TY - JOUR T1 - Quantitative testing of fMRI-compatibility of an electrically active mechatronic device for robot-assisted sensorimotor protocols JF - IEEE Transactions on Biomedical Engineering Y1 - 2018 A1 - Farrens, A.J. A1 - Zonnino, A. A1 - Erwin,Andrew A1 - O'Malley, M.K. A1 - Johnson, C.L. A1 - Ress, D. A1 - Fabrizio Sergi VL - 65 UR - http://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=8012485&tag=1 ER - TY - JOUR T1 - Effects of assist-as-needed upper extremity robotic therapy after incomplete spinal cord injury: a parallel-group controlled trial JF - Frontiers in Neurobotics Y1 - 2017 A1 - John M. Frullo A1 - Jared Elinger A1 - Ali Utku Pehlivan A1 - Kyle Fitle A1 - Kathryn Nedley A1 - Gerard Francisco A1 - Fabrizio Sergi A1 - Marcia K. O'Malley VL - 11 ER - TY - JOUR T1 - Kinesthetic feedback during 2DOF wrist movements via a novel MR-compatible robot JF - IEEE Transactions on Neural Systems and Rehabilitation Engineering Y1 - 2017 A1 - Erwin,Andrew A1 - O'Malley, M.K. A1 - Ress, D. A1 - Fabrizio Sergi VL - 25 UR - http://ieeexplore.ieee.org/document/7763863/ ER - TY - JOUR T1 - A Time-Domain Approach To Control Of Series Elastic Actuators: Adaptive Torque And Passivity-Based Impedance Control JF - IEEE/ASME Transactions on Mechatronics Y1 - 2016 A1 - Dylan P. Losey A1 - Andrew Erwin A1 - Craig G. McDonald A1 - Fabrizio Sergi A1 - Marcia K. O'Malley AB -

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'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.

VL - 21 UR - http://ieeexplore.ieee.org/abstract/document/7457670/ ER - TY - Generic T1 - Development, control, and MRI-compatibility of the MR-SoftWrist T2 - IEEE International Conference on Rehabilitation Robotics (ICORR) Y1 - 2015 A1 - Erwin,Andrew A1 - O'Malley, M.K. A1 - Ress, D. A1 - Fabrizio Sergi JF - IEEE International Conference on Rehabilitation Robotics (ICORR) PB - IEEE CY - Singapore ER - TY - JOUR T1 - Interaction control capabilities of an MR-compatible compliant actuator for wrist sensorimotor protocols during fMRI JF - IEEE/ASME Transactions on Mechatronics Y1 - 2015 A1 - Fabrizio Sergi A1 - Andrew Erwin A1 - Marcia K. O'Malley KW - compliant actuators. KW - Force control KW - functional MRI (fMRI) KW - MR-compatible robotics AB -

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.

VL - 20 ER - TY - Generic T1 - Compliant force-feedback actuation for accurate robot-mediated sensorimotor interaction protocols during fMRI T2 - International Conference on Biomedical Robotics and Biomechatronics (BioRob) Y1 - 2014 A1 - Fabrizio Sergi A1 - Andrew Erwin A1 - Brian Cera A1 - Marcia K. O'Malley JF - International Conference on Biomedical Robotics and Biomechatronics (BioRob) PB - IEEE ER - TY - Generic T1 - Design of a series elastic actuator for a compliant parallel wrist rehabilitation robot T2 - International Conference on Rehabilitation Robotics Y1 - 2013 A1 - Fabrizio Sergi A1 - Melissa M. Lee A1 - Marcia K. O'Malley JF - International Conference on Rehabilitation Robotics ER - TY - Generic T1 - Interaction control for rehabilitation robotics via a low-cost force sensing handle T2 - 6th Annual ASME Dynamic Systems and Controls Conference Y1 - 2013 A1 - Andrew Erwin A1 - Fabrizio Sergi A1 - Vinay Chawda A1 - Marcia K. O'Malley JF - 6th Annual ASME Dynamic Systems and Controls Conference CY - Palo Alto, CA ER -