Mechanical Systems

Abstract

In this chapter, several different control applications for mechanical systems are examined. The first system discussed is an autobalancing application. A perfectly balanced rotating object (i.e., the center of geometry and center of mass are coincident) will usually not undergo any vibration. However, due to the errors associated with geometric dimensions and the nonhomogeneity of the raw material, the construction of a perfectly balanced object is difficult to achieve using a standard manufacturing process. Due to the difficulty and/or expense required to construct a perfectly balanced ob-ject, some amount of vibration can be expected as an object rotates. This vibration can lead to performance degradation and/or failure of the mechanical system. These undesirable vibrational effects are often amplified during high-speed rotation. A simple solution to the imbalance problem is to introduce passive damping via selective placement of ball bearings. However, the use of a passive bearing often leads to an increase in friction, resulting in further degradation of the system performance. An alternative means to mitigate the vibrational effects of rotating systems is to produce frictionless forces (e.g., magnetic forces) that act on the rotating body. These forces can provide an autobalancing capability for the case of highspeed rotation-based systems (e.g., precision grinding, turbines, aircraft propellers, flywheels). However, since the slightest imbalance can induce very large and potentially destabilizing vibrations, an active control system that can generate the desired forces very precisely is needed.