Design of actuation system and minimization of sensor configuration for gait event detection for Gen 3.0 Portable Powered Ankle-Foot Orthosis (PPAFO)

Powered ankle-foot orthoses (AFOs), which are capable of providing assistive torque at the ankle joint, have significant potential as both assistance and rehabilitation devices. Technology advancements have led to great progression in the development of powered AFOs. Our group had developed the Portable Powered Ankle-Foot Orthosis (PPAFO) that was capable of providing bidirectional assistive torque at the ankle joint. Two generations of the PPAFO were previously developed. Both designs used two different off-the-shelf rotary actuators. This thesis consists of two studies focusing on the development of a new compact higher torque actuation system and the identification of a minimum sensor configuration for gait event detection for a powered AFO. Study 1 presents the design and evaluation of a new actuation system for the PPAFO (Generation 3.0). The actuation system utilized two dual-action linear actuators and a customized gear train. Compared with the previous designs, it generated higher torque and power while providing a thinner lateral profile. The new design had a total weight of (680g) and was capable of generating 32 Nm torque and 110 W power. While running under the same torque and power level as the previous designs, the new design offered better longevity (42.9% and 81.4% increases in normalized run time for test bench emulation and treadmill walking). Although the overall weight of the new actuation system had a 20% increase compared with previous design, it could generate 166.7% more torque and 120% more power, which will enable us to test the system at various torque and power settings. Study 2 investigated the minimum sensor configuration for detecting gait events. Knowledge of the expected orientation and behavior of a limb as related to specific events during the gait cycle (or state timing as a function of the percentage of the gait cycle, % GC) is essential to allow appropriate control of a powered AFO. A total of five sensors were selected (two force sensitive sensors, one ankle angle sensor, and two inertial measurement units (IMU)). The performances of selected sensor configurations were quantified and compared through state-based and event-based approaches in terms of gait state estimation and gait event detection timing, respectively. Gait data were collected from five healthy subjects while walking on a treadmill wearing the Gen 3.0 PPAFO. Results indicated that, while single IMU configurations (located on the shank or foot) both outperformed all other configurations (mean state estimation error: < 2% GC; mean event detection timing error: < 23 ms), the shank IMU was able to detect more gait events than the foot IMU. Since more detectable events could improve the system's robustness (i.e., adjusting to variable speeds) by updating estimation more frequently, a single shank IMU configuration was recommended for powered AFO applications

A Summary of NASA Rotary Wing Research: Circa 20082018

The general public may not know that the first A in NASA stands for Aeronautics. If they do know, they will very likely be surprised that in addition to airplanes, the A includes research in helicopters, tiltrotors, and other vehicles adorned with rotors. There is, arguably, no subsonic air vehicle more difficult to accurately analyze than a vehicle with lift-producing rotors. No wonder that NASA has conducted rotary wing research since the days of the NACA and has partnered, since 1965, with the U.S. Army in order to overcome some of the most challenging obstacles to understanding the behavior of these vehicles. Since 2006, NASA rotary wing research has been performed under several different project names [Gorton et al., 2015]: Subsonic Rotary Wing (SRW) (20062012), Rotary Wing (RW) (20122014), and Revolutionary Vertical Lift Technology (RVLT) (2014present). In 2009, the SRW Project published a report that assessed the status of NASA rotorcraft research; in particular, the predictive capability of NASA rotorcraft tools was addressed for a number of technical disciplines. A brief history of NASA rotorcraft research through 2009 was also provided [Yamauchi and Young, 2009]. Gorton et al. [2015] describes the system studies during 20092011 that informed the SRW/RW/RVLT project investment prioritization and organization. The authors also provided the status of research in the RW Project in engines, drive systems, aeromechanics, and impact dynamics as related to structural dynamics of vertical lift vehicles. Since 2009, the focus of research has shifted from large civil VTOL transports, to environmentally clean aircraft, to electrified VTOL aircraft for the urban air mobility (UAM) market. The changing focus of rotorcraft research has been a reflection of the evolving strategic direction of the NASA Aeronautics Research Mission Directorate (ARMD). By 2014, the project had been renamed the Revolutionary Vertical Lift Technology Project. In response to the 2014 NASA Strategic Plan, ARMD developed six Strategic Thrusts. Strategic Thrust 3B was defined as the Ultra-Efficient Commercial VehiclesVertical Lift Aircraft. Hochstetler et al. [2017] uses Thrust 3B as an example for developing metrics usable by ARMD to measure the effectiveness of each of the Strategic Thrusts. The authors provide near-, mid-, and long-term outcomes for Thrust 3B with corresponding benefits and capabilities. The importance of VTOL research, especially with the rapidly expanding UAM market, eventually resulted in a new Strategic Thrust (to begin in 2020): Thrust 4Safe, Quiet, and Affordable Vertical Lift Air Vehicles. The underlying rotary wing analysis tools used by NASA are still applicable to traditional rotorcraft and have been expanded in capability to accommodate the growing number of VTOL configurations designed for UAM. The top-level goal of the RVLT Project remains unchanged since 2006: Develop and validate tools, technologies and concepts to overcome key barriers for vertical lift vehicles. In 2019, NASA rotary wing/VTOL research has never been more important for supporting new aircraft and advancements in technology. 2 A decade is a reasonable interval to pause and take stock of progress and accomplishments. In 10 years, digital technology has propelled progress in computational efficiency by orders of magnitude and expanded capabilities in measurement techniques. The purpose of this report is to provide a compilation of the NASA rotary wing research from ~2008 to ~2018. Brief summaries of publications from NASA, NASA-funded, and NASA-supported research are provided in 12 chapters: Acoustics, Aeromechanics, Computational Fluid Dynamics (External Flow), Experimental Methods, Flight Dynamics and Control, Drive Systems, Engines, Crashworthiness, Icing, Structures and Materials, Conceptual Design and System Analysis, and Mars Helicopter. We hope this report serves as a useful reference for future NASA vertical lift researchers