Precision Research Of Precise Screen Printing Equipment Based On Machine Vision

With the development of the electronic manufacturing technology and theminiaturization of the components and denser packaging of components, the demands ofpositioning precision for SMT (Surface Mount Technology) equipments have become moreand more important. As the first step of SMT production process, the printing quality directlyaffect the subsequent processes, even the quality of the products. How to improve theprecision of the screen printer equipment has become an urgent problem. The precision of theparallel platform and the vision system are the guarantee of a higher printing accuracy. In thestudy, the precision of the parallel platform and vision alignment system are analysed andtested with the auto-vision screen printer, and an effective solution was proposed to improvethe precision of the screen printer.Firstly, the structure and function of screen printer system were introduced, the model ofthe parallel platform was provided, and the performance was analysed. Based on the analysisthe error model was established with differential coefficient. Then, the relation between theend effector pose error and the clearance was analysed, and a simplified model with clearanceof branched chain was given to get a general expression between the parallel platformposition and orientation errors by equivalention. Based on the analysis of precision andsensitivity, the precision synthesis was analysed by the Monte-Carlo method whichestablished theory basis for the parallel platform’s design.Secondly, the vision alignment system error was researched. In this paper several factorswere analysed with the impact of vision system, the light path and camera motion wereanalysed. According to the structure and function of the vision alignment system, the systemand random errors with image measurement was analysed and researched.Finally, according to the result of error analysis and practical test, a kind of clearanceeliminating and motion error compensation device of parallel platform structure was designed.And an image testing software was developed to calibrate the image measurement errors.The experiment results demonstrated that the precision and stability of the screen printerhas been improved obviously with the proposed solution. The results have improved thequality of the products and was very valueable in practical production.