A Comparison of Robot Wrist Implementations for the iCub Humanoid †

Divya Shah,Yuanqing Wu,Alberto Parmiggiani,Giorgio Metta,Alessandro Scalzo

doi:10.3390/robotics8010011

Divya Shah, Yuanqing Wu + Show 3 more

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https://doi.org/10.3390/robotics8010011

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Abstract

This article provides a detailed comparative analysis of five orientational, two degrees of freedom (DOF) mechanisms whose envisioned application is the wrist of the iCub humanoid robot. Firstly, the current iCub mk.2 wrist implementation is presented, and the desired design objectives are proposed. Prominent architectures from literature such as the spherical five-bar linkage and spherical six-bar linkage, the OmniWrist-III and the Quaternion joint mechanisms are modeled and analyzed for the said application. Finally, a detailed comparison of their workspace features is presented. The Quaternion joint mechanism emerges as a promising candidate from this study.

Highlights

Closed-chain mechanisms, parallel mechanisms, are reputed to exhibit favorable characteristics with respect to their serial counterparts, mainly due to the possibility of distributing the load on the output member to several kinematic chains assembled in parallel and reducing moving inertia by locating the motors on or close to the fixed frame
While the synthesis and optimization of translational parallel manipulators is a well understood problem that has been addressed in several works [1,2,3], the conceptual design of orientational parallel mechanisms with a large rotation range remains a challenging task
As mentioned in the previous sections a promising way to overcome the shortcomings of the current iCub mk.2 wrist implementation is to consider a new wrist design, to improve robustness, and dependability

Summary

Introduction

Closed-chain mechanisms, parallel mechanisms, are reputed to exhibit favorable characteristics with respect to their serial counterparts, mainly due to the possibility of distributing the load on the output member to several kinematic chains assembled in parallel and reducing moving inertia by locating the motors on or close to the fixed frame. Their potential advantages include: a larger payload to robot weight ratio, greater stiffness, better accuracy, and higher dynamic performance. The practical implementation of this class of mechanisms is considered for the wrist design of humanoid robots. The reference application here is the iCub, a 53DOF open-source humanoid robot developed to support research in embodied cognition [4]

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Discussion

Conclusion