A Spring-Loaded Mechanism with Near-Linear Stiffness in Six Degrees of Freedom

Abstract Although compliance is important for many robotic applications like human-robot interaction, adding this compliance in all 6 degrees of freedom (DoF) is technically challenging. Compliance can be introduced through simple elastic elements or through more complex compliant devices. Simple elastic elements (such as springs) are designed to behave in a single DoF. To achieve compliance in 6 DoF, many elastic elements or a compliant device (such as a remote center of rotation device) must be used. Creating 6-DoF compliance with multiple elastic elements is often not desirable, and existing 6-DoF compliant devices are complex, non-linear, and have a small range of motion. This paper expands on a previously proposed computer model for a new spring-loaded mechanism that exhibits near-linear 6-DoF compliance. This paper extends the computational analysis for this class of spring-loaded mechanisms. The effects of the number of samples, the sampled workspace, the number of springs, and the parameter inaccuracies on the predicted 6-DoF stiffness were investigated. Furthermore, a physical experiment was conducted to validate the computer model where a prototype was realized. This mechanism exhibits near-linear behavior over its entire workspace with as few as three springs. The model is robust to parameter perturbations, where for almost all parameters, 1% error of a parameter will yield <1% reduction in predicted accuracy. The computer model can accurately predict the stiffness of the prototype (<11% error), thereby validating the computational model.