Three position needle retraction

A needle insertion and retraction mechanism for an injector comprising a housing with a base defining an opening, the needle insertion and retraction mechanism comprising:

• an injection needle mounted to a needle holder, the needle holder being rotatable to unlock axial movement of the needle holder in a first direction, and the needle holder being linearly slidable between a retracted position, in which a tip of the injection needle is within the housing, and an extended position, in which the tip of the injection needle projects outward from the housing through the opening;
• a needle extension spring biased to push the needle holder in the first direction;
• a retraction slider engageable with the needle holder, the retraction slider being rotatable into an unlocked state and being linearly slidable in the unlocked state;
• a needle retraction spring biased to push the retraction slider in a second direction that is the opposite of the first direction;
• an activation button;
• a skin sensor defining a needle aperture, the skin sensor comprising an arm extending from the skin sensor and a safety latch extending from the skin sensor, the skin sensor being configured to move relative to the housing between a deployed position, in which the needle aperture is misaligned with the injection needle, and a withdrawn position, in which the needle aperture is aligned with the injection needle, the skin sensor being biased into the deployed position;
• wherein:
• in a pre-activated locked state of the needle insertion and retraction mechanism and before the injector is placed on a skin surface, the skin sensor is in the deployed position, in which the safety latch blocks axial movement of the activation button in the first direction, thereby locking the needle holder in the retracted position;
• in a primed unlocked state of the needle insertion and retraction mechanism and after the injector is placed on the skin surface, the skin sensor is moved to the withdrawn position;
• in an activation state of the needle insertion and retraction mechanism, the activation button is configured to be depressed to cause rotation of the needle holder to unlock axial movement of the activation button in the first direction, thereby enabling the needle extension spring to push the needle holder into the extended position;
• and
• in an armed state of the needle insertion and retraction mechanism and after the injector is removed from the skin surface, the skin sensor is returned to the deployed position, and wherein subsequent contact with the skin sensor is configured to engage the arm with the retraction slider to rotate the retraction slider into the unlocked state, whereby the needle retraction spring expands to retract the retraction slider, the needle holder, and injection needle.