# A Low-Cost Soft Robotic Hand Exoskeleton for Use in Therapy of Limited Hand-Motor Function
###### Abstract  
We present the design and validation of a low-cost, customizable and 3D-printed anthropomorphic soft robotic hand exoskeleton for rehabilitation of hand injuries using remotely administered physical therapy regimens. The design builds upon previous work done on cable actuated exoskeleton designs by implementing the same kinematic functionality, but with the focus shifted to ease of assembly and cost effectiveness as to allow patients and physicians to manufacture and assemble the hardware necessary to implement treatment. The exoskeleton was constructed solely from 3D-printed and widely available off-the-shelf components. Control of the actuators was realized using an Arduino microcontroller, with a custom-designed shield to facilitate ease of wiring. Tests were conducted to verify that the range of motion of the digits and the forces exerted at the fingertip coincided with those of a healthy human hand. soft; robotic; hand; exoskeleton; therapy; patients; stroke +
Footnote †: journal: Appliedto actively control each degree of freedom individually, leading researchers in the field to focus on under-actuated mechanisms. These under-actuated mechanisms must be connected to a structure that is compact and light enough to fit on the human hand, while still allowing for natural motion of the fingers. [PERSON] et.al. [23] define six methods for the construction of both rigid and non-rigid structures for robotic finger manipulation and provide details about common actuation systems seen in the field of hand rehabilitation robotics. The most common method of actuation involves the use of an under-actuated serial link superstructure fixed to a point on either the middle or distal phalange to control the flexion of the finger. While rigid-link manipulators provide excellent control and repeatability of motion, they are mechanically complex and require customization to align the manipulator joints to the finger joints. Two methods are shown where no rigid-link mechanical structure is required to facilitate actuation; tendon-driven mechanisms and flexible actuators. The Hand of Hope [30] and Festo Exohand [31] are two commercially available systems that utilize serial link manipulators to actuate fingers. The Hand of Hope was one of the first commercially available robotic hand rehabilitation mechanisms. While the Hand of Hope is a mechanically sound device, the limited range of motion in the metacarpophalangeal (MCP) and proximal interphalangeal (PIP) joints and the non-customizable nature of the design leave room for improvement. The Festo Exo-Hand [31] shows much improvement in these areas, due to user-specific dimensioning using 3D scanners and a laser sintering process. Improvement is also seen in the range of motion as well as the number of degrees of freedom controlled by the device. This improvement is achieved using eight proprietary pneumatic actuators. These improvements come at a cost. The user must be linked to a compressed air source through a bulky umbilical of pneumatic hoses, thus restricting mobility. The customization of each device, while favorable, is very expensive in both time and cost. The [PERSON] group [32] developed a robotic exoskeleton using custom-designed, naturally compliant soft actuators. This design utilizes custom molded, hydraulically controlled actuators created from a soft silicone rubber compound reinforced with mesh. The design is very low profile and light weight, weighing in at 285 g. However, the hydraulic pump system, weighing over 3 kg, must be attached to the patient for untethered use. The customizability of the exoskeleton, while desirable, poses the same time and cost issues as the serial link devices presented earlier. Academic research groups such as [PERSON] et al. [33] and [PERSON] et al. [34] have focused on developing tendon-driven systems that makes use of power-actuated tendons for adduction and a passive spring mechanism for abduction. [PERSON] et al.