During the jack screw design and its processing, the screw rod pretension is a kind of assembly which uses the locking nuts at the screw rods’ ends to impose a certain dragging force in its length direction to adjust the reverse direction tension of the rods. The reason for this lies in that when the rods are working, the thermal effect will elongate the rods, leading an unstable status of the rods’ length. The pretension design is to eradicate variables in its flexibility to obtain an expected stable movement precision.

Otherwise during the micro feed process, if the saddle dumping force or that of the working platform is bigger than the flexibility torque of the rods or nuts, there will be no position shifts of the working platform.

With a successive micro feeding when the accumulated flexible torque of the rods and nuts is bigger than the damping force of the working platform, the working platform this time will be shifted and moved.

So such theory indicates that though the overall micro feeding volume may not be affected, there will be real errors in practical lifts, micro feeding volume of each lift and the output of the controller, thus in return will severely impact the precision ratio of the whole processing techniques.