@proceedings {1885, title = {A Cable-based Series Elastic Actuator with Conduit Sensor for Wearable Exoskeletons}, year = {2017}, month = {05/2017}, publisher = {IEEE}, address = {Singapore}, keywords = {actuation system design, Actuators, cable tension control, cable tension measurement, cable-based series elastic actuator, cable-conduit transmission, cables (mechanical), compliance control, compliant force sensor, conduit sensor, DC motor, DC motors, deflection measurement, dynamic effect, Exoskeletons, Feedback, flexible cable conduit transmission, Force, Force control, force sensors, full wearable exosuit, gearbox, Hall effect sensors, Hall effect transducers, human arm, human-robot interaction, Impedance, Magnetic flux, physical assistance, robot dynamics, Robots, series elastic force sensor, soft exosuit, soft wearable exoskeleton, springs (mechanical), translational steel compression spring, transmission conduit, user interface, virtual impedance, wearable robotic device}, doi = {10.1109/ICRA.2017.7989790}, attachments = {https://mahilab.rice.edu/sites/default/files/publications/blumenschein2017ieee.pdf}, author = {L. H. Blumenschein and C. G. McDonald and M. K. O{\textquoteright}Malley} } @article {1723, title = {Interaction control capabilities of an MR-compatible compliant actuator for wrist sensorimotor protocols during fMRI}, journal = {IEEE/ASME Transactions on Mechatronics}, volume = {20}, number = {6}, year = {2015}, pages = {2678-2690}, abstract = {

This paper describes the mechatronic design and characterization of a novel MR-compatible actuation system designed for a parallel force-feedback exoskeleton for measurement and/or assistance of wrist pointing movements during functional neuroimaging. The developed actuator is based on the interposition of custom compliant elements in series between a non-backdrivable MR-compatible ultrasonic piezoelectric motor and the actuator output. The inclusion of physical compliance allows estimation of interaction force, enabling force-feedback control and stable rendering of a wide range of haptic environments during continuous scanning. Through accurate inner-loop

velocity compensation and force-feedback control, the actuator is capable of displaying both a low-impedance, subject-in-charge mode, and a high stiffness mode. These modes enable the execution of shared haptic protocols during continuous fMRI.\ 

The detailed experimental characterization of the actuation system is presented, including a backdrivability analysis, demonstrating an achievable impedance range of 22 dB, within a bandwidth of 4 Hz (for low stiffness). The stiffness control bandwidth depends on the specific value of stiffness: a bandwidth of 4 Hz is achieved at low stiffness (10\% of the physical springs stiffness), while 8 Hz is demonstrated at higher stiffness. Moreover, coupled stability is demonstrated also for stiffness values substantially (25\%) higher than the physical stiffness of the spring. Finally, compatibility tests conducted in a 3T scanner are presented, validating the potential of inclusion of the actuator in an exoskeleton system for support of wrist movements during continuous MR scanning, without significant reduction in image quality.

}, keywords = {compliant actuators., Force control, functional MRI (fMRI), MR-compatible robotics}, doi = {10.1109/TMECH.2015.2389222}, attachments = {https://mahilab.rice.edu/sites/default/files/publications/MR-compatible_actuator_v3.pdf}, author = {Fabrizio Sergi and Andrew Erwin and Marcia K. O{\textquoteright}Malley} } @proceedings {082211289622, title = {Disturbance observer based closed loop force control for haptic feedback}, volume = {9 PART B}, year = {2007}, note = {

Disturbance observer;Haptic feedback;Pseudostatic interactions;

}, pages = {1343 - 1349}, address = {Seattle, WA, United States}, abstract = {

Most commonly used impedance-type haptic interfaces employ open-loop force control under the assumption of pseudostatic interactions. Advanced force control in such interfaces can increase simulation fidelity through improvement of the transparency of the device, and can further improve robustness. However, closed loop force-feedback is limited both due to the bandwidth limitations of force sensing and the associated cost of force sensors required for its implementation. In this paper, we propose the use of a nonlinear disturbance observer for estimation of contact forces during haptic interactions. This approach circumvents the traditional drawbacks of force sensing while exhibiting the advantages of closed-loop force control in haptic devices. The feedback of contact force information further enables implementation of advanced robot force control techniques such as robust hybrid impedance and admittance control. Simulation and experimental results, utilizing a PHANToM Premium 1.0A haptic interface, are presented to demonstrate the efficacy of the proposed approach. Copyright {\textcopyright} 2007 by ASME.

}, keywords = {Computer simulation, Force control, Haptic interfaces, Robotics, Robustness (control systems)}, attachments = {https://mahilab.rice.edu/sites/default/files/publications/50-gupta-imece07.pdf}, author = {Abhishek Gupta and O{\textquoteright}Malley, M.K. and Volkan Patoglu} }