EVALUATION COMMITTEE

The Faculty Council has appointed the following adjudication committee to evaluate the thesis and the associated lecture: 

• Professor Natalie Mrachacz-Kersting, Albert–Ludwigs–Universität Freiburg
• Professor Sadasivan Puthusserypady Kumaran, Technical University of Denmark (DTU)

Chairman: Associate professor Maciej Plocharski, Department of Health Science and Technology (HST), Aalborg University

Moderator: Professor Lotte N. S. Andreasen Struijk, Department of Health Science and Technology (HST), Aalborg University

ABSTRACT

Individuals with severe motor impairments, such as tetraplegia caused by spinal cord injury (SCI) or conditions like amyotrophic lateral sclerosis (ALS), often experience a significant loss of upper-limb function and limited independence in activities of daily living (ADLs). Upper-limb exoskeletons (ULEs) offer a potential solution; however, current systems remain limited in addressing key biomechanical and usability challenges, particularly at the wrist. Existing wrist modules are often constrained by trade-offs between mechanical complexity, distal weight, and transmission performance. Actuation systems such as direct- and pneumatic-driven systems introduce bulk, while cable-driven approaches can suffer from friction and slack. In addition, wrist abduction-adduction (Ab-Ad), despite its importance for hand orientation in ADLs, is frequently omitted or insufficiently evaluated.

This PhD thesis investigates the design and functional impact of a tendon-driven wrist joint for ULEs, with a focus on enabling compact design, actuation and evaluating the role of wrist Ab-Ad assistance.  It consists of three sub-studies addressing actuation design, controlled validation, and evaluation in target users.

In study I, a compact and lightweight single-Bowden cable-driven abduction and clock-spring-driven adduction mechanism was developed to reduce slack and maintain consistent torque. Kinematic and dynamic modeling was used to estimate exoskeleton wrist joint torque and guide the selection of clock spring parameters. Experimental evaluation with five participants with no motor disability (NMD) demonstrated smooth motion and agreement with model predictions of spring parameters under varying arm positions and load conditions. In study II, the functional contribution of wrist Ab-Ad was assessed by integrating the mechanism as a sixth degree-of-freedom (DoF) of a five DoF ULE. In controlled experiments with eight NMD participants, wrist assistance clearly improved task performance when evaluated with and without the Ab-Ad joint. During drinking task, spill incidence was reduced from 56% to 3% and task success in a scratch stick task increased from 28% to 75%, without increasing task execution time. Further, a preliminary feasibility observation with one ALS individual indicated that the wrist module lightweight, supported ADL performance, was easy to don and doff and did not introduce discomfort during extended use. In study III, the six-DoF ULE was evaluated by six individuals with ALS or SCI using a non-invasive tongue robot interface and demonstrated improved task success when performing two ADLs with and without the wrist Ab-Ad joint, with drinking task performance increasing from 16.7% to 72.2% and scratch stick task performance from 16.7% to 77.8%. Participants reported no or low discomfort, good usability and with wrist Ab-Ad assistance. Participants consistently reported that the added wrist joint improved functionality during task execution while maintaining overall comfort. The results show that a tendon-driven, spring-assisted wrist exoskeleton mechanism can be implemented in a compact and wearable form while providing measurable functional benefits. In particular, the findings demonstrate that wrist Ab-Ad assistance contributes directly to improved task execution, addressing a limitation in current ULE designs.