CN110681004A - an automatic injector - Google Patents

Abstract

The invention provides an automatic injector which is characterized by comprising a propelling component, a starting component, a triggering component and a shell; the propelling component is positioned in the starting component, the propelling component comprises a propelling part and a limiting part, the propelling part is clamped with the limiting part to realize limiting, and the starting component ensures the braking of the propelling component before injection by fixing the limiting form of the propelling component; the trigger assembly accommodates the pre-filled syringe and pushes the actuation assembly out of the braking position after the injection begins; the housing encloses the entire syringe.

Description

an automatic injector

technical field

The invention relates to the field of medical instruments, in particular to disposable automatic injection equipment.

Background technique

The design principles of the existing disposable automatic injectors are very complicated, resulting in a large number of parts, generally more than 15, so the reliability is not high, the assembly is difficult, and the final product cost is too high.

CN110237366A discloses a medical injection device, including an outer cylinder and a pen cap, one end of the outer cylinder is provided with a detachable medicine storehouse, a replaceable standard cartridge medicine bottle is arranged in the medicine storey, and the inside of the outer tube is close to one end of the medicine storey A fixed sleeve is provided, the inner part of the fixed sleeve is axially moved with a push rod seat, the inside of the push rod seat is provided with a transmission ring that can be engaged with the end of the transmission rod, and the outer side of the transmission rod is sleeved with an axially slidable ring. Ratchet ring, one end face of the ratchet ring is unidirectionally engaged with the inside of the outer cylinder, the other end of the ratchet ring is axially provided with a first spring, and one end of the push rod seat is axially provided with a push rod seat which is withheld by the outer cylinder A spring, one end of the push rod extends through the push rod seat into the standard cartridge medicine bottle and is connected with the push block.

CN109999272A discloses a disposable adjustable injection device for insulin injection, comprising a protective cover, a disposable needle, a refill cover, a main body shell, a refill and an adjustment assembly, and one end of the main body shell is provided with a second boss , a refill sleeve is installed on the outside of the second boss, one end of the refill sleeve is provided with a threaded groove, the external thread of the second boss is screwed with the threaded groove, and the other side of the refill sleeve is One end is provided with a first boss, the outside of the first boss is screwed with a disposable needle, the inside of the disposable needle is inserted with a steel needle, and the inside of the refill sleeve is installed with a refill, so The outer part of the refill sleeve is sleeved with a protective cover, the other end of the main body shell is provided with an adjustment component, the inside of the main body shell is installed with a fixed sleeve, and one end of the fixed sleeve is protruded with a flange department.

CN102264417A discloses an injection device comprising: an elongated housing; a container carrier having a medicament container to which a needle is mounted; a puncture device comprising a separation cannula, a preloaded puncture spring device and a puncture retention device, wherein the preloaded puncture spring means is capable of acting on the separation sleeve and thereby on the container carrier for sliding movement of the container and needle, and the puncture retention means is capable of holding the a puncture spring device is maintained in a loaded state; an injection device comprising a plunger rod, a preloaded injection spring device and an injection retention device, wherein the plunger rod is arranged to act as a stop in the medicament container, the preloaded injection spring means capable of acting on said plunger rod to displace said stop within said container, and said injection retention means capable of maintaining said injection spring means in a charged state; retraction means, which comprising a preloaded retraction spring and a retraction retention device, wherein the preloaded retraction spring is arranged to act on the separation sleeve and thereby the container carrier, and the retraction retention device is capable of placing all said retraction spring remains in a loaded state; puncture sequence activation means capable of acting on puncture trigger means arranged on said separation sleeve for disconnecting said puncture retention means; injection trigger means, it is provided on the separation sleeve and is capable of breaking the injection retention means to initiate an injection sequence when the separation sleeve and plunger rod are moved to a specific position; and a retraction trigger means arranged on the separation sleeve And can disconnect the retraction holding device for initiating needle retraction when the plunger rod has moved to a certain position; it is characterized in that the device further comprises a damping device, the damping device comprises a compartment, the compartment Contains a volume of highly viscous liquid and is partially defined by the outer surface of the plunger rod and the inner surface of the cap, wherein the compartment is arranged with a channel through which the liquid is forced only when the injection sequence is initiated. Channels such that the volume within the compartment decreases with movement of the plunger rod in the container during the entire injection sequence, and thereby generates damping shear forces.

SUMMARY OF THE INVENTION

The technical problem to be solved by the present invention is to overcome the deficiencies of the prior art, and to provide a disposable automatic injector with a simple structure, a significantly reduced number of parts and high reliability in each injection step, and an injection method using the injector.

In order to achieve the above object, the present invention provides:

An automatic injector is characterized in that it includes a propulsion assembly, a starter assembly, a trigger assembly and a housing; the pusher assembly is located in the starter assembly, and the pusher assembly includes a pusher part and a limit part, and the pusher part passes through the limiter part The locking realizes the limit, and the activation assembly ensures the braking of the propelling assembly before injection by fixing the limit shape of the propulsion assembly; the trigger assembly accommodates the prefilled syringe, and after the injection starts, pushes the activation assembly to make it disengage from the brake the position; the housing is wrapped outside the propulsion assembly, the activation assembly and the trigger assembly;

Preferably, the propulsion component of the propulsion assembly includes a main spring sleeve and a main spring, the limiting component of the propulsion component includes a main shaft, and the activation assembly includes an activation sliding sleeve and an auxiliary spring;

The shaft body of the main shaft is hollow, one end of which is closed and has a first flange. The shaft body is respectively provided with a plurality of elastic first and second bumps according to the distance from the first flange to the farthest. , the first lug protrudes toward the outer surface of the shaft, and has an axial guide slope toward the first flange, and the second lug protrudes toward the inner surface of the shaft, toward the first flange Has an axial guide slope;

The main spring sleeve is located in the shaft body of the main shaft, one end of which is closed and the other end is open, the closed end can be inserted into the pre-filled syringe, and the sleeve body of the main spring sleeve is provided with a slot matching the second projection. , one end of the preloaded main spring is pressed against the closed end of the main spring sleeve, and the other end is against the closed end of the main shaft, and the second protrusion is stuck into the slot;

The starting sliding sleeve is sleeved outside the main shaft, the distal end of which has a second flange, the inner surface of the sliding sleeve is axially provided with a groove for accommodating the sliding of the first protrusion in it, one end of the groove is open, and the other side is open. One end is closed, and the opening is located at the flange end of the sliding sleeve. In the assembled state, the first protrusion and the second protrusion are completely located inside the starting sliding sleeve. There is an auxiliary spring, and the first protrusion is stuck at the closed end of the groove;

After the slot of the main spring sleeve is engaged with the second bump of the spindle shaft body, the sleeve body of the starting sliding sleeve tightly presses the second bump, so that the second bump of the main shaft shaft body and the slot of the main spring sleeve jamming, thereby enabling the starter assembly to be reliably fixed in the locked state.

Preferably, the trigger assembly comprises a syringe sleeve;

The syringe sleeve can make the pre-filled syringe slide freely in the sleeve, and the sleeve body is provided with a number of through grooves. the needle of the barrel;

Preferably, the casing is sleeved on the outside of the automatic injector, one end of which is fixed on the first flange, and the other end is shorter than the needle of the pre-filled syringe. The block can pass through the through groove of the syringe sleeve to catch the flange of the pre-filled syringe, so that the pre-filled syringe cannot move toward the injection direction. The length of the other end of the shell shorter than the needle determines the depth of puncture;

Preferably, the shaft wall part where the first and second bumps are located is hollowed out to form an elastic long strip;

Preferably, when the elastic strips of the first and second protruding blocks are located in a straight line, the strip width of the second protruding block is larger than the width of the grooves in the starting sliding sleeve, so that the long strips of the second protruding block are It will not be located in the space of the groove as a whole, to ensure that the inner wall of the starting sliding sleeve can tightly press the second bump;

Preferably, the closed end of the main spring sleeve is open, which is conducive to the timely discharge of the air between the main spring sleeve and the piston of the pre-filled syringe, and after the injection is started, the main spring sleeve and the piston are in quick and unobstructed contact;

Preferably, the housing and the first flange are fixed by snap connection;

Preferably, the shaft body of the main shaft is further provided with a plurality of elastic third protrusions, which protrude toward the outer surface of the shaft, and the distance from the first flange is greater than the first and second protrusions. The function of the third bump is to facilitate assembly, and temporarily fix the starting sliding sleeve and the auxiliary spring on the main shaft before the main spring sleeve and the main spring are assembled on the main shaft;

Preferably, one end of the needle cylinder sliding sleeve against the starting sliding sleeve has an inwardly protruding barb.

Preferably, a pre-filled syringe is included.

The present invention also provides a method for injection using the above-mentioned syringe, characterized in that the specific steps are:

Step 1: In the start-up stage, place the sleeve end of the syringe barrel on the skin to be injected and press down;

Step 2: In the puncture stage, the syringe sleeve 31 pushes the starter sleeve 21 to move upward relative to the needle until the needle touches the skin and continues to apply pressure, the needle begins to puncture into the skin, and the needle sleeve pushes the starter sleeve to continue to move upward until the needle The sliding sleeve completely enters the shell, and the predetermined subcutaneous piercing depth is reached at this time, and the puncturing is completed; during the puncturing process, the lower end of the sliding sleeve is started to move above the second bump, and the locked state of the second bump and the slot is blocked. Released, under the thrust of the main spring, the slot of the main spring sleeve slides along the axial guide slope of the second bump, and the second bump is elastically deformed outward until the slot completely leaves the second bump. In the engaged position, the main spring pushes the main spring cover to continue forward, and the front part of the main spring cover contacts and abuts the piston of the pre-filled syringe;

Step 3: In the injection stage, the pre-filled syringe and the housing are locked and fixed, the main spring continues to push the main spring cover and the piston, and the drug in the pre-filled syringe is injected into the patient's skin until the piston reaches the bottom of the syringe. injection ends;

Step 4: In the reset stage, move the automatic injector away, and the auxiliary spring pushes the needle sliding sleeve and the starting sliding sleeve to retreat. When the upper end of the starting sliding sleeve contacts the first bump, the upper end of the starting sliding sleeve moves along the first bump. The axial guide slope slides, and the first protruding block is elastically deformed inward, and then disengages from the starting sliding sleeve, until the barb of the sliding sleeve of the syringe catches the flange of the pre-filled syringe, and the injection procedure ends. At this point, the first bump has been disengaged from the starter sleeve and is enclosed in the housing. Because there is no guide slope, the first bump cannot re-enter the starter sleeve in the reverse direction. If the injector repeats step 1, The entire injection process will be blocked, avoiding the re-use of the auto-injector.

The present invention has the following beneficial effects with respect to the prior art:

1. The syringe is designed as a propulsion assembly, a starter assembly, a trigger assembly and a housing, and each component cooperates with each other, so that the structure of the whole syringe is simple and the number of parts is greatly reduced;

2. The propulsion component realizes the limit by engaging with the limit component, and the starting component ensures the braking of the propulsion component before injection by fixing the limit form of the propulsion component, and realizes the reliable braking of the starting component before injection;

3. The first bump is designed to have a one-way guide slope, which can effectively avoid the repeated use of the automatic injector after being matched with the starting sliding sleeve;

4. The second bump is designed to have a one-way guide slope, and after cooperating with the starting sliding sleeve, the braking and the switching of the propulsion state of the propulsion assembly can be realized simply and skillfully.

Description of drawings

The technical solutions of the present invention and its beneficial effects will be apparent through the detailed description of the specific embodiments of the present invention below in conjunction with the accompanying drawings.

Fig. 1: exploded view of each component of the syringe of the present invention;

Figure 2: sectional view of the internal structure of the syringe of the present invention in an assembled state;

Figure 3: side view of the main shaft of the syringe of the present invention;

Figure 4: side view of the main spring cover of the syringe of the present invention;

Figure 5: side view of the present invention's syringe start sliding sleeve;

Figure 6: side view of the syringe barrel sliding sleeve of the present invention;

Figure 7: The pre-fixed state diagram of the assembly of the syringe advancing assembly and the starting assembly of the present invention;

Figure 8: The final state diagram of the assembly of the syringe advancing assembly and the starting assembly of the present invention;

Figure 9: sectional view of the internal structure of the syringe of the present invention in an assembled state;

10-14: Diagrams of the injection process of the syringe of the present invention.

The part numbers in the figure are as follows:

11-Main shaft, 12-Main spring sleeve, 13-Main spring, 14-First flange, 15-First bump, 16-Second bump, 17-Slot, 18-Third bump, 21- Start sliding sleeve, 22-auxiliary spring, 23-second flange, 24-groove, 31-syringe sleeve sliding sleeve, 32-through groove, 33-barb, 4-housing, 41-block, 51- Prefilled syringe, 52-piston, 53-needle protector, 54-pen cap, 55-prefilled syringe flange.

Detailed ways

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, but not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative efforts shall fall within the protection scope of the present invention.

Example 1:

As shown in FIGS. 1-6 , an automatic injector includes a main shaft 11 , a main spring sleeve 12 , a main spring 13 , a start sliding sleeve 21 , an auxiliary spring 22 , a syringe sleeve 31 , a housing 4 and a prefilled syringe 51 ;

The shaft body of the main shaft 11 is hollow, one end of which is closed and has a first flange 14 . The shaft body 11 is provided with a plurality of elastic first protrusions from near to far away from the first flange 14 . 15 and a second bump 16, the first bump 15 protrudes toward the outer surface of the shaft, and has an axial guide slope toward the first flange 14, and the second bump 16 protrudes toward the inner surface of the shaft a protrusion, which has an axial guide slope towards the first flange 14;

In the assembled state, the main spring sleeve 12 is located in the shaft body of the main shaft 11, one end of which is closed and the other end is open. The closed end can be inserted into the pre-filled syringe 51, and the main spring sleeve 12 is provided with and One end of the preloaded main spring 13 is pressed against the closed end of the main spring sleeve 12 , and the other end is against the closed end of the main shaft 11 , and the second convex block 16 is snapped into the card groove 17 . ;

The starting sliding sleeve 21 is sleeved outside the main shaft 11, and the distal end thereof has a second flange 23. The inner surface of the sliding sleeve is axially provided with a groove 24 for accommodating the sliding of the first protrusion 15 therein. One end of the groove 24 is open and the other end is closed. The opening is located at the end of the starter sleeve 21 with the flange. The first protrusion 15 and the second protrusion 16 are completely located inside the starter sleeve 21. The first protrusion An auxiliary spring 22 is arranged between the edge 14 and the second flange, and the first protrusion 15 is clamped at the closed end of the groove;

After the slot 17 of the main spring sleeve 12 is engaged with the second bump 16 of the shaft body of the main shaft 11, the sleeve body of the starting sliding sleeve 21 tightly presses the second bump 16, so that the second bump of the shaft body of the main shaft 11 is pressed tightly. 16 and the slot of the main spring cover 12 are stuck, so that the main spring cover 12 is reliably fixed in the locked state with the preload of the main spring 13;

The syringe sleeve 31 can make the pre-filled syringe 51 slide freely in the sleeve, and the sleeve body is provided with a plurality of through grooves 32. The needle whose length exceeds the pre-filled syringe 51 wraps the pre-filled syringe 51 as a whole; the end of the syringe sleeve 31 against the start-up sleeve 21 has an inwardly protruding barb; the pre-filled syringe 51 With a piston 52, preferably a needle protective cover 53;

As shown in FIG. 9 , the housing 4 is sleeved on the outside of the automatic injector, one end of which is fixed on the first flange 14 , and the fixing method is preferably clip connection, and the length of the other end is shorter than that of the prefilled syringe 51 . Needle, there are several blocks 41 inside the housing 4, the blocks 41 pass through the through groove 32 of the syringe sleeve 31 to clamp the flange of the pre-filled syringe 51, so that the pre-filled syringe 51 cannot move toward the injection direction , the other end of the shell 4 is shorter than the length of the needle determines the depth of puncture;

Preferably, the auto-injector also has a protective cap 54, the cap 54 is pulled out during use, when the needle protective cover 53 exists, it is connected with the needle protective cover 53, and the needle protective cover is pulled out when the pen cap 54 is pulled out 53.

Embodiment 2

As shown in FIG. 3 , in this embodiment, the wall of the shaft body where the first and second bumps 15 and 16 are located is partially hollowed out to form an elastic long strip, and the first and second bumps 15 and 16 are located in the long On the strip, when the elastic strips of the first and second bumps 15 and 16 are in a straight line, the strip width of the second bump 16 is larger than the width of the groove 24 in the starting sliding sleeve 21, so that The long strip of the second protrusion 16 is not entirely located in the space of the groove 24 to ensure that the inner wall of the starting sliding sleeve 21 can tightly press the second protrusion 16 .

Embodiment 3

In this embodiment, the closed end of the main spring cover 12 has a hole, which is conducive to the timely discharge of the air between the main spring cover 12 and the piston of the pre-filled syringe 51. After the injection is started, the main spring cover 12 and the piston 52 quickly Accessible.

Embodiment 4

As shown in FIGS. 7-8 , in this embodiment, the shaft body of the main shaft 11 is further provided with a plurality of elastic third protrusions 18 , which protrude toward the outer surface of the shaft and are far from the first flange 14 . The distance is greater than that of the first and second bumps 15 and 16 . The function of the third projection 18 is to facilitate assembly, and to temporarily fix the starting sliding sleeve 21 and the auxiliary spring 22 on the main shaft 11 before the main spring sleeve 12 and the main spring 13 are assembled on the main shaft 11 .

Embodiment 5

As shown in Figures 10-14, a method of using the above-mentioned syringe for injection, the specific steps are:

Step 1: In the start-up stage, as shown in Figure 10, place the sleeve 31 end of the syringe on the skin to be injected and press down;

Step 2: puncture stage, as shown in Figure 11, the needle sleeve 31 pushes the starter sleeve 21 to move upward relative to the needle until the needle touches the skin, continue to apply pressure, the needle begins to puncture into the skin, and the needle sleeve 31 pushes the starter sleeve 31 to move upward relative to the needle. The sleeve 21 continues to move upward until the needle sliding sleeve 31 completely enters the housing 4, at this time the predetermined subcutaneous puncture depth is reached, and the puncturing is completed; during the puncturing process, the lower end of the sliding sleeve 21 is activated to move above the second bump 16 , the locked state of the second bump 16 and the slot 17 is released, under the thrust of the main spring 13, the slot 17 of the main spring sleeve 12 slides along the axial guide slope of the second bump 16, the said The second bump 16 is elastically deformed outward until the slot 17 completely leaves the engagement position of the second bump 16, the main spring 13 pushes the main spring cover 12 to continue forward, and the front of the main spring cover 12 contacts and abuts against the Filling the piston 52 of the syringe 51;

Step 3: In the injection stage, as shown in FIG. 12 , the pre-filled syringe 51 and the housing 4 are locked and fixed, and the main spring 13 continues to push the main spring cover 12 and the piston 52 to inject the medicine in the pre-filled syringe 51 To the patient's skin, until the piston 52 reaches the bottom end of the pre-filled syringe 51, the injection ends;

Step 4: In the reset stage, as shown in Figures 13-14, move the automatic injector away, the auxiliary spring 22 pushes the needle sliding sleeve 31 and the starting sliding sleeve 21 to retreat, when the upper end of the starting sliding sleeve 21 contacts the first bump At 15:00, the upper end of the starting sliding sleeve 21 slides along the axial guide slope of the first protrusion 15, the first protrusion 15 elastically deforms inwardly, and then comes out of the starting sliding sleeve 21 until the needle cylinder sliding sleeve 31 The barbs 33 of the prefilled syringe flanges 55 are caught, and the injection procedure ends. At this time, the first protrusion 15 has been disengaged from the starting sliding sleeve 21 and is enclosed in the housing 4. Since it does not have a guiding slope, the first protrusion 15 cannot re-enter the starting sliding sleeve 21 in the reverse direction. If step 1 is repeated, the entire injection process will be blocked, avoiding the repeated use of the auto-injector.

The above descriptions are only exemplary embodiments of the present invention, and are not intended to limit the scope of patent protection of the present invention. Any equivalent structure or equivalent process transformation made by using the contents of the description and drawings of the present invention, or directly or indirectly applied to other related The technical field of the present invention is similarly included in the scope of patent protection of the present invention.

Claims (12)

1. An autoinjector comprising a propulsion assembly, an activation assembly, a trigger assembly and a housing;

the propelling component is positioned in the starting component, the propelling component comprises a propelling part and a limiting part, the propelling part is clamped with the limiting part to realize limiting, and the starting component ensures the braking of the propelling component before injection by fixing the limiting form of the propelling component;

the trigger assembly accommodates the pre-filled syringe and pushes the actuation assembly out of the braking position after the injection begins;

the shell is wrapped outside the propelling component, the starting component and the triggering component.

2. The automatic injector of claim 1, wherein the propulsion component of the propulsion assembly comprises a main spring housing and a main spring, the limiting component of the propulsion component comprises a main shaft, and the activation assembly comprises an activation slide and an auxiliary spring;

the spindle body of the spindle is hollow, one end of the spindle body is closed and is provided with a first flange, a plurality of first bumps and second bumps with elasticity are respectively arranged on the spindle body from near to far away from the first flange, the first bumps protrude towards the outer surface direction of the spindle body, the first bumps are provided with axial guide slopes towards the first flange direction, the second bumps protrude towards the inner surface direction of the spindle body, and the second bumps are provided with axial guide slopes towards the first flange direction;

the main spring sleeve is positioned in the spindle shaft body, one end of the main spring sleeve is closed, the other end of the main spring sleeve is open, the closed end can be inserted into the pre-filled syringe, a clamping groove matched with the second bump is formed in the sleeve body of the main spring sleeve, one end of the pre-tightened main spring abuts against the closed end of the main spring sleeve, the other end of the pre-tightened main spring abuts against the closed end of the spindle, and the second bump is clamped into the clamping groove;

the starting sliding sleeve is sleeved outside the main shaft, a second flange is arranged at the far end of the starting sliding sleeve, a groove capable of accommodating the first lug to slide in the groove is axially formed in the inner surface of the sliding sleeve, one end of the groove is open, the other end of the groove is closed, the opening is located at the flange end of the sliding sleeve, the first lug and the second lug are completely located inside the starting sliding sleeve in an assembling state, an auxiliary spring is arranged between the first flange and the second flange, and the first lug is clamped at the closed end of the groove.

3. The autoinjector of any of claims 1-2, wherein the trigger assembly comprises a syringe slide;

the syringe sliding sleeve can enable the pre-filled syringe to freely slide in the sleeve, a plurality of grooves are formed in the sleeve body, one end of the syringe sliding sleeve props against the starting sliding sleeve, and the length of the other end of the syringe sliding sleeve exceeds the length of the needle head of the pre-filled syringe.

4. The automatic injector of any of claims 1-3, wherein said housing is fitted over the exterior of said automatic injector, and has one end fixed to said first flange and the other end shorter than the length of the needle of the pre-filled syringe, and a plurality of clips are provided inside said housing, said clips being adapted to engage said flange of the pre-filled syringe through slots in said syringe slide.

5. The automatic injector of claim 2, wherein the portion of the shaft wall where the first and second protrusions are located is hollowed out to form a flexible strip.

6. The automatic injector of claim 5, wherein when the resilient strips of the first and second projections are aligned, the width of the strip of the second projection is greater than the width of the groove in the activation sleeve.

7. The automatic injector of claim 2, wherein said closed end of said main spring housing is open.

8. The automatic injector of claim 4, wherein the housing and the first flange are secured by a snap fit.

9. The automatic injector of claim 2, wherein the shaft body of the main shaft further has a plurality of third resilient protrusions protruding toward the outer surface of the shaft body, and the third resilient protrusions are spaced from the first flange by a distance greater than the first and second protrusions.

10. The automatic injector of claim 2, wherein said barrel runner has an inwardly projecting barb at the end of said barrel runner that abuts against said actuating runner.

11. The automatic injector of any of claims 1-10, comprising a pre-filled syringe.

12. An injection method using the autoinjector of claim 11, comprising the specific steps of:

the method comprises the following steps: the starting stage, the needle cylinder sliding sleeve end of the injector is placed on the skin to be injected and pressed downwards;

step two: in the puncture stage, the syringe sliding sleeve 31 pushes the starting sliding sleeve 21 to move upwards relative to the needle until the needle contacts the skin, pressure is continuously applied, the needle starts to puncture into the skin, the needle sliding sleeve pushes the starting sliding sleeve to move upwards until the needle sliding sleeve completely enters the shell, and at the moment, the preset subcutaneous puncture depth is reached, and the puncture is finished; in the puncture process, the lower end of the starting sliding sleeve moves to the position above the second bump, the locking state of the second bump and the clamping groove is released, under the thrust action of the main spring, the clamping groove of the main spring sleeve slides along the axial guide slope of the second bump, the second bump elastically deforms outwards until the clamping groove completely leaves the clamping position of the second bump, the main spring pushes the main spring sleeve to continue to move forwards, and the front part of the main spring sleeve contacts and supports against the piston of the prefilled syringe;

step three: in the injection stage, the pre-filled syringe and the shell are fixedly clamped, the main spring continues to push the main spring sleeve and the piston, and the medicine in the pre-filled syringe is injected to the subcutaneous part of the patient until the piston reaches the bottommost end of the syringe, and the injection is finished;

step four: and in the resetting stage, the automatic injector is moved away, the auxiliary spring pushes the needle head sliding sleeve and the starting sliding sleeve to return, when the upper end of the starting sliding sleeve contacts the first bump, the upper end of the starting sliding sleeve slides along the axial guide slope surface of the first bump, the first bump elastically deforms inwards and then is separated from the starting sliding sleeve until the barb of the syringe sliding sleeve blocks the flange of the pre-filled syringe, and the injection procedure is finished.

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