Active Isolation and Damping of Vibrations for High Precision Laser Cutting Machine

High precision industrial machines suffer the presence of vibrations due to several noise sources: ground vibration, acoustic noise, direct force disturbances. These are sources of several problems at different levels and of different natures causing the performance losses on sensitive systems (Crede, 1951), (Rivin, 1979). In the last years the need of higher processing quality and throughput resulted in a continuing demand for higher accuracy. Therefore active isolation and vibration damping systems became mandatory to satisfy these requests (Preumont, 2002), (Hyde, 1997). In general, machine supports are designed for high stiffness to obtain a robust machine alignment with respect to its surroundings. However, in the presence of significant ground vibration levels the support stiffness is commonly sacrificed to reduce the transmission to the payload stage. Efforts to go towards these issues are recorded in several applications and the solutions are different for any particular situation, depending on the nature of the vibration sources, the amount of the disturbances and the machine environment. Three main categories of possible approaches can be identified: passive, active and semiactive configurations. Completely passive solutions have almost reached their maximum potential which is still not sufficient to satisfy stringent requirements. On the opposite, the exponential growth in electronics and actuators fields made the use of active and semi-active isolation more feasible. In particular, active control architectures allow to perform an effective isolation at low frequencies, which is a common requirement for very demanding applications like micrometer motion control, defect inspections, critical dimensions measurement and overlay metrology. Active control arrangements are provided with sensors, actuators and controllers (Watters, 1988). Each of them can be classified depending on their technology and physical working principle. For the application considered in this work, the main categories of sensors used are: displacement, velocity, acceleration, strain and force. In the same way, the most common types of actuators are: shape memory alloys, magnetic, piezoelectric, magnetostrictive and magneto-rheological fluids actuators (Thayer, 1998). The choice of sensors and actuators is strictly related to the type of application and requirements and has also influence on the selection of the control strategies to be