Determination of Ball Screw Preload
How is the preload for a ball screw determined? Applying preload to the nut within a ball screw assembly enhances the axial rigidity and positioning accuracy of the ball screw pair. Thus, when considering only the rigidity and positioning accuracy of the screw pair, a larger preload is more advantageous—it better eliminates axial clearance resulting from elastic deformation. Conversely, an overly small preload, even if it removes axial clearance, does not guarantee improved rigidity.
The reason lies in the fact that the preload must be sufficient to eliminate the "low-stiffness zone" in the preloaded nut. Due to inherent errors (such as lead deviations) between the screw and nut components in the preloaded segment of a double-nut system, contact deformation can create uneven stiffness: some small sections may become tighter, yielding higher contact stiffness, while others may remain looser, leading to lower contact stiffness. This latter scenario is what is termed the "low-stiffness zone." To boost axial contact stiffness, the preload must be large enough to eliminate these low-stiffness zones, thereby genuinely achieving enhanced axial rigidity.
That said, an excessively high preload is detrimental. It increases driving torque, reduces transmission efficiency, accelerates contact fatigue and wear between balls and raceways, and shortens the service life of the assembly.
Inspection Work After Ball Screw Installation
1. The rotation of the rotating system should be stable and flexible, with no jamming, looseness, or axial movement.
2. Check whether the rotating system collides or interferes with fixed parts.
3. Observe whether the supply or circulation of lubricating oil is normal, whether the gap of the sealing device is symmetrical, and whether all fasteners are loose.
4. Check whether the end face of the inner ring of the linear bearing reliably abuts against the end face of the shaft shoulder and whether there is a gap between them. In addition, it is necessary to inspect the rotation accuracy, axial limit accuracy, working clearance of the linear bearing rotating system, and other necessary inspection items.
When all the above inspection items are confirmed to be normal, the system can be put into use. However, if any abnormal signs are found, the use should be stopped immediately and the fault should be eliminated.
