Automatic balancing of centrifuges by means of fluids and solids

Automatic ball balancers (ABB) can be applied to rotating machinery in order to reduce the effective unbalance excitation and resulting deflections. The passive working mechanism does not necessitate active components such as sensors, control units and actuators. In an ABB several balls are enclosed in a cylindrical cavity and can orbit freely on a circular track positioned centrically to the axis of rotation of the equipped rotor. As inherent to the functional principle, the rotating speed has to exceed the first critical frequency for the balls to be positioned beneficially and counterbalancing the primary unbalance. During the transient phase prior to the rotor reaching the final operating speed and the balls adopting their final stationary resting position relative to the rotor system, the movement of the balls is strongly dependent on the environing fluid in the cavity. From gaseous environments to highly viscous oils a wide scope is available to design the ABB.
In current research a carbon fiber reinforced plastic rotor for medical centrifuges is equipped with an ABB and the ideal range for the density and viscosity of the fluid in the balancer is explored experimentally as well as by means of multi-body simulations incorporating the fluid structure interaction in the ABB.