CN105783782A - Surface curvature abrupt change optical contour measurement method - Google Patents

Abstract

The present invention discloses a surface curvature abrupt change optical contour measurement method. According to the method, an optical band image is obtained; mean filtering and binaryzation processing are performed on the optical band image; average gray calculation is performed on the binarized optical band image; an average gray algorithm is adopted to determine the special position of the curvature abrupt change of a step; in a 3D contour reconstruction process, corresponding recognition processing can be performed on a curvature abrupt change position, and the contour line of the curvature abrupt change position can be filtered out; and the contour of an object of which the surface is subjected to curvature abrupt change can be restored accurately.

Description

Optical profilometry method for surface curvature abrupt change

technical field

The invention belongs to the technical field of image processing, and in particular relates to an optical profile measurement method for sudden changes in surface curvature.

Background technique

With the development of manufacturing industries such as machinery, automobiles, and aerospace, and civil industries such as service, shoemaking, and toys, there are more and more needs to measure complex surfaces in the mold manufacturing industry. So far, optical three-dimensional profilometry technology has been developed for a long time, and there are many mature measurement methods. However, the measurement accuracy, automation, and self-adaptability of the existing 3D contour systems are generally low, especially for the measurement of complex structure contours, there are still many unsolved problems.

Three-dimensional measurement is an integral part of various intelligent autonomous systems in various application fields, such as manufacturing, inspection, document analysis, engineering design, criminal investigation scene trace analysis, automatic online inspection, quality control, robotics, medical diagnosis and military. part. With the advancement of modern detection technology, three-dimensional measurement technology has gradually become the focus of people's research, especially with the development of high and new technologies such as laser technology, computer technology and image processing technology, optical three-dimensional measurement technology has been widely used.

With the development of computer technology and optoelectronic technology, the non-contact rapid measurement technology of three-dimensional complex curved surface based on optical principle and computer image processing as the main method has also emerged as the times require. Reverse engineering refers to the collection of a large number of three-dimensional coordinate points from the real object, and the establishment of the geometric model of the object, and then the development of advanced technology for similar products. The reverse engineering of complex surfaces is also one of the difficulties of reverse engineering. It is based on Surface measurement planning, digital scanning and detection of the surface, and then surface reconstruction of the digital point cloud to generate a CAD model. The need to measure complex surfaces in manufacturing is increasing.

Due to its non-contact, high precision and high resolution, optical three-dimensional profile measurement has been widely used in CAD/CAE, reverse engineering, online inspection and quality assurance, multimedia technology, medical diagnosis, machine vision and other fields, and is recognized is the most promising method for 3D profile measurement.

For geometric objects with sudden changes in curvature, general three-dimensional measurement methods will fail. For example, in the line-structured laser method, when the line-shaped laser light knife is irradiated on the surface with a sudden change in curvature, affected by the sudden change in the surface, the laser band will become irregular without a large area, thus making the contour measurement fail.

Contents of the invention

The purpose of the present invention is to solve the above problems and provide an optical profile measurement method for sudden changes in surface curvature, which can accurately determine the position of sudden changes in the curvature of geometric objects and perform corresponding processing, so that the profile measurement will not be affected.

In order to solve the above technical problems, the technical solution of the present invention is: a method for measuring optical profilometry with abrupt changes in surface curvature, comprising the following steps:

S1: When the object under test is at position j, use computer software to send pulse modulation signals to modulate the laser, and the laser outputs a linear beam to illuminate the object under test; at the same time, use computer software to send a trigger signal to trigger the CCD image sensor to synchronously collect the object under test The light band image on the surface, and record the collected image as A ₁ , then turn off the laser, and the CCD camera collects the image at the same position again, and record it as A ₁₁ ;

S2: Process the images A ₁ and A ₁₁ obtained by locking imaging, and obtain a light band image I _j at this position with the background light removed;

S3: Binarize the light band image I _j obtained in the above S2;

S4: Calculate the average gray level of the light band image I _j after binarization, assuming that there are N pixels in the picture, and the gray value of the i-th pixel is N _i , then the light band image I _j The average grayscale is:

S5: Translate the object to be measured from position j along the guide rail to the position j+1, repeat steps S1 to S4, obtain the light band image I _j+1 continuous with the position of the light band image I, and calculate the light band image I Average gray level of _j+1

S6: Divide the average gray level of the light band image I _{j +1} by the average gray level of the light band image I j to obtain the ratio Make a judgment, if the ratio Then the light band image I _j+1 is a curvature mutation image, and this position is the curvature mutation position. At each position of the object to be measured, the computer software uses the three-dimensional surface contour reconstruction technology to perform simultaneous contour reconstruction. If the position is a curvature mutation position, then filter out the contour line of the position and return to S5; if the ratio Then there is no abrupt curvature change at this position, and return to S5 until the overall contour reconstruction of the object to be measured is completed.

Preferably, in step S3, the light band image is subjected to mean value filtering before binarization processing.

Preferably, the size of k in step S6 is related to the surface curvature of the object to be tested.

The beneficial effects of the present invention are: the optical profile measurement method for sudden changes in surface curvature provided by the present invention uses the average gray scale algorithm to judge the special position of sudden changes in step curvature, and can identify the positions of sudden changes in curvature during the process of three-dimensional contour reconstruction processing, and accurately restore the outline of the object with a sudden change in surface curvature.

Description of drawings

Fig. 1 is a flow chart of the optical profilometry method for sudden changes in surface curvature of the present invention;

Fig. 2 is the schematic diagram of the surface curvature abrupt change optical profilometry device of the present invention;

Fig. 3 is the schematic diagram of the measured object step of the present invention;

Fig. 4 is the grayscale image of the first step position of the present invention;

Fig. 5 is the gray scale image of step critical position of the present invention;

Fig. 6 is the grayscale image of the second step position of the present invention;

Fig. 7 is a step average gray scale change diagram of the measured object in the present invention;

Fig. 8 is an effect diagram of contour reconstruction of the steps of the measured object according to the present invention;

Explanation of reference signs: 1. Fixing frame; 2. CCD camera; 3. Line structure laser; 4. Displacement platform; 5. Object to be measured.

detailed description

The present invention will be further described below in conjunction with accompanying drawing and specific embodiment:

As shown in Fig. 2, the optical profile measuring device with sudden change in surface curvature of the present invention includes a fixed frame 1, two axisymmetric CCD cameras 2, three coplanar line-structured lasers 3, a displacement platform 4 and a computer. Two CCD cameras 2 are fixed to two adjacent pillars of the fixed frame 1 through a three-dimensional adjustment platform, and the intersection of the optical axes of the two CCD cameras is ensured at the center of the measurement area by adjusting the three-dimensional adjustment platform. The three line-structure lasers 3 are fixed on the other two pillars and the lower position of the fixed frame 1 through a two-dimensional adjustment platform, so that the angle between the three line-structure lasers 3 is 120° to ensure that each laser reaches the center of the measured object The axes are equidistant, so that the intensity of the laser light on the surface of the object is guaranteed to be the same.

Since the CCD camera and the line-structure laser are fixed on the fixed frame, it is necessary to realize the longitudinal scanning of the laser to the measured object to obtain a series of contour lines. If the CCD camera and the line-structure laser are moved to scan, then the stability and operability of the system Performance will drop and it will be difficult to control the scanning speed. In order to solve the above problems, this measurement system adopts the position of fixed CCD camera and line structure laser, and moves the position of the object to be measured relative to the laser to scan the object. In order to facilitate the control of the moving speed and distance of the object to be measured, the displacement platform 4 is placed On the guide rail below the middle part of the fixed frame 1 and ensure that the object to be measured 5 fixed on the displacement platform 4 is at the center point of the measurement area, the displacement platform 4 is driven by a stepping motor to move along the guide rail.

The computer is connected to a CCD camera to capture images, a stepper motor is connected to drive and control the movement of the displacement platform, and a line-structure laser is connected to control the light on or off of the line-structure laser.

The present invention also provides a method for measuring the optical profile of a sudden change in surface curvature based on the above device, the flow chart of which is shown in Fig. Form a laser light band of the cross-sectional profile of the test object on the surface of the test object, and then use the CCD camera to obtain the image of the light band, and transmit the acquired image to the computer to calculate the profile information of the test object, specifically including the following steps:

S1: When the object under test is at position j, use computer software to send pulse modulation signals to modulate the laser, and the laser outputs a linear beam to illuminate the object under test; at the same time, use computer software to send a trigger signal to trigger the CCD image sensor to synchronously collect the object under test The light band image on the surface, and record the collected image as A ₁ , then turn off the laser, and the CCD camera collects the image at the same position again, and record it as A ₁₁ ;

S2: Process the images A ₁ and A ₁₁ obtained by locking imaging, and obtain a light band image I _j at this position with the background light removed;

S3: Perform mean value filtering and binarization processing on the light band image I _j obtained in the above S2;

S4: Calculate the average gray level of the light band image I _j after binarization, assuming that there are N pixels in the picture, and the gray value of the i-th pixel is N _i , then the light band image I _j The average grayscale is:

S5: Translate the object to be measured from position j along the guide rail to the position j+1, repeat steps S1 to S4, obtain the light band image I _j+1 continuous with the position of the light band image I, and calculate the light band image I Average gray level of _j+1

S6: Divide the average gray level of the light band image I _{j +1} by the average gray level of the light band image I j to obtain the ratio Make a judgment, if the ratio Then the light band image I _j+1 is a curvature mutation image, and this position is the curvature mutation position. At each position of the object to be measured, the computer software uses the three-dimensional surface contour reconstruction technology to perform simultaneous contour reconstruction. If the position is a curvature mutation position, then filter out the contour line of the position and return to S5; if the ratio Then there is no abrupt curvature change at this position, and return to S5 until the overall contour reconstruction of the object to be measured is completed.

The surface curvature abrupt change optical profile measurement device of the present invention obtains the light band image of the complex surface profile through the laser locking imaging technology, and eliminates the influence of ambient light on the light band image. However, due to the uneven profile of the measured object itself, the surface For reasons such as sharp and uneven changes in reflectivity, the acquired light band image will have defects, or light band edge burrs, etc., which seriously affect the quality of the light band image. Therefore, in general image processing, we carry out the Some preprocessing is done, mainly image mean filtering algorithm and image binarization.

While binarizing the light strip image, we simultaneously use the average gray level algorithm to distinguish the position of the step curvature mutation from the image. Suppose there are N pixels in a processed grayscale image collected by the computer, and the grayscale value of the i-th pixel is N _i , then the average grayscale of this image is: When the position collected by the computer reaches the position where the curvature of the object changes suddenly, the displayed average gray level data will be significantly different from other non-mutated positions, so that these special positions can be easily judged.

The object to be tested in this embodiment is described by taking steps as an example. As shown in Figure 3, the object to be tested has four steps, and the two steps from bottom to top are respectively the first step and the second step. A vertical plane transition is used, which is the critical position of the step.

Figures 4 to 6 show the three images collected by the computer and preprocessed, all of which are grayscale images at this time. They are the image obtained by scanning the laser to the first step position of the measured object, the image obtained by scanning to the critical position of the step (this position is the position where the curvature of the object changes suddenly), and the image obtained by scanning to the second step.

After repeated experiments and tests, we found that the average gray level of the images measured at the first step position and the second step position fluctuates before 0.650-0.750, while for the critical position of the step with a sudden curvature change, the average gray level at this position is between 3.50 and 0.750. Floating between 3.90. It can be seen that the average gray level of the critical position of the step is much larger than the average gray level of the first step position and the second step position, and the former is five to six times that of the latter, so k=5 of the step of the object to be tested in this embodiment .

Because the measurement system undergoes a continuous scanning process, the images collected by the computer also have certain rules. First, a part of the pictures of the position of the first step is collected. After the first step is scanned by the laser, one or two images of the critical position of the step are collected. Picture, when we came to the position of the second step, a large number of pictures of the second step were collected. The change of the gray value during this process is shown in Figure 7. It can be intuitively found that when the object under test is located at position coordinate 6, The laser scans exactly where the curvature changes.

The specific process of measuring the step with the above-mentioned surface curvature abrupt change optical profilometry method is as follows:

The steps are fixed on the displacement platform at position 1, and the laser is modulated by sending a pulse modulation signal using computer software, and the laser outputs a linear beam to illuminate the object to be measured; at the same time, the computer software is used to send a trigger signal to trigger the CCD image sensor to synchronously collect the object to be tested The light band image on the surface of the object, and record the collected image as A ₁ , then turn off the laser, and the CCD camera collects the image at the same position again, which is recorded as A ₁₁ ; process the images A ₁ and A ₁₁ obtained by locking imaging, Obtain a light strip image I ₁ with background light removed at this position; perform mean filtering and binarization on the light strip image I ₁ to calculate the average gray level of the light strip image I ₁

The stepper motor drives and controls the displacement platform to move along the guide rail at a distance of 40mm to reach position 2, repeat the above steps to obtain the light band image I ₂ , and calculate the average gray level of the light band image I ₂ but The k value of 5 is less than the step, and there is no abrupt curvature change at position 2.

The stepper motor drives and controls the displacement platform to move 40mm along the guide rail to reach position 3, repeat the above steps to obtain the light band image I ₃ , and calculate the average gray level of the light band image I ₃ is 0.698; then The k value of 5 is smaller than that of the step, and there is no abrupt curvature change at position 3.

Continue to repeat the above steps to measure

When the step moves to position 6, the average gray level of its light band image I ₆ is measured is 3.792, which is the same as the average gray level of the light band image I ₅ ratio of Then the position 6 is the abrupt change position of the curvature, and the synchronous contour reconstruction filters out the contour line of this position.

The above steps are repeated until the overall contour reconstruction of the object under test is completed.

As shown in Figure 8, it is the outline reconstruction effect diagram of the steps from position 1 to position 11, in which the contour line at position 6 with sudden curvature change is filtered out, so a gap will be left, but because the width of the gap is extremely small, it can be ignored Excluding.

The surface curvature abrupt change optical profile measurement method of the present invention needs to process the image after obtaining the grayscale image of the laser light band that satisfies the target surface data of the measured object, and the present invention adopts thinning processing and mean value filtering to eliminate noise, and then binarize the image, and the present invention uses the average gray level algorithm to determine the position of the sudden curvature that is not conducive to contour reconstruction. After obtaining the contour data, the present invention adopts the shortest diagonal contour splicing to reconstruct the three-dimensional surface contour of the object with abrupt curvature, and finally displays the three-dimensional contour by means of VTK (visualization toolkit).

Those skilled in the art will appreciate that the embodiments described here are to help readers understand the principles of the present invention, and it should be understood that the protection scope of the present invention is not limited to such specific statements and embodiments. Those skilled in the art can make various other specific modifications and combinations based on the technical revelations disclosed in the present invention without departing from the essence of the present invention, and these modifications and combinations are still within the protection scope of the present invention.

Claims (3)

1. A surface curvature abrupt change optical profilometry method, is characterized in that, comprises the following steps: S1: When the object under test is at position j, use computer software to send pulse modulation signals to modulate the laser, and the laser outputs a linear beam to illuminate the object under test; at the same time, use computer software to send a trigger signal to trigger the CCD image sensor to synchronously collect the object under test The light band image on the surface, and record the collected image as A ₁ , then turn off the laser, and the CCD camera collects the image at the same position again, and record it as A ₁₁ ; S2: Process the images A ₁ and A ₁₁ obtained by locking imaging, and obtain a light band image I _j at this position with the background light removed; S3: Binarize the light band image I _j obtained in the above S2; S4: Calculate the average gray level of the light band image I _j after binarization, assuming that there are N pixels in the picture, and the gray value of the i-th pixel is N _i , then the light band image I _j The average grayscale is: S5: Translate the object to be measured from position j along the guide rail to the position j+1, repeat steps S1 to S4, obtain the light band image I _j+1 continuous with the position of the light band image I, and calculate the light band image I The average gray level Nave j+ ₁ of _j+1 ; S6: Divide the average gray level of the light band image I _{j +1} by the average gray level of the light band image I j to obtain the ratio Make a judgment, if the ratio Then the light band image I _j+1 is a curvature mutation image, and this position is the curvature mutation position. At each position of the object to be measured, the computer software uses the three-dimensional surface contour reconstruction technology to perform simultaneous contour reconstruction. If the position is a curvature mutation position, then filter out the contour line of the position and return to S5; if the ratio Then there is no abrupt curvature change at this position, and return to S5 until the overall contour reconstruction of the object to be measured is completed. 2. The method for measuring optical profilometry with sudden changes in surface curvature according to claim 1, characterized in that: in the step S3, the light band image is subjected to mean value filtering before binarization processing. 3. The method for measuring optical profilometry with sudden changes in surface curvature according to claim 1, characterized in that: the size of k in the step S6 is related to the surface curvature of the object to be measured.