US Patent 11801346 Autoinjector and method of injecting fluids

An autoinjector and method of injection are described. A power spring causes rotation of a drive nut about the central axis of the autoinjector that, in turn, causes a middle screw to rotate in the same direction as the drive nut and also to move in the distal direction while pushing a center screw in the distal direction that pushes the syringe and needle. The center screw also pushes a plunger that pushes the fluid out of the syringe. After injection, a locked retract screw is freed and rotates in the same direction as the middle screw causing the syringe to retract the syringe into the housing.