Control system for moving a large machine along a single axis

Claim 1

A control system for driving at least first and second motors to move a large machine along a single axis, said control system including at least first and second position loop servo systems driving the respective first and second motors to move respective first and second sides of the machine in the direction of the single axis, each position loop servo system comprising: (a) means for generating a first signal indicative of the commanded position of movement that the machine is to be moved by the respective motor; (b) means for generating a second signal indicative of the actual position of the respective side of the machine moved by that motor; (c) means responsive to the first and second signals for generating a signal indicative of the position error between the actual and commanded positions of the respective side of the machine; and (d) means responsive to the position error signal to generate a signal for driving the respective motor for moving the respective side of the machine toward the commanded position; said control system further comprising: (A) means responsive to the position error signals generated by each said position loop servo system for generating a difference error signal indicative of the difference between the actual position of each respective side of the machine along the single axis; and (B) means for coupling the difference error signal to said driving means for one of the motors for causing a change in movement of that motor in a direction to move each side of the machine toward the same actual position, whereby to cause the difference error signal to be reduced toward zero.