Numerical control servo system

A numerical control servo system comprising:

• a setting memory for setting a set numerical value indicative of the amount by which a movable member to be controlled should be shifted in position;
• means including a motor for shifting the position of said movable member;
• a pulse generator for generating a pulse each time said member is shifted a predetermined distance;
• a length-measuring counter for counting the pulses from said pulse generator to a measured numerical value;
• a digital subtractor for obtaining a difference between the set numerical value and the measured numerical value from said length-measuring counter;
• a D-A converter for converting the difference output from said digital subtractor into an analog speed reference signal;
• means for obtaining another analog signal corresponding to the shift speed of said movable member;
• an analog subtractor for obtaining a difference between said analog shift speed signal and said analog speed reference signal;
• means for controlling said motor in response to the output from the analog subtractor to shift the position of said member so that the output from the digital subtractor approaches zero;
• a deviation memory for writing therein the output from the digital subtractor at the start of the control operation;
• and
• correcting means for correcting directly or indirectly the set numerical value in accordance with the value stored in the deviation memory.