Sunday May 17, 2009 WorkShop sw-f1: Control Issues in the Micro/Nano-World


The objective of this workshop was to give an overview of current control techniques for systems in the micro/nano-world and MEMS/MOEMS/NEMS. Systems for microassembly and micromanipulation, micro/nano-positioning, imaging/measuring and manipulating systems with nanometer accuracy (AFM, etc.) were considered. These applications require a high position accuracy and sometimes a rapid response time, but the characteristics (e.g., hysteresis, creep, etc.) of the actuator and sensor materials (piezoelectric, SMA materials, etc.) frequently limit the performance. Moreover, the minute displacements in these systems lead to very low signal-to-noise ratio in the position measurements. Finally, sensors that can provide the required performances for micro/nano-manipulation tasks are often large and not easily integrated into the system, and sensors with small dimensions are often noisy and with limited dynamic ranges.

Motivation and objectives

During the last decade, the need of systems with micro/nanometers accuracy and fast dynamics has been growing rapidly. Such systems occur in applications including 1) micromanipulation of biological cells, 2) micrassembly of MEMS/MOEMS, 3) micro/nanosensors for environmental monitoring, 4) nanometer resolution imaging and metrology (AFM and SEM). The scale and requirement of such systems present a number of challenges to the control system design that will be addressed in this workshop. Working in the micro/nano-world involves displacements from nanometers to tens of microns. Because of this precision requirement, environmental conditions such as temperature, humidity, vibration, could generate noise and disturbance that are in the same range as the displacements of interest.

The so-called smart materials, e.g., piezoceramics, magnetostrictive, shape memory, electro-active polymer, have been used for actuation or sensing in the micro/nano-world. They allow high resolution positioning as compared to hinges based systems. However, these materials exhibit hysteresis nonlinearity, and in the case of piezoelectric materials, drifts (called creep) in response to constant inputs In the case of oscillating micro/nano-structures (cantilever, tube), these nonlinearities and vibrations strongly decrease their performances.

Many MEMS and NEMS applications involve gripping, feeding, or sorting, operations, where sensor feedback is necessary for their execution. Sensors that are readily available, e.g., interferometer, triangulation laser, and machine vision, are bulky and expensive. Sensors that are compact in size and convenient for packaging, e.g., strain gage, piezoceramic charge sensor, etc., have limited performance or robustness. To account for these difficulties, new control oriented techniques are emerging, such as[d the combination of two or more ‘packageable’ sensors , the use of feedforward control technique which does not require sensors, and the use of robust controllers which account the sensor characteristics. The aim of this workshop is to provide a forum for specialists to present and overview the different approaches of control system design for the micro/nano-world and to initiate collaborations and joint projects.

Webmaster: Micky Rakotondrabe.