Rotation resistant friction adapter for plunger driver of drug delivery device
A method and system are disclosed for driving a plunger in a drug reservoir. In some embodiments, a variable friction element interconnects between a pushing shaft and a wall of the reservoir. For example, rotation of a driving element in a first direction relative to the pushing shaft may advance the pushing shaft in the reservoir. The friction element may have increased friction resistance to rotation of the pushing shaft in the first direction in comparison to frictional resistance to advancing the pushing shaft. For example, the increased friction may result from wedging a radial element between the pushing shaft and the wall of the reservoir.
1. An assembly for driving a plunger and in a drug reservoir, the plunger dividing between a drug in a distal portion of the reservoir and a proximal opening of the reservoir; the assembly comprising:
a telescoping shaft that extends by rotation of a driving element in a first rotational direction with respect to a distal shaft;
a distal end of said distal shaft configured to engage the plunger; and
a friction element extending from said distal shaft, said friction element comprising a disk and a plurality of independent radial elements extending radially from the disk to contact an interior side wall of the reservoir, said radial elements extending from the disk toward the first rotational direction to wedge between said interior wall and said distal shaft when said distal shaft is rotated in said first rotational direction, said radial elements having respective leading edges and trailing edges, at least one of the leading edges extending radially from the disk at a first angle and a trailing edge associated with a same radial element as the at least one of the leading edges extending radially from the disk at a second angle, the first angle being different than the second angle.
2. The assembly of claim 1 , wherein each radial element includes a virtual sprag having a long axis and wherein said long axis intersects said interior side wall.
3. The assembly of claim 1 , further comprising:
a plunger interface configured to engage the plunger; said plunger interface rotationally linking said distal shaft and the plunger when said plunger interface is engaged to the plunger.
4. The assembly of claim 1 , further comprising:
a vent for releasing gas from a space between the friction element and the plunger.
5. The assembly of claim 4 , wherein
said vent is formed in at least one component selected from the group consisting of said friction element, between said friction element and said side wall of said reservoir, said distal shaft and between said distal shaft and said friction element.
6. The assembly of claim 5 , including at least two vents in a least two components and wherein said at least two vents are aligned such that gas passing through a first vent in a first of said two components is channeled to a second venter in a second of said components.
7. The assembly of claim 5 , further comprising
a user indicator visible from outside said drug reservoir and wherein said assembly is configured to move said indicator along a trajectory and wherein a position of said indicator indicates a status of the assembly.
8. The assembly of claim 7 , wherein said indicator is not visible from outside said reservoir over at least a portion of said trajectory.
9. The assembly of claim 1 , wherein said friction element is located proximal to said distal end of said distal shaft.
10. The assembly of claim 1 , wherein said wedging is longitudinal such that moving said distal shaft distally with respect to said reservoir reduces a normal force between said friction element and said interior wall.
11. The assembly of claim 1 , wherein a resistance to movement of said distal shaft in said first rotational direction due to friction between said friction element and said interior wall is higher than a resistance to movement of said distal shaft in a direction opposite said first rotational direction due to friction between said friction element and said interior wall.
12. The assembly of claim 1 , further comprising:
a second friction element extending from a drug delivery device to contact an exterior side wall of the reservoir when said reservoir is inserted into said drug delivery device, said second friction element is configured and oriented to wedge between said exterior wall and said reservoir when said reservoir is rotated in a second rotational direction.
13. The assembly of claim 12 , wherein said second rotational direction is opposite said first rotational direction.