A path following algorithm for mobile robots

This paper considers path following control for a robotic platform. The vehicle used for the experiments is a specially designed robotic platform for performing autonomous weed control. The platform is four-wheel steered and four-wheel driven. A diesel engine powers the wheels via a hydraulic transmission. The robot uses a Real Time Kinematic Differential Global Positioning System to determine both position and orientation relative to the path. The deviation of the robot to the desired path is supplied to two high level controllers minimizing the orthogonal distance and orientation to the path. Wheel angle setpoints are determined from inversion of the kinematic model. At low level each wheel angle is controlled by a proportional controller combined with a Smith predictor. Results show the controller performance following different paths shapes including a step, a ramp, and a typical headland path. A refined tuning method calculates controller settings that let the robot drive as much as possible along the same path to its setpoint, but also limit the gains at higher speeds to prevent the closed loop system to become unstable due to the time delay in the system. Mean, minimum and maximum orthogonal distance errors while following a straight path on a paving at a speed of 0.5 m/s are 0.0, -2.4 and 3.0 cm respectively and the standard deviation is 1.2 cm. The control method for four wheel steered vehicles presented in this paper has the unique feature that it enables control of a user definable position relative to the robot frame and can deal with limitations on the wheel angles. The method is very well practical applicable for a manufacturer: all parameters needed are known by the manufacturer or can be determined easily, user settings have an easy interpretation and the only complex part can be supplied as a generic software modul

An air-bearing weight offload system for ground test of heavy LSS structures

The capability and use of the Gravity Offload Facility (GOF) are discussed. Briefly explained are the: truss and base casting; carriage assembly; carriage weldment; vertical lift axis control; lifting cylinder; payload gimbal; motion base layout; and control processor

Modeling and Simulation of Mobile working machine Powertrain

Táto diplomová práca sa zaoberá vytvorením dynamického modelu mobilného pracovného stroja. Ciežom práce je vytvorenie blokového modelu pohonu štvorkolesového mobilného pracovného stroja. Model hydrostatického prevodu bol dodaný firmou Sauer-Danfoss. Model mobilného pracovného stroja bol vytvorený v programe MATLAB-Simulink. Dalšou časťou práce je výber typu riadenia hydrostatického prevodu a návrh riadiaceho algoritmu hydrostatického prevodu. Výstupom práce je blokový matematicko-fyzikálny model pohonu štvorkolesového mobilného pracovného stroja spolu s riadiacim algoritmom hydrostatického prevodu v prostredí MATLAB-Simulink.This thesis deals with dynamic model creation of four wheel drive mobile working machine. The goal of the thesis is to create powertrain model of mobile working machine. The hydrostatic transmission part of the model was supplied by the Sauer-Danfoss company. The model of mobile working machine was created in MATLAB-Simulink environment. The thesis is also devoted to selection of hydrostatic transmission control type and design of control algorithm. An output is mathematical and physical powertrain model of four wheel drive mobile working machine with hydrostatic transmission control algorithm in MATLAB-Simulink environment.

High-precision hydraulic pressure control based on linear pressure-drop modulation in valve critical equilibrium state

High precision and fast response are of great significance for hydraulic pressure control in automotive braking systems. In this paper, a novel sliding mode control based high-precision hydraulic pressure feedback modulation is proposed. Dynamical models of the hydraulic brake system including valve dynamics are established. An open loop load pressure control based on the linear relationship between the pressure-drop and coil current in valve critical open equilibrium state is proposed, and also experimentally validated on a hardware-in-the-loop test rig. The control characteristics under different input pressures and varied coil currents are investigated. Moreover, the sensitivity of the proposed modulation on valve's key structure parameters and environmental temperatures are explored with some unexpected drawbacks. In order to achieve better robustness and precision, a sliding mode control based closed loop scheme is developed for the linear pressure-drop modulation. Comparative tests between this method and the existing methods are carried out. The results validate the effectiveness and superior performance of the proposed closed loop modulation method