Automatic injection device with delay mechanism including dual functioning biasing member

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

• a shuttle for the syringe, said shuttle including a first latching element;
• a follower including a second latching element, 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 shuttle;
• a dual functioning biasing member having a torsional preloading and an axial preloading, said dual functioning biasing member acting between said shuttle and said follower to provide both a torsional force urging said follower to rotate relative to said shuttle and an axial force urging said shuttle away from said follower;
• whereby when said locking member moves to said release position during an injection, said dual functioning biasing member first forces 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, and then said dual functioning biasing member forces said shuttle axially relative to said follower to move said shuttle for retracting the syringe needle into the housing after injection.