Robotic assembly of flexible sheet metal parts

Two control problems encountered in robotic sheet metal assembly are addressed in this paper. They are the control of vibration when handling the sheet metal parts and the control of the contact state between the parts during assembly. For the first problem, a learning extremum controller (LEC) is proposed. Using a strain gauge based sensing device mounted on the robot gripper for vibration feedback, the orientation of the part relative to its path is controlled to reduce vibration. For the second problem, a sensor fusion system developed previously is used to provide feedback about the contact condition between two sheet metal parts. An integral contact controller (ICC) is used to correct any angular error between the parts to ensure full contact along the joint for subsequent welding. Experimental results confirmed the effectiveness of both control algorithms. The LEC reduced the vibration amplitude by up to 45%. The ICC reduced the angular error from 0.5° to 0.025° in 1.7 seconds