Full Paper Sheet Control Using Hybrid Automata

Some high speed color printers require that the sheets be accurately controlled in order to achieve a precise alignment of colors. To accomplish this goal a steerable nips mechanism has been proposed as the actuator. This steerable nips mechanism allows the sheet to be precisely controlled in longitudinal, lateral and skew directions. In this paper we develop a control strategy based on hybrid automata that precisely controls the position of the sheet. This hybrid control law has four finite states among which the system switches during the trajectories tracking process. Switching from one state to another is necessary since the normal control mode cannot be used when the trajectory being tracked requires the wheels to have zero angular velocity. The proposed controller is able to move the sheet from an initial position at rest to an arbitrary final position also at rest. The system model is nonlinear and subject to four nonholonomic constraints. Two of these constraints come from the fact that the velocities perpendicular to the wheels must be zero, and the other two constraints are due to the no-slip condition.