Design Of Omni-directional Mobile Platform Based On Single-motor Casters

With the quick development of artificial intelligence,electric driving,wireless and other new technologies in recent decades,the research on mobile platform has been deepening gradually.The mobile platform has shown an increasingly important position and role in all aspects of social production and life.Compared with traditional mobile platforms,omnidirectional mobile platforms has been widely used in industry,agriculture and service industries due to its ability to move freely in a narrow space and good maneuverability.It could be predicted that,the Omnidirectional mobile platform will be applicated in different fields in the near future.In this thesis,an fully-driven omni-directional moving platform with three casters(referred to as mobile platform),which are motor drived,is investigated.The platform is completed only by controlling the speed of the casters.The main research work is as follows:1.The kinematics model of the platform is established according to the pure rolling constraints with the orthogonal decomposition method.The analysis shows that there is singularity mode when the platform's velocity Jacobian matrix is irreversible and the platform will lose the omnidirectional movement ability.By coupling the turning angle with the steering angle kinematics,the dynamic coupling factor is introduced to identify the proximity between the current configuration and the singular configuration of the platform,and the ratio of the dynamic coupling is adjusted to get rid of the singular configuration for the platform.Lagrange method is used to establish the dynamics model of the platform,and the simulation results of dynamics are analyzed to eliminate the influence of steering angle on the energy consumption of the platform with MATLAB,and the dynamics model is simplified reasonably.2.The 3D body model of the platform is built with Solid Works,and imported into ADAMS software.The virtual prototype of the platform is set up from the aspects of parts materials,driving variables,contact friction force and co-simulation state variables,and the correctness of the virtual prototype set is verified based on ADAMS software.The ADAMS-MATLAB /Simulink co-simulation interface is defined,and based on the PID control principle,the accuracy of the kinematics model and the dynamics model of the platform are verified with the co-simulation method.3.In order to improve the motion accuracy in the case of load changes,a speed controller is designed based on the fuzzy PID control principle,and the stability of the controller is proved by using Lyapunov function.Finally,Matlab/Simulink-Adams co-simulation method is used to simulate the different working conditions of the platform under 0%(no-load),20%,50% and100% loads.The difference of the conventional PID control and fuzzy PID controller is compared and analyzed.The simulation results show that the fuzzy PID speed controller can suppress the influence of load change effectively,and make the actual speed of the platform converge to the reference speed quickly,stably and accurately.The control system shows strong robustness.4.The advantages and disadvantages of several obstacle avoidance methods are analyzed,and the traditional artificial potential field method is selected as the obstacle avoidance algorithm for the platform.The repulsive/gravitational potential field function and repulsive/gravitational potential field function of the traditional artificial potential field method are derived,and the effectiveness of the obstacle avoidance algorithm of the traditional artificial potential field is simulated and analyzed based on MATLAB.The results show that the algorithm will fail in some special cases,and there are problems of unreachable target and local stability with this algorithm.To solve these problems,the relative distance between the target point and the obstacle is introduced into the potential field function respectively to optimize the algorithm.Then a position controller is designed to solve the corresponding velocity component according to the planned obstacle avoidance trajectory,which is input to the speed controller for co-simulation analysis of the platform.The simulation results show that the optimized algorithm can effectively avoid the unreachable targets and local stability problems,and also the platform can avoid obstacles.