Grinding: The ball screw and roller are mainly used in rolling or turning, and the nut needs to be ground in the finishing process, and the grinding process is more difficult. At present, overseas ball/planetary roller screws apply rolling or turning processes in low-precision fields (such as transmission) and grinding processes in high-precision fields (such as machine tools). In the field of humanoid robots, the lead screw and roller are mainly rolled or turned, while the nut is ground.
The bottleneck of the process is nut grinding. The humanoid robot uses the reverse planetary roller screw, which is characterized by the nut being longer than the screw, such as the turning will cause the shock knife, so the grinding is more suitable, but the grinding rod and the grinding wheel need to go deep inside the nut, need to do a small diameter, and the grinding wheel has a minimum speed of 20m/s, so the speed needs to reach 40,000-50,000 RPM, and it is very difficult to maintain processing stability at high speed. In addition, in the planetary roller screw, because the nut is longer, the thread line needs to be processed is longer, and the single nut needs to grind 5 thread lines (only one ball screw nut), the processing cycle is long, the production beat is low, the cost is high, and the production difficulty is more difficult than the ball screw.