**Author details**

havior of closed loop current control as illustrated in Figure 19 (a and b). It can be noticed that the same current control applied to the two opposite electromagnets of the same actua‐ tion axis without electrical centering generates two different closed loop responses. Few mi‐ crons of Airgap generates differences of hundreds of Hertz on current control bandwidth.

Considering that this behavior is generated by a difference of inductance value of the two electromagnets, by acting on the position reference with offset corrections of the outer po‐ sition control, the rotor can be set to spin around a point where electrical parameters are equalized and current loop bandwidths of both the electromagnets are the same (Figure 19 (c and d)). Further studies and research are being conducted on this strategy since this process can be performed in an on-line automatic routine with an adaptive technique, able to change the control parameters of the inner current loop while the Airgap is chang‐

In this chapter the modeling, the design and the experimental tests phases of a rotor equip‐ ped with active magnetic bearings have been described. The description deals with rotordy‐ namic aspects as well as electrical, electronic and control strategies subsystem. The control design of a standard decentralized SISO strategy and the details of an innovative off-line electrical centering technique have been exposed.Experimental results have been exposed

ing, i.e. when the rotor is oscillating.

24 Advances in Vibration Engineering and Structural Dynamics

**Figure 18.** Electrical pole trend at varying of inductance value.

highlighting mainly rotordynamics and control aspects.

**5. Conclusions**

Andrea Tonoli, Angelo Bonfitto\* , Mario Silvagni and Lester D. Suarez

\*Address all correspondence to: angelo.bonfitto@polito.it

Mechanics Department, Mechatronics Laboratory – Politecnico di Torino, Italy

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**Chapter 2**

**Provisional chapter**

**Estimation and Active Damping of Unbalance Forces in**

Nowadays, rotordynamics is a technological field in which research is very active because in spite of basic phenomena have been widely studied, there are many aspects that still need theoretical and practical work in order to construct and analyze models to represent with more precision the dynamic behavior of real machines. Dynamic studies in rotordynamics usually are preformed by numerical simulations using the mathematical models reported in literature. The mathematical description of rotating systems allows the possibility to predict their dynamic behavior and to use this information for the design of control algorithms in order to preserve the desired stability and dynamic performance. The accuracy of a model is determined by comparing its response and the response of the real system to the same input signal [19]. Rotor systems are subjected, in an intrinsic way, to endogenous disturbances, centrifugal forces by the inevitable unbalance phenomenon. Magnitude of these unbalance forces depends on the rotor mass, angular speed and distance between geometric center and center mass of rotor [10, 11, 29]. This last parameter is known as eccentricity and represents one of the most difficult parameter to measure or to estimate in a rotor system

The recent trends in rotordynamic systems are moving to higher speeds, higher powers, lighter and more compact machinery, which has resulted in machines operating above one or more critical speeds and increasing the vibration problems [5, 31]. In literature, the unbalance phenomenon has been widely reported as the main source of undesired vibration in rotating machinery [5, 10, 11, 29]. An unacceptable level of vibration can cause failure in the bearings, high levels of noise, wearing in the mechanical components and eventually, catastrophic failures in machines [10, 29], hence, control algorithms are needed to reduce the unbalance effects and to take vibrations amplitudes to acceptable values for a safe machine operation.

> ©2012 Beltran-Carbajal 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 Beltran-Carbajal et al.; licensee InTech. This is an open access article 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 Beltran-Cerbajal et al.; licensee InTech. This is a paper 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.

**Estimation and Active Damping of Unbalance**

**Forces in Jeffcott-Like Rotor-Bearing Systems**

**Jeffcott-Like Rotor-Bearing Systems**

Gerardo Silva-Navarro and Manuel Arias-Montiel

and consequently, it is an important aspect for the accuracy model.

Additional information is available at the end of the chapter

Gerardo Silva-Navarro and Manuel Arias-Montiel

Additional information is available at the end of the chapter

Francisco Beltran-Carbajal,

Francisco Beltran-Carbajal,

http://dx.doi.org/10.5772/51180

**1. Introduction**

**Provisional chapter**
