Research On Motion Control Of Multi-wheeled Moving Structures

Multiple wheeled mobile structure is a classical nonlinear underactuated non-holonomic system,which is widely used in industrial production,aerospace,military and other fields.In recent years,preliminary achievements have been made in motion control of multiple wheeled mobile structures,but there are still many problems to be solved for tracking a target trajectory curve precisely.Such as,large cumulative position error caused by he initial speed error,parameter uncertainties in the dynamics model and external disturbances.In view of the above issues,this paper will discuss three kinds of wheeled mobile structures respectively.When the three wheeled mobile structure moves along a smooth curve,the center of the axle of rear wheels must meet the nonholonomic constraint of zero lateral velocity.Clarifying the constraint relationship between the motion speed and rotational speed of wheels,the dynamics model of the three wheeled mobile structure can be derived by combining nonholonomic constraints and the Euler-Lagrange equation.According to the key relationship between the trajectory curve and the motion speed,the target trajectory curve is converted into a speed target form.Then,the relative curvature is introduced to design the dynamical trajectory tracking target,which can be used to transform the original motion task into a general trajectory tracking control problem.For the tractor-trailer wheeled mobile structure,the nonholonomic constraint of zero lateral velocity should be also satisfied.Moreover,a key curvature function equation related to trajectory curves of the tractor and trailer must be satisfied.Based on the key motion law,appropriate torque controllers can be designed by using the dynamical tracking targe,so that the tractor and the trailer can precisely tracking different target curves,respectively.In fact,for designing the dynamical tracking target,an appropriate forward speed target can be chosen freely according to actual needs to reduce the cumulative position error caused by the initial speed error.Since the essence of the dynamical trajectory tracking target is the relative curvature of the target curve,tracking such dynamical target means tracking the curvature of the target curve.In this way,the speed error can not be accumulated,and the tracking precision issue is resolved fundamentally.This method is not only simple,easy to implement,but also has high tracking accuracy,which provides a new idea for the precise motion control design of other multiple wheeled mobile structures.