Machine tool feed axis position controller with runout correction of tool cutting edges

A position controller of a feed axis for a machine tool, the machine tool rotating a tool attached to a main spindle to machine a workpiece, the machine tool including a feed axis mechanism with a servo motor to drive a load in a predetermined linear axis direction, the position controller comprising:

• a position detector configured to detect a position of a movable part of the feed axis mechanism so as to control the position of the movable part in accordance with a position command value of a feed axis from a numerical control unit;
• a speed command operator configured to amplify a deviation between the position command value and a position detection value from the position detector;
• a first adder configured to add a speed feed forward and an output from the speed command operator to output a speed command value, the speed feed forward being obtained by differentiation of the position command value;
• a torque command operator configured to amplify a deviation between the speed command value and a speed detection value to output a feedback torque, the speed detection value being obtained by detection of the speed of the movable part by a speed detector or by differentiation of the position detection value;
• a second adder configured to add a torque feed forward and the feedback torque to output a torque command value, the torque feed forward being obtained by differentiating the speed feed forward and multiplying the differentiated value by a motor shaft conversion inertia of the movable part;
• a drive unit configured to drive the servo motor upon the torque command value;
• a runout amount correcting device configured to employ a value related to deviation between a command value and a detection value in physical quantity of the movable part as a reference signal, the runout amount correcting device being configured to calculate a position correction amount from rotation angle information of the main spindle and the reference signal, the rotation angle information being obtained from the numerical control unit;
• and
• a third adder configured to superimpose the position correction amount to the position command value to correct the position command value, wherein
• the runout amount correcting device is configured to estimate a runout amount of a cutting edge of the tool from the reference signal, the runout amount correcting device being configured to calculate the position correction amount such that influences of the respective cutting edges appearing in the reference signal are leveled.