smaller while the size of the angular sectors through which the sensor 11 is moved remains constant it will be appreciated that conversely when sensor 12 is moved by oscillating member 15 sensor 11 will initially move more quickly to its starting or normal position than sensor 12 it has been found that this arrangement wherein the returning sensor more quickly approaches its starting position has a favorable influence on control of the drive speed of the oscillating member 15 fig7 illustrates schematically a working example of a machine in which the control device of the invention may be used the machine is adapted for laying non woven fabrics reference is made to copending application ser no 775 022 filed mar 7 1977 by hille which copending application is incorporated by reference the machine comprises a conveyor belt 40 driven at constant speed for supplying fibrous material from a carding machine or the like the non woven material is laid uniformly on a laying belt 41 extending transversely to the conveyor belt 40 this is accomplished by a laying device which oscillates along a path transverse to the laying belt 41 laying the fleece uniformly on the belt the non woven material on conveyor belt 40 passes around guide roll 42 and drops on a storage belt 43 passing about guide rolls 44 45 at the end.