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Repeated lifting tasks are often required of industrial workers. Such repetitive loading of workers’ arms throughout the workday can lead to injury and fatigue. This paper details the development and prototyping of a wearable soft robotic device to augment a worker’s arms by sensing and mimicking the contractions of their arm muscles. The device shares lifting loads with the user’s muscles to increase their lifting capacity, thereby preventing injury and reducing fatigue. The human arm contains many muscles that coordinate to produce movement. However, as a simplified proof of concept, this project developed a prototype to augment just the biceps brachii muscle since it is the primary pulling muscle used in lifting movements. Key components of the prototype include a soft robotic actuator analogous to the biceps, a control system for the actuator, and a method of attaching the actuator to the user’s arm. The McKibben-inspired pneumatic muscle was chosen as the soft actuator of the prototype. The Electromyography (EMG) and pressure sensors are used to inform a hybrid control algorithm combining PID and model-based control methods. The method and results of the design and preliminary feasibility testing of the pneumatic muscle, the controlling algorithm, and the overall prototype are discussed in this paper. Based on these results, a wearable EMG controlled soft robotic arm augmentation could feasibly increase the endurance of industrial workers performing repetitive lifting tasks.

This paper presents the design and development of a pneumatic soft-and-rigid hybrid actuator system that consists of half-bellow shaped soft sections in-between block shape rigid sections. The hybrid actuator architecture allows for selective actuation of each soft section (acting as a joint) with precise control over its bending motion. The soft half-bellow section is designed as a series of hollow ridges extending straight to a flat base. This geometry provides forward and backward bending motion when subjected to positive and negative pressure, respectively. Bending occurs as the ridges of the soft section expand and contract more than the flat base due to pressure variations. The rigid sections serve as connections between soft actuator sections and enhance force transfer. As a case study, a hybrid actuator system was designed as a soft robotic digit with three soft joints and four rigid connecting sections. Finite element analysis was performed to evaluate the design parameters such as number of ridges and materials for the robotic finger. The joints (from proximal to distal) were designed to have four, three, and two ridges, respectively, to generate the desired range of angular motion. Fabrication of the finger was done with silicone rubber RTV-4234-T4 and PMC polyurethane rubber using a combination of compression molding and overmolding processes. The angular and translational displacements of the robotic finger were experimentally and numerically evaluated at different pressures. The trajectory of the fingertip is comparable to those reported in literature for continuous soft actuators with a similar length. The significance of this actuator system is that both range of angular and translational motions are achieved at low pressure, less than 70kPa, as opposed to reported pressures of greater than 100kPa. The presented results show the great potential of the soft robotic finger for use in robotic, rehabilitation, and assistive device applications.Copyright © 2015 by ASME