Study On The Key Techniques For Autobody Parts Measurement With Laser Triangulation

Body is the largest part of auto assemble, which is composed of nearly hundred parts. The manufacture qualities of the parts are vital to the whole body. Measurement should be the first thing for quality control. 100-percents-on line measurement is important for improving quality and reducing the cost.The contact measurement is widely used at present. CMM (Three-Coordinate Measuring Machines) and the traditional testing fixture are the mail mean .The testing tools convenience to give the relation and feedback of the space element, but are hard to fix and can't provide enough dates due to the inspection speed, also the Pliancy is bad. This method is suit for off-line Sampling inspection. Though CMM is high in precision, the speed is slow; probe has contact stress and must take radius compensation. Now the programmable gantry machine is used widely, but the probe move uninterrupted, for one measured point it is hard to measure several parameters at the same time. With the development of machine vision giving us a solution, which is non-contact, high precision and automatic used in monitoring and measuring industry productions. It can make 100-percents-on-line inspection true. Laser Triangulation measurement is widely used in vision inspection.The main works in the paper include:Give the theoretic modal of the auto-body parts laser multi-points measure system, the hardware and the function. Then make a deep research in the key technology in measurement. At last analyze some factors related to precision and give the method to decrease the error.(1) Introduce the present state of auto parts inspection, compared the measure means. Emphases the advantage of computer vision and application status quo.We use laser triangulation measurement in the paper, then introduce the principle and the key technique of it.(2) The measure system must have perfect functions to make the automatic true, from carrying the parts, locating to measuring, different units should cooperate smoothly. For the large parts they need hundreds of vision sensors which must transmit data in order. Using high- credible CAN (Control Area Network) as the communicate tool to connect the multi-sensors, control system and the master-computer. So first give the theoretic modal of system which based on CAN. Here introduce the working principle of sensor unit; give the drive Circuits of CAN, the interface between master PC and CAN. For controlling the multi-sensor we use design the switch circuit. At last give the function modal of the system and programmed the user interface.(3) In camera Calibration, A digital modal are given considered radial distortion. A series of space point were constructed using the draughtboard. The corners are extracted with SUNSAN operator during image processing. But there is a huge error compared with the coordination of space point after putting the image corner coordination into the camera modal. Here present an iterative arithmetic to correct all the parameters until the error within permission. Then use tri-interpolating to calculate the error of the unknown space point. In calculate the triangulation-structure parameter; we use the least-square principle to fitting the coefficient of the function between image coordinate and the height.(4) In the process of image processing, we try to use subpixel technique to improve the resolving power. We take an experiment-the detection of the hole on the sheet metal parts of auto body on spatial moment. For inspecting, a method based on non-contacted and digital image processing techniques is presented. Log algorithm is used first to calculate the edge image at pixel accuracy, and then spatial moment algorithm is used to reach at subpixel accuracy. Also the method to calculate other parameters is presented, such as diameter, location and roundness. Some factors impact measuring accuracy is analyzed finally. Results of experiment show that the method has the advantages of more accuracy and stability.(5) At last some factors affect the system accuracy are presented and the method of decreasing and correcting error are suggested. After taking a experimentation in the parts we give the accuracy of the system.The study conduces to the on-line inspection of auto parts and may give impulse to the real time supervisory control.