Abstract: A machine for screwing and unscrewing two rods comprises an annular carcass (11) forming a frame about a central axis (A) and, staggered in height on said carcass (11), upper and lower wrenches (12E, 12I) each adapted to grip two successive rods (13). One of said wrenches (12E), referred to hereinafter as the drive wrench, is mounted rotatably relative to the carcass (11) and said drive wrench (12E) at least comprises a plurality of cams (18) distributed circumferentially and each mounted to pivot about an axis (A') parallel to the central axis (A) between a retracted position in which they leave around said central axis (A) a space (19) sufficient for the rods (13) to pass through and a deployed position in which they intrude on said space (19) and are able conjointly to grip a rod (13) present in the latter. The machine is useful in drilling installations.

Abstract: A control device for lifting winches, in particular for drilling rigs, uses an electric motor able to operate in all four quadrants of the torque-speed diagram. A control circuit procures controlled excitation of the electric motor. A manipulator on a control panel controls the control circuit by establishing, according to its position, a given speed request instruction. An indexing circuit for controlling the control circuit is adapted, on the bases of predetermined end of travel positions and a given law relating the speed to the difference in height between a given end of travel position and the actual height at the time in question, to establish a given speed request instruction. A comparator passes to the control circuit only the speed request instruction that it receives representing the lower speed.