraction of the bellows is provided in a part of the bellows.

[0006]

Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing the entire configuration of an embodiment in which the optical path variable element of the present invention is applied to a non-contact two-dimensional code reader. The non-contact two-dimensional code reader includes an image forming optical system 1 for forming an image of a bar code BC, a CCD 2 arranged at an image forming position of the image forming optical system 1, and the image forming optical system 1. An optical path variable element 3 disposed between the CCD 2 and the optical path variable element for varying the image forming optical path length.
A half mirror 4 disposed in front of the CCD 2 to reflect a part of the image forming light in a right angle direction, and a splitting prism 5 for splitting the image forming light reflected by the half mirror 4
And a photodetector 6 on which the divided imaging light is formed.
It is composed of

This non-contact two-dimensional code reader forms a bar code BC at a subject position on a CCD 2 by an imaging optical system 1 and reads the bar code BC based on an image signal output from the CCD 2. Can be. A part of the light imaged by the imaging optical system 1 is reflected by the half mirror 4, is split into two by the splitting prism 5, and is imaged on the photodetector 6. The photodetector 6 can detect the in-focus state based on the relative position of the two formed images. Based on the detection result of the in-focus state, the control circuit 7 determines the amount of change in the optical path in the And the focusing control of the image formation in the CCD 2 is performed.

FIG. 2 is a diagram showing the internal structure of the optical path variable element 3,
FIG. 3 is a partially cutaway perspective view. The variable optical path element 3 includes a transparent first glass plate 11 having a circular shape and a transparent second glass plate 12 having a diameter slightly smaller than the first glass plate.
Are arranged opposite to each other in the thickness direction thereof, and a circular bellows 13 is interposed between the two glass plates 11 and 12. Both ends of the circular bellows 13 are respectively connected to the first and second glass plates 11. , 12 are closely fixed via annular retainers 14, 15. The circular bellows 13 is formed of a liquid-tight material, and is filled with a transparent liquid 16 having a light refractive index different from that of air. Here, of the retainers, the retainer 14 on the first glass plate 11 side has a U-shaped cross section inward, and an elastic film of rubber or the like is provided on the inner peripheral side thereof. The formed deformation film 17 is stretched. An air hole 18 is formed in a part of the outer peripheral surface to connect the outside of the deformable film 17 and the inside of the retainer 14 to the outside.

On the other hand, a short cylindrical yoke 19 is integrally attached at one end to the first glass plate 11 at the peripheral edge of the first glass plate 11.
A first coil 20 and a second coil 21 are supported side by side in the cylinder axis direction on the inner peripheral surface of the. The first coil 20 and the second coil 21 are set so as to be located in a magnetic field of a permanent magnet 22 described later.
A current controlled by the control circuit 7 (see FIG. 1) flows through 21. In this case, the winding directions of the coils 20 and 21 are reversed, or the direction of the DC current applied to the coils 20 and 21 is reversed, so that the coils 20 and 21 are opposite to each other in the above-described magnetic field. It is configured such that current flows. The first and second coils 20,
A short cylindrical permanent magnet 22 having an outer diameter smaller than the inner diameter of the permanent magnet 21 is disposed, and the permanent magnet 22 has a cylindrical axis aligned with the cylindrical axis of each of the coils 20 and 21. One end is fixed to the inner surface of the second glass plate 12. The permanent magnet 22 is connected to the yoke 1 described above.
9 cooperate with each other to generate magnetic fields in opposite directions to each of the coils 20 and 21.

In the non-contact two-dimensional code reader, the optical path variable element 3 is installed such that the first glass plate 11 is supported by a device fixing portion (not shown), and the first and second glass plates are provided. The liquid 16 filled in the bellows 13 with the liquids 11 and 12 is arranged at the optical axis position of the imaging optical system 1 so that the optical axis of the imaging optical system 1 and the center thereof substantially coincide with each other. In this state, the S pole generated at the tip of the cylindrical permanent magnet 22 and the N pole generated at the base end are
The poles are located inside the first coil 20 and the second coil 21, respectively. For this reason, when the first coil 20 and the second coil 21 are energized through the control circuit 7 and a current in the opposite direction is passed through each coil, as shown by arrows in FIG. Are located in mutually opposite magnetic fields generated between the permanent magnet 22 and the yoke 19, and therefore, according to Fleming's left-hand rule, each coil 20, 21 has a direction orthogonal to these magnetic fields and the winding direction of the coil. That is, a force is generated in a direction to extend or shorten the bellows 13. However, each coil 2
Since 0 and 21 are fixed by the first glass plate 11, the permanent magnet 22 in the movable state is moved in the axial direction, and accordingly, the second glass plate 12 integral with the permanent magnet 22 is moved to the bellows 13. While expanding and contracting the first glass plate 1
1 is moved in the thickness direction.

In such a configuration, the bar code BC on the object side of the non-contact two-dimensional code reader of FIG.
Is imaged by the imaging optical system 1, the imaged light passes through the liquid 16 in the bellows 13 of the optical path variable element 3 and is imaged on the CCD 2 and the photodetector 6. . The variable optical path element 3 includes a first glass plate 11 and a second glass plate 11.
Since the glass plate 12 and the transparent liquid 16 interposed therebetween function as a parallel flat plate, the optical path length is effectively increased by an optical path corresponding to the thickness and the light refractive index. To be precise, the thickness of each of the first and second glass plates 11 and 12 and the refractive index thereof, and the bellows 1
It is determined by the length of the liquid 16 in the direction 3 in the optical axis and its light refractive index.

Therefore, of the light formed by the image forming optical system 1, the light reflected by the half mirror 4 is split into two by the splitting prism 5, detected by the photodetector 6, and
When a detection output corresponding to the relative positions of the two images is input to the control circuit 7, the controlled current is output from the control circuit 7 to the first circuit.
And the second coils 20 and 21 flow. Then, the permanent magnet 22 and the second glass plate 12 are moved in the axial direction in accordance with the amount of electricity, and the bellows 13 is expanded and contracted in the axial direction to change its axial length. Thereby, as schematically shown in FIG. 4, the axial length of the liquid is changed and the optical path length is changed, so that the imaging positions P1 and P2 by the imaging optical system are changed by the optical path length Δ. Will be. Therefore, the control circuit 7 performs the feedback control of the optical path variable element 3 based on the image formation output of the photodetector 6, so that the bellows length can be appropriately controlled and the image formation can be focused.

The bellows 13 expands and contracts in the axial direction with the movement of the second glass plate 12, and the liquid 16 filled in the bellows 13 deforms the film provided on the retainer 14 in accordance with the expansion and contraction. By deforming the bellows 17, its volume change is absorbed, and the bellows 13 can be expanded and contracted. The first and second coils 20 and 21 and the permanent magnet 2
2 has an annular shape, in particular, an annular shape in this embodiment, the magnetic force is generated equally in the circumferential direction, and the second glass sheet 1 is formed.
2 can be relatively moved in a state parallel to the first glass plate 11. Further, since the driving mechanism can be arranged around the optical axis, the size of the device can be reduced. However, when high precision is required by this parallel movement, a guide mechanism for ensuring parallel movement may be provided between the two glass plates.

As described above, by using the variable optical path element of the present invention, focusing in the image forming optical system can be realized by expanding and contracting the bellows. Therefore, the configuration can be simplified as compared with the automatic focusing mechanism that drives the lens of the imaging optical system, and a low-cost focusing mechanism can be realized. Further, since focusing is possible, there is no need to reduce the aperture, and illumination with high illuminance and a light-sensitive element with high sensitivity are not required, and low cost can be maintained.

In the above embodiment, the mechanism for moving the second glass sheet with respect to the first glass sheet is used. However, the mechanism for moving the first glass sheet with respect to the second glass sheet is used. It may be. That is, the coil side may be moved.

It is needless to say that the optical path variable element used in this embodiment may be arranged on the object side of the imaging optical system. Further, if a liquid of a required material is used as the liquid to be filled in the bellows, it can be used as a concentration or spectral filter.

[0017]

As described above, the present invention relates to a bellows which can be expanded and contracted in the axial direction which defines a liquid-tight space between two light-transmitting transparent plates disposed opposite to each other. Is filled with a photorefractive liquid in the liquid-tight space, and 2
Since the transparent plates are relatively moved in parallel by a drive mechanism including a coil and a permanent magnet, the length (thickness) of the photorefractive liquid in the optical axis direction is changed by expanding and contracting the bellows. Thereby, the optical path length depending on the refraction of light can be arbitrarily changed. Therefore, if an automatic focusing mechanism is configured using this variable optical path element, a mechanism for driving the lens of the imaging optical system is not required, and a simple configuration of the automatic focusing mechanism can be constructed. In addition, it is not necessary to use a small aperture for increasing the depth of field, so that illumination with high illuminance and a light receiving element with high sensitivity are not required, and cost reduction can be realized. Further, since the relative force generated between the coil and the permanent magnet is used as the drive mechanism, the drive mechanism can be reduced in size and weight, which is advantageous in reducing the size of the optical device to which the present invention is applied. It will be.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram of a non-contact two-dimensional code reader to which a variable optical path element according to the present invention is applied.

FIG. 2 is a sectional view of an embodiment of an optical path variable element according to the present invention.

FIG. 3 is a perspective view in which a part of the variable optical path element of FIG. 2 is cut away.

FIG. 4 is a schematic diagram for explaining the operation of the present invention.

[Explanation of symbols]

 Reference Signs List 1 imaging optical system 2 CCD 3 optical path variable element 4 half mirror 6 photodetector 7 control circuit 11 first glass plate 12 second glass plate 13 bellows 16 liquid 19 yoke 20 first coil 21 second coil 22 permanent magnet

Claims (5)

[Claims] An optical system having an optical axis has two light-transmitting transparent plates opposed to each other in the direction of the optical axis on an optical path, and interposed between the transparent plates and between the two transparent plates. An axially expandable and contractable bellows that defines a liquid-tight space, a photorefractive liquid filled in the liquid-tight space, and a drive mechanism that relatively translates the two transparent plates, The driving mechanism is configured by a coil provided on one transparent plate side and a permanent magnet provided on the other transparent plate side, and a force generated when the coil is energized in the magnetic field of the permanent magnet. An optical path length variable element configured to relatively move the transparent plate. 2. The coil and the permanent magnet are arranged around the bellows and arranged at a position surrounding the bellows, and the coil is constituted by a winding arranged in the axial direction, 3. The variable optical path length element according to claim 2, wherein the magnet is magnetized in the axial direction. 3. The variable optical path length element according to claim 2, wherein the coil and the permanent magnet are arranged concentrically and annularly around the bellows. 4. The coil has a north pole in the axial direction of a permanent magnet,
4. The variable optical path length element according to claim 2, wherein the element is divided into two parts in the axial direction corresponding to the south pole, and wound in opposite directions in each divided area. 5. The variable optical path length element according to claim 1, wherein an elastic member is provided at a part of said bellows for absorbing a volume change of a liquid accompanying expansion and contraction of the bellows.