US Patent 7465289 Syringe firing mechanism

When a cover (10) of a syringe firing mechanism is pushed downwardly towards a housing (2) a flexible arm (12) is moved inwardly to release a trigger (8). This enables a drive member (6) to push down a plunger (5) of the syringe under the bias of a spring (7). When the injection is completed, release of the cover (10) causes the cover (10) to move back into contact with a corner of the drive member (6). A cam surface (15A) then pushes a flap (16) across, whilst bending a hinge (17), until the flap (16) enters the hollow interior of the drive member (6), thus enabling the syringe (1) to be withdrawn within the housing (2) under the bias of a spring (3).