Sensorized Mannequin Leg
tldr:
Preliminary design of a sensorized biomimetic human leg mannequin aimed to replace human test participants for exoskeleton related research studies
What:
This project was carried out at the Neural Rehabilitation Engineering Lab at the University of Waterloo, where I work as an undergraduate research assistant during my study terms. This project consists of multiple parts including but not limited to the design of each leg joint, sensorization for various external inputs such as 'skin' deformation, joint forces etc.
The first milestone was to create a knee prototype that mimics the instantaneous center of rotation (ICR) of a knee joint, which is not as simple as a hinge joint.
Several mechanisms were investigated, till I landed on a four bar linkage mechanism for the first prototype.
Why:
The main purpose of the mannequin leg is to replace human participants in exoskeleton related research studies to better characterize sensory inputs that otherwise rely on observational data. The knee joint was designed first since there are a lot of scientific literature available from various research groups.
How:
The design is based on a design and optimization paper by a research group from the School of Mechatronic Engineering, Changchun University of Technology [1]. It utilizes a four-bar linkage model to mimic the ICR of a human knee. I investigated several types of linkage models as background research to better understand the underlying mechanisms and dynamics of the motion. I also thoroughly studied the biomechanics and anatomy of the human knee to further enhance my understanding.
For the summer term, I built the CAD model of the first knee joint prototype on Solidworks based using a four bar linkage mechanism as shown in the figures to the right.
The ICR is represented by the intersection of the ACL and PCL linkages (marked with a star on Figure 1). The curved design of the ACL linkage and the top profile on the Tibial plate acts as stoppers to prevent hyperflexion of the joint.
The mechanism was physically tested by 3D printing a small scale prototype which worked as intended. This was the last task completed by me for the term.
What did I learn:
Human knee anatomy and biomechanics
Four bar linkage models such as the Chebyshev model
Mathematical models behind linkages such as the Freudenstein’s Equation and loop Closure Equations
What's next:
The team at NRE will continue to work on this project. The next step for me is to run an optimization model on Simulink to determine the optimal lengths of each linkage to produce the desired range of motion. This task will be continued in the Winter 2024 term.
References:
[1] M. Gao et al., “Design and optimization of exoskeleton structure of lower limb knee joint based on cross four-bar linkage,” AIP Publishing, https://pubs.aip.org/aip/adv/article/11/6/065124/991859/Design-and-optimization-of-exoskeleton-structure (accessed Jun. 1, 2023).