JP3920713B2 - Optical displacement measuring device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a technique for optically measuring an uneven shape on the surface of an object.
[0002]
[Prior art]
It is important for quality control of products to accurately measure the surface shape of an article. For example, it is necessary to inspect the presence or absence of a defect called “cast hole” in an aluminum cast product. In many cases, inspection is performed visually. However, the size of the defect may be about 0.2 to 0.5 mm, and skill is required for accurate inspection. However, since inspections are performed by humans, it is difficult to completely eliminate oversights even with caution. In addition, as the number of inspection targets increases, the number of inspection personnel must be increased, and sudden increases in production can be handled. It is difficult to have enough skilled workers immediately. Furthermore, the inner surface of a cylindrical member or a member with a deep hole is difficult to see from the outside, and is not suitable for visual inspection. Even if the presence or absence of a defect can be determined, it is impossible to measure the size and shape of the defect, and it is not possible to obtain sufficient information for analyzing the cause of the defect from the inspection result.
[0003]
In addition to visual inspection, various methods have been put to practical use as methods for inspecting defects as described above. The ultrasonic flaw detection method irradiates an object with ultrasonic waves and analyzes the reflected waves to inspect for the presence or absence of defects. According to this inspection method, not only the surface but also internal defects can be examined. However, the space between the ultrasonic probe and the object surface must be filled with a liquid such as water, which is a surface acoustic wave transmission medium, and handling is not easy. Moreover, although the eddy current flaw detection method is used as a stable and high-speed inspection method, there is a problem that it is expensive. On the other hand, as a method for simply and accurately inspecting the surface, there is optical displacement measurement using the principle of triangulation.
[0004]
[Problems to be solved by the invention]
The problems of the conventional surface shape measurement methods such as visual inspection, ultrasonic shortcoming flaw detection method, and eddy current flaw detection method have already been described. Therefore, here, optical displacement measurement using the principle of triangulation will be described. FIG. 5 shows the principle of a conventional measuring apparatus. Light emitted from a light source such as a laser or a light emitting diode toward the surface of the object is condensed through a light projecting lens and focused near the surface of the object. Here, the light is irradiated obliquely with respect to the object surface. The light reflected from the surface of the object passes through the light receiving lens and reaches the position detection element. Here, if there are scratches on the surface and the heights are different, the reflected light arrives at different positions on the position detection element. That is, a change in the height direction of the object surface is converted into a change in position on the position detection element. The position detection element generates a signal corresponding to the received position. The surface shape is measured from the change in the signal. This measuring method is capable of measuring the surface shape with a relatively simple apparatus with high accuracy, and a technique using this principle is described in, for example, JP-A-8-61940. However, according to this principle, the light must be irradiated obliquely to the surface of the object, and in order to detect the change in the height direction with high sensitivity, the light is detected between the surface of the object and the position detection element. A certain distance is required. For this reason, a certain amount of distance is required between the light source and the position detection element, and the displacement sensor must be measured with a certain distance from the object surface. For this reason, there is a limit to the inspection of the inner surface of a cylindrical member having a small inner diameter in combination with the displacement sensor becoming large to some extent. Therefore, it is conceivable to use a configuration as shown in FIG. 6 by providing a reflector between the light projecting lens and the object surface and between the object surface and the light receiving device. With this arrangement, even if the distance between the light source and the position detection element is small, light can be irradiated onto the object surface with a sufficient inclination, and the distance between the object surface and the position detection element does not need to be increased significantly. Sufficient sensitivity is obtained for changes in the height direction. However, the configuration of FIG. 6 requires two lenses and two reflectors, and the size and arrangement of these optical elements limit the distance, and miniaturization is still limited. An object of the present invention is to provide a small optical displacement sensor with a simple configuration, an optical measuring device capable of easily and highly accurately inspecting an inner surface of a cylindrical member having a small inner diameter, and an optical element suitable for the same. It is to be. It is another object of the present invention to provide an optical measurement device that can distinguish a defect from a defect even if a processed hole appears on the surface of the object.
[0005]
[Means for Solving the Problems]
In order to solve the above-described problems, an optical displacement sensor according to the present invention includes a light source, a curved surface for condensing light from the light source, and a reflective surface for changing the traveling direction of the light. A second optical element in which a first optical element, a curved surface for condensing light that has passed through the first optical element and reflected from the measurement surface, and a reflective surface for changing the traveling direction of the light are integrally formed And a position detection element for detecting light that has passed through the second optical element. A plurality of combinations of the light source, the first optical element, the second optical element, and the position detection element are provided and arranged side by side in the longitudinal direction of the rod-shaped member, thereby speeding up the inspection. An optical displacement measuring apparatus according to the present invention is an optical displacement measuring apparatus that measures the surface shape of the inner surface of a cylindrical member. In addition to the above-described optical displacement sensor, the optical displacement sensor is disposed inside the cylindrical member. A holding means for holding the optical displacement sensor, a rotating means for relatively rotating the optical displacement sensor and the cylindrical member, and a moving means for relatively moving the optical displacement sensor along the length direction of the cylindrical member; , The height data H output from the optical displacement sensor at each position is input, the maximum value or the minimum value of data h among the continuous fixed number of height data H is calculated, and the difference data Δ = H between the two is calculated. An image processing apparatus that calculates -h and a display unit that displays the difference data Δ are included. Furthermore, the optical element according to the present invention has a curved surface for condensing on a part of the surface, and changes the traveling direction of the light traveling through the curved surface to reflect toward the other part of the curved surface. It has a reflective surface.
[0006]
DETAILED DESCRIPTION OF THE INVENTION
An embodiment of the present invention will be described with reference to FIG. The optical displacement sensor 1 includes a light source 2 such as a laser or a light emitting diode. The light source 2 emits light substantially perpendicular to the surface of the object. The first optical element 3 is made of a transparent material such as glass or synthetic resin, and has a curved surface 3a and a reflecting surface 3b. Light from the light source enters the first optical element 3 through a part of the curved surface 3a. Here, the curved surface 3a has a shape such as a spherical surface or a cylindrical surface, and serves as a lens surface that collects light from the light source. This curved surface may be an aspheric surface considering various aberration corrections. The light traveling inside the first optical element 3 is reflected by the reflecting surface 3b and still travels inside the first optical element 3 while changing the traveling direction. And it goes out through the other part of the curved surface 3a. Also at this time, the curved surface 3a serves as a lens surface. The light emitted out of the first optical element 3 is focused near the surface of the object. A diaphragm 6 is provided at the entrance of the first optical element 3 and is configured to have a certain depth of focus. The light is irradiated obliquely with respect to the surface of the object, is reflected by the surface, and then enters the second optical element 4. Similarly to the first optical element, the second optical element 4 is made of a transparent material, and has a curved surface 4a and a reflecting surface 4b. The reflected light from the surface of the object enters the second optical element 4 through the curved surface 4a, is reflected by the reflecting surface 4b, changes the traveling direction, and then goes out through the other part of the curved surface 4a. An image is formed on the position detection element 5. Here, when the height varies depending on the uneven shape of the object surface, the light reaches different positions on the position detection element. The position detection device 5 converts the difference in the arrival position of the light into an electric signal or the like.
[0007]
As described above, the optical displacement sensor shown in FIG. 1 performs displacement measurement based on the principle of triangulation, whereas the conventional example shown in FIG. 6 requires at least two lenses and two reflectors, whereas the optical displacement sensor shown in FIG. The same optical path is constituted by only two optical elements 3 and 4. This is because a special optical element in which a lens surface and a reflecting plate are integrally formed is applied to the principle of triangulation. The first optical element 3 and the second optical element 4 can be formed by cutting a part of a transparent sphere to form a flat reflecting surface as shown in FIG. The curved surface is easy to make a spherical surface and has excellent light-collecting power, so it is versatile as a lens surface. However, it may be a cylindrical surface or a lens surface that constitutes an aspherical lens in consideration of various aberrations. Good. In addition to the flat surface, the reflecting surface may be a gentle curved surface that is convex outward so as to exhibit the effect of a concave mirror. Further, the reflection surface may be provided with reflection plates 3c and 4c such as metal plates to increase the reflection efficiency. Further, the surface of the optical element is formed flat, and the metal plate is embedded in the optical element. It may be formed. Note that it is preferable that the first optical element 3 and the second optical element 4 are designed to have the same shape because the components can be shared. Since this optical element can realize a complicated optical path in a small size and at low cost, it can be widely used in addition to an optical displacement sensor, and can also be applied to a photographer, an optical communication device, and the like.
[0008]
A pair of these light source, first optical element, second optical element, and position detection element can be provided in the displacement sensor body to form an optical displacement sensor. However, as shown in FIG. It can also be provided in a displacement sensor body made of a rod-shaped member. Since the configuration shown in FIG. 1 can be realized in a small size and at a low cost, a plurality of sets can be easily provided. This allows a plurality of locations on the surface of the object to be inspected at the same time, thereby reducing the inspection time. If the surface of the object is a plane, a plurality of combinations of light sources, first optical elements, second optical elements, and position detection elements may be arranged vertically and horizontally.
[0009]
【Example】
Next, an embodiment of the present invention will be described with reference to FIG. It is the example which applied this invention to the test | inspection of the inner surface of a cylindrical member. A light source, a first optical element, a second optical element, and a position detection element 5 are provided near the tip of the rod-shaped displacement sensor body 7. In this embodiment, the light source is a light-emitting diode that is cheaper and easier to handle than a laser, and the position detection element is an element that extends to PSD. The displacement sensor body 7 is placed inside a cylindrical member 8 that is an inspection object. The cylindrical member 8 is fixed to the attachment portion 9 with a bolt 10. A motor 11 is connected to the attachment portion 9 and rotates together with the cylindrical member 8. On the other hand, the displacement sensor main body 7 is connected to the moving means 12 so that it can advance and retreat in the length direction of the cylindrical member 8. Thus, in order to inspect the inner surface of the cylindrical member 8 with the optical displacement sensor, the displacement sensor main body 7 and the cylindrical member 8 are relatively rotated, and the length of the cylindrical member 8 is relatively set. It is necessary to scan while moving. Therefore, the displacement sensor main body 7 may be rotated around the axis of the cylindrical member 8, and the cylindrical member 8 may be moved back and forth in the length direction thereof. In such a case, it is easier to configure the apparatus by rotating the object and moving the displacement sensor body 7 back and forth in the same manner as a lathe.
[0010]
As described above, the height is measured while changing the position on the inner surface of the cylindrical member 8 by the rotation and the movement in the length direction, and the electric signal H (height data) corresponding to the height is measured. Occurs. The height data H is sent to the image processing device 13. Here, when the center of rotation of the cylindrical member 8 completely coincides with the center of the cylindrical member 8, the inner surface can be imaged even if the height data H is displayed as it is. However, it is difficult to mount the inspection body so that the rotation centers always coincide with each other. When there is a deviation in the rotation center, a sinusoidal wave appears during one rotation. FIG. 4A shows the height data H in this case. If this is displayed on the monitor, periodic undulations appear and it is difficult to find true defects. N height data H ₁ , H ₂ ... H _n are stored in the height data storage device of the image processing device 13. Data H ₁ is the current height data, H ₂ is the height data of the previous one, it is H _n is the height data of the previous n-1 times. In many cases, n may be about 3. The smoothing processing device 15 outputs the maximum value or the minimum value from the n pieces of height data H ₁ , H ₂ ... H _n as smoothed data h. FIG. 4B shows the smoothed data h. The portion where no defect exists is almost the same as the height data H, and even the portion where there is a defect is smoothed to become a curve almost similar to a sine wave. The subtracter 16 outputs difference data Δ between the height data H and the smoothed data h. FIG. 4C shows the difference data Δ, and the swell component due to the deviation of the rotation center is canceled out to show only the defect. The display signal generator 17 generates a display signal for displaying light and shade and contour lines on the display device 18 based on the magnitude of the difference data Δ. The display device 18 is a monitor screen such as a CRT and displays the surface shape based on the difference data Δ. In addition, when the sorting operation is not performed at the inspection site, it may be output to paper by a printer instead of the CRT, and an image output when a failure occurs can be analyzed retrospectively. The inspector has only to inspect based on the image on the display device 18 and can easily grasp not only the presence / absence of the defect but also the size and depth of the defect in a three-dimensional manner.
[0011]
As described above, according to the present embodiment, it is possible to easily measure the inner surface shape of the cylindrical member that is difficult to visually inspect with a simple apparatus by a simple procedure. Moreover, since the three-dimensional shape of the defect can be grasped, it can be used for analysis of a problem that the defect may cause and analysis of the cause of the defect, thereby realizing advanced product management. Further, the image processing of the present embodiment can cancel out the rotation center misalignment from the displayed image to a considerable extent, so that a highly accurate inspection can be performed even in a somewhat rough operation. In addition, although the inspection object of the present Example was the cylindrical member by aluminum casting, in such a component, the hole is often processed in the side surface. Such holes are usually referred to as “lateral holes”, which are the result of processing as designed and not defects. According to the apparatus of this embodiment, the horizontal hole is also clearly imaged so that it can be easily identified as a defect, and the presence or absence of a defect can be accurately determined even near a horizontal hole that tends to be a blind spot in a normal inspection method. it can.
[0012]
【The invention's effect】
As described above, the optical displacement sensor, the optical displacement measuring device, and the optical element according to the present invention have an effect that high-precision surface shape measurement can be realized with a small and inexpensive device and method with a simple configuration. Since skilled techniques are not required for mounting the inspection object or determining the presence or absence of defects from the image, there is an effect that labor can be saved in the inspection. Furthermore, according to the present invention, since the three-dimensional shape of the defect can be grasped, there is an effect that advanced quality management such as defect cause analysis can be realized.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram showing the principle of an optical displacement sensor according to the present invention.
FIG. 2 is a cross section showing an example of an optical displacement sensor according to the present invention.
FIG. 3 is a block diagram showing an example of an optical displacement measuring apparatus according to the present invention.
FIG. 4 is a graph showing height data, smoothed data, and difference data.
FIG. 5 is an explanatory diagram showing the principle of a conventional optical displacement sensor.
FIG. 6 is a block diagram showing an example of a conventional optical displacement sensor.
[Explanation of symbols]
1. 1. Optical displacement sensor 2. Light source First optical element 4. Second optical element 5. 5. Position detection element Aperture 7. 7. Displacement sensor body Cylindrical member (inspection object)
9. 9. Attachment part of inspection object Bolt 11. Motor 12. Moving means 13. Image processing device 14. Height data storage 15. Smoothing processor 16. Subtractor 17. Display signal generator 18. Display means 19. Projection lens 20. Light receiving lens 21. a reflector

Claims (3)

It is an optical displacement measuring device that measures the surface shape of the inner surface of a cylindrical member,
An optical displacement sensor, a holding means for holding the optical displacement sensor inside a cylindrical member, a rotating means for relatively rotating the optical displacement sensor and the cylindrical member, and the optical displacement sensor as a cylindrical member A moving means for relatively moving along the length direction of the display, and a display means for displaying the surface shape,
The optical displacement sensor includes a light source, a first optical element formed integrally with a curved surface for condensing light from the light source, and a reflective surface for changing the traveling direction of the light, and a first optical element. A second optical element formed integrally with a curved surface for condensing the light that has passed and reflected from the measurement surface and a reflective surface for changing the traveling direction of the light; and the light that has passed through the second optical element. It has a position detection element to detect ,
In the first optical element and the second optical element, light has an optical path that enters the inside through a curved surface, and is reflected by the reflecting surface and then exits through the curved surface of the same curved surface.
Optical displacement measuring device. 2. The optical displacement measuring device according to claim 1, wherein a plurality of combinations of the light source, the first optical element, the second optical element, and the position detecting element are provided side by side in the longitudinal direction of the rod-shaped member. . The height data H output from the optical displacement sensor at each position is input, the data h that is the maximum value or the minimum value among a certain number of continuous height data H is calculated, and the difference data Δ = H− between the two is calculated. The optical displacement measuring apparatus according to claim 1, further comprising an image processing apparatus that calculates h and a display unit that displays the difference data Δ.

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