Abstract
The existing method of calculation for the basic dynamic load rating mentioned in the ISO standard is based on the method used for the angular contact ball bearing and does not align with the one used for the linear bearing. The unit for the rating life, i.e., the Unit Running Life (URL) is defined in terms of 106 rev. As a result of this, the effect of linear stroke of the nut or screw shaft, lead, the number of starts, and the number of circulating ball circuits and their turns are not clearly reflected in the load rating formula. In this paper, the basic dynamic load rating and the life formula for the ball screw based on the method used for the linear bearing, i.e., in terms of an unit URL = 100 km is proposed and some representative calculation results for a ball screw are discussed. The results are summarized as follows: (1) Basic dynamic load rating Ca for standard stroke corresponding to the nut raceway length is defined, and a stroke factor is also defined for any stroke of the ball screw operation. (2) The Ca value for the ball screw is proportioned according to the number of ball circuits and their turns to the power of 0.7 as well as the number of starts. But, as the number of starts especially affects the nut raceway length and the number of balls, the Ca value becomes remarkably large.
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