Enhancing Voluntary Motion in Broad Patient Populations with Modular Powered Orthoses

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PROJECT ABSTRACT The overall goal of this project is to develop modular, lower-limb, powered orthoses that fit to user-specific weakened joints and control force/torque in a manner that enhances voluntary motion in broad patient populations. Conventional orthoses tend to immobilize joints, and emerging powered orthoses constrain voluntary motion by using highly geared electric motors and/or control methods that force the user to follow a specific gait pattern. Consequently, these devices have not seen widespread success across populations with weakened voluntary control due to stroke, advanced age, or musculoskeletal disorders. These heterogeneous populations require partial, not full, assistance of user-specific muscle groups during daily activities. However, there is a fundamental gap in knowledge about how to design and control powered orthoses to assist the user without constraining their motion. The central hypothesis of this project is that high-torque, low-inertia motor systems controlled with energetic objectives will enable modular powered orthoses to partially assist the joints. High-torque electric motors combined with minimal transmissions can be freely rotated (i.e., backdriven) by human joints, allowing the use of an emerging torque control method called energy shaping to reduce the perceived weight/inertia of the body during any motion. By mounting these modular actuators to commercial orthoses, this technology will be easily prescribed/configured by clinicians. The project aims are as follows: Aim 1: Develop design paradigm to enable backdrivable, modular powered orthoses. Hypothesis: A torque-dense “pancake” motor with a low gear ratio will provide high output torque, low backdrive torque, low acoustic noise, and energy efficiency in lightweight, powered orthosis joint modules. Aim 2: Develop torque control paradigm to facilitate voluntary motion assistance in orthoses. Hypothesis: Modular joint configurations of partial-assist orthoses will provide torque assistance by selectively offloading mass and inertia in the human body through energy shaping. Aim 3: Establish feasibility of assisting different populations with modular powered orthoses. Hypothesis: Assisting lower-limb musculature with modular powered orthoses will improve functional outcomes in subjects with chronic stroke or sarcopenia, and improve lifting/lowering posture in able-bodied subjects. This project will be technologically significant to the design of modular powered orthoses for enhancing voluntary motion, scientifically significant to understanding how to control body energetics to partially assist different joints in a task-invariant manner, and clinically significant to the widespread adoption of powered orthoses to restore mobility in broad populations with weakened voluntary control. The flexible assistance offered by this modular orthosis technology will have a profound impact on mobility and quality of life for tens of millions of Americans, as nearly 1 in 8 adults have a mobility limitation according to the U.S. CDC.