Study On The Designing And Actuating Behaviour Of Bistable Structures Based On Lateral Buckled Beams

Bistability is often observed in nature(e.g.,fast snapping to closure of Venus flytrap)and the life(e.g.,hair clippers).Recently,harnessing bistability in different structures and materials has attracted growing interest for high-performance actuators and robots.They have demonstrated broad and unique applications in high-speed locomotion,fast grasping,shape reconfiguration,and etc.The advantages of selecting bistable structures to design high-performance actuators and robots are as follows:firstly,due to the sudden release of stored strain energy,bistability enables both a fast movement and an amplified force output when snapping from one stable shape to the other distinct stable shape.Secondly,bistable structures do not need consuming additional energy to matain the deformed shape,providing an energy-efficient actuation mechanism.Thirdly,bistablility can largely enrich the deformed configurations.When connecting n bistable units in series or parallel or bybrid,it will form a multistable structures with a maximum number of 2~n different stable configurations,which can be reconfigurabed individually or combinatorically under appropriate actuation.The constrained one-dimensional buckling beam is the simplest bistable unit.The multistable structures designed by it have the advantages of strong loading bearing capacity and various shapes.In this thesis,based on analysizing the buckling deformations and snapping behavior of thin-walled beams,the bistable characteristics of the lateral buckled beams are studied.By adopting motor and pneumatic drving,the robots with motion behavior and gripper with operating capability are desined.The main works are listed below.The bistable lateral buckled beams are designed based on the lateral buckled mechanism.The equilibrium equations of the lateral buckling deformation are built,and solved by perturbation method.The theoretical model of the stable configurations of the bistable beams is obtained.With the combination of finite element and experimental methods,the applicability and limitations of the theoretical model are verified.In addition,the influences of beam length,beam width,beams thickness,distances and included angle between two beams on the displacement components and twisted angle are investigated,providing design reference for the reconfigurable structures.The snapping behavior of the bistable lateral buckled beams is studied.Based on modal superposition method,the energy equations are builed and solved by Lagrange method.The theoretical model predicts the snap-through behavior of bistable beams is obtained.Combination of the finite element and experimental methods,the influences of beam length,beam width,beams thickness,distances and included angle between two beams on the snap-through beahavior of the bistable buckled beam are investigated.The expressions of maximum force and moment versus beam length,beam width,beam thickness and distance between two beams are obtained through curve fitting,providing the design reference for the bistable acuator.According to the characteristics of the bistable beams’stable configurations,tow rows of buckled beams are assemebled in three methods to design the multistable structures,which reconfigurable shapes can be guided by displacements.The lateral buckling deformations of the two rows of beams are investigated through the theoretical method,which can be deduced from the theoretical model of one row of buckled beams.The experimental set-up is built to test the bearing capacity of the two rows of buckled beams with different stable shapes.The two rows of beams with strong shape adaptability and high bearing capacity are selected to design the crawling robot.Through actuating two linear motors in assembled in the robot,three modes of motion are investigated,including crawing in a flate road,crawing in a road with obstacle and crawing in a road with limited height.Through actuating one linear motor,a gripper is designed.Its capacity of grabing objects with different shapes,sizes and weights is studied.According to the characteristics of the bistable beams’snap-through behavior,the driving skin is designed to pack the lateal buckled beams.To test the performance of the bistable actuator,the pneumatic system is built.The influence of the inflatable pockets’s size and position on the actuated volume,dynamic force response and displacement are investigated through experiments.The actuator with mimnum actuated volume,maximum dynamic force response and steady displacements is selected to design the quardeped robot.The independent deformations of the four bistable actuators are controlled through pneumatic method,leading to seven gaits of the quardeped robot.The two reciprocating motions are investigated,including the linear galloping and turing galloping.