A Reluctance Actuator Gap Disturbance Testbed

Abstract

We have designed and built a Reluctance Actuator Gap Disturbance Testbed. The testbed emulates the short stroke and long stroke interaction of modern lithography stages. The testbed can be used to impart gap disturbance of the order of 10[mu]m to a target platten thereby providing a gap disturbance to the reluctance actuator. The testbed is equipped with three single-axis load cells that can measure a normal force, a roll torque and a pitch torque. We keep track of the orientation and position of the stage by using capacitance probes. The gap disturbance is imparted with three piezos capable of a stroke of 15[mu]m.We have also fabricated several reluctance actuators that fit into this testbed. These actuators use a two coil winding per core to prevent leakage and reduce stray torques. The cores of these actuators are made of Cobalt Iron, the soft magnetic material with the highest flux density saturation. Both a single actuator and a double actuator were fabricated. The double actuator can impart a roll torque as well as a normal force. Finite Element Method was utilized to design the actuators and to understand the nature of the rotational stiffness of the actuator. Experiments to do disturbance rejection were carried out and also different methods of force control (like Flux Feedback) are discussed and implemented