TASP PhD Seminar – Anna Clarke – “An Automatic Control System for Training Complex Kinesthetic Skills”

Work towards PhD degree under the supervision of  Prof. Per-Olof Gutman 

When: 19.7.2021 at 15:30

Where: Dan Kahn building, room # 217

Abstract: The main objective of this research is to develop a novel method for aiding human subjects acquire completely new sets of motor skills required for activities in unfamiliar or unnatural environments. The proposed study case is the free-fall stage of skydiving. At this stage aerial maneuvers are performed by changing the body posture and thus deflecting the surrounding airflow. The natural learning process is extremely slow due to unfamiliar free-fall dynamics, stress induced blocking of kinesthetic feedback, and complexity of the required movements. The key idea is to augment the learner with an automatic control system that would be able to perform the trained activity if it had direct access to the learner’s body as an actuator. The aiding system will supply the following visual cues to the learner: 1. Feedback of the current body posture; 2. The body posture that would bring the body to perform the desired maneuver; 3. Prediction of the future inertial position and orientation if the body retains its present posture. The system will enable novices to maintain stability in free-fall and perceive the unfamiliar environmental dynamics, thus accelerating the initial stages of skill acquisition. A Proof-of-Concept experiment was conducted, whereby humans controlled a virtual skydiver free-falling in a computer simulation, by the means of their bodies. This task was impossible without the aiding system, enabling all participants to complete the task at the first attempt. Computation of the visual cues required modeling of human body free-fall dynamics. A Skydiving Simulator comprising Biomechanical, Aerodynamic, and Kinematic models, dynamic equations of motion, and a virtual reality interface was developed and experimentally verified. Aerodynamic coefficients and skydiver related inputs were estimated via a modified Unscented Kalman Filter from experiments that involved execution of a large variety of free-fall maneuvers. A novel control method based on an Unscented Transform was developed for performing highly advanced maneuvers in a virtual way. The crux of the research was to convert the autonomous maneuver execution into motor learning aids. This process involved a thorough analysis of the movement repertoire of skydivers with varying level of skill. It was discovered that experienced athletes use 2-5 movement patterns for most maneuvers. Each movement pattern is a combination of body degrees-of-freedom that are activated proportionally and synchronously, as a single unit. The most significant discovery was that the dynamic characteristics of the plant, comprised by an environment and an actuated body, highly depend on the choice of movement patterns. Based on a number of study cases, we propose a novel hypothesis regarding human motor equivalence: The multiple body degrees-of-freedom are not necessarily redundant, but are needed for shaping the plant dynamics to enable performing desired maneuvers with a simple control law. Additionally, it was discovered that movement patterns may form synergies in order to achieve a desired trade-off between different dynamic characteristics, such as stability and agility. Based on these novel insights an unconventional sports technique analysis method was developed and demonstrated in a study case.