Automatic balancing is typically defined as continuous and "in-operation" compensation for imbalance. Ball balancers belong to a class of the automatic balancers often referred to as direct balancers or passive mass systems. In such systems thebalancing is achieved with free masses. These devices utilize the so-called phase shift by angleπ between the shaft deflection and the direction of effective imbalance at supercritical speeds. In its most basic form, ball balancers consist of an annularrace (chamber) partially filled with fluid and containing at least two compensating masses in the form of balls. In an idealized system, at speeds greater than the critical speed, the compensating masses, acted upon by the centrifical forces associatedwith synchronous whirling of the shaft, would position themselves opposite to the effective imbalance, thus balancing the shaft.The first ball balancer is generally attributed to Thearle (1]. After then, in excess of 150 patents related to ball balancers have been issued in North America, Japan, and Europe with the most recent U.S. patent by Taylor [2].
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