Research On Obstacle-Crossing Posture And Control Method Of Biped Robot Based On Ducted-fan Propeller

This paper mainly studied on the control method and posture optimization of biped robot overstepping large-size obstacles with help of ducted-fan propeller.Because biped robots are unstable systems with multiple DoFs(degrees of freedom)and non-linear constraints,it is a challenging task to control biped robots to complete the task of stepping large-size obstacles.The difficulty lies in the fact that when a biped robot crosses a large-size obstacle,the CoM(center of mass)of the biped robot needs to move forward largely so that the robot has more workspace to step over the obstacle.However,this collides with the stable constraints of biped robots.Moreover,there is no upper body to balance the overturning moments from gravity of the robot,which will be more prone to instability and fall.Even though there are some chances to finish the stepping task,the size of obstacles is limited largely.To overcome the contradiction between the biped robot crossing large size obstacles and maintaining the stability of the robot,this paper proposes a method that the biped robot can not only cross large size obstacles,but also it can surmount the problem of balance and stability in the crossing process.The method is utilizing the extra thrust provided by the external ducted fan propeller.In order to increase the force arm acting on the supporting foot and make the most use of the thrust,the ducted fan propeller is fixed at the front end of each foot.Through simplifying the 3-D biped robot to a planar redundant degree-of-freedom robot by means of robot's symmetry when crossing large-scale obstacles,its flexibility can be effectively enhanced.The quasi-static motion mode can effectively reduce the vibration and impact from the ground.The whole stepping process adopts stepping-sliding gaits,which can further expand the range of large size obstacles that biped robots can overstep.Before stepping,multiple curves as the path are planned for the biped robot followed by the stepping foot.Combining the quasi-static force balance constraints,kinematics constraints,obstacle avoidance constraints and parallel constraints,the surmountable boundary model and the minimum extra thrust posture optimization model can be established.Finally,the boundary that can be stepped,as well as variation of joints angles and thrusts consistent with stepping postures can be solved.The tests of the crossing results of two kinds of obstacles with different sizes are tested on the simulation platform and the prototype.The results show that it is effective that the proposed scheme of large-size obstacles surmounting by biped robot with ducted fan propeller.The stepping distance of biped robot is improved from 80% of the length of its legs at first to 97%,and it also can step a wide ditch with a height difference of 100 mm between the two sides of ditches.Finally,the biped robot can overstep 520 mm a wide horizontal ditch as fast as possible,in 8 seconds,reaching 113% of its leg length.At the same time,it also explored a large-size protruding obstacle,and the robot successfully avoided the collision between the biped robot's links and the obstacle,and completing the stepping task.