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General Model of an Omnidirectional Mobile Robot Suitable for Uneven Ground

Mecanum wheels are used when omnidirectional movability of a vehicle is desired. For achieving the movability it is important to have a model of this omni-directional platform. In order to apply the omni-directional vehicle with four Mecanum wheels both to plane ground and to uneven ground, this paper presents a general model. Firstly the kinematics and the dynamics of the model on plane ground are presented. Then it is presented that there are mainly four types of uneven ground and four classes of touch states between the Mecanum wheels and the uneven ground in common buildings. A kinematical model which is suitable for the uneven ground is illustrated. It is proved that this model is also suitable for plane ground. A mobile robot control system was established by using Simulink module of MATLAB. Introduction Omni-directional locomotion is a frequent solution in recent autonomous robots. Modern mobile robots use omni-directional locomotion in order to achieve additional maneuverability and efficiency. Previous researchers have proposed and developed omnidirectional mobile robots employing a wide variety of wheel types including rollers [1, 2], Mecanum wheels [3, 4], and spherical wheels [5, 6]. Among many types of omni-directional wheels, Mecanum wheels are widely used in various applications because Mecanum wheels-based drive mechanism guarantees excellent mobility as well as the stability of the system due to its use of the four wheels. Mecanum wheel was invented by the Swedish engineer Bengt Ilon in 1973[7, 8]. If these Mecanum wheels are applied to the service robots, the mobile system must be able to adapt to uneven ground in an actual environment. The service robots usually work in common buildings where most of the ground is plane. The kinematics and the dynamics in this case are presented in section 3 and 4. However, there is still local uneven ground in the buildings, such as wheelchair ramps, small steps duo to the decorations on floor. And note that Mecanum wheeled robots are sensitive to uneven ground. The reason is that the wheels are composed of a series of discrete and passive rollers. In order to broaden the application scope of this type of omnidirectional robot, in this paper, a general kinematical model is proposed in section 5. In section 6, a mobile robot control system was established by using Simulink module of MATLAB. Mechanical Wheel Design Mecanum wheels consist of a number of rollers around the circumference of the wheel hub. The rollers are orientated at some angle, α, from the axis of rotation of the wheel. Rollers can rotate about their own axis. For the developed platform, an angle α of 45° is used. All the four pairs of Mecanum wheels are independently controlled. The model drawn in SOLIDWORKS is shown in Figure 1. This wheel’s size and shape of each part are created as size and shape of the actual component. Figure 2