Theoretical and experimental analysis of self-compensating dynamic balancer in a rotating mechanism

A theoretical and experimental approach was used to investigate the motion and effectiveness of a Self-Compensating-Dynamic-Balancer (SCDB). This is a device intended to minimize the effects of rotor unbalance and vibratory forces on a rotating system during normal operation. The basic concept of an automatic dynamic balancer has been described in many U.S. patents. The SCDB is composed of a circular disk with a groove containing massive balls and a low viscosity damping fluid. The objective of this research is to determine the motion of the balls and how this ball motion is related to the vibration of the rotating system using both theoretical and experimental methods. The equations of motion of the balls were derived by the Lagrangian method. Static and dynamic solutions were derived from the analytic model. To consider dynamic stability of the motion perturbation equations were investigated by two different methods, i.e., Floquet theory and direct computer simulation. Based on the results of stability investigation, ball positions which result in a balanced system are stable above the critical speed and unstable at critical speed and below critical speed. To predict the motion of the balls and rotating disk, numerical simulations were carried out. Modal analysis was conducted to determine the actual critical speed of the rotating system used in the experimental work. Experimental results confirm the predicted ball positions. Based on the theoretical and experimental results when the system operates below and near the first critical speed, the balls do not balance the system. However, when the system operates above the first critical speed the balls can balance the system.