Strain measurement under the minimal controller synthesis algorithm and an extensometer design

In this paper, minimal controller synthesis (MCS) algorithm is used in the case of strain measurement for the first time. The MCS control is an adaptive control method and it can be recommended as a robust controller for the servohydraulic materials testing machine. The algorithm coped with various specimens, which have different materials and diameters. The control accuracy is important in materials testing due to the fact that even smaller overshoots or undershoots can cause undesirable results in cyclic loading. For this reason, the controller parameters needs to adjusted according to the changes in the plant parameters for acceptable plant output responses. In order to measure strain signal a simple LVDT extensometer was designed. In this set tests, two different specimens were used: aluminium alloy specimens of diameter 10 mm and EN24T steel specimens of diameter 7 mm. The MCS control was implemented in two degrees of freedom form and produced very satisfactory plant output responses owing to the fact that the results produced by the control are in the range of actual values. This indicates that the MCS control can be used in strain measurement very effectively. It may also indicate the possibility of using the MCS control other materials testing applications like strain control and temperature cycle tests.