Numerical and Experimental Studies on Dynamic Interactions of Robot Appendages with Granular Media

Abstract

Terramechanics plays an important role in the design and control of robots moving on granular surfaces. Traction capabilities, slippage, and sinkage of a robot are governed by the interaction of a robot's appendage (such as wheel, track or leg) with the operating terrain and how the terrain motion happens with respect to the appendage during such an interaction. In this dissertation work, dynamics of robot appendages interaction with granular media is explored through numerical and experimental studies. A two dimensional (2D) numerical model, constructed using the Discrete Element Method (DEM), is adapted to simulate lugged wheel interaction with granular media. Parametric studies on wheel performance are conducted for two different control schemes, namely, a slip-based control scheme and an angular velocity-based wheel control scheme. Furthermore, the soil flow pattern under the wheel is studied by examining the force distribution and evolution of force networks during the course of wheel travel.An experimental setup is designed to study the particle motion and force networks inside the media during dynamic forcing. Two different designs of robot appendages, a lugged and a single actuator pendulum are investigated. High speed imaging of photo-elastic particles under polarized light is used to visualize the force distributions inside the media. Qualitative behavior of force chains/networks evolution during interaction with the lugged wheel and pendulum is presented. In addition, quantitative measures of the interaction between appendage and granular media, such as, the driving torque values, appendage velocity, and particle motion are inferred from the experimental findings. Based on this work, insights can be gained into the design influences of robot appendages on performance and further understanding can be obtained on the behavior of granular media across different length scales. Furthermore, the numerical and experimental techniques developed and outcomes of this dissertation can serve as an important foundation for optimal design and control of different robot appendages interacting with deformable surfaces.