STIFFNESS OF A BALL SCREW WITH CONSIDERATION OF DEFORMATION OF THE SCREW, NUT AND SCREW THREAD - (PRELOADED DOUBLE NUT)

The stiffness in the axial direction of preloaded ball screws constructed from double nuts is calculated considering the elastic deformation of the screw shaft, the nut body, and the screw threads, in addition to the deformation due to Hertzian contact. The basic equations derived here could be applied in many cases of preloading schemes and the various states of an externally applied load. Moreover, the calculation can be carried out both for single- and double-circuit nuts. The calculated stiffness is low compared with that obtained when only the Hertzian contact effect is considered. The difference between the two calculated values becomes large as the spacing disc rigidity increases. At high rigidity of spacing disc, the externally applied load which releases the preload also becomes lower than that obtained with Hertzian contact deformation model. The calculated values of both the stiffness and the releasing load approximately agree with the experimental results.