Magnetic Suspension of Flexible Structures for Non-Contact Processing

This paper presents the magnetic suspension of elongated workpieces by using multiple electromagnetic actuators and multiple position sensors. Our particular focus is on the use of such suspensions in manufacturing processes such as coating and painting which can be facilitated by non-contact handling. We have developed a novel approach for the control of such non-contact suspensions through what we term sensor averaging and actuator averaging. The difficult stability and robustness problems imposed by the flexible dynamics of the workpiece can be overcome by taking a properly-weighted average of the outputs of a distributed array of N motion sensors (sensor averaging), and/or by applying a properly-weighted distributed array of M forces (actuator averaging) to the workpiece. The theory for these dual techniques is developed in detail in the paper. These approaches are shown to be independent of the specific boundary conditions or the longitudinal dimensions of the workpiece. We experimentally demonstrate the utility of our theory in the successful magnetic suspension of a 3 m long, 6.35 mm diameter, 0.89 mm wall thickness steel tube with varying boundary conditions. This suspension uses 8 two-degree-of-freedom actuators and 8 two-degree-of-freedom sensors distributed along the length of the workpiece.