Proprioceptive Actuator Design in the MIT Cheetah: Impact Mitigation and High-Bandwidth Physical Interaction for Dynamic Legged Robots

By Patrick M. Wensing, Albert Wang, Sangok Seok, D. Otten, J. Lang, Sangbae Kim. IEEE Transactions on robotics, 2017

424 citations recorded by the source corpus.

Designing an actuator system for highly dynamic legged robots has been one of the grand challenges in robotics research. Conventional actuators for manufacturing applications have difficulty satisfying design requirements for high-speed locomotion, such as the need for high torque density and the ability to manage dynamic physical interactions. To address this challenge, this paper suggests a proprioceptive actuation paradigm that enables highly dynamic performance in legged machines. Proprioceptive actuation uses collocated force control at the joints to effectively control contact interactions at the feet under dynamic conditions. Modal analysis of a reduced leg model and dimensional analysis of DC motors address the main principles for implementation of this paradigm. In the realm of legged machines, this paradigm provides a unique combination of high torque density, high-bandwidth force control, and the ability to mitigate impacts through backdrivability. We introduce a new metric named the “impact mitigation factor” (IMF) to quantify backdrivability at impact, which enables design comparison across a wide class of robots. The MIT Cheetah leg is presented, and is shown to have an IMF that is comparable to other quadrupeds with series springs to handle impact. The design enables the Cheetah to control contact forces during dynamic bounding, with contact times down to 85 ms and peak forces over 450 N. The unique capabilities of the MIT Cheetah, achieving impact-robust force-controlled operation in high-speed three-dimensional running and jumping, suggest wider implementation of this holistic actuation approach.

Subfields: Biomedical Engineering

View Paper: https://www.semanticscholar.org/paper/793f0a0c2ee71d20f719557ab5d90636963f62a1

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In Biomedical Engineering

Citations in the corpus

Dynamic Locomotion in the MIT Cheetah 3 Through Convex Model-Predictive Control (2018, methodology): “The robot utilizes the proprioceptive actuator technology developed for the Cheetah 2 robot [27], which had low inertia, easily backdrivable hip and knee actuators to mitigate impacts.”
MIT Cheetah 3: Design and Control of a Robust, Dynamic Quadruped Robot (2018, methodology): “The hardware design of Cheetah 3 builds on the actuation paradigm of the MIT Cheetah 1 and 2 robots [9].”
Mini Cheetah: A Platform for Pushing the Limits of Dynamic Quadruped Control (2019, background): “The open-loop output torque bandwidth of an actuator with the output locked is roughly equal to the natural frequency of the actuator inertia and compliance [11].”
Contact Model Fusion for Event-Based Locomotion in Unstructured Terrains (2018, background): “Rather than use perception to build a map of the terrain before attempting to cross it, proprioceptive sensing is sought via highly-transparent actuation [1], joint angle readings, and feedback from an Inertial Measurement Unit (IMU).”
Modular Hopping and Running via Parallel Composition (2017, background): “In addition, Wensing et al. (2017) characterize proprioception and bandwidth based on new models in the context of legged locomotion and show that the low-reduction drivetrain has superior performance on both counts.”