Nanometer range closed-loop control of a stepper micro-motor for data storage

We present a nanometer range, closed-loop control study for MEMS stepper actuators. Although generically applicable to other types of stepper motors, the control design presented here was particularly intended for one dimensional shuffle actuators fabricated by surface micromachining technology. The stepper actuator features 50 nm or smaller step sizes. It can deliver forces up to 5 mN (measured) and has a typical range of about 20 μm. The target application is probe storage, where positioning accuracies of about 10 nm are required. The presence of inherent actuator stiction, load disturbances, and other effects make physical modeling and control studies necessary. Performed experiments include measurements with openand closed-loop control, where a positioning accuracy in the order of tens of nm or better is obtained from image data of a conventional fire-wire camera at 30 fps.