Dose delivery device with gearing
In a dose setting mode of a dose delivery device, a dose selector is rotated to turn a nut, which thereby moves backward along a thread of a piston rod through a first axial distance. A gearing mechanism transmits the axial movement of the nut to a connector that moves backward, without rotation, through a second axial distance. In a dose delivery mode of the device, the dose selector is pushed forward and drives the connector to move forward through the second axial distance. The gearing mechanism transmits the axial movement of the connector to the nut, which pushes the piston rod forward, without rotation, through the first axial distance. The gearing mechanism includes a first gear that rotates without axial movement relative to the housing, and a second gear that rotates without axial movement relative to the nut.
1 . A dose delivery device, comprising:
a housing;
a piston rod configured to move axially without rotation relative to the housing, the piston rod comprising a piston rod thread;
a nut engaging the piston rod thread;
a dose selector rotationally locked to the nut;
a connector configured to move axially without rotation relative to the housing;
a first gear configured to rotate without axial movement relative to the housing, the first gear being coupled to the connector by a first engagement, the first engagement being a first helical thread; and
a second gear coupled to the nut so as to permit relative rotation but not relative axial movement between the second gear and the nut, the second gear being coupled to the connector by a second engagement and to the first gear by a third engagement.
2 . A dose delivery device according to claim 1 , wherein the second engagement is a straight track, which permits relative axial movement but prevents relative rotation between the second gear and the connector.
3 . A dose delivery device according to claim 2 , wherein:
the third engagement is a third helical thread;
the first and third helical threads are of the same handedness; and
the third helical thread has a smaller pitch than the first helical thread.
4 . A dose delivery device according to claim 1 , further comprising a dose dial sleeve configured to rotate without axial movement relative to the connector, the dose dial sleeve engaging the housing via a sleeve thread.
5 . A dose delivery device according to claim 4 , wherein the dose selector is axially movable relative to the dose dial sleeve, such that:
in a dose setting mode, the dose selector is rotationally locked to the dose dial sleeve but is rotationally disengaged from the connector; and
in a dose delivery mode, the dose selector is rotationally disengaged from the dose dial sleeve.
6 . A dose delivery device according to claim 5 , further comprising a click mechanism that acts between the dose selector and the connector to generate clicks as the dose selector rotates relative to the connector in the dose setting mode; and to lock the dose selector rotationally to the connector in the dose delivery mode.
7 . A dose delivery device according to claim 1 , wherein the nut and the connector are configured such that, when the nut is rotated the nut moves along the piston rod thread through a first axial distance, and the connector moves in the same direction through a second axial distance that is greater than the first axial distance.
8 . A dose delivery device comprising:
a housing;
a piston rod configured to move axially without rotation relative to the housing, the piston rod comprising a piston rod thread;
a nut engaging the piston rod thread;
a dose selector rotationally locked to the nut;
a connector configured to move axially without rotation relative to the housing;
a first gear configured to rotate without axial movement relative to the housing, the first gear being coupled to the connector by a first engagement, the first engagement being a first helical thread; and
a second gear coupled to the nut so as to permit relative rotation but not relative axial movement between the second gear and the nut, the second gear being coupled to the connector by a second engagement and to the first gear by a third engagement,
wherein the third engagement is a straight track, which permits relative axial movement but prevents relative rotation between the first and second gears.
9 . A dose delivery device according to claim 8 , wherein:
the second engagement is a second helical thread;
the first and second helical threads are of the same handedness; and
the second helical thread has a smaller pitch than the first helical thread.
10 . A method of operating a dose delivery device, which comprises a housing and a piston rod configured to move axially without rotation relative to the housing; the method comprising:
in a dose setting mode, rotating a dose selector relative to the housing, the dose selector being rotationally locked to a nut, which thereby moves in a backward direction along a thread of the piston rod through a first axial distance; and
transmitting the axial movement of the nut through a gearing mechanism to a connector that is configured to move axially without rotation relative to the housing, such that the connector moves in the backward direction from an initial position through a second axial distance greater than the first axial distance;
wherein the gearing mechanism comprises:
a first gear that rotates without axial movement relative to the housing, the first gear being coupled to the connector by a first engagement, the first engagement being a first helical thread; and
a second gear coupled to the nut so as to permit relative rotation but not relative axial movement between the second gear and the nut, the second gear being coupled to the connector by a second engagement and to the first gear by a third engagement.
11 . A method according to claim 10 , wherein the dose selector is coupled to the connector such that the dose selector also moves through the second axial distance.
12 . A method according to claim 10 , further comprising, in a dose delivery mode:
pushing the connector in a forward direction through the second axial distance to the initial position; and
transmitting the axial movement of the connector through the gearing mechanism, such that the nut and the piston rod move in the forward direction through the first axial distance.
13 . A method according to claim 12 wherein a dose dial sleeve also moves through the second axial distance, while rotating to follow a sleeve thread between the dose dial sleeve and the housing.
14 . A method according to claim 13 , wherein:
in the dose setting mode, the dose selector is rotationally locked to the dose dial sleeve; and
in the dose delivery mode, the dose selector is rotationally disengaged from the dose dial sleeve.