Partial force control of constrained floating-base robots

Legged robots are typically in rigid contact with the environment at multiple locations, which add a degree of complexity to their control. We present a method to control the motion and a subset of the contact forces of a floating-base robot. We derive a new formulation of the lexicographic optimization problem typically arising in multi-task motion/force control frameworks. The structure of the constraints of the problem (i. e. the dynamics of the robot) allows us to find a sparse analytical solution. This leads to an equivalent optimization with reduced computational complexity, comparable to inverse-dynamics based approaches. At the same time, our method preserves the flexibility of optimization based control frameworks. Simulations were carried out to achieve different multi-contact behaviors on a 23-degree-of-freedom humanoid robot, validating the presented approach. A comparison with another state-of-the-art control technique with similar computational complexity shows the benefits of our controller, which can eliminate force/torque discontinuities.

Authors

• Andrea Del Prete
• Nicolas Mansard
• Francesco Nori
• Giorgio Metta
• Lorenzo Natale

Keywords

• Foot
• Robots
• Force
• Force control
• Optimization
• Joints
• Matrix decomposition
• Partial Control
• Floating-base Robots
• Computational Complexity
• Contact Force
• Lexicographic
• Humanoid Robot
• Sparse Solution
• Robot Dynamics
• Legged Robots
• Rigid Contact
• System Dynamics
• Computation Time
• Optimal Control
• Diagonal Matrix
• Motor Control
• Free Parameters
• Control Problem
• Direct Control
• Quadratic Programming
• Joint Acceleration
• Constraint Forces
• Mass Matrix
• Left Foot
• Normal Force
• Joint Torque
• Acceleration Level
• Hierarchy Of Controls
• Tangential Force
• Arbitrary Vector