Analytical study and design characteristics of scratch drive actuators

Scratch drive actuators (SDAs) are one of the important microelectromechanical devices that have been recently used for many applications. This paper presents a new analytical model for the scratch drive actuators to facilitate the design of this device. In order to model the working states of SDA, three different static modes are considered: non-contact mode, transitional mode, and full-contact mode. The SDA is simplified as an L-shape plate with different boundary conditions in each mode. Using Euler Bernoulli theory, governing equations are derived and solved in every mode. The non-contact mode allows identifying the deflection and driving voltage at which the actuator plate reaches to the substrate. From the transitional mode, primary contact length is calculated and used for the analysis of full-contact mode. In the full-contact mode, where SDA is completely snapped down in its working cycle, the relationships between input voltage and design parameters, such as SDA geometry, contact length and step size, are obtained. In addition, output force, as another important design parameter, is characterized based on the physics and geometry of SDA. To validate our model, the results are also compared with accessible experimental data. This analytical model provides an efficient framework to estimate the design parameters of SDA before any expensive empirical process. (C) 2010 Elsevier B.V. All rights reserved.