Exploiting affordance symmetries for task reproduction planning

Many tool use tasks exhibit symmetries, such as the fact that a carrot can be cut anywhere along the blade of a knife, or that a nail can be struck from many directions by a hammer. This paper uses a previously proposed concept of affordance symmetries and extends it to enable such freedoms to be captured for robot programming by demonstration (RPbD). A reproduction planner is proposed which leverages these concepts by reducing the planning space to one where robot redundancy and symmetries are the only redundancies. Naturally, this improves planning time, but also allows the robots to properly exploit task redundancies to remain within the kinematic limitations of the robot. To illustrate the performance of the algorithm a simple example of teaching the robot to pour from one cup to another is used. The robot was able to perform the task successfully because it exploited task symmetries.