JP2694349B2 - Micro displacement measurement device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention is a micro-displacement measuring device for optically detecting a micro-displacement of an object to be measured.

[Conventional technology]

There are roughly four types of measuring methods for non-contact displacement measuring methods using light whose measuring accuracy is several μm or less. First, the light is emitted from the light output port to the DUT, and the intensity of the light reflected from the DUT is displaced by utilizing the correlation with the distance from the light output port to the DUT. It is a method of finding the quantity. Second, the light is emitted from the light emission port to the object to be measured, and is reflected or scattered from the surface of the object to be measured by a detector installed at a position forming a certain angle with a straight line connecting the light emission port and the object to be measured. Is a method of measuring the amount of displacement of the object to be measured by measuring the angle of light incident on the detector. A third method is to radiate coherent light from a laser or the like to the object to be measured, cause the light reflected from the object to be measured to interfere with the reference light, and detect the amount of displacement by measuring the interference light. Fourth, illuminate the object to be measured and capture the object with a detector such as a camera or a microscope.
This is a method of measuring the shape and dimension after performing electrical or optical processing such as image processing and image enlargement.

The above-mentioned method is used properly according to the shape and measurement location of the object to be measured and the dimensional accuracy. In particular, in the case where the disk and the cylinder have pores with a diameter of 1 mm or less in the center, the fourth measuring method has been conventionally used to measure the eccentricity of the inner diameter with respect to the outer diameter. The specific measuring method is as follows. That is, the circumference of the measured object is placed on the V portion of the fixed V-groove jig, the measured object is rotated, and the transmitted light or the end face is irradiated with the hole, so that the measured object forms a pore. 1 in the center
Measure the displacement of the inner diameter edge part when rotating. At this time, image processing is performed to clearly define the edge portion, the hole portion and the object to be measured are divided into black and white, and the displacement of the boundary is measured. Since the boundary displayed after image processing and the actual boundary change depending on the intensity of transmitted light and reflected light and the shape of the object to be measured, the boundary must be set in advance with a reference object similar to the object to be measured.

[Problems to be solved by the present invention]

When measuring the eccentricity of the inner diameter with respect to the outer diameter with a measurement accuracy of 1 μm or less for the object to be measured having a fine hole with a diameter φ1.0 mm or less in the center of the disk and cylinder, With the method described above, only the surface portion of the object to be measured can be measured, and when observing the edge of the edge at a high magnification, it is necessary to use a reference material similar to the object to be measured for the accuracy of the edge.

[Means for solving the problem]

As the measuring terminal, an optical fiber having a surface having an angle of 45 ° with the longitudinal axis at the tip and an outer diameter smaller than the inner diameter of the object to be measured is used. Then, the object to be measured is placed on the V block and rotated on the V block. An optical fiber terminal with a 45 ° beveled end face is inserted into the pore of the DUT, and coherent light such as laser light incident from the other end of the 45 ° beveled face passes through the optical fiber and is reflected by the 45 ° beveled face. From the side surface of the fiber, part of it returns to the light source side by Fresnel reflection, and the other part is emitted to the inner surface of the pore of the DUT, enters the reflection hole into the fiber again, is reflected at the 45 ° end surface, and returns to the light source side. The light reflected on the side surface of the optical fiber and the light reflected on the inner surface of the pore of the object to be measured cause interference in the fiber. The intensity of the interference changes depending on the amount of displacement between the side surface of the fiber and the inner surface of the pore of the object to be measured. Therefore, the amount of displacement is measured by taking out the interference light returning to the light source side and measuring the intensity thereof. The object to be measured is on the V block 1
The present invention provides a device for measuring the amount of eccentricity from the amount of displacement observed when rotating, and the present invention provides a device for measuring the amount of eccentricity inside the pores, and for measuring a minute amount of displacement without using the reference material. To do.

〔Example〕

 Hereinafter, examples of the present invention will be specifically described.

The measuring optical system path of the device of the present invention is shown in FIG. The DUT (1) has, for example, an inner diameter of 0.126 mm, an outer diameter of 2.500 mm, and a length of 1.
The inner surface and the outer surface of the alumina ceramic having a dimension of 2 mm are machined together with the inner surface and the outer surface thereof, and they are placed on the V block (2) and rotated while being in contact with the V block during measurement. An optical fiber (4) having an outer diameter of φ0.100 mm and a core diameter of 10 μm, which has an inclined end face (3) of 45 °, is inserted into the inner diameter of the object to be measured (1). The light source (9) is 1.3 μm
The light emitted from the light source (9) is collected by the lens system (7) and efficiently transmitted into the optical fiber (4) by using the semiconductor laser having the wavelength of. The isolator (6) removes the return light to the light source (9) in order to prevent fluctuations in the optical power and wavelength of the light source (9). On the other hand, the interference light reflected by the 45 ° oblique end face (3) is sent to the light receiving element (photodiode) (10) through the lens system (8) after being branched by the optical branching device (5), and the light intensity is increased. To be measured. The optical path of the 45 ° beveled surface (3) is shown in a larger scale in Fig. 2. The light (13) that has passed through the optical fiber (4) is reflected at the 45 ° beveled surface (3) and is reflected on the side surface of the fiber. The partially reflected light (14) is reflected again by the 45 ° slant end face (3), and the light that has passed through the side surface of the optical fiber (4) is located at a distance d from the side surface of the fiber under test (1). The reflected light (15) reflected by the inner surface 1a of the laser enters the optical fiber (4) again from the side surface of the fiber, is reflected by the 45 ° end face (3), interferes with the reflected light (14), and interferes with the interference light (16). ) And return to the light source side. Since the light intensity of the interference light (16) has a displacement amount as shown in FIG. 3, the displacement amount can be measured by measuring the change in the light intensity of the reflected light (16) 6. When measuring displacement of 0.3 μm or less, ± 0.05 is obtained by measuring in the region where the light intensity of the interference light (16) and displacement are linear.
It becomes possible to measure with the measurement accuracy of μm. If there is a displacement of more than 0.3 μm, the displacement Δd is Δd, where η is the number of interference fringes per rotation of the DUT and λ is the wavelength used.
= Η · λ / 4 and can be measured with a measurement accuracy of ± 0.1 μm. In the above description, an example is given in which the object to be measured has a pore in the center and the amount of displacement of the inner diameter of the pore is measured, but the invention is not limited to this, and a circular cross section near the 45 ° beveled surface is used. By arranging and rotating the object to be measured, the amount of displacement of the outer diameter of the object to be measured can be measured with high accuracy.

〔The invention's effect〕

In this way, when the object to be measured is an object to be measured, such as a disc or a cylinder having a small hole in the center, and the amount of eccentricity of the inner diameter with respect to the outer diameter is measured, the effects of the device of the present invention are as follows.

First, the inner diameter of the pores in the center of the object to be measured is limited to the minimum dimension depending on the outer diameter of the fiber to be inserted. Therefore, the outer diameter of the fiber can be theoretically reduced to the vicinity of the core diameter by etching or the like. However, when the outer diameter of the fiber becomes small, precise measurement is difficult due to bending and vibration of the fiber.
When is 5 mm, it can be measured without problems by adding a vibration isolation mechanism. Therefore, it is possible to measure an object to be measured having an inner diameter that can be measured without bringing a fiber having an outer diameter of 50 μm into contact with the inner surface.

Secondly, because the interference of light is used, the wavelength of the light used is reduced, and the measurement accuracy improves as the micro displacement measurement of λ / 4 or less is measured, and the eccentricity is usually measured with the measurement accuracy of 0.1 μm or less. can do.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a small displacement amount measuring apparatus according to an embodiment of the present invention, and FIG. 2 is a diagram showing an optical path in the vicinity of a 45 ° slant end face of an optical fiber 4 in the apparatus shown in FIG. FIG. 3 is a graph showing the relationship between the light intensity of the interference light and the displacement amount. 1 ... DUT, 10 ... Light receiving element, 2 ... V block, 11 ... Clad, 3 ... 45 ° bevel, 12 ... Core, 4 ... Optical fiber, 13 ... Passed light, 5 ... Optical branch Container, 14 ...... Reflected light 6 ...... Isolator, 15 ...... Reflected light 7 ...... Lens system, 16 ...... Interference light 8 ...... Lens system, 17 ...... Fiber support 9 ...... Light source

Claims (1)

(57) [Claims] 1. A 45 ° beveled surface is formed at one end of an optical fiber,
The other end is made to send coherent light from a light source, the 45 ° slanted end face is arranged on the surface to be measured, and the surface of the object to be measured is detected by a light receiving element via an optical branching device provided in the optical fiber. A micro-displacement measuring device characterized by being configured to detect the intensity of interference light due to reflected light from the side surface of an optical fiber and to measure the amount of displacement of the object to be measured.