Abstract: A drive mechanism comprises a support upon which a drive member is mounted for movement relative to a frame. The drive member comprises first and second elements which are relatively movable, the one of which may be mounted on the other. The elements are interconnected by a resilient member which transmits the drive therethrough, a drive input being coupled to a one element, a drive output to the other element. A detector generates a signal output responsive to relative movement of the elements which may serve to control a drive transmitted through the mechanism. In a preferred embodiment, the support is a rotatable screwed shaft and the first element a traveller thereon upon which the second element is slidably mounted, the elements being interconnected by helical springs.