Abstract: A roller screw actuator comprises a screw (112), a nut (114) coaxial with the screw and an outer drive member (202) rotatably supported on the nut. Several planetary rollers (116) are rotatably engaged between and with the screw and the nut. A gearing system (119) couples the planetary rollers to the outer drive member (202) and the nut, the arrangement being such that in a first, unjammed condition and in a second, jammed condition, the lead rate of the screw actuator is maintained substantially constant.

Abstract: A geared rotary actuator has a differential gear unit having a drive input and first and second outputs, an output driven member for connection to an external member to be driven by the actuator and first and second drive paths (200, 300) coupling the first and second outputs of the differential gear unit to the output driven member. Under normal conditions, drive is transmitted from the input drive to the output driven member via the differential gear unit (100) and the first drive path (200). However, if the first drive path (200) jams, drive is transmitted to the output driven member via the differential gear unit (100) and the second drive path (300). If the differential gear unit (100) jams, drive is transmitted to the output member (36) via the differential gear unit (100) and both the first and second drive paths. The gear ratio between the drive input and the output driven member remains substantially constant.