Patent Application
20160178884
1. Field of the Invention
The present invention relates to a small-diameter lenses unit for an endoscope used for, for example, the medical field, and an endoscope equipped with the same.
2. Description of the Related Art
In the related art, in the medical field or the industrial field, endoscopes for imaging the interior of a human being's body or the inside of a device or a structure have spread. As these types of endoscopes, there are electronic endoscopes in which an imaging unit including an imaging lens and an image pickup device is mounted on an insert section inserted into the inside of an object to be observed. In the electronic endoscopes, the light from a region to be imaged is image-formed on an imaging surface of the image pickup device by the imaging lens, and the image-formed light is converted into an electrical signal by the image pickup device, and is transmitted to an external image processing device or the like as a video signal via a signal cable. In the endoscopes, for expansion in the range of an object to be observed, reduction in the burden of a person to be observed, the simplification of structure, cost reduction, or the like, downsizing of the inset section has been mentioned as a challenge until now. In the electronic endoscopes, further downsizing and further diameter reduction of a distal end portion including the imaging unit have become important.
In order to achieve downsizing of optical instruments, such as an endoscope, for example, Japanese Patent Unexamined Publication No. 2013-200537 discloses an imaging mechanism and an endoscope in which a plano-concave lens is provided on an image pickup device side of a lenses unit, and a planar portion of the plano-concave lens is made to project from an end of the lens barrel and is fixed to a cover member that covers the surface of an image pickup device. Japanese Patent No. 3426378 discloses an endoscope objective lens having three lens groups capable of reducing distortion even in a spherical lens only and realizing cost reduction.
The imaging unit of the electronic endoscopes is generally configured to perform focus adjustment between the imaging lens and the imaging surface of the image pickup device, using a lens barrel that houses the imaging lens, and a frame body (distal end hard part) that holds the image pickup device. If realization of excellent optical performance is intended, in the configuration of the related-art imaging lens, a back focus becomes long. As a result, it is necessary to secure a predetermined distance from a final surface of the imaging lens to a cover member surface of the image pickup device. For this reason, it is difficult to realize the structure of fixing the imaging lens and the image pickup device with an adhesive or the like for the purpose of downsizing. In the endoscope objective lens described in Japanese Patent No. 3426378, the total optical length is about 6.51 mm to 7.22 mm, the back focus is about 0.70 mm to 0.87 mm, and the back focus is longer than the total optical length. Therefore, the imaging lens and the image pickup device cannot be fixed without interposing a frame body or the like. In the imaging mechanism described in Japanese Patent Unexamined Publication No. 2013-200537, the plane of the final surface on the image pickup device side is configured to be fixed to the cover member of the image pickup device, but there is no refractive power in the final surface. Therefore, this cannot contribute to the convergence of rays from a photographic subject, and a reduction in the aberration of an optical system. For this reason, it is difficult to obtain desired optical performance while achieving downsizing of the imaging lens.
An object of the invention is to provide a lenses unit for an endoscope and an endoscope that are able to realize the structure of fixing an imaging lens and an image pickup device with an adhesive or the like.
According to an aspect of the invention, there is provided a lenses unit used for an endoscope, including a lens barrel; a front group lens and a rear group lens housed inside the lens barrel; and an aperture arranged between the front group lens and the rear group lens. An imaging-side final surface of the rear group lens has a structure in which the imaging-side final surface is fixed to a cover glass of an image pickup device with an adhesive layer. A focal distance fF of the front group lens, a focal distance fB of the rear group lens, a focal distance fel of an entire optical lenses group including the front group lens and the rear group lens, a total optical length OL of the optical lenses group, and a metal back MB of the optical lenses group satisfy a relationship of fel/fF<0, fel/fB>0, and OL/MB>7.0.
According to another aspect of the invention, there is provided an endoscope including the above lenses unit for an endoscope; an image pickup device in which an imaging surface is covered with cover glass; an imaging-side final surface of the rear group lens in the lenses unit for an endoscope; and an adhesive layer formed by an adhesive resin with which the cover glass of the image pickup device is fixed.
According to the invention, the structure of fixing the imaging lens and the image pickup device with an adhesive or the like in the imaging unit of the endoscope can be realized.
Hereinafter, embodiments (hereinafter referred to as “present embodiment”) of a lenses unit for an endoscope and an endoscope, related to the invention, will be described in detail with reference to the accompanying drawings. The present embodiment illustrates a configuration example applied to a medical endoscope.
In
Directions used for explanation in this specification follow the description of directions in the respective drawings. Here, “top” and “bottom” respectively correspond to the top and bottom of video processor 19 put on the horizontal plane, and “front (distal end)” and “rear” respectively correspond to a distal end side of insert section 21 and a base end side of plug section 23 in an endoscope body (hereinafter referred to as “endoscope 11”).
As illustrated in
Insert section 21 has flexible soft portion 29 having a rear end connected to plug section 23, and distal end portion 15 that stretches to the distal end of soft portion 29. Soft portion 29 has a suitable length corresponding to methods, such as various kinds of endoscopy and endoscopic surgery.
Video processor 19 has socket section 27 that opens to front panel 25, and includes an image processing unit and a power source unit inside the device. A rear end of plug section 23 of endoscope 11 is inserted into and engaged with socket section 27, and thereby, endoscope 11 is able to transmit and receive electric power and various signals (video signals, control signals, and the like) between endoscope 11 and video processor 19.
The above-described electric power and various signals are led to soft portion 29 and distal end portion 15 from plug section 23 via transmission cable 31 (refer to
As illustrated in
As illustrated in
Mold resin 17 is made of, for example, a resin material having a light blocking effect, such as black resin. In this way, the connected and fixed region between lenses unit 35 and image pickup device 33 has a double structure in which an outer peripheral portion of adhesive resin 37 having a light-transmitting property, such as a transparent material that transmits rays of a subject image, is provided with and coated with mold resin 17 having a light blocking effect, such as black.
Circuit board 49 is mounted on the surface of image pickup device 33 opposite (rear side) to cover glass 43, and has capacitor 45 for a countermeasure against static electricity attached thereto. Transmission cable 31 is electrically connected to a rear portion of circuit board 49, and the connection region of circuit board 49 is covered with mold resin 17 for sealing. In the subsequent description, the term “adhesive” is used not in a strict meaning indicating a substance used to adhere surfaces of solid bodies to each other but in a broad meaning indicating a substance that can be used for connection of two objects, or a substance having a function as a sealing agent when the cured adhesive has high barrier properties against gas and liquid.
Lens barrel 39 is made of a cylinder material having high rigidity, for example, a metallic tubular member. By using a hard material for lens barrel 39, distal end portion 15 constitutes a hard part. As a metallic material that constitutes lens barrel 39, for example, nickel is used. Nickel has a relatively high modulus of rigidity and high corrosion resistance, and is suitable as a material that constitutes distal end portion 15. Instead of nickel, for example, a copper nickel alloy may be used. The copper nickel alloy also has high corrosion resistance, and is suitable as a material that constitutes distal end portion 15. As a metallic material that constitutes lens barrel 39, a material that can be manufactured by electroforming (electroplating) is preferably selected. Here, the reason why the electrocasting is used is because the dimensional precision of a member that is manufactured by electrocasting is as extremely high, at less than (so-called submicron precision) 1 μm, and the variation when a number of members are manufactured is small. As will be described below, lens barrel 39 is an extremely small member, and a dimensional error between the external and internal diameters thereof influences the optical performance (image quality) of endoscope 11. By constituting lens barrel 39 of, for example, a nickel electroforming pipe, endoscope 11 capable of securing high dimensional precision in spite of a small diameter and capturing a high-definition image is obtained.
The plurality of (three in an illustrated example) lenses (first lens L1 to third lens L3) formed of an optical material (glass, resin, or the like), and aperture 51 sandwiched between first lens L1 and second lens L2 are assembled into lens barrel 39 in a state where they are brought into close contact with each other in the direction of optical axis LC. First lens L1 and third lens L3 are fixed to the inner peripheral surface of lens barrel 39 with an adhesive over their whole circumferences. Since a front end of lens barrel 39 is hermetically closed (sealed) by first lens L1, and a rear end is hermetically closed (sealed) by third lens L3, lens barrel 39 is configured such that air or moisture does not enter the inside of the lens barrel. Therefore, air or the like cannot escape from one end of lens barrel 39 to the other end thereof. In the subsequent description, first lens L1 to third lens L3 are altogether referred to as optical lenses group LNZ. Optical lenses group LNZ formed by the plurality of lenses is not limited to the three-lens configuration, and the number of lenses is arbitrary so long as configurations having a front group lens and a rear group lens, such as two or more lenses or four or more lenses, are provided.
As illustrated in
Here, a circle that forms an outer periphery of lens barrel 39 has a relationship in which the circle is substantially inscribed on the square formed by image pickup device 33 and is circumscribed on the square formed by imaging surface 41. The positions of the center (an intersection point between diagonal lines of imaging surface 41) of imaging surface 41, the center (the center of the circle formed by the inner periphery of lenses unit 35) of lenses unit 35, and the center (the center of the circle formed by the outer periphery of lens barrel 39) of lens barrel 39 coincide with each other, and the optical axis LC passes through these positions. More exactly, a normal line passing through the center of imaging surface 41 is optical axis LC, and lenses unit 35 is aligned with image pickup device 33 such that optical axis LC passes through the center of lenses unit 35.
Next, a configuration example of optical lenses group LNZ (first lens L1 to third lens L3) in lenses unit 35 of endoscope 11 will be described.
The first embodiment illustrates a first configuration example of optical lenses group LNZ of lenses unit 35 in distal end portion 15 of the endoscope. In lenses unit 35 of the present embodiment, first lens L1 functions as the front group lens, and second lens L2 and third lens L3 function as the rear group lens. Here, first lens L1 is a leading lens of optical lenses group LNZ, and third lens L3 is a final lens of optical lenses group LNZ. Lenses unit 35 is configured such that, in order from a photographic subject side toward the imaging side, first surface L1R1 of first lens L1 that is the forefront surface has a concave surface, second surface L1R2 has a concave surface, first surface L2R1 of second lens L2 has a convex surface, second surface L2R2 has a convex surface, first surface L3R1 of third lens L3 has a concave surface, and second surface L3R2 that is a final surface has a concave surface.
Aperture 51 is provided between first lens L1 and second lens L2, that is, between the front group lens and the rear group lens. A gap between second surface L3R2 (final surface) of third lens L3 that is the concave surface, and cover glass 43 of image pickup device 33 is filled with adhesive resin 37, which in turn forms the adhesive layer.
In the first embodiment, focal distance fel of entire optical lenses group LNZ is set to fel=0.58 mm, focal distance fF of the front group lens (first lens L1) is set to fF=−0.714, and focal distance fB of the rear group lens (second lens L2 and third lens L3) is set to fB=0.481. If total optical length OL of optical lenses group LNZ is defined as the length from the forefront surface (first surface L1R1 of first lens L1) of the leading lens to the imaging surface (rear end surface of cover glass 43 of image pickup device 33 on the imaging side), entire optical length OL=2.287 mm is established, however, entire optical length OL may also be 2.0 mm to 2.7 mm.
If the length from a peripheral portion end surface of the final surface (second surface L3R2 of third lens L3) of the final lens to a front end surface of cover glass 43 of image pickup device 33 on the photographic subject side is defined as metal back MB, metal back MB=0.04 mm is established. However, MB may be 0.01 mm to 0.1 mm. Metal back MB may also be referred to as a back focus depending on the irregularities of the final surface of the final lens. Here, back focus BF and metal back MB will be unified and described as metal back MB, using metal back MB as a parameter of the concept including back focus BF. As illustrated in
In this case, fel/fF=−0.812, LAB=1.206, and OL/MB=38.12 are established, and
the relationship of fel/fF<0, fel/fB>0, and OL/MB>7.0 is satisfied.
Curvature radius rLbR2 (rL3R2) of the imaging-side final surface (second surface L3R2 of third lens L3) of the rear group lens is rLbR2=−214.043≠∞. Refractive index nbe (n3) of the final lens (third lens L3) of the rear group lens is nbe=1.68, refractive index nad of the adhesive layer is nad=1.52, and nbe≠nad is established.
Since Abbe number vbe (v3) of the final lens (third lens L3) of the rear group lens is vbe=31>25, and the refractive index of the final lens is nbe=1.68, the relationship of 1.40<nbe<1.90 is satisfied.
The forefront surface (first surface L1R1 of first lens L1) of the front group lens is a concave surface, and sag (SAG) amount d of the concave surface is d=0.021 mm, however, it may be d=−0.12 mm to 0.12 mm. Here, sag amount d of the concave surface and lens external diameter φ of optical lenses group LNZ becomes d/φ=0.021 when φ=1.0 mm is established, and the relationship of −0.1<d/φ<0.1 is satisfied.
The second embodiment illustrates a second configuration example of optical lenses group LNZ of lenses unit 35 in distal end portion 15 of the endoscope. In lenses unit 35 of the present embodiment, similar to the first embodiment, first lens L1 functions as the front group lens, and second lens L2 and third lens L3 function as the rear group lens. Here, first lens L1 is a leading lens of optical lenses group LNZ, and third lens L3 is a final lens of optical lenses group LNZ. Lenses unit 35 is configured such that, in order from a photographic subject side toward the imaging side, first surface L1R1 of first lens L1 that is the forefront surface has a concave surface, second surface L1R2 has a concave surface, first surface L2R1 of second lens L2 has a convex surface, second surface L2R2 has a convex surface, first surface L3R1 of third lens L3 has a concave surface, and second surface L3R2 that is a final surface has a convex surface.
In the second embodiment, focal distance fel of entire optical lenses group LNZ is set to fel=0.61 mm, focal distance fF of the front group lens (first lens L1) is set to fF=−0.79, and focal distance fB of the rear group lens (second lens L2 and third lens L3) is set to fB=0.501. Total optical length OL of optical lenses group LNZ is OL=2.300 mm. Metal back MB is MB=0.08 mm, however, it may be MB=0.01 mm to 0.1 mm. As illustrated in
In this case, fel/fF=−0.772, fel/fB=1.217, and OL/MB=37.1 are established, and
the relationship of fel/fF<0, fel/fB>0, and OL/MB>7.0 is satisfied.
Curvature radius rLbR2 (rL3R2) of the imaging-side final surface (second surface L3R2 of third lens L3) of the rear group lens is rLbR2=−1.345≠∞. Refractive index nbe (n3) of the final lens (third lens L3) of the rear group lens is nbe=1.55, refractive index nad of the adhesive layer is nad=1.52, and nbe≠nad is established.
Since Abbe number vbe (v3) of the final lens (third lens L3) of the rear group lens is vbe=71.7>25, and the refractive index of the final lens is nbe=1.55, the relationship of 1.40<nbe<1.90 is satisfied.
The forefront surface (first surface L1R1 of first lens L1) of the front group lens is a concave surface, and sag amount d of the concave surface is d=0.030 mm. Here, sag amount d of the concave surface and lens external diameter φ of optical lenses group LNZ become d/φ=0.030 when φ=1.0 mm is established, and the relationship of −0.1<d/φ<0.1 is satisfied.
Here, an example of the dimensions of the lenses unit for an endoscope and the endoscope related to the present embodiment is illustrated. Numerical values illustrated below show one specific example, and various examples can be considered according to applications, usage environments, or the like. As an example, in lenses unit 35, as in the above example, total optical length OL is 2.2 mm to 2.3 mm, lens external diameter φ is 1.0 mm, the longitudinal dimension of the imaging unit including lens barrel 39 and image pickup device 33 is about 2.5 mm, and the external diameter is about 1.1 mm. The length of distal end portion 15 on which the imaging unit is loaded is about 3.5 mm, and the maximum external diameter thereof is about 1.5 mm.
The above-described present embodiment is configured such that lenses unit 35 for an endoscope, the front group lens (first lens L1) having negative power, and the rear group lens (second lens L2, third lens L3) having positive power are provided, and total optical length OL is larger than metal back MB. Accordingly, metal back MB becomes smaller than total optical length OL, and the distance from the final surface of optical lenses group LNZ to the front end surface of cover glass 43 of image pickup device 33 becomes short. Therefore, it is possible to adopt a configuration in which optical lenses group LNZ and cover glass 43 of image pickup device 33 are directly adhered and fixed to each other with adhesive resin 37. Hence, the imaging unit can be made into a structure with high strength and with a small number of parts, the imaging lens with a short focal distance can be realized, and shortening of the length of the imaging lens and downsizing can be achieved.
In this way, in the present embodiment, a further small-sized imaging unit is realized by reducing the diameter of the imaging lens, achieving an optical design in which the length of the imaging unit including the imaging lens and the image pickup device is shortened, and adopting a structure in which the imaging lens and the image pickup device are directly fixed with the adhesive layer.
In the structure in which optical lenses group LNZ and cover glass 43 are directly fixed with the adhesive layer of adhesive resin 37, the final surface (L3R2) of optical lenses group LNZ is formed into a curved surface, and the refractive indexes of the final lens (third lens L3) and the adhesive layer are made different from each other. Accordingly, since the final surface of optical lenses group LNZ can be made to have refractive power, the convergence of the rays from a photographic subject that passes through lenses unit 35 can be further enhanced, this can contribute to a reduction in aberration. The number of lenses for obtaining required optical performance regarding the optical performance (resolution, chromatic aberration, distortion, or the like) of optical lenses group LNZ can be reduced. Therefore, it is possible to obtain desired optical performance while achieving downsizing and cost reduction of the imaging lens.
By making Abbe number vbe (v3) of the final lens (third lens L3) larger than 25 and making refractive index nbe (n3) fall within a range of 1.40 to 1.90, the chromatic aberration of magnification can be reduced, and can be made smaller than the pixel pitch of image pickup device 33. Therefore, color blurring in a peripheral portion of a captured image can be reduced.
By making the forefront surface (L1R1) of optical lenses group LNZ into the concave surface and setting sag amount d of the concave surface such that the absolute value of relative ratio d/φ to lens external diameter φ becomes smaller than 0.1, the forefront surface can be brought close to a plane and adhesion of dirt in using the endoscope can be reduced. The forefront surface (L1R1) of optical lenses group LNZ may be a convex surface. In this case, the sag amount of the convex surface is set such that the absolute value of d/φ becomes smaller than 0.1.
Although the various embodiments have been described above with reference to the drawings, the invention is not limited to these examples. It is apparent that a person skilled in the art may find various alternations and modifications within the scope of the appended claims, and it should be understood that they will naturally come under the technical scope of the present invention. The respective constituent elements in the above embodiments may be arbitrarily combined without departing from the scope of the invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2014-259324 | Dec 2014 | JP | national |
