Robust and versatile control of lower limb exoskeletons
Wolfgang Franz Rampeltshammer is a PhD student in the department Biomechanical Engineering.Promotors prof.dr.ir H Kooij , dr.E.H.F. Asseldonk and dr.ir. Keemink from the Faculty Technology and Engineering.
Lower limb exoskeletons are a useful tool to restore gait functionality. Depending on the users' needs, the device either works together with the user or fully takes over. In both cases, it is important that the device reacts appropriately.In this thesis, this human-robot interaction is investigated from a control perspective.The first part considers impacts of force control of the actuators - in this case series elastic actuators - on the user-exoskeleton interaction. Therefore, force controllers were theoretically and practically compared based on how transparent they are to user motion, how stable they are when interacting with arbitrary environments, and how well they track the desired forces (assistive). As a result of this investigation, magnitude and phase response of the apparent impedance were identified as critical, but opposing design targets to achieve optimal interaction with the user.In the second part, full gait assistance for users with complete spinal cord injury is investigated. Therefore, a trajectory generator based on constrained optimization was developed. This trajectory generator creates gait patterns based on high level targets, such as step length or ground clearance. With this, it is possible to quickly generate patterns for a variety of terrains, such as ramps it stairs. Additionally, patterns can be adjusted to user preferences and needs, such as limits in range of motion of individual joints. The possibility to adapt to user preferences and repeatedly test new patterns helps with improving their interaction with the exoskeleton.