Trigger mechanism for an inhaler
A breath-responsive metered dose inhaler having a trigger mechanism for triggering delivery of a medicament and a trigger mechanism chassis for locating the trigger mechanism within the inhaler, the trigger mechanism including a breath responsive member moveable upon inhalation of the user from a primed position in which the inhaler is prevented from delivering medicament, to a triggered position in which the medicament is delivered to the user, a spring which is flexible along its longitudinal axis, wherein the spring is configured to bias the breath responsive member from its triggered position to its primed position by flexure along its longitudinal axis.
1. A breath-responsive metered dose inhaler having a trigger mechanism for triggering delivery of a medicament and a trigger mechanism chassis for locating the trigger mechanism within the inhaler,
the trigger mechanism including:
a breath responsive member moveable upon inhalation of the user from a primed position in which the inhaler is prevented from delivering medicament, to a triggered position in which the medicament is delivered to the user,
a spring having a longitudinal axis, configured to be flexible along the longitudinal axis, and comprises a pre-load bend along the longitudinal axis when the breath responsive member is in the primed position,
wherein the spring is configured to bias the breath responsive member from the triggered position towards the primed position by flexure along the longitudinal axis of the spring.
2. The inhaler according to claim 1 , in which the spring is a helical spring.
3. The inhaler according to claim 2 , in which the flexure is a straightening flexure.
4. The inhaler according to claim 3 , in which the trigger mechanism comprises a toggle mechanism comprising the breath responsive member, wherein the helical spring is attached to the toggle mechanism.
5. The inhaler according to claim 4 , in which the helical spring has a first end attached to the breath responsive member and a longitudinally opposing second end attached to the trigger mechanism chassis.
6. The inhaler according to claim 5 , in which the helical spring is constrained by the trigger mechanism chassis, and the helical spring comprises a further bend giving rise to an increased biasing force in the triggered position.
7. The inhaler according to claim 6 , in which the helical spring is attached to the trigger mechanism chassis by an interference fit of the second end of the helical spring inside a sleeve of the trigger mechanism chassis or outside a boss of the trigger mechanism chassis.
8. The inhaler according to claim 7 , in which the helical spring is attached to the breath responsive member by an interference fit of the first end of the helical spring inside a sleeve of the breath responsive member or outside a boss of the breath responsive member.
9. The inhaler according to claim 8 , in which, during return of the breath responsive member from the triggered position to the primed position, the helical spring undergoes substantially no compression or tension along its longitudinal axis.
10. The inhaler according to claim 9 , in which the breath responsive member is constrained to pivot about a fixed axis and the helical spring engages the breath responsive member close to the fixed axis.
11. The inhaler according to claim 10 in which the breath responsive member is constrained to pivot about the fixed axis and the helical spring acts as a live pivot so as to define the fixed axis.
12. The inhaler according to claim 11 in which the breath responsive member is a vane.
13. The inhaler according to claim 12 which is a pressurized metered dose inhaler.