# A Low-Cost Soft Robotic Hand Exoskeleton for Use in Therapy of Limited Hand-Motor Function
###### Abstract
[33] incorporate a rigid exoskeleton to constrain joint motion, which is customizable using sliding linkages between joints and oversized rings to secure the structure to the finger, this design incorporates many of our desired features, but the use of a rigid exoskeleton adds unnecessary bulk and complicates the design of the system. [PERSON] et al. [9] focused their research on the development of a jointless structure to facilitate the implementation of their tendon-driven actuation method. The described jointless structure passes the tendons through channels sewn into the palmar side of a soft glove, while a semi-rigid material provides a passive extension force. The jointless design and tendon-driven method of actuation corresponds closely to the method we envisioned for our design. The rigid serial link method utilized in the Hand of Hope and Festo Exohand discussed earlier provides an excellent kinematic response and repeatability, but this actuation method requires hardware much too complicated for the end user to assemble and customize on their own [30; 31]. Tendon-driven actuation greatly simplifies the mechanical structure and thus is our chosen method of actuation. The previously presented designs that use this method, while simple in mechanical design, incorporate complicated custom electronics and control systems designed solely for academic pursuits. Our design aims to simplify the mechanical structure, electronics and control system to provide a system that can be easily assembled, customized and controlled by the end user. The [PERSON] group [35] present a soft pneumatic glove for hand rehabilitation fabricated using soft robotic technology. The soft actuators are made of elastomeric materials with integrated channels that function as pneumatic networks (PneuNets) which can be driven by air pressurization to produce bending motions in conformity with human fingers. The PneuNets approach to air-driven actuation is an alternative to fluidic McKibben actuators, which are compliant actuators based around a rubber tube surrounded by a braided shell. The group successfully shows that PneuNets can be embedded into a neoprene glove to enable a similar therapy modality as our approach, the difference being that the fabrication method they present is not easily accessible by a layperson and that the resulting glove would have to be tethered to a bulky air compression system. The [PERSON] group [36] presents technologies for embedding sensors in soft robotic gloves, which would augment the capabilities of our design. Their work presents methods for assembling the soft robotic glove from modular and individually fabricated pressure and strain sensors. While the addition of strain sensors on the upper side of each finger and pressure sensors to the underside would provide a plethora of information to the control system and indirectly the user, the fabrication technology of these sensors is beyond the capabilities of a layperson, since it includes making silicone casts and precise fabrication and embedding of the sensors in the soft robotic glove. [PERSON] and [PERSON] define the direction of soft robotics [37] in regards to their design, fabrication and control. Soft robotics vary widely in their design and fabrication methods, from fully compliant, to semi-soft, to a mix of hard-link and soft materials, manufactured in a variety of ways, from molds to 3D-printing; actuation from the most common pneumatic artificial muscles, to fluidic elastomer actuators, to a mix of hard and soft tendon-driven linkages; electronics from discrete to soft and stretchable; and computation and control from simple to advanced machine-learning-based models. The advent of 3D printers, makerspaces and the open-source initiative has put the means of manufacturing into the hands of the average person. Fundamentally, most medical devices and rehabilitation aides are sold through the physical therapy practice or obtained through a medical supplier, usually at great cost to the patient.