JPH0518084B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical device that achieves an autofocus function by deforming an optical surface made of an elastic body.

2. Description of the Related Art Conventionally, devices with an autofocus function have been widely used in cameras, optical disk devices, optical measurement devices, and the like. In such an optical device, focusing is performed by mechanically moving part or all of the imaging lens along the optical axis direction. In such a mechanical focusing mechanism, the driving mechanism for the lens that is moved for focusing tends to be large in size, and it is difficult to obtain extremely fast response.

Furthermore, conventionally, as a method for changing the focal length of an imaging optical element without moving optical members such as lenses or mirrors, a liquid is placed in an elastic container as shown in Japanese Patent Application Laid-Open No. 55-36857. There are those that change their shape using the hydraulic pressure, and those that
56-110403 and Japanese Patent Application Laid-Open No. 58-85415, devices using piezoelectric materials have been proposed.

However, the former so-called liquid lens requires a liquid reservoir, a pressurizing device, etc. and has a problem in making the element compact, while the latter has the disadvantage that its variable amount cannot be made very large.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned drawbacks and to provide an optical device having a variable focus mechanism with a simple configuration and good responsiveness.

The above object includes a container having an opening, a transparent elastic body housed in the container, and means for applying an external force to the elastic body, and the shape of the elastic body is changed by the means for applying the external force. The optical member has a structure in which the optical surface formed by the elastic body at the opening is changed by causing the elastic body itself to protrude or sink from the opening, thereby making the focus variable. An automatic focus comprising: a focus state detection means for detecting a focus state, and controlling the shape of the optical surface of the optical member according to a signal detected by the focus state detection means. This is accomplished by an optical device.

The elastic body of the optical member used in the optical device of the present invention deforms when force is applied to the object, and as long as the applied force is not too large (within the elastic limit),
It is possible to use a material that has a property (elasticity) of returning to its original state after deformation when the force is removed.

In a normal solid, the maximum strain (critical strain) within its elastic limit is about 1%. In addition, vulcanized elastic rubber has a very large elastic limit, and its limit strain is close to 1000%.

The elastic material has an elastic modulus depending on the characteristics of the optical device to which it is applied, and is generally used to easily obtain large elastic deformation or to make the state after deformation optically more homogeneous. Therefore, a material with a small elastic modulus is preferable.

In addition, the elastic modulus (G) is G=ρ/γ (ρ=stress,
γ=elastic strain). Further, elasticity that causes large deformation with small stress is called high elasticity or rubber elasticity, and therefore, this type of elastic body can be particularly preferably used in the device of the present invention.

Generally speaking, “rubber” is used as such a rubber elastic body.
Natural rubbers known as styrene butadiene rubber (SBR), butadiene rubber (BR), isoprene rubber (IR), ethylene propylene rubber (EPM, EPDM), butyl rubber (IIR), chloroprene rubber (CR), acrylonitrile Butadiene rubber (NBR), urethane rubber (U), silicone rubber (Si), fluorine rubber (FPM), polysulfide rubber (T), polyether rubber (POR, CHR, CHC)
etc. can be mentioned. All of these exhibit a rubbery state at room temperature. However, in general, polymeric substances take either a glass state, a rubber state, or a molten state, depending on the degree of Brownian motion of the molecules. Therefore, a polymeric substance exhibiting a rubbery state at the temperature at which the optical element is used can be widely used as an elastic body applied to the optical device of the present invention. The elastic modulus in the rubber state is mainly determined by the crosslinking state of the polymer chains that make up the elastic body, and therefore, for example,
Vulcanization of natural rubber is nothing but a process that determines its elastic modulus.

As for the elastic body, it is desirable to obtain large deformation with small stress, and for this purpose, adjustment of the crosslinking state is important. However, the decrease in elastic modulus (the tendency to exhibit large deformations at small stresses)
On the other hand, since this leads to a decrease in strength, it is necessary to appropriately select the elastic body to be used so that the strength can be maintained in accordance with the purpose of the optical element to be formed.
The elastic modulus is also measured by, for example, tensile, bending, or compression methods, depending on the type of stress depending on the usage of the optical member.

The elastic body has the elastic modulus of a normal solid.
10 ¹¹ ~ 10 ¹³ dyne/cm ² smaller than the rubber elastic material
Appropriately 10 ⁸ dyne/cm ² or less, preferably 10 ⁶
dyne/cm ² or less, particularly preferably 5×10 ⁵ dyne/cm ²
The lower limit is preferably as small as possible as long as the elastic body has a property of not spilling when the elastic body constitutes an optical member, unlike a normal liquid. Note that although optical devices are often used at room temperature, they may also be used at particularly high or low temperatures, so the above range of elastic modulus is at the operating temperature of the optical member.

The hardness and softness of an elastic body depend to some extent on its elasticity. JISK6301 stipulates a method of applying a small strain to the sample surface using a spring, and evaluating the hardness of rubber based on the degree of penetration, which can be easily determined.

However, when the elastic modulus is as low as 10 ⁶ dyne/cm ² or less, it cannot be measured using the above-mentioned method, and in that case, the penetration is evaluated using a 1/4-inch micro-consistency meter according to JISK2808.

In addition, if the elastic modulus is small, it is difficult to measure it by "tension-elongation", so compression (5
% deformation), and its value can be determined and its correspondence with the previous penetration degree can be determined.

Rubber elastic bodies are manufactured using the conventional vulcanization (crosslinking) process.
In addition to those that do not require vulcanization, such as ethylene-vinyl acetate copolymers and A-B-A type butadiene-styrene block copolymers, and chain polymers, etc. (by controlling the molecular chain length).

In all of these, the elastic modulus is controlled by adjusting the crosslinking state, the combination of molecules in the block copolymer, the gel state, etc.

Further, in addition to controlling the elastic body depending on the structure of the elastic body itself, it is also possible to change and adjust its properties by adding a diluent or a filler.

For example, silicone rubber (manufactured by Shin-Etsu Chemical;
KE104GEL (product name)) and catalyst (product name; Catalyst
−104, manufactured by Shin-Etsu Chemical Co., Ltd.) and a diluent (product name: RTV
When thinner (manufactured by Shin-Etsu Chemical Co., Ltd.) is added, as the amount added increases, the hardness and tensile strength decrease, and conversely, the elongation increases.

As a method for deforming the optical surface at the opening of the elastic body, in addition to external force, it is also possible to use the volume change due to thermal expansion/contraction, sol-gel change, etc. using the above-mentioned materials.

The member having an opening for forming the optical surface of the elastic body may be one in which the opening is provided in a flat plate, and when the elastic body is housed in a container and used, at least one part of the container is used. An opening may be provided in one wall. Although the aperture varies depending on the required optical effect, it is generally a circular aperture to form a convex or concave lens having a variable focal length.

Further, by providing an opening in the shape of a rectangular slit, a cylindrical lens and a torrent lens can be formed.

The shape of the elastic optical member formed by these openings can be changed arbitrarily by applying an external force to the elastic body or by changing the volume of the elastic body, and the degree of change can be determined by feedback while detecting the effect. It is possible to control it by

Further, it is also possible to provide this opening with a piezoelectric element such as a cylindrical piezo, which allows the element to be made significantly more compact.

All conventionally known methods can be used to apply an external force to the elastic body, but it is desirable to deform the elastic body using a feedback mechanism while detecting the optical effect. It is preferable to use a method that allows electrical control of an electromagnet, a stepping motor, a piezoelectric element, or the like. Further, the volume change due to heating can be performed using a heater provided outside or inside the elastic body. Although it goes without saying that the elastic optical member can take the form of an elastic lens or an elastic mirror, the following description will be made using an elastic lens.

1 to 3 show cross sections of typical basic configurations of elastic lenses used in the optical device according to the present invention, in which 1 is a cylindrical container with a circular opening 2; The transparent elastic body 4 is a movable part for pressurizing the elastic body, and is composed of an optically transparent parallel flat plate. FIG. 1 shows a state in which no pressure is applied.
FIG. 2 shows a state in which pressure is applied to the elastic body 3 through the movable part 4, and in this case, a part of the elastic body protrudes from the opening in the shape of a convex lens according to the magnitude of the applied pressure. FIG. 3 shows a state in which negative pressure is applied to the elastic body through the movable part 4, and in this case, the elastic body has a concave lens shape at the opening.

In this way, a desired optical surface shape can be realized at the opening by a portion of the elastic body depending on the magnitude of the external force applied to the movable part of the container. Further, it is desirable that the aperture plate 2' having the apertures 2 is optically opaque. Further, the movable part and the elastic body are bonded together using an adhesive or the like, if necessary. Further, if necessary, the elastic body and the inner wall surface of the container are entirely bonded. In addition, instead of the configuration shown in FIG. 1, as shown in FIG.
It is also possible to adopt a configuration in which pressure is applied by the movable part 6 having the following. Furthermore, as shown in FIG. 5, it is also possible to provide a plurality of openings 7 and 9 and to apply pressure to each of them to provide a different curvature. Further, by changing the size of the plurality of openings, different curvatures can be given to each of the openings. Further, as shown in FIG. 6, the elastic body 3 may be housed in a container 10 having an opening 13 formed inside the container. This opening 13 is formed by a cylinder 12 fixed to an optically transparent top lid 11 of the container, and by applying external pressure to the movable part 4, an optical surface made of an elastic body is formed into the opening 13. It is formed.

Here, any method can be used to apply pressure to the elastic body 3 by driving the movable part 4 or 6, and a simple method is to cut a thread in the container and then screw the movable part into the container. , a method of controlling a movable part using an electromagnet, etc., but the present invention is not limited to these methods. Also,
As an example of another elastic lens used in the present invention, as shown in FIG.
4, by expanding and contracting it in the radial direction, the elastic body 3 filled inside the piezo element is inserted into the cylindrical opening 15.
It is also possible to form an optical surface by protruding and settling from the surface.

Note that FIGS. 8 and 9 show specific examples of applying an external force to an elastic body. In FIG. The drive unit 1 having a disc-shaped movable part 20 and an opening 18 is
9, the optical surface of the aperture 18 is deformed. Also, Fig. 10 shows the electromagnet 2
6, the movable part 25 made of ferromagnetic material is moved to the container 27.
By moving the elastic body 3 in the depth direction, the optical surface at the opening 24 of the elastic body 3 can be deformed.

By using the elastic lens described above, an autofocus optical device can be realized without using almost any mechanically movable parts. Hereinafter, the optical device of the present invention will be explained using the drawings.

FIG. 10 is a diagram showing one embodiment of the optical device of the present invention, and this figure is an example in which the present invention is applied to an autofocus optical device for an optical disk. In the same figure,
30 is a semiconductor laser as a light source; 31 is a drive circuit for driving the semiconductor laser; 32 is a collimator lens that collimates the light beam emitted from the semiconductor laser 30; and 33 is a collimated light beam onto an optical disk surface, which will be described later. The guiding half mirror 34 is, for example, an elastic lens as described in FIG. 7, and functions as a condensing lens that condenses the collimated light beam. 35 is an optical disk, and 36 is a motor for rotating the optical disk. The light beam focused on the surface of the optical disk 35 by the elastic lens 34 is reflected by the optical disk, passes through the elastic lens 34 again, passes through the half mirror 33, and is guided to the focus state detection system 37. It will be destroyed. The focusing state detection system includes known means, for example, as shown in the same figure, light quantity sensors 39 and 39' set at defocus positions before and after the convergence position of the light beam via a half mirror 38, and the light quantity A combination of a focus state determination circuit 40 that determines the focus state based on the output signals of the sensors 39 and 39' may be used. The signal detected by the focus state detection system is guided to the elastic lens drive circuit 41,
Since the power of the elastic lens is controlled by the drive circuit, the thus configured feedback system maintains the correct convergence position of the light beam by the elastic lens on the surface of the optical disk 35.

FIG. 11 is a diagram showing another embodiment of the optical device of the present invention, and is a diagram showing the basic principle of an active type autofocus optical device used in cameras and the like. In the figure, reference numeral 50 denotes an elastic lens applied to the present invention, and the elastic lens is driven using, for example, a piezo element as explained in FIG. 7. Reference numeral 51 represents a drive circuit for driving the elastic lens, 52 represents an image plane of the elastic lens, and 53 represents an object to be photographed. Reference numeral 54 denotes an LED, which is installed at a position in a mirror image relationship with the image plane 52 with respect to the mirror 55. 57
is a CCD that detects the light emitted from the LED 54 and reflected by the subject 53, and the CCD is positioned in a mirror-reflection relationship with the image plane 52 with respect to the mirror 56. The light beam emitted by the LED 54 is reflected by the mirror 55, and the elastic lens 5
The light reaches the object 53 through a portion of the periphery of 0 that is not used for image formation, is reflected by the object, passes through the periphery of the elastic lens 50 again, and is imaged by the mirror 56 on the CCD 57 . The in-focus state is determined by detecting the blur of the imaged spot on the CCD by the in-focus state detection circuit 58. A signal is fed back from the focus state detection circuit to the elastic lens drive circuit 51 according to the focus state, and the power of the elastic lens is controlled by the signal. By the method described above, it is possible to realize an autofocus control device used in a camera or the like.

The above example is a so-called active type autofocus device that performs autofocus control using light emitted from an LED, etc., but it is a passive type autofocus device that performs autofocus using the light of the subject itself. It goes without saying that an off-orcus device can also be easily realized in accordance with the spirit of the present invention.

The following method is also effective as a method for driving the elastic lens used in the above-mentioned optical device. That is,
A minute high-frequency signal is always added to the signal generated by the elastic lens drive circuit, so that the elastic lens always repeats minute deformation at high frequency.
Due to such minute deformation, the focus position shifts by a minute amount, but the focus state detection circuit detects this shift in focus position, and in order to bring it into focus, the elastic lens is moved back and forth between the focus points. It is possible to determine in which direction the vehicle should be driven. With normal focus detection methods, it is possible to distinguish between in-focus and out-of-focus states, but it is difficult to determine in which direction the focus is out of focus, so quick driving is not possible. The method allows for fast response. Such a driving method is one of the effects of the present invention using an elastic lens, and such high-frequency driving is difficult with normal movement of the entire lens.

As described above, in the optical device according to the present invention, the optical system used in the optical device can perform focus control of the optical system without displacement in the optical axis direction, and can perform focus control with high response characteristics. is possible.

[Brief explanation of the drawing]

1, 2, 3, 4, 5, 6, 7, 8, and 9 are elastic lenses applied to the optical device of the present invention, respectively. 10 and 11 are diagrams each showing an embodiment of the optical device of the present invention. 30... Semiconductor laser, 31... Drive circuit,
32... Collimator lens, 33... Half mirror, 34, 50... Elastic lens, 37... Focus state detection system, 41, 51... Elastic lens drive circuit, 52... Image plane, 53... ...Subject, 54...
LED, 57...CCD, 58...Focus state detection circuit.

Claims (1)

[Claims] 1. A container having an opening, a transparent elastic body housed in the container, and means for applying an external force to the elastic body, wherein the shape of the elastic body is changed by the means for applying the external force, and the elastic body is An optical member whose focus is variable by having a body itself protrude or sink from the opening to deform the optical surface formed by the elastic body at the opening, and a focused state of the optical member. An automatic focusing optical device comprising: a focusing state detecting means for detecting the focusing state, and controlling the shape of the optical surface of the optical member according to a signal detected by the focusing state detecting means.