The Research On Vision Guided CMM Measuring Path Planning For Free Form Surface

Due to the current fluid mechanics and aerodynamics and aesthetic needs in the aerospace, shipbuilding, automobile and household appliances manufacturing industry of many products are free form surface modeling. The main tool for measurement and inspection of free form surfaces is three coordinate measuring machines (Coordinate Measuring Machine, CMM). General to the free surface is measured with CMM which need measurement planning. The measurement planning, for which CAD model is known, can carry on planning according to the characteristics of surface curvature. For the CAD model is unknown, the change of curvature surface are unable to obtain, therefore cannot make the measurement planning. This paper combines the advantages of visual measurement and CMM measurement, and put forward the main unknown CAD model objects to the measurement of vision guided CMM measuring path planning method for free form surface.The vision guided CMM measurement path planning for free form surface system is studied:the main research contents include the following aspects:(1) Introduce the principle of contact measurement and non-contact measurement, analysis the advantages and disadvantages of each. Combined with the three coordinate measuring machines existing in the laboratory, we proposed vision guided CMM measurement planning method for free form surface, draw the structure of the system, the measurement process system is given.(2) The parameters of vision guided CMM measurement calibration, including camera calibration and visual sensor structural parameters calibration, using the homogeneous coordinate conversion method to converts the vision measurement result into the CMM coordinate system. Put forward the integration of calibration algorithm, the parameters of the system are calibrated and analysis the calibration precision of the error. (3) The sub-pixel extraction method which is based on two times interpolation is used to extract the light stripe center, the three point sliding smoothing method is used to smooth the center of light stripe. Put forward an optimized method of sampling of free curve, which is slope difference adaptive method based on the curve, the distribution of sampling sites varied with the change of curvature. Analysis the error of the measuring system is analyzed.(4) Proposed the vision guided CMM measurement path planning method, through experiments we get the point cloud data with high precision which is distributed with the curvature of the free form surface, the experiment proved the feasibility of the system.