Design and Verification of a Compact Variable Stiffness Actuator With a Very Large Range of Stiffness
Date of Award
Master of Science (MS)
Schimmels, Joseph M.
Voglewede, Philip A.
Current conventional robots require high stiffness joints to provide absolute positioning accuracy in free space which also causes problems when operating in constrained space. To circumvent these problems, Variable Stiffness Actuators (VSAs) can be used to vary their stiffness to suit the task being performed. A new VSA was designed to provide a very large range of stiffness in a compact size. The Arched Flexure VSA uses a cantilevered beam acting as the flexure with a variable point of contact. It allows the joint to have continuous variable stiffness, have zero stiffness for a small range of motion, and rapid stiffness change. Finite element analysis was used to evaluate flexture stiffness. The flexure geometry was optimized for two different objectives. In the first case, the flexture was optimized for maximum stiffness range. This optimization resulted in a stiffness ratio of 1200. In the second case, the flexture was optimized for both maximum stiffness range and constant relative sensitivity. This optimization resulted in a stiffness ratio of 100. A small proof-of-concept VSA actuator based on the constant relative sensitivity alternative was designed, built, and tested. The VSA provided a stiffness ratio of 55, a little more than half of that expected for the flexure alone. The VSA weighed 1.45 pounds and fits within a 4.5 inch by 2 inch by 5 inch volume. The VSA provides the anticipated free joint range for zero stiffness and provides 360 degrees of rotation. It changes from minimum to maximum stiffness in 0.12 seconds.