Robot Dynamics Constraint For Inverse Kinematics

Inverse Kinematics is a fundamental tool in Cartesian/Operational Space control. Recent approaches make use of Quadratic Programming Optimization to obtain desired joint velocities or accelerations from Cartesian references. QP based IK also permits to specify constraints to affect the solution. Constraints are fundamental and necessary when working with real robotic hardware since they prevent possible damages: joint limits, self collision avoidance and joint velocity limits are examples of such constraints. In this work we present a constraint to take into account joint torque limits based on the robot dynamics and force/torque sensor measurements. Despite the robot dynamics can be naturally expressed at acceleration level, our main goal is to specify this constraint in a resolved motion rate control IK. For this reason we formulate it also at the velocity level to be used in any IK QP based scheme. Hence, this formulation allows to generate dynamically feasible motions of the robot even in simple IK velocity based schemes. We apply this constraint to our humanoid robot COMAN while performing a Cartesian task which requires high torques in some joints. The constraint is developed inside the OpenSoT library.