the feed roll and rotatable about an axis each feed tray defines a nip with the feed roll measuring elements are coupled to each feed tray for emitting signals representing an extent of excursion of the respective feed tray as the fiber material passes through the respective nip a control and regulating device is connected to the measuring elements for receiving the signals therefrom movable wall elements are arranged side by side parallel to the reserve chute width and form part of at least one of the reserve chute walls setting members are connected to the wall elements for moving the wall elements in sections in a direction parallel to the reserve chute depth for varying the size thereof application_number US 39244899 A description turning to fig1 upstream of a roller card unit 1 a fiber feeder is located having a vertically oriented reserve chute 2 charged from above with a mixture i of air and finely opened fiber material fiber tufts such charging may be effected for example by a condenser or by a supply and distributor duct 3 in the upper region of the reserve chute 2 air outlet openings 4 are provided through which the transporting air ii leaves the reserve chute after being separated from the fiber tufts iii by.