JP3009521B2 - Measurement endoscope - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a measuring endoscope which is inserted into a small area such as the inside of a human body organ or the inside of industrial equipment to measure the unevenness of its surface shape.

[0002]

2. Description of the Related Art Conventionally, as a measurement endoscope for measuring irregularities on the surface of internal organs and the like, a measurement endoscope utilizing a line-shaped diffraction pattern of laser light by a diffraction grating is generally known. This diffraction pattern is projected onto the surface of the object to be measured by a projection lens, and when this projected image is observed from a position having parallax by an image sensor such as a solid-state image sensor, the line pattern is deformed according to the unevenness of the surface. appear. for that reason,
By calculating the displacement of the brightness from the reference position for each bright part of the linear pattern on the surface of the measured object based on the image signal of the image sensor, it is possible to measure the uneven shape of the object surface It is.

A fringe scanning method is one of the methods for measuring the surface shape of an object. This measurement method has three features: high-precision measurement, measurement that does not depend on contrast unevenness, and the difference between concave and convex can be automatically determined. The fringe scanning method is also used for shape inspection of an optical element such as a lens, but it is considered appropriate to use a projection type fringe scanning method for a measurement endoscope. If the projection fringe scanning method is applied to a measurement endoscope, only the unevenness information can be obtained without being affected by the color change of the lesion.

[0004]

However, in this type of measurement endoscope, if unevenness occurs in the contrast of a line pattern due to the color of the surface of an object to be measured or the depth of irregularities, accurate surface measurement is required. There is a problem that can not be performed. Further, there is no example in which the projection fringe scanning method is used for measuring an object shape in a narrow area, and it cannot be used for a small and small-diameter optical system such as an endoscope.

SUMMARY OF THE INVENTION In view of the above problems, an object of the present invention is to provide a measurement endoscope capable of measuring unevenness on the surface of an object without being affected by unevenness in contrast of measurement light.

[0006]

The measuring endoscope according to the present invention comprises an interference fringe generating means for generating interference fringes on the surface of the object to be measured, and an interference fringe for scanning the interference fringes on the surface of the object to be measured. Scanning means, and imaging means for capturing a projection image of interference fringes,
Computing means for computing information on the unevenness of the surface of the object to be measured based on the image signal from the imaging means based on the principle of the fringe scanning method.

[0007] The measurement endoscope of the present invention includes the interference fringe generator.
Configuration means to project interference fringes on the surface of the object to be measured
And, the interference fringe scanning means makes the interference fringes orthogonal to the fringe direction.
To move the image pickup means in the front direction.
Light intensity on the surface of the DUT caused by the movement of the interference fringes
Is configured to be readable, and the arithmetic unit is configured to read the change.
The change in light intensity at each point on the surface of the measured object
To be configured to operate using the principle of the fringe scanning method
From the depth and height of the irregularities on the surface of the workpiece
It is characterized by the following .

Accordingly, in the measurement endoscope of the present invention, the interference fringes are projected on the surface of the object by the interference fringe generating means, and the interference fringes are moved in the direction orthogonal to the fringe direction by the interference fringe scanning means. The state of the change in light intensity on the surface of the object to be measured is read by the imaging unit, and the change in light intensity at each point on the surface of the object to be measured is calculated by the arithmetic unit using the principle of the fringe scanning method. The depth and height of the unevenness can be determined.

FIG. 1 is an explanatory view showing the principle of the measuring means according to the present invention. In FIG. 1, 1 is a light source for emitting a laser beam B, and 2 and 3 are lenses constituting a beam expander for expanding the laser beam B. 4, a beam splitter for splitting the expanded beam, 5 a fixed reflecting mirror for reflecting the beam reflected by the beam splitter 4, 6 for reflecting the beam passing through the beam splitter 4, and suitable for the incident optical axis Movable mirror 7 arranged at an inclined angle
Is an electrostrictive element capable of moving the movable reflecting mirror 6 along the incident optical axis under the control of a computer described later, and 8 is a projection for enlarging the reflected beams from the two reflecting mirrors 5 and 6 superimposed by the beam splitter 4. It is a lens, and the two beams that have passed through the projection lens 8 interfere with each other to create a strong optical field in space.

Reference numeral 9 denotes an object to be measured whose two beams passing through the projection lens 8 are irradiated on its surface 9a. When the beam is placed at a measurement position in an optical field, the intensity of the interference light is reduced on the surface 9a by interference fringes. Appears as 10. This fringe 10 is called a Young's interference fringe. When the surface 9a of the DUT 9 is a flat surface, the fringe 10 is a substantially straight fringe at a position not far from the optical axis of the irradiation light. However, if the surface 9a has irregularities, it becomes a stripe deformed according to the irregularities. Also, if the position of the movable reflecting mirror 6 is changed by the electrostrictive element 7,
The phase of the interference light on “a” changes, and the interference fringe 10 moves in a direction orthogonal to the fringe direction.

Reference numeral 11 denotes a camera or image sensor which is arranged at a predetermined angle with respect to the surface 9a of the object 9 and captures images of the interference fringes 10 and changes thereof.
Is a computer that calculates and outputs the depth and height of the unevenness from the change in the light intensity at each point on the surface 9a of the object to be measured based on the image signal read in step (1).

As described above, the present invention measures the unevenness using the principle of the fringe scanning method. Next, the principle of the fringe scanning method performed by the computer 12 will be described. When the interference fringes generated by the two light beams having the intersection angle α are projected onto the surface of the measurement object at the incident angle θ, the position of each measurement point on the surface is represented by x and y coordinates, and the interference fringes have the shape f of the surface. (X,
y), the light intensity distribution I _n (x,
y) is given by the following equation. I _n (x, y) = a (x, y) + b (x, y) cos [2π (x / d _x + Φ (x, y)) − φ _n ] ‥‥ (1) where a (x, y): average light intensity b (x, y): fringe contrast φ _n : initial phase of interference light d _x : fringe interval (on the surface of the object to be measured) in x direction Φ (x, y): surface shape Function for bumps.

Further, d _x is given by the following equation. _{λ d x = d / cos θ} = ─────────── ‥‥ (2) 2sin (α / 2) cos θ where, d: fringe spacing. Further, the function Φ (x, y) relating to the unevenness of the surface shape in the equation (1) can be represented by Φ (x, y) = f (x, y) sin θ / d ‥‥ (3).

Here, by scanning the interference fringes,
The function Φ (x,
The information of y) is represented by a (x,
y) and b (x, y) can be measured separately. When the initial phase φ _n is changed by 90 ° and four different interference intensity distributions when φ _n = nπ / 2 (n = 0,1,2,3) ‥‥ (4) are used,
Cos [2π (x / d _x + Φ (x,
y)) − φ _n ] is calculated as follows: I ₁ −I ₃ 2π (Φ (x, y) + x / d _x ) = tan ⁻¹ (─────) mod 2π ‥‥ (5) I ₀ − it can be expressed as I _2. The phase value obtained here is 0
Since it is 2π and there is a discontinuity point, phases are smoothly connected by adding and subtracting 2π before and after the discontinuity point. Further, the second term x / d _x on the left side of the equation (5) can be easily removed from Φ (x, y) because this term changes uniformly with respect to the x axis, and (3) ) Can be used to obtain the surface height f (x, y).

Under the above-described configuration, the laser beam B emitted from the light source 1 passes through the lenses 2 and 3 and is spread to an appropriate size.
And is reflected again by the fixed reflecting mirror 5. Some beams pass through the beam splitter 4 and are reflected by the movable reflecting mirror 6 at a predetermined angle with respect to the incident optical axis. Then, the two beams reflected by the two reflecting mirrors 5 and 6 pass through and are reflected by the beam splitter 4 and are superimposed on each other, and are irradiated onto the surface 9a of the object 9 via the projection lens 8 at a predetermined intersection angle. You.

Accordingly, the two beams interfere with each other and project a substantially linear interference fringe on the surface 9a.
A stripe 10 deformed according to the irregularities on a appears. The interference fringe 10 is imaged by the camera 11. Then, when the electrostrictive element 7 is operated by energization from the computer 12 and the movable reflecting mirror 6 changes its position along the incident optical axis, the reflected beam of this reflecting mirror 6 is reflected on the surface 9a of the object to be measured. Since the phase changes, the interference fringe 10 moves in a direction orthogonal to the fringe direction. The change of the stripe 10, that is, the change of light intensity is read by the camera 11 and input to the computer 12. Then, from the change in the light intensity at each point on the surface 9a after the scanning of the interference fringes 10, the depth and height of the concavities and convexities at each point are obtained by the arithmetic expression based on the principle of the above-described fringe scanning method. .

As described above, according to the principle of the present invention, even if the contrast due to the color of the surface of the object to be measured or the depth of the unevenness is uneven, the light intensity changes due to the movement of the interference fringes.
The unevenness of “a” can be measured, and is not affected by uneven contrast. Further, the judgment of the concave and the convex can be made automatically.

[0018]

Embodiments of the present invention based on the above-described principle will be described below with reference to FIGS. FIG. 2 is an explanatory view of a main part showing the first embodiment of the present invention, in which the device under test 9, the camera 11, and the like are omitted. In the drawing, reference numeral 14 denotes a polarizing beam splitter for dividing light incident from the light source 1 into two polarized lights, and 15 denotes a quarter-wave plate disposed between the polarizing beam splitter 14 and the fixed reflecting mirror 5, and a polarizing beam splitter. One polarized light component reflected by the splitter 14 is polarized by passing through the quarter-wave plate 15 twice between the fixed reflecting mirror 5 and the fixed reflecting mirror 5, and is transmitted through the polarizing beam splitter 14. Reference numeral 16 denotes a の 間 に wavelength plate disposed between the polarizing beam splitter 14 and the movable reflecting mirror 6. The other polarized component passing through the polarizing beam splitter 14 reciprocates twice with the movable reflecting mirror 6. The light is polarized by passing through the quarter-wave plate 16, reflected by the polarization beam splitter 14, and superimposed on the above-mentioned polarized light component.

Reference numeral 17 denotes a coupler lens through which the two beams superimposed by the polarization beam splitter 14 pass, 18 denotes a polarization-maintaining optical fiber having one end connected to the coupler lens 17, and 19 connects to the other end of the fiber 18. Head. In the head 19, reference numeral 20 denotes a birefringent plate (a polarizing prism or the like) disposed in front of the lens 21. Two beams guided from the polarizing beam splitter 14 to the polarization plane preserving optical fiber 18 have polarization directions orthogonal to each other. By adjusting the crystal axis of the birefringent plate 20 with respect to these beams, one polarized beam becomes ordinary light and the other polarized beam becomes extraordinary light.
Only the other polarized beam is given a lateral displacement (see FIG. 3). Due to this effect, a difference occurs in the propagation directions of the two beams that pass through the projection lens 8 and irradiate the object to be measured. Reference numeral 22 denotes a polarizing plate disposed between the birefringent plate 20 and the projection lens 8 and passing only two orthogonal polarization components.

Here, immediately after the exit end of the polarization-maintaining optical fiber 18, it is tilted with respect to the optical axis via a lens 21 and the x- and y-polarization axes of the exit end of the polarization-maintaining optical fiber 18 are arranged. Birefringent plate 20 having an optical axis aligned with one
Is arranged to separate the light beam that has exited the polarization-maintaining single-mode fiber 18 into two. Further, by providing a polarizing plate 22 having a polarizing axis inclined by 45 ° with respect to the optical axis of the birefringent plate 20, only the coherent component of the two polarized components is extracted to form interference fringes.

In this embodiment, as a means for splitting light for each polarization component, a method of arranging the crystal axis of the birefringent plate 20 at an angle with respect to the optical axis is used. Birefringent crystals such as rutile, calcite, and sapphire are used. Further, as a means for splitting light for each polarization component, a double image prism such as a Savart plate, a Senarmont prism (compensator), a lotion polarizing prism, a Wollaston prism, or the like can be used.

FIG. 4 shows a cross section of the polarization-maintaining optical fiber 18 used in this embodiment. Polarization-maintaining optical fiber 1
8 is formed so that a difference in refractive index between the x-axis direction and the y-axis direction occurs by providing stress applying portions 18a and 18b around the core 18c of a normal single mode fiber.

In the case of this embodiment, the electrostrictive element 7 and the like constituting the fringe scanning section are disposed outside the endoscope, and only the head 19 is viewed through the forceps channel and the like together with the polarization-maintaining optical fiber 18. Used in mirrors. The surface 9a of the object to be measured
The interference fringe 10 projected on top of the image guide, not shown, differs from the principle of the present invention described above.
You may make it observe with a CD camera.

As for the configuration inside the head 19, instead of the above configuration, the two beams emitted from the fiber 18 are again divided into two optical paths by a polarizing device such as a polarizing fiber coupler or a polarizing beam splitter. Alternatively, by giving a polarization rotation effect to one of the beams, the polarization directions of the two beams may be matched to project the interference fringe on the surface 9a of the device under test. As described above, according to the present embodiment, a measuring unit using the principle of the projection fringe scanning method can be employed in an endoscope that requires a small and small-diameter optical system.

FIG. 5 shows a second embodiment of the present invention. In the figure, reference numeral 23 denotes a wavelength-changeable, for example, dye laser, F center laser, or temperature stabilized semiconductor laser. 24 is an optical fiber for guiding light from the light source from the coupler lens 17 to the head 25, and 26 is an optical fiber disposed in the head 25 and
A lens for converting the light emitted from 4 into a plane wave; 27, a beam splitter whose reflection surface is disposed at a slight inclination from an angle of 45 ° with respect to the optical axis of the incident plane wave;
Is a reflection coat made of aluminum or the like, which is attached to two adjacent side surfaces of the beam splitter 27 and has surfaces 28a and 28b for reflecting light passing through the beam splitter 27 and light reflected therefrom, respectively. Are arranged at different distances from the light splitting point in the beam splitter 27, so that a phase difference occurs between the two lights respectively reflected by the reflection coat. still,
As the beam splitter 27, a beam splitter whose one side surface is slightly inclined with respect to the optical axis of the incident light may be used. In this case, a half mirror may be used instead of the beam splitter 27.

In this embodiment, the beam splitter 2
A part of the light incident on 8 is reflected and reflected again on the surface 28b of the reflection coat 28, and another part of the light passes through the beam splitter 27 and is reflected on the surface 28a of the reflection coat 28. The two lights are superimposed and travel toward the projection lens 8, but their traveling directions are shifted from each other by the inclination angle of the reflection surface of the beam splitter 27, and a phase difference is caused by being reflected by the surfaces 28 a and 28 b of the reflection coat 28. . Therefore, the interference fringes 10 are projected on the surface 9a of the object to be measured through the projection lens 8. Then, by changing the wavelength of the light source 23, the phase difference between the two lights that generate the interference fringes is changed, and fringe scanning is performed.

In this embodiment, only the head 25 and the optical fiber 24 are arranged inside the endoscope, and the light source 23 and the wavelength changing device (not shown) are arranged outside the endoscope. or,
Instead of the light source 23 described above, a small laser such as a semiconductor laser may be arranged on the incident side of the lens 26 in the head 25. In this case, the optical fiber 24 or the like becomes unnecessary, and the supply current may be changed through the electric cable to change the wavelength of light.

In this embodiment, the size of the apparatus can be reduced as compared with the above-described first embodiment, and the distance from the light division position to the irradiation position of the interference fringes can be reduced as compared with the first embodiment. The short length has the advantage that the projected interference fringes and fringe scanning are stable against external influences. Note that a polarizing beam splitter is used instead of the beam splitter 27, and the polarizing beam splitter and the surfaces 28a and 28b of the reflection coat 28 are used.
If a quarter-wave plate is inserted between the first and second wavelengths, interference fringes can be efficiently generated. In this case, it is necessary to insert a polarizing plate between the polarizing beam splitter and the projection lens 8.

Next, FIG. 6 shows a third embodiment of the present invention, in which 30 is an optical fiber into which a laser beam emitted from the light source 1 is introduced through the coupler lens 17.
Numeral 31 denotes a fiber type optical demultiplexer which branches the light in the optical fiber 30 and propagates in the optical fibers 32 and 33, respectively.
Reference numeral 4 denotes a fiber type phase shifter which is disposed on one optical fiber 33 and uses a stress or the like capable of changing the phase of light propagating in the fiber 33.
A head provided with a pair of lenses 36 and 37 for expanding the beams emitted from these tips, respectively. An interference fringe is formed on the object by the beams emitted from the lenses 36 and 37. Is projected.

Since the apparatus according to the present embodiment is mostly constituted by fiber type optical elements, there is an advantage that the diameter of the endoscope can be reduced.

FIG. 7 shows a fourth embodiment of the present invention. In FIG. 7, reference numeral 39 denotes an optical fiber through which a laser beam emitted from the light source 1 or the like propagates, and reference numeral 40 denotes LiNbO ₃ provided on a head 41. A crystal plate 42 is formed on the crystal plate 40 and is divided into two optical waveguides in the middle, 43 is a coupler lens interposed between the optical fiber 39 and the optical waveguide 42, and 44 is a branched lens. This is a phase shifter that is provided in one of the optical waveguides 42 and can change the phase of light using an electro-optic effect or the like. In this embodiment, the size of the head 41 can be further reduced as compared with the above-described embodiments.

FIG. 8 is an explanatory view showing a fifth embodiment of the present invention. In FIG. 8, for example, a dye laser, an F center laser, or a semiconductor stabilized in temperature which can change the wavelength is shown. Light from a light source 23 composed of a laser or the like is guided to the coupler lens 17, 46 is a multi-mode optical fiber into which light from the light source 23 is introduced via the coupler lens 17, and 47 is a crimp-fixed multi-mode optical fiber 46. Reference numeral 48 denotes an electrostrictive element having one end attached to the flat plate 47, and 49 denotes a drive circuit for applying a high-frequency voltage to the electrostrictive element 48. In a head 25 connected to the other end of the multi-mode optical fiber 46, a lens 26 for converting light emitted from the multi-mode optical fiber 46 into a plane wave, and a reflecting surface having an angle of 45 ° with respect to the optical axis of the plane wave A beam splitter 27 arranged at a slight inclination from the light source, and a reflecting surface 28 arranged on a side surface at a different distance from a light splitting point in the beam splitter 27.
a and 28b, and a reflection coat 28 for generating a phase difference in light reflected on each reflection surface, and a projection lens 8 are provided. In the fringe scanning in the present embodiment, by changing the wavelength of the light source 23, fringe scanning is performed by changing the phase difference between two lights that generate interference fringes.

When the multi-mode optical fiber 46 is used, the emission pattern of the multi-mode optical fiber 46 includes a speckle pattern caused by a modal interference component, and an interference fringe is generated on the surface of the measured object using such light. When you do
A light intensity distribution occurs as if linear interference fringes were superimposed on the speckle pattern. If such a light intensity distribution is used as it is, the measurement accuracy deteriorates. Therefore,
In the present embodiment, the speckle pattern is averaged by changing the refractive index in the multi-mode optical fiber 46 by using the electrostrictive element 48 to prevent the measurement accuracy from deteriorating.

That is, when the driving circuit 49 drives the electrostrictive element 48, the stress is applied to the multi-mode optical fiber 46 via the flat plate 47. Thereby, the refractive index in the multimode optical fiber 46 can be changed periodically, and the modal interference component generated in the multimode optical fiber 46 can be averaged over time. The light emitted from the multimode optical fiber 46 is
The beam is split and overlapped by the beam splitter 27 toward the projection lens 8, and at this time, the beam splitter 27
The traveling directions are deviated from each other due to the inclination angle, and the light is reflected on the surfaces 28a and 28b of the reflection coat 28, so that a phase difference is generated between them. Thereby, the projection lens 8
, A linear interference fringe is projected on the surface of the object to be measured.

As described above, in this embodiment, since the multi-mode optical fiber 46 is used as the optical waveguide, light can be used more efficiently than when a single-mode optical fiber is used. Therefore, bright interference fringes can be obtained.

FIG. 9 is an explanatory view showing a sixth embodiment of the present invention. In this embodiment, the light source 23, the multi-mode optical fiber 46, the head 25, and the like have the same configuration as that of the above-described fifth embodiment, but the means for temporally averaging the modal interference component is different. In the figure, a multimode optical fiber 46 is wound several times around the outer periphery (circumference) of the electrostrictive element 50 instead of the flat plate 47. When a high-frequency voltage is applied to the electrostrictive element 50 by the drive circuit 49, the electrostrictive element 50 expands and contracts,
Stress is applied to the multimode optical fiber 46. Thereby, the modal interference component in the multimode optical fiber 46 can be averaged over time.

In this case, as compared with the fifth embodiment, stress can be applied to the long multimode optical fiber 46, so that the modal interference component can be averaged at a relatively low voltage.

FIG. 10 is an explanatory view showing a seventh embodiment of the present invention. In the figure, reference numeral 51 denotes a light source unit configured to emit coherent linearly polarized light and control the oscillation direction angle (azimuth angle) θ of the linearly polarized light, and 52 denotes a light source unit 5
A quarter-wave plate for changing the phase difference between polarized waves orthogonal to each other with respect to the light emitted from 1, an objective lens 53, an image guide 54, and an eyepiece 55. When performing measurement, an image is captured using a camera or the like instead of the eyepiece lens 55, and calculation is performed.

According to the present embodiment, the phase difference between the polarization components is propagated to the distal end thereof using the polarization-maintaining optical fiber 18 to perform the phase shift, and the phase shift means can be arranged on the hand side. The tip can be miniaturized, and the generated interference fringes can be observed through the objective lens 53, the image guide 54 and the eyepiece 55. Furthermore, since the means for performing an external phase shift can change the phase difference without changing the phase difference by dividing the light into polarized light components and changing the phase difference with a single light beam, The advantage is that the interference fringes and fringe scanning projected against external influences are stable. In addition, there is an advantage that the configuration is simple, the device can be manufactured at a low cost, the adjustment at the time of condensing light on the fiber is easy, and the product can be easily manufactured. In this embodiment, even if the quarter-wave plate 52 and the polarization-maintaining single-mode fiber 18 are arranged in a different order, the effect is the same.

FIG. 11 shows a specific example in which the light source unit 51 includes a linearly polarized coherent light source 51a such as a semiconductor laser or a He--Ne laser and a half-wave plate 51b as a rotation controllable element. It is shown. Here, 51c and 56 are collimating lenses, 5
Reference numeral 7 denotes a projection lens.

FIG. 12 shows a change in the polarization state of light by each optical element shown in FIG. Assuming that the oscillation direction of the linearly polarized light is 45 °, the linearly polarized light is は.
After passing through the wave plate 51b, only the vibration direction rotates by the angle 2θ. Next, by passing through a quarter-wave plate 52 whose azimuth is set to 45 °, the polarization state changes as shown in FIG. In this case, the 波長 wavelength plate 52
The azimuth angle of 45 ° means that the azimuth of the quarter-wave plate 52 is 4 with respect to the x and y polarization axes at the incident end of the polarization-maintaining optical fiber 18.
5 ° means tilted.

In this configuration, the rotated linearly polarized light after passing through the half-wave plate 51b passes through the quarter-wave plate 52, so that the phases of the x and y components are continuously changed. The two components x and y have the same intensity, and a constant state is realized. This light beam is transmitted by the polarization-maintaining optical fiber 18. For this reason, the change in the phase difference between the x and y components created by rotating the half-wave plate 51 b on the hand side and passing through the quarter-wave plate 52 is used as the output end of the polarization-maintaining optical fiber 18. Therefore, the interference fringes can be scanned without mechanically moving the tip of the polarization-maintaining single-mode fiber 18. Further, the configuration is simple, and the distal end of the polarization-maintaining single-mode fiber can be made compact.

As described above, according to the seventh embodiment, the half-wave plate 51b is rotated as the phase shift means, and the phase difference between the polarization components is transmitted to the exit end using the polarization-maintaining optical fiber. Since the phase shift means can be arranged near the hand, not only can the front end of the apparatus be made compact, but also the phase control can be performed relatively easily. Furthermore, the external phase shift means does not split the light according to the polarization component and changes the phase difference and then combines the light, but instead changes the phase difference with a single light beam, so that it is not affected by external influences. There is an advantage that the generated interference fringes and fringe scanning are stable. Further, the structure is simple, inexpensive and easy to manufacture, and the adjustment of the light condensing on the polarization-maintaining single-mode fiber 18 is easy. Thus, it can be seen that the embodiment shown in FIG. 11 has exactly the same effects as the embodiment shown in FIG.

Hereinafter, the polarization state in the seventh embodiment is shown by numerical expressions. From these equations, it can be seen that the intensity of the interference fringes does not change with respect to the rotation angle θ of the half-wave plate 51b, and only the phase of the x and y components changes at a speed of 4θ. FIG. 13 shows the state of this phase change.

[0045]

In the seventh embodiment, the relationship between the polarization axis of the polarization-maintaining single-mode fiber 18 and the optical axis of the quarter-wave plate 52 and the relationship between the polarization axis and the optical axis of the birefringent plate 20 are as follows. , 45
There is no problem if the angles corresponding to each other are the same, not limited to °. Incidentally, 0 ° the half-wave plate 51b is phase shifting means, 90 °, 180 °, to each other phase, such as 270 ° 9
Stopping at each phase position shifted by 0 ° , the object image is taken into the computer 12 for each position and analyzed, or
By continuously rotating the two-wavelength plate 51b and using an integrated image of the object at each phase position, stereoscopic measurement can be performed.

In the seventh embodiment, as shown in FIG. 14, a light source unit 51 for generating linearly polarized light whose oscillation direction can be changed is a coherent light source 5 for emitting circularly polarized light.
A combination of 1d and a rotatable quarter-wave plate 51e may be included. Hereinafter, a state where the １ ／ wavelength plate 51e is fixed to π / 4 and combined with coherent light is shown by an equation.

[0048]

As shown in FIG. 15, the light source unit 51 may include a combination of a linearly polarized laser light source 51a and a Faraday element 51f. in this case,
The oscillation direction of the linearly polarized light can be changed by the voltage applied to the Faraday element 51f. That is, this combination utilizes the optical rotation of the crystal.

Further, as shown in FIG. 16, the light source unit 51 may include a combination of a linearly polarized laser light source 51a and two types of liquid crystal plates 51g and 51h. In this case, the power supply connected to the two liquid crystal plates 51g and 51h is turned on and off, respectively, so that the vibration direction of the linearly polarized light can be changed to four types. This is an example. That is, the liquid crystal panel 51g is connected to the power supply O.
The liquid crystal plate 51h is used as an optical rotator whose optical rotation angle switches from 0 ° to 90 ° when the power is turned ON / OFF when the optical rotation angle is switched from 0 ° to 45 °.

Further, by rotating the linearly polarized laser light source 51a itself on, for example, a rotating base,
The oscillation direction of the linearly polarized light may be changed.

Next, a phase variable element (an optical element capable of changing only the phase difference between mutually orthogonal polarized lights, such as the optical element shown in FIGS.
Another example of the rotatable half-wave plate 51b and the fixed quarter-wave plate 52) will be described.

FIG. 17 shows an example in which a Babinet Soleil plate 58 is used as a phase difference variable element. That is, FIG.
In 7, the phase difference can be changed by moving the Babinet Soleil plate 58 in a direction (arrow) orthogonal to the optical axis. This change in phase difference is transmitted to the distal end by the polarization-maintaining optical fiber 18 and the polarization component is separated by the birefringent plate 20, so that the interference fringes to be generated can be scanned.

FIG. 18 shows an example in which a crystal 59 having an electro-optical effect is used as a phase difference variable element. As the crystal 59, LiNbO ₃ , LiTaO ₃ , K
DP may be used. That is, the electrode plate 6 sandwiching the crystal 59
When an electric field is generated in the crystal in a direction perpendicular to the optical axis by connecting a voltage controller 62 to the voltage controller 61 and a voltage controller 62, the refractive index difference in the polarization directions perpendicular to each other changes. The light transmitted through the crystal 59 transmits the change of the phase difference to the tip thereof by the polarization-maintaining optical fiber 18, is separated into each polarization component by the birefringent plate 20, and generates interference fringes on the measured object. When the voltage applied to the crystal 59 by the voltage controller 62 is changed, the interference fringes move.

FIG. 19 shows an example in which a liquid crystal device 63 is used as a phase difference variable element. In this example, the phase difference between the polarization components of the light passing therethrough changes in accordance with the magnitude of the voltage applied to the liquid crystal, and this phase difference is transmitted by the polarization-maintaining optical fiber 18 to the tip thereof, The interference fringes can be moved in the same manner as described above. In this case, as in the example of FIG. 18, a voltage controller such as a variable resistor as a phase shift means can be arranged at hand.
Not only can the endoscope end portion be miniaturized, but also the configuration can be simplified, and there is an advantage that adjustment and control operation of incident light to the polarization-maintaining optical fiber are easy.

FIG. 20 is an explanatory view showing an eighth embodiment of the present invention. In the figure, 64 is an optical isolator, the 65 coupling lens, 66 is a semiconductor laser driving unit. Other components are 1, because it is substantially the same as those used in FIGS. 5 and 11, using the same reference numerals to the same members as used in FIGS. 1, 5 and 11 , And the description thereof will be omitted.

In this embodiment, the polarization maintaining optical fiber 18
The optical path difference is provided between the orthogonal polarization components by the birefringence of (1) to reduce the wavelength shift amount. As a result, the two light beams that interfere with each other pass through almost the same optical path, and thus are hardly affected by disturbance, and the distal end portion can be downsized because there is no movable element in the distal end portion.

In the eighth embodiment, the phase difference is 2π
In order to change only the value, the following expression should be satisfied. ^{2π = (2πΔλ / λ 2)} L (n x -n y) ‥‥ (6) where, n _x is the x-axis direction of the refractive index of the polarization-maintaining optical fiber 18, n _y is polarization-maintaining optical fiber 18 Is the refractive index in the y-axis direction, L is the length of the polarization-maintaining optical fiber 18, λ is the wavelength of the used light, and Δλ is the wavelength shift amount. From the equation (6), the wavelength shift amount required ^{Δλ = λ 2 / [L (} n x -n y)] becomes ‥‥ (7). Therefore, if the wavelength of the light from the light source is changed continuously or stepwise by the shift amount obtained by the equation (7), the fringe scanning method can be applied.

As the wavelength variable light source, a semiconductor laser or a dye laser can be used. In particular, a semiconductor laser can easily shift the wavelength of emitted light by changing the supply current. The wavelength shift can also be performed by combining a white light source and a variable wavelength filter.

In the eighth embodiment, the wavelength tunable light source 23
Is collimated by the collimator lens 51c, and is inserted into the isolator 6 for removing return light.
Pass 4 Then, the light enters the polarization-maintaining single-mode fiber 18 through the coupling lens 65.

Assuming that the axial direction of the polarization-maintaining optical fiber 18 is inclined by 45 ° with respect to the polarization direction of the incident laser beam, x of the light passing through the polarization-maintaining optical fiber 18 is obtained.
A phase difference occurs between the polarized light component and the y-polarized light component. The light that has propagated in the polarization-maintaining single-mode fiber 18 is collimated by a collimator lens 56, and then enters the birefringent plate 20 as in the seventh embodiment. The crystal axis of the birefringent plate 20 matches one of the polarization components of the two incident lights. Therefore, the optical axis of the other polarization component that becomes extraordinary light with respect to the birefringent plate 20 is shifted. Then, when these lights pass through the polarizing plate 22, linear interference fringes are formed. When this interference fringe is projected on the surface of the object to be measured by the projection lens 57 and the fringe is observed by the imaging device 11 such as a CCD camera, an image distorted according to the unevenness of the surface can be obtained. When the wavelength shift is performed, the phase difference between the two lights forming the interference fringes changes, and the interference fringes move. When the image at this time is taken into the computer 12 by the imaging device 11 and analyzed, irregularities on the surface of the object to be measured can be measured.

Originally, this type of device had almost no difference in optical path length, and could not apply the phase shift method by wavelength shift. However, as is apparent from the above description, according to the present invention, the phase shift method based on the wavelength shift can be applied by utilizing the optical path length difference due to the birefringence of the polarization-maintaining optical fiber.

[0063] Here, the refractive index difference of polarization-maintaining optical fiber _{18 (n x -n y) =} 3 × 10 -4, a wavelength λ = 0.78μ
m and the fiber length L = 50 m, when these are substituted into the above equation (7), the required wavelength shift amount is Δλ = 40
pm. This value is such that mode hopping does not occur even when a semiconductor laser is used as a light source.

FIG. 21 is an explanatory view showing a ninth embodiment of the present invention. This embodiment is different from the eighth embodiment in that an optical path difference between two orthogonal polarization components is obtained by two birefringent plates 68 and 69 inserted in the optical path. Also in this embodiment, since the polarization maintaining optical fiber 18 is used,
Although an optical path difference occurs between the two polarization components, if the length of the polarization-maintaining optical fiber is limited by the specifications of the product, the phase difference is adjusted by the birefringent elements 68 and 69 to optimize the phase difference. Is corrected so as to obtain Since the configuration and operation of the entire apparatus are the same as those of the eighth embodiment, the same reference numerals are given to the same components as those of the eighth embodiment, and the detailed description is omitted.

FIG. 22 is an explanatory view showing a tenth embodiment of the present invention. In this embodiment, the birefringent plates 68 and 69 are eliminated,
The ninth embodiment differs from the ninth embodiment in that an optical fiber 70 is used instead of the polarization-maintaining optical fiber 18 and a phase plate 71 is inserted between the collimator lens 56 and the birefringent plate 20. In the tenth embodiment, the amount of wavelength shift is reduced by making the difference in optical path length of the birefringent plate 20 sufficient.
As a result, the two light beams that interfere with each other pass through almost the same optical path, and thus are hardly affected by disturbance. Since the configuration and operation of the entire apparatus are the same as those of the eighth embodiment, the same reference numerals are given to the same components as those of the eighth embodiment, and the detailed description is omitted. In the case of the present embodiment, an optical path length difference occurs in the birefringent plate 20 itself for splitting light.
The phase plate 71 may be omitted depending on the required wavelength shift amount.

FIG. 23 is an explanatory view showing an eleventh embodiment of the present invention. This embodiment is different from the ninth embodiment in that a polarization beam splitter 72 is used instead of the birefringent plates 68 and 69 to provide an optical path length difference. In this embodiment, light emitted from the wavelength variable light source 23 is incident on the polarization beam splitter 72 and is split into transmitted polarized light and reflected polarized light. The reflected polarized light passes through the quarter-wave plate 72a, is reflected by the mirror 72b, and is again reflected by the quarter-wave plate 72a.
a and enters the polarization beam splitter 72. Since this polarized light passes through the quarter-wave plate 72a twice, the oscillation direction is rotated by 90 °. Therefore, this polarized light passes through the polarizing beam splitter 72. And
After passing through the quarter-wave plate 72c, it is reflected by the mirror 72d,
The light passes through the quarter-wave plate 72c again and enters the polarization beam splitter 72, where it is reflected and coupled to the coupling lens 6
Go to 5. Accordingly, the optical path length differs between the polarized light transmitted through the polarizing beam splitter 72 and the reflected polarized light. These polarizations propagate through the polarization-maintaining optical fiber 18, are split by the birefringent plate 20, and produce interference fringes. According to the eleventh embodiment, the wavelength shift amount suitable for the light source can be changed by changing the positions of the mirrors 72b and 72d. In this embodiment, the same components as those in the above-described embodiments are denoted by the same reference numerals.

FIG. 24 is an explanatory view showing a twelfth embodiment of the present invention. In this embodiment, the phase shift from the optical fiber 33 is performed.
Have used terms and a wavelength tunable light source 23 that data 34 has been removed
That a point different from the third embodiment shown in Figure 6. In the twelfth embodiment, the difference in optical path length is obtained by using two fibers having different lengths.By simply lengthening one optical fiber, the difference in optical path length can be provided. There is an advantage that a larger optical path length difference can be provided as compared with the embodiment. In this case, if the materials of the two fibers are different, the refractive index is different, so that the optical path length difference can be further increased. Since the basic configuration and operation of this embodiment are the same as those of the third embodiment, the same components as those of the third embodiment are denoted by the same reference numerals.
Detailed description is omitted.

FIG. 25 is an explanatory view showing a thirteenth embodiment of the present invention. In this embodiment, a phase difference variable element 73 is provided at the distal end portion of the endoscope so that a phase shift is performed. From the light source 51 a, the polarization maintaining optical fiber 18 through the linearly polarized light is propagated to the tip, the phase difference variable element 73, the two polarization components only remain phases of the same amount of light is changed. This allows
Scanning of the interference fringes is performed without changing the contrast of the interference fringes. In this case, the azimuth angle of the linearly polarized light is selected such that the light amounts of two orthogonal polarization components divided by the birefringent plate 20 are the same.

FIG. 26 is an explanatory view showing a fourteenth embodiment of the present invention. In this embodiment, the semiconductor laser light source 51a and the phase difference variable element 73 are disposed at the end of the endoscope.
As in the thirteenth embodiment, only the phase difference between two orthogonal polarization components of the linearly polarized light emitted from the light source 51a is changed, so that interference fringes are generated.

FIG. 27 is an explanatory view showing a fifteenth embodiment of the present invention. In this embodiment, a variable wavelength laser light source 23 and a phase plate 71 are provided at the tip of the endoscope, and the interference fringes are scanned by changing the wavelength of the laser light emitted from the light source 23. I have. That is, the phase plate is arranged so that the oscillation direction of the linearly polarized light emitted from the light source 23 and the azimuth of the phase plate 71 are at 45 °, and an optical path length difference is given between two orthogonal polarization components, and the wavelength is adjusted. By changing the phase difference, a phase difference is generated. In this case, the birefringent plate 20
Has the function of splitting the optical path into two, and at the same time, the function of causing an optical path length difference between the two split optical paths. Therefore, if the wavelength shift amount is large, the phase plate 71 can be omitted.

The polarization-maintaining optical fiber 18 used in each of the above embodiments may be replaced by an optical fiber having a certain degree of polarization. The electrostrictive element, the wavelength changing device of the light source, the fiber type phase shift, and the phase difference variable element constitute interference fringe scanning means.

[0072]

As described above, the measuring endoscope according to the present invention comprises: an interference fringe generating means for generating interference fringes; an interference fringe scanning means for scanning interference fringes; an imaging means for imaging interference fringes; Since there is provided a calculating means for calculating unevenness information on the surface of the object to be measured from the image signal, the unevenness can be accurately measured without being affected by the unevenness of the contrast of interference fringes projected on the object to be measured. It can be effectively used for observing a lesion inside a human body organ or an internal defect of an industrial pipe such as a gas pipe.

[Brief description of the drawings]

FIG. 1 is a schematic explanatory view showing a principle diagram of a measuring means according to the present invention.

FIG. 2 is an explanatory view of a main part showing a first embodiment of the present invention.

FIG. 3 is an enlarged view showing a state of light separation in a birefringent plate used in the first embodiment.

FIG. 4 is an end view of the polarization-maintaining optical fiber in the first embodiment.

FIG. 5 is an explanatory view of a main part showing a second embodiment of the present invention.

FIG. 6 is an explanatory view of a main part showing a third embodiment of the present invention.

FIG. 7 is an explanatory view of a main part showing a fourth embodiment of the present invention.

FIG. 8 is an explanatory view of a main part showing a fifth embodiment of the present invention.

FIG. 9 is an explanatory view of a main part showing a sixth embodiment of the present invention.

FIG. 10 is an explanatory diagram showing a basic configuration of a seventh embodiment of the present invention.

FIG. 11 is an explanatory diagram showing a specific configuration of a seventh embodiment of the present invention.

FIG. 12 is an explanatory diagram showing a change in a polarization state of light of each optical element shown in FIG. 11;

FIG. 13 is a diagram showing a state of a phase change in a seventh embodiment.

FIG. 14 is an explanatory view of a main part showing a first modification of the seventh embodiment.

FIG. 15 is an explanatory view of a main part showing a second modification of the seventh embodiment.

FIG. 16 is an explanatory view of a main part showing a third modification of the seventh embodiment.

FIG. 17 is an explanatory view of a main part showing a fourth modification of the seventh embodiment.

FIG. 18 is an explanatory view of a main part showing a fifth modification of the seventh embodiment.

FIG. 19 is an explanatory view of a main part showing a sixth modification of the seventh embodiment.

FIG. 20 is an explanatory view of a main part showing an eighth embodiment of the present invention.

FIG. 21 is an explanatory view of a main part showing a ninth embodiment of the present invention.

FIG. 22 is an explanatory view of a main part showing a tenth embodiment of the present invention.

FIG. 23 is an explanatory view of a principal part showing an eleventh embodiment of the present invention.

FIG. 24 is an explanatory view of a main part showing a twelfth embodiment of the present invention.

FIG. 25 is an explanatory view of a principal part showing a thirteenth embodiment of the present invention.

FIG. 26 is an explanatory view of a principal part showing a fourteenth embodiment of the present invention.

FIG. 27 is an explanatory view of a main part showing a fifteenth embodiment of the present invention.

[Explanation of symbols]

Reference Signs List 1 light source 4, 27 beam splitter 5, 6 reflecting mirror 7, 48, 50 electrostrictive element 9 device under test 10 interference fringe 11 camera 12 computer 14, 72 polarization beam splitter 18 polarization plane preserving optical fiber 20, 56, 68, 69 Birefringent plate 22 Polarizing plate 23 Variable wavelength light source 28 Reflection coat 31 Fiber type optical demultiplexer 34 Fiber type phase shifter 44 Phase shifter 46 Multimode optical fiber 51 Light source unit 51a Laser light source 51b 1/2 wavelength plate 51c Coherent light source 51d 1 / 4 wavelength plate 51e Faraday element 51f, 51g Liquid crystal plate 58 Babinet Soleil plate 59 Crystal having electro-optical effect 63 Liquid crystal device 64 Optical isolator 70 Optical fiber 73 Phase difference variable element

Continued on the front page (72) Inventor Katsunori Sakiyama 2-43-2 Hatagaya, Shibuya-ku, Tokyo Inside Olympus Optical Industry Co., Ltd. (72) Inventor Toshikazu Takayama 43-2-2 Hatagaya, Shibuya-ku, Tokyo Olympus Optical (56) References JP-A-2-297515 (JP, A) JP-A-2-95201 (JP, A) JP-A-63-160634 (JP, A) JP-A-60-256443 (JP, A A) (58) Field surveyed (Int. Cl. ⁷ , DB name) G01B 9/00-11/30 102 A61B 1/00-1/32 G02B 23/24-23/26

Claims (2)

(57) [Claims] 1. A measurement endoscope for measuring irregularities on a surface of an object to be measured, an interference fringe generating unit for generating interference fringes on the surface of the object to be measured, an interference fringe scanning unit for scanning the interference fringes, A measurement device comprising: an imaging unit that captures a projection image of the interference fringe as an image; and a calculation unit that calculates unevenness information on the surface of the workpiece based on an image signal from the imaging unit. Endoscope. 2. The method according to claim 1, further comprising:
The interference fringe scanning means is configured to project interference fringes.
The interference fringes can be moved in a direction orthogonal to the fringe direction.
And the imaging means is generated by the movement of the interference fringes.
It is configured to be able to read the change in light intensity on the surface of the object to be measured.
And calculating the arithmetic means with the read surface of the DUT.
Changes in light intensity at each point are performed using the principle of the fringe scanning method.
By calculating the
The depth and height of the
The measurement endoscope according to claim 1 .