Anisotropy Analysis And Optimal Control Of Continuous Alternate Omni-directional Wheel And Mobile Robot

As a3DOF mobile system, the omni-directional mobile robot is suitable for movement in narrow space with flexible motion characteristic. The omni-directional wheel is the key factor of the mobile robot as the main movement mechanism. Currently, the Mecanum wheel is widely used. But Mecanum wheel has some shortcomings, such as difficult in production, the "shock" phenomenon occurs during the movement due to uncertain axial movement contact points. This article tries to find a way to study another omni-directional wheel—single-row continuous alternate wheel. Considering the current researches of the alternate wheels, the single-row continuous alternate omni-directional wheel and the mobile robot are optimal designed and manufactured. The anisotropy of the wheel and its impact on the layout of the wheels and self-lock characteristics are studied. At last, based on the analysis of such mobile robot drive control features, optimal control strategise are proposed.The main researches and conclusions of this article contain the following aspects:1、This article puts forward the optimal designing of a single-row continuous alternate wheel, and solves the structural problem of the layout of the omni-directional mobile robot. At first, the structure of the wheel is introduced with simple structure and easy installation advantages through the Y-shaped brackets which are made for fixing rollers. Through analyzing and summarizing the rules and conditions of the omni-directional mobile robot, the full range motion arrangements of three wheels, four wheels and six wheels are proposed. Considering the drive capability, body stability and controllability of the system, the arrangement of the four wheels is chosen as the actual bodywork.2、Designing and implementation of the electrical control system are introduced. The analysis and comparison of different control methods in the mobile robot are proposed, including selections of the master controller, means of communication, types of the motor drive. Taking into account the characteristics of the mobile robot, electrical control system which is suitable for the mobile robot and the major software design ideas are described.3、The anisotropy of the mobile robot is analyzed, including the following three main aspects: (1) The self-lock characteristics of the mobile robot is analyzed and solved. Through analyzing the composition of the friction force on different contact points when the wheel moves, the experiment system is established. The relationships between friction coefficient with ground media, contact points are measured by experiments. And the omni-directional wheel self-lock angle (friction angle) is proposed. Self-lock characteristics of the mobile robot on the slope in all directions is solved through theoretical and experimental analysis.(2) The anisotropy of the robot speed is analyzed based on kinematic equation. The speed of the mobile robot in each direction is different through theoretical calculation. Simulation results by ADAMS software and theoretical calculation results are the same.(3) Dynamic equations of the system are obtained according to the nonholonomic system of Rolls equations. The acceleration anisotropy of the mobile robot is obtained in all directions by theoretical and experimental analysis. The rollover and backward conditions of the mobile robot moves on the slope are calculated, and the model is simulated by using ADAMS software. The theoretical basis for system practical application is provided.4, The optimal control method of the mobile robot based on single-row continuous alternate wheel is obtained, mainly including two aspects:(1) A dual PI control of motor torque and speed can be used in special directions by analyzing the four wheels drive mobile robot redundancy features and drive features. The mobile robot consists four wheels is a redundant system. In order to reduce the squeeze between the four wheels (squeeze is a part of the motor force, no contribution to the mobile robot, but harmful to the joint), a dual PI control system includes vehicle speed and motor output torque is established. Experimental results show that when the mobile robot moves along the forward direction (forward direction refers to the direction of the velocity perpendiculars to the axis of the adjacent wheels), the efficiency can be increased by13%. And when the mobile robot moves obliquely (oblique direction means that the angle of velocity and axis of the adjacent wheels is45°), the efficiency can be increased by6%. Meanwhile, the stability of the vehicle speed is also increased.(2) In order to solve moment distribution problem of the mobile robot in the acceleration process, efficiency maximization of the constraint equation is added from the mobile robot dynamics equation. From the theoretical and experimental analysis, related to the other control methods, the efficiency can be increased by2%to3%by using the method of efficiency maximization.