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.

However, industrial hydraulic systems are highly complex and show nonlinear dynamic behavior. The main nonlinearities are due to compressibility of the hydraulic fluid, the flow-pressure relationship in the servo valve, friction forces and internal and external leakage in the actuator.

Hydraulic 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 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.

The nonlinear and linearized mathematical models were represented on Simulink environment, in order to compare and analyze the response and dynamic behavior. Then, each one of the three control strategies were implemented on Simulink, and compared and analyzed over the linear and nonlinear hydraulic system plants to obtain the pertinent conclusions. Finally, it was obtained that the Scheduling Sliding Mode control shows the best dynamic performance in terms of settling time with a little overshoot and great disturbance tolerance.

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 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.

Future work will include experimental validation of the developed dynamic control system. All three strategies will be implemented in the Dynamics and Structural Control Lab at Universidad Industrial de Santander. The implementation will be made using an MTS double rod hydraulic actuator, a MOOG 760 servo valve and a Quanser Q-USB-8 controller, in addition to data acquisition system


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

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Aerospace, Bioengineering, Applied Mechanics, Design Engineering Division, Advanced Energy Systems, Manufacturing Engineering Division, Noise Control and Acoustics, Nondestructive Evaluation, Diagnosis, and Prognosis (NDPD), Nuclear Engineering Division, Process Industries Division, Fluids Engineering, Heat Transfer, Materials, Microelectromechanical Systems, Safety Engineering and Risk Analysis, Computers & Information in Engineering


Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2020/volume/84478

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