Activation mechanism for drug delivery device

A drug delivery device comprising:

• a housing defining a shell having a proximal end and a distal end and a longitudinal axis extending between the proximal end and the distal end thereof;
• an injection assembly at least partially disposed within the housing at the proximal end thereof, the injection assembly comprising a needle or a cannula;
• a shield slidably coupled to the housing, the shield extending a distance beyond the proximal end of the housing;
• and a drive assembly at least partially disposed within the housing and operably coupled to the injection assembly and the shield, the drive assembly comprising:
• a nut;
• a trigger ring;
• and a plunger rod guide operably coupled to a driving mechanism comprising a torque spring, wherein upon moving the shield axially towards the distal end of the housing, a retraction profile commences where the drive assembly administers a medicament via the injection assembly, wherein a peak resistance force is exerted prior to the needle or cannula contacting a user's skin, and wherein the peak resistance force is generated by at least one of:
• a frictional force exerted between the plunger rod guide and the trigger ring generated by the driving mechanism;
• a frictional force exerted between the trigger ring and the nut generated by the driving mechanism;
• or a force generated by the nut and exerted between the trigger ring and the nut.

A drug delivery device comprising:

• a housing having a proximal end, a distal end, and a longitudinal axis extending between the proximal end and the distal end thereof;
• an injection assembly at least partially disposed within the housing at the proximal end thereof, the injection assembly including a needle or a cannula having an endpoint;
• a shield slidably coupled with the housing, the shield having an extended position wherein at least a proximal end of the shield extends a distance beyond the proximal end of the housing;
• and a drive assembly at least partially disposed within the housing and operably coupled with the injection assembly and the shield, the drive assembly comprising:
• a nut;
• a trigger ring;
• a plunger rod guide operably coupled to a driving mechanism comprising a torque spring, wherein upon moving the shield axially towards the distal end of the housing a predetermined distance, a retraction profile commences whereby the drive assembly administers a medicament via the injection assembly, wherein a peak resistance force is exerted just prior to the needle or cannula contacting a user's skin, and wherein the peak resistance force is generated by at least one of:
• a frictional force exerted between the plunger rod guide and the trigger ring generated by the driving mechanism;
• or a frictional force exerted between the trigger ring and the nut generated by the driving mechanism.