Delay mechanism for automatic injection device

In an automatic injection apparatus having a housing, a needled syringe with a plunger, and a plurality of biasing elements for moving the needled syringe in a first direction within the housing to extend the needle of the syringe beyond the housing, to advance the plunger to force syringe contents through the needle for an injection, and to retract the needle within the housing after injection, a delay mechanism comprising:

• a shuttle for the syringe, said shuttle including a first latching element;
• a follower including a second latching element and a cammable surface, said second latching element for cooperating with said first latching element to limit motion of said shuttle relative to said follower in a second direction opposite the first direction;
• a locking member movable within said housing from a locking position to a release position by engagement with the syringe plunger during an injection, said locking member, when in said locking position, preventing rotation of said follower relative to said shuttle, said locking member, when in said release position, allowing rotation of said follower relative to said shuttle;
• a damping compound between said follower and a supporting surface to dampen rotation of said follower relative to said shuffle;
• a driver rotatably fixed relative to said shuttle and including a camming surface;
• and
• a driver biasing element for forcing said driver from a first position to a second position when said locking member moves to said release position, whereby during movement of said driver to said second position, said driver camming surface engages said follower cammable surface to force said follower to rotate relative to said shuttle from a latching position, at which said first and second latching elements cooperate, to an unlatching position, at which said second latching element is disengaged from said first latching element to allow movement of said shuttle for retracting the syringe needle into the housing after injection.