Research On Key Techniques Of Integration And Information Fusion Between Stereo Vision And CMM

Measuring a free curve or surface is an important component in the reverse engineering. Many researchers and scholars have fixed their eyes upon it. Computer stereo vision and coordinate measuring machine(CMM) belong to two kind of measuring equipment respectively. They have their respective merits and drawbacks. As a representative of non-touching measuring equipment, computer stereo vision has many merits, such as fast measuring speed, agility, broad sampling scope and convenience of extracting the boundary contours and characters. However, the drawback is its lower measuring precision. As a touching equipment, CMM has many advantages such as higher measuring precision, strong adaptability and robusticity. However, being a point-by-point touching measuring equipment, its obtaining the three dimensional measuring data of prototype is directed by the man-made measuring rules. It is much lower efficiency, and is excessively depended on the experience of manipulator to digitize the product. When there is no digital geometric prototype of product, it is difficult to properly distribute the measuring points.An integrated measuring equipment is suggested which is composed of seam-laser stereo vision equipment and CMM. It is a promising measuring equipment due to its high efficiency, high precision and high intelligentizing. The efficiency and the precision will become much higher if we can fuse the information obtained by these two different types of equipments.This paper will devote to investigate some key techniques of information fusion between the seam-laser stereo vision equipment and CMM. The contents include the following:1) Active contour models. Active contour models (or snake models) provide a method of obtaining the curve contour in the image produced by seam-laser stereo vision. The measuring data are dense, unorderly, and there is no topology relationship between them. They can not be applied to erect CAD models directly. Active contour models establish a topology relationship among these measuring data.2) B-spline approaching. The solution to active contour models is traditionally through the difference method, which includes large amount of curve data. It is not convenient to save them and to manipulate in the following procedure. Approaching the curve by B-spline will largely cut down the amount of curve data to be stored. It also makes the curve smoother and is easier to manipulate in the following procedures.3) Deformation of B-spline curve. The Physical model based deformation of B-spline curve keeps the contour character of the whole curve well. It will not produce local bump like the local curve deformation to hurt the contour character of the whole curve. The deformation is just like a crooked stick to produce a deformation under the external forces in mechanics, or like a smooth error curve fitted by given conditions adding up to original curve in mathematics. This paper will apply this deformation technique of B-spline curve to realize the information fusion between the seam-laser stereo vision equipment and CMM, in order to revise the curve measured by seam-laser stereo vision through the accurate data measured by CMM. This will increase the measuring precision measured by seam-laser stereo vision, and cut down the amount of data measured by CMM, so the efficiency and the precision will be promoted.4) Calibration of camera. The calibration of camera erects a corresponding relationship between the space points and the points in the camera images. It is a very important step to realize stereo vision. The tip center of the CMM touch probe is regarded as the space points to calibrate the camera, which set up a relationship of coordinate systems between two measuring equipments, and the two coordinate systems are unified into unitary CMM coordinate systems.5) Compensating of tip radius of CMM. Compensating of tip radius is a key problem in CMM. It has a great influence to its measuring accuracy. According to the contour curves which have been figured out,the normals of touching points can be computed, and the postions of touching points also can be decided. Hence, the proplem of compensating of tip radius of CMMM is solved, and at the same time the compensating of tip radius in a plane is also realized.