Sensor for cyclically scanning the height of a pile

A feeder for cyclically sensing the height of a feed pile in a sheet processing machine through which sheets periodically travel, includes a cyclically drivable drive cam, a lever drive transmission having a sensing roller spring-biased into continuous contact engagement with the cyclically drivable drive cam during travel of the sheets, a four-bar linkage guide transmission having two levers disposed above one another and being articulatingly affixed, at one respective end thereof, to a support frame, a coupler having a downwardly directed vertical extension, the levers, at respective other ends thereof, being articulatingly supported at a spaced distance from one another on the coupler, a feeler foot for sensing the height of the feed pile being secured to the vertical extension of the coupler, an entrainer stop secured to the lever drive transmission, a stop face formed on the guide transmission and disposed in a manner corresponding to the entrainer stop so as to be cyclically engageable thereby for raising the feeler foot, and spring means affixed at one bearing location thereof to the support frame and at another bearing location thereof to the guide transmission and having a spring force for pressing the stop face in a direction towards the entrainer stop.