Error Analysis of Digitally Controlled Servo Hydraulic Actuators for Structural Testing.

Advanced control strategies, such as a model-based control, are essential to improve accuracy of servo hydraulic actuators in structural testing. Such control strategies require a servo-loop, often referred to as an inner-loop, of the actuator to be digitally controlled. To make the best use of digitally controlled inner-loops that have numerous advantages over conventional analog counterparts, a thorough understanding of the actuator inner-loop is needed. This study presents an error analysis of digitally controlled servo hydraulic actuators with a focus on sources and growth of errors in the actuator inner-loop. First, effects of errors such as measurement errors and electrical noises on the performance of servo hydraulic actuators are analytically investigated. Then, using detailed models of those errors and an open-loop servo hydraulic actuator, an extensive numerical simulation is performed to evaluate the effect of errors on the actuator performance. Numerical results show that the displacement measurement error has an undesirable influence on the actuator responses in the high-frequency range. Such responses make it difficult to accurately assess structural and nonstructural systems in the high-frequency range using the hydraulic actuators. In particular, velocity and acceleration responses of the hydraulic actuator are highly sensitive to the displacement measurement error. This investigation provides fundamental knowledge that is required for an effective use of digitally controlled servo hydraulic actuators. [ABSTRACT FROM AUTHOR]