Research On Motion Planning Across Barriers For Bionic Frog Robot

Legged jumping robot shows better mobility,dexterity and ability of jumping across obstacle,which makes it suitable to achieve the task such as spying,detecting,rescue,anti-terror and so on instead of human in unstructured environment,so it is a frontier task in robot field.Frog's jumping movement has the characteristic of strong burst and good jumping performance,therefore,frog is selected as bionic prototype to design bionic frog robot without elastic actuators.Its take-off process is a nonlinear,multivariable,underactuated,strongly coupled kinematics and dynamics process.Due to actuator constraints limitation,the study of given takes-off mission is challenging for control theory and motion planning.Considering the passive relationship between the robot's foot and the ground,in order to improve versatility of jumping motion,some key problems are studied on motion and force transmission performance,take-off posture optimization,take-off mission planning and control,obstacle avoidance planning and attitude adjustment,the touchdown impact and stability.Simulations have also been performed to test the methods presented in the dissertation.The discussed contents are listed as follows:(1)Modeling and force transmission performance of bionic frog robotBased on motion bionic principle,according to the characteristics of frog's body structure and jumping movement,a mechanism model of bionic frog robot is presented by simplifying joints and bone structure of frog.In view of passive constraint between the robot foot and the ground in the take-off stage,bionic frog robot can be regarded as an under-actuated redundant manipulator system,and the mapping from the joint driving torque to the acceleration of center of mass is established,and an improved dynamic directional manipulability is presented,which is a measure of transmission performance between force and motion for bionic frog robot in the take-off stage.(2)Optimization of initial take-off postureCombined with the driving constraints and the take-off dynamics constraint conditions,an improved particle swarm optimization algorithm is presented.From the perspective of improving the take-off performance,the take-off posture is optimized by making the velocity of center of mass in the take-off moment and energy consumption during take-off stage as the objective function.The excessive joint torque amplitude problem caused by the improvement of the acceleration performance is solved and a reference trajectory is provided for mission space planning of the take-off process.(3)Workspace Planning and Control of take-off stageThe motion planning problem is explored on bionic frog robot with a given take-off task.According to the requirement of mission space in take-off phase,the trajectory planning in workspace is planned through the variable quintic polynomial.By partial feedback linearization,the inertia coupling between active and passive joints is disposed,and the workspace control strategy is proposed.Furthermore,based on reaching law,the sliding mode controller is designed to track the desired trajectory.(4)Planning of toe across obstacle and posture adjustment of flight stageIn order to improve the terrain adapting ability of bionic frog robot,a motion planning method on toe across obstacle and posture adjustment is presented in flight stage.The method firstly develops the workspace biased RRT algorithm,and an initial planning of the toe movement of jumping over obstacle and body posture adjustment of flight stage is achieved.Then considering the initial planning results as route points,a cubic spline optimization method is proposed to achieve a smooth and continuous toe trajectory,which,in the meanwhile,meets the constraints.Finally,based on the principle of conservation of angular momentum and Resolved Motion Rate Control,a predictor-corrector control algorithm is proposed to achieve continuous trajectory tracking in terms of speed in the workspace.(5)Analysis of touchdown impact and stabilityConsidering the compliant character between the frog's foot and the ground,the frog's forefoot is simulated to a uniform flexible beam.Based on the Hertz contact theory and nonlinear damping theory,a continuous contact-collision model is established between foot and the ground,and then a rigid-flexible coupling dynamic equation of the robot system is built through the assumed mode and Lagrange method.The basic conditions of touchdown stability of bionic frog robot are given,and a discrimination method is made to analyze the impact of parameters of initial conditions on touchdown stability.The main contributions of this dissertation consist in mechanism analysis,mechanical properties,workspace planning of take-off stage,planning across obstacle,touchdown stability conditions and analytical methods of jumping robot and analysis of the conditions of touchdown stability,which are significant for the study of jumping robot,providing reference value both in theory and application.