JP2009186368A - Shape measuring apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a shape measuring apparatus for accurately measuring a shape of an inspecting object with a simple constitution even if an optically abnormal part exists on the surface of the inspecting object. <P>SOLUTION: This shape measuring apparatus comprises a slit projection optical system 2 for irradiating the inspecting object 10 with illumination light having a predetermined irradiation pattern, at least object-side telecentric imaging optical systems 4-7 that have an optical axis different from the slit projection optical system 2 and image-form the light from the inspecting object 10 on an imaging surface of an imaging element 7, and an arithmetic section for calculating the shape of the inspecting object 10 using a signal from the imaging element 7. The slit projection optical system 2 and imaging optical systems 4-7 are movable in the optical axis direction of the imaging optical systems 4-7 while the relative positional relation is kept the same. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a shape measuring apparatus.

  Conventionally, in the non-contact three-dimensional shape measurement, a method based on a light cutting method of a slit light projection method as described in JP-A-7-260444 (Patent Document 1) is generally performed. In this method, the slit light projector and the camera are integrated, and the camera is within a plane perpendicular to the slit light irradiation surface (which may be referred to as a cut surface in an imaginary plane serving as a measurement reference). These optical axes are arranged so as to form a predetermined angle with the irradiation direction of the slit light.

  The slit light is reflected and / or scattered on the surface of the test object, and an image of the slit light on the surface of the test object is captured by the camera. At this time, since the optical axis of the camera is at an angle with the irradiation direction of the slit light, the point at which the slit light intersects the test object is observed differently according to the distance from the slit light source of the test object, Therefore, the imaged positions are different. The height information of the point on the test object can be calculated from the displacement of the position of the slit image. The position of the slit light source and the camera can be moved as a unit relative to the test object to obtain a three-dimensional shape of the entire test object.

In general, the slit light has a certain width, so that the image of the slit light to be imaged spans a plurality of pixels of the image sensor, and which pixel truly intersects the test object with the slit light. I don't know if it shows a dot. In order to cope with this, the slit light projector and the camera are moved together in a direction perpendicular to the longitudinal direction of the slit light, and the position where the amount of light received by the camera pixel is maximized is the surface of the object to be examined. The shape of the test object is calculated as indicating the position (intersection of the slit light and the test object).
JP 7-260444 A Japanese Patent No. 3282331

  However, when the object to be scanned is scanned with the slit light projector and the camera integrated as described above, the pixels of the camera shift the points on the object to be examined one after another. For this reason, if there is a portion with a different surface state such as reflectance or texture on the object to be examined, a change in the amount of light occurs. In addition, in an image sensor such as a CCD or CMOS, the sensitivity between pixels is not always strictly constant but varies.

  For this reason, as described above, the slit light projector and the camera are moved together in the direction perpendicular to the longitudinal direction of the slit light, and the position where the amount of light received by the pixel of the camera becomes the maximum is the position of the surface of the test object. However, if there is a portion with a different optical state on the surface of the object to be examined, the position where the light quantity is maximum is erroneously detected, resulting in a detection error.

  Therefore, as disclosed in Japanese Patent No. 3282331 (Patent Document 2), the position of the test object and the imaging camera is fixed, and the projection angle of the slit light is changed to maximize the scattered light from the test object. There is a way to get the value. However, if there is an error in setting the projection angle of the slit light, there is a problem that the detection sensitivity varies depending on the distance to the object to be detected. In addition, the imaging camera is required to have a deep depth of focus. However, if the depth of focus is increased, an imaging optical system with high resolving power cannot be used, which causes a problem in increasing accuracy.

  The present invention has been made in view of such circumstances, and with a simple configuration, even if there is an optically heterogeneous portion on the surface of the object to be measured, the shape measuring device can accurately measure the shape of the object to be tested. It is an issue to provide.

  A first means for solving the problem includes an illumination optical system that irradiates an object with illumination light having a predetermined irradiation pattern, an optical axis different from the illumination optical system, and A shape measuring device comprising at least an object-side telecentric imaging optical system that forms an image on the imaging surface of the imaging device, and an arithmetic unit that calculates the shape of the test object using a signal from the imaging device The illumination optical system and the imaging optical system can be moved in the optical axis direction of the imaging optical system while maintaining the same relative positional relationship. is there.

  The second means for solving the problem is the first means, and the shape calculation device is configured to detect each pixel of the imaging element when the illumination optical system and the imaging optical system move. Based on the position of the illumination optical system and the imaging optical system when the output is maximum for each pixel, the height (position) information in the optical axis direction is detected for each pixel. And calculating the shape of the object to be measured.

  A third means for solving the problem is the first means or the second means, wherein the irradiation pattern to be irradiated and the imaging surface of the imaging optical system are shine via the imaging optical system. It is characterized by meeting the proofing conditions.

  A fourth means for solving the problem is any one of the first to third means, and a light beam forming the irradiated irradiation pattern is an optical axis of the illumination optical system. A slit-shaped light beam having a cross-sectional length direction in a direction perpendicular to a plane including the optical axis of the imaging optical system, or a plane including the optical axis of the illumination optical system and the optical axis of the imaging optical system A plurality of slit-shaped light beams having a length direction of a cross section in a vertical direction and arranged at intervals in a direction perpendicular to the optical axis of the illumination optical system. .

  According to the present invention, it is possible to provide a shape measuring apparatus that can accurately measure the shape of a test object even if there is an optically different portion on the surface of the test object with a simple configuration.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing an outline of an optical system of a shape measuring apparatus which is a first example of an embodiment of the present invention. A slit light projection optical system 2 is disposed on the measuring head 1 and is attached so that the longitudinal direction of the light beam is oriented in a direction perpendicular to the paper surface of FIG. Therefore, in FIG. 1, the illumination light is expressed only in the short direction, and thus is expressed by a straight line indicated by 3.

  In the slit projection optical system 2, the illumination light 3 is relative to the optical axes of the imaging optical systems 4 to 7 on a plane including the optical axis of the imaging optical systems 4 to 7 and the optical axis of the illumination light (paper surface in FIG. 1). It is attached to the measuring head 1 so as to form a predetermined angle θ.

  The imaging optical system includes a first lens group 4, an imaging optical system aperture stop 5, and a second lens group 6. In the vicinity of the front focal position of the first lens group 4, the optical axis 3 and the imaging of the slit projection optical system 2 are captured. The optical axes of the optical systems 4 to 7 intersect (a plane perpendicular to the plane (the paper surface of FIG. 1) including the optical axis of the slit projection optical system 2 and the optical axes of the imaging optical systems 4 to 7). A plane including the optical axis of the projection optical system 2 is a plane serving as a measurement reference, and is sometimes referred to as a “cut plane”. An imaging optical system aperture stop 5 is disposed at the rear focal position of the first lens group 4 and is object side telecentric. Therefore, the point captured by the predetermined pixel of the image sensor 7 is a point on a line parallel to the optical axis on the object side from the first lens group 4. That is, when an xyz orthogonal coordinate system is used and the z-axis direction is the optical axis, the x-coordinate and y-coordinate of the object-like point imaged by a predetermined pixel are constant.

  Further, the second lens group 6 is arranged so that the above-described imaging optical system aperture stop 5 coincides with the front focal position, so that the image side telecentric image is formed. The image side telecentric simplifies the calculation of the shape, but the image side telecentricity is not necessarily an essential condition for the present invention.

  The imaging element 7 is disposed on the irradiation surface of the illumination light beam 3 so as to be inclined with respect to the optical axes of the imaging optical systems 4 to 7 so as to satisfy the Scheinproof condition. That is, as shown in FIG. 1, when the object plane a (indicated by a line because it is perpendicular to the paper surface in FIG. 1) is inclined by θ with respect to the optical axes of the imaging optical systems 4 to 7, the image plane is When tilted by θ ′ (θ ′ is an angle satisfying tanθ = βtanθ ′ where β is the projection magnification of the imaging optical system), a point on the object plane can be observed in focus (in focus). . Furthermore, since the present embodiment is a double-sided telecentric optical system, the projection magnification β of the imaging optical system is indicated by the ratio of the focal length of the second lens group to the focal length of the first lens group 4.

  In this way, the shine proof condition is satisfied, and the point on the object to be examined and the point where the illumination light intersects forms an image on the image sensor surface 7. For this reason, unless the relative position of the slit light projection optical system 2 and the imaging optical systems 4 to 7 is changed, a high-resolution optical system having a large aperture stop diameter of the imaging optical system can be used, and the focal depth is reduced. Therefore, the position of the direction can be detected with higher accuracy.

  In the present embodiment, the slit projection optical system 2 and the imaging optical systems 4 to 7 are fixedly arranged on the measurement head 1 and moved by the measurement head drive mechanism 8 in the optical axis direction of the imaging optical system. ing.

  FIG. 2 shows the principle of measuring the distance to the test object in this way. Since the object 10 is illuminated from the position where the slit light projection optical system 2 is moved to 2a, 2b, 2c... By the movement of the measuring head driving mechanism 8, 3a, 3b, 3c is formed on the surface of the object 10. The position irradiated by the illumination light moves as in. When this state is observed with the imaging optical systems 4 to 7, as described above, the imaging optical system is front telecentric. The point is on a line parallel to the optical axis of the system.

  In FIG. 2, it is assumed that the slit light projection optical system 2 is observed at the position B that is just in focus when it is at the position 2b. When the slit light projection optical system 2 is at the positions 2a and 2c, it is observed in a defocused state.

  FIG. 3 shows the relationship between the amount of received light received by the corresponding pixel on the image sensor 7 and the position of the slit light projection optical system. The amount of received light is maximized when the slit light projection optical system is in position 2b in focus. Therefore, if the distance to the test object in this state is calculated, the distance to the test object can be accurately known. In this way, the position where the amount of received light is maximized is detected in all the pixels on the image sensor 7, and the pixel 10 observing the test object 10 is detected from the position of the slit light projection optical system at that time. The distance of the corresponding point in the optical axis direction can be obtained.

  As a modification of the embodiment of the present invention, a pattern may be projected instead of the slit light (in the claims and the means for solving the problems, the slit light is also illumination light having a predetermined irradiation pattern. Treated as). As an example of the pattern, the slit has a length direction in a direction perpendicular to a plane including the optical axis of the slit projection optical system 2 and the optical axis of the imaging optical system (a plane like the paper surface of FIG. 1), and the slit A plurality of slit-shaped light beams (stripe patterns) arranged at intervals in the direction perpendicular to the optical axis of the projection optical system 2 can be used. By using a plurality of stripe patterns in this way, measurement can be performed using a plurality of slit lights at a time, and the measurement time can be shortened.

  Instead of the stripe pattern, a spatial code pattern indicating a spatial code may be used. The spatial code pattern is, for example, one having different slit widths, or one that can be regarded as one slit is composed of a plurality of small slits, and the number of small slits is different. When such a spatial code pattern is used, it can be understood which spatial code pattern corresponds to the pattern imaged by the imaging device, and the calculation process is facilitated.

  When projecting such a plurality of patterns, the pattern projection optical system is preferably telecentric. This is because, if telecentric, the shape of the pattern does not change depending on the position irradiated on the object to be examined.

  FIG. 4 shows an outline of the optical system of the shape measuring apparatus according to the second embodiment of the present invention which is an example thereof. Since the image pickup system is the same as that in FIG. The light emitted from the light source 21 is collected by the collector lens 22 and arranged so as to form an image on the illumination aperture stop 24 via the mask 23 on which the projection pattern is written. The illumination light stop 24 is arranged at the front focal position of the illumination condenser lens 25, and the projection pattern is projected telecentrically. For this reason, since the interval of the slit pattern observed at each point on the image sensor 7 is constant, the fringe pattern is observed with a uniform period on all surfaces even when the fringe pattern is projected, and the measurement accuracy becomes uniform. You can

  As described above, according to the embodiment of the present invention, since the observation position of the test object does not change with respect to each pixel of the imaging optical system, the surface of the test object is not affected by the influence of the texture of the surface of the test object. Position detection can be performed. In addition, since the slit projection optical system 2 and the imaging optical system are fixed, they are simply moved in the direction of the optical axis of the imaging optical system, so that measurement can be performed with high accuracy.

  In the present embodiment, the slit projection optical system 2 and the imaging optical system are mechanically fixed to the measurement head and integrated, but it is not always necessary to mechanically integrate, and relative It is only necessary that movement that does not change the positional relationship is possible.

It is a figure which shows the outline | summary of the optical system of the shape measuring apparatus which is the 1st example of embodiment of this invention. It is a figure which shows the detail of the measuring method by embodiment of this invention. It is a figure which shows the change of the light quantity which one pixel light-receives by the measurement by embodiment of this invention. It is a figure which shows the outline | summary of the optical system of the shape measuring apparatus which is the 2nd Embodiment of this invention.

Explanation of symbols

1: measurement head, 2: slit projection optical system, 3: slit light, 4: first imaging lens group, 5: imaging optical system aperture stop, 6: second imaging lens group, 7: imaging element, 8: measurement head Drive mechanism, 10: object to be inspected, 21: light source, 22: collector lens, 23: projection pattern mask, 24: illumination system aperture stop, 25: condenser lens

Claims (4)

  An illumination optical system that irradiates the test object with illumination light having a predetermined irradiation pattern, and an optical axis different from that of the illumination optical system, and at least forms an image of light from the test object on the imaging surface of the imaging device A shape measuring apparatus comprising: an object side telecentric imaging optical system; and a calculation unit that calculates a shape of the test object using a signal from the imaging element, the illumination optical system and the imaging optical system; The shape measuring apparatus is capable of moving in the optical axis direction of the imaging optical system while maintaining the same relative positional relationship.   The shape measuring device according to claim 1, wherein the shape calculating device detects an output intensity of each pixel of the image sensor when the illumination optical system and the imaging optical system move, For each pixel, the height (position) information in the optical axis direction is calculated based on the positions of the illumination optical system and the imaging optical system when the output becomes maximum, and the shape of the object to be measured A shape measuring apparatus for calculating   3. The shape measuring apparatus according to claim 1, wherein the irradiation pattern to be irradiated and the imaging surface of the imaging optical system satisfy a Scheinproof condition via the imaging optical system. A shape measuring device.   4. The shape measuring apparatus according to claim 1, wherein a light beam that forms the irradiated irradiation pattern is an optical axis of the illumination optical system and an optical axis of the imaging optical system. A slit-shaped light beam having a longitudinal direction of the cross section in a direction perpendicular to the plane including the length of the cross section in a direction perpendicular to the plane including the optical axis of the illumination optical system and the optical axis of the imaging optical system A shape measuring apparatus comprising a plurality of slit-shaped light beams having a vertical direction and arranged at intervals in a direction perpendicular to the optical axis of the illumination optical system.

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