Proprioceptive Actuator

An actuator that senses and controls joint force from motor current alone, with no dedicated force sensor.

This is an actuator design philosophy proposed and systematically laid out by Sangbae Kim's group at MIT's Biomimetic Robotics Lab for the MIT Cheetah (Wensing et al., IEEE T-RO 2017). The approach pairs a large-diameter, high-torque motor with a single-stage, low-ratio planetary reducer, keeping transmission friction low and reflected inertia (the motor rotor's inertia as seen from the joint's output) low, so the joint can be backdriven by external force. This means motor current can fairly accurately reflect the force on the joint, enabling high-bandwidth force control without any extra force sensor, and letting the leg absorb landing impacts compliantly. Today's “quasi-direct-drive” joint modules, used across quadruped robots and many humanoid robots, trace back to this same idea.

ExampleThe joints of MIT's Mini Cheetah use a roughly 6:1 single-stage planetary reducer, estimating foot contact force from current alone to perform moves like backflips.

Also called

Proprioceptive Actuation

Related

Quasi-Direct Drive · Backdrivability · Reflected Inertia · MIT Mini Cheetah Actuator · Torque Control · Sensorless Force Estimation

Sources

Proprioceptive Actuator Design in the MIT Cheetah (Wensing et al., IEEE T-RO 2017)