Leveraging Natural Load Dynamics with Variable Gear-ratio Actuators

TL;DR

This paper introduces a robotic system with variable gear-ratio actuators that adapt to load dynamics, significantly reducing actuator torque and power while enhancing speed, strength, and robustness through a model-based control algorithm.

Contribution

It presents a novel control algorithm for automatic gear-ratio selection and a new 3-DoF robot arm with discrete gear-ratios, demonstrating improved efficiency and robustness.

Findings

Order-of-magnitude reduction in actuator torque and power.

Enhanced robot speed and load handling capabilities.

Increased robustness to disturbances.

Abstract

This paper presents a robotic system where the gear-ratio of an actuator is dynamically changed to either leverage or attenuate the natural load dynamics. Based on this principle, lightweight robotic systems can be made fast and strong; exploiting the natural load dynamics for moving at higher speeds (small reduction ratio), while also able to bear a large load through the attenuation of the load dynamics (large reduction ratio). A model-based control algorithm to automatically select the optimal gear-ratios that minimize the total actuator torques for an arbitrary dynamic state and expected uncertainty level is proposed. Also, a novel 3-DoF robot arm using custom actuators with two discrete gear-ratios is presented. The advantages of gear-shifting dynamically are demonstrated through experiments and simulations. Results show that actively changing the gear-ratio using the proposed control algorithms can lead to an order-of-magnitude reduction of necessary actuator torque and power, and also increase robustness to disturbances.