Series Clutched Actuation for Collision Tolerant High-Speed Robots

Collisions at high speed can severely damage robots with non-backdrivable drivetrains. Adding an overload clutch in series can improve the robot's collision tolerance without compromising its high dynamic performance. This paper aims at determining the speed above which overload clutches are required in a 2-link manipulator arm. Furthermore, the optimal clutch topology as function of the impact velocity is investigated. Thirdly, it is evaluated if adding clutches can lower the impact force on the arm. Finally, the maximum speed is identified below which impact-aware robot control is possible. The latter requires that none of the clutches decouple during an intentional collision with the environment. These answers are obtained through collision simulations and experiments with a custom build two-link arm. It was found that adding a clutch reduces the torque experienced by the drivetrain by an order of magnitude and below the limit momentary peak torque of the strain wave gears that are used. Adding a clutch to the elbow joint of the two-link arm was effective in protecting the shoulder as well if the impact occurred at the tool center point. With respect to a rigid elbow joint, the clutched elbow joint reduced the collision force at the tool by only 8%. To demonstrate that the arm is impact-aware, a box of 8 kg is approached, impacted and pushed at a 1 m/s without decoupling a clutch, nor damaging the robot's hardware.