A compact, compliant, and biomimetic robotic assistive glove driven by twisted string actuators

It is desirable but difficult to develop wearable robotic devices that have a compact form factor, sufficient range of motion to perform activities of daily living and produce enough force to allow for the manipulation of the environment and objects. Conventional actuation approaches produce high force and power output but require external pressure sources or are heavy and bulky. Twisted string actuators produce high force amplification from low torque motors and require no complicated appendages, making them attractive for wearable robotic devices. However, studies that quantify the performance of twisted string actuators to conventional spooled-motor configuration are lacking. Further, it is difficult to implement bi-directional drive using twisted string actuators without making the system more complicated. In this paper, an in-depth comparison of twisted string actuators to spooled-motor configuration is presented. In addition, a robotic assistive device that leverages the advantages of twisted string actuators is presented. Supercoiled polymer strings are used in the device for both monitoring the position change through resistance changes and simultaneously provide passive force for the glove to return to neutral position. Fingertip force of more than 7 N is achieved with the glove that weighs 186 grams including the electronics. Further, picking everyday objects is demonstrated.