Abstract: An improved unbalance vibration generator adapted to be driven at varying rotational speeds while maintaining a substantially constant exciting force throughout a range of rotational speeds. The generator includes an unbalance mass comprising first and second unbalance masses journaled for rotation and angularly offset from each other 180.degree. about the axis of rotation. The first unbalance mass is journaled on the axis of rotation and the second unbalance mass is radially movable in relation thereto. This radial movement is restrained by cam and spring means which provide predetermined non-linear restraint of the second unbalance mass relative to the first unbalance mass.

Abstract: The screening motion of a screening machine is changed by adding ballast, while the machine is in operation, to selected closed compartments moving with the vibrating assembly. In the preferred embodiment, the ballast is added through flexible tubing which is inserted through ports that close with spring loaded oil hole caps. When the tubing is pulled from the ports, the caps snap closed to capture the ballast in the selected compartments.

Abstract: A sieve for screening material such as ore or coal wherein the sieve member extends horizontally and is supported at its edges by longitudinal sidewalls and at the center by a longitudinal intermediate wall and a vibratory oscillatory drive force is applied to the intermediate wall twice that of the sidewalls by rotating eccentric weights for the intermediate wall and sidewalls with the intermediate wall eccentric weight being twice that of the sidewalls eccentric weights and the rotating weights interconnected by flexible shaft drives and a main drive motor driving all of the weights in rotation.

Abstract: A vibratory structure of a screening apparatus has two shafts connected to rotate together by a toothed belt. Each shaft carries an eccentric weight which may be adjusted relative to the position of the shaft. The amplitude and frequency of the screening apparatus may be easily adjusted by adjustment of the weights and change of the transmission ratio between the two shafts.