Automatic injection pen and debugging method thereof

Abstract

According to the automatic injection pen and the debugging method thereof, the distance between the first end of an injection push rod and a piston is L, and L is larger than 0; the injection spring abuts against the injection push rod and is used for exerting elastic force which moves towards the piston in the first direction on the injection push rod, when the push rod locking assembly is unlocked, the injection push rod impacts the piston in an accelerated mode under the action of the elastic force, and under the combined action of the momentum of the injection push rod and the injection spring, the piston is easily converted into a movable state from a static state. As for the automatic injection pen provided by the embodiment, the preset elastic force of the injection spring does not need to be obviously larger than the resistance of the piston in the static state, in the injection process, the elastic force of the injection spring does not cause continuous acceleration of the piston after the injection pen is started, and the use feeling of a user can be improved.

Description

Technical Field

[0001] The present application relates to the technical field of medical devices, and particularly to an auto-injector and a debugging method thereof. Background Art

[0002] An auto-injector is a drug delivery device that can automatically inject a liquid medicine into the human body by injection. It has the advantages of being easy to carry and convenient to use, and overcomes many defects of traditional syringes.

[0003] The key to the auto-injector achieving automatic injection lies in that a pre-compressed spring is provided inside. After the push rod locking assembly is unlocked, the auto-injector starts to inject by pushing the piston through this spring. Generally speaking, in order to ensure that the piston can be normally pushed, the pre-compressed spring of the injector needs to overcome at least the starting resistance of the piston in the syringe body in the static state. Therefore, the elastic force of the pre-set compression spring inside the injector is often significantly greater than the resistance when the piston slides in the syringe body, resulting in the piston accelerating continuously when sliding after the injector starts, and the injection speed being too fast before the injection is completed, causing the user to feel obvious pain. Summary of the Invention

[0004] In view of this, the embodiments of the present application provide an auto-injector and a debugging method thereof to solve at least one problem in the background art.

[0005] In a first aspect, the embodiments of the present application provide an auto-injector, including:

[0006] A syringe body, the axis of the syringe body is along a first direction, and the inside of the syringe body is used for storing a medicament;

[0007] A piston, the piston is installed in the syringe body, and when the piston moves along the first direction, it is used to extrude the medicament stored in the syringe body;

[0008] An injection push rod, the injection push rod is coaxially arranged with the syringe body, the first end of the injection push rod is aligned with the piston along the first direction, and the distance between the first end of the injection push rod and the piston is L, where L>0;

[0009] An injection spring, the injection spring abuts against the injection push rod and is used to apply an elastic force along the first direction towards the movement of the piston to the injection push rod;

[0010] A push rod locking assembly, the push rod locking assembly is used to lock the injection push rod to limit the movement of the injection push rod. When the push rod locking assembly is unlocked, its locking of the injection push rod can be released.

[0011] In an alternative embodiment, when the piston is in a static state, the resistance to the movement of the injection push rod is N2, and when the piston is in a movable state, the resistance to the movement of the injection push rod is N3;

[0012] When the push rod locking assembly locks the injection push rod, the elastic force of the injection spring on the injection push rod is N4, and N4 < N2.

[0013] In an alternative embodiment, N4 ≥ N3, and the piston can reach the head of the syringe body under the push of the injection push rod.

[0014] In an alternative embodiment, the automatic injection pen further includes a trigger assembly. When the trigger assembly moves, it can squeeze the injection push rod to release the locking of the push rod locking assembly on the injection push rod.

[0015] In an alternative embodiment, the resistance of the trigger assembly to the movement of the injection push rod is N1, and N4 > N1.

[0016] In an alternative embodiment, the push rod locking assembly includes:

[0017] A wing-shaped structure fixed on at least one side of the injection push rod and protruding from the side wall of the injection push rod in a direction perpendicular to the first direction;

[0018] A guiding sleeve sleeved outside the injection push rod. At least one side wall of the guiding sleeve is provided with a guiding chute, and the guiding chute includes a chute body extending in the first direction and a limiting groove extending in a direction perpendicular to the first direction. The limiting groove communicates with the chute body;

[0019] At least a part of the wing-shaped structure is received in the guiding chute. When at least a part of the wing-shaped structure is located in the limiting groove, the movement of the injection push rod in the first direction is restricted.

[0020] In an alternative embodiment, the trigger assembly includes a trigger sleeve sleeved outside the guiding sleeve. The inner wall of the trigger sleeve has ribs capable of squeezing the wing-shaped structure. When the ribs squeeze the wing-shaped structure located in the limiting groove, the wing-shaped structure moves from the limiting groove to the chute body.

[0021] In an alternative embodiment, the elastic force of the injection spring has a linear or non-linear relationship with its length change amount.

[0022] In an alternative embodiment, the injection spring adopts a constant force spring.

[0023] In a second aspect, an embodiment of the present application provides a debugging method for an automatic injection pen, including the following steps:

[0024] S1, assembling the syringe body, the piston, the injection push rod and the injection spring, and pre-compressing the injection spring so that the compression amount of the injection spring reaches L0, and making the injection push rod abut against the piston to lock the injection push rod;

[0025] S2, unlocking the injection push rod, and applying a certain thrust to the injection push rod until the piston changes from a static state to a moving state, measuring the instantaneous speed of the piston or the average speed V1 over a period of time at this time, and when the piston reaches the end of the syringe body, measuring the instantaneous speed of the piston or the average speed V2 over a period of time again;

[0026] S3, adjusting L0 or adjusting the length or elastic coefficient of the injection spring according to the ratio of V2 to V1 measured in step S2, repeating step S2 until the ratio of V2 to V1 is within a preset range, determining the length and elastic coefficient of the injection spring, and setting the value of L0 to L1;

[0027] S4, assembling the syringe body, the piston, the injection push rod and the injection spring, and pre-compressing the injection spring so that the compression amount of the injection spring reaches L1, and the injection push rod is abutted against the piston; further compressing the injection spring so that the distance between the end of the injection push rod and the piston reaches L2, and locking the injection push rod;

[0028] S5, unlocking the injection push rod, measuring the instantaneous speed of the piston or the average speed V3 over a period of time, and when the piston reaches the end of the syringe body, measuring the instantaneous speed of the piston or the average speed V4 over a period of time again;

[0029] S6. Adjust L2 according to the ratio of V4 to V3 measured in step S5, repeat step S5 until the ratio of V4 to V3 is within a preset range, determine the length and elastic coefficient of the injection spring, and set the value of L2 to L, thereby obtaining the automatic injection pen described in the first aspect.

[0030] In an optional embodiment, in step S2 or step S5, the movement process of the piston is photographed by a high-speed camera to obtain V1, V2, V3 or V4.

[0031] In the automatic injection pen provided by the embodiment of the present application, the distance between the first end of the injection push rod and the piston is L, where L>0; the injection spring abuts against the injection push rod and is used to apply an elastic force to the injection push rod in the first direction towards the piston. When the push rod locking assembly is unlocked, the injection push rod accelerates and impacts the piston under the action of the elastic force. Under the combined action of its own momentum and the injection spring, the piston is easily transformed from a static state to a movable state. Therefore, for the automatic injection pen provided in this embodiment, the preset elastic force of the injection spring does not need to be significantly greater than the resistance of the piston in the static state. Therefore, during the injection process, the elastic force of the injection spring will not cause the piston to continuously accelerate after the injection pen is started, and the user experience can be improved.

[0032] The debugging method of the automatic injection pen provided by the embodiment of the present application can optimize the movement speed of the piston of the above automatic injection pen, so that the injection speed and the injection completion time are appropriate when the automatic injection pen is used, and the user experience can be improved.

[0033] Additional aspects and advantages of the present application will be given in part in the following description, become apparent in part from the following description, or be learned through the practice of the present application. Description of the Drawings

[0034] The drawings described herein are used to provide a further understanding of the present application, and constitute a part of the present application. The schematic embodiments and descriptions thereof of the present application are used to explain the present application and do not constitute an improper limitation of the present application. In the drawings:

[0035] Figure 1 is a schematic diagram of the component composition of the automatic injection pen provided by the embodiment of the present application;

[0036] Figure 2 is a schematic cross-sectional view of the structure of the automatic injection pen provided by the embodiment of the present application;

[0037] Figure 3 is Figure 2 an enlarged view of part A of

[0038] Figure 4 is a schematic diagram of the connection relationship between the injection push rod and the guide sleeve provided by the embodiment of the present application;

[0039] Figure 5 is Figure 4 an enlarged view of part F of

[0040] Figure 6 is a schematic diagram of the connection relationship between the injection push rod and the trigger sleeve provided by the embodiment of the present application;

[0041] Figure 7 is Figure 6 an enlarged view of part E of

[0042] The reference numerals in the drawings are:

[0043] 6. Syringe body

[0044] 7. Piston

[0045] 8. Injection push rod; 801. Wing-shaped structure

[0046] 9. Injection spring

[0047] 10. Guide sleeve; 1002. Guide chute; 10020. Chute main body; 10021. Limit groove

[0048] 11. Trigger sleeve; 1102. Rib Detailed implementation manners

[0049] In order to make the technical solutions and beneficial effects of the present invention more obvious and understandable, the following will be described in detail by listing specific embodiments. Among them, the attached drawings are not necessarily drawn to scale, and local features can be enlarged or reduced to more clearly show the details of local features; unless otherwise defined, the technical and scientific terms used herein have the same meanings as those in the technical field to which this application belongs.

[0050] In the description of the present invention, the orientation or positional relationship indicated by terms such as "center", "longitudinal", "transverse", "length", "width", "thickness", "height", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", etc. is based on the orientation or positional relationship shown in the attached drawings. It is only for the convenience of simplifying the description of the present invention, rather than indicating that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, that is, it cannot be understood as a limitation to the present invention.

[0051] In the present invention, the terms "first" and "second" are only used for the purpose of clear description, and cannot be understood as the relative importance of the indicated features or the number of the indicated technical features. Therefore, the features defined with "first" and "second" can clearly include at least one such feature. In the description of the present invention, the meaning of "a plurality" is at least two, such as two, three, etc.; the meaning of "several" is at least one, such as one, two, three, etc.; unless otherwise clearly and specifically defined.

[0052] In the present invention, unless otherwise clearly defined, terms such as "installed", "connected", "linked", "fixed", "set" shall be understood in a broad sense. For example, "connected" can be a fixed connection, a detachable connection, or an integral one; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, and can also be the communication inside two components or the interaction relationship between two components. 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.

[0053] In the present invention, unless otherwise clearly defined, the first feature being "on", "above", "over" and "upon", "under", "beneath", "below" or "underneath" the second feature can be that the first feature is in direct contact with the second feature, or the first feature and the second feature are in indirect contact through an intermediate medium. Moreover, the first feature being "above", "over" and "upon" the second feature can be that the first feature is directly above or 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", "below" and "underneath" the second feature can be that the first feature is directly below or obliquely below the second feature, or merely indicates that the horizontal height of the first feature is lower than that of the second feature.

[0054] To thoroughly understand the present application, detailed steps and detailed structures will be presented in the following description to explain the technical solution of the present application. The preferred embodiments of the present application are described in detail as follows. However, in addition to these detailed descriptions, the present application can also have other implementation manners.

[0055] An embodiment of the present application provides an auto-injector pen, as Figures 1-3 shown, which includes: a syringe body 6, a piston 7, an injection push rod 8, an injection spring 9, and a push rod locking assembly.

[0056] The axial direction of the syringe body 6 is along a first direction, and the interior of the syringe body 6 is used for storing medicament. The two ends of the syringe body 6 along the first direction are a head and a tail respectively. Among them, the head is used for installing a needle, and the tail is used for loading the medicament and the piston 7.

[0057] The piston 7 is installed in the syringe body 6. When the piston 7 moves along the first direction, it is used to extrude the medicament stored in the syringe body 6. The injection push rod 8 is coaxially arranged with the syringe body 6. The first end of the injection push rod 8 is aligned with the piston 7 along the first direction, and the distance between the first end of the injection push rod 8 and the piston 7 is L, where L > 0. The injection spring 9 abuts against the injection push rod 8 and is used to apply an elastic force to the injection push rod 8 to move it towards the piston 7 along the first direction.

[0058] In this embodiment, the injection spring 9 is an important component for realizing automatic injection. The principle is that in the initial state of the auto-injector pen, the internal injection spring 9 is pre-compressed. Before the injection spring 9 returns to its original length, it can continuously push the injection push rod 8 and the piston 7 to move through elastic force, realizing automatic injection.

[0059] The push rod locking assembly is used to lock the injection push rod 8 to restrict the movement of the injection push rod 8. When the push rod locking assembly is unlocked, its locking of the injection push rod 8 can be released. The function of the push rod locking assembly is to make the start of the auto-injector pen manually controllable. The push rod locking assembly can be unlocked under the operation of the user to start the automatic injection. On the other hand, it also plays a role in ensuring that the automatic injection is not triggered before the user's operation.

[0060] In the auto-injector pen provided by the embodiment of the present application, the distance between the first end of the injection push rod 8 and the piston is L, where L>0; the injection spring 9 abuts against the injection push rod 8 and is used to apply an elastic force to the injection push rod 8 to move it in the first direction towards the piston 7. When the push rod locking assembly is unlocked, the injection push rod 8 accelerates and impacts the piston 7 under the action of the elastic force. Under the combined action of its own momentum and the injection spring 9, the piston 7 is easily transformed from a stationary state to a moving state. Therefore, for the auto-injector pen provided in this embodiment, the preset elastic force of the injection spring 9 does not need to be significantly greater than the resistance of the piston 7 in the stationary state. Therefore, during the injection process, the elastic force of the injection spring 9 will not cause the piston 7 to continuously accelerate after the injector pen starts, which can improve the user experience.

[0061] In an optional embodiment, when the piston 7 is in a stationary state, the resistance to the movement of the injection push rod 8 is N2. When the piston 7 is in a moving state, the resistance to the movement of the injection push rod 8 is N3, where N2 is constant and N3 is constant at a specific speed, that is, when the piston 7 moves at a constant speed, N3 is unchanged, or when the movement speed of the piston 7 changes little, the change in the magnitude of N3 is also small; when the push rod locking assembly locks the injection push rod 8, the elastic force of the injection spring 9 on the injection push rod 8 is N4, and N4 < N2. In this embodiment, the elastic force N4 when the injection spring 9 is pre-compressed is set to be smaller than the resistance N2 generated by the piston 7 in the stationary state, which can reduce the gap between N3 and N4, avoid the piston 7 from accelerating significantly after starting to move, and can effectively reduce the injection speed and reduce the user's injection pain.

[0062] In an optional embodiment, N4 ≥ N3, and the piston 7 can reach the head of the syringe body 6 under the push of the injection push rod 8. In this embodiment, N4 is designed to be greater than or equal to N3, so that during the automatic injection process, the piston 7 hardly accelerates when it starts to move. It can be understood that N4 cannot be designed too small to prevent the speed of the piston 7 from dropping to 0 before it moves to the head of the syringe body 6.

[0063] This embodiment also provides a debugging method for an auto-injector pen, including the following steps:

[0064] S1. Assemble the syringe body 6, the piston 7, the injection push rod 8 and the injection spring 9, and pre-compress the injection spring 9 so that the compression amount of the injection spring 9 reaches L0. Abut the injection push rod 8 against the piston 7 and lock the injection push rod 8.

[0065] S2. Unlock the injection push rod 8 and apply a certain thrust to the injection push rod 8 until the piston 7 changes from a stationary state to a moving state. Measure the instantaneous speed of the piston 7 at this time or the average speed V1 within a period of time. When the piston 7 reaches the end of the syringe body 6, measure the instantaneous speed of the piston 7 again or the average speed V2 within a period of time.

[0066] S3. Adjust L0 or adjust the length or elastic coefficient of the injection spring 9 according to the ratio of V2 to V1 measured in step S2. Repeat step S2 until the ratio of V2 to V1 is within a preset range. Determine the length and elastic coefficient of the injection spring 9, and set the value of L0 as L1.

[0067] S4. Assemble the syringe body 6, the piston 7, the injection push rod 8 and the injection spring 9, and pre-compress the injection spring 9 so that the compression amount of the injection spring 9 reaches L1. Abut the injection push rod 8 against the piston 7. Further compress the injection spring 9 so that the distance between the end of the injection push rod 8 and the piston 7 reaches L2, and lock the injection push rod 8.

[0068] S5. Unlock the injection push rod 8 and measure the instantaneous speed of the piston 7 at this time or the average speed V3 within a period of time. When the piston 7 reaches the end of the syringe body 6, measure the instantaneous speed of the piston 7 again or the average speed V4 within a period of time.

[0069] S6. Adjust L2 according to the ratio of V4 to V3 measured in step S5. Repeat step S5 until the ratio of V4 to V3 is within a preset range. Determine the length and elastic coefficient of the injection spring 9, and set the value of L2 as L to obtain the auto-injector pen of the above-mentioned embodiment.

[0070] Preferably, in the debugging method of the auto-injector pen of this embodiment, in step S2 or step S5, the movement process of the piston 7 is photographed by a high-speed camera to obtain V1, V2, V3 or V4. In this embodiment, the method of photographing by a high-speed camera can effectively measure the movement speed of the piston 7 in the syringe body 6.

[0071] The debugging method of the auto-injector provided by the embodiments of the present application can optimize the movement speed of the piston 7 of the above auto-injector, making the injection speed and injection completion time appropriate when the auto-injector is in use, and can improve the user experience.

[0072] The L in this embodiment needs to be adjusted according to different injectors. For example, L can be between 3 mm and 30 mm, preferably 15 mm. Since there are many variables in the movement process of the piston 7, it is difficult to quantify the parameter selection of each component of the auto-injector in this embodiment. This embodiment provides a debugging method for the auto-injector that combines measurement and experiment.

[0073] According to different situations, different spacings L2 are set in step S6: for example, when the difference between N3 and N2 is not very large, the spacing L2 between the injection push rod 8 and the piston 7 can be adjusted smaller. When the injection push rod 8 contacts the piston 7, it can easily push the piston 7. At this time, the resistance to start the piston 7 is overcome mainly by the thrust of the injection spring 9, and the momentum of the injection push rod 8 is auxiliary. In the case where N4 is slightly larger than N3, the acceleration of the piston 7 is not obvious, the auto-injection speed is relatively stable, and the injection completion time is longer, and the user will not feel obvious pain.

[0074] When the difference between N3 and N2 is large, the spacing L2 between the injection push rod 8 and the piston 7 can be adjusted larger. In this way, at the moment when the injection push rod 8 contacts the piston 7, the injection push rod 8 has accelerated for a period of time and obtained a relatively large momentum. At this time, N4 can be less than N2. At this time, the resistance to start the piston 7 is overcome mainly by the momentum of the injection push rod 8 and supplemented by the thrust of the injection spring 9. Under this design, N4 is also close to N3, the acceleration of the piston 7 is not obvious, the auto-injection speed is relatively stable, and the injection completion time is longer, and the user will not feel obvious pain.

[0075] In step S3, when the ratio of V2 to V1 is measured to be too large, the debugging measures that can be taken include but are not limited to reducing the pre-compression amount L0 of the injection spring 9, selecting an injection spring 9 with a smaller elastic coefficient, selecting an injection spring 9 with a shorter length, etc.; when the ratio of V2 to V1 is measured to be too small, the debugging measures that can be taken include but are not limited to increasing the pre-compression amount L0 of the injection spring 9, selecting an injection spring 9 with a larger elastic coefficient, selecting an injection spring 9 with a longer length, etc. When the ratio of V2 to V1 is within the preset range, it indicates that the speed change of the piston 7 in the starting stage and the ending stage of the movement is not large, indicating that the parameters of the adjusted injection spring 9 are appropriate, and the spring with these parameters can be used.

[0076] After step S3 is completed, the selection of the injection spring 9 is completed. In steps S4 to S6, by further compressing the injection spring 9, the distance between the end of the injection push rod 8 and the piston 7 reaches L2. This process is over-compression of the injection spring 9, and its function is to enable the end of the injection push rod 8 to have a certain kinetic energy when it contacts the piston 7, prompting the piston 7 to enter a moving state. When the piston enters the moving state, since the parameters of the injection spring 9 have been determined previously, in step S6, the ratio relationship between V4 and V3 is very different from the ratio relationship between V2 and V1 measured previously, which facilitates the rapid completion of step S6.

[0077] Therefore, in the debugging method provided in this embodiment, by splitting the system resistance suffered by the injection push rod 8 itself and the starting resistance of the piston into two test stages, various parameters can be determined successively, and the overall debugging time is greatly reduced, significantly accelerating the debugging progress.

[0078] In an optional embodiment, the automatic injection pen of this embodiment further includes a trigger assembly. When the trigger assembly moves, it can squeeze the injection push rod 8 to release the locking of the push rod locking assembly on the injection push rod 8. In this embodiment, by setting the trigger assembly, it is convenient for the user to operate the push rod locking assembly to lock or unlock.

[0079] In an optional embodiment, the resistance of the trigger assembly to the movement of the injection push rod 8 is N1, and N4 > N1. In this embodiment, considering that some trigger assemblies may hinder the movement of the injection push rod 8, designing N4 to be greater than N1 can prevent the injection spring 9 from not starting normally.

[0080] In an optional embodiment, as Figures 1-5 shown, the push rod locking assembly includes: a wing-shaped structure 801 and a guide sleeve 10. The wing-shaped structure 801 is fixed on at least one side of the injection push rod 8 and protrudes from the side wall of the injection push rod 8 in a direction perpendicular to the first direction; the guide sleeve 10 is sleeved outside the injection push rod 8. As Figure 4 shown, a guide chute 1002 is formed on at least one side wall of the guide sleeve 10. As Figure 5 shown, the guide chute 1002 includes a groove body 10020 extending in the first direction and a limit groove 10021 extending in a direction perpendicular to the first direction ( Figure 5 the second direction in it), and the limit groove 10021 communicates with the groove body 10020. At least part of the wing-shaped structure 801 is received in the guide chute 1002. When at least part of the wing-shaped structure 801 is located in the limit groove 10021, the movement of the injection push rod 8 in the first direction is restricted. In this embodiment, the wing-shaped structure 801 is used in cooperation with the guide chute 1002 to achieve rapid unlocking of the injection push rod 8 and generate a certain guiding effect.

[0081] In an alternative embodiment, as Figure 1 , Figure 2 , Figure 6 , Figure 7 shown, the triggering assembly includes a triggering sleeve 11 sleeved outside the guiding sleeve 10. The inner wall of the triggering sleeve 11 has ribs 1102 capable of squeezing the wing-shaped structure 801. When the ribs 1102 squeeze the wing-shaped structure 801 located in the limiting groove 10021, the wing-shaped structure 801 moves from the limiting groove 10021 to the groove body 10020. In this embodiment, by providing the triggering sleeve 11, the thrust generated by the movement of the triggering sleeve 11 in the first direction can be converted into the thrust on the wing-shaped structure 801 in the second direction through the ribs 1102, realizing the rapid unlocking of the injection push rod 8.

[0082] In an alternative embodiment, the elastic force of the injection spring 9 has a linear or non-linear relationship with its length change. In this embodiment, the injection spring 9 can be an ordinary spring, that is, the elastic force has a linear relationship with its length change and follows Hooke's law, with a lower cost. A special spring with a non-linear relationship between the elastic force and its length change can also be selected, such as a constant force spring, which can make the elastic force provided by the injection spring 9 hardly decay during the entire injection process, facilitating the uniform movement of the piston 7, keeping the automatic injection speed constant, and improving the user experience.

[0083] It should be understood that the above embodiments are all exemplary and do not cover all possible implementation manners included in the claims. Without departing from the scope of the present disclosure, various deformations and changes can be made based on the above embodiments. Similarly, any combination of the technical features of the above embodiments can be made to form additional embodiments of the present application that may not be explicitly described. Therefore, the above embodiments only represent several implementation manners of the present application and do not limit the protection scope of the patent of the present application.

Claims

1. An automatic injection pen, characterized in that: include: A syringe body (6), the axial direction of the syringe body (6) is along a first direction, and the interior of the syringe body (6) is used to store medicine; A piston (7), wherein the piston (7) is installed in the syringe body (6), and when the piston (7) moves in a first direction, it is used to squeeze out the medicine stored in the syringe body (6); An injection push rod (8), the injection push rod (8) being coaxially arranged with the syringe body (6), the first end of the injection push rod (8) being aligned with the piston (7) along a first direction, the first end of the injection push rod (8) being at a distance L from the piston (7), L>0; an injection spring (9), the injection spring (9) abutting against the injection push rod (8) and being used to apply an elastic force to the injection push rod (8) to move toward the piston (7) along a first direction; A push rod locking assembly is used to lock the injection push rod (8) to limit the movement of the injection push rod (8); when the push rod locking assembly is unlocked, the locking of the injection push rod (8) can be released.

2. The automatic injection pen according to claim 1, characterized in that: When the piston (7) is in a stationary state, the resistance to the movement of the injection push rod (8) is N2, and when the piston (7) is in a moving state, the resistance to the movement of the injection push rod (8) is N3; When the push rod locking assembly locks the injection push rod (8), the elastic force of the injection spring (9) on the injection push rod (8) is N4, and N4<N2.

3. The automatic injection pen according to claim 2, characterized in that: N4≥N3, and the piston (7) can reach the head of the syringe body (6) under the push of the injection push rod (8).

4. The automatic injection pen according to claim 2, characterized in that: The automatic injection pen further comprises a trigger assembly, which can squeeze the injection push rod (8) when it is activated, so that the injection push rod (8) is unlocked by the push rod locking assembly.

5. The automatic injection pen according to claim 4, characterized in that: The resistance of the trigger assembly to the movement of the injection push rod (8) is N1, and N4>N1.

6. The automatic injection pen according to claim 4, characterized in that: The push rod locking assembly comprises: A wing-shaped structure (801) is fixed to at least one side of the injection push rod (8) and protrudes from the side wall of the injection push rod (8) in a direction perpendicular to the first direction; A guide sleeve (10) is sleeved on the outside of the injection push rod (8), and a guide slot (1002) is provided on at least one side wall of the guide sleeve (10), wherein the guide slot (1002) comprises a slot body (10020) extending along a first direction and a limiting slot (10021) extending perpendicular to the first direction, and the limiting slot (10021) is connected to the slot body (10020); The wing-shaped structure (801) is at least partially accommodated in the guide groove (1002). When the wing-shaped structure (801) is at least partially located in the limiting groove (10021), the movement of the injection push rod (8) along the first direction is restricted.

7. The automatic injection pen according to claim 6, characterized in that: The trigger assembly comprises a trigger sleeve (11), wherein the trigger sleeve (11) is sleeved on the outside of the guide sleeve (10), and the inner wall of the trigger sleeve (11) has ribs (1102) capable of squeezing the wing-shaped structure (801), and when the ribs (1102) squeeze the wing-shaped structure (801) located in the limiting groove (10021), the wing-shaped structure (801) moves from the limiting groove (10021) to the groove body (10020).

8. The automatic injection pen according to claim 1, characterized in that: The elastic force of the injection spring (9) is in a linear or nonlinear relationship with the change in its length.

9. A method for debugging an automatic injection pen, characterized in that: The following steps are involved: S1, assembling the syringe body (6), the piston (7), the injection push rod (8) and the injection spring (9), and pre-compressing the injection spring (9) so that the compression amount of the injection spring (9) reaches L0, and making the injection push rod (8) abut against the piston (7) to lock the injection push rod (8); S2, unlocking the injection push rod (8), applying a certain thrust to the injection push rod (8) until the piston (7) changes from a static state to a moving state, measuring the instantaneous speed of the piston (7) or the average speed V1 over a period of time at this time, and when the piston (7) reaches the end of the syringe body (6), measuring the instantaneous speed of the piston (7) or the average speed V2 over a period of time again; S3, adjusting L0 or adjusting the length or elastic coefficient of the injection spring (9) according to the ratio of V2 to V1 measured in step S2, repeating step S2 until the ratio of V2 to V1 is within a preset range, determining the length and elastic coefficient of the injection spring (9), and setting the value of L0 to L1; S4, assembling the syringe body (6), the piston (7), the injection push rod (8) and the injection spring (9), and pre-compressing the injection spring (9) so that the compression amount of the injection spring (9) reaches L1, and the injection push rod (8) abuts against the piston (7); further compressing the injection spring (9) so that the distance between the end of the injection push rod (8) and the piston (7) reaches L2, and locking the injection push rod (8); S5, unlocking the injection push rod (8), measuring the instantaneous speed of the piston (7) or the average speed V3 over a period of time, and when the piston (7) reaches the end of the syringe body (6), measuring the instantaneous speed of the piston (7) or the average speed V4 over a period of time again; S6, adjust L2 according to the ratio of V4 to V3 measured in step S5, repeat step S5 until the ratio of V4 to V3 is within a preset range, determine the length and elastic coefficient of the injection spring (9), and set the value of L2 to L, thereby obtaining the automatic injection pen as described in any one of claims 1 to 8.

10. The debugging method of the automatic injection pen according to claim 9, characterized in that: In step S2 or step S5, the movement process of the piston (7) is photographed by a high-speed camera to obtain V1, V2, V3 or V4.

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