Power driving mechanism for needleless injector and needleless injector
By employing a power drive mechanism with a two-stage elastic component in the needle-free injector, the piston rod is driven in two stages, which solves the problems of uneven drug diffusion and inconsistent injection depth, improves injection effect and vaccine utilization, and reduces cost and power consumption.
Patent Information
- Application Number
- CN202511336438.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-09-18
- Publication Date
- 2025-10-31
AI Technical Summary
Existing needle-free injectors have difficulty achieving uniform drug diffusion and consistent injection depth during injection, and the issues of cost and volume have not been effectively resolved.
The power drive mechanism employs a dual-stage elastic component, including a primary spring and a secondary spring. By controlling the unequal compression elasticity of these components, the piston rod is driven in two stages: first, it pierces the skin at high speed, and then injects the medication at low speed, ensuring uniform diffusion of the medication.
It achieves efficient penetration and uniform diffusion of the drug solution, improves injection effect and vaccine utilization, reduces driving power consumption, and is low in cost and simple in structure.
Smart Images
Figure CN120859709A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of drive mechanism technology, and more specifically to a power drive mechanism for a needleless injector and a needleless injector. Background Technology
[0002] Needle-free injectors can be used to administer vaccines to pigs. The required injection depth varies depending on the specific medication, but there are certain requirements. During injection, a sufficiently fast jet must first pierce the epidermis, and then a certain holding pressure must be maintained to continuously inject the medication into the body. An excessively high jet speed can lead to over-deep injection, while an excessively low jet speed can cause medication spillage or insufficient injection volume.
[0003] In addition, due to differences in skin thickness among pigs of different ages, differences in the types of oil-based vaccines, and differences in the required injection depth, higher requirements are placed on the injection quality of needle-free injectors in order to achieve a relatively ideal injection effect.
[0004] In existing technologies, the power components of needle-free injectors generally use methods such as springs, electromagnetic drives, and pneumatic control. If the pressure setting of a single-spring power system is too low, the pressure may decay rapidly, resulting in insufficient puncture, leakage of the drug, and inadequate diffusion. If the pressure is too high, it may cause subcutaneous bleeding, excessive injection depth, and failure to achieve the expected immune effect. Other power solutions, such as electromagnetic drives, are too expensive, while pneumatic control has the problem of excessive size. Summary of the Invention
[0005] The purpose of this invention is to provide a power drive mechanism for a needle-free injector and a needle-free injector, thereby solving the following technical problems: How to improve the injection effect of needle-free injectors at low cost.
[0006] The objective of this invention can be achieved through the following technical solutions: In a first aspect, the present invention discloses a power drive mechanism for a needleless injector, including a pre-compression block and a piston rod movably disposed in the pre-compression block; a limiting part is provided at one end of the piston rod away from the pre-compression block, and a primary elastic part and a secondary elastic part are provided between the limiting part and the pre-compression block; When the limiting part moves toward the pre-compression block to compress the primary elastic part and the secondary elastic part simultaneously, the compression elastic forces of the primary elastic part and the secondary elastic part are not equal.
[0007] In a further embodiment of the present invention: the primary elastic part is a primary spring, and the secondary elastic part is a secondary spring.
[0008] In a further embodiment of the present invention: the primary spring is an inner spring sleeved on the piston rod, and the secondary spring is an outer spring sleeved outside the inner spring; the inner spring and the outer spring have the same stiffness and length; the limiting part includes a first protrusion and a second protrusion fixedly disposed on the surface of the piston rod, the first protrusion and the second protrusion being at different distances in the axial direction; wherein, the first protrusion is used to block and compress the inner spring when the limiting part moves toward the pre-compression block, and the second protrusion is used to block and compress the outer spring when the limiting part moves toward the pre-compression block; the pre-compression block blocks the inner spring and the outer spring at the same position in the axial direction.
[0009] In a further embodiment of the present invention: the primary spring is an inner spring sleeved on the piston rod, and the secondary spring is an outer spring sleeved outside the inner spring; the inner spring and the outer spring have the same stiffness and length; the preload block includes a first protrusion and a second protrusion, the first protrusion and the second protrusion being at different distances in the axial direction; wherein, the first protrusion is used to block and compress the inner spring when the limiting part moves toward the preload block, and the second protrusion is used to block and compress the outer spring when the limiting part moves toward the preload block; the limiting part blocks the inner spring and the outer spring at the same position in the axial direction.
[0010] In a further embodiment of the present invention: the preload block is provided with an axial distance adjustment mechanism for adjusting the distance of the preload block in the axial direction.
[0011] In a further embodiment of the present invention: the limiting part is provided with an axial distance adjustment mechanism for adjusting the distance of the pre-compression block in the axial direction.
[0012] In a further embodiment of the present invention: the primary spring is a high-stiffness spring, the secondary spring is a low-stiffness spring, and the stiffnesses of the high-stiffness spring and the low-stiffness spring are not equal; the high-stiffness spring and the low-stiffness spring are connected in series and sleeved on the piston rod.
[0013] In a further embodiment of the present invention: the high-stiffness spring and the low-stiffness spring are made of the same material but have different wire diameters.
[0014] In a further embodiment of the present invention: the high-stiffness spring and the low-stiffness spring are made of the same material, but have different densities.
[0015] Secondly, the present invention also discloses a needleless injector, including the power drive mechanism for a needleless injector as described above.
[0016] The beneficial effects of this invention are: (1) The power drive mechanism for needleless injector of the present invention includes a pre-compression block and a piston rod that is movably inserted through the pre-compression block. A limiting part is provided at the end of the piston rod away from the pre-compression block. A primary elastic part and a secondary elastic part are provided between the limiting part and the pre-compression block. By controlling the compression elastic force of the primary elastic part and the secondary elastic part to be unequal during compression, the piston rod can be driven in two stages. The elastic driving force of the first stage is stronger than that of the second stage. Therefore, the piston rod can be driven at high speed first and then at low speed.
[0017] (2) The needleless injector of the present invention is provided with the above-mentioned power drive mechanism. When needleless injection is performed, the power drive mechanism is released to drive the drug liquid into the skin. In the first stage, the piston rod 100 moves at high speed, generating an instantaneous pressure of up to 20 MPa or more, driving the drug liquid to pierce the skin, achieving high-pressure piercing, ensuring piercing effectiveness, and reducing leakage. In the second stage, the piston rod 100 maintains a continuous pressure of 5-10 MPa, reducing the pressure peak of the drug injection stage, so as to ensure uniform diffusion of the drug liquid, achieving low-pressure injection, better consistency of injection depth, and higher control of intradermal injection depth, thereby ensuring that the injection effect reaches the best, improving vaccine utilization and immunization efficiency. Moreover, the power drive device has a simple structure and low cost. The pressure reduction in the low-pressure injection stage can reduce the driving power consumption, reduce the impact force, and improve the life and stability of the internal components of the needleless injector. Attached Figure Description
[0018] The invention will now be further described with reference to the accompanying drawings.
[0019] Figure 1 This is a schematic diagram of the power drive mechanism for a needleless injector in Embodiment 1 of the present invention; Figure 2 This is a schematic diagram of the power drive mechanism for a needleless injector in Embodiment 3 of the present invention; Figure 3 This is a schematic diagram of the power drive mechanism for a needleless injector in Embodiment 5 of the present invention; Figure 4 This is a schematic diagram showing the connection between the high-stiffness spring and the low-stiffness spring in Embodiment 5 of the present invention; Figure 5 This is a schematic diagram of the power drive mechanism for a needleless injector in Embodiment 7 of the present invention; Figure 6 This is a schematic diagram showing the connection between the high-stiffness spring and the low-stiffness spring in Embodiment 7 of the present invention.
[0020] In the diagram: 100, piston rod; 200, preload block; 201, preload ring one; 202, preload ring two; 301, inner spring; 302, outer spring; 401, high stiffness spring; 402, low stiffness spring; 500, limiting part; 501, collar one; 502, collar two. Detailed Implementation
[0021] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0022] Example 1
[0023] Please see Figure 1 This embodiment discloses a power drive mechanism for a needleless injector, including a pre-compression block 200 and a piston rod 100 movably passing through the pre-compression block 200; a limiting part 500 is provided at one end of the piston rod 100 away from the pre-compression block 200, and a primary elastic part and a secondary elastic part are provided between the limiting part 500 and the pre-compression block 200. When the drive mechanism is working, the position of the pre-compression block 200 is fixed. When the limiting part 500 moves toward the pre-compression block 200 to compress the primary elastic part and the secondary elastic part at the same time, the compression elasticity of the primary elastic part and the secondary elastic part is not equal.
[0024] In this embodiment, the primary elastic part is a primary spring, and the secondary elastic part is a secondary spring. Specifically, the primary spring is an inner spring 301 sleeved on the piston rod 100, and the secondary spring is an outer spring 302 sleeved outside the inner spring 301. The inner spring 301 and the outer spring 302 have different diameters, but both are coaxially arranged with the piston rod 100. The inner spring 301 and the outer spring 302 have the same stiffness and length, and both are helical springs made of silicon-manganese alloy. It should be noted that the material selection for the inner spring 301 and the outer spring 302 is not limited to the silicon-manganese alloy material in this embodiment. In other embodiments, the material of the inner spring 301 and the outer spring 302 can also be selected according to the pressure and manufacturability. For example, in other embodiments, the material of the inner spring 301 and the outer spring 302 can also be piano wire.
[0025] In this embodiment, the limiting part 500 includes a first protrusion and a second protrusion fixedly disposed on the surface of the piston rod 100. The first protrusion and the second protrusion are at different distances in the axial direction. The first protrusion is used to block and compress the inner spring 301 when the limiting part 500 moves toward the pre-compression block 200, and the second protrusion is used to block and compress the outer spring 302 when the limiting part 500 moves toward the pre-compression block 200. The blocking positions of the pre-compression block 200 on the inner spring 301 and the outer spring 302 in the axial direction are the same.
[0026] Specifically, in this embodiment, the first protrusion and the second protrusion are respectively a first collar 501 and a second collar 502, which are fixedly sleeved on the outside of the piston rod 100 and connected in sequence. The first collar 501 is located on the side close to the pre-compression block 200. The outer diameters of the first collar 501 and the second collar 502 are different. The outer diameter of the first collar 501 is larger than the inner diameter of the inner spring 301 and smaller than the inner diameter of the outer spring 302, so that when the limiting part 500 moves toward the pre-compression block 200, only the inner spring 301 is blocked and compressed. The outer diameter of the second collar 502 is larger than the inner diameter of the inner spring 301 and smaller than the inner diameter of the outer spring 302, so that when the limiting part 500 moves toward the pre-compression block 200, only the inner spring 301 is blocked and compressed.
[0027] The preload block 200 is provided with an axial distance adjustment mechanism to adjust the distance of the preload block 200 in the axial direction; by adjusting the distance of the preload block 200 in the axial direction, the compression amount of the inner spring 301 and the outer spring 302 can be controlled, thereby adjusting the driving force of the piston rod 100.
[0028] The working principle of this embodiment: In the initial state, the inner spring 301 is compressed between the first collar 501 and the preload block 200, and the outer spring 302 is compressed between the second collar 502 and the preload block 200. When the right end of the piston rod 100 is released, the piston rod 100 moves to the left under the action of elastic force. During this process, the movement state of the piston rod 100 has two stages. In the first stage, the inner spring 301 and the outer spring 302 are driven by elastic force together. When the outer spring 302 returns to its initial length, the inner spring 301 is still in a compressed state. At this time, the first stage ends and the second stage begins, in which the inner spring 301 drives the piston rod 100 by elastic force alone until the inner spring 301 returns to its original state. The elastic driving force in the first stage is obviously stronger than that in the second stage, so the piston rod 100 can move at high speed first and then at low speed.
[0029] Example 2
[0030] This embodiment discloses a needleless injector, wherein the power drive mechanism is the power drive mechanism for the needleless injector in Embodiment 1.
[0031] The working principle of this embodiment: As described in Example 1 regarding the working principle of the power drive mechanism, the power drive mechanism has two power drive stages. The elastic driving force in the first stage is stronger than that in the second stage, thus enabling the piston rod 100 to move at high speed first and then at low speed. When performing needle-free injection, the power drive mechanism is released to drive the drug solution into the skin. In the first stage, the piston rod 100 moves at high speed, generating an instantaneous pressure of up to 20 MPa or more, driving the drug solution to pierce the skin and achieve high-pressure piercing. In the second stage, the piston rod 100 maintains a continuous pressure of 5-10 MPa to ensure uniform diffusion of the drug solution and achieve low-pressure injection, thereby ensuring the best injection effect.
[0032] Example 3
[0033] Please see Figure 2 This embodiment discloses a power drive mechanism for a needleless injector, including a pre-compression block 200 and a piston rod 100 movably passing through the pre-compression block 200; a limiting part 500 is provided at one end of the piston rod 100 away from the pre-compression block 200, and a primary elastic part and a secondary elastic part are provided between the limiting part 500 and the pre-compression block 200. When the drive mechanism is working, the position of the pre-compression block 200 is fixed. When the limiting part 500 moves toward the pre-compression block 200 to compress the primary elastic part and the secondary elastic part at the same time, the compression elasticity of the primary elastic part and the secondary elastic part is not equal.
[0034] In this embodiment, the primary elastic part is a primary spring, and the secondary elastic part is a secondary spring. Specifically, the primary spring is an inner spring 301 sleeved on the piston rod 100, and the secondary spring is an outer spring 302 sleeved outside the inner spring 301. The inner spring 301 and the outer spring 302 have different diameters, but both are coaxially arranged with the piston rod 100. The inner spring 301 and the outer spring 302 have the same stiffness and length, and both are helical springs made of silicon-manganese alloy. It should be noted that the material selection for the inner spring 301 and the outer spring 302 is not limited to the silicon-manganese alloy material in this embodiment. In other embodiments, the material of the inner spring 301 and the outer spring 302 can also be selected according to the pressure and manufacturability. For example, in other embodiments, the material of the inner spring 301 and the outer spring 302 can also be piano wire.
[0035] In this embodiment, the pre-compression block 200 includes a first protrusion and a second protrusion. The first protrusion and the second protrusion are at different distances in the axial direction. The first protrusion is used to block and compress the inner spring 301 when the limiting part 500 moves toward the pre-compression block 200, and the second protrusion is used to block and compress the outer spring 302 when the limiting part 500 moves toward the pre-compression block 200. The limiting part 500 blocks the inner spring 301 and the outer spring 302 at the same position in the axial direction.
[0036] Specifically, in this embodiment, the first protrusion and the second protrusion are respectively a preload ring 201 and a preload ring 202 that are fixedly sleeved on the outside of the piston rod 100 and connected in sequence. The preload ring 201 is located on the side close to the limiting part 500. The outer diameters of the preload ring 201 and the preload ring 202 are different. The outer diameter of the preload ring 201 is larger than the inner diameter of the inner spring 301 and smaller than the inner diameter of the outer spring 302, so that when the limiting part 500 moves toward the preload block 200, only the inner spring 301 is blocked and compressed. The outer diameter of the preload ring 202 is larger than the inner diameter of the inner spring 301 and smaller than the inner diameter of the outer spring 302, so that when the limiting part 500 moves toward the preload block 200, only the inner spring 301 is blocked and compressed.
[0037] The working principle of this embodiment: In the initial state, the inner spring 301 is compressed between the preload ring 201 and the limiting part 500, and the outer spring 302 is compressed between the preload ring 202 and the limiting part 500. When the right end of the piston rod 100 is released, the piston rod 100 moves to the left under the action of elastic force. During this process, the movement state of the piston rod 100 has two stages. In the first stage, the inner spring 301 and the outer spring 302 are driven by elastic force together. When the outer spring 302 returns to its initial length, the inner spring 301 is still in a compressed state. At this time, the first stage ends and the second stage begins, in which the inner spring 301 drives the piston rod 100 by elastic force alone until the inner spring 301 returns to its original state. The elastic driving force in the first stage is obviously stronger than that in the second stage, so the piston rod 100 can move at high speed first and then at low speed.
[0038] Example 4
[0039] This embodiment discloses a needleless injector, wherein the power drive mechanism is the power drive mechanism for needleless injectors in Embodiment 3.
[0040] The working principle of this embodiment: As described in Example 3 regarding the working principle of the power drive mechanism, this power drive mechanism has two power drive stages. The elastic driving force in the first stage is stronger than that in the second stage, thus enabling the piston rod 100 to move at high speed first and then at low speed. When performing needle-free injection, the power drive mechanism is released to drive the drug solution into the skin. In the first stage, the piston rod 100 moves at high speed, generating an instantaneous pressure of up to 20 MPa or more, driving the drug solution to pierce the skin and achieve high-pressure piercing. In the second stage, the piston rod 100 maintains a continuous pressure of 5-10 MPa to ensure uniform diffusion of the drug solution and achieve low-pressure injection, thereby ensuring the best injection effect.
[0041] Example 5
[0042] Please see Figure 3 This embodiment discloses a power drive mechanism for a needleless injector, including a pre-compression block 200 and a piston rod 100 movably passing through the pre-compression block 200; a limiting part 500 is provided at one end of the piston rod 100 away from the pre-compression block 200, and a primary elastic part and a secondary elastic part are provided between the limiting part 500 and the pre-compression block 200. When the drive mechanism is working, the position of the pre-compression block 200 is fixed. When the limiting part 500 moves toward the pre-compression block 200 to compress the primary elastic part and the secondary elastic part at the same time, the compression elasticity of the primary elastic part and the secondary elastic part is not equal.
[0043] In this embodiment, the primary elastic part is a primary spring, and the secondary elastic part is a secondary spring; specifically, the primary spring is a high-stiffness spring 401, and the secondary spring is a low-stiffness spring 402. The stiffness of the high-stiffness spring 401 and the low-stiffness spring 402 are not equal; the high-stiffness spring 401 and the low-stiffness spring 402 are connected in series and sleeved on the piston rod 100.
[0044] Please see Figure 4 The high-stiffness spring 401 and the low-stiffness spring 402 are made of the same material and have the same density, but different wire diameters. Specifically, the wire diameter of the high-stiffness spring 401 is smaller than that of the low-stiffness spring 402. Under the same pressure, the low-stiffness spring 402 has a larger compression stroke.
[0045] The working principle of this embodiment: In the initial state, the inner spring 301 is compressed between the first collar 501 and the pre-compression block 200, and the outer spring 302 is compressed between the second collar 502 and the pre-compression block 200. When the right end of the piston rod 100 is released, the piston rod 100 moves to the left under the action of elastic force. During this process, the movement state of the piston rod 100 has two stages. The first stage is driven by the elastic force of the high stiffness spring 401 alone. At this time, the low stiffness spring 402 is in a fully compressed state. When the low stiffness spring 402 is at the compression critical point (that is, the last moment before the reset movement begins), the first stage ends and the second stage begins. The high stiffness spring 401 and the low stiffness spring 402 are driven together by elastic force until the high stiffness spring 401 and the low stiffness spring 402 return to their original state. The elastic driving force in the first stage is obviously stronger than that in the second stage, so the piston rod 100 can move at high speed first and then at low speed.
[0046] Example 6
[0047] This embodiment discloses a needleless injector, wherein the power drive mechanism is the power drive mechanism for the needleless injector in Embodiment 5.
[0048] The working principle of this embodiment: As described in Example 5 regarding the working principle of the power drive mechanism, this power drive mechanism has two power drive stages. The elastic driving force in the first stage is stronger than that in the second stage, thus enabling the piston rod 100 to move at high speed first and then at low speed. When performing needle-free injection, the power drive mechanism is released to drive the drug solution into the skin. In the first stage, the piston rod 100 moves at high speed, generating an instantaneous pressure of up to 20 MPa or more, driving the drug solution to pierce the skin and achieve high-pressure piercing. In the second stage, the piston rod 100 maintains a continuous pressure of 5-10 MPa to ensure uniform diffusion of the drug solution and achieve low-pressure injection, thereby ensuring the best injection effect.
[0049] Example 7
[0050] Please see Figure 5-6 This embodiment discloses a power drive mechanism for a needleless injector. Compared with the power drive mechanism in embodiment 5, the only difference is that the high-stiffness spring 401 and the low-stiffness spring 402 have the same material and wire diameter, but different densities.
[0051] Example 8
[0052] This embodiment discloses a needleless injector, wherein the power drive mechanism is the power drive mechanism for the needleless injector in Embodiment 7.
[0053] In the description of this invention, it should be understood that the terms "upper," "lower," "left," and "right," etc., indicating orientation or positional relationships based on the orientation or positional relationships shown in the accompanying drawings, are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation or specific orientational structure and operation. Therefore, they should not be construed as limitations on the invention. Furthermore, "first" and "second" are only for descriptive purposes and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, a feature defined with "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, unless otherwise stated, "multiple" means two or more.
[0054] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal communication between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.
[0055] The foregoing has provided a detailed description of one embodiment of the present invention, but this description is merely a preferred embodiment and should not be construed as limiting the scope of the invention. All equivalent variations and modifications made within the scope of the claims of this invention should still fall within the patent coverage of this invention.
Claims
1. A power drive mechanism for a needle-free injector, characterized in that, It includes a pre-compression block (200) and a piston rod (100) that is movably inserted in the pre-compression block (200); a limiting part (500) is provided at one end of the piston rod (100) away from the pre-compression block (200), and a primary elastic part and a secondary elastic part are provided between the limiting part (500) and the pre-compression block (200); When the limiting part 500 moves toward the pre-compression block (200) to compress the primary elastic part and the secondary elastic part at the same time, the compression elastic forces of the primary elastic part and the secondary elastic part are not equal.
2. The power drive mechanism for a needle-free injector according to claim 1, characterized in that, The primary elastic component is a primary spring, and the secondary elastic component is a secondary spring.
3. The power drive mechanism for a needle-free injector according to claim 2, characterized in that, The primary spring is an inner spring (301) sleeved on the piston rod (100), and the secondary spring is an outer spring (302) sleeved outside the inner spring (301). The inner spring (301) and the outer spring (302) have the same stiffness and length. The limiting part (500) includes a first protrusion and a second protrusion fixed on the surface of the piston rod (100). The distance between the first protrusion and the second protrusion in the axial direction is different. The first protrusion is used to block and compress the inner spring (301) when the limiting part (500) moves toward the pre-compression block (200), and the second protrusion is used to block and compress the outer spring (302) when the limiting part (500) moves toward the pre-compression block (200). The blocking position of the pre-compression block (200) on the inner spring (301) and the outer spring (302) in the axial direction is the same.
4. The power drive mechanism for a needle-free injector according to claim 2, characterized in that, The primary spring is an inner spring (301) sleeved on the piston rod (100), and the secondary spring is an outer spring (302) sleeved outside the inner spring (301). The inner spring (301) and the outer spring (302) have the same stiffness and length. The preload block (200) includes a first protrusion and a second protrusion. The distance between the first protrusion and the second protrusion in the axial direction is different. The first protrusion is used to block and compress the inner spring (301) when the limiting part (500) moves toward the preload block (200), and the second protrusion is used to block and compress the outer spring (302) when the limiting part (500) moves toward the preload block (200). The limiting part (500) blocks the inner spring (301) and the outer spring (302) at the same position in the axial direction.
5. The power drive mechanism for a needle-free injector according to claim 3 or 4, characterized in that, The preload block (200) is provided with an axial distance adjustment mechanism to adjust the distance of the preload block (200) in the axial direction.
6. The power drive mechanism for a needle-free injector according to claim 3 or 4, characterized in that, The limiting part (500) is provided with an axial distance adjustment mechanism to adjust the distance of the pre-compression block (200) in the axial direction.
7. The power drive mechanism for a needle-free injector according to claim 2, characterized in that, The first-stage spring is a high-stiffness spring (401), and the second-stage spring is a low-stiffness spring (402). The stiffness of the high-stiffness spring (401) and the low-stiffness spring (402) are not equal. The high-stiffness spring (401) and the low-stiffness spring (402) are connected in series and sleeved on the piston rod (100).
8. The power drive mechanism for a needle-free injector according to claim 7, characterized in that, The high-stiffness spring (401) and the low-stiffness spring (402) are made of the same material but have different wire diameters.
9. The power drive mechanism for a needle-free injector according to claim 7, characterized in that, The high-stiffness spring (401) and the low-stiffness spring (402) are made of the same material, but have different densities.
10. A needle-free injector, characterized in that, Includes the power drive mechanism for a needleless injector as described in claim 1.