Limb sensorimotor function plays an important role in activities of daily living (ADLs) and quality of life. Spinal cord dysfunctions, such as cervical spondylotic myelopathy (CSM), often affect limb function and limit independence. In this paper, we apply technologies from the emerging field of soft robotics to develop Soft Robotic 3rd Arms (SR3As) that branch out of the body — thus providing an artificial limb that enables effective execution of ADLs for CSM patients and the like.
Soft robotics is a fairly recent addition to the field of robotics. Differing from traditional, “hard”, robotics, soft robotics are made of flexible materials such as silicone rather than stiff materials such as metals. One such soft robotic actuator is the fiber-reinforced actuator (FRA). Fabricated utilizing a combination of silicone bladder(s) and inextensible materials, these actuators are able to perform one of various motions through changes of pressure .
Supernumerary limbs (3rd arms), in contrast, are extra robotic limbs that can function cooperatively or independently of the user’s own limbs. These differ from exoskeletal robotics, as they are not fixated to the user’s limb to augment strength, but rather are placed elsewhere on the body to assist in tasks that would otherwise require multiple people. Examples of such devices include MIT/Boeing’s supernumerary arms to assist in the assembly of aircraft fuselage  or the supernumerary hand Softhand .
Combining these two concepts, an articulate SR3A was created (Fig. 1). By replacing traditional actuators with soft actuators, the limb is not only lighter, but it also better replicates the equivalent human limb. In addition to these benefits, the SR3A would also need to be less expensive to fabricate and actuate than an arm using rigid body components. This paper presents the design of a proof-of-concept prototype of a SR3A utilizing soft robotic actuators that could be used to assist individuals with hand impairments perform ADLs.