JP2009092596A - System and method for inspecting dimensions - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a dimension inspecting system capable of state inspection by an image and of highly precise dimension measurement by utilizing a telecentric optical system. <P>SOLUTION: In the telecentric optical system, on the focal point of a front lens group a diaphragm of small aperture is provided so as to selectively focus only parallel light to the lens principal axis. By shifting the position of the diaphragm on the perpendicular plane to the principal axis of the lens, a parallel light tilting a little to the principal axis of the lens can be focused, and thus the correct measurement of the tilting object is made possible without moving the lens body, the imaging means and the measurement object. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a dimensional inspection system and a dimensional inspection method that enable a state inspection by an image and highly accurate dimensional measurement using a telecentric optical system.

Conventionally, a telecentric optical system in which a principal ray is parallel to a lens optical axis is known. Among these, the optical system in which the light incident on the lens from the object is parallel to the optical axis even outside the optical axis is called an object-side telecentric optical system, and the light traveling from the lens toward the image is parallel even outside the optical axis. An optical system is referred to as an image side telecentric optical system. Further, an optical system having a telecentric structure on both the object side and the image side is referred to as a double-sided telecentric optical system.
According to this double-sided telecentric optical system, the principal ray is parallel to the optical axis, so even if the position of the object moves, the size of the image does not change. When capturing images of different workpieces with the same optical system, it can be said that it is effective when the workpiece positioning in the optical axis direction is rough.

Examples of the double-sided telecentric optical system as described above include a telecentric lens system and an image measuring device disclosed in Patent Document 1, for example.
That is, in this telecentric lens system, the front lens group, the rear lens group arranged so that the front focal point coincides with the rear focal point of the front lens group, the rear lens group and the rear lens of the front lens group A diaphragm mechanism arranged at a position where the front focal point of the group coincides, and the diaphragm mechanism is provided with a numerical aperture changing mechanism for changing the numerical aperture. It can be used for a wide range of applications up to observation with high resolution.

JP 2003-232999 A

  That is, in Patent Document 1, the focal depth and resolution are uniquely determined for one lens group, and by changing the numerical aperture, observation and measurement can be performed with a wide focal length and resolution. .

  By the way, when the dimension measurement of the measurement target is performed using the both-side telecentric optical system as described above, since the angle of view is 0 ° in the telecentric optical system, the dimension measurement in the direction orthogonal to the optical axis is performed. Useful.

However, in order to accurately measure the dimensions, it is assumed that the measurement target is correctly arranged with respect to the lens main axis. In a telecentric optical system, since an image is formed by parallel rays, if the measurement target is inclined with respect to the lens main axis, the shape captured as an image is different, and accurate dimension measurement is impossible. For this reason, until now, it has been necessary to physically correct the measurement object or the angle of the lens and perform measurement again.
In particular, in the inspection process of industrial products, when measuring dimensions with a depth using this telecentric lens, it is necessary to physically correct the angle of the measurement object or lens for the above reasons, and the mechanism of the inspection apparatus There is a problem that the inspection cycle time becomes long.
In the telecentric optical system according to the present invention, a diaphragm having a small aperture is placed at the focal position of the front lens unit to selectively form only light rays parallel to the lens main axis. Focusing on the fact that parallel rays slightly tilted with respect to the lens main axis can be imaged by shifting the position on a plane orthogonal to the lens main axis, and without moving the lens body, imaging means, and measurement object, the lens main axis It is an object of the present invention to provide a dimension inspection system and a dimension inspection method that enable accurate dimension measurement of an inclined measurement object by forming an image of parallel rays with an angle arbitrarily changed.

  To achieve the above object, a first aspect of the present invention is a telecentric optical system that forms a projection image from a measurement object (W) set via a surface light source (L), and a projection by the telecentric optical system. The telecentric optical system includes an image pickup means (3) for picking up an image and an image processing device (4) for processing an image pickup signal from the image pickup means (3) and displaying it as a shadow image. ) Is provided with a movable diaphragm portion (8) whose displacement can be adjusted on a plane orthogonal to.

  As a result, according to the setting method of the measurement object (W), the movable diaphragm portion (8) is displaced and adjusted on the surface orthogonal to the lens main axis (Z), so that the deflected parallel light is converted into a telecentric optical system. , And an equivalent image of the measurement object (W) as it is can be formed.

  According to a second aspect of the present invention, the telecentric optical system is such that the front focal point coincides with the focal points of the front lens (5) facing the measurement target (W) and the front lens (5) opposite to the measurement target (W). A front lens (5) and a rear lens (6) arranged so that the focal point (7) of the front lens (5) coincides with the front focal point of the rear lens (6). A movable diaphragm (8) having a displacement adjustable on a surface orthogonal to the lens main axis (Z) passing through the rear lens (6) is provided.

  By adjusting the displacement of the movable diaphragm (8) on a plane orthogonal to the lens main axis (Z), the telecentric optical system can form an image of inclined parallel rays with respect to the lens main axis (Z). .

  According to a third aspect of the present invention, the movable aperture portion (8) in the telecentric optical system is provided in accordance with the deflection state of the main axis when the measurement target (W) is set with respect to the lens main axis (Z) of the telecentric optical system. The displacement is adjusted on a plane orthogonal to the lens main axis (Z).

  By adjusting the displacement of the movable diaphragm (8) on the surface orthogonal to the lens main axis (Z) even when the measurement object (W) is set, even if it is deflected with respect to the lens main axis (Z). The telecentric optical system forms an image of an inclined parallel light beam with respect to the lens main axis (Z) to form an equivalent image of the measurement object (W) as it is.

  The invention according to claim 4 forms a projection image of the measurement object (W) irradiated by the surface light source (L) with a telecentric optical system, acquires the projection image as an electric signal, and uses the electric signal as an image. The object to be measured and displayed as an image, and the object to be measured (W) is set to be shifted from the lens main axis (Z) of the telecentric optical system when performing inspection or measurement based on this image ( By adjusting the displacement of the movable diaphragm (8) in the telecentric optical system on a plane orthogonal to the lens main axis (Z) according to the deflection state of W), the telecentric optical system allows the measurement object (W ) Projection image is obtained.

  Even if the object to be measured (W) is set with a deviation from the lens main axis (Z) of the telecentric optical system, the movable diaphragm (8) in the telecentric optical system is on the plane orthogonal to the lens main axis (Z). By adjusting the displacement with the telecentric optical system, it is possible to form an inclined parallel light beam with respect to the lens main axis (Z) and form a projection image as it is as the measurement target (W).

  The invention described in claim 5 is characterized in that the image pickup means (3) comprises a CCD camera.

  As a result, the image formed by the parallel rays that have passed through the rear lens (6) is converted into an electrical signal, sent to the image processing device (4), subjected to image processing, and displayed as a corresponding image for grasping the state. Can be used for dimension measurement.

  The invention according to claim 6 is characterized in that the measurement object (W) is a flat tube of a finned tube heat exchanger.

  Thereby, it is possible to accurately form a projected image of the refrigerant tube and measure the thickness.

  The invention according to claim 7 is characterized in that the measurement object (W) is a monolith support for an exhaust gas purification catalyst.

  Thereby, the penetration degree can be accurately grasped from an accurate projection image of the monolith support for exhaust gas purification catalyst.

  Furthermore, the invention described in claim 8 is characterized in that the measurement object (W) is a lattice body.

  Thereby, it is possible to accurately measure the lattice size by accurately capturing the lattice body in the projected image.

  In addition, the code | symbol in the bracket | parenthesis of each said means is an example which shows a corresponding relationship with the specific means of embodiment mentioned later.

Hereinafter, an example of an embodiment of a dimensional inspection system according to the present invention will be given and described with reference to the accompanying drawings.
FIG. 1 schematically shows a dimensional inspection system 1.
The dimensional inspection system 1 includes a lens barrel 2 that accommodates a telecentric optical system (described later) disposed toward a measurement target W set via a surface light source L installed on an inspection table S, and is connected to the lens barrel 2. The image pickup means 3 and the image processing device 4 that performs image processing and displays the electrical signal applied to the image from the image pickup means 3 are provided.

  The lens barrel 2 that accommodates the telecentric optical system has a substantially conical outer shape. The telecentric optical system has a relatively large-diameter front lens 5 that faces the measurement target W and is opposite to the measurement target W. A rear lens 6 having a smaller diameter than that of the front lens 5 is provided so as to be aligned with the focal point of the front lens 5 on the side. The front lens 5 and the rear lens 6 are disposed so that their optical axes coincide with each other as the lens principal axis Z, and the lens principal axis Z coincides with the central axis in the height direction of the measurement target W. The lens barrel 2 is positioned and set so that

  The imaging means 3 is a CCD camera 3 provided with a CCD as an image sensor disposed at an image forming position by a light beam from the rear lens 6 in the lens barrel 2. It is converted into an electrical signal as an image signal applied to the measurement target W by the CCD and sent to the image processing apparatus 4 described later. The CCD constituting the CCD camera 3 is arranged adjacent to the rear lens 6 in the lens barrel 2 with the axis centered on the lens main axis Z.

  Next, the image processing apparatus 4 uses a known desktop personal computer. In the image processing apparatus 4, predetermined signal processing is performed from an electrical signal as an image signal applied to the measurement target W output by the CCD, and is displayed as a display signal on the display dp. Based on the displayed display signal Dimension measurement is performed by visual inspection or by installed software.

A movable diaphragm unit is located at a focal position 7 between the front lens 5 and the rear lens 6 as a telecentric optical system in the lens barrel 2 where the focal point of the front lens 5 coincides with the front focal point of the rear lens 6. 8 is provided. The movable aperture 8 has a predetermined aperture diameter, allows the focal light from the front lens 5 to pass through, and forms parallel light by the rear lens 6 to be connected to the CCD camera 3 behind. I try to make it image.
The movable diaphragm unit 8 can be shifted within a predetermined range on a plane (on the focal position 7) orthogonal to the passing lens main axis Z by a known driving means (not shown). .

The dimension inspection system according to the present invention is configured as described above. Next, as shown in FIG. 1, an example in which dimension measurement of a measurement target W is performed will be described.
First, as shown in FIG. 1, the lens barrel 2 containing the telecentric optical system is positioned and moved with respect to the measurement target W set on the inspection table S in the dimension inspection system 1 via the surface light source L, and the measurement is started. For the preparation work.
That is, the lens main axis Z that is the optical axis of the front lens 5 and the rear lens 6 that are telecentric optical systems in the lens barrel 2 is positioned and set so as to coincide with the central axis in the height direction of the measurement target W. .

  Next, of the light passing through the measurement object W with the surface light source L on, the light passing through the front lens 5 as a light beam parallel to the lens principal axis Z is collected, and the focal point of the front lens 5 and the rear lens 6 passes through the movable aperture 8 at the focal position 7 with respect to the front focal point 6, passes through the rear lens 6, becomes parallel light, and forms an image on the CCD camera 3 that is an imaging means behind the rear lens 6. it can.

Therefore, when the measurement target W is positioned in the field of view so that the lens main axis Z and the central axis in the height direction of the measurement target W are parallel to each other as shown in FIG. Are collimated when passing through the front lens 5, pass through the movable aperture 8 at the focal point 7 between the focal point of the front lens 5 and the front focal point of the rear lens 6, and then the rear lens. 6 passes through 6 and becomes parallel light, and can be formed as a projected image as it is on the CCD camera 3 which is the imaging means behind the rear lens 6.
As a result, the image signal is converted into an electric signal by the CCD camera 3, and the image processing apparatus 4 performs predetermined signal processing from the electric signal as the image signal and displays it on the display dp as the display image as it is as the measurement target W. Therefore, accurate dimension measurement can be performed based on the displayed display image.

  However, when the measurement target W is set on the inspection table S in an inclined state as shown in FIG. 2, what is projected from under the measurement target W with the parallel light of the surface light source L is applied to the front lens 5. The incident image is formed as a projected image as it is on the CCD camera 3 behind the rear lens 6, and as a result, is displayed on the display dp of the image processing device 4 as an image in which the side surface portion of the measurement target W is added. Therefore, if it remains as it is, accurate dimension measurement cannot be performed.

Therefore, as shown in FIG. 3, the movable diaphragm 8 at the focal position 7 between the focal point of the front lens 5 and the front focal point of the rear lens 6 is orthogonal to the lens main axis Z that passes through the driving means (not shown). By shifting on the surface (on the focal position 7), the inclined parallel rays incident on the front lens 5 along the both inclined end surfaces of the measurement object W pass through the shifted movable diaphragm portion 8 and are moved to the rear lens. 6 passes through 6 and becomes parallel light, and can be imaged on the CCD camera 3 which is an imaging means behind the rear lens 6.
At this time, the image processing device 4 can perform predetermined signal processing from an electrical signal as an image signal and display it on the display dp as a display image of the measurement target W as it is. Therefore, based on the displayed display image Accurate dimension measurement can be performed (see FIG. 3).

  As described above, according to the present invention, in the telecentric optical system, the movable diaphragm portion 8 between the front lens 5 and the rear lens 6 is shifted on the focal position 7 to be slightly inclined with respect to the lens main axis Z. The light beam can be imaged, and the accurate dimensions of the tilted measurement object can be obtained by imaging the parallel light beam at any angle with respect to the lens main axis without moving the lens body, imaging means, or measurement object. This means that the original purpose of enabling measurement has been achieved.

As described above, the present invention has shown and described the procedure for measuring the dimension of the measurement target W. Of course, the present invention is not limited to dimension measurement, and can be used in applications that make use of the characteristics of the telecentric optical system. .
For example, the measurement target W can be a flat tube of a fin-tube heat exchanger, and is useful when measuring the thickness dimension of the flat tube.
Since a plurality of flat tubes are provided in the product, if a telecentric optical system is used, even when the same workpiece is photographed, the angle of view is 0 degrees, so an image without distortion can be obtained. It is.

In addition, the present invention is suitable as the measurement object W when inspecting the penetration degree of the monolith support for exhaust gas purification catalyst.
The monolithic carrier for exhaust gas purification catalyst has a function of purifying the gas discharged from the engine by touching the catalytic substance coated on the monolithic carrier, and has many cells formed on one side. This is effective for efficiently inspecting whether or not it is penetrated.

Furthermore, the measurement target W is effective for measuring the dimensions of a lattice formed on a wide surface.
That is, according to the telecentric optical system, it is possible to obtain an image without distortion without being affected by the parallax regardless of whether the image point is at the center position of the screen or the peripheral position of the screen. For this reason, the grid formed on a wide surface is projected under the same conditions in both the central part and the peripheral part of the screen, which is effective for dimension measurement without error.

It is typical structure explanatory drawing which shows an example of the dimension inspection system concerning this invention. It is the schematic diagram which showed the display image concerning the image obtained when the test object is inclined and set. It is typical structure explanatory drawing which showed the effect | action of the dimension inspection system concerning this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Dimensional inspection system 2 Lens barrel 3 CCD camera 4 Image processing device 5 Front lens 6 Rear lens 7 Focus position 8 Movable diaphragm W Measurement object L Surface light source S Inspection table

Claims (8)

A telecentric optical system for forming a projection image from a measurement object (W) set via a surface light source (L);
Imaging means (3) for capturing a projection image by the telecentric optical system;
An image processing device (4) that performs image processing on the imaging signal from the imaging means (3) and displays it as a shadow image;
The telecentric optical system includes a movable diaphragm (8) whose displacement can be adjusted on a plane orthogonal to the lens main axis (Z). The telecentric optical system includes a front lens (5) facing the measurement target (W),
A rear lens (6) disposed so that the front focal point coincides with the focal point of the front lens (5) on the opposite side of the measurement target (W);
A lens main axis (Z) passing through the front lens (5) and the rear lens (6) at a focal position (7) where the focal point of the front lens (5) and the front focal point of the rear lens (6) coincide. The dimensional inspection system according to claim 1, further comprising a movable diaphragm portion (8) capable of adjusting a displacement on a plane orthogonal to.   With respect to the lens main axis (Z) of the telecentric optical system, the movable stop portion (8) in the telecentric optical system is moved to the lens main axis (Z) according to the deflection state of the main axis when the measurement target (W) is set. The dimensional inspection system according to claim 1, wherein the displacement is adjusted on a plane orthogonal to. The measurement object (W) irradiated by the surface light source (L) forms a projection image with a telecentric optical system, obtains the projection image as an electrical signal, performs image processing on the electrical signal, and displays it as a shadow image. In performing inspection or measurement based on this image,
The movable aperture portion (8) in the telecentric optical system is moved according to the deflection state of the measurement target (W) on which the measurement target (W) is set with respect to the lens main axis (Z) of the telecentric optical system. A dimension inspection method characterized in that a projection image of the measurement object (W) is obtained by a telecentric optical system by adjusting displacement on a plane orthogonal to the lens main axis (Z).   The dimensional inspection system according to claim 1, wherein the imaging means (3) comprises a CCD camera.   The dimensional inspection system according to any one of claims 1 to 3, wherein the measurement object (W) is a flat tube of a fin-tube heat exchanger.   The dimensional inspection system according to any one of claims 1 to 3, wherein the measurement object (W) is a monolith support for an exhaust gas purification catalyst.   The dimensional inspection system according to any one of claims 1 to 3, wherein the measurement object (W) is a lattice body.

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