Configuration Design And Motion Planning Of The Dual-platform Staggered Hybrid Hexapod Robot “Xuangui”

There are a large number of narrow,dangerous and complex underground spaces in cities that are not suitable or inaccessible for humans to enter,such as air-raid shelters in disrepair,underground coal mines where accidents have occurred,military projects,and concealed tunnels.The development and reuse of such narrow,dangerous and complex underground spaces is of great significance,involving many fields such as national defense security,and the national economy and the people’s livelihood,and is an important symbol of smart cities.In this paper,we design a hexapod robot “Xuangui” based on the hybrid mechanism,which relies on the alternate staggering of the upper and lower platforms of the parallel mechanism to move.The R&(2-UPU/2-RPR)hybrid mechanism is used as the body of the hexapod robot Xuangui,which can satisfy the requirements of the hexapod robot Xuangui to enter the underground space to perform its tasks such as transportation,inspection,and maintenance.Firstly,the overall configuration design of the hexapod robot Xuangui is carried out,including the design of the body mechanism of the hexapod robot Xuangui and the design of the leg structure fixed to the platform.The dimensions of the key components of the hexapod robot Xuangui and the installation position of the sensors are also designed.Secondly,the kinematics of 2-UPU/2-RPR redundant parallel mechanism is analyzed.The coordinate systems of 2-UPU/2-RPR redundant parallel mechanism is established by screw theory and the number of degrees of freedom of the mechanism is verified.By the analyzing of the characteristics of the mechanism and ensuring the constraint relationship of mechanism,the inverse solution equation of the mechanism is obtained using closed-loop vector method.The positive solution equation of the mechanism is constructed by the convergence characteristics of the particle swarm optimization algorithm.According to the given input parameters,the positive solution example of the mechanism is obtained,and the fitness curve of the positive solution of the mechanism is obtained using Matlab software.Then the velocity Jacobian matrix of the mechanism is obtained based on the inverse solution equation of the mechanism position.Then,the singularity of 2-UPU/2-RPR redundant parallel mechanism is analyzed by Jacobian matrix.The workspace of the mechanism is obtained usinglimit position exploration method,and its shape is regular and continuous,indicatingthat the mechanism has good kinematic performance.Thirdly,the statics and dynamics of the hexapod robot Xuangui are analyzed.The equilibrium equations of forces and moments are obtained by the rod removel method.The statics simulation shows that the hexapod robot has a large loading capacity.Then,the dynamics analysis of the hexapod robot Xuangui are carried out to obtain its dynamics equations,and modal analysis is performed to obtain the first-order to sixth-order modal vibration patterns of the hexapod robot Xuangui supported by two groups of six legs and each group of three legs,and the harmonic response of the hexapod robot Xuangui is analyzed on this basis to obtain the frequency-displacement curve and the sensitivity frequency of the hexapod robot Xuangui are obtained,which is of guidance for the avoidance of robot resonance and the diagnosis of robot faults.Then,the stability analysis and gait planning of the hexapod robot Xuangui are carried out.The center of gravity projection method is used to analyze the motion stability of the hexapod robot Xuangui.Considering the stability of the hexapod robot Xuangui and the interference of the legs,the motion limit parameters of the hexapod robot Xuangui are obtained,including the maximum moving stride and the maximum zero radius angle of a single rotation in an intermittent cycle.The space-occupying coefficient,movement order,movement stride and the variation of rod length of each branch chain of the two groups of legs fixed on the two platforms of the hexapod robot Xuangui during the movement of the hexapod robot Xuangui are studied.The foot-end trajectory of the hexapod robot Xuangui is planned by using the non-impact composite cycloid,which greatly avoids the impact of the hexapod robot Xuangui when the leg is in contact with the ground.Finally,the hexapod robot Xuangui is modeled and its obstacle surmounting performance in different terrain environments is analyzed.Through the Motion module built in Solid Works software,the simulation of the dual-platform staggered hexapod robot Xuangui based on R&(2-UPU/2-RPR)hybrid mechanism is carried out in four working conditions: walking on the flat ground,climbing the convex platform,crossing the gully and turning with zero radius.A series of parameters such as the position,gait and center of gravity of the hexapod robot Xuangui are obtained.By comparing the simulation results with the theoretical trajectory,it is concluded that the two-platform centroids of the hexapod robot Xuangui are similar in the vertical direction.The dual-platform staggered hexapod robot “Xuangui” based on R&(2-UPU/2-RPR)hybrid mechanism has a wide application prospect in the development and reuse of underground space due to its superior performance such as adaptability to terrain and zero radius turning ability in narrow environment.