# Development of a Wearable Finger Exoskeleton for Rehabilitation
###### Abstract  
This research work shows a new architecture of a novel wearable finger exoskeleton for rehabilitation; the proposed design consists of a one degree of freedom mechanism that generates the flexion and extension movement for the proximal, medial and distal phalange of the fingers to assist patients during the rehabilitation process, after neurological trauma, such as a stroke. The anatomy and anthropometric measures for the hand were used to define the design of the mechanism. In the analytic part, the representative equations for the forward and inverse kinematic analysis of the fingers are obtained, also a dynamic analysis is presented. The position and displacement continued for the structural analysis, were developed by following a static analysis, to know the deformation that the structure links show when an external load is applied in the mechanism. As result, a prototype was manufactured with acrylonitrile butadiene styrene (ABS) using an additive manufacturing machine. additive manufacturing; finger exoskeleton; rehabilitation robotics; robot design and simulation; wearable device +
Footnote †: journal: Medical  
hand. An electric motor is used for actuation [4]. To reduce the load and the weight, in [5], a device is proposed based on linear electric actuators with a mechanism with two DOF for each finger which allows a maximum force of 10 N, a reduced vertical load (maximum 6 cm with respect to the back of the hand) and a weight of 0.5 kg for the whole device. [PERSON] et al. [6] created a thumb exoskeleton for the main purpose of rehabilitation of lost thumb functions and to add thumb opposition to the therapy process. The exoskeleton allows flexion/extension and abduction/adduction to work in combination to achieve circular cone-shaped opposition using a single active linear actuator and passive joints to transmit the motion through a four-bar linkage (redundant) mechanism. Additionally, the spread of soft-robotic applications has led to some preliminary examples of human exoskeleton systems based on elastomeric materials or fluid structures [7; 8]. The Hand Spring Operated Movement Enhancer (HandSOME) uses elastic cords as springs to assist with finger and thumb extension and provides an assistance profile that emulates torque versus extension angle profiles for passive movement [9]. Gloreha-Hand Robotic Rehabilitation is a wearable glove for the human hand. The glove is composed of one pneumatic actuator located on the upper side of the forearm and several elastic transmissions, which are moved by the actuator to properly transmit displacements, speed, and forces to one or more impaired fingers during a rehabilitation session [10]. As regards actuation systems, cable-driven solutions are widely employed for their implicit simplicity [11; 12; 13], while rigid actuator architectures (based on linear actuators or hydraulic ones) may have problems due to the associated weights and encumbrances [14; 15]. An interesting solution is described in [16], where the authors developed a HEXOSYS with a four-DOF mechanism (one actuated and three passive) for the finger that can apply a continuous force of 45 N with a total weight of 1 kg. The drawback of this solution is the high vertical load and the impossibility of applying this mechanism to all four fingers. Nevertheless, current solutions for single-DOF mechanisms are mainly related to assisting grasping gestures but with very simplified kinematics [17]. Concerning mechanisms, multi-phalanx or multi-degree-of-freedom (DOF) kinematic chains have been proposed [18; 19; 20; 21; 22; 23]. [PERSON] [24] describes an exoskeleton based on a three-DOF mechanism, with three electric motors, which are very powerful (flexo-extension with 5 N maximum force) and precise, but are very heavy and bulky (0.5 kg and maximum height concerning the back of the hand of 8 cm for a one-finger mechanism).