Research On Coordinated Control Technology Of Multi-Wheel Drive For 6×6 Unmanned Ground Platform

Ground unmanned platform is a kind of ground mobile platform which has power and does not need human driving,widely used in the construction of community economy and national defense modernization,especially in the military field.Wheeled ground unmanned platform can meet the needs of various complex pavement,and the distributed drive become an important research content of the driving control for wheeled ground unmanned platform,as a new type of transmission structure.The multi-wheel drive system needs to distribute the whole control objectives to the hub motors in real time and coordinately.When the external environment disturbs,the coordinated operation of the driving wheels can be ensured by adjusting the whole control objectives and changing the distribution method.In this paper,a coordinated control strategy of multi-wheel drive is designed for a 6×6 unmanned platform,which can adapt to complex driving conditions and realize stability control of straight running.The main contents are as follows:First of all,this paper compares the research status of coordinated control technology of multi-wheel drive at home and abroad,and analyses the shortcomings of the current research,to explain the content arrangement of this paper.Vehicle dynamics model is the basis of control strategy design and verification,but 6× 6 unmanned ground platform is a special vehicle,and there is no ready-made model to use.This paper establishes a dynamic model of a 9-DOF 6×6 unmanned ground platform based on the simplification of the model,including hub motor model,tire model,vehicle body dynamic model and wheel dynamic model,and carries out simulation debugging of accelerated working conditions for the dynamic model established.The tire force under different road adhesion coefficients is solved by the longitudinal-lateral combined working condition tire model,while tire force in the pure working condition is obtained by looking up the tire data table.Secondly,in this paper,a yaw moment decision-making algorithm for stability control of straight running is designed based on sliding mode control,taking sideslip angle and yaw angular velocity as control variables,establishing a sliding surface according to yaw angular velocity,heading angle and lateral offset,combining with the modified two-degree-of-freedom vehicle reference model,to determine the desired yaw moment.Through simulation analysis,under the influence of lateral slope and lateral wind,the determined yaw moment can control the yaw angular velocity,heading angle and lateral offset at the expected value,and the unmanned ground platform can maintain stable state of straight running.Then,the coordinated control strategy of multi-wheel drive is studied in this paper,including total driving force decision-making,torque distribution and anti-skid driving,on the basis of yaw moment decision-making algorithm.And the design and simulation modeling of coordinated control strategy for multi-wheel drive are completed.A feedforward and feedback PI control method is used in the total driving force decisionmaking for constant speed cruise control,through simulation analysis,the speed overshoot and stability time are both ideal.Torque distribution methods based on axle load ratio and objective optimization of tire load rate are both designed,through simulation analysis,the effect of torque distribution based on objective optimizing of tire load rate is better for lateral stability of the unmanned ground platform.When the road adhesion coefficient is low,driving anti-slip limit driving torque is obtained based on sliding mode control,restricting driving torque of hub motor to avoid excessive slip of driving wheel,through simulation analysis,the slip rate can be controlled within a reasonable range to avoid excessive slip of driving wheels.Finally,the coordinated control strategy of multi-wheel drive designed in this paper is fully validated by simulation.The road surface setting module and GUI interface module in the simulation model established in this paper are used to set the simulation parameters of road adhesion coefficient,slope value and lateral wind,completing simulation validation of longitudinal slope,docking road,split road,lateral slope and lateral wind.Under each simulation condition,the control strategy designed in this paper has achieved ideal results.