In modern CNC machine tools, the backlash has been eliminated by

The correct option is preloaded ball screws.

In modern CNC (Computer Numerical Control) machine tools, precision and accuracy are of utmost importance. Backlash refers to the clearance or play in a mechanical system caused by the gaps between mating parts (such as screw threads and nut threads) when the direction of motion is reversed. This gap leads to a temporary loss of motion or positioning error during reversal.

To eliminate this issue:
1. Ball Screws: Standard lead screws are replaced by ball screws, which utilize recirculating steel balls between the screw shaft and the nut. This changes the sliding friction to rolling friction, greatly reducing wear and increasing efficiency.
2. Preloading: To completely eliminate backlash, the ball nut assembly is "preloaded". Preloading applies an internal axial force (load) within the nut, typically by using two nuts separated by a spacer or a spring, or by shifting the lead of the threads. This forces the recirculating balls to remain in continuous contact with both sides of the screw and nut threads, thereby eliminating any physical axial play or clearance.

Other mechanisms like rack and pinion, ratchet and pinion, and slider crank mechanisms do not inherently eliminate backlash to the sub-micron levels required in high-precision CNC machinery.