Learning Task Execution Hierarchies for Redundant Robots

Abstract: Modern robotic systems, such as mobile manipulators, humanoids, and aerial robots with arms, often possess high redundancy, enabling them to perform multiple tasks simultaneously. Managing this redundancy is key to achieving reliable and flexible behavior. A widely used approach is the Stack of Tasks (SoT), which organizes control objectives by priority within a unified framework. However, traditional SoTs are manually designed by experts, limiting their adaptability and accessibility. This paper introduces a novel framework that automatically learns both the hierarchy and parameters of a SoT from user-defined objectives. By combining Reinforcement Learning and Genetic Programming, the system discovers task priorities and control strategies without manual intervention. A cost function based on intuitive metrics such as precision, safety, and execution time guides the learning process. We validate our method through simulations and experiments on the mobile-YuMi platform, a dual-arm mobile manipulator with high redundancy. Results show that the learned SoTs enable the robot to dynamically adapt to changing environments and inputs, balancing competing objectives while maintaining robust task execution. This approach provides a general and user-friendly solution for redundancy management in complex robots, advancing human-centered robot programming and reducing the need for expert design.