In an apparatus for operating a feed device for fibre material, for example, a hopper feeder, there is provided a drivable, endless conveyor belt guided around two rotatable rolls. R12, R21, R22, R22, R31, R32, R41,Y, a, b, p, a, and w are defined herein. The substrate has a first side, a second side and an opening extending from the first side to the second side. The controller module sends a control signal to the electrical actuator in response to control data received from the remote transceiver. The installation thus constructed is extraordinarily flexible, since the immersion movement does not have to correlate with the translational movement. The first portion is dimensioned to fit within the recessed portion of the casing such that the rail cam is positioned to receive the mounting rail and the at least one first-portion signal port is aligned, in a complementary fashion, with the at least one casing signal port.