Implementation of Adaptive and Proportional-Integral Algorithms in Servo Hydraulic Fatigue Testing Machines

The process of failure due to oscillating forces is referred as fatigue, which is the main cause of mechanical failures.
Experimental research in this area for validation of theoretical results requires a tension-compression fatigue testing
machine equipped with special capabilities. The organized control of force plays an important role in the validity of test
results and is an essential part of fatigue testing machines. The main aim of this paper is to enhance the control unit of
servo-hydraulic fatigue testing machines in order to reduce settling time. The most important issue is uncertainties in
the measurement of the specimen’s stiffness. In this study, the parameters related to mathematical model of fatigue
testing machines are detected and the proportional-integral controller is designed and implemented. The obtained results
of implementation of this controller shows that the settling time related to the fatigue testing of parts with low stiffness
is more than what is expected. Thus, an adaptive controller is proposed and implemented in order to reduce the settling
time. So as to obtain more appropriate response to disturbance, the proposed algorithm is combined with the
proportional-integral controller. Using this novel controller decreases settling time by 25 % and makes the system
response to measurement noise and disturbance more desirable.