Geometrical synthesis method and parametric optimization of galloping robot leg mechanism

Abstract

Subject of Research. The paper presents geometrical synthesis results of kinematic schemes for a femur and a whole leg mechanisms of a cheetah robot, which is able to jump in place and run at various speed. We substantiate the topology of mechanisms, describe their operation principles, characteristics and distinctive features, involving the controlled reconfiguration of mechanisms for changing the trajectory of the ground-contact point, and the use of flexible elements and links with variable length to ensure energy-efficient locomotion. Method. A structure scheme of the whole cheetah robot leg was obtained by attaching four movable links to the femur mechanism, imitating large and small tibial bones, metatarsus and sartorius muscle. The obtained structure was decomposed into three mechanism components: a “minitaur”, two-rocker four-bar lambda mechanism and a rocker-slider mechanism. The kinematic schemes of the above-mentioned mechanisms were synthesized by the method of extreme discrete positions with the result that the kinematic scheme of the whole leg with intermediate positions was obtained. The parametric optimization algorithm was described and the minitaur objective function was given using mathematical programming. Main Results. The kinematic scheme of the whole cheetah robot leg is obtained in the first approximation without taking into account the robot dynamics, location of flexible elements and their resonance necessary for the resonance behavior in order to achieve energy-efficient movement. Modeling results of the robot dynamics according to the synthesized scheme are given. Stable behavior is obtained both while jumping in place and running. Practical Relevance. The study is carried out for the development of an energy-efficient four-legged galloping cheetah robot performing energy recovery with the help of flexible elements. The synthesized kinematic scheme is applicable for detailed analyzes of dynamics, kinetostatics, energy recovery and losses upon impact with the ground surface, and for the robot prototype design.