| Bionic legged robots have become research hotspot in the field of robotics due totheir excellent dynamic performance and strong adaptability in unknown environment.A number of typical legged robots prototypes have been built in recent years. However,the weakness of existing bionic robots is their large energy consumption and hugetouchdown impact because of the stiff actuation of the revolute joints, thus restrictingtheir application in high speed dynamic hopping locomotion. Therefore, studies onintroducing flexible elements to the revolute joint and its influence on the dynamiccharacteristics of robot hopping locomotion will make great contribution to reality.The thesis is supported by National Hi-tech Research and Development Program ofChina (863Program, Grant No.2011AA040701). Present research is focused on asimplified one-legged robot by introducing torsional spring into its hip joint, and aimsto reveal the influence of introduction of flexible elements on the dynamiccharacteristics of robot hopping motion by studying the passive and active control ofcompliant joint. The research is based on dynamical equations, Poincare map and fixedpoint theory.Firstly, the simplified dynamical planar model of one-legged robot with complianthip joint was established. Next, the dynamic differential equations of stance phase andflight phase were derived. Poincare map of one entire hopping cycle was built. Thenquasi-periodic solution was obtained based on fixed point searching under passivehopping motion condition, and its stability was also analyzed. Meanwhile, bycomparison with the dynamic characteristics of equivalent SLIP model of robot withstiff joint, the influence of introduced compliant joint on the stability of robot hoppingmotion under passive condition was evaluated.Secondly, active control was designed to compliant hip joint. Stable fixed pointssearching of the robot’s periodic hopping motion was conducted and their distributionmap was obtained. Then we focused on a typical fixed point and analyzed its stability.Energy consumption evaluation functions were established, and we studied the role oftorsional spring in energy transfer process by energy consumption analysis of the fixedpoint. In addition, varying the stiffness of torsional spring, drawing the relation map ofenergy consumption and torsional spring’s stiffness, by analysis and comparison, theinfluence law of varying torsional spring’s stiffness on the dynamic characteristic ofrobot hopping motion was discovered.Finally, the virtual prototype of one-legged robot was built in Adams with specialdesign in control strategy of start progress of robot. The active control method ofcompliant joint was modified based on the difference between simulation model and thetheory model. Next, the simulation of robots stable hopping motion was conducted on the co-simulation platform of Matlab and Adams. The results pointed out the role oftorsional spring in energy transfer process of robot hopping and proved the effectivenessof active control method and verified the correctness of theoretical analysis. |
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