**1. Introduction**

26 Will-be-set-by-IN-TECH

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107-114.

No.10, pp. 4421-4424.

*Structures*, Vol. 19, No. 045003, pp. 1-10.

High precision industrial machines suffer the presence of vibrations mostly due to two noise sources: ground vibration and direct force disturbances. They can generate several problems at different levels and of different natures, causing performance losses on sensitive systems (Crede, 1951), (Rivin, 1979).

In the last years the growing processing quality level and the need to increase throughput resulted in a continuing demand for higher accuracy. Therefore active isolation and vibration damping systems became mandatory to satisfy these requests (Pneumont, 2002), (Hyde, 1997).

In general, machine supports are designed for high stiffness to obtain a robust machine alignment with respect to its surroundings. However, when significant ground vibration levels occur, the support stiffness is commonly sacrificed to reduce vibration 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 vibration sources, the amount of disturbances and the machine environment.

Several actuation technologies are used to face this kind of problem: shape memory alloys, electromagnetic, piezoelectric, magnetostrictive and magneto-rheological fluids actuators (Thayer, 1998). Among them, electromagnetic actuators revealed themselves as effective and performing. Methods for vibration suppression can be classified in a rough approach in three families: passive, active and semi-active actuators. 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

© 2012 Chiaberge et al., licensee InTech. This is an open access chapter distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2012 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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.

In general, 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. 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 employed. Depending on the type of controller, the system model can be used only to support the control design or can play itself a fundamental role on the control action (model based strategies) (Beadle et al, 2002), (Sullivan, 1997). Typically the main control approaches are feedback, classical or model based, and feed-forward technique, mostly with adaptive reference filtering (Anderson, 1996).

This chapter focuses on the evaluation of an active isolation and vibration damping device mounted in the working cell of a micro-mechanical laser center, which is based on active electromagnetic actuators. Two different models and three control strategies are developed and illustrated.

To clarify the goal of this study it is important to point out that: a) the vibration damping is defined as the reduction of the response amplitude of the system within a limited bandwidth near the natural frequencies of the system; b) vibration isolation is defined as the attenuation of the response of the system after its corner frequency to cut-off all the disturbances after that frequency, while allowing all the signals below it to pass with no alterations.

The machine object of study is composed by two main parts: a frame support and a payload stage where the laser cutting operation is performed. The system performance in terms of accuracy and precision is reduced by the presence of two main vibration sources: the ground and the stage itself. The active device should meet two goals: the payload vibrations damping and the reduction of the transmissibility of ground disturbances.

In this work, after a review of the major actuators families usually employed to damp and isolate high precision machines, the phases followed to design, implement and validate the proposed device are illustrated with a particular emphasis on the mechatronics aspects of the project.

A detailed analysis of the plant components is reported along with an exhaustive explanation of the design criteria followed for the choice of supports, actuation and sensing subsystems. The actuation block consists in four electromagnetic Lorentz type actuators (two per axis).

The absolute velocities of the frame support and of the stage are measured by means of eight geophone sensors to determine the amount of disturbances (Huan, 1985), (Riedesel, 1990). The considerations leading to the choice of this sensing system are reported along with the description of the related signal conditioning stage. The design of the supports between the ground and the frame and of the connections between the frame and the stage is also explained.

Furthermore, all the subsystems described in the first part of the chapter are modeled along with their interactions. The Lagrange equations approach is used to represent the system behavior and in particular the links between the mechanical and electrical subsystems are illustrated.

514 Smart Actuation and Sensing Systems – Recent Advances and Future Challenges

reference filtering (Anderson, 1996).

and illustrated.

the project.

(two per axis).

inspections, critical dimensions measurement and overlay metrology.

architectures allow to perform an effective isolation at low frequencies, which is a common requirement for very demanding applications like micrometer motion control, defect

In general, 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. 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 employed. Depending on the type of controller, the system model can be used only to support the control design or can play itself a fundamental role on the control action (model based strategies) (Beadle et al, 2002), (Sullivan, 1997). Typically the main control approaches are feedback, classical or model based, and feed-forward technique, mostly with adaptive

This chapter focuses on the evaluation of an active isolation and vibration damping device mounted in the working cell of a micro-mechanical laser center, which is based on active electromagnetic actuators. Two different models and three control strategies are developed

To clarify the goal of this study it is important to point out that: a) the vibration damping is defined as the reduction of the response amplitude of the system within a limited bandwidth near the natural frequencies of the system; b) vibration isolation is defined as the attenuation of the response of the system after its corner frequency to cut-off all the disturbances after that

The machine object of study is composed by two main parts: a frame support and a payload stage where the laser cutting operation is performed. The system performance in terms of accuracy and precision is reduced by the presence of two main vibration sources: the ground and the stage itself. The active device should meet two goals: the payload vibrations

In this work, after a review of the major actuators families usually employed to damp and isolate high precision machines, the phases followed to design, implement and validate the proposed device are illustrated with a particular emphasis on the mechatronics aspects of

A detailed analysis of the plant components is reported along with an exhaustive explanation of the design criteria followed for the choice of supports, actuation and sensing subsystems. The actuation block consists in four electromagnetic Lorentz type actuators

The absolute velocities of the frame support and of the stage are measured by means of eight geophone sensors to determine the amount of disturbances (Huan, 1985), (Riedesel, 1990). The considerations leading to the choice of this sensing system are reported along with the description of the related signal conditioning stage. The design of the supports between the ground and the frame and of the connections between the frame and the stage is also explained.

frequency, while allowing all the signals below it to pass with no alterations.

damping and the reduction of the transmissibility of ground disturbances.

Two models are developed: a) four degrees of freedom model and b) six degrees of freedom model. Both of them include the plant, the sensing, the control and the actuation blocks. Time and frequency domain computations are carried out from the models to evaluate vibration levels and displacements and to identify which control parameters need to be carefully designed to satisfy the requirements.

The last section exposes in detail the proposed control strategies along with the modeling approach validation. Three different control strategies are developed:

