Locomotion Design And Evaluation Of Dynamic Tensegrity

Tensegrity systems is a class of special pin-jointed bar assemblies in which the discontinuous compression elements are surrounded by continuous tension elements,leading to a tension-integrity system.Due to the interaction effect between form and force,the tensegrity can be controlled by actuators and transferred between different states,and the tensegrity possesses more than one states is classified into dynamic tensegrity.The general dynamic tensegrity model is proposed to describes the state of tensegrity under arbitrary actuating strategy.The actuations are selected as variable,the geometric parameters are selected to define the position and configuration in arbitrary time,and the dynamic tensegrity model is expressed after the conditions and control objectives are given.The incremental procedure based on dynamic relaxation method and genetic algorithm is utilized in path tracking and strategy optimization respectively in the model.The locomotion gait of dynamic tensegrity including crawling gait and rolling gait is studied.The six-strut tensegrity is chosen as a typical model to search for the locomotion gait with the closed triangle and opened triangle contacting to ground respectively under different arrangement of payload.A series of basic locomotion gaits and actuating strategies are given after the optimization of arrangement and actuating length of actuators.For the rolling gait,the influence of actuation and payload is analyzed and the gait is classified according to the rotation time and rotation axis.The evaluation system of dynamic tensegrity is presented with a series of evaluation index.The deformability of dynamic tensegrity under actuators is described through controllable volume and the ability to carry a payload is estimated.The locomotion of six-strut dynamic tensegrity is analyzed from two aspects:for single gait,the distance,direction and speed of gait are focused on and for continuous locomotion,the ability of long-distance travel and obstacle crossing are focused.The stability and energy consumption are analyzed as well to give a comprehensive evaluation for six-strut dynamic tensegrity.The locomotion of dynamic tensegrity in slope is studied.On account of the change of position of mass center in slope,the dynamic tensegrity may maintain a form different from flat and results in different characteristics.The maximum gradient for dynamic tensegrity to stay static is analyzed and gradeability under basic locomotion gait obtained in flat terrain is tested.The climbing gait of six-strut dynamic tensegrity is searched to realize a climb in 10 degrees slope in different directions.The path planning of dynamic tensegrity is studied with two possible path planning method presented.The path based on basic gait simplifies the path planning process to the combination of gaits,thus realizing quick path tracking and path planning.The path based on free gaits describes the path under arbitrary actuating strategy.The unlimited property of actuating strategy provides possibility to search for a path under arbitrary situations and the feasibility of path based on free gaits is verified through the over-obstacle locomotion.The concept of dynamic tensegrity was verified through physical model experiment.A small-scale six-strut tensegrity model was manufactured with the compression elements replaced by miniature linear actuators.The crawling and rolling gaits of tensegrity model were tested,showing the capability of locomotion and the reliability of locomotion design.The long-distance travel through path based on basic gait was proved valid as well.This study has accomplished the locomotion design,path planning and evaluation of six-strut dynamic tensegrity,and provides a reference to the design process of a general dynamic tensegrity.