Research

In order to provide therapy in a functional context, controls for wearable orthoses need to be robust and intuitive. We have previously introduced an intuitive, user-driven, EMG based orthotic control, but the process of training a control which is robust to concept drift (changes in the input signal) places a substantial burden on the user. In this paper, we explore semi-supervised learning as a paradigm for wearable orthotic controls. We are the first to use semi-supervised learning for an orthotic application. We propose a K-means semi-supervision and a disagreement-based semi-supervision algorithm. This is an exploratory study designed to determine the feasibility of semi-supervised learning as a control paradigm for wearable orthotics. In offline experiments with stroke subjects, we show that these algorithms have the potential to reduce the training burden placed on the user, and that they merit further study.

Jumping spiders (Salticidae) regularly jump gaps many times their body length—behavior characteristic of the family and central to their life history. As they leap, they spin a silk dragline that connects them to the surface they started from. A safety line should the jump fail, this dragline is also thought to be a control mechanism, with tension enabling the manipulation of orientation and trajectory. A unique method for shaping movement, this novel locomotor phenomena has not been explored experimentally. Using high-speed cameras and Salticus scenicus, we quantified jumps by spiders crossing gaps of three distances, then directly tested how silk-tension forces influence jumps by using rapidly moving platforms to experimentally “ablate” and re-enable silk-based forces mid-jump. We also quantified the material properties of jump-spun silk and developed physics-based models to estimate silk forces and explore how silk-based tension-forces influence jumps. For all jumps, spiders showed backwards rotation at takeoff, with rotational magnitude increasing with jump distance. However, rotation reversed mid-jump in longer jumps, with spiders achieving similar landing orientations regardless of distance. Ablating tension late in the jump delayed counter-rotation, providing direct evidence that silk tension is necessary to accomplish this maneuver. Model-derived tension-force estimates fell within measured silk strengths, with jump-spun silk possessing the high-performance characteristics of capture-web silk spun by other spiders despite far higher spin-speeds (~600mm/s). Our work suggests silk-tension facilitates the decoupling of orientation at landing from jump distance—thus although silk-tension slows jumpers, it seems to effectively increase the jump range of these spiders.

A device to quantitatively assess the ulnar collateral ligament of the thumb was developed to facilitate rapid and accurate diagnosis of the ligamentous injury known as Skier’s thumb.