Date of Award

Spring 2020

Document Type


Degree Name

Master of Science (MS)


Mechanical Engineering

First Advisor

Schimmels, Joseph

Second Advisor

Voglewede, Philip

Third Advisor

Juang, Shuguang


This thesis presents the designs and test results for two antagonistic, cable-driven, variable stiffness actuator designs. Each of these variable stiffness actuators is compact, has a large range of controllable stiffness, and limits the inertia at the robotic link it is controlling. Each design consists of a cable running through a set of three pulleys. Tension on the cable displaces a linear spring, which moves along a path designed to achieve quadratic spring behavior. One design uses a variable radius path to achieve the nonlinear elastic behavior while the other uses a fixed radius (lever) path.A quasi-static model of each mechanism was developed to assess the performance of each design in matching the desired nonlinear (quadratic) elastic behavior of the ideal system. Eight geometric parameters of each design were optimized to match the desired behavior. Prototypes of the optimized designs were built and tested to evaluate performance.While the results of the parametric optimization predicted that the variable radius design would more closely match the desired elastic behavior, the added complexity of this design resulted in inadequate performance. Test results for the fixed radius design matched the desired behavior well and ultimately proved to be better for achieving controllable linear stiffness at a robotic joint.

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