Damping in Compliant Actuation: A Review

Abstract

This article has been accepted for inclusion in a future issue of this journal. Content is final as presented, with the exception of pagination.C ompliant actuator technology aims at building robots capable of physically interacting with humans and the environment, matching the versatility and capacity of biological systems. Recently, it underwent a significant evolution with the introduction of damping to improve performance. Such development reflects several aspects, including energy saving and oscillation mitigation. However, large damping values tend to increase the system impedance, worsening robot resilience and human safety during impacts. That suggests the importance of a correct tradeoff.This article reviews the application of damping solutions to compliant actuation. We classify damper systems based on the amount of active control, their physical operation principle, and the topological position of the damping element used in the various actuators. Then we study the fields of application of these devices and analyze how different design aspects correlate with one another and applications. This analysis yields insight into how design choices can influence the characteristics of actuators and the robots using them, from the viewpoint of robot resilience, human safety, power consumption, and energy storage. Finally, we provide an annotated database of the papers considered to conduct this review. OverviewThe field of compliant robotic actuation has been growing [1],[2], motivated by the intention of building robots able to cope with unknown environments [3], behave safely in humanrobot interaction [4], tolerate shocks [5], store energy [6], [7], and move agilely on legs [8]- [10]. Nevertheless, when compared to rigid equivalent robots, compliant actuation underperforms in some domains. Among other aspects, reduced control authority bandwidth can lead to undesired oscillations and vibrations [11], which can, in turn, reduce precision, compromise stability, and waste energy. Through the years, it became clear that to mitigate such limitations [12], which can jeopardize the very advantage of using compliant actuation in the first place, the inclusion of some form of damping action [13] is mandatory.

Muscle prestimulation tunes velocity preflex in simulated perturbed hopping

“… 41 , 42 , is carried by the force–velocity relation, and whether a trade-off exists between the force–velocity relation’s stabilizing effect and control effort. From a technical perspective, understanding low-level control of the force–velocity relation can promote bio-inspired designs for assistive robotic devices, as numerous studies have suggested that implementing (tunable) dampers can improve the system performance and facilitate robustness against external perturbations 17 , 43 .…”

SPIRO: A Compliant Spiral Spring–Damper Joint Actuator With Energy-Based Sliding-Mode Controller

“…Similarly, the activation of the damping pipe results in distinct profiles for the true damping B s due to varying pressures. This means that the damping constant B c contained within the spring will change relative to the pressure that inflatable pipes exert, as shown in (2). Additionally, the distance d p between the damping pipes and spring helical lines is interpreted to accurately track the effect of damping on double-sided spring.…”

“…However, conventional electric motors have limitations when it comes to tasks that require flexibility, energy efficiency, and safe interaction with the load side. For example, achieving optimal robot locomotion requires a delicate balance of stiffness and damping [1], [2]. This challenge becomes particularly significant when actuators need to directly interact with humans, such as in manipulators for active task support [3]- [5] or as assistive mechanisms in human locomotion [6]- [9].…”

Design and control of a compliant robotic actuator with parallel spring-damping transmission

“…Therefore, the demand for tunable damper is proposed. The variable damping actuators (VDAs) [25, 26] can change its physical damping to suppress the system oscillation. Laffranchi utilized a piezoelectric damper [26], which essentially operates as a friction damper by actively controlling friction force to mimic viscous damping effect.…”