Phlexor: A Residual Force Controlled, Synergy-Based Hand Exoskeleton for Grasping Assistance

Abstract

As a result of stroke, millions across the United States struggle with limited upper extremity function, specifically limited hand dexterity. Hand exoskeletons are designed to improve and restore hand motor function as well as quality of life. However, providing robust and intuitive user control remains challenging due to reliability issues or limited applicability to daily life scenarios. Phlexor’s control method addresses these obstacles by using a force sensor placed within a button on the palm which utilizes the residual isometric grip force of the ring and little finger to actuate the remaining three fingers. Phlexor uses a differential mechanism consisting of a single bevel gear and three spur gears to power separate rack-and-pinions, stimulating the natural postural synergies of the hand and supporting multiple variations of grasps with a single servo motor. A spring-driven slider placed on the dorsal side of the hand allows the user to mechanically fix the thumb in three different positions, enabling them to create opposition when needed. To improve the user’s donning and doffing experience, Phlexor is designed to attach to the dorsal side of the hand using compliant clasps. The inexpensive design prioritizes a lightweight and compact profile on the hand and arm while simultaneously achieving consistent movement. Future studies look to validate the functionality of Phlexor to both restore the user’s ability to perform acts of daily living and rehabilitate natural biomechanical functionality.