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Design and application of a motion platform in three degrees of freedom.

Aalesund University College is building the first full-size high-speed craft simulator in Norway. In preparation of the construction of the simulator there has been built a small-scale motion simulator to test the possibilities to imitate the movements of the ship. The model is based on a Stewart platform in three degrees of freedom roll, pitch and heave. The platform deck is moved by three DC-servomotors through three legs situated at the corners of an equal sided triangle with its center aligned with the mass center of the deck. The movements of the ship are generated in a ship simulator on a PC, and the primary signals are transformed to equivalent manipulating signals to the three servo drives. These signals are converted to analog voltages which are applied as the reference signals to a Pulse Width Modulation card controlling each motor. There has been done comprehensive testing of the motion simulator, and it seems like the platform will imitate the movements of a ship in a satisfactory way. As part of the testing there has also been developed a control loop for manipulating the path of a moving object, e. g. a ball or a wheel, on the platform. For this purpose a camera is used to measure the position and velocity of the object in the x- and y-directions and the results used to make the object follow a given reference path. Different regulator strategies have been tried, like pole placement, optimum control, fuzzy logic and neural networks. The results have been satisfactory and the object is controlled to move in a circle or 8-curve or from point to point as decided.