Research On Slippage Prediction And Teleoperation Of Wheeled Mobile Robots

In recent years, with the widespread use of wheeled mobile robots(WMR) in various applications(e. g., the planetary explortation projects and field disaster exploration), many scholors have started to pay more attention on this aspect. Now,most of related literatures are based on the assumption of ideally pure rolling.However, when the WMR runs on a soft terrain(e. g. lunar surface), slippage will inevitably happen at the surface between wheel and terrain, which will disturb the WMR’s kinematic and dynamic models and further induce the WMR’s teleoperation become much more complicated. Therefore, it is necessary to research on the teleoperation of WMR with slippage.In order to compensate for information(environment and motion) of the slave robot(WMR) at the operator site, this paper based on the physics engine Vortex from CMLabs, combining with the previous research, further improves a WMR simulation platform-ROSTDyn 1.1. Aiming at implementing an arbitrary motion of WMR, we improved the algorithm of solving the parameters related with the terramechanical model, and introduced a damping to decrease the normal vibration;through decreasing the desplay frequency and increasing the compute frequency, the prediction fidelity and speed can be further improved. Tests of simulation speed show that ROSTDyn 1.1 can do a real-time simulation, and the comparison of the prediction and experiment results confirms a good fidelity of ROSTDyn 1.1.In order to eliminate the slippage prediction errors, induced by the contact model’s limitation and the terrain parameters’ fluctuation, this paper presents a method for on-line model parameters modification. After eliminating the asynchronous errors in data by data identification, aiming at the sensitive parameters, the modification model can be obtained combining the dynamic prediction errors; meanwhile, an effective coefficient is also proposed to compensate for the model’s nonlinearity. The simulations and experiments by a WMR and ROSTDyn 1.1 verified that the proposed method is effective and can fast eliminate most slippage prediction errors.Aiming at the problems of WMR’s teleoperation on a soft terrain, this paper firstly build the WMR kinematic model under the wheel’s slippage; and thepassivity analysis shows that when the rate of the slippage is negative, the interaction between the wheel and terrain(environment termination) will present a shortage of passivity(SOP). Then, a time-deomain passivity control(TDPC) and a SOP compensation are proposed to compensate for the environment termination’s nonpassivity, and the system’s stability is guaranteed by Llewellyn’s criterion; then,three methods are proposed to eliminate the communication channel’s influence caused by the constant time-delay. Lastly, through a WMR bilateral teleoperation system, experiments of the proposed controllers demonstrate that the nonpassivity of the environment termination can be compensated for completely as well as the communication channel’s influence, and the system is stable with a good tracking performance and force transparency.Aiming at the WMR’s teleoperation with the coupling of movement and rotation,we build the WMR’s kinematic model under the influence of the slippage at two sides of the WMR, and the passivity analysis indicates this model is active to some extent. We designed the WMR bilateral teleoperation system, and a new compensation for the environment termination is also proposed; then, the stability of the whole teleoperation system is guaranteed by designing the system’s passivity;meanwhile, the force tracking transparency is also analyzed. The WMR experimental results show that the proposed method can generate a stable system with a good force tracking transparency on the linear velocity and angular velocity.In a high-risky environment, when the WMR teleoperation system cannot obtain enough feedback information to guarantee the performance, a new trilateral teleoperation scheme for haptic teleoperation control of a WMR is proposed based on the prediction system in this paper, which make the two mobile robots’ linear velocities follow the master haptic interface’s position each other through the shared control. The ET’s nonpassivity of the predictor and the slave robot is compensated for by the SOP controller proposed in this paper; the system’s stability conditions are given by guaranteeing its passivity; and theory analysis shows that the force felt by the human operator is about equal to the predictor’s plus the slave’s.Experiments of the system demonstrate the proposed WMR trilateral teleoperation system is stable and obviousely improves the operator’s sensability on the slave environment and other information.In general, the research results of this paper can support many ideas and basis for the dynamic prediction and teleoperation of the WMR with slippage; and it can also be seen as a reference for the future planetary exploration projects of China.