# Design and Model-Based Safety Verification of a Volitional Sit-Stand Controller for a Powered Knee-Ankle Prosthesis

> **NIH NIH F31** · UNIVERSITY OF MICHIGAN AT ANN ARBOR · 2022 · $40,635

## Abstract

ABSTRACT
Sit-stand transitions, the motions executed by individuals to stand up or sit down, are an important determinant
of overall mobility and a common source of falls. Unilateral amputees using standard passive prostheses are
further challenged by sit-stand transitions due to muscle and joint asymmetries they exhibit between the sound
and amputated sides, often resulting in debilitating back pain. Powered knee-ankle prostheses can produce
enough torque to assist meaningfully during sit-stand transitions and can meet design criteria such as
producing smooth motion on the amputated side that matches the sound side. Controllers for these prostheses
can be designed to allow user-driven control of the leg. However, the production of high torques not directly
commanded by the user comes with increased risks. This is of particular concern because these legs must be
adopted outside of controlled lab environments. Thus, any powered prosthesis must demonstrably meet design
and safety criteria. While safety-critical medical devices, such as pacemakers, are subjected to extensive
testing and validation procedures, there is no agreed-upon standard in the powered prosthetics field for how to
define and measure safety. Prior work on sit-stand controllers has focused only on measuring a limited number
of outcomes with respect to one design criterion on a small number of subjects, providing no guarantees about
safety. The set of techniques known as formal verification provides powerful tools to reason about the behavior
of systems that are composed of interacting mechanical, software, and biological modules. Given a model of a
system, formal verification allows us to probe the system’s behavior over an infinite range of possibilities that
cannot be replicated in the lab during a typical testing session. These methods can then guide real-world
testing, and alert system designers to problematic regions of execution. In this project, I propose to apply
formal verification techniques to design a volitional controller for sit-stand transitions with provable safety
guarantees, using physics-based models and novel mathematical formulations of safety.
The University of Michigan Robotics Institute is one of the top institutes of its kind in the US and provides an
ideal environment and infrastructure for the successful completion of this research. The Robotics Institute gait
lab has all of the necessary equipment needed for powered prosthesis research, including two state-of-the-art
prosthetic legs, and access to advanced computational resources such as the Great Lakes high performance
computing cluster. Drs. Gregg and Ozay have proven expertise relevant to the aims of this project, and will
provide mentorship that will guide my research, my training, and the attainment of my career goals.

## Key facts

- **NIH application ID:** 10388466
- **Project number:** 1F31EB032745-01
- **Recipient organization:** UNIVERSITY OF MICHIGAN AT ANN ARBOR
- **Principal Investigator:** Daphna Raquel Raz
- **Activity code:** F31 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2022
- **Award amount:** $40,635
- **Award type:** 1
- **Project period:** 2022-03-01 → 2024-02-29

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10388466

## Citation

> US National Institutes of Health, RePORTER application 10388466, Design and Model-Based Safety Verification of a Volitional Sit-Stand Controller for a Powered Knee-Ankle Prosthesis (1F31EB032745-01). Retrieved via AI Analytics 2026-05-26 from https://api.ai-analytics.org/grant/nih/10388466. Licensed CC0.

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