sub-projects - active prosthetic ankle
Curved Spring energy model
In order to predict the energetics and stiffness of arbitrarily shaped composite leaf springs, I created an analytical beam bending model using Castigliano’s 2nd theorem and a root-finding method to find solutions for large deflections. By stitching boundary conditions between beam sections, the model lets you sequentially build a beam out of any number of straight and curved pieces, and compute across it as if it were a single structure.
Sweep functions across variables allows this method to be used to explore the design space and find optimal spring shapes. This work is now the core method used by the lab to design leaf springs that fit the design envelope and specifications of new prosthetic ankle concepts.
https://github.com/ljjh20/SPASM
Experimental CHARACTERISATION pipeline for loaded, deforming structures
I developed a high-throughput methodology for characterising the deformation of complex, sometimes non-linear structures, both as verification for analytical system models, and as a performance verification for existing prototypes. To this end I fused the load-deformation data from an Instron machine with the tracking data from a custom vision pipeline to determine the torque-angle relationship, energy storage and distribution, and torsional stiffness. The algorithm and image processing pipeline turned images with depth information into deformation trajectories through time, and made it robust to changes in lighting, camera position and marker placement. This pipeline is now a lab resource to characterise the static response of new prosthetic ankle designs.
Electromechanical design
Through comprehensive characterisation and modelling of our existing powered ankle concepts, we conceived a new modular SEA-based architecture with decoupled sub-systems, featuring an out runner drone motor for more torque, and a generative housing to reduce weight and footprint (not yet published). This architecture can be reconfigured to act as a positive net work powered ankle prosthetic, or as a quasi-passive microprocessor ankle with active damping and position control. This design is currently being prototyped, with the following notable engineered elements:
A generative frame for minimal size and weight while meeting structural and fatigue requirements
A custom out-runner motor housing with minimal inertia to hold a roller screw transmission
A set of custom carbon fiber springs with different stiffnesses for a range of user weights and walking speeds
A motor control board and power delivery board with a boost converter to reduce battery voltage