Dynamics and control of fast automated guided vehicles for high load applications.

Abstract

Automated Guided Vehicles (AGV) are important components of modern automated transport systems. Increasing the system efficiency and throughput requires the use of heavy vehicles travelling at high speeds. As the AGV's payload capacity and travelling speed increases, the ensuing increase in lateral acceleration requires thorough dynamic modelling and more sophisticated controller design. To establish the sufficient level of model complexity necessary for this work, a 3-DOF nonlinear dynamic model comprising yaw, lateral, and roll motions is developed. The suspension, lateral and longtudinal load transfer, nonlinear behaviour of tires, and steering dynamics are included in this model. The model also comprises the effect of actuators, differential gear box, steering and tractive gear boxes. The model is validated through simulations and comparison with other models. A dynamic-based approach to the control of a typical transport interfactory AGV in a semi structured environment is studied. The 2-DOF side slippage free dynamic model comprising steering and actuators dynamics is used to design the controller. The input-output feedback linearization technique is employed to linearize the nonlinear dynamics of the vehicle. To improve robustness in the presence of parameter uncertainty, modelling errors and disturbance, a Boundary Layer Sliding Mode (BLSM) controller is adopted. The BLSM controller is later modified to improve performance and enhance robustness, using simultaneous variable boundary layer and multiple sliding surfaces strategies. Simulations based on the 3-DOF nonlinear model show the satisfactory results for the Modified Boundary Layer Sliding Mode (MBLSM) controller.