A novel XY-Theta alignment stage for screen printing and its accuracy analysis

A novel Three-degrees-of-freedom (3-DOF) planar parallel alignment stage is developed for precision positioning of screen printing in industry. With three short PRP chains for driving and four rollers for supporting the movable platform, the stage is actually a 3-PRP planar parallel robot, which is not only ideal for precision positioning solution for wafers and printed circuit boards in all sizes, but also can be reformed to support a large screen and stencil easily. In this paper, an XY-Theta alignment stage, as well as its direct and inverse kinematic are presented firstly. Considering many performance indices used in the past do not work perfectly when applied to parallel robots with translational and rotational degrees of freedom, a simple but useful method is presented to analyze the maximum position and orientation errors subjected to input errors and structure parameter errors. Then an experiential input method is proposed to improve the input accuracy. And comparison experiments with a vision-based measuring device between the experiential input method and the normal input are conducted, which indicate the former one could lead to a better positioning accuracy.