Characteristic switching of a multilayer thin electrostatic actuator by a driving signal for an ultra-precision motion stage

The present paper describes the characteristic switching of a multilayer thin electrostatic actuator supported by only lubricating oil and its application in the control of an ultra-precision fine stage. Friction forces often deteriorate the response and positioning accuracy of a control system. However, they generate a large holding force, which is needed to precisely maintain the stage position in fine stages. When the lightweight electrode layers in the electrostatic actuator are supported by only lubricating oil, the contact condition between the electrode layers can be changed by the attractive forces resulting from the driving signal, which consequently influences the frictional effect. Thus, suitable driving signals have the potential to adjust the frictional effect for fine motion with a large holding force and a wide and fast motion. In this paper, suitable driving signals for switching between two frictional conditions (i.e., low friction for the wide and fast motion and high friction for the fine motion with a large holding force) are examined and clarified. First, the relationship between the driving signals and the working range of the actuator is explained. Then, the holding force characteristics and the driving signals for switching between the frictional conditions are discussed. Finally, the actuator control system is designed based on the findings. The control system includes a PID compensator and a driving signal unit that generates two driving signals. One driving signal provides a driving mode with a holding force for a working range smaller than 250 nm. The other driving signal provides a wide driving mode for a working range wider than 250 nm under low-friction conditions. The driving signal is determined so as to quickly change the frictional effect. A combination of these modes (referred to as the dual driving mode) is implemented in the actual multilayer electrostatic actuator, and its effectiveness is validated experimentally. The actuator exhibits a positioning error of less than 14 nm with a continuous holding force of 0.205 N.

► The multilayer thin electrostatic actuator is supported by only lubricating oil.
► The characteristic switching of the electrostatic actuator is proposed.
► The relationship between the characteristics and the driving signals are discussed.
► The control system is designed based on the characteristic switching.