Elsevier

Mechatronics

Volume 72, December 2020, 102467
Mechatronics

Investigation of The Effects of Contact Forces Acting on Rollers Of a Mecanum Wheeled Robot

https://doi.org/10.1016/j.mechatronics.2020.102467Get rights and content

Abstract

In this study, the effects of contact forces on the rollers of a mecanum wheeled robot are investigated. Modeling structures are constructed for the cases of single and multiple contact forces. A simulation environment is developed to examine these two cases. A theoretical model is proposed in order to reflect reality in the simulation environment. It is shown that single contact force assumption generates vertical vibration in a mecanum wheeled robot which is never desired in a real application. It is also demonstrated that adding more contact forces on a roller of a mecanum wheel's model decreases the transition distance between the rollers and thus creates smaller vibrations. An experimental setup, containing a four wheeled mecanum robot, is designed and built, and used for performing experiments to make verifications. Reference trajectory, simulation results obtained using single and multiple contact force cases and the experimental results are presented together to make comparisons. The details of the model proposed, simulation environment developed, experimental system designed and the results obtained are given in this paper.

Introduction

Autonomous vehicles have been commonly using in transportation tasks in industrial applications. They can be designed as wheeled, tracked or legged according to the type of application. One of them, which is quite popular today and has been adapted to the automation lines in the last couple of years, is mecanum wheeled manned/unmanned robots/vehicles. The answer of why mecanum wheeled robots/vehicles are popular is “mobility”. Mecanum wheels increase the mobility, allow for omni-directional movement and give possibility to the vehicle to do desired path tracking tasks with less maneuvers. A mecanum wheel is constructed by the use of rollers (i.e. generally nine rollers are used to build a mecanum wheel). One roller is active, makes contact with the surface, the other eight are inactive. This reduces the ratio of friction. This also enables that a complex path and series of maneuvers are not needed for controlling the heading of a mecanum vehicle. Each wheel is motorized so that only the control of the wheels needed to be activated would be enough. This capability gives also power efficiency. By this way the traction batteries, used for the heavy-duty applications, can be more effectively used.

In a general approach in the modeling of the mecanum wheels and mecanum wheeled vehicles, a single point contact is assumed. This enables to construct a simple mathematical model, which gives ability to use a simple control system structure. Unfortunately, this assumption does not reflect reality. In this study, it is shown that when a single contact force assumption is used, a mecanum wheeled vehicle cannot trace a reference trajectory without a pre-defined tracking error band. This means that the vehicle model created using single contact force assumption is not enough to catch up the reality. It is proposed that multiple contact forces should be used for creating models for the mecanum wheels in order to get results close to the responses obtained in real applications. These proposes are verified by performing simulations obtained in a simulation environment developed by the connection of SolidWorks CAD program and Simscape toolbox of Matlab-Simulink. A four wheeled mecanum robot is also designed and built. It is suited with actuators, motion drivers, microprocessors, communication modules, etc. The simulation results are experimentally verified using this experimental platform. The simulation and experimental results are presented together so as to show the behavior of the mecanum wheeled robot in different test scenarios, in which single and multiple force assumptions are used.

The outline of this paper is constructed as follows: the next section is about the literature studies. Third section is prepared for presenting the problem statement. The next section gives the modeling structures. Kinematic and dynamic models of a mecanum wheeled vehicle are presented in this section. Fifth section introduced the simulation environment and the experimental setup developed. The next section is about the simulation and experimental studies. The last section shows the analysis and conclusion and the future plans about the study.

Section snippets

Literature Survey

There are many studies in the literature related to design, construction, modeling and control of the mecanum wheels and mecanum wheeled vehicles/robots. In this section of the paper, some of them are reviewed to show the place of the state-of-art researches of the mecanum wheeled vehicles.

Song and Byun [1] introduced steerable omnidirectional wheels having 1-DOF steering system. It was shown that steerable wheels provided good tipping stability. Cooney et al. [2] presented the common slippage

Problem Statement

Mathematical model for a mecanum wheeled vehicle/robot is constructed using the point contact force approach given in Figure 1. In this figure, lateral, longitudinal and vertical directions are set by x-y-z coordinate axes, respectively. Weight of the platform is given by W. Angular rotation and the angular velocity for each wheel are indicated by θ and θ˙, respectively. Length, wide and height information of the platform are demonstrated by L, d and h, respectively. Normal forces in

Comparison of Single and Multiple Contact Forces Acting on a Roller

In a general approach, analysis of a mecanum wheel is constructed by considering that only one contact force effects the system (Figure 4 - Motion occurs between the contact point C0 of the roller-8 and point C1 of the roller-7. This generates errors in the rotation center of the wheel indicated by ε). If the accuracy expectation is high enough, this approach needs improvement (Figure 4 – Motion should be defined on the curve of the rollers. This makes the value of ε closer to zero). The

Kinematic Model

Mathematical model of a mecanum wheeled robot is constructed using a free body diagram given in Figure 10. Coordinate axis (y-x) is located at the geometrical center of the robot. Angular velocities of each wheel are defined as ω1, ω2, ω3 and ω4 (θ˙i=ωi). Wheel radius is specified by R. L and d are used for dimensions of the chassis. V1, V2, V3 and V4 show the heading velocities of the mecanum wheels. Longitudinal and lateral velocities of the robot are described by Vy and Vx, respectively.

Experimental Setup

In order to make verifications, a mecanum wheeled forklift robot is designed and manufactured in this study. The 3D-CAD model and the manufactured robot are presented in Figure 12. The robot vehicle has four mecanum wheels, each of them nine rollers. The rollers are made of polyurethane. The weight, width, length and height of the robot are 6.7 kg, 450 mm, 625 mm, 380 mm, respectively. The radius of the mecanum wheels is 50 mm.

Mecanum wheels are driven using 12V DC motors (Figure 13), which are

Simulation and Experimental Studies

Simulation environment is created by the connection of SolidWorks and Simscape toolbox of Matlab-Simulink. The CAD model designed is imported to Matlab-Simulink first. Then, the necessary kinematic-dynamic equations and required relationships are embedded into the Matlab function facility of Simulink. A general view of the simulation environment developed is illustrated in Figure 14. The main block diagram, which runs under the simulation environment developed, is also presented in Figure 15.

Analysis and Conclusion

In this paper, the effects of the contact forces on a roller of a mecanum wheel are investigated. Problem related to using single contact force assumption in modeling of a mecanum wheel is defined. The solution procedure, why the multiple contact forces should be used, is introduced. The use of both single and multiple contact force considerations are tested in a simulation environment developed for this study. The simulation results indicate that the use of single contact force generates

Credit author statement

All authors have participated in (a) conception and design, or analysis and interpretation of the data; (b) drafting the article or revising it critically for important intellectual content; and (c) approval of the final version.

Declaration of Competing Interest

None.

Gokhan Bayar is studying on the subjects of mechatronics, robotics and control. His main interest is autonomous ground vehicles. He has been working on design, construction, modeling and control of mobile robots and autonomous ground robots. He has also been using his research experiences in the area of autonomous ground vehicles used in tree fruit orchard applications. Dr. Bayar completed his Bachelor Science degree in Mechanical Engineering Department. He got his M.Sc. and Ph.D. degrees in

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    • Cited by (0)

    Gokhan Bayar is studying on the subjects of mechatronics, robotics and control. His main interest is autonomous ground vehicles. He has been working on design, construction, modeling and control of mobile robots and autonomous ground robots. He has also been using his research experiences in the area of autonomous ground vehicles used in tree fruit orchard applications. Dr. Bayar completed his Bachelor Science degree in Mechanical Engineering Department. He got his M.Sc. and Ph.D. degrees in the Mechanical Engineering Department of Middle East Technical University, Ankara, Turkey. He also worked in an autonomous agricultural ground vehicle project conducted in the Robotics Institute of Carnegie Mellon University in Pittsburgh, PA, USA in his Ph.D studies. Currently, he is a full time faculty at the Mechanical Engineering Department of Zonguldak Bulent Ecevit University.

    Salih Ozturk obtained B.S. degree in Mechanical Engineering from Zonguldak Bulent Ecevit University, Zonguldak Turkey in 2018. He is currently a master student in Mechanical Engineering department of Zonguldak Bulent Ecevit University. He is conducting researches on the topics of design, construction and control of mobile robots, and modeling of simulation systems.

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