With the growing aging population, there is an increasing demand and opportunity to develop exoskeletons, which are typically designed for military or industrial use, to be used on a daily basis to provide power assistance. Such exoskeletons could be used by the physically impaired and injured, in addition to the elderly.
This report describes the design of a power-assist exoskeleton specifically for the pronation and supination motion of the forearm. The exoskeleton is controlled by two push-button sensors to indicate the direction of rotation, which is controlled by the user at all times. As a safety precaution, visual feedback was implemented to confirm the user’s inputs were received by the exoskeleton and that the robot is actuating. A stepper motor, whose torque is transferred to the system using a bidirectional winch system, is used such that the exoskeleton is able to output such holding torques to lock the position of the arm. The mechanical structure is composed of various PVC and ABS coupling hubs, which form a stationary and rotating unit. The exoskeleton is fixed onto the user’s forearm through a blood pressure cuff, and torque is transferred from the motor to the user’s wrist through a custom-carved Styrofoam wrist cuff.
From testing, the average running torque of the system ranged from 5.24 Nm to 9.17 Nm for motor speeds from 60 rpm to 45 rpm, respectively, which confirmed that decreasing motor speeds increased running torque. The amount of holding torque could not be quantified because the testing setup was unable to produce sufficient loads (>55Nm) to move the system out of its fixed position. However, when in “idle”, the system still produced a holding torque of 30 Nm, suggesting a significant source of torque transfer loss in the system.
The exoskeleton was worn by a user and tested for comfort, usability and overall functionality. While there were a few sources of discomfort that were expected, the robot was able to actuate the proper motions for the user and provide powered assistance.
Overall, the system was able to pronate, supinate and hold the user’s forearm as controlled, demonstrating that the exoskeleton successfully provided powered-assistance.
Ngai, Michelle, "Design of a Forearm Exoskeleton for Supination/Pronation Assistance in Daily Activities" (2010). EE 4BI6 Electrical Engineering Biomedical Capstones. Paper 53.