The SoftHand Pro platform: a flexible prosthesis with a user-centered approach

Among commercially-available upper-limb prostheses, the two most often used solutions are simple hook-style grippers and poly-articulated hands, which present a higher number of articulations and show a closer resemblance to biological limbs. In their majority, the former type of prostheses is body-powered, while the second type is controlled by myoelectric signals. Body-powered grippers are easy to control and allow a simple form of force feedback, frequently appreciated by users. However, they present limited versatility. Poly-articulated hands afford a wide range of grasp and manipulation types, but require enough residual muscle activation for dexterous control. Several factors, e.g. level of limb loss, personal preferences, cost, current occupation, and hobbies can influence the preference for one option over the other, and is always a result of the trade-off between system performance and users' needs. The SoftHand Pro (SHP) is an artificial hand platform that has 19 independent joints (degrees-of-freedom), but is controlled by a single input. The design of this prosthesis is inspired by the concept of postural synergies in motor control and implemented with soft-robotic technologies. Their combination provides increased robustness, safe interaction and the execution of diverse grasps. The potential of the SHP is fully unleashed when users learn how to exploit its features and create an intimate relationship between the technical aspects of the prosthesis design and its control by the user. The great versatility of the SoftHand Pro (a reasearch protpotype) permitted its adaptation to the user requirements. This was experienced by the SoftHand Pro Team during the preparation for different CYBATHLON events (from 2016 to 2020). The mixed power and dexterous hand operations required by each task of the race is inspired by everyday tasks. Our prosthesis was driven by different pilots, with different habits and backgrounds. Consequently, the hand control modality was customized according to the user's preferences. Furthermore, the CYBATHLON tasks had some variations in this period, promoting the continuous development of our technology with a user-centered approach. In this paper, we describe the participation and preparation of the SoftHand Pro Team from 2016 to 2020 with three pilots and two different activation modalities, hybrid body-controlled and myoelectric control. We introduced our pilots, the implementation of the two control modalities, and desc