Drive Mechanism for use in a Drug Delivery Device

Abstract

The disclosure is directed to a drive mechanism for use in a drug delivery device having a cartridge, the mechanism comprising a base element, a toothed piston rod movable from a first retracted position corresponding to a full cartridge to a second extended position corresponding to an empty cartridge, wherein the piston rod is guided within and movable relative to the base portion, and a drive gear having a pinion, which is rotatably held in the base element and in meshed engagement with the toothed piston rod, wherein the toothed piston rod comprises multiple rigid rod pieces which are connected by hinges, and a drive spring, which is fixed to the base element with one end and fixed to the drive gear with another end and which exerts a force or torque to the drive gear for rotating the drive gear relative to the base element, which rotation results in a movement of the toothed piston rod. The drive spring is charged during manufacture or assembly, wherein the energy stored in the drive spring is sufficient to move the piston rod (from the first to the second position. The disclosure is also directed to a drug delivery device.

Claims

1-15. (canceled)

16. A drive mechanism for use in a drug delivery device having a cartridge, the mechanism comprising: a base element, a toothed piston rod movable from a first retracted position corresponding to a full cartridge to a second extended position corresponding to an empty cartridge, wherein the piston rod is guided within and movable relative to the base portion, and a drive gear having a pinion, which is rotatably held in the base element and in meshed engagement with the toothed piston rod, wherein the toothed piston rod comprises multiple rigid rod pieces which are connected by hinges, and a drive spring, which is fixed to the base element with one end and fixed to the drive gear with another end and which exerts a force or torque to the drive gear for rotating the drive gear relative to the base element, which rotation results in a movement of the toothed piston rod, wherein the drive spring is charged during manufacture or assembly, wherein the energy stored in the drive spring is sufficient to move the piston rod from the first to the second position.

17. The drive mechanism according to claim 16, wherein the drive gear comprises at least two separate components that are rotationally fixed and axially movable relative to each other.

18. The drive mechanism according to claim 16, wherein the drive gear is axially displaceable and rotationally fixed with respect to the pinion.

19. The drive mechanism according to claim 16, wherein a compression spring is arranged between the pinion and the drive gear.

20. The drive mechanism according to claim 16, wherein the drive spring is a power spring or a torsion spring.

21. The drive mechanism according to claim 16, comprising a clutch provided by a splined portion of the drive gear and a corresponding splined portion of the base element, wherein the drive gear is axially movable along its rotational axis between a first position in which the drive gear is rotationally constrained to the base element by engagement of the clutch and a second position in which the clutch is disengaged and relative rotation between the base element and the drive gear is allowed.

22. The drive mechanism according to claim 21, comprising a compression spring arranged to bias the drive gear into its first position relative to the base element.

23. The drive mechanism according to claim 22, further comprising a trigger being axially movable in the direction of the axis of rotation of the drive gear, wherein actuation of the trigger results in an axial movement of the drive gear into its second axial position.

24. The drive mechanism according to claim 16 further comprising a setting element rotatable relative to the base element, wherein rotation of the setting element relative to the base element is limited by rotational stops defining a zero dose position and also a maximum dose position; and wherein the drive gear is configured to engage the setting element when moved from the first into the second position such that the setting element is rotationally constrained to the drive gear.

25. The drive mechanism according to claim 24, wherein the setting element is configured as a number wheel provided with a series of markings on an outer circumference.

26. A drug delivery device comprising a drive mechanism comprising: a base element, a toothed piston rod movable from a first retracted position corresponding to a full cartridge to a second extended position corresponding to an empty cartridge, wherein the piston rod is guided within and movable relative to the base portion, and a drive gear having a pinion, which is rotatably held in the base element and in meshed engagement with the toothed piston rod, wherein the toothed piston rod comprises multiple rigid rod pieces which are connected by hinges, and a drive spring, which is fixed to the base element with one end and fixed to the drive gear with another end and which exerts a force or torque to the drive gear for rotating the drive gear relative to the base element, which rotation results in a movement of the toothed piston rod, wherein the drive spring is charged during manufacture or assembly, wherein the energy stored in the drive spring is sufficient to move the piston rod from the first to the second position and; further comprising a dose setting member for setting user variable doses of a medicament and rotatable relative to the base element wherein the dose setting member and the setting element respectively comprise spline features configured to engage corresponding spline features on a trigger in a first axial position of the trigger such that the trigger rotationally constrains the setting element to the dose setting member.

27. The drug delivery device according to claim 26, wherein movement of the trigger from the first into a second axial position rotationally decouples the trigger from the dose setting member and the setting element.

28. The drug delivery device according to claim 27, further comprising a feedback mechanism generating an audible and/or tactile feedback at the end of dose dispensing, the feedback mechanism comprising a flexible clicker arm on the base element configured to override a protrusion on the setting element to produce the audible and/or tactile feedback, wherein when the drive gear is in a second position, in which relative rotation between the drive gear and the base element is allowed, the drive gear engages the clicker arm in such way that the effective length of the clicker arm is reduced.

29. The drug delivery device according to claim 26, wherein the cartridge contains a medicament.

30. The drug delivery device according to claim 26, wherein the device is a disposable injection device.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0064] Certain embodiments will now be described in further detail with reference to the accompanying schematic drawings, wherein

[0065] FIG. 1 shows an exploded view of an injection device comprising a drive mechanism;

[0066] FIG. 2 a cut view of the device of FIG. 1;

[0067] FIG. 3 a perspective view of the device of FIG. 1 with parts removed;

[0068] FIGS. 4a-c perspective views of different components of the device of FIG. 1;

[0069] FIG. 5 a perspective view of the device of FIG. 1 with parts removed;

[0070] FIG. 6 a perspective view of the number wheel;

[0071] FIG. 7 a top view of the device of FIG. 1;

[0072] FIG. 8 a perspective view of parts of the drive mechanism in accordance with a further embodiment;

[0073] FIG. 9 the last dose nut mechanism of the device of FIG. 1 in a cut view;

[0074] FIGS. 10a-c a dispense sequence of the drive mechanism of the device of FIG. 1 in a cut view;

[0075] FIG. 11 a perspective view of the base element in accordance with a further embodiment;

[0076] FIGS. 12a-b parts of the drive mechanism in accordance with a further embodiment in a perspective view;

[0077] FIG. 13 parts of the drive mechanism in accordance with a further embodiment in a perspective view; and

[0078] FIG. 14 parts of the drive mechanism in accordance with a further embodiment in a cut view.

DETAILED DESCRIPTION

[0079] FIGS. 1 and 2 show views of the drug delivery device 1. FIG. 1 illustrates the component parts incorporated into the injection device which are a casework 10 or body with an upper or outer casework 13 and a lower casework 14, a cartridge holder 20, a base element or chassis 30, a trigger or dose button 40, a dose setting or dial member 50 with a dial cover 51, a last dose nut 60, a trigger spring 80, a prism 90, a setting element or number wheel 100, a drive gear 110, a flexible piston rod 120, a drive spring 130 and a medicament cartridge 140. The dial cover 51 is rigidly fixed into the dial 50. The upper casework 13 and the lower casework 14 form together the casework 10 of the housing. The upper casework 12 has an opening into which prism 90 is inserted and permanently fixed. Chassis 30 comprises a bearing, which may have the form of a cut open cylinder located at the centre of chassis 30, for receiving the pinion 114 of the drive gear 110.

[0080] As shown in FIG. 2, the button 40 is axially constrained between the dial 50 and drive gear 110. The number wheel 100 is axially constrained between the chassis 30 and the upper casework 13. It is free to rotate, relative to the upper casework 13, between two fixed, rotational stops formed by abutments on the number wheel 100 and the upper casework 13.

[0081] As the detailed views in FIGS. 4a to 4c of the dial 50 (FIG. 4a), the button (FIG. 4b) and the number wheel (FIG. 4c) show, the button 40 has inner spline/tooth features 42 that interface with corresponding inner spline/tooth features 52 on an inner surface of the dial 50 and spline/tooth features 43 that interface with corresponding spline/tooth features 103 on a radial inner surface of the number wheel 100. These interfaces disconnect during dose delivery. The dial 50 is axially constrained to the casework 10 via retention features (not shown) and is further rotationally constrained, via the splined/tooth interface 52/42, to the button 40 during dose selection. The spline features 103 of the number wheel 100 interact with the button 40 during dialing. Further, on an inner surface, the number wheel 100 also has spline/tooth features 104 that interact with the corresponding drive features of the drive gear 110 during dispense. On the outer circumferential surface, the number wheel is provided with markings that indicate the set dose.

[0082] The drive spring 130 is provided in the form of a helical torsion spring and is attached at one end to the chassis 30 and at the other end to the drive gear 110. The drive spring 130 is charged for life, which means that the drive spring is fully charged during assembly and does not require charging by the user until the entire content of the cartridge 140 is dispensed.

[0083] The drive gear 110 is axially constrained between the chassis 30 and number wheel 100 and biased away from the chassis 30 by the trigger spring 80 that is provided in the form of a compression spring. It travels axially with the button 40 when the button 40 is pressed to commence dose delivery. During dose selection, the drive gear 110 is in splined engagement with the chassis 30 and hence locked against rotation, but when it travels axially as the button 40 is depressed downwardly for dose delivery this spline engagement is disconnected. Similarly, the separate spline features between the number wheel 100 and the drive gear 110 are engaged when the button 40 is depressed. The trigger spring 80 applies a force between the chassis 30 and drive gear 110 to separate them. In an “at rest” condition, prior to pressing the button 40, this ensures that the drive gear 110 is rotationally coupled to the chassis 30 and that the button splines 42 are engaged with the dial 50.

[0084] The flexible piston rod 120 is located within the chassis 30 and is engaged with the drive gear 110 via a rack and pinion interface so that counter-clockwise (CCW) rotation of the drive gear 110 advances the flexible piston rod 120 towards a bung in the cartridge 140. The pinion 114 is rotatably held in the chassis 30 and is in meshed engagement with the piston rod 120. The piston rod 120 is a single component with discrete rigid rod pieces or segments 121 connected together by thin sections of material which form flexible hinges 122. The end faces of the segments 121 are planar and, when the piston rod 120 is straightened the adjacent segment faces abut each other, allowing the component to withstand a compressive load. Segments 121 are shaped as a flat plate provided with rack teeth 123 on one side and a flange on the opposite side. The segment facing towards the cartridge comprises a pressure foot for contacting the cartridge bung. As the piston rod 120 is advanced, via the rack 123 and pinion 114 engagement with the drive gear 110, the trailing segments 121 of piston rod 120 are drawn into engagement with the drive gear pinion 114. The subsequent segments 121 drive the preceding segments, loading them in compression, and apply a force to the bung. As the piston rod 120 advances, the first segment moves out of a support provided by the chassis 30. Without additional support it is likely that the piston rod 120 would buckle under this compressive loading. The additional support to prevent buckling is created by the inner side wall of the cartridge 140 providing constraint to the outer surfaces of the piston rod 120.

[0085] The distal end of the flexible piston rod 120 acts on a bung within the liquid medicament cartridge. The liquid medicament cartridge 140 is housed within the cartridge holder 20. The cartridge holder 20, chassis 30 and outer/upper casework 13 and lower casework 14 and the prism 90 are fixed rigidly relative to one another.

[0086] The drug delivery device can be operated to deliver a number of user variable doses of medicament from the cartridge 140, via a needle (not shown). The device is disposable and is delivered to the user in a fully assembled condition ready for use. The mechanism provides separate user interfaces for setting and delivery of a dose. In short terms, a dose is set by rotating dial 50 located on the face of the device. Delivery of a dose is initiated by pressing dose button 40, positioned in the centre of the dial 50, and dose delivery will continue while the dose button 40 remains depressed, until the complete set dose has been delivered. The mechanism provides audible, visual and tactile feedback, all three on the setting and delivery of each dose. Any dose size can be selected between zero and a pre-defined maximum, in increments to suit the medicament and user profile. The mechanism permits cancelling of a dose without any medicament being dispensed by rotation of the dial 50 in the opposing direction to when selecting a dose.

[0087] The force required to actuate the dose button 40 and the distance which it has to move are small, providing a significant ergonomic advantage, particularly for those users with impaired dexterity. The mechanism requires consistent user input forces to set a dose and initiate the delivery of a dose, which are insensitive to variations in the force required to displace the bung within the cartridge 140. The dial 50 is disengaged during dose delivery so that it does not rotate, which improves handling of the device during use. The device has relatively low part count, very compact size and is particularly attractive for cost sensitive device applications.

[0088] In the following use and function of the device will be described in more detail.

[0089] FIG. 3 shows the device 1 in the ‘at rest’ condition. Dose marking ‘0’ on the number wheel is visible through the prism 90. The drive spring, which is fully charged during assembly of the device or which is pre-wound, applies a torque to the drive gear 110 when zero dose units are dialed. The drive gear 110 is prevented from rotating, under the action of this torque, by a clutch mechanism formed by the spline interface with the chassis 30. As shown in the enlarged extract of FIG. 3, the splined interface comprises outer spline/tooth features 113 on an outer circumferential surface of the drive gear 110 that engage with inner spline/tooth features 31 on an inner circumferential surface of the chassis 30. By relative axial displacement, the drive gear 110 and the chassis 30 can be decoupled so that the drive gear 110 can rotate under the force of the drive spring.

[0090] To dial a variable dose of liquid medicament, the user rotates the dial 50 in clockwise (CW) direction. The spline features provided on the underside of the dial, and on the button and the number wheel are engaged (see FIG. 4). FIG. 5 shows the spline interfaces during dose dialing. As the enlarged section of FIG. 5 illustrates, rotation of the dial 50 generates an identical rotation in the button 40 due to the spline interface 52/42 between the button 40 and the dial 50. Further, because of the spline interface 43/103 between the button 40 and the number wheel 100, the number wheel 100 is also caused to rotate. The drive gear 110 is prevented from rotating due to the engagement of its splined teeth 113 with the splined teeth 31 of the chassis 30 (see FIG. 3). As shown in FIG. 6, the number wheel 100 has two fixed rotational stops, namely a maximum dose stop 101 and a zero dose stop 102 formed by an abutment. On an inner surface of the upper casework, respective counter abutments are provided. CW rotation of the dial 50 rotates the number wheel 100 away from a zero unit stop formed by said counter abutment on the casework 13 and towards a maximum unit stop formed as a counter abutment surface on the upper casing 13. The dial 50 can be rotated by the user in both CW and CCW directions when the number wheel 100 is not in contact with the zero dose or maximum dose stop abutments in the casework 13. The zero unit abutment 102 prevents CCW rotation of the dial 50 below the zero unit position. The maximum dose abutment 101 prevents setting of a dose greater than the mechanism maximum.

[0091] In FIG. 7, a top view of the drive mechanism is shown, where the dial 50 is provided with a dial clicker 54 in the form of a flexible arm that clicks against a series of protrusions on the upper casework 13. The clicker 54 is hidden from view of the user by the dial cap 51 which clips onto the dial 50. Since during dose delivery the dial 50 does not move, the dial 54 clicker only operates during dialing of a dose. The dial clicker 54 biases the number wheel relative to the prism through the dial 50 ensuring that only whole units of medicament are dialed.

[0092] In FIG. 8, an alternative of the clicker mechanism is presented. This clicker mechanism works axially between the dial 50 and the drive gear 110. Helical teeth 112 on the drive gear 110 may react against a rigid clicker arm 55 on the dial 50. As each unit is dialed by rotating the dial 50 around the axis of rotation 110 of the drive gear 110, the drive gear is forced axially downwards by the depth of the teeth 112, and then returns to its original axial height under the action of the trigger spring. This causes the audible click as each unit is dialed. During delivery, the dial clicker 55 is disengaged through the axial travel of the button 40 and drive gear 110 moves away from the dial 50. This embodiment is advantageous in terms of robustness as the metal spring is likely to be more robust than a plastic arm. In addition, multiple contact faces can be used to spread the load more evenly, reducing damage, without increasing the torque required to overcome the clicker. FIG. 8 also shows that the outer circumferential surface of the drive gear 110 is generally provided with the two sets of splined teeth 111 and 113, wherein the first set 111 is for engagement with correspondingly formed spline features 104 on the number wheel and wherein the second set 113 is provided for engagement with the chassis 30.

[0093] In FIG. 9, the last dose mechanism is displayed. The last dose nut 60 is located between the number wheel 100 and the drive gear 110. It is rotationally coupled to the drive gear 110 via a splined interface 64 provided on a radial inner surface of the last dose nut 60 and on a radial outer surface of the drive gear 110 that enables relative axial displacement but prevents relative rotation. For example, the splined interface 64 may include axially extending ribs on the radial inner surface of the last dose nut 60 that engage in respective axially extending grooves on the radial outer surface of the drive gear 110. Further, the last dose nut 60 is engaged with the number wheel 100 by a thread engagement wherein the last dose nut is provided with a helically extending groove forming an outer thread 62 engaging a helically extending counterpart in the number wheel so that the last dose nut 60 moves along a helical path relative to the number wheel 100 when relative rotation occurs between the number wheel 100 and the drive gear 110 (i.e. during dialing). Relative rotation of the number wheel 100 and the drive gear 110 around the rotational axis 117 causes the last dose nut 60 to travel axially towards the last dose abutment 105 (end stop) on the number wheel 100. Depending on how many units have already been delivered by the mechanism, during selection of a dose, the last dose nut 60 may contact its last dose abutment 105. The abutment prevents further relative rotation of the number wheel 100 and the drive gear 110, and therefore limits the dose that can be selected. The position of the last dose nut 60 is determined by the total number of relative rotations between the number wheel 100 and drive gear 110, which have occurred each time the user sets a dose. With the mechanism in a state in which a dose has been selected, the user is able to deselect any number of units from this dose. Deselecting a dose is achieved by the user rotating the dial 50 CCW. The relative rotation between the number wheel 100 and the drive gear 110 causes the last dose nut 60 to return axially, away from the last dose abutment 105.

[0094] In FIGS. 10a to 10c, a sequence in the drive mechanism to dispense a dose is shown. FIG. 10a shows the device after a dose has been dialed. The zero stop abutment on the number wheel has been rotated away from its counter-abutment. The button 40 is engaged with the number wheel 100 via the spline interface 43/103 and the dial is engaged with the button 40 via the spline interface 52/42. When the button 40 is depressed in an axial direction along the axis of rotation 117, the button 40 moves relative to the dial 50 and the number sleeve 100 so that the button 40 disengages from the spline features 52 of the dial 50 and disengages from the spline features 103 from the number wheel 100.

[0095] The drive gear 110 moves axially with the button 40 against the force of the trigger spring 80, and when the button 40 is partially depressed (FIG. 10b), the drive gear 110 engages the splined teeth 111 on its outer circumferential surface with the spline features 104 on the number wheel 100. As the button is fully depressed (FIG. 10c), the drive gear 110 disengages from the chassis locking teeth or spline feature 31 and is now able to rotate relative to the chassis 30. In other words, the drive gear 110 is movable from a first ‘at rest’ to a second actuated position where the drive gear is disengaged from the chassis 30.

[0096] After the button 40 is fully depressed, the drive gear 110 and the number wheel 100 are rotationally locked and free to rotate under the action of the drive spring 130. The button 40 is disengaged from all spline teeth and therefore the mechanism can rotate relative to the button 40 and the dial 50.

[0097] The pinion 114 of the drive gear 110 acts on the teeth of the piston rod 120 causing the medicament to be dispensed. At the end of dose, the number wheel 100 zero stop abutment stops against the stop feature in the outer casework 13 causing the mechanism to stop. During delivery of a dose, the drive gear 110 and the number wheel 100 rotate together, so that no relative motion in the last dose nut 60 occurs.

[0098] The dose delivery clicker arm is a compliant cantilever beam integrated into the chassis 30, which interfaces axially with ratchet features on the drive gear 110 (not shown). The ratchet teeth spacing corresponds to the drive gear 110 rotation required to deliver a single dose unit. During dispense, as the drive gear 110 rotates, the ratchet features engage with the clicker arm to produce an audible click with each dose unit delivered.

[0099] When the button 40 is released, the trigger spring 80 causes the drive gear 110 and hence the button 40 to travel axially to their at-rest position. This travel causes the drive gear 110 spline teeth 113 to mesh with the chassis 30 again, locking the drive gear 110 against further rotation. The drive gear 110 also disengages its spline teeth 111 from the number wheel 100. The button 40 then re-engages its spline teeth features 42 and 43 with the dial 50 and the number wheel 100. The user is then free to dial their next dose when required.

[0100] In FIG. 11, a further embodiment is shown in which the spline teeth on the chassis are angled or have an angled face on their lower surface so that when the button 40 is released, the re-engagement of the spline teeth 31 fractionally backwinds the drive gear 110 thereby removing the engagement of the number wheel 100 to the zero dose stop abutment. Alternatively, the angled spline teeth may be provided on the dial gear 110. The angled features removes the effect of clearances in the mechanism (for example due to tolerances) which could otherwise lead to slight advancement of the piston rod and medicament dispense when the device is dialed for the subsequent dose, due to the number wheel zero dose stop no longer restraining the mechanism and instead the restraint returning to the splines between the drive gear and the chassis.

[0101] In FIGS. 12a and 12b a mechanism to indicate the end of dose is shown. The end of dose mechanism produces an audible click at the end of dose when the mechanism reaches its zero position. The click is created by interaction between a flexible clicker arm 36 on the chassis 30, the drive gear 110 and the number wheel 100. The volume of the click increases during dose delivery and is likely to be masked by the dial clicker when the user dials the device to or from zero. With respect to FIG. 12a, during dialing, the button 40 and the drive gear 110 are spaced axially away from the chassis 30, and the flexible clicker arm 36 is able to over-ride the protrusion 106 on an inner diameter of the number wheel 100 with minimum torque due to its large effective cantilever length L1 and therefore the volume of the audible click will be low. During dose delivery, when the button 40 and hence drive gear 110 are pushed axially towards the chassis 30, the inner surface of the clicker arm 36 contacts the drive gear 110 when the arm over-rides the bump feature or protrusion 106 of the number wheel 100. This contact with the drive gear 110 reduces the effective length of the clicker arm to L2 (FIG. 12b), thereby increasing its stiffness which leads to an increase in the volume of the audible click produced when the dose returns to zero.

[0102] Instead of a torsion spring, a power spring may be assembled. FIG. 13 is a perspective view of the device with a power spring fitted on the chassis. When using a torsion spring as the drive spring 130, the end-form of the spring can be fixed to the drive gear that moves axially when the button is pressed. The small amount of button travel and hence axial travel of drive gear 110 does not have a significant effect on the performance of the torsion spring. However, in particular when using a power spring, it may be beneficial that the inner end-form of the spring does not move axially with the drive gear. To implement this feature, another embodiment includes a drive gear that is split into two components that are rotationally fixed but that can move axially relative to each other.

[0103] The embodiment shown in FIG. 14 includes a drive gear that includes two separate components that are rotationally fixed and axially movable relative to each other by spline engagement. The upper first drive gear component 119a constitutes the engagement section with the number wheel 100 and is also urged by the button 40 in downward direction during dispense. On a central section on the underside of the first drive gear component 119a, the protruding section of the first drive gear component 119a is received in an opening of the lower second drive gear component 119b. The components 119 and 119b interface by way of a spline connection formed on the outer diameter of the protruding section and on an inner diameter of the receiving section (opening) so that relative axial movement is possible like a telescope but relative rotation between the first drive gear component 119a and the second drive gear component 119b is prevented. The trigger spring 80 is arranged in said opening between the first drive gear component 119a and the second drive gear component 119b.

[0104] The lower component 119b does not move axially and secures the inner leg of the power spring 130. It also contains the pinion 114 that drives the flexible piston rod 120. The upper drive gear component 119a moves axially with the button travel relative to the second drive gear component 119b and interfaces with the number wheel 100 and the last dose nut 60. Alternatively, the pinion 114 may be part of an arbor that constitutes the second component. The two parts 119a and 119b are biased apart by the trigger spring 80, which also gives the advantage that during dose delivery, since both components are rotating together, the spring does not add any frictional losses that the drive spring 130 must overcome. When the button is actuated, which means that the button 40 is moved in downward direction so that the clutch between the drive gear 110 and the number wheel 100 is released, the trigger spring is compressed.

REFERENCE NUMERALS

[0105] 1 drug delivery device [0106] 10 body (casework) [0107] 13 upper casework [0108] 14 lower casework [0109] 20 cartridge holder [0110] 30 chassis (base element) [0111] 31 spline teeth [0112] 36 clicker arm [0113] 40 dose button [0114] 42 spline teeth [0115] 43 spline teeth [0116] 50 dial (dose setting member) [0117] 51 dial cover [0118] 52 spline teeth [0119] 54 dial clicker [0120] 55 dial clicker [0121] 60 last dose nut [0122] 62 outer thread [0123] 64 splined interface [0124] 80 trigger spring [0125] 90 prism [0126] 100 number wheel (setting element) [0127] 101 maximum stop [0128] 102 zero stop [0129] 103 spline teeth [0130] 104 spline teeth [0131] 105 end stop [0132] 106 protrusion [0133] 110 drive gear [0134] 111 spline teeth [0135] 112 helical teeth [0136] 113 spline teeth [0137] 114 pinion [0138] 117 Axis of rotation of drive gear [0139] 119a first drive gear component [0140] 119b second drive gear component [0141] 120 flexible piston rod [0142] 121 segment (rigid rod piece) [0143] 122 hinge [0144] 123 rack teeth [0145] 130 drive spring [0146] 140 cartridge