Backlash correction apparatus and method of numerical controller

A backlash correction apparatus of a numerical controller of a ball screw-transferred table characterized in that, a position controller sends to a velocity controller a velocity command signal in accordance with a position command signal, and accordingly when the table is transferred to a certain position, a position detector and a velocity detector detect and feed back to the position controller and the velocity controller a present position value and the transfer velocity value, respectively, comprising:

• a command direction memory means for storing a command direction value of the position command;
• a feedback velocity/direction memory means for storing a present transfer direction value;
• a previous direction memory means for storing a previous transfer direction value;
• a reverse direction detection means for operating on the command direction value, the previous transfer direction and the present transfer direction and outputting therefrom a resultant correction direction value;
• a backlash data memory means for storing a backlash error value corresponding to a pitch position of the ball screw for transferring the table;
• a correction data operation means for reading from the backlash data memory means backlash error corresponding to the present position value of the table detected by the position detector and computing and outputting therefrom backlash correction values by adding to the read backlash error the correction direction values applied thereto from the reverse direction detection means;
• and
• a correction data output means for outputting the backlash correction values applied thereto from the correction data operation means to the position controller.