FIBERSCOPE

Abstract: A fiberscope having a covering tube, an image fiber for transmitting picture images and equipped with an optical system at its tip end for focusing an image of an object to be observed, and light guides for transmitting light and placed along with said image fiber. The image fiber and the light guides are enclosed in said covering tube. A plastic body formed of substantially transparent material and convex shape is provided at front ends of the light guides. Liguid guide passages are also provided between an inner peripher­ al surface of the covering tube and outer peripheral surfaces of the image fiber and the light guides. Outlet ends of the light guides are arranged in positions substantially symmet­ rical with respect to an outlet end of the image fiber, and outlet ends of the liquid guide passages are arranged in positions substantially symmetrical with respect to the outlet end of the image fiber.

Description: This invention relates to a fiberscope and to a method of forming an end portion of the fiberscope according to the preambles of claims 1 and 5, respectively. The fiberscope is utilizable for optically observing or examining dark places such as the interiors of blood vessels and the heart. There is a known fiberscope as means for optically observing the interiors of blood vessels and the heart, the fiberscope comprising, as shown in Figs. 1 through 3, a plurality of light guides 9 for transmitting light beams from a light source 3 to a region 5 being observed (the interior of a blood vessel 7 in Fig. 2) through a flexible coating tube 1; an image transmitting fiber 11 equipped with an image focusing lens 19 at the tip thereof, and a liquid guide passage 15 for introducing a physiological saline solution from a syringe 13 and forming a transparent zone by temporarily removing the blood flowing in front of the light guides 9 and the image focusing lens 19 at the tip of the image fiber 11 in the region 5 being observed. In that case, it is needed to secure a physiological saline flush having a flow rate equivalent to that of blood at the tip of the coating tube 1 so as to form the above-described transparent physiological saline solution zone. The liquid guiding passage 15 is unnecessary when a zone without the presence of an opaque solution such as blood is optically probed. Referring to Figs. 4 through 7, the construction of the tip of a fiberscope equipped with a conventional liquid guide passage will be described. Fig. 6 is a vertical sectional view of the tip portion. Fig. 4 is a sectional view taken on line A-A' of Fig. 6. Fig. 5 is a sectional view taken on line B-B' of Fig. 6. Fig. 7 is a perspective view of the tip thereof. In those Figures, an image pick-up adaptor 23 for coupling the image focusing lens 19 and the tip of the image fiber 11 is adhesive-bonded and fixed to a recess (reference number 39 of Fig. 10) in a molded tip portion 21 wherein the tips of the light transmitting guides 9 are buried by the method described later. Moreover, the outer face of the molded tip portion 21 and the coating tube l are adhesive-bonded and fixed. The coating tube 1 is prepared from polyethylene or vinyl chloride plastics, etc. and about 2.8 mm and 2.2 mm in outer and inner diameters, respectively. The adhesion-between the outer face of the molded tip portion 21 and the coating tube 1 is reinforced by filling a coating-tube bonding aperture 25 with an epoxy resin adhesive to deal with an impact at the time of flushing. As shown in Fig. 7, the flush flow 27 is thus formed. The molded tip portion 21 is, as shown in Fig. 6, also slightly positioned back by ΔL₁ from the front face of the coating tube 1 in order to remove the blood from the front face of the image focusing lens 19 and the light guides 9 efficiently. Referring to Figs. 8 through 10, subsequently, the method of preparing the aforementioned molded tip portion 21 will be described. As shown in Fig. 8, a fluoroplastic molding die 31 with an aperture 2 mm in diameter and about 10 mm in depth is first prepared and a bundle 33 of plastic fibers for use as light transmitting guides 9 and a fluoroplastic dummy tube 35 for forming the recess (reference number 39 of Fig. 10) in the molded tip portion 21 are inserted into a throughhole 29. The gap between the throughhole 29 of the molding die 31 and the bundle of the plastic fibers 33 as well as the dummy tube 35 is filled with epoxy resin. The profile shown in Fig. 9 is obtained by grinding one end face and removing the molding die 31 from the molded piece 37 after it is hardened. The dummy tube 35 is then pulled out of the molded piece 37 and part of the tube 35 is cut out so that the molded tip portion 21 having the recess 39 may be formed as shown in Fig. 10. Figs. 11a and 11b illustrate the construction of another conventional fiberscope comprising a molded tip portion 41 having a central aperture for inserting and fixing a pick-up adaptor, liquid guide passages 15 on the left- and right-hand sides and a plurality of light guides 9 for transmitting light, the light guides being buried in an annular form. The conventional fiberscopes as disclosed in, for example, EP-A-0 119 614 and having the construction illustrated in Figs. 1 through 11 poses the following problems: (1) The angle of view (α of Fig. 12) of a fiberscope is determined by the focal length of the image focusing lens and the outer diameter of the image fiber. Although the angle of view may exceed 100 degrees depending on the condition, it is normally about 70 degrees. However, since the angle of illumination (β of Fig. 12), i.e., the maximum angle of opening of illumination is determined by NA (the Numerical Apertures) of the optical fiber as a light guide for transmitting light, it is relatively small when a lens is hardly usable in front of the light guides whose tips are distributed in an annular form as a bundle of optical fibers is used to form the light guides. The numerical apertures is determined by the refractive indices of the core and the clad and, in the case of a fiber for transmitting visible light such as a plastic fiber, its value is 0.6 at the greatest. Consequently, the angle of illumination β is limited to about 50 degrees under liquid such as blood where the fiberscope is mainly intended for use. For that reason, observation is impossible within a region 43 where the angle of illumination β is smaller than that of view α, as shown in Fig. 12. (2) On the other hand, because the edge of the tip of the conventional fiberscope is obviously sharp, as shown in Fig. 7, it may damage the inner wall of the blood vessel, ureter, etc. (3) As the outlets of the light guides are one-sided relative to the axial position of the image fiber, there is caused deflection in the distribution of illumination within the visual field. The shortcoming becomes conspicuous particularly when the position of an object being observed is close to the fiberscope. (4) As the outlet of the liquid guide passage for introducing a flush is one-sided relative to the axial position of the image fiber, there is caused deflection in the visual field by flushing. An endoscope having a smoothly curved distal end face is disclosed in US-A-4 319 563. The endoscope comprises of an inner tube enclosing a bundle of image transmitting fibers having a lens set arranged at the distal end. Arranged around the inner tube is a plurality of light conducting optical fibers for illumination, all of which is disposed inside an outer tube. The light conducting optical fibers and the inner tube are exposed directly to the outside through an opened distal end of the outer tube. The exposed end face is formed into a smooth, spherical convex shape. A method of contact-bonding lenses to fiber end faces is disclosed in Electronic Letters (volume 11, no. 20, October 1975, pages 477 to 480). Thereby the adhesive is placed in a jig and the upright fiber is dipped into the liquid from above under control of a micrometer drive while being observed from the side through a microscope. Lenses with radii from 70 µm to greater than 120 µm could be achieved. SUMMARY OF THE INVENTION In view of the above-described problems inherent in the prior art, it is an object of the present invention to provide a fiberscope offering an enlarged angle of illumination and thus a wide visual field with a blunt tip. Another object of the Present invention is to provide a fiberscope capable of providing uniform visual field resulted from flushing and providing uniform distribution of illumination. In order to accomplish the above-described objects, the fiberscope according to the present invention as described above, further comprises a substantially solid transparent plastic body secured to the end of the fiberscope whereby the plastic body completely covers the front end surface of the light guide means and entire open end of the tube, and has a convex surface substantially flush with but not covering the light receiving surface of the lens. The substantially transparent plastic body in a convex shape on the front faces of the light guides for transmitting light has the effect of enlarging the angle of illumination derived from the light guides. Moreover, the tip of the fiberscope is made blunt because of the convex plastic body. Further, the fiberscope according to the present invention comprises an image fiber for transmitting plastic picture images, light guides for transmitting light and, a tube adapted to cover them. At the tip of the fiberscope, the outlets of the light guides are arranged in positions substantially symmetrical about the outlet of the image fiber, and the outlets of the liquid guide passages, according to a preferred embodiment are arranged in positions substantially symmetrical about the outlet of the image fiber. BRIEF DESCRIPTION OF THE DRAWINGS In the drawings: Figs. 1 - 12 illustrate a conventional fiberscope; Fig. 1 is a constructional view of the fiberscope system; Fig. 2 is a perspective view of the tip of the fiberscope inserted in the region where an object being observed is present; Fig. 3 is a sectional view of the part inserted into the blood vessel; Fig. 4 is a sectional view taken on line A-A' of Fig. 6; Fig. 5 is a sectional view taken on line B-B' of Fig. 6; Fig. 6 is a vertical sectional view of the tip of the fiberscope; Fig. 7 is a perspective view of the tip thereof; Figs. 8 - 10 illustrate the method of preparing the molded tip portion; Fig. 11a is a perspective view of the tip of another conventional fiberscope; Fig. 11b is a cross-sectional view of the fiberscope shown in Fig. 11a; Fig. 12 illustrates the relation between the angles of illumination and view at the tip of the conventional fiberscope; Fig. 13 is a perspective view of a preferred embodiment of the present invention illustrating the tip of a fiberscope equipped with a liquid guiding passage; Fig. 14 is a perspective view of an embodiment of the present invention in the form of a fiberscope without the liquid guiding passage; Fig. 15 illustrates the relation between the angles of illumination and view at the tip of the fiberscope according to the present invention; Figs. 16 - 19 illustrate the method of preparing the substantially transparent convex plastic body according to the present invention; Figs. 20 and 21 illustrate a basis for enlarging the angle of illumination; Fig. 22 is a graph representing the related equations; DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to Figs. 13 through 22, various embodiments of the present invention will be described. Fig. 13 is a perspective view of the tip of a fiberscope with a liquid guide passage. A drop of substantially transparent resin is hardened on the front faces of light guides for transmitting light, except those of an image focusing lens 19 and a liquid guide passages 15, and the former is covered with a substantially transparent plastic body 45 in a convex shape extending up to the periphery of the tip of a coating tube 1. As for the resin, use can be made of epoxy resin, ultraviolet-curing silicon, arcylic plastics, urethane resin, etc. Fig. 14 is a perspective view of a fiberscope without a liquid guide passage, wherein a drop of substantially transparent resin is hardened on the faces of light guides for transmitting light, except that of the image focusing lens 19, and the former is covered with the substantially transparent plastic body 45 extending up to the periphery of the tip of the coated tube 1. As is obvious from Figs. 13 and 14, if the front faces of light guides for transmitting light beams are covered with the substantially transparent convex plastic body 45, the angle of illumination β will become greater, as shown in Fig. 15, than that without such a plastic body (Fig. 12) and it will permit an increased range of observation. As shown in Figs. 13 and 14, the fiberscope with a blunt edge may not damage the soft tissue of the blood vessel, ureter, etc. Subsequently referring to Figs. 16 through 19, the method of forming the substantially transparent convex plastic body will be described by taking the case of applying the present invention to the conventional fiberscope equipped with a liquid guide passage shown in Fig. 11. In reference to Fig. 16, such a method roughly comprises protruding the pick-up adaptor 23 from the molded tip portion to a suitable extent, adhesion-bonding the adaptor 23 thereto to prevent the plastics from attaching to the image focusing lens 19, inserting a dummy tube 47 of fluoroplastics to prevent the liquid guide passage for the flush flow from being clogged with the plastics and dropping substantially transparent suitable plastics 49 from upside to the tip portion. Since the plastics has suitable viscosity, there is formed a convex swell in proportion to the periphery of the pick-up adaptor 23 and the side of the dummy tube 47. The surface of the convex plastic is smooth because of the surface tension of the plastics. Accordingly, the front face of the fiberscope excluding the image focusing lens 19 and the liquid guide passage for the flush flow is covered with a smooth substantially transparent convex plastic body by pulling out the dummy tube 47 after the resin is hardened. It is suggested to drop the plastics by the following method, which comprises inserting the tip of the fiberscope into a mold 51 of fluoroplastics and buffing the front face thereof (excluding the pick-up adaptor) as shown in Fig. 17, lowering the tip by about ΔL₂ = 0.2 mm from the plastic molding die 51, protruding the pick-up adaptor 23 by ΔL₃ = 0.3 mm, inserting the dummy tube 47 into the adaptor 23 and dropping the substantially transparent plastics 49 while the tip of the fiberscope is being inserted into the plastic molding die 51 as shown in Fig. 19. The buffing acts to improve the adhesion between the plastics 49 and the molded tip portion 41 while reducing the light transmission loss. By lowering the tip of the fiberscope by ΔL₂, the plastics is prevented from flowing out of the edge and the connection between the periphery of the coating tube 1 and the convex plastic body 45 is considerably smoothed. Moreover, the protrusion of the pick-up adaptor 23 by ΔL₃ allows the adjustment of the quantity ΔZ of the protrusion of the convex plastic body 45. Referring to Figs. 20 through 22, the relation between the quantity ΔZ of the protrusion of the convex plastic body 45 and the angle β of illumination will be described. In Figs. 20 and 21, given the diameter D; refractive index nL; number of apertures NA of the group of light guides 53 having a convex 55 at their tips; the curvature radius R of the convex; the quantity ΔZ of the protrusion of the convex; the optic axis Z; the angle γ₀ between line OQ connecting the center O and a point Q on the periphery of the convex, and the optic axis Z; the angle γ between line OP connecting a point P on the convex and the center ), and the optic axis Z; ϑ = sin⁻¹ (NA/nL); the refractive index nW of the external portion (such as water); and the angles β₁, β₂ between the radiated light and the optic axis when the light at an angle of ϑ to the optic axis is refracted by the convex and radiated, (i) when 0 ≦ γ < ϑ shown in Fig. 20, since nWsin(β₁ - γ) = nLsin(ϑ - γ) nWsin(β₂ + γ) = nLsin(ϑ + γ), β₁ = sin⁻¹{(nL/nW)sin(ϑ - γ)} + γ (1) β₂ = sin⁻¹ {(nL/nW)sin(ϑ + γ)} - γ (2) (ii) when ϑ < γ ≦ γ₀ shown in Fig. 21, since nWsin(γ - β₁) = nLsin(γ - ϑ) nWsin(β₂ + γ) = nLsin(ϑ + γ), β₁ = γ - sin⁻¹{(nL/nW)sin(γ - ϑ)} (3) β₂ = sin⁻¹{(nL/nW)sin(ϑ + γ)} - γ (4) β₁ < β₂ from the equations (1) - (4) and, as the maximum value of β₂ is considered: β₂ = sin⁻¹{(nL/nW)sin(ϑ + γ₀) - γ₀, the angle of illumination β is given by β = 2sin⁻¹ [(nL/nW)sin {sin⁻¹(NA/nL) + γ₀}] - 2γ₀ (5) when ϑ = sin⁻¹(NA/nL) is taken into consideration. However, since γ₀ = sin⁻¹(D/2R) and ΔZ = R(1 - cosγ₀), the required quantity γZ of protrusion will be obtained from nL, nW, NA and D if the desired angle of illumination β is determined. Given nL = 1.49, nW = 1.33 and NA = 0.47 as in a general case, the equation (5) will be represented by a graph of Fig. 22. (1) Accordingly, assuming β = 60° and D = 1.7 mm as γ₀ = 37°, R = 1.7/2sin37° = 1.4 mm Therefore, ΔZ = 1.4(1 - cos37°) = 0.28 mm. (2) Assuming β = 70° and D = 1.7 mm as γ₀ = 42°, R = 1.7/2sin42° = 1.3 mm Therefore, ΔZ = 1.3(1 - cos42°) = 0.33 mm According to the above-described embodiments of the present invention, the front faces of light guides for transmitting light are covered with a substantially transparent convex plastic body so that the enlarged angle of illumination can widen the visual field of a fiberscope. The presence of the convex plastic body, moreover, makes the tip of the fiberscope blunt and may least damage an object being observed. As the convex plastic body can Simply be obtained by dropping substantially transparent resin and hardening it, production cost is reducible compared with the use of a lens. When plastic fibers are used as the light guides for transmitting light, the convex plastic body protects their end faces. The intensity of illumination upon the object being observed becomes uniform because of the convex plastic body.

Claims: A fiberscope comprising image fiber means (23) having lens means (19) at one end of said image fiber means for focusing an image of an object to be observed on the end of the image fiber means for transmission therethrough, said lens means having a light receiving surface for receiving light from an object, a covering tube (1) having an open end surrounding said image fiber means with at least a portion of said lens means protruding beyond said open end of said tube, light guide means (9) for transmitting light to an object extending through said tube adjacent said image fiber means and having a front end surface adjacent said open end of said covering tube, characterised in that it further comprises: a substantially solid transparent plastic body (45) secured to the end of said fiberscope, said body completely covering said front end surface of said light guide means (9) and said entire open end of said tube (1) and having a convex surface substantially flush with but not covering said light receiving surface of said lens (19). A fiberscope according to claim 1 wherein said plastic body (45) is formed from one of epoxy resin, ultraviolet curing silicon resin, arcylic resin or urethane resin. A fibrescope according to claim 1, wherein liquid passage means (15) are provided between an inner peripheral surface of said covering tube (1) and outer peripheral surfaces of said image fiber means (23) and said light guide means (9), and extend through said plastic body to provide a flow of transparent liquid to flush undesirable material away from said light receiving surface of said lens means. A fiberscope according to claim 3 wherein said light guide means (9) is comprised of a plurality of light guides arranged substantially symmetrically around said lens means (19) and said liquid passage means (15) are comprised of a plurality of liquid passages having outlet ends in the convex surface of said body (45) and arranged in substantially symmetrical relationship with respect to said lens means. A method of forming a transparent convex plastic body (45) at a tip of a fiberscope except over an image focusing lens (19) of an image pick-up fibre means (23), comprising the steps of: a) inserting the tip of the fiberscope upwardly into a molding die (51); b) lowering the tip by a given amount in the molding die (51); c) protruding the image pick-up fibre means (23) from said tip of the fiberscope to a given extend to prevent plastic from attaching to the image focusing lens (19); d) dropping transparent plastics from above to the tip of the fiberscope while the tip is inserted in the molding die (51) to cover the tip but not the image pick-up fibre means (23); and e) hardening the transparent plastics.

Inventors: AWAZU, KUNIO C/O OSAKA WORKS, NISHIKAWA, MITSURU C/O OSAKA WORKS, TSUNO, KOICHI C/O OSAKA WORKS
Applicants: SUMITOMO ELECTRIC INDUSTRIES LIMITED
Application year: 1986
Main classification: A61B1
IPC codes: G02B23, A61B1