Dosing device with final dose protection

Abstract

A drug delivery device with a final dose protection function comprises a shell, a dose cylinder used for setting a dose is installed in the shell, a dose button capable of driving the dose cylinder to rotate is installed in the rear end of the dose cylinder, and a clutch is arranged between the dose button and the dose cylinder. After the clutch is meshed with the dose cylinder, the dose button rotates to drive the dose cylinder to rotate to achieve dose setting, after the clutch is separated from the dose cylinder, the dose cylinder can rotate freely to achieve dose injection, the clutch and the dose button can rotate synchronously, and when the dose cylinder cannot rotate, the dose button and the clutch rotate in situ. According to the invention, the clutch is additionally arranged between the dosage cylinder and the dosage button to realize strict control of dosage setting.

Description

Technical Field

[0001] The present invention belongs to the technical field of drug delivery devices, and particularly relates to a drug delivery device with a last-dose protection function. Background Art

[0002] With the development of insulin pen technology, the current requirements for insulin pens already include: (1) enabling multiple small-dose injections, generally capable of injecting at least 5 times with a maximum single-injection dose of (60 IU); (2) facilitating the adjustment of the single-injection dose, with an adjustment range of 0 - 60 IU and high adjustment accuracy (up to 1 IU); (3) when adjusting the dose, it can be visually scaled or the pen can emit a sound to facilitate self-operation by patients with poor eyesight or even blindness; (4) during injection, the operation is simple, and the pen also emits a sound during the injection process to indicate that the injection is in progress.

[0003] CN117224781A discloses a drug delivery device with dose setting and callback functions, including a cartridge holder. The rear end of the cartridge holder is connected to a housing. A screw is installed inside the housing to move forward and deliver drugs according to the set dose during injection; a rotor, threadedly connected to the screw, is used to rotate and drive the screw to move axially forward during injection; a rotating shaft, the front end of which is connected to the rear end inside the rotor, is used to drive the rotor to rotate during injection and can axially move relative to the rotor, and can cooperate with the screw to control the last-dose setting during the axial movement; a differential nut, installed outside the rear end of the rotating shaft, is used for differential adjustment and driving the axial movement of the rotating shaft; a differential screw, fixed inside the housing and arranged between the differential nut and the dose setting cylinder, is threadedly connected to both the differential nut and the dose setting cylinder; a dose setting cylinder, which can engage with the bushing and drive the bushing to rotate during injection, and is also used to drive the differential nut to rotate synchronously; a bushing, connected to the inner side of the rear end of the rotating shaft, is used to drive the rotating shaft to rotate during injection. When performing the last-dose setting with this structure, when the dose setting cylinder is rotated clockwise, the synchronously rotated differential nut clockwise drives the rotating shaft to axially displace proximally. When the step provided inside the rotating shaft abuts against the flange of the push rod, the rotating shaft cannot continue to move proximally. Since the rotating shaft and the differential nut are circumferentially connected, when the rotating shaft cannot move proximally, the differential nut cannot move proximally either. And since the differential nut and the dose setting sleeve are axially grooved connected, the dose setting sleeve cannot rotate clockwise either. However, the user can still resist the resistance and continue to set 2 - 3 unit doses, resulting in incorrect dose setting. Summary of the Invention

[0004] Aiming at the problems existing in the above background art introduction, the purpose of the present invention is to provide a drug delivery device with a last-dose protection function that can strictly control the dose setting.

[0005] The technical solution adopted by the present invention is:

[0006] A drug delivery device with last-dose protection, comprising a housing, a dose cylinder for setting a dose is installed inside the housing, a dose button for driving the dose cylinder to rotate is installed at the rear end of the dose cylinder, a clutch is arranged between the dose button and the dose cylinder, the clutch can be engaged with the dose cylinder and then drive the dose cylinder to rotate by the rotation of the dose button to achieve dose setting, after the clutch is separated from the dose cylinder, the dose cylinder can rotate freely to achieve dose injection, and when the clutch and the dose button rotate synchronously and the dose cylinder cannot rotate, the dose button and the clutch rotate in place.

[0007] Further, a protruding tooth is arranged at the end of the dose cylinder, and an engaging internal tooth matched with the protruding tooth is arranged inside the clutch. When the engaging internal tooth is engaged with the protruding tooth, the rotation of the dose button can drive the dose cylinder to rotate to achieve dose adjustment. During injection, the clutch is separated from the dose cylinder, and the dose cylinder can rotate freely to achieve dose injection.

[0008] Further, ratchet teeth are arranged on the clutch, an inner ring of ratchet teeth matched with the ratchet teeth is arranged inside the dose button, and the dose button is circumferentially and annularly connected with the clutch. When the dose cylinder cannot rotate after the drug is injected, due to the arrangement of the clutch, when the dose button is rotated continuously, the dose button and the clutch rotate in place, so that no matter how much force is applied, the clutch unloads the force and cannot break through the resistance to continue to achieve dose setting, thereby controlling the wrong setting of the dose.

[0009] Further, a screw, a rotor, a rotating shaft, a differential nut, a fixed cylinder and a bushing are installed inside the housing, a push plate is installed at the front end of the screw, the rotor is threadedly connected with the screw and is used to rotate and drive the screw to move forward axially to convey the drug during injection, and can cooperate with the fixed cylinder to make an injection sound; the fixed cylinder is fixed inside the housing and is arranged between the differential nut and the dose cylinder, the fixed cylinder is threadedly connected with both the differential nut and the dose cylinder for differential adjustment, and is rotationally connected with the rotor and axially limits the rotor; the front end of the rotating shaft is connected to the rear end inside the rotor and is used to drive the rotor to rotate during injection, and it can axially move relative to the rotor, and the rotating shaft can cooperate with the screw to control the last-dose setting during the axial movement process; the differential nut is installed inside the dose cylinder and can rotate synchronously with the dose cylinder and drive the rotating shaft to axially move; the bushing is connected to the inner side of the rear end of the differential nut and axially moves driven by the differential nut; a clutch tooth is installed between the bushing and the dose cylinder, the clutch tooth is fixedly connected with the bushing, the clutch tooth is meshed with the dose cylinder, and the clutch tooth can cooperate with the dose cylinder to make a dose-setting sound during axial movement, and is meshed with the dose cylinder during injection and driven by the dose cylinder to rotate synchronously with the bushing.

[0010] Further, protruding one-way ratchet teeth are arranged on the outer surface of the rotor, and notches are evenly arranged in a ring inside the fixed cylinder, and the one-way ratchet teeth cooperate with the notches to make an injection sound during rotation.

[0011] Further, engaging teeth are evenly distributed axially on both the dosing cylinder and the clutch gear. When the dosing cylinder rotates, the engaging teeth on the dosing cylinder and the engaging teeth on the clutch gear are in sliding fit to generate sound for dose setting.

[0012] Further, the rotor is connected to the rotating shaft through an axial groove, the rotating shaft is connected to the bushing through an axial groove, and the differential nut is connected to the dosing cylinder through an axial groove. The rotating shaft is connected to the differential nut through a circumferential ring, and the differential nut is connected to the bushing through a circumferential ring.

[0013] Further, a flange is provided at the rear end of the screw, and a step is provided inside the front end of the rotating shaft. The flange and the step can be in contact for limit control to set the final dose.

[0014] Further, a cover plate is fixedly installed at the end of the fixed cylinder. A return knob is meshingly connected to the cover plate. The return knob is sleeved outside the screw, and a return spring is provided between the return knob and the cover plate. When the return knob disengages from the meshing state, the screw can be driven by the return spring to move back to its original position.

[0015] Further, the outer shell is connected to the rear end of the pen core holder. A medicine core is installed inside the pen core holder, and a detachable pen cap is provided at the front end of the pen core holder.

[0016] Compared with the prior art, the remarkable advantages of the present invention include:

[0017] 1. A clutch is added between the dosing cylinder and the dose button to strictly control the dose setting.

[0018] 2. The rotating shaft can cooperate with the screw during axial movement to control the final dose setting and prevent sub-dose injection.

[0019] 3. The dose setting process and the injection process are realized through the cooperation of components between the dosing cylinder, the fixed cylinder, the differential nut, the rotating shaft, the bushing, and the rotor. The structure is simple and reasonable.

[0020] 4. The rotor cooperates with the fixed cylinder during injection to generate sound to remind the user of the injection dose.

[0021] 5. The cooperation between the dosing cylinder and the clutch gear generates sound to remind the user of the dose setting.

[0022] 6. After the screw is returned to its original position by the return knob, the medicine core can be replaced and the device can be used continuously. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 is an exploded schematic view of the present invention.

[0024] Figure 2 is a sectional schematic view of the present invention in the natural state.

[0025] Figure 3 It is a schematic cross-sectional view in the dose adjustment state of the present invention.

[0026] Figure 4 It is a schematic cross-sectional view in the dose injection state of the present invention.

[0027] Figure 5 It is a schematic view of the cooperation structure of the clutch and the dose cylinder of the present invention.

[0028] Figure 6 It is a schematic view of the structure of the dose cylinder of the present invention.

[0029] Figure 7 It is a schematic view of the internal structure of the dose button of the present invention.

[0030] Figure 8 It is a schematic view of the structure of the clutch of the present invention.

[0031] Figure 9 It is a schematic view of the internal structure of the clutch of the present invention.

[0032] In the figure: 1. Differential nut; 2. Dose cylinder; 21. Stopping part; 22. Protruding teeth; 23. Groove; 3. Cartridge holder; 4. Rotor; 5. Dose button; 51. Inner ring ratchet teeth; 6. Clutch; 61. Ratchet teeth; 62. Engaging inner teeth; 7. Injection spring; 8. Clutch teeth; 9. Screw; 10. Fixed cylinder; 11. Return spring; 12. Return knob; 13. Cover plate; 14. Bushing; 15. Rotating shaft; 16. Lens; 17. Outer shell; 18. Pen cap; 19. Pusher plate. Detailed implementation manners

[0033] The present invention will be further described below in conjunction with specific embodiments, but the present invention is not limited to these specific implementation manners. Those skilled in the art should recognize that the present invention covers all alternative solutions, improvement solutions and equivalent solutions that may be included within the scope of the claims.

[0034] In the description of the present invention, it should be understood that the orientation or positional relationships indicated by the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "clockwise", "counterclockwise", etc. are based on the orientation or positional relationships shown in the drawings. These are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, it should not be construed as a limitation to the present invention. In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include one or more of such features. In the description of the present invention, unless otherwise specified, the meaning of "a plurality" is two or more, unless otherwise clearly defined.

[0035] In the present invention, unless otherwise clearly specified and defined, the terms "mounted", "connected", "coupled", "fixed", etc. shall be construed in a broad sense. For example, it may be a fixed connection, a detachable connection, or an integral connection; it may be a mechanical connection or an electrical connection; it may be directly connected or indirectly connected through an intermediate medium, and it may be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0036] In the present invention, unless otherwise clearly specified and defined, the first feature being "on" or "under" the second feature may include the direct contact between the first and second features, or may include the situation where the first and second features are not in direct contact but in contact through additional features therebetween. Moreover, the first feature being "above", "over" and "on top of" the second feature includes that the first feature is directly above and obliquely above the second feature, or merely indicates that the horizontal height of the first feature is higher than that of the second feature. The first feature being "under", "beneath" and "underneath" the second feature includes that the first feature is directly below and obliquely below the second feature, or merely indicates that the horizontal height of the first feature is lower than that of the second feature.

[0037] See Figures 1-9, this embodiment provides a drug delivery device with last-dose protection, including a housing 17. A dose cylinder 2 for setting the dose is installed inside the housing 17. A dose button 5 capable of driving the dose cylinder to rotate is installed at the rear end of the dose cylinder 2. A clutch 6 is arranged between the dose button 5 and the dose cylinder 2. After the clutch 6 and the dose cylinder 2 are engaged, the dose cylinder 2 is driven to rotate by the rotation of the dose button 5 to achieve dose setting. After the clutch 5 is separated from the dose cylinder 2, the dose cylinder 2 can rotate freely to achieve dose injection. When the clutch 6 and the dose button 5 rotate synchronously and the dose cylinder 2 cannot rotate, the dose button 5 and the clutch 6 spin in place. Specifically, a clutch 6 is arranged between the dose button 5 and the dose cylinder 2. A protruding tooth 22 is arranged at the end of the dose cylinder 2. An engaging internal tooth 62 that cooperates with the protruding tooth 22 is arranged inside the clutch 6. A ratchet tooth 61 is arranged on the clutch 6. An inner ring ratchet tooth 51 that cooperates with the ratchet tooth 61 is arranged in a circle inside the dose button 5. The dose button 5 and the clutch 6 are circumferentially connected. When the engaging internal tooth 62 and the protruding tooth 22 are engaged, the rotation of the dose button 5 can drive the dose cylinder 2 to rotate to achieve dose adjustment. During injection, the clutch 6 is separated from the dose cylinder 2, and the dose cylinder 2 can rotate freely to achieve dose injection. When the dose cylinder 2 cannot rotate after the drug is injected, due to the setting of the clutch 6, when the dose button 5 is rotated continuously, the dose button 5 and the clutch 6 spin in place. Thus, no matter how much force is applied, the force is unloaded by the clutch 6, and the dose setting cannot be continued by breaking through the resistance, thereby controlling the incorrect setting of the dose.

[0038] In this embodiment, the outer shell 17 is connected to the rear end of the cartridge holder 3. A medicated core is installed inside the cartridge holder 3. A detachable pen cap 18 is provided at the front end of the cartridge holder 3. Inside the outer shell 17, a screw 9, a rotor 4, a rotating shaft 15, a differential nut 1, a fixed cylinder 10, and a bushing 14 are installed. A push plate 19 is installed at the front end of the screw 9. The rotor 4 is threadedly connected to the screw 9 and is used to rotationally drive the screw 9 to axially move forward to deliver medicine during injection, and can cooperate with the fixed cylinder 10 for injection sound generation; the fixed cylinder 10 is fixed inside the outer shell 17 and is disposed between the differential nut 1 and the dosing cylinder 2. The fixed cylinder 10 is threadedly connected to both the differential nut 1 and the dosing cylinder 2 for differential adjustment, and is rotationally connected to the rotor 4 and axially limits the rotor 4; the front end of the rotating shaft 15 is connected to the inside of the rear end of the rotor 4 and is used to drive the rotor 4 to rotate during injection, and it can axially move relative to the rotor 4. The rotating shaft 15 can cooperate with the screw 9 to control the final dose setting during axial movement; the differential nut 1 is installed inside the dosing cylinder 2 and can rotate synchronously with the dosing cylinder 2 and can drive the rotating shaft 15 to axially move; the bushing 14 is connected to the inner side of the rear end of the differential nut 1 and axially moves under the drive of the differential nut 1; a clutch gear 8 is installed between the bushing 14 and the dosing cylinder 2. The clutch gear 8 is fixedly connected to the bushing 14. The clutch gear 8 is meshed with the dosing cylinder 2. The clutch gear 8 can cooperate with the dosing cylinder 2 for dose setting sound generation during axial movement, and is meshed with the dosing cylinder 2 during injection and then driven by the dosing cylinder 2 to rotate the clutch gear 8 and the bushing 14 synchronously; a dose button 5 capable of driving the dosing cylinder 2 to rotate is installed inside the rear end of the dosing cylinder 2. An injection spring 7 is provided between the dose button 5 and the bushing 14.

[0039] In this embodiment, a lens 16 for observing the dose setting is snap-fitted on the outer shell 17. A stop bar is provided at one snap-fitting part of the lens 16. A stop portion 21 capable of cooperating with the stop bar to limit the maximum dose setting is provided on the outer surface of the dosing cylinder 2. The present invention is limited by the cooperation of the stop bar provided on the lens 16 and the stop portion 21 of the dosing cylinder 2, ensuring the reliability of the limitation, that is, when the stop bar abuts against the stop portion 21, no matter how much rotational force is applied, the dosing cylinder 2 cannot continue to rotate to increase the dose. The stop bar extends along both ends of the snap-fitting part, and the end of the snap-fitting part protrudes from the side surface of the stop bar. The stop portion 21 is provided with a groove 23 for accommodating the snap-fitting part. When the stop portion 21 abuts against the stop bar, the snap-fitting part enters the mouth of the groove 23 to ensure the reliability of the abutment.

[0040] Specifically, the outer surface of the rotor 4 in this embodiment is provided with protruding one-way ratchet teeth. The inner ring of the fixed cylinder 10 is evenly provided with notches. The one-way ratchet teeth cooperate with the notches during rotation to inject and generate sound. The one-way ratchet teeth limit the rotation direction of the rotor 4 to only rotate counterclockwise. It is possible to set that each rotation of a unit will emit a prompt sound to remind the user of the injection dose. The meshing teeth are evenly arranged in the axial direction of the dose cylinder 2 and the clutch teeth 8. When the dose cylinder 2 rotates, the meshing teeth on the dose cylinder 2 and the meshing teeth on the clutch teeth 8 are in sliding fit to set the dose and generate sound. The rotor 4 is axially groove-connected to the rotating shaft 15, the rotating shaft 15 is axially groove-connected to the bushing 14, and the differential nut 1 is axially groove-connected to the dose cylinder 2. The rotating shaft 15 is circumferentially ring-connected to the differential nut 1, and the differential nut 1 is circumferentially ring-connected to the bushing 14. Among them, the axial groove connection is a structure in which a rib or rib platform cooperates with a long strip-shaped groove, and the circumferential ring connection of two sections is a structure in which a ring rib or ring platform cooperates with a ring groove or ring rib. The circumferential ring connection between the rotor 4 and the fixed cylinder 10 restricts the axial movement of the rotor 4, and the rotor 4 can rotate relative to the fixed cylinder 10. The circumferential ring connection between the rotating shaft 15 and the differential nut 1 drives the rotating shaft 15 to move axially through the differential nut 1, and the rotating shaft 15 and the differential nut 1 can rotate relative to each other. The rear end of the screw 9 is provided with a flange, and the front end inside of the rotating shaft 15 is provided with a step. The flange and the step can be in contact for limit control of the final dose setting.

[0041] In this embodiment, a cover plate 13 is fixedly installed at the end of the fixed cylinder 10. A return knob 12 is meshingly connected to the cover plate 13. The return knob 12 is sleeved outside the screw 9. A return spring 11 is arranged between the return knob 12 and the cover plate 13. When the return knob 12 is disengaged from the meshing state, the screw 9 can be driven to move back to its original position under the drive of the return spring 11.

[0042] When adjusting the dose of the present invention: Rotate the dose knob 5, and the dose cylinder 2 and the differential nut 1 will rotate synchronously and move upward, and the bushing 14, the clutch teeth 8, and the rotating shaft 15 will move upward at the same time. At this time, the clutch teeth 8 will jump and make a sound (in the natural state, the clutch teeth 8 and the dose cylinder 2 are in a biting state). When the single maximum dose is adjusted, the rotation of the dose cylinder 2 is blocked by the blocking strip on the lens 16.

[0043] When injecting the dose of the present invention: Hold down the dose knob 5, and the clutch 6 will disengage from the dose cylinder 2. The three teeth of the rotating shaft 15, the clutch teeth 6, and the dose cylinder 2 will be in a biting state. At this time, the rotating shaft 15, the clutch teeth 6, the differential nut 1, and the bushing 14 will rotate and move downward along with the dose cylinder 2. The bushing 14 will drive the rotor 4 to rotate, and the rotation of the rotor 4 causes the screw 9 to move axially forward.

[0044] When replacing the medicine core of the present invention: after removing the medicine core, the teeth of the knob 12 and the teeth of the cover plate 13 are disengaged from the bite, and the knob 12 can be rotated freely. When rotating, the screw rod 9 is driven to rotate and can return to its original position. After reaching the position, install the medicine core and it can be used again.

[0045] A clutch 6 is added between the dose cylinder 2 and the dose button 5 of the present invention to strictly control the dose setting; the rotating shaft 15 can cooperate with the screw rod 9 during the axial movement to control the final dose setting and prevent sub-dose injection; the dose setting process and the injection process are realized through the cooperation of the components between the dose cylinder 2, the fixed cylinder 10, the differential nut 1, the rotating shaft 15, the bushing 14, and the rotor 4, and the structure is simple and reasonable; the rotor 4 cooperates with the fixed cylinder 10 to make a sound during injection to remind the user of the injection dose; the dose cylinder 2 cooperates with the clutch teeth 8 to make a sound to remind the user of the dose setting. After returning the screw rod 9 to its original position by retracting the knob 12, replace the medicine core and continue to use.

Claims

1. A drug delivery device with last dose protection, comprising a housing (17), a dose barrel (2) for setting a dose being installed in the housing (17), a dose button (5) capable of driving the dose barrel to rotate being installed in the rear end of the dose barrel (2), characterized in that: A clutch (6) is arranged between the dosage button (5) and the dosage barrel (2). After the clutch (6) and the dosage barrel (2) are meshed, the dosage button (5) drives the dosage barrel (2) to rotate to achieve dosage setting. After the clutch (6) and the dosage barrel (2) are separated, the dosage barrel (2) can rotate freely to achieve dosage injection. The clutch (6) and the dosage button (5) can rotate synchronously, and when the dosage barrel (2) cannot rotate, the dosage button (5) and the clutch (6) rotate in place.

2. A drug delivery device with last dose protection according to claim 1, characterized in that: The end of the dosage barrel (2) is provided with a protruding tooth (22), and the interior of the clutch (6) is provided with a meshing internal tooth (62) that cooperates with the protruding tooth (22).

3. A drug delivery device with last dose protection according to claim 2, characterized in that: The clutch (6) is provided with ratchet teeth (61), the dosage button (5) is provided with an inner circle of ratchet teeth (51) cooperating with the ratchet teeth (61), and the dosage button (5) is connected to the clutch (6) in a circumferential ring.

4. A drug delivery device with last dose protection according to claim 1, characterized in that: The housing (17) is provided with a screw (9), a rotor (4), a rotating shaft (15), a differential nut (1), a fixed cylinder (10), and a bushing (14). A push plate (19) is installed at the front end of the screw (9). The rotor (4) is threadedly connected to the screw (9) for rotating and driving the screw (9) to move axially forward to deliver the drug during injection, and can cooperate with the fixed cylinder (10) to produce injection sound. The fixed cylinder (10) is fixed in the housing (17) and arranged between the differential nut (1) and the dosage cylinder (2). The fixed cylinder (10) is threadedly connected to the differential nut (1) and the dosage cylinder (2) for differential adjustment, and is rotationally connected to the rotor (4) and axially limits the rotor (4). The front end of the rotating shaft (15) is connected to the rear end of the rotor (4) for driving the rotor (4) to rotate during injection, and can move axially relative to the rotor (4). The shaft (15) can cooperate with the screw (9) to control the final dose setting during the axial movement; the differential nut (1) is installed on the inner side of the dose barrel (2) and can rotate synchronously with the dose barrel (2) and can drive the rotating shaft (15) to move axially; the bushing (14) is connected to the inner side of the rear end of the differential nut (1) and moves axially under the drive of the differential nut (1); a clutch tooth (8) is installed between the bushing (14) and the dose barrel (2), the clutch tooth (8) is fixedly connected to the bushing (14), the clutch tooth (8) is meshed with the dose barrel (2), the clutch tooth (8) can cooperate with the dose barrel (2) to make a sound when moving axially, and mesh with the dose barrel (2) during injection and is driven by the dose barrel (2) to rotate synchronously with the bushing (14); a dose button (5) that can drive the dose barrel (2) to rotate is installed in the rear end of the dose barrel (2).

5. A drug delivery device with last dose protection according to claim 4, characterized in that: The outer surface of the rotor (4) is provided with protruding one-way ratchets, and the inner ring of the fixed cylinder (10) is provided with evenly distributed notches, and the one-way ratchets cooperate with the notches to produce injection sound during the rotation process.

6. A drug delivery device with last dose protection according to claim 4, characterized in that: The dosage barrel (2) and the clutch tooth (8) are evenly provided with meshing teeth in the axial direction, and when the dosage barrel (2) rotates, the meshing teeth on the dosage barrel (2) and the meshing teeth on the clutch tooth (8) slide and cooperate with each other to produce a dosage setting sound.

7. A drug delivery device with last dose protection according to claim 4, characterized in that: The rotor (4) and the rotating shaft (15), the rotating shaft (15) and the bushing (14), and the differential nut (1) and the dosage barrel (2) are all connected by axial grooves, and the rotating shaft (15) and the differential nut (1), and the differential nut (1) and the bushing (14) are all connected by circumferential rings.

8. A drug delivery device with last dose protection according to claim 4, characterized in that: The rear end of the screw (9) is provided with a flange, and the front end of the rotating shaft (15) is provided with a step. The flange and the step can contact and limit to control the final dose setting.

9. A drug delivery device with last dose protection according to claim 4, characterized in that: A cover plate (13) is fixedly mounted on the end of the fixed cylinder (10), and a retraction knob (12) is meshedly connected to the cover plate (13). The retraction knob (12) is sleeved outside the screw rod (9), and a retraction spring (11) is arranged between the retraction knob (12) and the cover plate (13). When the retraction knob (12) is out of meshing state, the screw rod (9) can be driven by the retraction spring (11) to move back to its original position.

10. A drug delivery device with last dose protection according to claim 1, characterized in that: The housing (17) is connected to the rear end of the pen core frame (3), a medicine core is installed in the pen core frame (3), and a detachable pen cap (18) is provided at the front end of the pen core frame (3).

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