Lab of Professor Keith Buffinton
In contrast to rigid-body robots used in manufacturing and transportation, soft-robotic systems allow for automation in delicate environments where human safety is of concern. Within the field of soft-robotics, pneumatically-controlled Fiber Reinforced Elastomeric Enclosures (FREEs) have emerged as one possible solution to the lack of compliant actuators available commercially. FREEs produced from thin-walled latex tubes and helically wound cotton fibers exhibit elongation, rotation, expansion, and off-axis bending when pressurized. Decoupled, these motions are reasonably well understood. However, the dynamic response, which is crucial to understanding the coupling between certain motions, is largely unexplored.
Through experimentation and mathematical modeling, this project has focused on altering material properties such as length, thickness, mass, and winding angle to characterize the dynamic properties of a FREE. The natural frequency, log decrement, and damping ratio are crucial properties to the creation of a realistic model to explain the motion of a FREE as it performs motions within a workspace. These tests have largely shown that a FREE can be modeled as spring-mass-damper system with rotational natural frequencies inversely related to mass moment of inertia.
Following the dynamic response research, a comprehensive mapping of the workspace has been performed using a custom two-camera imaging system that records the pressures required to reach various points in the workspace. Using vision and pressure data, a control system that allows for real-time user control via intuitive input, tracking with reduced vibration, and adjustment for variances in the physical characteristics of FREEs has been developed. Given the current state of manufacturing tolerances and the material degradation of FREEs over prolonged pressure excitation, having a robust control system is paramount to demonstrating the practicality of FREEs in commercial products.
This research was performed in conjunction with Bucknell’s Compliant Materials and Robotics Systems Laboratory led by Dr. Keith Buffinton, Professor of Mechanical Engineering and the Robotic and Motion Laboratory at the University of Michigan.
January 2019 – Present