Abstract: A motor driven stock feed apparatus for feeding stock along a lengthwise path to maintain a slack loop in the stock. A loop size sensor includes four vertically spaced infrared beam emitters mounted at one side of an upright plane containing the lengthwise path of strip stock and four vertically spaced infrared beam sensors mounted at an opposite side of the upright plane. The infrared beam emitters are operated to emit a continuous train of pulses. A missing pulse detector associated with each infrared beam sensor senses missing pulses in the train of pulses received by the beam sensor and operates a motor speed control to increase and decrease the speed of the stock feed apparatus.