
We describe an optimization-based framework to perform complex locomotion skills for robots with legs and wheels. The generation of complex motions over a long-time horizon often requires offline computation due to current computing constraints and is mostly accomplished through trajectory optimization (TO). In contrast, model predictive control (MPC) focuses on the online computation of trajectories, robust even in the presence of uncertainty, albeit mostly over shorter time horizons and is prone to generating nonoptimal solutions over the horizon of the task’s goals. Our article’s contributions overcome this trade-off by combining offline motion libraries and online MPC, uniting a complex, long-time horizon plan with reactive, short-time horizon solutions. We start from offline trajectories that can be, for example, generated by TO or sampling-based methods. Also, multiple offline trajectories can be composed out of a motion library into a single maneuver. We then use these offline trajectories as the cost for the online MPC, allowing us to smoothly blend between multiple composed motions even in the presence of discontinuous transitions. The MPC optimizes from the measured state, resulting in feedback control, which robustifies the task’s execution by reacting to disturbances and looking ahead at the offline trajectory. With our contribution, motion designers can choose their favorite method to iterate over behavior designs offline without tuning robot experiments, enabling them to author new behaviors rapidly. Our experiments demonstrate complex and dynamic motions on our traditional quadrupedal robot ANYmal and its roller-walking version. Moreover, the article’s findings contribute to evaluating five planning algorithms.
Artificial intelligence, Biomechanics of Bipedal Locomotion in Robots and Animals, model predictive control, Robot, Astronomy, Biomedical Engineering, Reinforcement Learning Algorithms, Trajectory, Geometry, Control (management), FOS: Medical engineering, Sampling-Based Motion Planning Algorithms, Probabilistic Roadmaps, Time horizon, Systems engineering, Task (project management), Engineering, Artificial Intelligence, Online algorithm, Control theory (sociology), FOS: Mathematics, Control of Locomotion, Online model, Model predictive control, trajectory optimization, Real-Time Planning, robotics, Motion (physics), Physics, wheeled and legged locomotion, Horizon, Mathematical optimization, Statistics, robotics; wheeled and legged locomotion; model predictive control; offline motion library; trajectory optimization, Reinforcement Learning, Computer science, Optimal Motion Planning, Algorithm, Operating system, offline motion library, Trajectory optimization, Physical Sciences, Computer Science, Computation, Online and offline, Computer Vision and Pattern Recognition, Mathematics
Artificial intelligence, Biomechanics of Bipedal Locomotion in Robots and Animals, model predictive control, Robot, Astronomy, Biomedical Engineering, Reinforcement Learning Algorithms, Trajectory, Geometry, Control (management), FOS: Medical engineering, Sampling-Based Motion Planning Algorithms, Probabilistic Roadmaps, Time horizon, Systems engineering, Task (project management), Engineering, Artificial Intelligence, Online algorithm, Control theory (sociology), FOS: Mathematics, Control of Locomotion, Online model, Model predictive control, trajectory optimization, Real-Time Planning, robotics, Motion (physics), Physics, wheeled and legged locomotion, Horizon, Mathematical optimization, Statistics, robotics; wheeled and legged locomotion; model predictive control; offline motion library; trajectory optimization, Reinforcement Learning, Computer science, Optimal Motion Planning, Algorithm, Operating system, offline motion library, Trajectory optimization, Physical Sciences, Computer Science, Computation, Online and offline, Computer Vision and Pattern Recognition, Mathematics
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