Fixture control by hydraulic actuation using a reduced workpiece model

In this paper the dynamic behaviour of a part and an actuated fixture system is studied. The part is modelled using the finite element method. Subsequently, a reduced model is established using the Craig-Bampton reduction method in order to create a small-sized model, accurately describing the dynamic behaviour of the part. The clampers and locators of the fixture are modelled as springs. The fixture frame is considered to be much stiffer than the locators such that it provides the zero displacement boundary conditions to the locators. A hydraulic actuator is utilized to provide the adaptive clamping forces. A methodology is presented to obtain the reduced model of the part and to couple it with the model of the active fixture. After investigating proportional control, lag, and lead filters for dynamic compensation, the analysis shows that position feedback can be used effectively to minimize unnecessary displacement of the workpiece.