Cut-to-length control method of round large bar

The invention discloses a cut-to-length control method of a round large bar. The method comprises the following steps: (1) calibrating a position X between a start measurement point and a ranging point, setting the cut length P of the large bar, and obtaining a variable error set (delta)an according to different moving speeds of a roller table; (2) setting the moving speed of the roller table as e, and giving a variable error (delta)a according to the moving speed e and the variable error set (delta)an; (3) measuring the distance S between the end surface of the large bar and the measurement point, and calculating the actual cut length L=X-S+(delta)a; (4) comparing to judge whether L is equal to P; and if L=P, starting cutting; (5) after the cutting, giving f=C*e for the moving speed of the roller table after the start measurement point, wherein C is an integer greater than or equal to 10; (6) setting a protection distance B of a measurement device, and continuing the measurement of S; comparing to judge whether S is less than B; and if S is less than B, starting a protection action by the measurement device; and (7) if the protection time T is up, automatically lifting the measurement device and returning to step (3), wherein T is calculated by a formula shown in the specification.