Centrifugal Pendulum Vibration Absorbers—Theory and Practice

Reciprocating mechanical systems, such as pumps and compressors, present a nonuniform dynamic load to the driving motor. These load variations and their interactions with the dynamic characteristics of the motor result in dynamic torque variations on the rotor which have very significant harmonic components. These torque variations contribute to undesirable dynamic loading of the mounting frame and subsequent transmission of vibrations and noise into the supporting structure. Centrifugal pendulum absorbers offer an excellent means for the elimination of the effects of some of these torque harmonics. Since most reciprocating machinery operates over a speed range depending on load conditions, the centrifugal absorber is an excellent means for insuring that the suppression of vibrations is insensitive to speed and local conditions. While the virtues of centrifugal absorbers are well known as are the differential equations describing the dynamics of the absorbers, the literature does not address the case of real absorbers with distributed mass properties. This paper presents a derivation of the equations of motion for the rotor and the distributed mass pendulum, along with those insights and techniques necessary for the practical design of a centrifugal pendulum system. The tuning of the pendulum is discussed along with damping requirements. A case study is presented where a set of pendulums is employed on the rotor of an air compressor driven by a close-coupled electric induction motor. In the case study, first and second harmonic rotor torques (30 percent and 9 percent, respectively, of the average rotor torque) are eliminated with 3.77 lb and 0.83 lb pendulums in a 3-horsepower, 875 rpm machine.