In some existing omnidirectional mobile robots, the movement of each wheel is generally controlled by one driven motor cooperates with one steering motor, such design will increase the energy consumption. This paper investigates an omnidirectional mobile robot based on a special coupling system, so as to solve the above problem. We propose a unique robot’s steering method by designing the parallelogram connecting rod as the coupling system, which makes each wheel only need to be equipped with one motor to complete omnidirectional motion and always keep unchanged robot’s attitude. In theory, we conduct the structural analysis, dynamic analysis and kinematic analysis of the mobile robot and explain why our system is under-actuated. In experiments, the square trajectory and the serpentine trajectory are exploited to verify the rationality of design and theoretical derivation by comparing the simulation results with the experimental results. By performing mobile robot walking experiments under different ground condition respectively, the stability and adaption of the under-actuated omnidirectional mobile robot is also favourably confirmed. After detailed theoretical analysis and the support of experiments, it is carried out that the under-actuated mechanism proposed in this paper can indeed realize the movement of the robot in all directions. As well as the attitude of the robot always keeps constant, as we expected, enables to realize the steering of robot flexibly even in a narrow space.

Introduction

In recent years, with the rise of artificial intelligence technology, the robots have been applied to several fields. Such as the climbing robots for detecting tasks [1], [2], mobile robots that can be used in home and industrial environments [3]. Particularly, mobile robot as an important branch of robotics has received a great attention by most countries [4]. The earliest appeared is the wheeled robot developed by Stanford, which is primarily capable of self-service reasoning, planning and control in complex environments [5]. As time goes by, the relevant researches on mobile robots are also deepening with the assistance of advanced technology. A mass of omnidirectional mobile robots have been applied widely due to the emergence of omnidirectional wheel technology. In order to meet the use of mobile robots in different scenarios, the choice of wheel mechanism is particularly important [3]. Among them, the design scheme of Mecanum wheel is proposed in 1973 and is subsequently exploited [6], [7]. In [8], presents an omni-directional mobile robot using four custom-made mecanum wheels, each wheel is independently powered using a precisian gear DC motors. The KUKA company in Germany takes full advantage of its own robot development and launches the YouBot robot into people’s view [9], [10]. Subsequently, KUKA introduces the omniMove large mobile robot platform, which has flexible mobility and powerful load capacity despite its bulk [11].