JP3487963B2 - Inspection method for transparent objects - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for inspecting a transparent object, and more particularly to a method for obtaining a transparent object in a non-contact manner using an optical method. 2. Description of the Related Art As a method for non-contact inspection of an accurate shape of a transparent object (including a nearly transparent object in this case), a conventionally-developed method such as a light cutting method or stereo vision is used. If it is used, most of the projected light rays are transmitted through the surface of the transparent object, and the light rays reflected on the transparent object surface are extremely small, so that the method cannot be applied. Accordingly, the present invention provides a method capable of accurately and non-contactly acquiring a shape of a transparent object which cannot be inspected by a conventional inspection method. In particular, it is an object of the present invention to be able to grasp the shape even when the transparent object has an irregular shape. In order to solve the above-mentioned problems, a method for inspecting a transparent object according to the present invention comprises projecting a pattern light onto a transparent test object arranged on an opaque object, A first step of obtaining an imaging pattern monitored again through the test object after being projected onto the opaque object through the test object, and a portion indicating the existence area of the test object in the monitored imaging pattern. A second step of creating a large number of initial models of a three-dimensional shape serving as a bottom surface, and a third step of calculating, in each of the obtained models, a sample pattern that will be monitored when the pattern light is irradiated. And comparing each of the sample patterns with the imaging pattern and selecting some of the models corresponding to the sample patterns close to the imaging pattern. Step 4; a fifth step of combining the selected models; and the third and fourth steps are repeated again for the combined three-dimensional model,
A sixth step of acquiring the shape of the test object. When the shape of the transparent object is irregular and cannot be predicted, the shape cannot be obtained analytically from the amount of deformation of the imaging pattern. For this reason, in the above method, an initial model that is a large number of samples is generated in advance, and an imaging pattern that would be obtained when projecting pattern light in the initial model is calculated and obtained as a sample pattern. Then, some sample patterns close to the actually obtained imaging pattern are selected, and models corresponding to the sample patterns are synthesized to create a new model. A sample pattern is calculated for this new model, a sample pattern closer to the actual imaging pattern is selected, and a new model is synthesized.
Thus, the shape of the test object is predicted. Hereinafter, a method for inspecting a transparent object according to the present invention will be specifically described with reference to the drawings. FIG. 1 shows a first embodiment of the present invention. In FIG. 1, a pattern light 1 (in this case, parallel slit light) is applied to a transparent object 4 arranged on an opaque object 3 from a pattern light projector 2. Is projected. The projected pattern light 1 is refracted on the surface of the transparent object 4 and forms a deformed pattern on the opaque object 3. This deformation pattern is photographed by an imaging device such as a TV camera 5 and the deformation state of the pattern is taken into the image processing device 6. The imaging pattern monitored by the TV camera 5 is, as shown in FIG.
The image pickup pattern 8 in which the area where is present is deformed is displayed. The deformation pattern light on the opaque object 1 is T
When heading toward the V camera 3, it is refracted again by the surface of the transparent object 4. However, since the surface of the opaque object 1 has some diffuse reflection components, the position of the TV camera 3 is generally not particularly defined and observation is not possible. It is possible. When the shape of the transparent object 4 is irregular, the obtained object pattern 8
It is difficult to analyze the shape of. Therefore, in this embodiment, a sample pattern obtained by projecting pattern light onto various three-dimensional samples prepared in advance is used,
This is for estimating the shape of the transparent object 4. The method will be described below with reference to the flowchart shown in FIG. In step S0, an image pickup pattern obtained by projecting pattern light onto a transparent object 4 as a test object is input to an image processing device 6. In step S1,
The existence range of the transparent object 4 is determined from the imaging pattern 7.
This is to determine the existing position in the screen when the transparent object 4 is viewed from above. The image shown on the TV monitor 7 is analyzed, and first, a linear pattern of the peripheral portion without the transparent object is extracted. Then, a portion having a large displacement is extracted as the outer periphery of the transparent object 4. In step S2, an initial model is generated within the range where the transparent object 4 exists. Figure 4 shows the initial model
As shown in (a), the existence range is defined as a bottom surface, and a point 9 having a height H taken at a randomly determined position within the range is defined as a vertex and a cone formed by connecting the edges of the bottom surface. This is further converted into the height of each point in the transparent object area as shown in FIG. 4B, and smoothing is applied to the entire surface to obtain a smooth surface. The position of the vertex 9 is changed, and many such initial models are generated. Next, in step S3, an imaging pattern which would be obtained when pattern light is projected on these initial models is obtained by calculation. This calculation process includes the following three processes (A), (B) and (C). (A) In this process, where the slit light projected from the projector is projected on the opaque object 14 is calculated. This calculation procedure will be described with reference to FIG. For the model 10, the pattern light projector 11
Are arranged on the computer such that the three-dimensional arrangement is the same as the configuration shown in FIG. Next, many slit lights 12 projected from the pattern light projector 11
All are sampled at appropriate intervals, and the slit light 12 is set as a set of many light beams 13. This ray 13
Is refracted at the surface of the model 10 and projected to a location 15 on the opaque object 14 or directly to a location 15 on the opaque object 14 without passing through the model 10. The projected position 15 is calculated for all the light rays 13 and used as projection position data. (B) In this process, a position on the opaque object 14 at which the line of sight corresponding to each pixel of the imaging camera reaches is calculated. This calculation procedure will be described with reference to FIG. It is assumed that the imaging camera 16 is arranged on the computer such that the three-dimensional arrangement of the imaging camera 16 is the same as the configuration shown in FIG. The imaging camera 16 has a plurality of pixels 17, and a line of sight 18 corresponding to each of the pixels 17.
There is. This line of sight 18 is refracted at the surface of the model 10 and reaches a certain position 19 on the opaque object 14 or directly reaches a certain position 19 on the opaque object 14 without passing through the model 10. By collating the position 19 with the projection position data 15 (described in (C)), it can be determined whether or not the line of sight 18 captures the light beam 12 projected from the pattern light projector 11. (C) In this process, it is determined whether or not the position 15 where the light beam 12 is projected can be captured by the line of sight 18. This procedure will be described with reference to FIG. On the surface of the opaque object 14, the projection positions 15 of the light rays 13 are discretely distributed. On this opaque object 14, a certain line of sight 1
Assuming that the position 4A reaches the position 19A, there is a projection position 15 around the position 19A. Further, if another line of sight 14B reaches the position 19B, it is assumed that the line of sight 14A does not catch the light beam 12 because there is no projection position 15 around the position 19B. The above operations (B) and (C) are performed on all the pixels 17, and the pixels 17 corresponding to the line of sight 18 capturing the light beam 12 are made bright, and the others are made dark, so that the calculation is performed from the model 10. Imaging pattern can be obtained. Next, in S4, the actual imaging pattern and S3
Is evaluated for each slit light line for the imaging pattern of each model calculated in step (1), and one-hundredth of the initial model having a small error is selected. FIG. 6 shows a method for evaluating the imaging pattern. For each line of slit light on the opaque object 14,
The shift amount 18 between the line 16 of the actual imaging pattern and the imaging pattern 17 of the model is calculated. This value is calculated for all the lines of the pattern and the sum is taken as the evaluation value of the model. In S5, when the evaluation value of the model selected in S4 is smaller than a preset reference value, this model is set to the shape of the transparent object. However, in most cases, this criterion is not satisfied, so the model is deformed in S6. In S6, a number of new models are created by combining the plurality of models selected in S4. This creation method is shown in the plan view of FIG. Two models 20, 21 are selected from the plurality of models selected in S4, and then divided into four at the same position by randomly generated vertical and horizontal lines, one of which is randomly replaced, and a new one is created. Model 22. This is combined between a plurality of models to obtain a large number of new models. At this time, a step is generated at the joint, so that the model is smoothed by smoothing the height. In some models combined as described above, the shape of the surface of the object is slightly changed, and the model is deformed by smoothing processing. For this combination and many transformed models,
By performing S4 and selecting some models having good evaluations, better approximation can be performed. This S6, S
If the processing of S3 and S4 is performed under the condition of S5, that is, the evaluation value is smaller than the reference value, a model approximating the actual shape of the transparent object 4 can be obtained on the image processing apparatus. In addition,
In S5, if the number of times the steps from S3 to S6 are repeated exceeds a specified number, the processing can be terminated in order to shorten the calculation time. As described above, according to the present invention, even if the transparent object has an irregular shape, the shape can be grasped.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view showing an embodiment of an inspection apparatus using the transparent object inspection method of the present invention. FIG. 2 is a view showing an imaging pattern monitored by the apparatus. FIG. 4 is a flowchart showing the inspection process of the method for inspecting a transparent object according to the present invention; FIG. 4 is a perspective view showing an initial model created by the method; FIG. FIG. 7 is an explanatory view of a process of evaluating a model in the same method. FIG. 7 is a plan view illustrating a process of synthesizing a model in the same method. [Description of References] 1,12 pattern light 2,11 pattern light projector 3,14 opaque object 4 Transparent object 5 TV camera 6 Image processing device 7 TV monitor 8 Imaging pattern 10 Model 17 pixels

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-2-302879 (JP, A) JP-A-57-147004 (JP, A) JP-A-3-199945 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) G01B 11/00-11/30 G06T 1/00

Claims (1)

(57) Claims 1. A pattern light is projected onto a transparent test object arranged on an opaque object, and after being projected onto the opaque object through the test object, the pattern light is again projected. A first step of obtaining an imaging pattern monitored through the object to be inspected; and a second step of creating a number of initial models of a three-dimensional shape having a bottom surface indicating a region where the object to be inspected in the monitored imaging pattern. And, in each of the obtained models, a third step of calculating and creating a sample pattern that will be monitored when the pattern light is irradiated, and comparing each of the sample patterns with the imaging pattern, A fourth step of selecting some of the models corresponding to the sample patterns close to the imaging pattern; and a fourth step of combining the selected some models. Steps and the model for the synthesized three-dimensional shape, again the third,
A sixth step of repeating the fourth step to obtain the shape of the test object, and a sixth step of inspecting the transparent object.