Modeling and implementation of solder-activated joints for single actuator, centimeter-scale robotic mechanisms

Abstract

This thesis explains when, and why, solder-based phase change materials (PCMs) are best-suited as a means to modify a robotic mechanism's kinematic and elastomechanic behavior. The preceding refers to mechanisms that possess joints which may be thermally locked and unlocked via a material phase change within the joint. Different combinations of locked and unlocked joints yield different one-DOF mechanisms states. A single actuator is used to control motion allowed by the different states. By reducing the number of required actuators, solderlocking joints enable the creation of compliant centimeter-scale mechanisms that can perform a multiplicity of tasks. Herein, this thesis presents physics-based design insights that provide understanding of how solder-based material properties and joint design dominate joint performance characteristics. First order models are used to demonstrate selection of suitable PCMs and how to set initial joint geometry prior to fine tuning via detailed FEA models and experiments. The first order models result in order-of-magnitude estimates of the locking and unlocking times for the joints. The insights and models are discussed in the context of two case studies. Squishbot1 is a crawling robot that uses a single spooler motor and three solder-locking joints to crawl and steer. Squishbot 1 is able to reconfigure its joints in approximately 10 seconds. SquishTendons utilizes solder-locking joints to actuate a compliant structure with a single motor. The second robot used the complete set of models and rules to improve on the performance of Squishbotl. SquishTendons can unlock and lock its joints in less than 6 seconds.