Analysis and visualization of the contact force solution space for multilimbed mobile robots
Abstract
One of the inherent problems of multi-limbed mobile robotic systems is the problem of multi-contact force distribution; the contact forces and moments at the feet required to support it and those required by its tasks are indeterminate. A new computationally efficient method for describing and visualizing the solution space and generating an optimal solution for the contact force distribution for multi-limbed robots in three-dimensional space is presented. Specifically, two different cases are addressed where three elements (feet or cables) are in contact with the environment: the ‘one cable-two feet contact case’ and the ‘three feet contact case’. The two methods are similar in concept, but the ‘three feet contact case’ is more general and thus can also be used for the one cable-two feet contact case or for grasp planning for multi-fingered robotic hands. The optimal solution is found using a two-step approach: first finding the description of the entire solution space for the contact force distribution for a statically stable stance under friction constraints, and then choosing an optimal solution in this solution space which maximizes the objectives given by the chosen optimization criteria. This two-step approach will allow more options and freedom in choosing the final solution that not only satisfies the static equilibrium and friction constraints, but also can satisfy other special conditions under consideration at that instant. Describing the entire solution space first will give an intuitive visual map of how well the solution space is formed for the given conditions of the system, and choosing a solution in that space next will indicate where this solution is positioned in the solution space to give insight into the quality of the chosen solution and to provide robustness against disturbances. Two representation schemes, the ‘force space graph’ and the ‘solution volume representation’ are developed for describing the solution space and as a tool for choosing the optimal solution. The ‘margin against slip with contact point priority’ optimization method is developed for choosing the optimal solution, and ideas for other optimization criteria are discussed. Examples with discussions are presented to illustrate certain aspects of the method and to demonstrate how to handle special cases.
Degree
Ph.D.
Advisors
Cipra, Purdue University.
Subject Area
Mechanical engineering
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