@article {1815, title = {Quantitative testing of fMRI-compatibility of an electrically active mechatronic device for robot-assisted sensorimotor protocols}, journal = {IEEE Transactions on Biomedical Engineering}, volume = {65}, number = {7}, year = {2018}, pages = {1595-1606}, doi = {10.1109/TBME.2017.2741346}, url = {http://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=8012485\&tag=1}, attachments = {https://mahilab.rice.edu/sites/default/files/publications/Farrens2018\%20-\%20Quantitative\%20testing\%20fMRI-comp.pdf}, author = {Farrens, A.J. and Zonnino, A. and Erwin,Andrew and O{\textquoteright}Malley, M.K. and Johnson, C.L. and Ress, D. and Fabrizio Sergi} } @article {1798, title = {Effects of assist-as-needed upper extremity robotic therapy after incomplete spinal cord injury: a parallel-group controlled trial}, journal = {Frontiers in Neurobotics}, volume = {11}, number = {26}, year = {2017}, attachments = {https://mahilab.rice.edu/sites/default/files/publications/fnbot-11-00026.pdf}, author = {John M. Frullo and Jared Elinger and Ali Utku Pehlivan and Kyle Fitle and Kathryn Nedley and Gerard Francisco and Fabrizio Sergi and Marcia K. O{\textquoteright}Malley} } @article {1809, title = {Kinesthetic feedback during 2DOF wrist movements via a novel MR-compatible robot}, journal = {IEEE Transactions on Neural Systems and Rehabilitation Engineering}, volume = {25}, number = {9}, year = {2017}, pages = {1489-1499}, doi = {10.1109/TNSRE.2016.2634585}, url = {http://ieeexplore.ieee.org/document/7763863/}, attachments = {https://mahilab.rice.edu/sites/default/files/publications/Erwin2017\%20-\%20MR\%20SoftWrist_0.pdf}, author = {Erwin,Andrew and O{\textquoteright}Malley, M.K. and Ress, D. and Fabrizio Sergi} } @article {1829, title = {A Time-Domain Approach To Control Of Series Elastic Actuators: Adaptive Torque And Passivity-Based Impedance Control}, journal = {IEEE/ASME Transactions on Mechatronics}, volume = {21}, number = {4}, year = {2016}, pages = {2085 - 2096}, abstract = {

Robots are increasingly designed to physically interact with humans in unstructured environments, and as such must operate both accurately and safely. Leveraging compliant actuation, typically in the form of series elastic actuators (SEAs), can guarantee this required level of safety. To date, a number of frequency-domain techniques have been proposed which yield effective SEA torque and impedance control; however, these methods are accompanied by undesirable stability constraints. In this paper, we instead focus on a time-domain approach to the control of SEAs, and adapt two existing control techniques for SEA platforms. First, a model reference adaptive controller is developed, which requires no prior knowledge of system parameters and can specify desired closed-loop torque characteristics. Second, the time-domain passivity approach is modified to control desired impedances in a manner that temporarily allows the SEA to passively render impedances greater than the actuator{\textquoteright}s intrinsic stiffness. This approach also provides conditions for passivity when augmenting any stable SEA torque controller with an arbitrary impedance. The resultant techniques are experimentally validated on a custom prototype SEA.

}, issn = {1083-4435}, doi = {10.1109/TMECH.2016.2557727}, url = {http://ieeexplore.ieee.org/abstract/document/7457670/}, attachments = {https://mahilab.rice.edu/sites/default/files/publications/Losey_TMECH.pdf}, author = {Dylan P. Losey and Andrew Erwin and Craig G. McDonald and Fabrizio Sergi and Marcia K. O{\textquoteright}Malley} } @proceedings {1756, title = {Development, control, and MRI-compatibility of the MR-SoftWrist}, year = {2015}, month = {08/2015}, pages = {187-192}, publisher = {IEEE}, address = {Singapore}, attachments = {https://mahilab.rice.edu/sites/default/files/publications/Erwin2015\%20-\%20MR\%20SoftWrist.pdf}, author = {Erwin,Andrew and O{\textquoteright}Malley, M.K. and Ress, D. and Fabrizio Sergi} } @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 {1743, title = {Compliant force-feedback actuation for accurate robot-mediated sensorimotor interaction protocols during fMRI}, year = {2014}, month = {08/2014}, publisher = {IEEE}, attachments = {https://mahilab.rice.edu/sites/default/files/publications/Sergi2014\%20-\%201DOF\%20MR\%20devices.pdf}, author = {Fabrizio Sergi and Andrew Erwin and Brian Cera and Marcia K. O{\textquoteright}Malley} } @proceedings {1650, title = {Design of a series elastic actuator for a compliant parallel wrist rehabilitation robot}, year = {2013}, month = {06/2013}, attachments = {https://mahilab.rice.edu/sites/default/files/publications/Sergi_SEA_paper_2.pdf}, author = {Fabrizio Sergi and Melissa M. Lee and Marcia K. O{\textquoteright}Malley} } @proceedings {1703, title = {Interaction control for rehabilitation robotics via a low-cost force sensing handle}, year = {2013}, address = {Palo Alto, CA}, attachments = {https://mahilab.rice.edu/sites/default/files/publications/Erwin2013\%20-\%20RiceWrist-Grip.pdf}, author = {Andrew Erwin and Fabrizio Sergi and Vinay Chawda and Marcia K. O{\textquoteright}Malley} }