DYNAMIC MODELING OF SPINDLE DRUM MASS UNBALANCE AND VIBRATION BEHAVIOR IN COTTON HARVESTERS
Keywords:
cotton harvester, spindle drum, mass unbalance, 2-DOF rotor dynamics, critical speed, bearing fatigue life, ISO 1940-1.Abstract
In modern mechanical cotton harvesting, the vertical spindle drum assembly operates under severe cyclic dynamic conditions. During prolonged shifts, cotton fibers saturated with vegetal waxes and mineral dust accumulate non-uniformly along the drum periphery, inducing substantial dynamic unbalance. This research develops a closed-form two-degree-of-freedom (2-DOF) analytical model of a spindle drum mounted on viscoelastic bearing supports. The system natural angular frequency is determined analytically at ω_n = 166.67 rad/s, corresponding to a primary critical resonance speed of n_cr = 1591.55 rpm with a 4.8-fold dynamic amplitude magnification. Orbit simulations demonstrate that field unbalance masses (50–200 g) generate specific unbalances of 166.7 to 666.7 μm, violating ISO 1940-1 Grade G16 balance tolerances by 2.4 to 9.6 times. Under ISO 281 fatigue analysis, dynamic reaction forces reaching 1.84 kN reduce rolling element bearing rating life (L_10h) by 35.7% to 64.8%. These findings provide vital quantitative vibration thresholds for bearing condition monitoring in cotton pickers.
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