JPH0433003B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Technical Field> The present invention relates to a minute displacement meter using a multi-core fiber having a periodic pixel arrangement for observing a subject having a periodic pattern on its surface.

<Prior art> Medical endoscopes and industrial fiberscopes use multi-core fibers formed from a bundle of multiple optical fibers that maintain individually determined relative positional relationships at the objective end and eyepiece end. There is. Such multi-core fibers include those in which pixel lines are in a fixed one-to-one relative positional relationship only at both ends of the object end and eyepiece end, and those in which a large number of pixel lines are fused and integrated over the entire area of the multi-core fiber. things are known. The former method is usually called a lamination method, and a method for manufacturing multi-core fibers using multi-component fibers is known. The latter is called the multi-method and is known as a method for producing quartz-based multi-core fibers. In all of these multi-core fibers, the pixel fibers are packed in a hexagonal close-packed arrangement and are regularly arranged. It is known that when a measurement object with a periodic pattern is observed using such a multi-core fiber, moiré fringes are observed in the observed image of the multi-core fiber due to the regularity of the shading of the measurement object.

This is because the arrangement of the individual pixels of the multi-core fiber has a regularity like hexagonal close-packing, so the regularity of the shading of the image at the input end face of the multi-core fiber of the object to be measured is the same as the arrangement of the individual pixels of the multi-core fiber. This is because when the regularity approaches , moiré fringes occur. As a method for removing such moire fringes, a multi-core fiber is known in which the regularity of the pixel arrangement is eliminated by randomizing the core diameter of the pixel fiber.

By the way, moiré fringes are generally well known as a means of magnifying and measuring minute rotational displacements of objects. In Figure 1, 1 and 2 are equal periods.
It is a rectangular lattice with 2ω, and moiré fringes are observed when they are overlapped at an angle of θ.

Assuming that the interval between the moire fringes is W, W=ω/2 sin (θ/2) (1) If the rectangular grating 2 is displaced by ω in the direction perpendicular to the grating lines, the moire fringes move by W. That is, the amount of displacement of the rectangular grid 2 is magnified by 1/{2sin(θ/2)} times and observed. Therefore, even with ordinary multi-core fibers, a rectangular grid is attached to the object to be measured by utilizing the regularity of the pixel arrangement, and moiré fringes are created from this and the regularity of the pixel arrangement of the multi-core fiber, and moiré fringes are created based on the displacement of the object to be measured. It is conceivable to measure the displacement of the object to be measured from the amount of change in moiré fringes.

However, since the pixel fiber arrangement of a normal multi-core fiber has a hexagonal close-packed structure, the pixel arrangement has a mutual inclination of 60 degrees and regularity in three directions, as shown in Figure 1. Compared to the case of such a rectangular grid having regularity in one direction, the observed moiré fringes are more complex, making it difficult to detect minute displacements of the object to be measured.

<Purpose of the Invention> The present invention involves attaching a rectangular grid to a measurement target and measuring minute displacements of the measurement target at a location far away from the measurement target using a multi-core fiber with a periodic structure that can measure the displacement of the measurement target. The purpose is to provide a minute displacement meter that can perform measurements.

<Specific means for solving the problem> The configuration of the minute displacement meter that achieves this purpose is as follows:
P ₁ on many mutually parallel rows with the above row spacing.
A multi-core fiber consisting of cores arranged adjacent to each other with an interval P ₂ smaller than P ₁ and an image of the rectangular lattice on the object to be measured are placed on the end face of the multi-core fiber, and the core row spacing of the multi-core fiber is
P ₁ and an imaging lens that forms an image such that the period is equal to the period of the lattice stripes of the rectangular lattice and that the lattice lines of the rectangular lattice and the core row are inclined at an angle θ; and an imaging tube provided at the other end of the multi-core fiber; , displays the image signal converted into an electrical signal by the image pickup tube.
It is characterized by consisting of a CRT monitor.

<Example> An example of a multi-core fiber with a periodic structure used in the present invention will be described with reference to the drawings.

FIG. 2 is a cross-sectional view of a multi-core fiber with a periodic structure. In Figure 2, 3-1, 3-
2, . . . 3-23 is a core, and 4 is a cladding placed around the core. The refractive index of the core glass is selected to be larger than that of the cladding glass to obtain desired light propagation characteristics. As an example, the core is made of germanium-doped quartz and the cladding is made of pure quartz. As shown in FIG. 2, in the multi-core fiber with a periodic structure used in the present invention, three cores form a row with a row spacing of P ₁ .
-1,3-2,...3-10;3-11,3-12
...3-20;... are arranged. In addition, within each core row, the center spacing of the cores is arranged at P ₂ , and P ₁
>Selected as shown in P ₂ . Core 3-1, 3-2,
...3-10 forms a rectangular lattice as shown in FIG. 1 when viewed as a whole. That is, core row 3-
1, 3-2, ... 3-10 form one opening as a whole, and core rows 3-11, 3-12,
...3-20 forms another opening, and the same applies to the following, and as a whole, a large number of core rows forming a rectangular lattice in the cross section of the multi-core fiber are arranged. The core rows forming these openings are arranged at a row interval of _P1 . On the other hand, in the core rows forming each opening, the cores adjacent to each other are arranged at a core spacing _P2 smaller than the row spacing _P1 . As will be described later, when moire fringes are generated between the measurement target using lattice stripes corresponding to the row spacing P ₁ , the moire fringes will be generated at the core spacing P ₂ included in each core row. This is to prevent this from occurring. The multi-core fiber with a periodic structure used in the present invention shown in FIG. 2 is a conceptual diagram, and the number of core rows forming a lattice and the number of cores within a row are shown to be much smaller than the actual number.

To create a multi-core fiber with a periodic structure used in the present invention, as shown in Figure 3, an optical fiber preform consisting of a germanium-doped quartz core and a pure quartz cladding is formed in a jacket tube by the VAD method. A pure quartz spacer is interposed between the arrays to form a multi-core fiber base material.
Next, the multi-core fiber preform is melt-spun from the lower end to form a multi-core fiber of a desired diameter. 6-1, 6-2, 6-3 in Figure 3
... is an optical fiber preform consisting of a germanium-doped quartz core and a pure quartz cladding formed by the VAD method, 5-1, 5-2... are pure quartz spacers, and these spacers 5-1, 5-2... are multi-core. Column spacing of core arrays forming a rectangular lattice of fibers
It is meant to give P ₁ . 7-1, 7-2
... is a groaning pure quartz rod, and 8 is a glass jacket tube.

Specific examples of the multi-core fiber base material forming the multi-core fiber with a periodic structure used in the present invention are shown below. The jacket tube 8 shown in Figure 3 has an inner diameter of 90 mm, an outer diameter of 100 mm, and a length of 150 mm.
A quartz pipe with a closed bottom end was used. Optical fiber preform that forms pixels (core/cladding ratio)
0.5) is spun to 2 mmφ without coating, cut to have a single length of 100 mm, and as shown in Figure 3, 30 fibers are placed in each row between spacers 5-1, 5-2,... The cores were arranged in 15 rows. Spacer 5-1, 5
-2... prepares a plate-shaped pure quartz of 60 mm x 10 mm x 2 mm, and optical fiber preforms 6-1, 6-2,...
inserted between the columns. Optical fiber preform 6
-1, 6-2, ..., spacers 5-1, 5-2, ... and the jacket tube 8, place a 0.5mm pure quartz rod between them.
Spun into φ, cut into lengths of 100 mm, and between these
was filled. Thereafter, the internal pressure of the jacket tube 8 was reduced, and the whole was melted and integrated in an annular heating furnace to form a solid rod-shaped multi-core fiber preform, which was drawn using a spinning device to have an outer diameter of 1 mmφ. To maintain strength, a coating of silicone and vinyl chloride resin was applied immediately after spinning. 30 for each column like this
We obtained a multicore fiber as shown in Fig. 2, which has 15 core rows in a rectangular lattice. The core row spacing P ₁ of this multi-core fiber is approximately 40 μm, and the core spacing is approximately 40 μm.
_P2 was approximately 20 μm.

Next, FIG. 4 shows an embodiment of a minute displacement meter according to the present invention that measures minute displacements of an object using a multi-core fiber having such a periodic structure.

In FIG. 4, reference numeral 9 denotes an object to be measured, 10 a rectangular grating pasted so that the grid lines are perpendicular to the displacement direction of the object to be measured, 11 an imaging lens, and 12
13 is a multi-core fiber used in the present invention, 13 is an image pickup tube that converts the image propagated through the multi-core fiber 12 into an electrical image signal, and 14 is a CRT monitor that displays the image signal of the image pickup tube.

According to the minute displacement meter according to the present invention, a rectangular grid 10 is pasted onto the measurement target 9 so that the grid lines are oriented perpendicular to the direction of displacement of the measurement target. The image of this rectangular grating is captured by the imaging lens 11 on the end face 12a of the multi-core fiber 12 having a periodic structure.
image on top. In addition, the multi-core fiber end face 12
The period of the lattice fringes of the image of the rectangular lattice on a is made to match the pixel aperture row spacing P ₁ of the multi-core fiber, and the image of the rectangular lattice 10 is made such that both lattice lines overlap at a relatively small angle θ. The optical relationship between the imaging lens and the multi-core fiber end surface 12a is determined so that the image is formed on the multi-core fiber end surface. Therefore, when a minute displacement ω of the measurement object 9 occurs, the multi-core fiber end face 12a
The amount of movement W of the moiré fringes above is given by W=mω/2sin(θ/2) (2). Here, m is the magnification (or reduction) magnification of the imaging lens 11. The image formed on the multi-core fiber end face 12a propagates through the multi-core fiber 12, is photoelectrically converted by the image pickup tube 13, and is magnified and observed as an electrical pixel signal on the CRT monitor 14 as shown in FIG. be done.

Each aperture core row has the periodic structure explained above.
An imaging lens 11 with a focal length of 4 mm is attached to the tip 12a of a multi-core fiber of 30 fibers, 15 rows, P ₁ = 40 μm, P ₂ = 20 μm.
As shown in FIG. 4 at a distance of 40 mm, a reflective rectangular grating 10 (ω = 200 μm) is mounted on the measurement object 9 on the movable table, and the direction of the rectangular grating 10 and the opening row of the multi-core fiber tip 12a are aligned. When installed so that the direction is tilted by θ = 10°, the multi-core fiber 1 is
CRT monitor 14 placed far away via 2
In the image above, it was confirmed that the moiré fringes moved by 5 to 6 cores. Incidentally, in order to accurately measure the displacement of the object to be measured using the minute displacement meter shown in FIG. 4, it is necessary to make the interval _P2 between adjacent cores as small as possible. On the other hand, since the multi-core fiber used in the present invention is required to have the ability to transmit images, it is necessary to suppress the coupling of light between adjacent cores, so-called crosstalk, to a level that does not pose a practical problem. It is empirically known that when a silica fiber with a refractive index difference of 2% is used, the minimum distance between adjacent cores is approximately 6 μm. In this example, the core spacing was 20 μm, and cross There is no problem with talk. On the other hand, increasing the core spacing P ₂ is not a good idea as it will reduce the number of cores within a unit cross section, which will lower the resolution.

Although the embodiments described above are examples of quartz-based multi-core fibers melt-spun using a multi-layer method, it is also possible to form multi-core fibers with a periodic structure formed by intervening spaces using a lamination method.

<Effects of the Invention> By using the multi-core fiber with the periodic structure shown in the present invention, a minute displacement meter is constructed that can measure minute displacements of the object to be measured at separate locations.
Conventionally, moiré fringes are formed between a rectangular grating attached to the measurement target and a rectangular measuring grating, and this moire fringe image is photoelectrically converted and processed nearby to convert it into an electrical signal, which is then received at a distant point. However, in harsh environments such as explosion-proof, high temperature, radioactive or toxic processing where the environment of the object to be measured cannot be accessed by humans, electrical means such as this can be used. It was inevitable that things would be destroyed and become unusable, or their functions would be seriously impaired. However, according to the minute displacement meter using a multi-core fiber with a periodic structure according to the present invention, it has become possible to accurately measure minute displacements with high reliability even in these environments.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram of displacement measurement using moire fringes, Fig. 2 is a cross-sectional view of a multi-core fiber with a periodic structure used in the present invention, and Fig. 3 is a base material of the multi-core fiber with a periodic structure used in the present invention. An explanatory diagram of the structure, FIG. 4 is a configuration diagram of a minute displacement meter according to the present invention. In the drawing, 1 and 2 are rectangular grids, 3-1, 3-2...
3-23 is core, 4 is clad, 5-1, 5-
2, . . . are spacers, 6-1, 6-2, . . . are optical fiber preforms, 7-1, 7-2, . 1 is an imaging lens, 12 is a multi-core fiber, 13 is an image pickup tube, and 14 is a CRT monitor.

Claims (1)

[Claims] 1. A measurement object with a rectangular grid pasted thereon and a number of mutually parallel rows with a predetermined inter-row spacing P ₁ are measured from cores arranged adjacent to each other at a spacing P ₂ smaller than the above-mentioned inter-row spacing P ₁ . The image of the rectangular lattice on the object to be measured is placed on the end face of the multi-core fiber, and the distance between the core rows of the multi-core fiber is equal to the period of the lattice stripes of the rectangular lattice, and the lattice lines of the rectangular lattice and the core rows are at an angle. an imaging lens that forms an image tilted at θ, an imaging tube provided at the other end of the multi-core fiber, and a CRT that displays image signals converted into electrical signals by the imaging tube.
A minute displacement meter characterized by consisting of a monitor.