Device for controlling the means delivering sheets to a machine

A device for controlling the means delivering sheets from a stack (4) to a machine for processing them, comprising at least one mechanism (1) for lifting the stack, a sheet-inserting means comprising gripping means (29), means for detecting the upper level of the stack comprising a detector of the front level (32) of the stack (4) connected to an input of a computer (37) acting on at least one electric motor (11) of the stack-lifting mechanism (1), and means for raising the stack (4) in dependence on the upper level, characterised in that the detector of the front level (32) of the stack (4) comprises means for measuring the extent of variations in the level of the stack and in that an input of the computer (37) is also connected to a source of information (17) relating to the supply frequency in real time and to the nominal thickness of the sheets, and the output of the computer (37) is connected to at least one frequency varying means (42) for controlling the electric motor or motors (11), the computer (37) being designed so that the value of the signal appearing at its output characterises the difference between the measured level of the stack (4) and the level calculated on the basis of the said nominal thickness and the said supply frequency and generates a variation in the frequency of the one or more varying means (42) tending to modify the rate of advance of the motor (11) in order to make the measured level coincide with a set level.