CPC A61M 5/31583 (2013.01) [A61M 5/31553 (2013.01); A61M 2005/3143 (2013.01); A61M 2005/3152 (2013.01); A61M 2205/0216 (2013.01); A61M 2205/0222 (2013.01); A61M 2205/42 (2013.01)] | 20 Claims |
1. A drive mechanism for a drug delivery device, the drive mechanism comprising:
a dose selector; and
a housing and a ratchet with a gear element comprising a plurality of gear teeth connected with the dose selector and a pawl element rotationally constrained to the housing comprising at least one pawl tooth,
wherein the at least one pawl tooth engages with the plurality of gear teeth and is located opposite to the plurality of gear teeth,
wherein one of the gear element and the pawl element moves forth and back relative to the other element of the gear element and the pawl element along a first direction for de-engagement and re-engagement of opposite gear teeth and the at least one pawl tooth when the gear element rotates relative to the housing during dose setting using the dose selector,
wherein one or both of the pawl element and the gear element comprises a noise reduction characteristic at a surface which dampens noise produced when a tooth or teeth of a respective other element of the pawl element and the gear element moves or move back into re-engagement when the gear element rotates relative to the pawl element,
wherein the noise reduction characteristic comprises at least one of:
a helical form of the plurality of gear teeth and a corresponding helical form of the at least one pawl tooth,
a beveled form of the plurality of gear teeth and a corresponding beveled form of the at least one pawl tooth, and
an elastomeric material surface layer or an elastomeric material body at a predefined section of one or both of at least part of the plurality of gear teeth and the at least one pawl tooth.
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