Force balancing of variable payload by active force-balanced reconfiguration of the mechanism

When dynamically balanced mechanisms and robots are used for pick and place motion, the payload influences the dynamic balance. The payload can be a cause of serious vibrations which for instance can reduce the accuracy of the mechanism considerably. In such a case reconfiguration of the mechanism during pick and place motion can help correct the dynamic balance. Due to rapid motion and short cycle times however, the reconfiguration has to be done rapidly and can be a cause of serious vibrations in itself. To eliminate these vibrations, the reconfiguration should preferably be done in a dynamically balanced way. Since moment balancing can conveniently be done actively in any situation, this article focusses on force-balanced reconfiguration of mechanisms to force balance variable payload. Three fundamental approaches to force-balanced reconfiguration were obtained: (1) reconfiguration by relocating the balancing mass, (2) reconfiguration by relocating the center-of-rotation of the link with balancing mass and (3) reconfiguration by changing the value of the balancing mass. It is shown that under certain circumstances a mechanism with payload can be force balanced by force-balanced reconfiguration. In addition, all approaches can be applied to either obtain partial force-balance of the mechanism with payload in a perfectly force-balanced way, or to obtain perfect force balance of the mechanism with payload in a partially force-balanced way, i.e. for which the vibrations during reconfiguration are reduced.