Latest Papers

ASME Journal of Mechanisms and Robotics

  • Mechanical Characterization of Supernumerary Robotic Tails for Human Balance Augmentation
    on August 31, 2023 at 12:00 am

    AbstractHumans are intrinsically unstable in quiet stance from a rigid body system viewpoint; however, they maintain balance, thanks to neuro-muscular sensory control properties. With increasing levels of balance related incidents in industrial and ageing populations globally each year, the development of assistive mechanisms to augment human balance is paramount. This work investigates the mechanical characteristics of kinematically dissimilar one and two degrees-of-freedom (DoF) supernumerary robotic tails for balance augmentation. Through dynamic simulations and manipulability assessments, the importance of variable coupling inertia in creating a sufficient reaction torque is highlighted. It is shown that two-DoF tails with solely revolute joints are best suited to address the balance augmentation issue. Within the two-DoF options, the characteristics of open versus closed loop tails are investigated, with the ultimate design selection requiring trade-offs between environmental workspace, biomechanical factors, and manufacturing ease to be made.

Robust Attitude Controller Design for an Uncommon Quadrotor With Big and Small Tilt Rotors


In this article, a robust attitude controller design for an uncommon quadrotor aerial vehicle is discussed. This aerial vehicle is designed to have two big rotors on the longitudinal axis to increase the lift capacity and flight endurance, and two small tilt rotors on the lateral axis to stabilize the attitude. Similar to other multirotors, linearization of the full nonlinear model and using an appropriate rotor mixing matrix give the approximate diagonal attitude model of this quadrotor around hover. However, this ideal model lacks sensor delays, uncertain parameters, flexible modes of a structure, and inexact decoupling dynamics. Therefore, using this model in the control design limits the achievable attitude control performance. Unlike most studies, a system identification method is applied to estimate a more accurate model and increase the resulting attitude control performance. The aim of this paper is to obtain a suitable nominal model with accompanying uncertainty using robust control criterion in the system identification. In this way, an uncertain model that gives high performance in the subsequent robust control design is obtained. The experimental results show that this combined identification and robust control procedure improves attitude control performance compared to existing classical controller design methods.

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