טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentTresser Shachar
SubjectInvestigation of Mechanical Self-Balancing for Rigid Rotors
DepartmentDepartment of Mechanical Engineering
Supervisor Dr. Itzhak Porat
Full Thesis text - in Hebrew Full thesis text - Hebrew Version


Abstract

Unbalance is one of the most critical issues in rotating machinery. Unbalance may cause vibrations of the system, excessive wear and even immediate failure. The present research deals with an investigation of a mechanical system which automatically balances rotors, without need of any control or external interference. The device is based on balls which are free to move in a race, which is located on the rotor. Given certain conditions, the balls tend to place themselves in positions that counterbalance the rotor. This device seems to be ideal for machines with an amount of unbalance that changes in time, such as washing machines, CD drives or machines that accumulate corrosion with time, since the balls adapt their position to the given unbalance at any time.

The present study includes a numerical and experimental investigation of automatic ball balancers. This study proposes a new dynamic model for the balancer, which includes two degrees of freedom for each ball. The new dynamic model enables modeling of transitions from slipping to pure rolling of the balls and vice versa. In addition to the new dynamic model, the study also includes a thorough investigation of the effect of rolling friction. It is shown that for typical values, rolling friction may cause the balls to settle in undesired locations, resulting in residual unbalance, which may even be larger than the initial unbalance. The study also shows an inquiry of the influence of different parameters on the balls' position error, and on the residual unbalance of the rotor. A statistical inquiry was conducted both numerically and experimentally, in order to find the influence of rolling friction and other parameters on the system.