Image Number 2 for United States Patent #4745815.
A non-jamming ballscrew actuator system which includes an inner screw, an intermediate ballscrew internally threaded on the inner screw, and an outer ballscrew nut rotatably mounted about the ballscrew. An actuator is operatively associated with a load to be actuated and connected to the inner screw for axial movement therewith. A drive rotates the ballscrew nut to axially move the ballscrew. A first brake prevents rotation of the ballscrew, and a second brake prevents rotation of the inner screw. In the event of jamming between the ballscrew and ballscrew nut, the first brake is released to allow the ballscrew to threadingly drive the inner screw and, thereby, move the actuator. In the event of failure of the drive, the second brake is released to allow reaction movement of the actuator means in response to load forces.