Author : Qingfeng Lou
Publisher :
ISBN 13 :
Total Pages : pages
Book Rating : 4.:/5 (119 download)
Book Synopsis Modelling and State Estimation of Exploration Rovers by : Qingfeng Lou
Download or read book Modelling and State Estimation of Exploration Rovers written by Qingfeng Lou and published by . This book was released on 2019 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: "State estimation is an important element in rover exploration missions. The objective of state estimation is to determine the pose and velocity of the rover by processing measurements from onboard sensors. It usually includes fusing measurement data from different types of sensors. Wheel encoders represent one of the fundamental categories of sensors used for estimation.The so-called classical wheel odometry is widely used in various rover applications. It estimates the rover state by tracking the motions of the two middle wheels in the differential drive based on the related wheel encoders. However, this technique has certain limitations. First, it does not employ redundant measurements. As a consequence, input noise can lead to large uncertainties in the estimated results. Second, it contains a nonlinear estimation model because of the trigonometric functions of the rover orientation. The linearization process that propagates the mean and covariance of the estimated state introduces additional errors. More importantly, it cannot detect the wheel slip and accumulates large estimated errors for rover travelling on soft terrain.The objective of this thesis is to investigate how state estimation can be improved by combining wheel encoder measurements with kinematics, dynamics, and terramechanics modelling. Kinematic and dynamic models are developed in the thesis for a range of rover maneuvres. The interaction between the wheels and soft terrain is also modelled and analyzed employing terramechanics models. A procedure for online soil parameter identification is proposed based on the sensitivity analysis of the terrain traction forces with respect to the variations of the soil parameters.Three state estimation techniques at different levels are developed.The first one is kinematics-based estimation. An estimation model using the Kalman Filter approach is established based on the kinematic model of the rover that relates the velocity of the chassis to the motion all wheels.The chassis velocity components with respect to the chassis-fixed coordinate system are selected as system state variables. The encoder measurements from all wheels are fused together to provide redundant measurements. The longitudinal and lateral types of slip of all wheels are modelled as random Gaussian noise. The continuous-time Kalman Filter is employed to process the estimation model and measured data.The second technique proposed is dynamics-based estimation. The rover dynamics and terramechanics are combined to represent the relations between the rover motion and wheel/terrain interaction forces. The variables of the chassis velocity, wheel velocity, wheel slip, motor torque, and terrain reaction forces can be determined using the measurements from wheel encoders and the combined dynamic and terramechanics model.The third method developed puts forward a framework that integrates the previous two techniques. The accuracy of estimation is generally related to how well the slip under the wheels can be determined. A new decomposition of wheel slip is proposed here to conflicting and compatible slip components. This decomposition takes into account the rover kinematics that represents the geometric constraints among the wheels. These two slip components can then be considered separately using the two techniques described above. The state of the rover considering the conflicting slip component can be estimated using the kinematics-based technique and the compatible slip component can be solved for using the dynamics-based technique. This resulting combined method provides the best solution. The proposed estimation techniques were investigated and validated by experiments employing two rover prototypes"--
