On the Value of Estimating Human Arm Stiffness during Virtual Teleoperation with Robotic Manipulators

Abstract

Teleoperated robotic systems are widely spreading in multiple different fields, from hazardous environments exploration to surgery. In teleoperation, users directly manipulate a master device to achieve task execution at the slave robot side; this interaction is fundamental to guarantee both system stability and task execution performance. In this work, we propose a non-disruptive method to study the arm endpoint stiffness. We evaluate how users exploit the kinetic redundancy of the arm to achieve stability and precision during the execution of different tasks with different master devices. Four users were asked to perform two planar trajectories following virtual tasks using both a serial and a parallel link master device. Users' arm kinematics and muscular activation were acquired and combined with a user-specific musculoskeletal model to estimate the joint stiffness. Using the arm kinematic Jacobian, the arm end-point stiffness was derived. The proposed non-disruptive method is capable of estimating the arm endpoint stiffness during the execution of virtual teleoperated tasks. The obtained results are in accordance with the existing literature in human motor control and show, throughout the tested trajectory, a modulation of the arm endpoint stiffness that is affected by task characteristics and hand speed and acceleration.

An Uncontrolled Manifold Analysis of Arm Joint Variability in Virtual Planar Position and Orientation Telemanipulation

“…Despite the mechanical and dynamical differences between Sigma and Omni, our results suggest that the differences in the kinematic solution adopted by users may require higher statistical power to be investigated. On the other hand, differences in the master devices could also be evened out by dynamic adaptation (as described in [13]) that would allow for similar R v modulations and mean values.…”

“…The trajectories of the two tasks were divided into eight parts, characterized by three levels of absolute curvature (Fig. 3.1) that were analytically obtained for each point along the bidimensional trajectories as in Buzzi et al [13].…”

“…Instead of freezing the arm joints in the same solutions, experts exploit this redundancy, and use this variability in their arm joints to increase performance. To develop intuitive teleoperation systems and controllers, and to further understand redundancy exploitation in the human arm, it is beneficial to model the exploitation of arm kinematic and kinetic redundancy in different teleoperation and manipulation conditions [13], [14].…”

Biomimetic adaptive impedance control in physical Human Robot Interaction

“…The offline stiffness estimation algorithm follows the steps presented in [31]. The users' arm and thorax kinematics are measured using optoelectronic cameras (Vicra -Northern Digital, Ontario, Canada, 20 Hz sampling rate) and electromagnetic sensors (Aurora -Northern Digital, Ontario, 30 Hz sampling rate) and 10 surface EMG signals are acquired using a multichannel ADC (TMSi Porti -Twente Medical Systems International, Oldenzaal, Nederland, 2048Hz sampling rate).…”

“…We present the development of a model-based stiffnessmimicking adaptive impedance controller for adjusting the dynamic properties of a master device to increase accuracy in a virtual targeting task. Using an off-line musculoskeletal model algorithm based on kinematic and dynamic data, the cartesian hand stiffness modulation was evaluated [31]. The proposed biomimetic controller accounts for the changes in the arm stiffness while performing the task, adapting the master device's damping coefficient in order to reflect the natural, anisotropic, stiffness characteristics.…”