Mobile manipulation: Encoding motion planning options using task motion multigraphs

This paper introduces the concept of a task motion multigraph, a data structure that can be used to reveal a difficulty specific to mobile manipulation: the possibility of planning in different state spaces in order to achieve the same goal. The different options reflect the mobile manipulator's ability to use different hardware components to perform a required task. For instance, a humanoid robot can open a door with its left arm or with its right arm. Thus, motion planning can be performed in the left arm's state space or in the right arm's state space. Given the specification of a task, it is shown how to encode the available motion planning options in a task motion multigraph. An algorithm that computes sequences of motion plans for mobile manipulators using the newly introduced notion is presented and evaluated. The algorithm makes use of information from the task motion multigraph to prioritize the spaces for which motion plans are computed. Experimental results show that reduced planning times can be obtained when considering the available planning options.