1. Institute of Robotics and Information Automatic System (IRIAS), Nankai University, Tianjin 300071, China;
2. Tianjin Key Laboratory of Intelligent Robotics (tjKLIR), Tianjin 300071, China
For an omnidirectional mobile robot with active caster wheels, a redundant encoders based dead reckoning method is proposed, and a trajectory tracking controller is further presented in the presence of velocity saturation constraints. Specifically, the reasons for wheel slipping are analyzed firstly, and then a passive caster wheel with redundant encoders are designed and equipped on the robot, inspired by the fact that the passive caster wheels present less slipping than the active casters. Subsequently, the dead reckoning problem is transformed into an equality-constrained linear least square problem. Experimental results show that, compared with the traditional dead reckoning method without redundant encoders, the proposed dead reckoning method alleviates the effects of the slipping on localization and improves the localization precision. Considering that the practical velocities are bounded for motors, a trajectory tracking controller is designed in the presence of such input saturation constraints, and the stability is proven by Lyapunov-based techniques while ensuring the velocity saturation constraints to be satisfied. Both simulation and experimental results demonstrate that the proposed controller presents superior performance, while satisfying the control saturation constraints.
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