Control system for grinding machine

A surface grinder comprising a wheelhead arranged to drive a grinding wheel, means defining a reference plane, means including a pulse responsive motor for moving said wheelhead and wheel in elevation above the reference plane, a source of motor drive pulses, means providing a first train of pulses, resolver means coupled to said means for generating a second train of pulses at the same frequency as said first train, means for comparing the phase difference of the pulses of said first and second trains, means for providing a third train of pulses at a frequency substantially higher than pulses of said first and second trains proportional in number to the magnitude of the phase difference between pulses of said first and second trains and one direction of phase difference, and providing a fourth train of pulses of the same frequency as said third train proportional in magnitude to the magnitude of the phase difference between pulses of said first and second trains and the other direction of phase difference, pulse counting means for accumulating the difference in the number of the pulses of said third and fourth trains and establishing a numerical representation thereof, each of the pulses of said third and fourth trains representing an increment of distance between the cutting surface of said wheel and said reference plane, means for visually displaying the distance represented in said counting means, a grinding wheel dresser adapted to be moved into contact with said grinding wheel and reduce the radius thereof, a second pulse responsive motor adapted to move said dresser into contact with said grinding wheel, means for applying motor drive pulses to said second motor, means for selecting a predetermined dressing dimension for said wheel and storing said dimension, dresser pulse counting means adapted to count pulses applied from said pulse source to said second motor and permit application of a number of pulses representative of a preselected dressing dimension to said second motor, and means responsive to application of drive pulses to said second motor for applying a number of pulses of one of said third and fourth pulse trains to said pulse counting means to modify the difference therein in accordance with the dressing dimension.