Stroke switchable dual stop pipetting device and pipetting method

Abstract

This invention discloses a pipetting device and method with switchable stroke and dual stops, including a pipette body and a piston assembly. The piston assembly includes a piston rod and a piston, and also includes an operation button assembly, comprising a primary sleeve and a secondary sleeve. The primary sleeve forms the user pressing part, and the secondary sleeve is connected to the piston rod. A locking mechanism has a locked state and an unlocked state. In the locked state, the primary sleeve and the secondary sleeve are relatively fixed. In the unlocked state, the secondary sleeve is allowed to slide independently along the axial direction relative to the primary sleeve. A transmission mechanism is located inside the operation button assembly. When the locking mechanism is in the unlocked state and the primary sleeve is stopped, the transmission mechanism transmits the pressing force applied to the operation button assembly to the secondary sleeve, driving it to continue downward. By setting a lockable two-stage sleeve operation assembly and an internal transmission mechanism, the stroke control that relies solely on touch is replaced, achieving precise and reliable positioning and switching of the two stop points of the pipette.

Description

Technical Field

[0001] This invention belongs to the field of pipette technology, and particularly relates to a pipetting device and method with switchable stroke and dual stops. Background Technology

[0002] Traditional manual pipettes typically have a piston with two key positions: a first stop and a second stop. The working principle is as follows: First, pressing the button pushes the piston to the first stop, expelling a set volume of gas. Releasing the button returns the piston to its initial position, creating negative pressure to precisely aspirate an equal volume of liquid. When drainage is needed, the piston is pushed back to the first stop to expel the main volume of liquid. Then, pressing the button further pushes the piston to the second stop, using additional gas to completely expel any remaining liquid film at the tip, ensuring complete and accurate drainage.

[0003] There is no clear mechanical limit or tactile distinction between these two stop points, and switching between them relies entirely on the operator's feel and experience. This leads to two main problems in actual use: First, during the venting / suction phase, if the first stop point is accidentally pressed, the piston stroke will be too long, resulting in a gas volume greater than the set value. This may lead to the suction of excessive liquid or even the suction of liquid into the pipette body, causing contamination and damage. Second, during the venting phase, if the button is not pressed to the second stop point, the residual liquid film cannot be completely drained, resulting in an actual venting volume less than the set value, introducing system error. Summary of the Invention

[0004] Purpose of the invention: In order to overcome the shortcomings of the prior art, the present invention provides a pipetting device and pipetting method with switchable stroke. By setting a lockable two-stage sleeve operation component and a built-in transmission mechanism, the stroke control that relies solely on manual feel is replaced, so as to achieve accurate and reliable positioning and switching of the two stop points of the pipetting gun.

[0005] Technical solution: To achieve the above objectives, the present invention provides a stroke-switchable dual-stop pipetting device, comprising a gun body and a piston assembly within the gun body, the piston assembly comprising a piston rod and a piston, and further comprising:

[0006] The operation button assembly is axially movable on the gun body and includes a primary sleeve and a secondary sleeve that are coaxially arranged and axially sliding relative to each other; the primary sleeve constitutes the user pressing part, and the lower end of the secondary sleeve is connected to the piston rod.

[0007] The locking mechanism has a locked state and an unlocked state; in the locked state, the primary sleeve and the secondary sleeve are relatively fixed; in the unlocked state, the secondary sleeve is allowed to slide independently along the axial direction relative to the primary sleeve.

[0008] A transmission mechanism is disposed inside the operation button assembly; when the locking mechanism is in the unlocked state and the first-stage sleeve is stopped by a limit, the transmission mechanism is used to transmit the pressing pressure applied to the operation button assembly to the second-stage sleeve, driving it to continue to descend.

[0009] Furthermore, the gun body is provided with a first stop and a second stop;

[0010] When the locking mechanism is in the locked state, the first-stage sleeve and the second-stage sleeve are pressed down synchronously, and their downward stroke is limited by the first stop, causing the piston to move to the first stop point;

[0011] When the locking mechanism is in the unlocked state, the first-stage sleeve stops descending to its travel limit after being restricted by the first stop. At this time, the transmission mechanism drives the second-stage sleeve to continue descending until its travel is restricted by the second stop, causing the piston to move to the corresponding second stop point.

[0012] Furthermore, the transmission mechanism includes a deformable or movable transmission component; in the unlocked state, when the primary sleeve is limited, the continued application of pressing pressure causes the transmission component to deform or move, thereby applying a downward driving force to the secondary sleeve.

[0013] Furthermore, the transmission component is an elastic transmission component; the operation button assembly also includes a button and a button lever connected to the button; the first end of the elastic transmission component is hinged to the primary sleeve, and the second end is movably connected to the button lever via a slider; a contact is provided at the top of the secondary sleeve;

[0014] In the unlocked state, pressing the button drives the button lever to move downward, forcing the elastic transmission component to deflect and deform and press the contact, thereby driving the secondary sleeve to move downward.

[0015] Furthermore, the bottom of the button lever is provided with a horizontal guide rail, and the slider slides in cooperation with the horizontal guide rail; the second end of the elastic transmission member is connected to the slider through a second hinge structure, and the first end is connected to the inner wall of the primary sleeve through a first hinge structure.

[0016] Furthermore, the locking mechanism includes a locking pin and a locking blind hole provided on the secondary sleeve; the gun body has a vertical slot; the tube wall of the primary sleeve has a radial hole; the locking pin can operate through the radial hole and selectively engage or disengage from the locking blind hole to achieve locking or unlocking.

[0017] Furthermore, it also includes a return spring system, which comprises a primary sleeve return spring and a pressure spring;

[0018] A retaining ring is provided on the outer periphery of the button rod. Under normal conditions, the retaining ring abuts against the inner top of the primary sleeve.

[0019] The primary sleeve return spring is elastically disposed between the operation button assembly and the gun body to provide the overall return force of the button assembly;

[0020] The pressure spring is elastically disposed between the button and the first-stage sleeve, and is used to provide downward preload to the first-stage sleeve.

[0021] Furthermore, the reset spring system also includes a secondary sleeve reset spring, wherein the secondary sleeve obtains an upward reset force through the secondary sleeve reset spring, and the secondary sleeve, through the force provided by the secondary sleeve reset spring, keeps the contact always against the rod wall of the elastic transmission member.

[0022] Furthermore, the first stop is an annular protrusion disposed on the inner wall of the gun body, and the outer periphery of the primary sleeve is provided with a limiting shoulder that cooperates with the annular protrusion; the second stop is a protruding structure disposed inside the gun body, and the lower end of the secondary sleeve abuts against the second stop when it is fully descending.

[0023] A pipetting method using a stroke-switchable double-stop pipetting device includes the following steps:

[0024] S1. State preparation: Ensure that the locking mechanism is in the locked state, so that the primary bushing and the secondary bushing are relatively fixed;

[0025] S2, Precise Liquid Aspiration: Press down the operation button assembly to drive the piston to the first stop point defined by the first stop part to vent the gas corresponding to the set liquid transfer volume; then release the operation button assembly, the piston returns to its original position, and based on the precise volume marked at the first stop point, an equal volume of liquid is aspirated by negative pressure;

[0026] S3, Stroke switching: When it is necessary to completely drain the sucked liquid, switch the locking mechanism to the unlocked state;

[0027] S4. Complete drainage: Press the operation button assembly again to first drive the piston to move back to the first stop point to drain the main liquid; continue to apply pressure to drive the piston past the first stop point through the transmission mechanism until it is limited to the second stop point by the second stop part, and use the additional blowing stroke to completely drain the residual liquid.

[0028] Beneficial effects: This invention solves the problems of excessive liquid aspiration and residual liquid discharge caused by the reliance on manual feel in traditional pipettes. First, the mechanical hard stop and status locking ensure absolute consistency of the endpoint of each stroke, greatly improving the volumetric accuracy and repeatability of pipetting operations. Second, it effectively protects the pipette body, preventing contamination and damage caused by accidental liquid aspiration into the pipette body, thus extending the service life of the equipment. Furthermore, the clear two-stage operating feel and explicit mechanical status indicators reduce the difficulty of operation. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the overall structure of the present invention;

[0030] Figure 2 for Figure 1 Enlarged schematic diagram of the middle section structure;

[0031] Figure 3 A schematic diagram showing the structure of a pipette piston moving to the position corresponding to the first stop point P1;

[0032] Figure 4 This is a schematic diagram showing the structure of a pipette piston moving to the position corresponding to the second stop point P2. Detailed Implementation

[0033] The invention will now be further described with reference to the accompanying drawings.

[0034] This invention discloses a dual-stop pipetting device with switchable stroke, the key feature of which lies in decomposing the traditional single-stroke operation button into a two-stage structure that allows for selective linkage and separation, and incorporating a transmission mechanism that can still transmit driving force in the separated state. It can be used for pipetting operations of liquid samples in laboratories, such as food testing and agricultural product testing, and has a very wide range of applications.

[0035] Specifically, such as Figure 1 As shown, the pipette includes a body 1 and a piston assembly inside the body 1. The piston assembly includes a piston rod 2 and a piston 3. The body 1 serves as a shell supporting and housing all internal components, and a precision cylinder is installed inside. The piston 3 slides and seals within the cylinder. The piston rod 2 acts as a rigid connector, transmitting the movement of the piston 3 to the operating end, or transmitting the action of the operating end to the piston 3, thereby changing the volume of the sealed cavity and realizing the aspiration and dispensing of liquid.

[0036] like Figure 1 and Figure 2 As shown, the pipette of the present invention further includes: an operation button assembly, a locking mechanism 4, and a transmission mechanism, wherein:

[0037] The operation button assembly, axially movable on the gun body 1, includes a primary sleeve 5 and a secondary sleeve 6 coaxially arranged and axially sliding relative to each other. The primary sleeve 5, as the outer component for user operation, constitutes the main source of the pressing feel. The secondary sleeve 6, as the inner drive rod, is a key component in the power transmission path. The coaxial nesting and relative sliding design of the two is the structural basis for achieving two-stage stroke separation. The primary sleeve 5 constitutes the user pressing part, and the lower end of the secondary sleeve 6 is connected to the piston rod 2. Thus, the user's operation of the primary sleeve 5 can selectively drive or not drive the secondary sleeve 6 and piston rod 2, depending on the state of the locking mechanism 4.

[0038] The locking mechanism 4 has a locked state and an unlocked state. In the locked state, the primary sleeve 5 and the secondary sleeve 6 are relatively fixed; at this time, they form a rigid whole and move together. In the unlocked state, the secondary sleeve 6 is allowed to slide independently along the axial direction relative to the primary sleeve 5; at this time, they are decoupled, ensuring the second independent stroke.

[0039] A transmission mechanism is located inside the operation button assembly. This is the key to the invention, solving the problem of how to continue driving the secondary sleeve 6 when the movement of the primary sleeve 5 is stopped in the unlocked state. When the locking mechanism 4 is in the unlocked state and the primary sleeve 5 is stopped, the transmission mechanism transmits the pressing force applied to the operation button assembly to the secondary sleeve 6, driving it to continue downward. This transmission mechanism, acting as a force conversion and transmission intermediary, can receive the input force from the upper part of the still-pressed operation button assembly and redirect this force around the stopped primary sleeve 5 body to the secondary sleeve 6, thereby pushing it to complete the remaining stroke. This design ensures that the driving of the second stroke no longer depends on the user's vague tactile feedback to continue pressing, but is actively executed by a defined mechanical structure, guaranteeing that the second stop point is reliably reached.

[0040] like Figure 1 , Figure 2 , Figure 3 and Figure 4 As shown, the gun body 1 is provided with a first stop part 1a and a second stop part 1b inside.

[0041] When the locking mechanism 4 is in the locked state, the primary sleeve 5 and the secondary sleeve 6 are pressed down synchronously, and their downward stroke is limited by the first stop part 1a, causing the piston 3 to move to the first stop point P1, corresponding to... Figure 3In the locked state, the primary sleeve 5 and the secondary sleeve 6 are rigidly connected and move downwards together until they are mechanically stopped by the first stop 1a. The core function of this first stop point P1 is to precisely define the end point of the piston 3's gas discharge stroke, thereby calibrating the set volume of liquid to be removed. When the user releases the button, the piston 3 returns precisely to its initial position under the action of the return spring, thus completing the accurate suction of the set volume of liquid. Through mechanical hard limiting, absolute consistency of each venting stroke is ensured, thereby guaranteeing the accuracy of the suction volume and preventing liquid from being sucked into the gun body due to overpressure.

[0042] When the locking mechanism 4 is in the unlocked state, the first-stage sleeve 5 descends to its travel limit and stops due to the restriction of the first stop 1a. At this time, the transmission mechanism drives the second-stage sleeve 6 to continue descending until its travel is restricted by the second stop 1b, causing the piston 3 to move to the corresponding second stop point P2. Figure 4 In the unlocked state, the drainage operation is performed. Piston 3 is first pushed to the first stop point P1 to complete the main liquid drainage. Then, the transmission mechanism is activated, driving piston 3 to continue to the second stop point P2. The function of the second stop point P2 is to provide an additional, defined blowing stroke to ensure that the liquid in the nozzle is completely emptied. Through independent mechanical limits (second stop part 1b) and a reliable transmission mechanism, it is forcibly ensured that the blowing stroke is executed to the correct position every time, completely solving the volume error caused by incomplete drainage.

[0043] like Figure 4 As shown, the transmission mechanism includes a deformable or movable transmission component 11. In the unlocked state, when the primary sleeve 5 is limited, the continued pressing pressure causes the transmission component 11 to deform or move, thereby applying a downward driving force to the secondary sleeve 6. In the unlocked state, the principle of force transmission is as follows: when the primary sleeve 5 is limited, the user's continuous pressing pressure does not directly push the secondary sleeve 6, but is converted into energy that drives the deformation or movement of an intermediate transmission component. This transmission component then converts the direction of the force and applies it to the secondary sleeve 6. This successfully solves the power transmission problem when there is a stationary intermediate component (primary sleeve 5) in the driving path, ensuring that the driving of the second segment no longer depends on the user's vague feeling of continuing to press down, but is guaranteed by a definite mechanical deformation or movement process, thus ensuring that the second stop point P2 is reliably and repeatedly reached.

[0044] like Figure 2As shown, the transmission component is an elastic transmission component 11, which is a preferred and efficient embodiment of the transmission component. The operation button assembly also includes a button 71 and a button lever 72 connected to the button 71. The button lever 72 serves as a direct carrier for introducing the user's finger pressure into the internal mechanism. The first end of the elastic transmission component 11 is hinged to the primary sleeve 5, giving it a rotation fulcrum; the second end is movably connected to the button lever 72 via a slider 17, allowing the downward movement of the button lever 72 to pull this end. The top of the secondary sleeve 6 is provided with a contact 62, serving as the driven point. In the unlocked state, pressing the button 71 drives the button lever 72 downward, forcing the elastic transmission component 11 to deflect and deform, thus pressing the contact 62, thereby driving the secondary sleeve 6 downward. The vertical component of the pressure constitutes the effective power driving the secondary sleeve 6 downward. This achieves efficient and smooth conversion of the linear motion of the button lever 72 into a linear driving force on the secondary sleeve 6 through the lever-like deformation of an inclined elastic lever. The structure is compact, the transmission process is smooth, and clear force feedback is provided.

[0045] The button lever 72 has a transverse guide rail 16 at its bottom, and the slider 17 slides in conjunction with the transverse guide rail 16. This structure limits the slider 17 to slide only in a direction perpendicular to the axis of the button lever 72. The second end of the elastic transmission member 11 is connected to the slider 17 through a second hinge structure 13, and the first end is connected to the inner wall of the primary sleeve 5 through a first hinge structure 12. When the button lever 72 moves down and the primary sleeve 5 is stationary, the second end of the elastic transmission member 11 is pulled down. Since the slider 17 is constrained on the transverse guide rail 16, this end point cannot move down freely, but is forced to move laterally along the guide rail. This lateral displacement directly causes the inclined elastic transmission member 11 to produce a deterministic inward bending deformation, thereby precisely pressing against the contact 62. Through the simple transverse guide rail constraint, the complex spatial linkage motion is simplified into a controllable motion, ensuring that the trajectory and degree of deformation of the elastic transmission member 11 are highly consistent each time, thus making the driving force and displacement of the second stroke extremely stable, greatly improving the reliability and durability of the mechanism.

[0046] It should be noted that the elastic transmission component 11 is a transmission rod that combines structural rigidity with controllable elastic deformation capability. It is made of a material with a high elastic limit and good fatigue resistance, such as spring steel, phosphor bronze, or high-elasticity engineering plastics (e.g., polyoxymethylene (POM)). This rod has a slender structure with mounting holes at both ends for hinged connections, connecting to the inner wall of the primary sleeve 5 and the slider 17 via a first hinge structure 12 and a second hinge structure 13, respectively. In operation, the rod does not undergo significant extension or contraction, but rather small, controllable elastic bending deformation under pressure. The key lies in utilizing the material's own elasticity to convert the linear displacement of the button rod 72 into a bending displacement of the rod body, thereby changing the direction of the force and transmitting it to the contact 62.

[0047] The locking mechanism 4 includes a locking pin 41 and a locking blind hole 61 disposed on the secondary sleeve 6; the gun body 1 has a vertical slot 1c; the tube wall of the primary sleeve 5 has a radial hole 51; the locking pin 41 can operably pass through the radial hole 51 and selectively engage or disengage from the locking blind hole 61 to achieve locking or unlocking. More specifically, the locking pin 41 is threadedly engaged with the radial hole 51, and locking or unlocking is achieved by rotating the locking pin 41; alternatively, the locking pin 41 is a sliding pin and is equipped with an elastic element that keeps it normally closed.

[0048] The invention also includes a reset spring system comprising a primary sleeve reset spring 15 and a pressure spring 14. A retaining ring 7a is provided on the outer periphery of the button lever 72, which, under normal conditions, abuts against the inner top of the primary sleeve 5. The primary sleeve reset spring 15 is elastically disposed between the operating button assembly and the gun body 1 (e.g., its upper end abuts against the button 71, and its lower end abuts against the gun body 1), providing the overall reset force for the button assembly. The pressure spring 14 is elastically disposed between the button 71 and the primary sleeve 5, and is normally in a compressed state, providing downward pre-pressure to the primary sleeve 5. This pre-pressure has two functions: first, it ensures a solid and precise operating feel by starting the first segment of the stroke without any idle travel; second, it maintains a fixed position on the limiting shoulder 52 of the primary sleeve 5 in a free state, further ensuring the repeatability accuracy of the first stop point P1.

[0049] like Figure 1 and Figure 2 As shown, an axial guide structure 8 is provided between the inner wall of the primary sleeve 5 and the outer wall of the secondary sleeve 6 to restrict their relative circumferential rotation. The axial guide structure includes a guide protrusion 81 provided on the inner wall of the primary sleeve and a guide ring 82 provided on the outer wall of the secondary sleeve. The guide ring 82 has a groove 820, which slides and engages with the guide protrusion 81.

[0050] The reset spring system also includes a secondary sleeve reset spring 10. A support portion 9 is provided at the bottom of the guide protrusion 81, and the secondary sleeve reset spring 10 is disposed between the guide ring 82 and the support portion 9. The secondary sleeve 6 obtains an upward reset force through the secondary sleeve reset spring 10, and the force provided by the secondary sleeve reset spring 10 keeps the contact 62 always against the rod wall of the elastic transmission member 11. The advantages are: First, at the end of the second stroke or during any operational gap, the secondary sleeve 6 can be reliably pushed back to its initial upper position. Second, and more importantly, this spring force keeps the contact 62 at the top of the secondary sleeve 6 always against the rod wall of the elastic transmission member 11. This means that zero-clearance fit is achieved between the transmission pairs, ensuring that when the elastic transmission member 11 begins to deform, the driving force can be applied to the secondary sleeve 6 immediately and without delay. When the user presses the second stage, they experience a continuous and smooth increase in resistance, providing clear, delicate, and precise operational feedback, while avoiding impact, noise, and wear caused by gaps.

[0051] More specifically, the first stop 1a is an annular protrusion provided on the inner wall of the gun body 1, and the outer periphery of the primary sleeve 5 is provided with a limiting shoulder 52 that cooperates with the annular protrusion; the second stop 1b is a protruding structure provided inside the gun body 1, and the lower end of the secondary sleeve 6 abuts against the second stop 1b when it is fully descending.

[0052] A pipetting method using a stroke-switchable double-stop pipetting device includes the following steps:

[0053] S1. State preparation: Ensure that the locking mechanism 4 is in the locked state, so that the primary sleeve 5 and the secondary sleeve 6 are relatively fixed;

[0054] S2, Precise liquid aspiration: Press down the operation button assembly to drive the piston 3 to the first stop point P1 defined by the first stop part 1a to vent the gas corresponding to the set liquid transfer volume; then release the operation button assembly, the piston 3 returns to its original position, and based on the precise volume marked at the first stop point P1, aspirates an equal volume of liquid by negative pressure.

[0055] S3, Stroke switching: When it is necessary to completely drain the sucked liquid, switch the locking mechanism 4 to the unlocked state;

[0056] S4. Complete drainage: Press the operation button assembly again to first drive the piston 3 to move to the first stop point P1 to drain the main liquid; continue to apply pressure to drive the piston 3 past the first stop point P1 through the transmission mechanism until it is limited by the second stop part 1b to the second stop point P2, and use the additional blowing stroke to completely drain the residual liquid.

[0057] In summary, this invention solves two core problems of traditional pipettes: excessive aspiration and residual liquid discharge, which are caused by reliance on tactile feedback. First, the mechanical hard stop and status locking ensure absolute consistency at the end of each stroke, greatly improving the volumetric accuracy and repeatability of pipetting operations. Second, it effectively protects the pipette body, preventing contamination and damage caused by accidental liquid aspiration, thus extending the equipment's lifespan. Third, the clear two-stage operating feel and explicit mechanical status (lock pin position) indication reduce the difficulty of operation. Finally, the ingenious transmission and locking mechanism is reliable, easy to implement and industrialize, and improves performance without excessively increasing manufacturing costs.

[0058] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A stroke-switchable dual-stop pipetting device, comprising a pipette body (1) and a piston assembly within the pipette body (1), the piston assembly comprising a piston rod (2) and a piston (3), characterized in that: Also includes: The operation button assembly is axially movable on the gun body (1) and includes a primary sleeve (5) and a secondary sleeve (6) that are coaxially arranged and axially slidable relative to each other; the primary sleeve (5) constitutes the user pressing part, and the lower end of the secondary sleeve (6) is connected to the piston rod (2); The locking mechanism (4) has a locked state and an unlocked state; in the locked state, the primary sleeve (5) and the secondary sleeve (6) are relatively fixed; in the unlocked state, the secondary sleeve (6) is allowed to slide independently along the axial direction relative to the primary sleeve (5); The transmission mechanism is located inside the operation button assembly. When the locking mechanism (4) is in the unlocked state and the first-stage sleeve (5) is stopped, the transmission mechanism is used to transmit the pressing pressure applied to the operation button assembly to the second-stage sleeve (6) to drive it to continue to descend.

2. The stroke-switchable double-stop pipetting device according to claim 1, characterized in that: The gun body (1) is provided with a first stop (1a) and a second stop (1b) inside. When the locking mechanism (4) is in the locked state, the first-stage sleeve (5) and the second-stage sleeve (6) are pressed down synchronously, and their downward stroke is restricted by the first stop (1a), causing the piston (3) to move to the first stop point (P1). When the locking mechanism (4) is in the unlocked state, the first-stage sleeve (5) stops after descending to its travel limit due to the restriction of the first stop (1a). At this time, the second-stage sleeve (6) is driven to continue descending through the transmission mechanism until its travel is restricted by the second stop (1b), so that the piston (3) moves to the corresponding second stop point (P2).

3. A stroke-switchable double-stop pipetting device according to claim 1 or 2, characterized in that: The transmission mechanism includes a deformable or movable transmission element (11); in the unlocked state, when the primary sleeve (5) is limited, the continued application of pressing pressure causes the transmission element (11) to deform or move, thereby applying a downward driving force to the secondary sleeve (6).

4. The stroke-switchable double-stop pipetting device according to claim 3, characterized in that: The transmission component is an elastic transmission component (11); the operation button assembly also includes a button (71) and a button rod (72) connected to the button (71); the first end of the elastic transmission component (11) is hinged to the first-stage sleeve (5), and the second end is movably connected to the button rod (72) through a slider (17); a contact (62) is provided at the top of the second-stage sleeve (6). In the unlocked state, pressing the button (71) drives the button lever (72) to move down, forcing the elastic transmission member (11) to deflect and press the contact (62), thereby driving the secondary sleeve (6) to move down.

5. A stroke-switchable double-stop pipetting device according to claim 4, characterized in that: The bottom of the button rod (72) is provided with a horizontal guide rail (16), and the slider (17) slides in cooperation with the horizontal guide rail (16); the second end of the elastic transmission member (11) is connected to the slider (17) through the second hinge structure (13), and the first end is connected to the inner wall of the first-stage sleeve (5) through the first hinge structure (12).

6. The stroke-switchable double-stop pipetting device according to claim 1, characterized in that: The locking mechanism (4) includes a locking pin (41) and a locking blind hole (61) provided on the secondary sleeve (6); the gun body (1) has a vertical slot (1c); the tube wall of the primary sleeve (5) has a radial hole (51); the locking pin (41) can be operated through the radial hole (51) and selectively engage or disengage from the locking blind hole (61) to achieve locking or unlocking.

7. The stroke-switchable double-stop pipetting device according to claim 1, characterized in that: It also includes a return spring system, which comprises a primary sleeve return spring (15) and a pressure spring (14). A retaining ring (7a) is provided on the outer periphery of the button rod (72). Under normal conditions, the retaining ring (7a) abuts against the inner top of the first-stage sleeve (5). The primary sleeve return spring (15) is elastically disposed between the operation button assembly and the gun body (1) to provide the overall return force of the button assembly; The pressure spring (14) is elastically disposed between the button (71) and the first-stage sleeve (5) to provide downward pre-pressure to the first-stage sleeve (5).

8. A stroke-switchable double-stop pipetting device according to claim 7, characterized in that: The reset spring system also includes a secondary sleeve reset spring (10), the secondary sleeve (6) obtains an upward reset force through the secondary sleeve reset spring (10), and the secondary sleeve (6) keeps the contact (62) against the rod wall of the elastic transmission member (11) by the force provided by the secondary sleeve reset spring (10).

9. A stroke-switchable double-stop pipetting device according to claim 1, characterized in that: The first stop (1a) is an annular protrusion provided on the inner wall of the gun body (1), and the outer periphery of the first-stage sleeve (5) is provided with a limiting shoulder (52) that cooperates with the annular protrusion; the second stop (1b) is a protruding structure provided inside the gun body (1), and the lower end of the second-stage sleeve (6) abuts against the second stop (1b) when it is fully descending.

10. The pipetting method of a stroke-switchable double-stop pipetting device according to claim 2, characterized in that: Includes the following steps: S1. State preparation: Ensure that the locking mechanism (4) is in the locked state, so that the first-level sleeve (5) and the second-level sleeve (6) are relatively fixed; S2, Precise liquid aspiration: Press down the operation button assembly to drive the piston (3) to move to the first stop point (P1) defined by the first stop part (1a) to vent the gas corresponding to the set liquid transfer volume; then release the operation button assembly, the piston (3) returns to its original position, and based on the precise volume marked at the first stop point (P1), a liquid of the same volume is aspirated by negative pressure; S3, Stroke switching: When it is necessary to completely drain the absorbed liquid, switch the locking mechanism (4) to the unlocked state; S4. Complete drainage: Press the operation button assembly again to drive the piston (3) to move to the first stop point (P1) to drain the main liquid; continue to apply pressure to drive the piston (3) past the first stop point (P1) through the transmission mechanism until it is limited by the second stop part (1b) to the second stop point (P2), and use the additional blowing stroke to completely drain the residual liquid.

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