Formative Usability Assessment of a Rehabilitative Hand Exoskeleton – Directions for User-Friendly Physical Interfaces
Authors: Süner Pla Cerdà Sedef , Şahin Batuhan , Bilge Arıkan Kutluk 
Published: August 2024

Robotic training with exoskeletons has shown promise in the recovery of motor functions within clinical rehabilitation settings [1]. Hand exoskeletons, which is a sub-category of such wearable robotic devices, aim to aid patients in regaining their motor functions. These robotic devices are designed to manipulate the joints of the fingers, primarily for the purposes of rehabilitation and/or interaction. Current hand exoskeleton systems pose numerous usability issues due to challenges stemming from the system complications dictated by the complexity of hand kinematics. Size, bulk and weight are among those complications governing most rigid exoskeletons, negatively affecting the devices' comfort, adjustability, portability and wearability [2]. Many systems have low technology readiness levels, posing challenges for acceptability, marketability and home deployment [3].This paper presents a formative usability test study involving eight healthy individuals to identify user-centred criteria and directions for improving the usability of a hand exoskeleton system. Early identification of potential usability issues is crucial in eliminating those problems during design iterations. The proposed robotic exoskeleton is a two-degree-of-freedom, fully actuated system. It is designed for the index finger using an optimization technique that minimises a cost function which is composed of the isotropy measure and the required actuator torque. It is controlled by an admittance-based control system. The formative usability test was applied as a procedure accompanying the motor learning tests for system validation. The test adopted a qualitative approach combining structured observations during exoskeleton use to complete motor control tasks as they interact with a virtual dynamical system in a leader-follower modality. The observations were followed by semi-structured interviews immediately after use. All sessions were video recorded for thematic analysis.Qualitative findings from the formative usability tests revealed issues related to use comfort, wearability, simplicity and perceived safety of the proposed exoskeleton system. Based on these findings, practical design recommendations will be provided to enhance the donning and doffing of the device, adjustability of finger connections to accommodate anthropometric ranges, material selection and component layout for improved physical comfort. The outcomes of this study are expected to contribute to both the usability improvements of the current system and serve as a reference to the research community in general while developing user-friendly physical interfaces for wearable robotics.[1] Prange GB, Jannink MJA, Groothuis-Oudshoorn CGM, et al. Systematic review of the effect of robot-aided therapy on recovery of the hemiparetic arm after stroke. J Rehabil Res Dev. 2006; 171–183.[2] Ferguson PW, Shen Y, Rosen J. Hand Exoskeleton Systems—Overview. Wearable Robotics: Systems and Applications. 2020; 149–175.[3] Martinez-Hernandez U, Metcalfe B, Assaf T, et al. Wearable Assistive Robotics: A Perspective on Current Challenges and Future Trends. Sensors. 2021, Vol 21; 6751.