Design and Performance of Nonlinear Control for an Electrohydraulic Actuator Used on Shaker Table

Abstract

Abstract Hydraulic actuators are widely used in industrial applications due to their excellent power-size relation, their capacity to apply high forces indefinitely, and their high response. Hydraulic servo systems combine the advantages of hydraulic actuators with the versatility of electronics to give the most powerful actuators in modern industrial applications like robotics, aerospace industry, mining, testing equipment, and production lines. Hydraulic dynamic systems are usually described by linear or linearized models around operating points. In this work a nonlinear dynamic and mathematic model for the position control of a double rod hydraulic servo actuator was developed. Three control strategies were implemented: optimal control (LQR), control by Feedback Linearization, and Sliding Mode Control. For the optimal control (LQR) strategy a linearized model of the hydraulic actuator was developed around a specific operating point, contrary to the Feedback Linearization and Sliding Mode control that have a wide operation range and the nonlinear model was used. The Sliding Mode control was designed using a scheduling switch to change between two sliding mode controls and to avoid the chattering problem a solution base in the limit region was used. Furthermore, it was obtained that depending on the industrial application and the requirements of the position control of a hydraulic actuator, engineers can decide which control strategy to apply. Scheduling sliding mode control is better for industrial applications where it is important to have a rapid and accurate response, low control effort, low energy consumption, and robustness in the presence of disturbances. Feedback linearization control is also an excellent control strategy with rapid response and low control effort. But in certain applications, where there is no fast response, nor extreme precision needed, the LQR control is a great option.