JPS6252504A - Fiber scope - Google Patents

Abstract

PURPOSE:To eliminate a decrease in contrast and to make an observation image sharp by bending an image fiber at >=1 position and putting the bent part in an ocular lens barrel. CONSTITUTION:The image fiber 3 is heated and fused, and bent to an about 1-10mm radium of curvature, and the image fiber is covered with a protective coating 5; and the ocular lens barrel 1 is fitted to one end of the fiber and an abjective lens barrel 6 is fitted to the other end. Then, an ocular 2 is put in the ocular lens barrel 1 and an objective 7 is stored in the objective lens barrel 6. Bent parts 41-44 of the image fiber 3 are put in the ocular lens barrel 1 to prevent the operativity from being spoiled. Consequently, stray light is removed and the contrast of an image on an original screen is reproduced faithfully.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to a fiberscope using a fused multi-core image fiber as an image guide.

2. Description of the Related Art When an image is transmitted through an image fiber, the transmitted image suffers from a reduction in contrast and color smearing at certain wavelengths. Possible causes of this include light seepage between the cores and propagation of the Tararad mode. These stray lights cause a specific color such as red or green to bleed around an image transmitted by an image fiber, particularly an image transmitted by an incandescent light bulb or fluorescent light, or make the image appear white overall.

Here, considering the normalized frequency (V value), V = π
d n v7τ7λ d: Core diameter n; Core refractive index Δ; Core-cladding relative refractive index difference λ; Wavelength. Therefore, - As an example, when determining the V value in an image fiber, the normal quartz-based image 7 fin <
-c has values of about d=5 gm, n=1.5, and Δ=0.015, so when λ=0.6 m, V=6.8.

When transmitting an image using an image fiber having such a small V value, especially when the object to be observed is under white light or fluorescent light, a red or green color haze is observed around the object. This phenomenon is thought to be because in image fibers with small V values, there are some relatively low-order cutoff frequencies in the visible light region, and light at these wavelengths leaks out of the core and propagates to the surroundings as stray light. ing.

In order to remove this stray light, it is conceivable to place a light absorber between pixels in a bundle type image guide, but this configuration cannot be used when a fused multi-core type image fiber is used as an image guide.

Therefore, in the case of fused multi-core image fibers, the V value between adjacent pixels is conventionally changed by changing the pixel diameter or changing the refractive index difference (see inside the image fiber cross section). By making the V values of the pixels randomly arranged as a whole), stray light is spread over the entire visible range, or whitened, rather than at a specific wavelength (for example, red or green), making the observed image easier to see. It has been proposed to improve the image fiber (Crosstalk characteristics of image fibers, p. 1202, Proceedings of the 1981 National Conference of the Institute of Electronics and Communication Engineers).
, Japanese Patent Publication No. 60-52802 "R Image Fiber").

Problems to be Solved by the Invention However, with the conventional configuration in which the V values of pixels are randomly arranged, it is possible to remove the presence of a specific color blur in a part of the observed image, but it is difficult to eliminate stray light. This whitened stray light causes a decrease in the contrast of the observed image. In other words, with the conventional technology, a decrease in the contrast of the transmitted image was unavoidable.

SUMMARY OF THE INVENTION An object of the present invention is to provide a fiberscope that eliminates color blurring at specific wavelengths and a reduction in contrast due to white noise, and provides a clear observed image.

Means for Solving the Problems According to the present invention, the image fiber is bent at at least one location, and the bent location is housed in the eyepiece tube.

Of the light propagating through the working core, light near the cutoff wavelength is very likely to be emitted. The extent of this emission increases as the fiber is bent to a smaller diameter. Conversely, a fiber that is bent very strongly will emit light with a shorter wavelength than the cutoff wavelength to the outside of the core, and as a result, only the propagation mode will propagate.

In other words, the radiation mode that is emitted outside the core near the cutoff wavelength and propagates to surrounding pixels, causing a smearing phenomenon, is removed by bending the fiber.

Since the stray light itself is removed in this way, unlike simply whitening the stray light, there is no reduction in contrast.

Furthermore, since the bent portion of the fiber is housed within the eyepiece tube, operability is not impaired.

Embodiment FIG. 1 shows a first embodiment. In this embodiment, the image fiber 3 is crank bent at 90' at four locations, 41, 42, 43, and 44, respectively. This image fiber is a fused multi-core image fiber with multiple cores in one fiber, and its diameter is usually quite thick (in order to increase the resolving power of a fiberscope, the number of pixels must be increased). For example, if the number of pixels is 30,000 to 50,000, the diameter of the image fiber is 2 mm to 4 mm.
), simply applying force will reduce the radius of curvature from 5 to 10 m.
Therefore, in this embodiment, the image fiber 3 is heated and melted to provide a strong bend with a radius of curvature of about 1 to 10 mm.

The fiberscope is constructed by covering the image fiber 3 with a protective coating 5, attaching an eyepiece tube l to one end thereof, and attaching an objective lens tube 6 to the other end. An eyepiece lens 2 is housed in an eyepiece barrel 1, and an objective lens 7 is housed in an objective lens barrel 6.

Therefore, the above bending points 41 to 4 of the image fiber 3 are
4 is housed within this eyepiece tube l so as not to impair operability. - Figure 2 shows a second embodiment. In this embodiment, the image fiber 3 is crank-bent only at one point 4, and the eyepiece tube 1 is also bent 90' in accordance with the bending of the image fiber 3. By bending the image fiber 3 and the eyepiece tube l as in this embodiment, the optical axis can be freely changed.

Next, we will compare the transmitted images between a conventional fiberscope with the configuration shown in Fig. 3, which does not bend the image fiber, and the fiberscope of the present invention, in which the image fiber is bent at two points (crank bending with a radius of curvature of 2 mm). I compared them. In FIG. 3, the screen 31 is white with a black circle drawn in the center.The screen 31 is illuminated with an incandescent light bulb 32, transmitted through a fiberscope 33, and the transmitted image is captured using a TV camera. Take a photo.

The camera controller 35 includes a monitor 36 and a plotter 37.
An observation image 38 is displayed on a monitor 36, a scanning line 39 that crosses the center of the black circle is specified, and the signal on this scanning line 39 is plotted on a plotter 37.

In this way, measurement results as shown in FIG. 4 were obtained. In conventional fiberscopes, the contrast deteriorates due to the addition of stray light, but in the fiberscope of the present invention, such stray light is removed and the contrast and last of the original image on the screen 31 are faithfully reproduced. I understand.

Effects of the Invention According to the fiberscope of this invention, it is possible to obtain an observation image with high contrast, and there is extremely little blurring of the image even when using an internal luminous body such as an incandescent light bulb or an object with extremely high brightness. The part of the present invention is housed in the eyepiece tube, so the operability is the same as that of conventional fiberscopes.The present invention is particularly useful for short fiberscopes where leakage light easily propagates, especially rigid scopes, borescopes, etc. is effective for a straight fiberscope with a length of about 1 m at most.

[Brief explanation of drawings]

FIG. 1 is a partially cutaway side view of a first embodiment of the invention, FIG. 2 is a partially cutaway side view of the second embodiment,
FIG. 3 is a schematic diagram of the measurement system, and FIG. 4 is a graph showing the measurement results. ■...Eyepiece tube 2...Eyepiece lens 3...
・Image fiber 4.41-44...Bending point 5...Protective coating 6...Objective lens barrel 7...
Objective lens 31...Screen 32...Incandescent bulb 33...Fiber scope 34...
TV camera 35...camera controller

Claims (2)

[Claims] (1) The image guide has a fused multi-core image fiber with multiple cores in one fiber, and an objective lens barrel is attached to one end of this image fiber, and an eyepiece barrel is attached to the other end. A fiberscope characterized in that the image fiber is bent at at least one location, and the bent location is housed in the eyepiece tube. (2) A fiberscope characterized in that the bending portion of the image fiber is bent with a radius of curvature of 10 mm or less.