Cable-driven underactuated wearable robotic devices for hand assistance

• Main Author: Bernardo, Alexandre Pinto Sales de Noronha
• Other Authors: Domenico Campolo
• Format: Thesis-Doctor of Philosophy
• Language: English
• Published: Nanyang Technological University 2023
• Subjects: Engineering::Mechanical engineering::Bio-mechatronics; Engineering::Mechanical engineering::Robots; Science::Medicine::Biomedical engineering; Engineering::Mathematics and analysis::Simulations
• Online Access: https://hdl.handle.net/10356/165023
• Institution: Nanyang Technological University

Wearable robots have shown promise for providing high-intensity, repetitive training in post-stroke rehabilitation settings, but also for aiding in performing activities of daily life. Most current robotic solutions make use of either rigid or soft mechanisms. The former can provide more power with accurate control at the cost of bulkiness with the risk of joint misalignment. These are generally more convenient for use in a clinical scenario, especially due to the need for a grounded, stationary system. The latter are typically lighter and more adaptable, but more difficult to control in a precise manner, particularly at the joint level. However, due to their light weight, they are feasible for applications which require a portable system. A hybrid approach, where rigid and soft elements are used in tandem, combine the advantages of both soft and rigid mechanisms and have come into prominence in recent years. They have the potential of delivering precise control in a lightweight implementation, increasing their wearability. Nevertheless, there is still a shortage of available solutions illustrating the capacities of a hybrid approach. In this thesis, we introduce a hybrid device for assisting the hand of impaired subjects. To this end, structures composed of identical serially-linked rigid elements connected by flexible joints have been created. These underactuated structures (i.e. with more Degrees of Freedom than Degrees of Actuation) are placed on the dorsal side of the fingers and are attached via soft fabric sleeves. Wires are routed antagonistically through the elements, such that controlling the tension applied on them results on flexion or extension of the structure. We incorporate rigid components with elastic joints to, on one hand, mechanically prevent unnatural motion of the hand, and on the other hand, achieve modelled finger trajectories that follow human-like motions. The large number of elements endows the structure with compliance to the user's fingers, resulting in the improved safety and comfort---characteristic of soft devices. The aims of this project were to (1) establish the potential of wearable exoskeletons for daily assistance; (2) develop a hybrid device that provides assistance to all five fingers in a safe manner by following natural hand motion; (3) demonstrate the stiffness modulation capabilities of the structures directly attached to the fingers. 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 activity of the Biceps Brachii, Anterior Deltoid and Extensor Digitorum Communis 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 and Proximal Interphalangeal joints, and a moderate error for the Distal Interphalangeal 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 postural synergy of unique users' hands. Lastly, we have preliminarily indicated that modulation of the stiffness of the structures is possible. This is fundamental to achieve grasps that are resistant to external perturbations – a capability particularly relevant to daily assistance. These aforementioned achievements show promise that warrants future improvements of this system to implement it as a device used by hemiparetic patients.