Wheel slip-sinkage and its prediction model of lunar rover

Coordinated control of slip ratio for wheeled mobile robots climbing loose sloped terrain

A challenging problem faced by wheeled mobile robots (WMRs) such as planetary rovers traversing loose sloped terrain is the inevitable longitudinal slip suffered by the wheels, which often leads to their deviation from the predetermined trajectory, reduced drive efficiency, and possible failures. This study investigates this problem using terramechanics analysis of the wheel-soil interaction. First, a slope-based wheel-soil interaction terramechanics model is built, and an online slip coordinated algorithm is designed based on the goal of optimal drive efficiency. An equation of state is established using the coordinated slip as the desired input and the actual slip as a state variable. To improve the robustness and adaptability of the control system, an adaptive neural network is designed. Analytical results and those of a simulation using Vortex demonstrate the significantly improved mobile performance of the WMR using the proposed control system.

Path-following control of wheeled planetary exploration robots moving on deformable rough terrain

The control of planetary rovers, which are high performance mobile robots that move on deformable rough terrain, is a challenging problem. Taking lateral skid into account, this paper presents a rough terrain model and nonholonomic kinematics model for planetary rovers. An approach is proposed in which the reference path is generated according to the planned path by combining look-ahead distance and path updating distance on the basis of the carrot following method. A path-following strategy for wheeled planetary exploration robots incorporating slip compensation is designed. Simulation results of a four-wheeled robot on deformable rough terrain verify that it can be controlled to follow a planned path with good precision, despite the fact that the wheels will obviously skid and slip.

Development of Grousers with a Tactile Sensor for Wheels of Lunar Exploration Rovers to Measure Sinkage

This paper presents a grouser developed for the wheels of lunar exploration rovers to measure sinkage. The wheels, which are intended to traverse loose soil such as lunar regolith, contain grousers that transfer thrust to the wheels and thus to the body of the rover. The interaction between the wheel (with grousers) and the loose soil can be described using a kinematic model. When traversing loose soil, the wheel sinks into the soil, which necessitates knowledge of the entrance angle needed in order to avoid this problem. If the entrance angle is known, the sinkage can be measured in real time before adverse conditions occur. Because of the importance and usefulness of detecting the entrance angle of the wheel, we herein propose a grouser with an embedded tactile sensor. A strain gauge on the surface of the grousers serves as the tactile sensor. In order to confirm the precision of the proposed grouser, we have performed tests on a rigid surface and loose soil surfaces.

Experimental study and analysis of the wheels’ steering mechanics for planetary exploration wheeled mobile robots moving on deformable terrain

Due to the requirements of challenging planetary exploration missions with wheeled mobile robots (WMRs), the driving mechanics of WMRs’ wheels moving on the deformable terrain has been researched intensively, but the mechanics of the wheels’ steering is lacking research. Systematic steering experiments were carried out using a single-wheel testbed for wheels moving on a lunar soil simulant with different radii, widths, lug heights, and lug numbers under different vertical loads. The influence of the eccentric distance and motion state, such as the steering motor’s angular velocity, steering angle, and initial wheel sinkage, were also studied. The experimental results are illustrated with plenty of figures and analyzed based on the preliminary steering mechanics model to draw conclusions. The steering resistance moment is caused by the lateral bulldoze stress and the shearing stress at the bottom of the wheel. The wheel sinkage and steering moment of resistance increase with an increase in steering angle, which could be fitted with exponential functions. The steering moment is the increasing function of the wheel sinkage, eccentric distance, vertical load, and wheel width. The conclusions, empirical models, and experimental data can be taken as references to the optimal design of a steering mechanism and the development/verification of a wheel’s steering mechanics model.