Abstract: A geared rotary actuator comprising first and second reduction gear trains, an earth for fixing the actuator in use, and an output member moveable relative to said earth for connection to a component to be moved by the actuator, said first and second reduction gear trains each including a respective rotary input member and a respective output, said first and second gear train input members being arranged in use to be driven by respective sources of rotary movement and said gear trains having fixed, equal, step-down gear ratios between their input and output, and, the actuator further including output summing means interconnecting said outputs of said first and second gear reduction trains with said output member of the actuator whereby movement of said output member relative to said earth in response to rotation of said gear train input members is the sum of the movements of said gear train outputs.

Abstract: A geared rotary actuator comprising first and second reduction gear trains, an earth for fixing the actuator in use, and an output member moveable relative to said earth for connection to a component to be moved by the actuator, said first and second reduction gear trains each including a respective rotary input member and a respective output, said first and second gear train input members being arranged in use to be driven by respective sources of rotary movement and said gear trains having fixed, equal, step-down gear ratios between their input and output, and, the actuator farther including output summing means interconnecting said outputs of said first and second gear reduction trains with said output member of the actuator whereby movement of said output member relative to said earth in response to rotation of said gear train input members is the sum of the movements of said gear train outputs.