JP2007155571A - Device for measuring inside diameter of through hole and inner wall observation device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a device for measuring an inside diameter of a through hole that can obtain high measuring precision without receiving influence on a difference of the inside diameter of the through hole to be measured. <P>SOLUTION: The device for measuring the inside diameter of the through hole has a projection system A for projecting a measuring light flux on an object to be measured 7 having the through hole 7-1 through a chart plate 5 having an opening part in a region on a circumference centering an optical axis, and a light receiving system B having a photoelectric detector 9 for detecting a center position of a condensed image formed by a reflection light flux on an inner wall 7-2 of the through hole 7-1. The device is provided with a means 3 for regulating a condensed angle of a light flux projected on the object to be measured 7 in the device for measuring the inside diameter of the through hole 7-1 on the basis of a signal from the photoelectric detector 9. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a through hole inner diameter measuring device and an inner wall observation device capable of measuring the inner diameter of a through hole with high accuracy.

Conventionally, a light beam from a pinhole arranged in a predetermined pattern centered on the optical axis is incident on the inner wall surface of the through-hole, and the light reflected by the inner wall surface of the through-hole is received, and the image formation position of the pinhole is determined. A through-hole inner diameter measuring device that measures the inner diameter of the through-hole by observing is known.
Japanese Patent Publication No.2672771

  By the way, in this type of apparatus, the accuracy of measuring the inner diameter increases as the center position of the pinhole image on the CCD camera is obtained more accurately. For this purpose, it is necessary to reduce the spot diameter of the pinhole image on the inner wall and on the CCD camera. In addition, if light other than that reflected by the inner wall enters the CCD camera, the contrast of the pinhole image on the CCD camera decreases, thereby reducing the accuracy of the image processing and, consequently, the measurement accuracy. It is also necessary to configure so that light other than the light reflected by the inner wall does not enter the CCD camera.

  On the other hand, the diameter of the through hole to be measured is large and small, and there is a demand for an apparatus that enables measurement with high measurement accuracy that satisfies these conditions regardless of the diameter.

  Further, in this type of conventional apparatus, although the inner diameter of the through hole can be measured, the state of the inner wall surface of the through hole cannot be observed, and an apparatus capable of observing the inner wall has been desired. In particular, if the inner diameter of the through hole is small and the length of the through hole is long, the inner wall cannot be observed with a normal microscope.

  In response to the request for solving these problems of the conventional apparatus, the present invention measures the inner diameter of a through hole that can obtain high measurement accuracy without being affected by the difference in the inner diameter of the through hole to be measured. An object is to provide an apparatus.

  It is another object of the present invention to provide a through-hole inner wall observation device that can easily observe the inner wall of a through-hole even if the inner diameter is a small through-hole.

  A through-hole inner diameter measuring apparatus according to the present invention includes a projection system for projecting a measurement light beam onto a measurement object having a through-hole via a chart plate having an opening in a region on the circumference centered on the optical axis. A light receiving system having a photoelectric detector for detecting a center position of a condensed image formed by a reflected light beam on the inner wall of the through hole, and an inner diameter of the through hole based on a signal from the photoelectric detector Is provided with means for adjusting the condensing angle of the light beam projected onto the object to be measured.

  The through-hole inner wall observation apparatus according to the present invention projects the measurement light beam of the ring-shaped region onto the inner wall of the through-hole of the object to be measured via the chart plate having an opening in the ring-shaped region centered on the optical axis. And a light receiving system having a photoelectric detector for receiving an image of the inner wall illuminated by the measurement light beam in the ring-shaped region, and the projection position of the ring-shaped illumination light beam is defined as a through-hole. The image of the inner wall is sequentially acquired by the photoelectric detector while being moved in the axial direction.

  According to the through hole inner diameter measuring apparatus according to the present invention, high measurement accuracy can be obtained without being affected by the difference in inner diameter of the through hole to be measured.

  According to the through hole inner wall observation apparatus according to the present invention, the inner wall of the through hole can be easily observed even if the through hole has a small inner diameter.

  DESCRIPTION OF EMBODIMENTS Embodiments of a through hole inner diameter measuring device and an inner wall observation device according to the present invention will be described below with reference to the drawings.

  FIG. 1A shows an optical arrangement of an inner diameter measuring device for a through hole, which is reflected by a projection system A for projecting a measurement light beam onto an object to be measured having a through hole and an inner wall of the object to be measured. And a light receiving system B for receiving the reflected light.

  The projection system A includes a fiber bundle 1 from which light from a light source is guided and a measurement light beam is emitted from an emission end face 1a, and a light source imaging lens 2 for forming an end face image of the fiber bundle 1 on a circular aperture stop 3. The condenser lens 4 for guiding the measurement light beam emitted from the circular aperture stop 3, the chart plate 5, and the projection lens 6.

  Assuming that the focal length of the condenser lens 4 is f1, the condenser lens 4 and the circular aperture stop 5 are arranged at the front focal position separated by the focal length f1. As shown in FIG. 3, the chart plate 5 has a plurality of pinholes (5-1, 5-2,..., 5-8) arranged on the circumference around the optical axis I. It is arranged at a rear focal position that is separated from the condenser lens 4 by a focal length f1.

  With this arrangement, the principal ray MA of the light beam from the circular aperture stop 3 is guided parallel to the optical axis I to illuminate the chart plate 5, and this illumination system constitutes a Kohler illumination system. Each measurement light beam transmitted through the plurality of pinholes (5-1, 5-2,..., 5-8) of the chart plate 5 illuminated by the Koehler illumination system is guided to the projection lens 6.

  The projection lens 6 forms a plurality of spot images P1, P2,..., P8 on the inner wall 7-2 of the through hole 7-1 of the object 7 to be measured. The light beams that form the spot images P1, P2,..., P8 and reflected on the inner wall 7-2 are spot images P1 ′, P2 ′,. 'Form. The imaging lens 8 and the CCD camera 9 constitute a light receiving system B. With this optical arrangement, the positions (centers) of the spot images P1 ′, P2 ′,... P8 ′ formed on the CCD camera 9 from the optical axis I due to the difference in the inner diameter of the through hole 7-1 of the object 7 to be measured. The position of the through hole 7-1 is calculated by detecting the positions of the spot images P1 ′, P2 ′,..., P8 ′ based on the signal from the CCD camera 9. Is.

  Here, in order to detect the positions of the spot images P1 ′, P2 ′,... P8 ′ on the CCD camera 9 with high accuracy, the positions on the inner wall 7-2 of the object 7 to be measured and on the CCD camera 9 are measured. It is necessary to make the spot diameter of the spot images P1 ′, P2 ′,. Hereinafter, reference will be made to this condition.

Here, as shown in FIG. 1B in an enlarged manner, the DUT 7 has a through hole 7-1 having an inner diameter of 2r and a length d, and is most likely on the inner wall 7-2 of the through hole 7-1. The conditions for forming a small spot image P1 and forming the smallest pinhole image P1 ′ on the CCD camera 9 will be described below. From general optical diffraction theory, the minimum spot diameter when light of wavelength λ is collected by a lens is
1.2λ / NA (Formula 1)
It is. Here, NA is called a numerical aperture, and when the light collection angle of the collected light is θ,
NA = sin (θ / 2) (Formula 2)
Is defined. Therefore, the larger the θ, the smaller the spot diameter.

On the other hand, if the distance from the entrance of the through hole 7-1 of the object to be measured 7 to the formation position of the spot image P1 on the inner wall 7-2 is L, the maximum value of θ is from the position of the spot image P1 to the through hole 7. -1 angle to estimate the diameter of the entrance 7-1a (in the future, the unit of the angle is radians), that is, θ = arctan (2r / L) (Formula 3)
It becomes.

  That is, the condition that the diameter of the incident light beam at the entrance 7-1a of the through hole 7-1 coincides with the diameter of the hole maximizes θ.

For the light receiving system B, light traveling at an angle θ ′ from which the exit 7-2b of the through hole 7-1 is seen from the position of the spot image P1 out of the light beam reflected by the inner wall 7-2 is incident on the CCD camera 9. . θ 'is the same as Equation 3 θ' = arctan (2r / (d-L)) (Equation 4)
It becomes. Here, the larger θ ′ is, the smaller the spot diameter of the pinhole image P1 ′ on the CCD camera 9 is, and the measurement accuracy is increased. That is, when θ = θ ′ or L = d / 2, both θ and θ ′ can be increased in a balanced manner, which is the most favorable condition.

  Further, each light beam from each pinhole (5-1, 5-2,..., 5-8) is incident on the through-hole 7-1 so that the light collection angle θ of each light beam is maximized. For this purpose, it is preferable that the respective light beams intersect near the entrance of the through hole 7-1.

In order to satisfy such a condition, as shown in FIG. 1, the principal ray MA of the light beam emitted from the pinholes 5-1 and 5-2 (only two are shown for convenience in FIG. 1) provided in the chart plate 5. Is configured to be incident on the projection lens 6 in parallel with the optical axis I, and the entrance 7-1a of the through-hole 7-1 is disposed in the vicinity of the position away from the projection lens 6 by the focal length f2 of the projection lens 6. . At this time, the position of the chart plate 5 is set to a distance of f2 + Z from the projection lens 6. At this time, the relationship between f2, z and L is from the lens imaging formula.
f2 ² = L × z (Formula 5)
It becomes. By doing so, the principal rays of the respective light beams collected by the projection lens 6 intersect at the position of the focal point f2 of the projection lens 6. Therefore, the entrance 7-1a of the through hole 7-1 is provided at this intersection position. Just match.

  Next, as shown in FIG. 2, when the position of the spot image P1 is slightly shifted from the inner wall 7-2 of the DUT 7 by a shift amount e, the light beam L1 reflected by the inner wall 7-2 and the inner wall 7 -2 light beams L2 of direct light emitted from the outlet 7-1b of the through-hole 7-1 without being reflected at -2. Among these, the light beam L1 for measuring the inner diameter is a light beam reflected by the inner wall 7-2, whereas the light beam L2 of the direct light that is directly reflected on the imaging lens 8 without being reflected by the inner wall 7-2. This results in harmful reflections such as erroneous detection of the position of the pinhole image P1 ′ detected by the CCD camera 9. This harmful reflected light beam (light beam L2) becomes more prominent as the position where the pinhole image P1 is formed is closer to the inner wall 7-2.

  If the condensing angle θ incident on the through hole 7-1 is large, light is emitted at the entrance 7-1a of the through hole 7-1 as shown in FIG. 2, and the obtained light beam L3 is reflected by each lens or the like. Then, it may become stray light and enter the CCD camera 9 to adversely affect the measurement.

  Therefore, it is better that the condensing angle θ of the light beam incident on the through hole 7-1 is slightly smaller than the value represented by (Expression 3). Here, if the divergence angle of the direct light emitted from the through-hole 7-1 is Δθ, it is harmful if the condensing angle θ of the light beam emitted from the projection lens 6 is smaller by Δθ than the value shown in (Equation 3). The generation of direct light can be prevented. From FIG. 2, it can be seen that Δθ can be reduced as the position of the spot image P1 is closer to the inner wall 7-2. The higher the accuracy of the inner diameter of the through hole 7-1 of the measured object 7 and the positioning accuracy of the measured object 7 during measurement, the closer the position of the spot image P1 can be set to the inner wall 7-2.

To summarize the above, the converging angle θ of the light beam emitted from the projection lens 6 from (Expression 3) and (Expression 4)
θ = arctan (2r / L) ―Δθ
θ = arctan (2r / (d−L)) − Δθ, where Δθ≈e / L + e / (d−L) (Formula 6)
When the smaller one of the values is selected, harmful light that has an adverse effect is eliminated, and the minimum spot diameter can be obtained, so that the measurement accuracy can be maximized.

Thus, in order to set the condensing angle to θ indicated by (Expression 6), it is necessary to set the angle of light incident on the projection lens 6 to φ (see FIG. 1). The relationship between φ and θ is from the lens formula: φ ≒ (f2 + L) θ / (f2 + z) (Formula 7)
It becomes. Here, θ is a value represented by Expression 6, and an example is given when the focal position of the projection lens 6 and the entrance 7-1a of the through hole 7-1 of the object 7 to be measured are matched.

Here, as shown in FIG. 1, the principal ray MA of each light beam emitted from the pinholes 5-1 and 5-2 of the chart plate 5 is parallel to the optical axis I, and the interval thereof is the same as that of the pinhole 5-1. Since the interval between the spot image P1 and the spot image P2 formed by the luminous flux is set to be equal to the interval 2R of 5-2, the inner diameter design value 2r of the object to be measured 7 is set. From the imaging formula
R = (f2 + z) r / (f2 + L) (Formula 8)
It becomes.

Here, r / R is the imaging magnification of the projection lens 6. Therefore, the hole diameter c of the pinholes 5-1 and 5-2 is calculated from the equation 1.
c <(1.2λ / NA) × R / r (Formula 9)
The following conditions are recommended.

  However, when the intensity of the light source is not sufficient, the brightness of the spot image P1 'on the CCD camera 9 may be insufficient under the condition of Expression 9. In that case, it is possible to make the hole diameter c larger than the size indicated by (Equation 9). At that time, the spot diameter of the spot image P1 is larger than the size indicated by (Expression 1), but if θ satisfies the condition of (Expression 6), the contrast of the contour of the image of the spot image P1 remains high. It is possible to maintain the accuracy, and it is possible to prevent the accuracy from being remarkably reduced by a device for image processing.

From (Equation 8), in order for the illumination light incident on the chart plate 5 to have a diameter of 2R or more and the angle of the light emitted from the pinholes 5-1 and 5-2 to be φ, the numerical aperture NA ′ of the illumination light is From optical formula
NA '= sin (φ / 2) (Formula 10)
It is necessary to. A Koehler illumination system generally used in commercially available microscopes is suitable as an illumination system for achieving such conditions.

As described above, the Kohler illumination system according to the present invention includes a fiber bundle 1 having a diameter b as a light source, a light source imaging lens 2, a circular diaphragm 3, and a condenser lens 4 having a focal length f1. Thus, the circular diaphragm 3 and the chart plate 5 are arranged in the vicinity of the respective focal positions of the condenser lens 4.
Therefore, the aperture diameter a of the circular diaphragm 3 is
a = 2 × f1 sin (φ / 2) (Formula 11)
In this apparatus, the size of the opening diameter a can be adjusted so as to obtain an appropriate angle φ. This adjustment mechanism may be constituted by a variable aperture used in a camera or the like, or a plurality of circular aperture stops having various aperture diameters a are prepared, and an appropriately sized circular aperture stop is provided in the optical path. You may comprise so that it may arrange | position.

The exit end face 1a of the fiber bundle 1 that functions as a light source may be disposed directly in the vicinity of the circular diaphragm 3, but for adjustment of the diaphragm aperture diameter a of the circular diaphragm 3, improvement in exchange operability of lamp replacement, etc. The exit end face 1a of the fiber bundle 1 as the light source is imaged on the circular diaphragm 3 by the light source imaging lens 2. Let M be the imaging magnification. The diameter b of the fiber bundle 1 must be increased so that the image diameter when the exit end face image of the fiber bundle 1 is formed on the circular stop 3 is larger than the value of the aperture diameter a shown in (Equation 11). I must. That means
b> a / M (Formula 12)
It is necessary to.

  Next, an example in which the inner diameter of the through hole 7-1 of the DUT 7 is large will be described with reference to FIG. Under this condition, it is necessary to increase the diameter of the projection lens 6 as can be estimated from FIG. 1. However, it may be difficult to obtain the projection lens 6 having a large diameter technically. However, since the inner diameter is large in this case, a sufficiently large value of θ can be obtained, so that the spot diameters of the spot images P1 and P2 can be made sufficiently small even if the above-described conditions are relaxed.

  That is, as shown in FIG. 8, the intersection of the principal rays MA of the light beams from the pinholes 5-1 and 5-2 and the projection lens 6, the entrance 7-1 a of the through-hole 7-1 of the object 7 to be measured, Are not necessarily matched, and the intersection may be shifted from the focal point of the projection lens 6 toward the projection lens 6 by a shift amount indicated by Δf2. As can be estimated from FIG. 8, the optimum amount of deviation Δf2 is determined by the diameter of the projection lens 6 and the inner diameter of the through hole 7-1 of the object to be measured 7. In this case, the principal ray MA of the light flux from the pinholes 5-1 and 5-2 is not parallel, and its angle is determined by the value of the shift amount Δf2, and slightly deviates from the exact conditions of the Koehler illumination system. Specifically, an adjustment mechanism is provided so that the circular diaphragm 3 is moved away from the condenser lens 4 along the optical axis I by a deviation amount Δf1. The intersection and the circular aperture 3 are in a conjugate relationship with respect to the condenser lens 4 and the projection lens 6. If comprised as mentioned above, the measurement precision of the internal-diameter measuring apparatus of a through-hole can be improved to the maximum.

  In the conventional apparatus, the number of pinholes of the chart plate 5 is four, but in this embodiment, eight pinholes 5-1 to 5-8 are provided as shown in FIG. . When the number of pinholes is large, the number of measurement points increases in proportion to the number of pinsholes, and a more accurate shape measurement of the inner diameter can be performed. Therefore, as shown in FIG. 4, a ring-shaped slit opening 5 a that is optically equivalent to increasing the number of pinholes may be provided. It is recommended that the slit width c ′ at that time satisfies the condition of (Equation 9).

  In the embodiment, since the distance between the center of gravity of each of the pinhole image P1 and the pinhole increase P2 is calculated by image processing based on the signal from the CCD camera 9 functioning as a two-dimensional sensor, the CCD camera 9 As the number of pixels increases, the measurement accuracy increases. However, the CCD camera 9 having a large number of pixels is expensive. Therefore, as shown in FIG. 5, an image can be collected while rotating the CCD line-shaped sensor array 9a about the optical axis I. Since the pinhole image P1 and the pinhole image P2 are in symmetrical positions around the optical axis I, both can be captured at once by the line-shaped sensor array, and the pinhole image in the longitudinal direction of the line-shaped sensor array What is necessary is just to obtain | require each gravity center of P1 'and pinhole image P2', and to obtain | require the space | interval. In this case, the chart plate 5 can correspond to any one of the pinholes 5-1 to 5-8 shown in FIG. 3 or the ring-shaped opening 5a shown in FIG. As a result, image processing becomes simple calculation and the price of the camera can be kept low.

  Alternatively, as shown in FIG. 5B, as many line sensor arrays 9b as the number of pinholes may be arranged radially. In this case, the sensor rotation mechanism can be omitted, and the image data capturing time can be shortened and the measurement time can be shortened.

  Next, a method for calculating the center positions of the pinhole images P1 'to P8' will be described. In the conventional apparatus, the center of the pinhole image P1 'is calculated by calculating the center of gravity of the light intensity distribution of the image. However, if noise is mixed in the signal of the CCD camera 9 or light harmful to the reflected light from the inner wall 7-2 of the object 7 to be measured, that is, stray light is mixed, as shown in FIG. The distribution is a distribution having a distortion D that is not symmetrical. In such a case, the position of the calculated center of gravity is displaced, resulting in a measurement error. However, for example, the positions of Q1 and Q2 having half the maximum intensity h1 (half-value points) have a large inclination of the light intensity distribution, and even if noise or stray light is mixed, the positions themselves are not greatly displaced.

  Therefore, by setting the center of Q1 and Q2 as the center position HC of the pinhole image, a highly accurate inner diameter measurement value can be obtained. Even when the slit image 5a is used, the same effect is obtained by performing the same calculation.

  In addition, although the calculation is complicated, many methods have been proposed for determining the centers of the pinhole images P1 ′ to P8 ′ and the slit image in accordance with the situation of noise and stray light mixing, and these methods are used in the present invention. It is also possible to apply.

  Next, an example of the through-hole inner wall observation device for observing the inner wall of the through-hole will be described with reference to FIG. In this case, a chart plate 5 having a ring-shaped opening 5a shown in FIG. 4 is used. In this case, a ring-shaped inner wall image Im1 as shown in FIG. 7A is formed on the CCD camera 9, and when this ring-shaped image is developed into a rod-shaped linear image by image processing, FIG. It is possible to obtain a rod-shaped inner wall image Im2 as in FIG. Then, images are sequentially acquired while moving the object to be measured 7 along the direction of the optical axis little by little with a resolution equal to or less than the depth of focus of the CCD camera 9, and the rod-shaped image in FIG. Therefore, it is piled up while shifting. This superposition is performed by the image processing unit 10 based on a signal from the CCD camera 9. An image Im3 obtained at this time is shown in FIG. The image obtained in FIG. 7C is an image of the inner wall 7-2 of the through hole 7-1.

  Thereby, in the case of the through hole of the circuit board of the electronic circuit as the DUT 7, the state of the conductive plating film on the inner wall of the through hole can be inspected. When the conductive plating film is not uniform and there is a crack, the light reflectance at that portion is low, so a clear crack image can be obtained. The crack of the conductive plating film has a great influence on the characteristics of the electronic circuit, and this apparatus can provide an effective inspection method.

It is explanatory drawing of the through-hole internal diameter measuring apparatus concerning this invention, Comprising: (a) is the optical figure, (b) is an enlarged view of the through-hole shown to (a). It is a figure for demonstrating the deviation | shift amount of the pinhole image formed in the through-hole shown in FIG. It is a top view of the chart board shown in FIG. It is a figure which shows the modification of the chart board shown in FIG. It is explanatory drawing which shows the other example of the photoelectric detector shown in FIG. 1, Comprising: (a) shows the one-dimensional linear sensor array as a photoelectric detector, (b) is arrange | positioned radially as a photoelectric detector. A line-shaped sensor array is shown. It is a figure which shows the light quantity distribution of the pinhole image formed with the light beam reflected by the inner wall of the through-hole shown in FIG. It is a figure which shows the inner wall image formed in the CCD camera shown in FIG. 1, Comprising: (a) shows a ring-shaped image, (b) shows the inner wall image formed in the CCD camera shown in (a) in a rod shape. The developed image is shown, and (c) is a diagram showing a state in which the images developed in the rod shape shown in (b) are sequentially obtained to form an inner wall image from the entrance to the exit side of the through hole. It is an optical diagram which shows the modification of the through-hole internal diameter measuring apparatus shown in FIG.

Explanation of symbols

3 ... Circular aperture (means)
7-1 ... through hole 7-2 ... inner wall 9 ... CCD camera (photoelectric detector)
A ... Projection system B ... Light receiving system

Claims (13)

A projection system for projecting a measurement light beam onto a measurement object having a through hole through a chart plate having an opening in a region on the circumference around the optical axis, and a reflected light beam on the inner wall of the through hole In a through hole inner diameter measuring device that has a light receiving system having a photoelectric detector for detecting the center position of the formed condensed image and measures the inner diameter of the through hole based on a signal from the photoelectric detector,
A through-hole inner diameter measuring apparatus comprising means for adjusting a condensing angle of a light beam projected onto the object to be measured.   The principal ray of the light beam projected on the object to be measured is configured to intersect the optical axis in the vicinity of the entrance of the through hole of the object to be measured, and the adjustment of the condensing angle is performed by the inner wall of the through hole. 2. The through-hole inner diameter measuring device according to claim 1, wherein the through-hole inner diameter measuring device is adjusted to give a maximum condensing angle within a constraint that direct light that is not reflected does not enter the photoelectric detector.   The chart plate has a plurality of pinholes arranged on a circumference around an optical axis, and the projection system has a plurality of pins on an inner wall of the through hole by a light beam transmitted through the plurality of pinholes. The through-hole inner diameter measuring apparatus according to claim 1, further comprising a projection lens for forming a hall image.   The chart plate has a ring-shaped opening centered on the optical axis, and the projection system forms a ring-shaped image on the inner wall of the through hole by a light beam transmitted through the ring-shaped opening. The through-hole inner diameter measuring apparatus according to claim 1, comprising: an imaging lens.   The projection system has a projection lens for forming a condensed image on the inner wall of the through hole of the object to be measured by the light beam transmitted through the opening of the chart plate, and the light receiving system receives the photoelectric sensor by the reflected light beam on the inner wall. An imaging lens for forming a condensed image on the detector; an entrance of a through-hole of the object to be measured is disposed near a focal position of the projection lens; and an exit of the through-hole of the object to be measured is The projection system is disposed in the vicinity of a focal position of the imaging lens, and the projection system provides a maximum condensing angle so that only light reflected by the inner wall of the through hole is incident on the photoelectric detector. Item 2. The through-hole inner diameter measuring device according to Item 1.   The projection system includes a condenser lens for illuminating the chart plate with a measurement light beam, and a circular diaphragm having a circular opening is arranged at a front focal position of the condenser lens, and the rear focal position of the condenser lens The through-hole inner diameter measuring apparatus according to claim 1, further comprising a Koehler illumination optical system in which a chart plate is arranged, and adjusting a condensing angle by adjusting an aperture diameter of the circular diaphragm.   The through-hole inner diameter measuring device according to claim 6, further comprising an adjusting unit that adjusts a position of the circular diaphragm in an optical axis direction.   The through-hole inner diameter measuring apparatus according to claim 1, wherein the photoelectric detector is a two-dimensional sensor.   2. The through-hole inner diameter according to claim 1, wherein the photoelectric detector is a line-shaped sensor array, and the line-shaped sensor array is rotatably arranged around the optical axis of the light receiving system. measuring device.   The through-hole inner diameter measuring device according to claim 1, wherein the photoelectric detector is a linear sensor array arranged radially around the optical axis of the light receiving system.   The center position of the condensed image obtained by the photoelectric detector is detected based on the center of gravity position of the light amount distribution of the condensed image or the center position of the half-value point of the maximum intensity of the condensed image. The through-hole inner diameter measuring apparatus as described.   A projection system for projecting a ring-shaped measurement light beam onto the inner wall of the through hole of the object to be measured via a chart plate having a ring-shaped opening centered on the optical axis, and illumination with the ring-shaped measurement light beam A light receiving system having a photoelectric detector for receiving an image of the inner wall, and moving the projection position of the ring-shaped illumination light beam in the axial direction of the through-hole by the photoelectric detector. A through hole inner wall observation device characterized by sequentially acquiring.   An image processing unit is provided for developing ring-shaped inner wall images sequentially detected by the photoelectric detector into linear inner wall images, and superimposing the developed inner wall images while sequentially shifting them to form a composite inner wall image. The through-hole inner wall observation apparatus according to claim 12, wherein:

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