Geared rotary actuator

A geared rotary actuator having:

• a differential gear unit having a drive input and first and second reduced outputs;
• an output driven member for connection to an external member to be driven by the actuator;
• said second drive path includes an output carrier for carrying the first drive path such that:
• a first drive path comprising a first balanced planetary configuration coupling said first output of the differential gear unit to said output driven member;
• a second drive path comprising a second balanced planetary configuration;
• and an output carrier carrying said first and second balanced planetary configurations;
• wherein said second balanced planetary configuration couples said second output of the differential gear unit to said output driven member by way of said output carrier;
• and wherein the arrangement is such that:
• under normal conditions drive is transmitted from the input drive to the output driven member via said differential gear unit and said first drive path;
• in response to jamming or binding of said first drive path said first drive path and said second drive path are caused to rotate en bloc thereby to transmit drive to said output, driven member via said differential gear unit and said second drive path;
• and in response to jamming or binding of said differential gear unit, drive is transmitted to said output member via said differential gear unit and both said first and second drive paths;
• the arrangement being further such that the gear ratio between said drive input and said output driven member remains substantially the same.