Analysis and optimization of an electromagnetic actuator with passive gravity compensation

In the high-precision positioning systems, e.g. the wafer stage in lithography machine, the temperature rise of actuators is strictly restricted to guarantee a stable measurement environment for laser interferometers. Unfortunately, for the z-axis actuators, a constant levitation force component is required to incessantly support the moving mass of the wafer stage at the cost of copper loss. In this paper, an electromagnetic actuator with passive gravity compensation is described. The novel actuator combines the active Lorentz force with the passive magnetic force, thus can be used to support the moving mass of the fine stage or some multi-degree-of-freedom short-stroke positioning devices. Compared with the traditional z-axis actuators (e.g. voice coil motors), the copper loss and temperature rise of the active coils in the proposed actuator is significantly reduced, which is beneficial to the high-precision positioning applications.