Configuration Design And Motion Planning Of A 3-UPU Parallel Hexapod Robot For Long Heavy Object Cooperative Handling

Long and heavy objects such as steel pipes,gun bodies,telegraph poles,and felled trees are often heavy.In narrow and rough terrain environments such as underground spaces,municipal tunnels,and dense forests,that cannot be accessed by lifting devices,manual handling is currently the main method,with two or more people lifting or shouldering,and even some heavy objects cannot be moved by manpower.This paper proposes a hexapod robot based on a 3-UPU parallel mechanism.Two identical 3-UPU parallel hexapod robots can simulate a “two person lifting heavy object scenario” to replace manual collaborative handling these long heavy objects.It can be applied to a variety of complex terrains,such as narrow and rough terrain,potholed terrain.The main research contents of this paper are as follows:Firstly,a three platform 3-UPU parallel hexapod robot with two groups of 3-UPU parallel mechanisms as its body is proposed,which can not only make full use of the advantages of large load capacity of the parallel mechanism,but also adapt to narrow,rough and complex terrain,and has flexible steering.Different from the current foottype robot with the leg structure as the parallel mechanism,this three platform hexapod robot with the parallel mechanism as the body and relying on the mutual staggered motion of the moving platform and the static platform of two groups of parallel mechanisms can reduce the number of driving parts and rods to simplify the structure.The degrees of freedom of 3-UPU parallel mechanism are calculated based on screw theory to satisfy the motion requirements of the hexapod robot body to realize threedimensional translations in three directions within the space range.The overall structure of the hexapod robot is designed,including the body structure,heavy object clamping device,and leg structure,etc.The walking,turning and obstacle crossing abilities of 3-UPU parallel hexapod robot on flat terrain are analyzed,respectively.Secondly,the kinematics of the hexapod robot body,i.e.two groups of 3-UPU parallel mechanisms,is analyzed.The inverse position solutions of the two 3-UPU parallel mechanisms are solved based on closed-loop vector method.The forward position solutions of the two 3-UPU parallel mechanism are solved based on particle swarm algorithm.Based on the inverse solutions,the Jacobian matrices of the two parallel mechanisms are obtained,and the singularity of the mechanisms is analyzed.By writing MATLAB program,the workspace of two groups of parallel mechanisms is obtained using limit position exploration method.The analysis shows that the workspace of the mechanism is continuous without voids,and the motion performance is good.Thirdly,the dynamics of the mechanism is analyzed.The first-order and secondorder motion influence coefficient matrices of the mechanism are calculated,respectively.The forces of the mechanism are analyzed,and the Lagrangian dynamics model is established.The static stiffness is analyzed.The robot is imported into ANSYS software for statics performance simulation analysis.After applying pressure to the robot,the positions of the maximum stress and maximum strain are obtained by analyzing the stress concentration points and deformations in three different situations.Fourthly,the gait planning and stability of the hexapod robot are analyzed.Taking non-interference between platforms as the starting point,the maximum step length and step height of the hexapod robot along forward and transverse directions are calculated and set.After setting the step length,the equivalent rod lengths of the hexapod robot in these two directions are calculated,including the motion order,the occupation factor,etc.,and the variations of the displacement,velocity and acceleration curves in the two directions are calculated according to the step length and step height.The positions of the center of gravity and the stability margins when moving in two directions are obtained using the center of gravity projection method.The data shows that the hexapod robot can always walk stably under the set step length and step height.Finally,the motion of the hexapod robot is simulated.The motions of a single hexapod robot walking on flat terrain,climbing obstacles and crossing obstacles are simulated and analyzed.The variation of the center of gravity of each platform with time is obtained under various situations.The results show that the upper platform can remain stable and the weight placed on the upper platform can always remain stable within a certain range of terrain fluctuation.