Automatic feedback mechanism and a medicament delivery device with user feedback capability

1. An automatic feedback mechanism for a medicament delivery device, which notifies a user of a start of expulsion of medicament from a medicament container, wherein the automatic feedback mechanism comprises:

a plunger rod comprising a first section and second section, where the second section extends distally from the first section and comprises a longitudinal axially extending radial opening,

a tubular extension member having a radial space defined by an inner perimeter and an inner distal surface, wherein the tubular extension member is arranged to receive the plunger rod in the radial space, and wherein the tubular extension member has flexible tongues configured to releasably lock the plunger rod in a pre-tensioned state,

a tubular operation member arranged to receive the tubular extension member, which tubular operation member is movable relative to the tubular extension member, wherein the tubular operation member in a first position is arranged to press the flexible tongues radially inwards to lock the plunger rod in the pre-tensioned state,

a first resilient member arranged to be received inside the plunger rod to exert a force in the proximal direction, and

a signal generating member arranged to partially surround the plunger rod and having a distal transversal end portion which in a first position is at a distance D from the inner distal surface of the tubular extension member when the plunger rod is in the pre-tensioned state,

wherein in an assembled state, movement of the tubular operation member causes the flexible tongues to expand radially releasing the plunger rod to travel proximally and allowing the first resilient member to move the signal generating member distally the distance D such that the distal transversal end portion hits the inner distal surface generating an audible signal.

2. The feedback mechanism as claimed in claim 1 wherein the signal generating member comprises an elongated U-shaped bracket having two longitudinally extending flexible legs provided with angled radial feet extending radially outward to secure the signal generating member in the first position.

3. The feedback mechanism as claimed in claim 2 wherein the radial feet in the first position have a radial extension that exceeds the transverse dimension of the radial space of the tubular extension member and where the radial feet in a second position have a radial extension that is less than the transverse dimension of the radial space of the tubular extension member.

4. The feedback mechanism as claimed in claim 3 wherein the radial feet in the first position have a radial extension that exceeds the radial extension of the radial feet when in the second position.

5. The feedback mechanism as claimed in claim 1 , wherein the first section is provided with a first guide structure arranged to support and flex the signal generating member radially outwards, and to guide axial displacement of the signal generating member.

6. The feedback mechanism as claimed in claim 5 , wherein in the initial position of the plunger rod, the axial overlap between the first section and the signal generating member corresponds to the distance of axial displacement of the plunger rod necessary for commencement of medicament expulsion.

7. The feedback mechanism as claimed in claim 5 , wherein the signal generating member has legs arranged to interact with the first guide structure.

8. The feedback mechanism as claimed in claim 5 , wherein the first guide structure comprises axial grooves in which the signal generating member is arranged to slide.

9. The feedback mechanism as claimed in claim 5 , wherein the second section is arranged contiguous to the first section, which second section is aligned with the first guide structure, allowing radial inwards flexing of the signal generating member towards its radially unbiased state.

10. The feedback mechanism as claimed in claim 9 , wherein the second section extends to the distal end of the plunger rod.

11. The feedback mechanism as claimed in claim 9 , wherein the plunger rod has a third section arranged distally from and contiguous to the second section, which third section is defined by a second guide structure axially aligned with the longitudinal axially extending radial opening, and arranged to support and flex the signal generating member radially outwards.

12. The feedback mechanism as claimed in claim 11 , wherein the tubular extension member has first engagement means for engaging with the signal generating member in the initial position of the plunger rod, and wherein the tubular extension member has radial openings arranged distally from and aligned with the first engagement means, for allowing the signal generating member to flex radially outwards.

13. The feedback mechanism as claimed in claim 1 , wherein the first section extends to the distal end of the plunger rod.

14. A medicament delivery device comprising a feedback mechanism as claimed in claim 1 , further comprising a linearly displaceable medicament delivery member cover configured to interact with the tubular operation member.

15. An automatic feedback mechanism for a medicament delivery device comprising:

a hollow plunger rod comprising a first section and second section, where the second section extends distally from the first section and comprises a longitudinal axially extending radial opening;

a first resilient member positioned within the hollow plunger rod in a pre-tensioned state to exert a force against the inside of the hollow plunger rod in a proximal direction;

a signal generating member positioned to partially surround the plunger rod, where the signal generating member has a distal transversal end portion located at a distal end of a U-bracket, where the U-bracket terminates in two distal ends, with each distal end having a radial foot extending radially outward;

wherein releasing the tension of the first resilient member moves the signal generating member distally such that the distal transversal end portion hits an inner distal surface of the medicament delivery device generating an audible or tactile signal.

16. The automatic feedback mechanism of claim 15 further comprises a first guide structure arranged to support the U-bracket such that the distal ends of the U-bracket are flexed radially outward to enable the radial feet to engage with a tubular extension member.

17. The automatic feedback mechanism of claim 15 wherein the first section comprises a first guide structure that supports and flexes the distal ends of the U-bracket radially outward and guides and axial displacement of the signal generating member.

18. The automatic feedback mechanism of claim 15 wherein the first section is contiguous with the second section, where the first section supports and flexes the distal ends of the U-bracket radially outward and the second section allows the distal ends to flex radially inward as the U-bracket moves distally relative to the plunger rod.

19. The automatic feedback mechanism of claim 18 where the plunger rod further comprises a third section arranged distally from and contiguous to the second section, where the third section has a second guide structure axially aligned with the longitudinal axially extending radial opening in the plunger rod and supports and flexes the distal ends of the U-bracket radially outwards.