Characterization of stiction effects of an electrostatic micro positioner for probe storage

We start by presenting a short explanation of the micro actuator working principle. The main contribution of this paper is the characterization of the coefcient of stiction between two silicon nitride parts of a MEMS actuator. Having one at contact surface while the other is composed of many relatively sharp circular bumps, has the advantage that the effective contact area is drastically reduced. The stiction coefcient varies between 0-0.53 for the device conguration presented. The exact value depends closely on the electrostatically applied force which presses the textured part on to the smooth one. Individual measurements used are highly accurate (typically within 5 nm noise band) and identical measurements for the characterization of stiction show only a small variation, typically under 25nm on a range of 11.8m

Stick-slip actuation of electrostatic stepper micropositioners for data storage-the µWalker

This paper is about the /spl mu/Walker, an electrostatic stepper motor mainly intended for positioning the data probes with respect to the storage medium in a data storage device. It can deliver forces up to 1.7 mN for ranges as large as 140 /spl mu/m. Controlling the stick-slip effects at the sliding surfaces is of central importance for reliable operation. A model is introduced to estimate the operating voltage of the actuator plate, which is an essential part of the /spl mu/Walker. Several methods to obtain displacements smaller than one nominal step (/spl ap/ 50 nm) are discussed, as well as how to increase the step repeatability and accuracy

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

Closed-Loop Control of a Micropositioner Using Integrated Photodiode Sensors

A closed-loop control system with photodiode position sensors has been implemented in a microball bearing supported linear electrostatic micromotor to improve accuracy and reliability. The fabrication sequence of the previously developed micromotor was modified to integrate a photodiode-based position sensing mechanism. Proportional control law is used in the control system and device step response is analyzed for several step sizes at various maximum applied voltages by varying the constant of proportionality. Two critical functions for micropositioning applications have been demonstrated; the device can establish a necessary frame of reference for coordinate-based positioning and autonomously respond to arbitrary disturbances. The closed-loop position control system presented in this work illustrates the feasibility and functionality of smart microsystems using integrated feedback sensors