DEVELOPMEN OF AUTOMATED TRACTION CONTROL SYSTEM FOR FLEXIABLE WHEELS WITH APPLICATION TO MARS EXPLORATION ROVERS

摘要

This study focuses on a control algorithm to optimize the traction force and minimize the slippage. The contribution is the development of a model which is an extension to the Bekker theory for flexible wheels to predict the tractive performance for a metal flexible wheel by using the geometric model of the wheel in deformation. The key elements of the method are to obtain the wheel ground contact angles, wheel-ground contact length and ground pressure. Ground pressure plays an important role in determining the wheel model because when the critical pressure is less than average ground pressure the flexible wheel acts as a rigid wheel so to evaluate wheel flexibility, different wheel stiffness were used during this study. In order to limit the reaction time and minimize the probability of slip, control techniques based on rover physical models were developed. In the methodology, soil database from pervious Mars exploration rover was used and the wheel deformation for each soil type was calculated for the database. Consequently when the rover moves over terrain of varying soil characteristics the wheel deformation can estimate the soil type (Simple on board sensors were employed to measure the wheel deformation online). With the intentions of achieving desired outcome drawbar pull is computed by knowing the soil type and the traction model of flexible wheel to attain the optimal tractive ability and the torque which is directly related to energy consumption.