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Operational stability loading feeder

Operational stability

Operational stability of a loading feeder

The shown loading feeder is used for transporting sheet metals in the automotive industry. With a cycle rate of maximum 28 [min-1] single sheets are raised by about 250 [mm] and set down after a horizontal carrying of up to 3 [m].

For a prototype, several cracks at the steel welded construction were observed. A static FE analysis considering the load due to the maximum accelerations could not explain these cracks.

Operating vibration measurements showed that at the highest cycle rate the lowest vibration mode of the loading feeder is resonantly excited, resulting in vibration displacements of up to 4 [mm]. The natural frequency of the related mode shape is located at approximately 7.5 [Hz], which is far above the cycle rate. However, due to the strongly non-harmonic movement, this mode is effectively excited anyway.

An excitation spectrum obtained from the operating vibration measurements reveals that in addition to the cycle rate a large number of harmonics are observed, especially for the vertical direction.

Considering this additional dynamic load the reason for the cracks can be explained. The FE analysis was used to develop suitable redesign measures. The loading feeder was globally stiffened in order to raise the lowest natural frequency. In addition, the local stress maxima were reduced by selective stiffening measures. Finally the driving profile was adjusted. Thus, no more cracks occurred.

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