This thesis presents the design and control of a cable-actuated mobile snake robot. The goal of this research is to reduce the size of snake robots and improve their locomotive efficiency by simultaneously actuating groups of links to fit optimized curvature profiles. The basic functional unit of the snake is a four-link, single degree of freedom module that bends using an antagonistic cable-routing scheme. Elastic elements in series with the cables and the coupled nature of the mechanism allow each module to detect and automatically respond to obstacles. The mechanical and electrical designs of the bending module are presented, with emphasis on the cable-routing scheme, key optimizations, and the use of series elastic actuation. An approximate expression for the propulsive force generated by a snake as a function of its articulation (i.e. the number of links it contains divided by its body length) is derived and a closed-form approximation for the optimal phase offset between joints to maximize the speed of a snake is obtained by simplifying a previous result. A simplified model of serpentine locomotion that considers the forces acting on a single link as it traverses a sinusoid is presented and compared to a detailed multibody dynamic model. Control strategies for snake robots with coupled joints are developed, along with a feedback linearization of the joint dynamics. Experimental studies of force control, locomotion, and adaptation to obstacles using a fully integrated prototype are presented and compared with simulated results. / MS / This thesis presents the development of a cable-driven snake robot, with the goal of decreasing the size and mass of these devices and increasing their efficiency. Snake robots have potential applications in exploration and manipulation in cluttered or confined environments. The cable transmission system presented in this thesis allows for multiple links in a snake robot to be actuated simultaneously, allowing for increased articulation in a robot of fixed size and mass. Serpentine locomotion, in which a sinusoidal wave is propagated down the robot’s length, is a silent and energy-efficient mode of transportation, widely employed in the animal kingdom. Snake robots achieve serpentine locomotion by driving their joints sinusoidally, with adjacent joints moving asynchronously, with the time lag between joints set by the value of a phase offset. An expression for the optimal phase offset to maximize forward velocity is derived by simplifying a previous result from the literature. An approximation of the dynamics of serpentine locomotion for a snake traveling at constant velocity is then derived, and this model is used to obtain an approximate limiting expression for the propulsive force generated per link as a function of the number of links in the snake. Methods to control a snake composed of coupled linkages are explored and the mechatronic design of a fully integrated prototype is presented. Experiments on force control, locomotion and turning, and detection and interaction with obstacles using the prototype are then described.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/91983 |
| Date | 30 January 2018 |
| Creators | Racioppo, Peter Charles |
| Contributors | Mechanical Engineering, Ben-Tzvi, Pinhas, Wicks, Alfred L., Zuo, Lei |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Detected Language | English |
| Type | Thesis |
| Format | ETD, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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