APPARATUS AND METHOD FOR PHOTOELECTRIC DETECTION OF THE HEIGHT OF A STACK OF SHEET MATERIAL

摘要

An apparatus for sensing changes in the height of a stack of sheet material positioned on a lift table for seriatim advancement of the sheets from the top of the stack to a processing machine, and for controlling the raising of the lift table to position the stack from a predetermined lowered level to a feeding level in response to activation of a photoelectric detection element when the stack is depleted to the predetermined lowered level. An illuminating means projects a light beam onto a movable reflective sensing member resting on top of the stack and the beam is reflected from the sensing member to the photoelectric element in any one of a plurality of paths as determined by the height of the stack. So long as the beam path is directed within a range so as to be intercepted by the photoelectric element, the photoelectric element remains inactive and the stack is between the feeding and the predetermined lowered level. However, as the stack is depleted to the predetermined lowered level the reflected beam is no longer within the range to be intercepted by the sensitive element thereby activating the photoelectric element which, in turn, actuates drive means for raising the lift table to position the stack at the feeding level.