JP2000121331A - Optical type hole shape measuring method and apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve a measurement of the correct diameter of a hole by using two images different in the length of the optical path to remove image distortions associated with axial deviation. SOLUTION: An inner circumference wall surface of a hole 2 to be measured is irradiated from a light source by an irradiation optical system and reflected light on the wall surface is caught as observation images individually with an image surface 1 and an image surface 2 arranged at positions different in the length of the optical path thereof. Spatial position P of a reflection point on the wall surface is determined based on an angle β of the reflected light determined from position information θ, R1 and R2 in the image surfaces 1-2, the angle α of the known irradiation luminous flux and the layout dimensions R0, L1 and L2 of the optical system to measure the shape of the hole 2 to be measured from the spatial position information.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical hole shape measuring method and a measuring apparatus applied to, for example, measuring the inner diameter of a minute hole.

[0002]

2. Description of the Related Art To directly measure the inner surface of a hole by a contact means, there is a great limitation on the measurable hole diameter depending on the size of a probe. Therefore, a non-contact measurement method using an optical measurement microscope or a projector is widely used for measuring the inner diameter of the small-diameter hole. However, in this case, the measurement target is limited to a small-diameter hole having a low aspect ratio (hole length / inner diameter) formed in a thin plate-shaped object to be measured that can represent the hole shape by the shape of the hole end face. Can be

On the other hand, in order to measure a fine hole having a high aspect ratio, Japanese Patent Application Laid-Open No. H8-43032 (Nagano Precision Industrial Laboratory) or Japanese Patent Application No. 9-1059 has been proposed.
No. 17 (Mitutoyo Corporation) and the like have been proposed. In any of these methods, as shown in FIG. 1, an object to be measured is obtained from a diameter r of an observation image obtained at a predetermined magnification m by using an opening angle α of a ring-shaped light beam and an optical system arrangement dimension f. In this method, the diameter R of the first hole 2 is obtained. That is, this measuring method utilizes specularly reflected light on the inner surface of the hole 2 when light passes through the inside of the hole 2, and from the shape of the image formed by the reflected light, from the optical axis center of the reflection position. The distance R is regarded as the radial dimension of the hole 2 to derive the hole diameter, thereby enabling measurement of a very small hole having an extremely high aspect ratio.

[0004]

However, in the above method, the angle of incident light (incident angle) and the angle of reflected light (reflection angle)
Must be the same, and an error occurs if the inner surface of the hole 2 is inclined with respect to the center of the optical axis of the optical system as shown in FIG. Even if the change in diameter due to the slight tilt is slight, the light leverage effect resulting from the angle change of the reflected optical axis causes the actual cross-sectional shape of the observation image shown by the solid line to be compared with the actual cross-sectional shape shown by the broken line in the figure (viewed image). The fluctuation becomes remarkable.

For example, the posture of the DUT 1 with respect to the optical axis is defined by an offset, a pitch angle, and a yaw angle. If the inclination in the direction of an axis perpendicular to the plane of the paper is pitching, FIG. Shows a case where a pitch angle occurs. If the yaw angle is not 0 °, the observed image shape in FIG. 2 is further distorted.

In actual measurement, the inner surface of the hole, such as the taper or bend of the hole 2, always changes in inclination with a change in the hole diameter. Also, although the details of the hole shape were originally unknown,
It is impossible to suppress the deviation amount of the axis of the DUT 1 to a known amount or less. Therefore, care must be taken when applying the optical method to the measurement of the inner diameter of a small-diameter hole.For example, when measuring a tapered hole, measures such as performing calibration with a standard sample having the same taper angle are required. is there.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an optical hole shape measuring method capable of accurately measuring a hole shape by removing an image distortion caused by an axis deviation by measuring using two images having different optical path lengths. And a measuring device.

[0008]

In order to achieve the above object, an optical hole shape measuring method of the present invention irradiates a light beam to an inner peripheral wall surface of a hole to be measured by an irradiation optical system, and reflects reflected light on the wall surface. In an optical hole shape measuring method in which an observation optical system captures the observation image as an observation image and measures the shape of the measurement target hole from position information on the image plane of the observation image, the position of the light path of the reflected light is different at the wall surface. From the reflected light at the image plane of the observation light, the angle of the reflected light with respect to the optical axis, the angle with respect to the optical axis of the illuminating light beam, and the arrangement dimensions of the optical system. The spatial position of the reflection point is obtained, and the shape of the hole to be measured is measured based on the spatial position information.

Therefore, in the measuring method of the present invention, the angle of the reflected light with respect to the optical axis is obtained from the position information on the image plane of the two observation images captured at the positions where the optical path lengths of the reflected light are different,
From this and the known value, that is, from the angle with respect to the optical axis of the irradiation light beam and the arrangement dimensions of the optical system, the spatial position of the reflection point on the wall surface is determined to measure the shape of the measurement target hole, Even if the axis of the measured object does not coincide with the center of the optical axis, image distortion due to the axial displacement of the measured object can be removed from the two images, and the hole shape can be measured accurately without complicated positioning.

In the above measurement method, if the maximum value of the light intensity of each of the observation images or the median value of the light receiving area is used as the position information, an error associated with the size of the received contour can be minimized. Further, while maintaining a constant offset and tilt angle of the object to be measured having the hole to be measured with respect to the optical axis of the optical system, the object to be measured is translated in the optical axis direction of the optical system, and By measuring the shape of the hole that changes in the axial direction, it is possible to measure the entire shape of the hole to be measured of the measured object in the axial direction.

The optical hole shape measuring apparatus of the present invention irradiates a light beam on the inner peripheral wall surface of the hole to be measured, captures the reflected light on the wall surface as an observation image, and performs the measurement from position information of the observation image on the image plane. In an optical hole shape measuring device for measuring the shape of the target hole, an irradiation optical system that generates light from a light source into a light beam inclined at a predetermined angle with respect to the optical axis and irradiates the inner peripheral wall surface of the target hole with An observation optical system having a plurality of position detection means arranged respectively corresponding to positions where the optical path length of the reflected light is different, and capturing an observation image of the reflected light on the wall surface as two-dimensional position information, Angle with respect to the optical axis of the reflected light obtained from position information on the image plane of the observation image captured by each position detection means of this observation optical system,
Computing means for determining a spatial position of a reflection point on the wall surface from an angle of the irradiation light beam with respect to an optical axis and an arrangement size of the optical system, and measuring a shape of the measurement target hole based on the spatial position information. Features.

Therefore, according to the measuring apparatus of the present invention, the position detecting means are respectively arranged corresponding to the positions where the optical path lengths of the reflected light are different, and the position of the observation image captured by each of the position detecting means is reduced. From the angle of the reflected light with respect to the optical axis obtained from the position information, the angle of the irradiation light beam with respect to the optical axis, and the arrangement size of the optical system, the spatial position of the reflection point on the wall surface is obtained to measure the shape of the hole to be measured. Therefore, even if the axis of the DUT does not coincide with the center of the optical axis, image distortion due to the axial displacement of the DUT can be removed from the two images with high accuracy without troublesome positioning. The hole shape can be measured.

In the above measuring apparatus, the irradiation optical system includes, for example, a ring-shaped parallel light generating means for generating light from a light source into a ring-shaped parallel light having an open angle, It is preferable that the first lens unit be configured to generate the ring-shaped parallel light into a ring-shaped conical light beam having a predetermined opening angle and irradiate the inner peripheral wall surface of the measurement target hole. With such a configuration, since the light beam can be simultaneously irradiated on the entire inner surface of the measurement target hole, the shape of the measurement target hole can be efficiently measured.

Further, the observation optical system includes, for example, a second lens means for receiving the reflected light on the wall surface, a beam splitter means for splitting the light transmitted through the second lens means into a plurality of optical paths, Desirably, a configuration including a plurality of two-dimensional image sensors arranged at positions having different optical path lengths on each optical path divided by the beam splitter means is provided. With such a configuration, a part of the optical path can be shared, so that the cost can be reduced and the whole can be made compact.

At this time, if the maximum value of the light intensity of the observation image received by the two-dimensional image sensor or the median value of the light receiving area is used as the position information, an error associated with the size of the received contour is minimized. be able to. Further, if the moving object for moving the object to be measured in parallel in the optical axis direction of the optical system and the moving amount detecting means for detecting the moving amount of the object to be measured by the moving unit are provided, It is possible to measure the shape of the hole at each portion in the axial direction of the hole to be measured, and to measure the shape of the tapered hole in addition to the linear circular hole.

[0016]

Preferred embodiments of the present invention will be described below in detail with reference to the accompanying drawings. First,
The measurement principle of the present invention will be described with reference to FIG. In the figure, a ring-shaped light beam having a known opening angle α (the angle formed with the center of the optical axis) is generated by an irradiation optical system, and is incident on the inner surface of a measurement target hole 2 of the DUT 1. The DUT 1 is
When viewed from the polar coordinate origin on the optical axis center, the offset N,
It is an object of the present invention to determine the shape of the measurement target hole 2 without depending on these N, M, and γ when the positioning is performed at the distance M and the maximum inclination angle γ.

Here, for the sake of simplicity, attention is focused only on the light reflected at one point on the inner surface of the hole 2. As shown in the figure, the light beam reflected on the inner surface of the hole 2 passes through the hole 2 and emerges on the opposite side, and is formed into an image on an image plane using an observation optical system. At this time, the resolution of measurement is ensured by obtaining an image optically enlarged at a predetermined magnification by the observational optical system.

When the image plane 1 is located at a distance L1 from the reference position of the irradiation optical system, the distance in the radial direction of the image due to the reflected light on the image plane 1 is R1. At the same time, if the image plane 2 is located at a distance L2 from the reference position of the irradiation optical system, the distance in the radial direction of the image due to the reflected light on the image plane 2 is R2. Assuming that the position of the reflection point is P, using a polar coordinate system whose origin is the reference position of the irradiation optical system, P = (R,
L, θ). Here, since θ can be directly obtained by detecting the two-dimensional position on the image plane, the position of P is geometrically determined by calculating the remaining R and L from known amounts and other detected amounts. Can be specified.

When viewed from the polar coordinate origin on the optical axis, R1 and R2 are determined from the two-dimensional positions of the two images corresponding to the rotational angle coordinate position θ about the optical axis, and tan β is determined corresponding to the θ.
At this time, it is not necessary to carefully consider the above-described positional shift amounts N, M, and γ of the DUT 1 on the optical system.

For the actual calculation, the image plane arrangements Ll and L2
Is derived from the difference (R1-R2) between the image positions R1 and R2 corresponding to the difference (L2-L1), the known amount α, L1 , R0 (incident light arrangement) and the detected amount R1, the geometrical R
And L can be obtained.

R = (R1 · tanα + L1 · tanα · tanβ + R0 · tanβ) / (tanα + tanβ) (1) L = (R1−R0 + L1 · tanβ) / (tanα + tanβ) (2) where tanβ = (R1 -R2) / (L2-L1).
By performing the above-described measurement of the position of the reflection point all around the inner surface of the hole 2, measurement is performed by acquiring coordinate data of the hole shape.

Next, for example, while N and γ are kept constant, the DUT 1 is translated in the direction of the optical axis to position M at another value, and the measurement is repeated in the same process to obtain the shape in the axial direction. Perform the measurement. Thereby, for example, it is possible to measure the shape of the inner surface of the hole having an inclination such as a tapered hole by an optical method. In addition, there is no error due to misalignment of the object to be measured with respect to the optical system, and it is not necessary to mount the device in a conventional manner.

Next, the DUT 1 is measured using the above-described measurement principle.
A specific device configuration for measuring the inner diameter of the hole 2 will be described with reference to FIG. The hole shape measuring apparatus shown in the figure is an irradiation optical system 11 for forming light from a light source (not shown) into a ring-shaped conical light beam having a predetermined opening angle and irradiating the inner peripheral wall surface of the hole 2 of the DUT 1. And the hole to be measured 2
Observation optical system that captures the reflected light from the wall as an observation image 2
1, a moving means 31 for moving the device under test 1 in parallel in the optical axis direction of these optical systems 11 and 21, and overall control of the entire apparatus, and the above-described optical information obtained from the observation optical system 21. And an arithmetic control means 41 such as a personal computer for calculating the hole shape by performing an arithmetic operation on the calculation formula.

The irradiation optical system 11 includes a ring-shaped parallel light generating means 12 for generating light from a light source into a ring-shaped parallel light having an open angle, and a ring-shaped parallel light from the ring-shaped parallel light generating means 12. And a first lens means 13 for generating a ring-shaped conical light beam having a predetermined (known) opening angle and irradiating the inner surface of the hole 2 of the DUT 1. Here, the method of generating the ring-shaped parallel light by the ring-shaped parallel light generating means 12 is not described because there are various methods, but it is desirable that the light intensity inside the light beam is as uniform as possible.

The observation optical system 21 is provided with the hole 2 to be measured.
Lens means 2 for receiving light regularly reflected on the inner peripheral wall surface of the lens
2 and a plurality of light beams (2
And a plurality of (two) position detecting means arranged in each of the optical paths divided by the beam splitter means 23 and at positions where the optical path lengths of the reflected light are different. And two-dimensional image sensors 24 and 25, and image processing means 26 for processing two-dimensional image information obtained by the two-dimensional image sensors 24 and 25. Here, the second lens means 22
Are arranged such that the front focal plane is located at a position shared by the rear focal plane of the first lens means 13. As a result, light emitted from the second lens means 22 is emitted as ring-shaped parallel light having a certain opening angle. In addition,
The method of realizing the first and second lens means 13 and 22 may be only a single lens, a combination of a plurality of lenses, or an aspherical lens.

The moving means 31 includes a table 32 on which the device under test 1 is placed, and the table 32
And a drive motor 33 that translates in the direction of the optical axis 1 and 21. The rotation angle of the drive motor 33, that is, the amount of movement of the table 32 is detected by the amount of movement detection means 34 such as a rotary encoder, and then input to the arithmetic and control means 41.

The arithmetic control means 41 has built-in calculation software for executing the above-mentioned calculation in advance, and starts up the light source of the irradiation optical system 11 and activates the Processing means 2
6, the amount of movement is detected by the forward / reverse rotation drive of the drive motor 33 and the data taken from the amount of movement detection means 34, and the geometric calculation at that position is executed.
The results are sequentially displayed on the attached monitor.

In the above, by starting the calculation software,
The next measurement mode is executed. First, in the irradiation optical system 11, the ring-shaped parallel light from the ring-shaped parallel light generating means 12 is converted into a ring-shaped conical light beam having a known opening angle by the first lens means 13, and the generated ring-shaped conical light beam is generated. Is guided to the inner peripheral wall surface of the measurement target hole 2 of the DUT 1. At this time, the ring-shaped conical light beam is focused on the focal point f1 near the inner surface of the hole 2. This is to increase the accuracy of the measurement position by narrowing the irradiation range, and it is not always necessary to condense light on the inner surface of the hole.

The light specularly reflected on the inner surface of the hole 2 is converted into a ring-shaped parallel light having a certain opening angle by the second lens means 22 and reaches the beam splitter means 23. Then
The ring-shaped parallel light is split by the beam splitter means 23 into transmitted light and reflected light, and received by the two-dimensional image sensors 24 and 25, respectively.

The detected images formed on the two-dimensional image sensors 24 and 25 are detected in the same ring-shaped distribution as the screen image figure shown in FIG. 3, and are detected by the image processing means 26 from the center of the optical axis. The signal is converted into an electric signal having X, Y coordinate distribution, and is taken into the arithmetic and control unit 41.

The arithmetic control means 41 measures the respective radii R1, R2 (see FIG. 3) while sweeping a range of 0 to 360 ° from the origin position from the captured image data, and calculates β derived therefrom. Then, the polar coordinate position P (R, L, θ) of the reflection point is obtained by substituting the above into the above-described geometric calculation formula. That is, hole 2
Since the opening angle of the ring-shaped conical light beam incident on the light source is known from the ring-shaped parallel light generated on the light source side and the characteristic value of the first lens means 13, the aperture shape of the hole shape is determined based on the above-described measurement principle based on the arrangement dimensions of the optical system. Perform measurements.

In order to determine the values of R1 and R2 from the information detected by the ring-shaped light beams received by the two-dimensional image sensors 24 and 25, θ
The center position of the light beam obtained from the brightness distribution in the light receiving area is used for the light receiving area width detected when is designated.
For example, if the luminance distribution of the light receiving area is a Gaussian distribution, the position where the luminance is maximum may be used, and there is not much difference even if the center position of the light receiving area is used. If the brightness distribution of the light receiving area is uniform, it is appropriate to use the center position of the light receiving area.

The thinning processing for determining the position is as follows.
The calculation can be performed by the image processing unit 26 or by the calculation control unit 41. The calculation control unit 41 executes the above-described calculation based on the thinned coordinate data. The arithmetic control means 41 detects the amount of movement of the table 32 while driving the drive motor 33 from the measurement origin position, and repeats the measurement and calculation at the movement position, thereby obtaining the table 32 in the depth direction of the hole 2. Polar coordinate position P of reflection point while monitoring the ring pattern of all observed images
(R, L, θ) are obtained, and the calculation results are sequentially displayed on an attached monitor.

The above measurement mode is continued until the table 32 moves in parallel from the origin position to the limit position, and it is determined that there is no reflection pattern at the limit position, that is, at the rear end or the frontmost side of the hole. Then, the arithmetic and control unit 41 stops the driving of the drive motor 33 and performs control to return the table 32 to the measurement origin position again. After the table 32 returns to the origin position, the end is displayed on the monitor.

As the display form of the above calculation results, for example, if the hole 2 of the DUT 1 is a circular hole, its average radius or diameter, roundness, maximum In addition to displaying numerical values such as a minimum value, a deviation value, and the depth or depth of a hole, a two-dimensional or three-dimensional figure can also be displayed. Also, if a tapered hole is used, the taper angle and the like can be displayed.

After the end display, the end processing is performed by operating the keyboard or the mouse, or the storage processing is performed as necessary.
When the end processing is performed, the measurement mode standby state is set again. Further, in the present embodiment, a personal computer is used as the arithmetic control means 41, but it is needless to say that a dedicated processing device can be used instead.

[0037]

As described above, according to the optical hole shape measuring method and measuring apparatus according to the present invention, even if the axis of the object and the center of the optical axis do not coincide with each other, the object can be measured from the two images. Image distortion due to axial displacement can be removed, and accurate hole shape measurement can be performed without complicated positioning.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing the concept of a conventional technique.

FIG. 2 is an explanatory diagram showing a defect of the conventional technique.

FIG. 3 is an explanatory view showing a measurement principle of the method of the present invention.

FIG. 4 is an explanatory diagram showing a device configuration of the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 object to be measured 2 measurement target hole 11 irradiation optical system 12 ring-shaped parallel light generating means 13 first lens means 21 observation optical system 22 second lens means 23 beam splitter means 24 two-dimensional image sensor (position detecting means) 25 Two-dimensional image sensor (position detecting means) 26 Image processing means 31 Relative moving means 32 Table 33 Drive motor 34 Moving amount detecting means 41 Calculation control means (Calculating means)

Claims (8)

[Claims] 1. An irradiation optical system irradiates an inner peripheral wall surface of a measurement object hole with a light beam, a reflected light on the wall surface is captured as an observation image by an observation optical system, and the measurement object is obtained from position information of the observation image on an image plane. In the optical hole shape measuring method for measuring the shape of the hole, at positions where the optical path lengths of the reflected light are different, the reflected light on the wall surface is captured as an observation image, and the position is obtained from positional information on the image plane of each observation image. From the angle of the reflected light with respect to the optical axis, the angle of the irradiation light beam with respect to the optical axis, and the arrangement dimensions of the optical system, the spatial position of the reflection point on the wall surface is determined, and the shape of the measurement target hole is measured based on the spatial position information. An optical hole shape measuring method. 2. The optical hole shape measuring method according to claim 1, wherein a maximum value of the light intensity of each of the observed images or a median value of a light receiving area is used as the position information. Measuring method. 3. The optical hole shape measuring method according to claim 1, wherein an offset and a tilt angle of an object to be measured having the hole to be measured with respect to an optical axis of the optical system are kept constant. Translate the object to be measured in the optical axis direction of the optical system,
An optical hole shape measuring method, wherein a shape of the hole to be measured that changes in the axial direction is measured. 4. A method for irradiating a light beam on an inner peripheral wall surface of a hole to be measured,
In an optical hole shape measuring apparatus which captures reflected light on the wall surface as an observation image and measures the shape of the measurement target hole from position information on the image plane of the observation image, the light from the light source is directed to a predetermined position with respect to the optical axis. It has an irradiation optical system that generates a light beam inclined at an angle and irradiates the inner peripheral wall surface of the measurement target hole, and a plurality of position detection means respectively arranged corresponding to positions where the optical path length of the reflected light is different. An observation optical system that captures the observation image of the reflected light on the wall surface as two-dimensional position information, and the reflected light obtained from the position information on the image plane of the observation image captured by each position detection unit of the observation optical system. From the angle with respect to the optical axis, the angle of the irradiation light beam with respect to the optical axis, and the arrangement size of the optical system, the spatial position of the reflection point on the wall surface is obtained, and the spatial position information is used to determine the shape of the hole to be measured. Optical hole shape measuring apparatus characterized by comprising a calculating means for measuring. 5. The optical hole shape measuring apparatus according to claim 4, wherein the irradiation optical system generates ring-shaped parallel light generating means for generating light from a light source into ring-shaped parallel light having an open angle. And first lens means for generating ring-shaped parallel light from the ring-shaped parallel light generating means into a ring-shaped conical light beam having a predetermined opening angle and irradiating the inner peripheral wall surface of the measurement target hole. Characteristic optical hole shape measuring device. 6. The optical hole shape measuring apparatus according to claim 4, wherein the observation optical system includes a second lens unit that receives light reflected on the wall surface, and the second lens unit. It is composed of beam splitter means for splitting transmitted light into a plurality of optical paths, and a plurality of two-dimensional image sensors arranged at positions having different optical path lengths on each optical path split by the beam splitter means. An optical hole shape measuring device, characterized in that: 7. The optical hole shape measuring apparatus according to claim 5, wherein a maximum value of the light intensity of the observation image received by the two-dimensional image sensor or a median value of a light receiving region is set as the position information. Characteristic optical hole shape measuring device. 8. The optical hole shape measuring apparatus according to claim 4, wherein said moving means moves said object to be translated in a direction parallel to an optical axis of said optical system, and said moving means comprises: An optical hole shape measuring apparatus, comprising: a moving amount detecting means for detecting a moving amount of an object to be measured.