On the Micro-Behavior of rolling element of linear motion bearing

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The sliding unit of linear motion bearing is borne by many rolling element that run on the rail track. When the motion becomes rather small, its rolling behavior becomes non-linear and visco-elastic, according to the properties of deformation of asperities of the surface, lubricant and so on. This research aims to clarity such micro behavior characteristic of a rolling element.The micro rolling motion of one element(dia 4 mm) was experimentally observed. In order to keep the contact condition constant, the parallel motion mechanism was constructed using 2 stainless sheet metals of 50 um thickness. This mechanism s rigidity in rolling direction is very high, though flexible in the normal direction. The drive force was measured by strain gage, and the displacement(rolling motion) was measured by gap-sensor(10V/25 um).Cyclic experiment was performed with loading and unloading the driving force.under no lubricants. When the stroke was 9 um, hysteresis was observed between force and displacement characteristic. On the other hand, when the stroke was 1 um, no hysteresis was observed and the behavior was just like a spring. Normal force has a effect on its characteristic. When the normal force become large, the hysteresis becomes small. This may come from change in contact condition.Under the condition with lubricant, there is no change in hysteresis property, however, the force-displacement property has changed as to the rigidity becomes small.Free vibration experiment in normal direction were also performed. From these results, it was found that the dumping properties varies non-linearly according to the amplitude of vibration and normal force.