Drive mechanism for a drug delivery device and drug delivery device

A lead screw, a lead screw nut and a drive member are aligned with an axis defining an axial direction and an opposite axial direction. A coupling between the lead screw and the lead screw nut allows a helical movement of the lead screw with respect to the lead screw nut at least in the axial direction. The lead screw is coupled with the drive member, the coupling generating a helical movement of the lead screw with respect to the drive member when the drive member is moved in the axial direction with respect to the lead screw. A dispense stop feature of the lead screw nut and a dispense stop feature of the drive member prevent the generation of the helical movement of the lead screw when a specified end position of the drive member is approached.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a U.S. National Phase Application pursuant to 35 U.S.C. §371 of International Application No. PCT/EP2011/067418 filed Oct. 5, 2011, which claims priority to European Patent Application No. 10186736.4 filed Oct. 6, 2010. The entire disclosure contents of these applications are herewith incorporated by reference into the present application.

FIELD OF DISCLOSURE

The present invention relates to a drive mechanism for a drug delivery device, especially for a device that is designed for the delivery of fixed doses.

BACKGROUND

Portable drug delivery devices are used for the administration of a drug that is suitable for self-administration by a patient. A drug delivery device is especially useful in the shape of a pen, which can be handled easily and kept everywhere available. A drug is delivered by means of a drive mechanism, which may also serve to set the dose to be delivered. A type of drug delivery device is constructed to be refillable and thus reusable many times.

DE 102 37 258 B4 describes a drug delivery device in the shape of an injection pen, which has a drive mechanism with elements that are rotated relatively to one another around a common axis.

SUMMARY

It is an object of the present invention to disclose a new drive mechanism for a drug delivery device and a drug delivery device comprising a new drive mechanism.

This object is achieved by a drive mechanism according to claim1and a drug delivery device according to claim10. Further objects are achieved by embodiments according to the dependent claims.

The drive mechanism for a drug delivery device comprises a lead screw, a lead screw nut and a drive member, aligned with an axis defining an axial direction and an opposite axial direction. A coupling between the lead screw and the lead screw nut allows a helical movement of the lead screw with respect to the lead screw nut at least in the axial direction. The lead screw is coupled with the drive member, the coupling generating a helical movement of the lead screw with respect to the drive member when the drive member is moved in the axial direction with respect to the lead screw. The coupling is overridden to prevent a helical movement of the lead screw with respect to the drive member when the drive member is moved in the opposite axial direction with respect to the lead screw. A dispense stop feature of the lead screw nut and a dispense stop feature of the drive member interact and thereby prevent the generation of the helical movement of the lead screw when a specified end position of the drive member is approached.

In an embodiment of the drive mechanism the dispense stop features have corresponding contact surfaces, which are oblique to the axis.

Preferably, a generation of the helical movement of the lead screw is prevented by an interaction of the oblique contact faces. As an example, an interaction comprises a sliding movement of at least one of the oblique contact faces on the other oblique contact face. In particular, the drive mechanism may be configured such that the oblique contact face of the dispense stop feature of the drive member is enabled to slide along the oblique contact face of the dispense stop feature of the lead screw nut. Thereby, a rotation of the drive member may be caused, in particular a rotation of the drive member relative to the lead screw nut. An inclination of at least one of the oblique contact faces may correspond to the pitch of a thread of the drive member engaging with the lead screw.

In a further embodiment of the drive mechanism the dispense stop features have corresponding contact surfaces, which are provided as end faces and inhibit a rotation of the drive member with respect to the lead screw nut at least in one direction.

In a further embodiment of the drive mechanism the dispense stop feature of the lead screw nut has the shape of a prism or truncated prism.

In a further embodiment of the drive mechanism the dispense stop features guide the drive member with respect to the lead screw nut in a helical movement having the same pitch as the helical movement of the lead screw with respect to the drive member.

As an example, such a movement may be generated by the interaction of oblique contact faces of the dispense stop features, in particular by the interaction of oblique contact faces having an inclination corresponding to a pitch of a thread of the drive member engaging with the lead screw.

A further embodiment of the drive mechanism comprises a flexible guide feature of the lead screw and a screw thread of the drive member. The coupling of the lead screw with the drive member is provided by the flexible guide feature engaging the screw thread. The screw thread has the same pitch as the helical movement of the lead screw with respect to the drive member.

A further embodiment of the drive mechanism comprises stop features of the lead screw, which inhibit the helical movement of the lead screw when the drive member is moved in the opposite axial direction with respect to the lead screw.

In a further embodiment of the drive mechanism the dispense stop feature of the lead screw nut is formed as an integral part of the lead screw nut, and the dispense stop feature of the drive member is formed as an integral part of the drive member.

In a further embodiment of the drive mechanism the drive member and the lead screw nut are rotationally locked.

A drug delivery device that is provided with the drive mechanism may comprise a body, which has a distal end and a proximal end, which are spaced apart in the direction of the axis of the drive mechanism.

The body can be any housing or any component that forms part of a housing, for example. The body can also be some kind of an insert connected with an exterior housing. The body may be designed to enable the safe, correct, and/or easy handling of the device and/or to protect it from harmful liquids, dust or dirt. The body can be unitary or a multipart component of tubular or non-tubular shape. The body may house a cartridge, from which doses of a drug can be dispensed. The body can especially have the shape of an injection pen.

The term “distal end” refers to a part of the body or housing which is intended to be arranged at a portion of the drug delivery device from which a drug is dispensed. The term “proximal end” refers to a part of the body or housing which is remote from the distal end. The term “distal direction” refers to a movement in the same direction as a movement from the proximal end towards the distal end, not specifying a point of departure nor an end point, so that the movement may go beyond the distal end. The term “proximal direction” refers to a movement in the direction opposite to the distal direction.

The term “lead screw” encompasses any element, whether unitary or of multipart construction, that is provided to transfer a movement to a piston, thus working as a piston rod, especially for the purpose of dispensing a drug. The lead screw may be flexible or not.

The drive mechanism can be used to expel a drug from a receptacle or cartridge inserted in the body of a drug delivery device. The drug delivery device can be a disposable or re-usable device designed to dispense a dose of a drug, especially a liquid, which may be insulin, a growth hormone, a heparin, or an analogue and/or a derivative thereof, for example. The drug may be administered by a needle, or the device may be needle-free. The device may be further designed to monitor physiological properties like blood glucose levels, for example. Each time the lead screw is shifted in the distal direction with respect to the body, a certain amount of the drug is expelled from the drug delivery device.

The term “drug”, as used herein, preferably means a pharmaceutical formulation containing at least one pharmaceutically active compound,

wherein in a further embodiment the pharmaceutically active compound comprises at least one human insulin or a human insulin analogue or derivative, glucagon-like peptide (GLP-1) or an analogue or derivative thereof, or exedin-3 or exedin-4 or an analogue or derivative of exedin-3 or exedin-4.

In the following, a more detailed description of examples and embodiments of the drive mechanism is given in conjunction with the appended figures.

DETAILED DESCRIPTION

FIG. 1shows a cut-away view of an injection pen comprising the drive mechanism. The drive mechanism is arranged in a body1having a distal end2and a proximal end3. A lead screw5is arranged along an axis4of the device. A screw thread6of the lead screw5is coupled to a drive feature of a lead screw nut7engaging the screw thread6, in order to guide a helical movement of the lead screw5with respect to the lead screw nut7. In further embodiments, the screw thread and the drive feature can be reversed such that the lead screw is provided with discrete drive features and the lead screw nut is provided with a helical screw thread. The lead screw nut7is rotationally locked to the body1.

The embodiment shown inFIG. 1comprises a drive member8, which can be operated by the user by means of a button9, which is arranged at the proximal end3and juts out of the body1. The drive member8is coupled or engaged with the lead screw5. This is achieved, in this embodiment, by means of a screw thread18of the drive member8and a flexible guide feature15of the lead screw5. The drive member8can especially be a drive sleeve of essentially cylindrical shape, the axis of the drive sleeve being arranged parallel to the axis4of the device. The lead screw5may be disposed to enter the drive member8.

A removable and attachable part11of the body1may be provided as a cartridge holder. When this part11is removed from the rest of the body1, a cartridge12can be inserted. When the part11is attached to the body1, the lead screw5is brought into contact with a piston13, which is provided to expel a drug from the cartridge12. A bearing14may be arranged between the lead screw5and the piston13in order to prevent any damage that might be caused by a relative movement between the lead screw5and the piston13. The lead screw5functions as a piston rod to advance the piston13in the distal direction.

During a delivery operation, the lead screw5is helically moved in the distal direction with respect to the body1. The lead screw5is guided by the lead screw nut7, which is engaged with the screw thread6of the lead screw5. Stop features17(shown inFIG. 3described below) are provided in the screw thread6of the lead screw5to enable a set operation, by which a fixed dose that is to be dispensed can be preset. For this purpose, the drive member8is drawn in the proximal direction relatively to the body1and to the lead screw5. The drive member8is coupled with the lead screw5. In the embodiment shown inFIG. 1, the coupling is achieved with the screw thread18of the drive member8and the flexible guide feature15of the lead screw5. During the set operation, the lead screw5must not be moved. Therefore, the engagement between the drive member8and the lead screw5is temporarily released during the set operation. This may be achieved by a deformation of the flexible guide feature15to override the screw thread18of the drive member8. In spite of the engagement between the drive member8and the lead screw5, the drive member8can therefore be moved without being rotated, while the lead screw5stays stationary with respect to the body. Overriding the engagement between the drive member8and the lead screw5is facilitated by flexible guide features15, which can be bent towards the central axis4. A rotation of the drive member8with respect to the body1may be prevented by guide features10, which may be protruding elements of the body1engaging an axial groove in the outer surface of the drive member8, for instance.

After the drive member8has been moved a distance corresponding to the pitch of the screw thread18of the drive member8, the flexible guide feature15of the lead screw5reengages the screw thread18of the drive member8, and the user can advance the lead screw5by pushing the drive member8back in the distal direction. This method of operation by disengaging and reengaging the lead screw5with the drive member8relies entirely on the lead screw5remaining substantially stationary during the setting operation. Should the lead screw5rotate or move axially during setting, then the drive member8would very likely not correctly reengage with the lead screw5and thus cause dose inaccuracy. Therefore, the lead screw nut7guiding the helical movement of the lead screw5with respect to the body1is rotationally locked to the body1at least during the dispense operation and, furthermore, the lead screw5is provided with stop features interfering with the rotation of the lead screw5in such a manner that the rotation is inhibited in the positions of the lead screw5which are obtained after the drug delivery and before the setting of a new dose. The rotation of the lead screw5is thus locked with respect to the lead screw nut7, and the lead screw nut7is prevented from rotating relatively to the body1. Therefore, when the drive member8is drawn in the proximal direction, the relative linear motion between the drive member8and the lead screw5causes the engagement of the drive member and the stationary lead screw5to be overridden and thus the engagement between the drive member8and the lead screw5to be released. The stop features are therefore preferably arranged at least on the distal sidewall of the screw thread6of the lead screw5, while the screw thread6may be smooth, forming a helix, on its proximal sidewall. When the drive member8is pushed in the distal direction, a guide means of the lead screw nut7engaging the screw thread6of the lead screw5stays in contact with the smooth proximal sidewall of the screw thread6, thus enabling a smooth helical movement of the lead screw5sliding through the opening of the lead screw nut7. Therefore, the stop features do not interfere with the relative motion of the lead screw5with respect to the lead screw nut7during the dispense operation.

The stop features may especially be provided by recesses of a helical groove forming the screw thread6of the lead screw5. The recesses can have contact faces arranged transverse to the axis4and interrupting the smooth helix of the relevant sidewall of the groove forming the screw thread6. The contact faces may especially be flat portions, essentially perpendicular to the axis4or at least having zero helix angle, but may comprise a rake angle in the radial direction. A drive feature of the lead screw nut7may be formed in such a manner that it enters the recesses and stops on the contact face. When the drive feature of the lead screw nut7comes into contact with one of the flat portions, the generally perpendicular orientation of the flat portion with respect to the axis4causes the guidance of the helical movement of the lead screw5with respect to the body1to be stopped. It may be favorable if the drive feature of the lead screw nut7that engages with the screw thread6of the lead screw5and is stopped in the recesses is made up of one or more individual drive features and is not formed by a completely continuous helix. The stop features are arranged in such a fashion that, after a dose of the drug has been fully delivered and the device is ready for the next dose to be set, one of the stop features is in a position ready to stop the rotation of the lead screw5when the drive member8is pulled in the proximal direction. The axial load exerted on the lead screw5is then compensated by the drive feature of the lead screw nut7engaging the relevant stop feature, particularly contacting the essentially flat portion of the relevant recess. This acts to lock the rotation of the lead screw5rather than rotate it, because the lead screw nut7is rotationally locked to the body1at least during the operations of setting and dispensing a dose. Essentially, the flat surfaces on the screw thread6are designed to prevent a back-driving of the lead screw5during a set operation. The motion of the lead screw5may thereby be restricted to the distal direction.

FIG. 2shows an enlarged detailed view of the arrangement of the lead screw nut7and the drive member8. In the embodiment shown inFIG. 2, the dispense stop feature19of the lead screw nut7has the shape of a truncated prism. A surface of the dispense feature19is oblique to the axis4and faces a corresponding dispense stop feature20of the drive member8, which is provided with a triangular recess matching the dispense stop feature19of the lead screw nut7. This shape of the dispense stop features19,20is especially favourable, because both a rotation and a purely axial movement of the drive member8are inhibited. The dispense stop features19,20thus help to ensure that accurate doses of the drug are dispensed with each device actuation. To achieve accurate doses, it is essential that the axial and rotational position of the drive member8relative to the lead screw nut7is identical at the end of each dose delivery. The geometry of the dispense stop features19,20is designed to achieve this.

In the embodiment according toFIG. 2, the dispense stop features19,20present the shape of right-angled triangles, with the hypotenuse of each triangle arranged oblique to the axis4and matching the helix angle of the internal thread18of the drive member8, thus forming corresponding contact surfaces22, which are oblique to the axis4. The surfaces that correspond to a side of the triangle are arranged along the axis4and are provided as end faces23to inhibit a rotation of the drive member8with respect to the lead screw nut7in the direction of rotation of the lead screw5during the drug delivery. This means that as the drive member8axially engages with the lead screw nut7by means of the dispense stop features19,20, it is guided along a helical path until the end faces23of the triangular dispense stop features19,20engage, thus ensuring that the end position of the drive member8is accurately controlled both axially and rotationally. Because the angle of the hypotenuse22of the triangular dispense stop features19,20matches the helix angle of the thread18of the drive member8, this also ensures that the lead screw5will not be moved by the drive member8when the dispense stop features19,20are in contact. When the drive member8approaches its specified end position, the dispense stop features19,20force the movement of the drive member8into a helix that matches the helix of the thread18, so that the movement of the drive member8does not change the position of the lead screw5. The end of the drug delivery is thus very precisely determined.

FIG. 2shows an axial opening of the lead screw nut7. This opening or gap can be used as a guide feature21, which may provide the rotational locking of the lead screw nut7with respect to the body1, for example. Instead, other locking means may be provided.

FIG. 3shows an enlarged detailed view of the distal end of the lead screw5. In this embodiment the lead screw5comprises a screw thread6and a further screw thread16, which are intertwined and are provided with separate entries (“two-start” thread). The lead screw nut7engages the screw threads6,16of the lead screw5. Stop features17may be provided on one screw thread6or on both screw threads6,16. The pitch of the screw threads6,16can be adapted to the pitch of the thread18of the drive member8in order to provide a desired ratio of the speeds of advancement of the lead screw5and the drive member8.

The dispense stop features19,20of the lead screw nut7and the drive member8improve the dose accuracy and prevent an incorrect dosage, which might occur because of mechanical play of the device components. As the dispense stop features19,20can be formed as integral parts of the lead screw nut7and the drive member8, the manufacturing is facilitated and no additional components are necessary.