Development of an Assistive Ankle-Foot Exoskeleton with Sensorized Silicone-Based Insole

Abstract Millions of people with disabilities, the elderly, and individuals suffering from physical deformities rely on assistive devices to perform basic actions and movements. With the increasing number of these individuals, the lack of available medical equipment/assistive personnel, and the size, bulkiness, and cost of assistive devices found in rehabilitation centers, there has been a growing interest in the research for lighter, portable, and cost-effective personal external assistive devices. In this paper, a new prototype of an ankle-foot exoskeleton was engineered with low-cost printed material that maintains structural integrity while providing appropriate comfort and support for the wearer. This ankle-foot exoskeleton was fabricated using thermoplastic polyurethane (TPU) and polylactic acid (PLA), common materials used for three-dimensional printing. The printed pieces were combined with zinc-nickel hinge joints to create a one-degree-of-freedom (DOF) support system. Finite element analysis on both fabricated parts indicates an average safety factor of 4 at applied loads of 700 N and 100 N to the foot and calf sections respectively. A pressure insole system consisting of a silicone-based pressure mold, force-sensitive resistors, and a microcontroller circuit was developed to measure foot pressure experienced during standing and stepping motion. This exoskeleton was also subjected to actuation tests via an external torque motor to obtain ankle trajectory profiles at various walking speeds.