CASE STUDIES: MODAL ANALYSIS FOR DESIGN IMPROVEMENTS OF TWO INDUSTRIAL SPATIAL SHEET FORMING AND FEEDING MACHINES

摘要

Data on the critical speed and natural mode frequency bands of industrial machines form very important design information. Industrial machines designed without being concerned with how close their operating speeds are in relation to their natural mode frequencies may become inherently troubled systems that cannot perform their tasks. The article presents two case studies on such machines and design improvements done using modal analysis techniques. Both of these machines have RSSR space mechanism as the nonuniform motion generating drive system. One of these machines is used for sheet metal forming via pinion-rack drive. The other is used to feed paper bags from a stack to a conveyor via suction cups. The former had been experiencing rapid fatigue failure of the pinion and rack teeth, the latter simply vibrated the suction cups on the paper bags instead of picking them. Model analyses of these mechanisms showed that they were being operated in the very neighborhood of their fundamental critical speeds, and that the stiffnesses of the flexible couplings played considerable role in their dynamic behaviors. Recommended and implemented design changes are discussed.