Task primitives for the discrete event modeling and control of 6-DOF assembly tasks

A novel approach to the modeling and control of six degree-of-freedom (DOF) assembly tasks using polygonal pacts is presented. The assembly process is modeled as a discrete event system. Three key features of the assembly process are shown to be essential for a comprehensive understanding and effective control of the assembly task. It is also shown that discrete event modeling highlights these key aspects of the assembly process. Next the assembly process is broken down into its task primitives, or fundamental states of contact. It is shown that with only two primitives, the entire assembly process can be represented. These two task primitives are a surface-vertex contact and an edge-edge contact. The significance of this development is demonstrated. Petri nets are then used to give the discrete event model its necessary mathematical description for robotic control applications. The control methodology, again based on the two primitives, establishes a powerful framework which is robust and flexible in the control of assembly. Finally, simple experiments are discussed in which a successful 6-DOF assembly was completed