Cable-driven underactuated wearable robotic devices for hand assistance

Abstract

To address the first aim, we carried out a feasibility clinical trial with ten post-stroke patients performing Activities of Daily Living (ADLs). We evaluated the physiological and kinematic effects of using a preliminary version of our hand exoskeleton that supported only finger extension combined with an elbow-assisting soft wearable robot (exosuit). We observed a reduction in the mean electromyographic (EMG) activity of the Biceps Brachii (BB), Anterior Deltoid (AD) and Extensor Digitorum Communis (EDC) muscles, as well as in the coactivation of pairs of muscles typically associated with pathological synergies. Questionnaires filled out by the participants, alongside discussions with healthcare professionals, provided positive and constructive feedback. This encouraged our continued efforts to develop and refine the device to expand its functionalities.The next step was to develop a model of the behaviour of the structures for defined input tensions on the wires. The main design parameter considered in the model is the rotational stiffness of the joints. By selecting different joint stiffness values, specific motions can be achieved. An optimisation-based framework was developed to automatically adjust the design of the structures to the dimensions of the user's hands. The optimisation goal was to follow the first postural synergy of the hand, which is known to encode a large amount of information regarding common patterns of human hands in daily life.We experimentally verified the created model, and obtained low error of the angular trajectory of the structure's joints, also observing low Cartesian position error of the elements. Then, a 3D-printed index finger (dimensioned following the average male user) was actuated by a structure, and the finger's angular trajectories were compared to the simulated ones. Low errors were obtained for the Metacarpophalangeal (MCP) and Proximal Interphalangeal (PIP) joints, and a moderate error for the Distal Interphalangeal (DIP) joint. Importantly, we observed that the stiffness of the structure could be modulated by controlling the tensions applied on the flexion and extension tendons: increasing the co-contraction of the tendons resulted in an increased stiffness at the joints. The fingertip forces exerted by the structure were evaluated, and reached the desired threshold corresponding to the values typically applied by therapists on low to moderately impaired stroke patients. Finally, in a qualitative manner, we demonstrated the successful grasping of a diverse set of objects typically used in rehabilitation settings.The first main contribution of this thesis is the demonstration of the potential that wearable robots have in aiding the upper limbs of impaired users in ADLs. This provides an important building block of evidence towards the use of robotic devices for assistance. The next main contribution is an underactuated mechanism for hand assistance. This is coupled with an automatic, model-based procedure that designs structures optimised to achieve the first postur...