Abstract
Motion control in dynamic environments is one of the most important problems in using mobile robots in collaboration with humans and other robots. In this paper, the motion control of a four-Mecanum-wheeled omnidirectional mobile robot (OMR) in dynamic environments is studied. The robot’s differential equations of motion are extracted using Kane’s method and converted to discrete state space form. A nonlinear model predictive control (NMPC) strategy is designed based on the derived mathematical model to stabilize the robot in desired positions and orientations. As a main contribution of this work, the velocity obstacles (VO) approach is reformulated to be introduced in the NMPC system to avoid the robot from collision with moving and fixed obstacles online. Considering the robot’s physical restrictions, the parameters and functions used in the designed control system and collision avoidance strategy are determined through stability and performance analysis and some criteria are established for calculating the best values of these parameters. The effectiveness of the proposed controller and collision avoidance strategy is evaluated through a series of computer simulations. The simulation results show that the proposed strategy is efficient in stabilizing the robot in the desired configuration and in avoiding collision with obstacles, even in narrow spaces and with complicated arrangements of obstacles.
Highlights
With the advancement of technology and the invention of new wheels with special structures, omnidirectional mobile robots (OMRs) have been presented and widely used recently in industrial applications, space exploration, medical fields etc. [1,2,3]
In this paper, modeling, control and motion planning of a four wheel OMR has been investigated in dynamic environments
The parameters and ingredients of the control system and the online trajectory planning algorithm have been specified through special stability and performance analysis of the closed loop system
Summary
With the advancement of technology and the invention of new wheels with special structures, omnidirectional mobile robots (OMRs) have been presented and widely used recently in industrial applications, space exploration, medical fields etc. [1,2,3]. The motivation of this work is to develop an online motion planning and obstacle avoidance strategy for OMR as a part of its feedback control system to stabilize the robot in desired position and orientation in the presence of static and moving obstacles. This approach makes it possible to control the state variables and to plan the robot’s trajectory between obstacles simultaneously based on the robot’s dynamic model and its physical constraints and limitation.
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