How to compensate for screw backlash on Fanuc?

The mechanical clearance error of CNC machine tools refers to the comprehensive error caused by mechanical clearance from the beginning of the machine tool kinematic chain to the execution part. For example, in the feed chain of machine tools, the error comes from the gap caused by the key connection between the motor shaft and the gear shaft, the gear pair gap, the gap between the gear and the screw caused by the key connection, the gap caused by the key connection in the coupling, and the wire. Lever nut clearance, etc., these errors do not exist when moving in one direction.

The machine tool backlash error refers to the error between the movement amount of the machine tool actuator and the theoretical value (programmed value) when the machine tool actuator changes from forward motion to reverse motion due to the existence of mechanical gap in the machine tool transmission chain. Finally, it is reflected as the error of machining accuracy superimposed on the workpiece. When the CNC machine tool table changes direction in its direction of motion, the existence of backlash will cause the servo motor to idle and the table to have no actual movement, which is called stalling.

For example, in G01 cutting motion, the reverse deviation will affect the accuracy of the interpolation motion. If the deviation is too large, it will cause the situation of "the circle is not round enough and the square is not square enough"; and in the G00 rapid positioning motion, the reverse deviation will affect the machine tool. The positioning accuracy reduces the position accuracy between holes during drilling, boring and other hole processing.

If the value of such a backlash is small, it will have little impact on the machining accuracy and no measures are needed; if the value is large, the stability of the system will be significantly reduced and the machining accuracy will be significantly reduced, especially for curve machining, which will affect the size. Tolerance and curve consistency, backlash must be measured and compensated at this time.
Especially for CNC machine tools that use semi-closed loop control, the backlash will affect the positioning accuracy and repeated positioning accuracy. This requires us to pay attention to and study the factors, effects, and compensation functions of backlash when using CNC machine tools. During study and practice, we carefully summarized and discovered some regular errors in the automatic backlash compensation process, and took appropriate processing measures to improve the processing accuracy of parts.

Reverse clearance: Because there must be a certain gap between the screw and the nut, when changing from forward rotation to reverse rotation, within a certain angle, although the screw rotates, the nut has to wait until the gap is eliminated. In order to drive the worktable to move, this gap is the backlash, but it must be reflected in the rotation angle of the screw.