Constrained Model Predictive Control For Six-DOF Vibration Isolator Of The Absolute Marine Gravimeter

Measuring absolute gravity acceleration from a ship or aircraft is essential in gravimetry. Unlike conventional ground measurement, absolute marine gravimeters are disturbed in six degrees-of-freedom. Among the six degrees-of-freedom, the translation along the Z-axis and the rotations around the X-axis and Y-axis have the main influences on the measured gravity acceleration. Thus a six-degrees-of-freedom vibration isolator with output constraints is developed in this paper. The structure of the vibration isolator is based on the Stewart platform, and the state-space dynamic model with disturbances is established via the Newton-Euler method. A constrained model predictive controller is then designed for the vibration isolator. The controller handles the constraints of the three dominant degrees-of-freedom explicitly. Finally, the simulation is performed to validate the presented isolator. The external disturbances in six degrees-of-freedom are well attenuated, besides the motion of the three dominant degrees-of-freedom is within the designed constraints. Thus, the precision of the absolute marine gravimeter can be satisfied with this six-degrees-of-freedom vibration isolator.