Machine Vision's Research And Application In The SMM Of SMT

The research platform in this paper is QSP-2 surface Mounting Machine in SMT Laboratory of the Electrical and Mechanical Engineering College in Soochow University. Based on the original equipment, upgrading the hardware and software of the controlling system, the machine vision system is designed to solve these problems: 1) PCB positioning; 2) make certain the coordinate location of the Up Looking Camera; 3) chip component mounting compensation.When the PCB is fixed, the Down Looking Camera will be carried by the mount head to the top of a reference point to obtain its image. This image is operated by linear stretch, median filtering, the maximum variance threshold, gray value of the closed, gradually narrow the search area and shape heart methods, then the reference point's center coordinate in the image is transformed into the coordinate in the machine coordinate system. After getting the coordinates of another reference point by the same way, the deviation between PCB board and the standard position will be knew.Because the system was newly built, the Up Looking Camera was re-installed, so making certain the coordinate location of the Up Looking Camera is very important. For the center of the image corresponding to the center of the Up Looking Camera, moving the mount head, getting some images of chip component, then transform the different coordinate between the component center and the image center into the coordinate in the machine coordinate system. So the center coordinate of the Up Looking Camera in the machine coordinate system would be got hold of.When a component is sucked by the nozzle, it may occur that the location the nozzle sucked is not the center of the component or the component is deflected, if the component is placed directly, it makes error mount. So getting the image of the component, when it moves to the target location, then the image will be operated by method as mentioned and the pixel division method to find the feature points, using least squares fitting them into a straight line. The deflected angle can be obtained from the slope of the line. The method used to find the coordinate of the reference point in the machine coordinate system also can be used to detect the deviation between the nozzle and the center of component. Then servo control system compensate for the two kinds of deviation. Experiments show that the deviation can be accurately corrected and compensated by the method of the SMM's vision system.