On a Two-DoF Parallel and Orthogonal Variable-Stiffness Actuator: An Innovative Kinematic Architecture

Matteo Malosio,Francisco Ramìrez Reyes,Giovanni Legnani,Lorenzo Molinari Tosatti,Hermes Giberti,Francesco Corbetta

doi:10.3390/robotics8020039

Matteo Malosio, Francisco Ramìrez Reyes + Show 4 more

Open Access

https://doi.org/10.3390/robotics8020039

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Abstract

Variable-Stiffness Actuators are continuously increasing in importance due to their characteristics that can be beneficial in various applications. It is undisputed that several one-degree-of-freedom (DoF) solutions have been developed thus far. The aim of this work is to introduce an original two-DoF planar variable-stiffness mechanism, characterized by an orthogonal arrangement of the actuation units to favor the isotropy. This device combines the concepts forming the basis of a one-DoF agonist-antagonist variable-stiffness mechanism and the rigid planar parallel and orthogonal kinematic one. In this paper, the kinematics and the operation principles are set out in detail, together with the analysis of the mechanism stiffness.

Highlights

A Variable-Stiffness Actuator (VSA) permits the adjustment of both the position and stiffness of the load [1]
To the authors’ knowledge only one two-DoF mechanism enabling planar movements has been developed up to now [9]. This is a cable-driven device arranged on a triangular framework, with three non-linear Series Elastic Actuators (SEA)
To take the existing architecture one step further and enhance the isotropy in terms of stiffness and decoupling of degrees of freedom, an original kinematics two-DoF planar solution based on two orthogonal tendon-driven VSA actuation schemes was developed and is presented in this work

Summary

Introduction

A Variable-Stiffness Actuator (VSA) permits the adjustment of both the position and stiffness of the load [1]. To the authors’ knowledge only one two-DoF mechanism enabling planar movements has been developed up to now [9] This is a cable-driven device arranged on a triangular framework, with three non-linear SEAs. Due to the presence of three tendons, the possibility to adjust the stiffness of the load along different directions is limited. To take the existing architecture one step further and enhance the isotropy in terms of stiffness and decoupling of degrees of freedom, an original kinematics two-DoF planar solution based on two orthogonal tendon-driven VSA actuation schemes was developed and is presented in this work. The architecture presented within this work uses only four actuators, being the minimum number required to control both the equilibrium position and the mechanical stiffness of a mobile mass along two orthogonal directions.

Kinematics

Force and Stiffness Analysis

Conclusions