A multi-stage lead screw mechanism

Abstract

This invention relates to a multi-stage ball screw mechanism, belonging to the field of electromechanical servo systems. This invention is a multi-stage planetary roller screw transmission mechanism, employing an integrated design of the primary nut and secondary screw, and an integrated design of the primary and secondary nuts and actuator rod. This effectively reduces the radial dimension of the transmission mechanism and increases structural strength. With the secondary nut as the largest outer envelope component, the primary screw pair is nested within the secondary, and the tertiary screw within the primary, resulting in a more compact structure. The roller diameter of each screw pair can be designed independently, solving the problem of mismatch between the radial dimension and load-bearing capacity of multi-stage ball screw pairs. This achieves a large extension stroke and high load-bearing capacity within a small installation space, with adjustable radial dimensions and controllable end-output speed ratio.

Description

Technical Field

[0001] This invention belongs to the field of electromechanical servo systems and relates to a multi-stage lead screw mechanism. Background Technology

[0002] A multi-stage linear transmission mechanism is a mechanical system that combines two or more transmission units to achieve motion transformation, speed regulation, force gain, or stroke increase. Its core value lies in its ability to meet the demands of high speed ratios, long strokes, or high load outputs within a compact installation space, which is difficult to achieve with a single-stage transmission. It is a key fundamental component for modern equipment to achieve high performance, high precision, and complex motions, and is widely used, especially in heavy machinery, telescopic booms, and aerial work platforms.

[0003] Currently, in this field, multi-stage hydraulic transmission, with its multi-stage nested sleeve structure, can achieve long stroke and high load-bearing capacity within a limited space. However, this transmission method, which uses hydraulic oil as a medium, naturally faces the challenge of sealing and preventing leakage. Especially in the field of multi-stage hydraulic cylinders, as the number of sleeve stages increases, the number of dynamic sealing links also increases, significantly reducing sealing reliability. Wear at any stage of the seal can lead to hydraulic oil leakage, polluting the environment, affecting transmission efficiency at best, and causing mechanical failure at worst. Under the development trend of green and electric servo mechanisms, there is an urgent need to design a multi-stage linear transmission mechanism with high reliability and a large effective stroke, based on electromechanical transmission.

[0004] Currently, some scholars have conducted research on multi-stage ball screws. For example, CN114607741A describes a multi-stage ball screw mechanism that achieves multi-stage extension and retraction with a large stroke through the series nesting of ball screws. However, the rotational input of the last two stages of the screw relies solely on the magnetism of the ferromagnetic material to connect with the rotating shaft in the inner cavity of the first-stage screw. This results in low reliability when subjected to large torques. Furthermore, to meet the large stroke requirements, the rotating rod is excessively long and unsupported, leading to weak structural rigidity and insufficient reliability. CN113685526A describes a parallel multi-stage planetary roller screw pair structure. In this structure, the input of the next stage of the screw pair relies on the transmission cylinder structure of the previous stage. As the stroke increases and the number of stages increases... Increasing the number of cylinders requires lengthening and increasing the number of cylinders, which must rotate synchronously with the lead screw. This results in a large moment of inertia and operating losses for the entire mechanism. Furthermore, the parallel lead screw arrangement occupies too much space, making it unsuitable for compact spaces where volume is a constraint. CN113833820A describes a hybrid standard and reverse multi-stage heavy-duty electric cylinder structure, which also uses a parallel structure and occupies too much space. CN116498723A describes a series multi-stage planetary roller lead screw pair structure. This structure increases in size from the inside to the outside according to the transmission sequence. The third-stage lead screw pair is the outermost layer, which is a large-diameter thin-walled structure. This makes it difficult to manufacture, has a large radial dimension, and the connection end with the load is an ultra-large cavity, resulting in weak rigidity when extended.

[0005] In summary, multi-stage hydraulic transmission mechanisms currently suffer from inherent problems such as low sealing reliability and high leakage risk, while multi-stage screw transmission mechanisms have issues with large radial dimensions and weak structural rigidity. Summary of the Invention

[0006] The technical problem solved by this invention is to overcome the shortcomings of the prior art and propose a multi-stage ball screw mechanism to solve the problems of leakage in multi-stage hydraulic transmission seals and the mismatch between the radial dimensions and load-bearing capacity of multi-stage ball screw pairs. This mechanism achieves a large extension stroke and high load-bearing capacity in a small installation space, with adjustable radial dimensions and controllable end output speed ratio.

[0007] The solution of the present invention is: a multi-stage lead screw mechanism, comprising: a first-stage lead screw, a first-stage roller, a first-stage nut, an adapter shaft, a tapered roller bearing, a second-stage nut, a third-stage nut, an angular contact ball bearing, a third-stage roller, a third-stage lead screw, a second guide plate, and a housing; The first-stage lead screw includes an input section and a working section. The input section is connected to a servo motor or reducer and serves as the input for the entire mechanism. The working section is the first cylindrical cavity, which is integrated with the input section and extends into the first-stage nut. The first-stage nut, which is the second cylindrical cavity, is sleeved on the outside of the working section of the first-stage lead screw, forming the first annular cavity in the radial direction; Several primary rollers are evenly distributed circumferentially within the first annular cavity, and each primary roller is threadedly engaged with a primary nut and a primary lead screw to form a primary lead screw pair. The adapter shaft is a third cylindrical cavity, which includes a rod-shaped cavity and a stepped base cavity, which are connected. The rod-shaped cavity extends into the first cylindrical cavity of the first-stage lead screw and is engaged by a spline. The stepped base cavity includes a stepped part and a base part. The stepped part is sleeved inside the first-stage nut and forms a second annular cavity in the radial direction. The base part is radially connected to the second-stage nut. The tapered roller bearing, located in the second annular cavity, supports the rotational motion of the adapter shaft and transmits the axial motion of the primary nut to the adapter shaft. The secondary nut is a fourth cylindrical cavity, which is sleeved on the outside of the primary nut. It includes a first section, a middle section, and a tail section connected in sequence. The inner wall of the first section and the outer wall of the primary nut form a third annular cavity in the radial direction. The inner wall of the middle section and the outer wall of the adapter shaft base are connected by spline engagement. The stepped structure of the tail section is axially fixedly connected to the tertiary nut. Several secondary rollers are evenly distributed circumferentially in the third annular cavity, and each secondary roller is threadedly engaged with the primary nut and the secondary nut to form a secondary lead screw pair; The three-stage nut has a stepped cavity structure, including a base and a stepped cavity; the base is axially fixed to the end of the tail section of the second-stage nut; the stepped cavity and the second guide plate form a fourth annular cavity in the radial direction; The second guide plate is provided with a second rectangular key structure, which cooperates with the rectangular groove of the housing to guide the axial movement of the third-stage nut and the second-stage nut; The angular contact ball bearing, located in the fourth annular cavity, supports the rotation of the third and second stage nuts; The three-stage lead screw has a columnar structure. One end passes through the three-stage nut and extends into the rod-shaped cavity of the adapter shaft, forming a fifth annular cavity radially with the three-stage nut. The other end is located outside the stepped cavity structure of the three-stage nut and is connected to the load. Several tertiary rollers are evenly distributed circumferentially in the fifth annular cavity, and each tertiary roller is threadedly engaged with the tertiary lead screw and the tertiary nut to form a tertiary lead screw pair; the tertiary lead screw pair has the same thread direction as the primary lead screw pair and the opposite thread direction to the secondary lead screw pair. The housing is a cylindrical structure, fitted onto the outside of the secondary nut, forming a sixth annular cavity in the radial direction; the housing is connected to the bearing seat that fixes the primary lead screw.

[0008] Furthermore, the motion mode of the first-stage lead screw pair is as follows: The primary lead screw meshes with several circumferentially distributed primary rollers, converting rotary motion into axial motion of the primary nut. The axial motion speed... (mm / s), where, The thread lead of the first-stage leadscrew. (r / min) represents the input rotational speed of the entire mechanism; The distance that the first-stage roller moves on the first-stage lead screw is the stroke of the first-stage lead screw pair. (mm).

[0009] Furthermore, the motion pattern of the secondary lead screw pair is as follows: The rotary input of the secondary nut is converted into its own axial motion through the planetary motion of several secondary rollers, and the axial motion speed is... (mm / s), where The thread lead of a first-stage nut. The rotational speed of the secondary nut is, and (r / min); The distance the secondary roller moves on the primary nut is the stroke of the secondary lead screw pair. (mm).

[0010] Furthermore, the motion pattern of the aforementioned three-stage lead screw pair is as follows: The three-stage nut converts its rotational motion into axial motion of the three-stage lead screw relative to the three-stage nut through the planetary motion of several three-stage rollers. The axial motion speed is... (mm / s), where, (mm) represents the thread lead of the third-stage lead screw. The rotational speed of the three-stage nut is, and (r / min) The distance that the three-stage rollers move relative to the three-stage lead screw is the stroke of the three-stage lead screw pair. (mm); The total stroke of the multi-stage lead screw machine is: .

[0011] Furthermore, the first-stage nut is internally equipped with a first left internal gear ring and a first right internal gear ring with the same internal tooth phase, and the first left internal gear ring is located on the input side of the mechanism, while the first right internal gear ring is located on the other side; both are connected to the first-stage roller through the internal teeth on the inner wall and the external teeth on the outer wall of the roller.

[0012] Furthermore, the first right internal gear ring is cut into 3 or 4 segments, and each segment has two radially intersecting stop pin holes machined on it. The cutting arc angle θ of each segment must satisfy the following:

[0013] in: For the minor diameter of the thread of a first-grade nut (6), The outer radius of the first right internal gear ring (7) is denoted as .

[0014] Furthermore, the secondary nut is equipped with a second left internal gear ring and a second right internal gear ring with the same internal tooth phase, and the second left internal gear ring is located on the input side of the mechanism, while the second right internal gear ring is located on the other side; both are connected by meshing with the external teeth of the secondary roller through the internal teeth of the inner wall. The cutting and segmentation process for the second right internal gear ring is the same as that for the first left and right gear rings.

[0015] Furthermore, it also includes: a first guide plate and a third guide plate; The first guide plate is axially fixedly connected to the end of the second cylindrical cavity of the first stage nut located on the input side of the mechanism; the first guide plate is provided with a first rectangular key structure, which cooperates with the rectangular groove of the housing to restrict the rotation of the first stage nut and provide guide support; The third guide plate is fixedly connected to the connecting plate structure located on the part of the third-stage lead screw outside the stepped cavity structure of the third-stage nut; the third guide plate is provided with a third rectangular key structure, which cooperates with the rectangular groove of the housing to limit the rotation of the third-stage lead screw and guide the axial movement.

[0016] Furthermore, a first slider is provided inside the first cylindrical cavity of the first-stage lead screw; one end of the first slider extends into the rod-shaped cavity of the adapter shaft and is fixedly connected to the rod-shaped cavity through a threaded connection structure; the first slider moves axially along the inner cavity of the first-stage lead screw under the drive of the adapter shaft and plays a guiding and supporting role for the adapter shaft.

[0017] Furthermore, a second slider is provided inside the rod-shaped cavity of the adapter shaft; the second slider is fixedly connected to the three-stage lead screw, and moves axially along the rod-shaped cavity of the adapter shaft under the drive of the three-stage lead screw, and plays a guiding and supporting role for the three-stage lead screw. The advantages of this invention compared to the prior art are: (1) The three-stage lead screw pairs of this invention all adopt a planetary roller transmission design. Compared with multi-stage ball screw pairs, they have the structural characteristics of multi-point contact and small lead, and can be designed to have a stronger load-bearing capacity and a larger reduction ratio under the same size and specifications. Moreover, the power transmission between the first and second stages of this invention is realized through a spline structure, and the second and third stages are connected by screws to have a common power input, which can solve the problems of unstable power transmission and large loss in the three-stage linkage process, and has high reliability.

[0018] (2) The three-stage transmission of the present invention adopts a series structure, which has the advantages of compact structure and small space size compared with the parallel structure. In addition, the outer envelope radial dimension of the three-stage transmission structure of the present invention is adjustable. By increasing the number of external threads of the first-stage and second-stage lead screws, and then adjusting the diameter ratio of the rollers and lead screws according to the kinematic relationship of the planetary roller lead screw, the diameter of the rollers can be reduced, the number of circumferential rollers can be increased, and the radial space dimension of the entire transmission structure can be reduced.

[0019] (3) The present invention designs guide disc structures that are fixed by screws for the first-stage nut, second-stage nut and third-stage lead screw. The guide discs are all fitted with the housing through sliding keyways, which not only guide the axial movement of each stage, but also support the structure of each stage when it extends axially, thus solving the problem of weak structural rigidity when the multi-stage structure extends in series. In addition, a slider structure is designed at the retracted end of the third-stage lead screw, which, together with the guide disc, strengthens the support for the final stage transmission, effectively avoiding the problem of end-stage load jamming, improving operational reliability and end-stage output accuracy. Attached Figure Description

[0020] Figure 1 This is a cross-sectional view of a multi-stage planetary roller screw assembly according to an embodiment of the present invention; Figure 2 This is a schematic diagram of the internal gear ring according to an embodiment of the present invention; Figure 3 This is an external view of the adapter shaft according to an embodiment of the present invention; Figure 4 This is an external view of the third-stage nut according to an embodiment of the present invention; Figure 5 This is an external view of the second guide disk according to an embodiment of the present invention; Figure 6 This is a diagram showing the external shape of the third-stage lead screw according to an embodiment of the present invention. Detailed Implementation

[0021] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0022] like Figure 1 As shown, a multi-stage planetary roller screw transmission mechanism includes a first-stage screw 1, a first-stage roller 2, a first left flange 3, a first wire locking ring 4, a first left internal gear ring 5, a first-stage nut 6, a first right internal gear ring 7, a first right flange 8, a first slider 9, a transition shaft 10, a round nut 11, a tapered roller bearing 12, a bearing cap 13, a second-stage nut 14, a third-stage nut 15, a third internal gear ring 16, a third flange 17, a third wire locking ring 18, a third guide plate 19, a round nut 20, a bearing outer ring cap 21, an angular contact ball bearing 22, a second guide plate 23, a third-stage roller 24, a third-stage screw 25, a second slider 26, a second right internal gear ring 27, a second right flange 28, a second-stage roller 29, a second left internal gear ring 30, a second left flange 31, a second wire locking ring 32, a first guide plate 33, a housing 34, and several connecting screws.

[0023] The first-stage lead screw 1 is mounted on a bearing housing via two angular contact bearings and a locking nut at the input end. Its left end is directly connected to the motor or a reducer via a spline or key, serving as the input to the entire multi-stage transmission mechanism. The input speed is... (r / min). The first-stage lead screw 1 engages with multiple circumferentially distributed first-stage rollers 2, and transmits the motor output force and speed to the first-stage nut 6 through the planetary motion of the first-stage rollers 1, thereby driving the first-stage nut 6 to move axially.

[0024] The primary nut 6 is axially fixed to the adapter shaft 10 via the tapered roller bearing 12 and bearing cap 13 at its right end, and drives the adapter shaft 10 to move axially. The primary lead screw 1 has internal splined teeth machined inside, which mesh with the external splined teeth on the adapter shaft 10, driving the adapter shaft 10 to rotate. The other end of the adapter shaft 10 also has external splined teeth machined, which mesh with the internal teeth on the secondary nut 14, driving the secondary nut 14 to rotate. The outer ring of the primary nut 6 has multi-start threads, and it also acts as the secondary lead screw, driving the secondary nut 14 to move axially. The secondary lead screw pair has threads with the opposite direction of rotation to the primary lead screw pair. The secondary nut 14 rotates and pushes itself out axially. The secondary nut 14 drives the tertiary nut 15 to move axially and rotate. Similarly, the tertiary nut 15 converts the rotational motion into the axial motion of the tertiary lead screw, driving the end load of the tertiary lead screw 25 to extend and retract axially.

[0025] The outer ring of the first-stage lead screw is machined with a multi-start thread, and its lead is... (mm), and engages with multiple circumferentially distributed single-head primary rollers 2 via threaded transmission, converting rotary motion into axial motion of a primary nut 6, the speed of which is... (mm / s), the distance that the first-stage roller 2 can move on the first-stage lead screw 1 is the stroke of the first-stage lead screw pair. (mm).

[0026] To ensure that the multiple primary rollers 2 have a stable revolution-rotation ratio, a first left internal gear ring 5 and a first right internal gear ring 7 with the same phase are installed on the primary nut 6. To ensure that the first right internal gear ring 7 can smoothly pass through the minor diameter of the primary nut 6 and be installed in the designated position, the first right internal gear ring 7 needs to be cut into segments, and the cutting arc angle θ of each segment must satisfy the following:

[0027] in: For a Class I nut, the thread minor diameter is 6. This refers to the outer radius of the first right internal gear ring 7. Depending on the size of the lead screw assembly, it can generally be divided into 3 or 4 segments; this embodiment uses 4 segments, such as... Figure 2 As shown, each toothed ring has two radially intersecting anti-falling pin holes machined on it to ensure that each inner toothed ring will not fall off under gravity. Additionally, a locating pin hole 7-2 needs to be machined on the first toothed ring 7-1 to ensure that it has the same internal tooth phase as the first left inner toothed ring 5. At the same time, the outer diameter of the first right flange 8 must be smaller than the minor diameter of the thread of the first-stage nut 6. This makes it easy to install.

[0028] Meanwhile, the first guide plate 33 is connected to the first stage nut 6 by screws. The rectangular key structure on it can cooperate with the rectangular groove of the housing 34 to restrict the rotation of the first stage nut 6 and provide guiding support.

[0029] Furthermore, splined internal teeth are machined at the end of the inner cavity of the first-stage lead screw 1, which engage with the external teeth on the adapter shaft 10 with a small clearance spline to transmit the output torque of the motor to the adapter shaft 10.

[0030] In addition to the long external spline 10-1 structure machined on the adapter shaft 10 to engage with the internal spline of the primary lead screw 1, it also has a short external spline structure 10-2 that engages with the secondary nut 14 via spline, transmitting torque to the secondary nut and causing it to rotate. The rotational speed... (r / min). Simultaneously machined with positioning holes and threaded connection structure 10-3, responsible for connecting the first slider 9 and ensuring the coaxiality of the first slider 9 and the adapter shaft 10, such as... Figure 3 As shown. The first slider 9 moves axially within the cavity of the first-stage lead screw 1 under the drive of the adapter shaft 10, and plays a guiding and supporting role for the adapter shaft 10.

[0031] The adapter shaft 10 has a bearing mounting surface 10-4 machined on it, and a double-row tapered roller bearing 12 is mounted on it. The inner ring of the bearing is blocked by a locking nut 11 and a shaft shoulder, and the outer ring is blocked by a first-stage nut 6 and a bearing cap 13. The bearing supports the rotational movement of the adapter shaft 10 and transmits the axial movement of the first-stage nut 6 to the adapter shaft 10.

[0032] Furthermore, the outer surface of the first-stage nut 6 is machined with multi-start external threads, with a lead of... (mm), the primary nut 6 also functions as the secondary lead screw. The motion of the secondary lead screw pair is as follows: because the degree of freedom of the secondary lead screw relative to the secondary nut 14 is constrained, the rotational input of the secondary nut 14 is converted into its own axial motion through the planetary motion of multiple secondary rollers 29, with a motion speed of... (mm / s), the distance that the secondary roller 29 can move on the primary nut 6 is the stroke of the secondary lead screw pair. (mm). In order to ensure that the secondary lead screw pair and the primary lead screw pair can extend and retract synchronously, the thread direction of the outer surface of the secondary nut 14, the secondary roller 29 and the primary nut 6 is opposite to that of the primary lead screw pair.

[0033] Similarly, to ensure that the multiple secondary rollers 29 have a stable revolution-rotation ratio, a second left internal gear ring 30 and a second right internal gear ring 27 with the same phase are installed on the secondary nut 14. The principle for splitting the second right internal gear ring 27 is the same as that for the first left and right gear rings 7. At the same time, the outer diameter of the second right flange 28 must be smaller than the minor diameter of the thread of the secondary nut 14. This makes it easy to install.

[0034] The third-stage nut 15 is machined with an outer flange structure 15-1, which is fixed to the second-stage nut 14 through a hole-shaft fit and screws. Its rotation speed (r / min), while simultaneously adjusting the speed according to the secondary nut 14. Axial movement. It is machined with an end face boss 15-2, and the boss's circular surface is evenly distributed with pin holes 15-3 to facilitate the installation of the locating pin of the third internal gear ring 16 on the left side; it is also machined with a bearing mounting surface 15-4 and external threads 15-5, such as... Figure 4 As shown, a back-to-back angular contact ball bearing 22 is installed, which supports the rotation of the third-stage nut 15 and the second-stage nut 14. The inner ring of the bearing is fixed by the shaft shoulder and the locking nut 20, and the outer ring of the bearing is fastened with screws by the outer ring cover 21 and the second guide plate 23.

[0035] The second guide plate 23 is machined with a bearing shoulder 22-1 and a guide rectangular key 22-2. The rectangular key can mate with the rectangular groove of the housing 34, guiding the axial movement of the third-stage nut 15 and the second-stage nut 14. Figure 5 As shown.

[0036] The three-stage nut 15 converts its rotational motion into axial motion of the three-stage lead screw 25 relative to the three-stage nut 15 through the planetary motion of multiple three-stage rollers 24. The thread lead of the three-stage lead screw 25 is... (mm), then the axial speed of the three-stage lead screw 25 is (mm / s), the distance that the third-stage roller 24 can move relative to the third-stage screw 25 is the stroke of the third-stage screw pair. (mm).

[0037] Three-stage lead screw 25 Figure 6 As shown, it is machined with a lead of The external thread structure 25-1 (mm) has a square groove and a threaded hole 25-2 machined on its left end. The square groove engages with the square protrusion on the second slider 26. The threaded hole connects the third-stage lead screw 25 and the second slider 26. The second slider 26 moves axially within the cavity of the adapter shaft 10 under the drive of the third-stage lead screw 25, and provides guidance and support for the third-stage lead screw 25. A connecting plate structure 25-3 is machined on the third-stage lead screw 25, which is fixed to the third guide plate 19 by screws.

[0038] Furthermore, the third guide plate 19 is machined with two rectangular key structures, which cooperate with the guide groove of the housing 34 to restrict the rotational degree of freedom of the three-stage lead screw 25 and guide its axial movement.

[0039] Similarly, in order to ensure the extension and retraction of the third-stage lead screw pair and the synchronization of the first two stages, the thread direction on the third-stage lead screw 25, the third-stage roller 24 and the third-stage nut 15 is the same as that of the first-stage lead screw pair.

[0040] Based on the nesting relationship of the three-stage planetary roller screw pair, the axial velocity of the end output load can be derived as follows: (mm / s), the total stroke of this multi-stage transmission mechanism is: .

[0041] Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make possible changes and modifications to the technical solutions of the present invention by utilizing the methods and techniques disclosed above without departing from the spirit and scope of the present invention. Therefore, any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solutions of the present invention shall fall within the protection scope of the technical solutions of the present invention.

Claims

1. A multi-stage lead screw mechanism, characterized in that, include: First-stage lead screw (1), first-stage roller (2), first-stage nut (6), adapter shaft (10), tapered roller bearing (12), second-stage nut (14), third-stage nut (15), angular contact ball bearing (22), third-stage roller (24), third-stage lead screw (25), second guide plate (23), housing (34); The first-stage lead screw (1) includes an input section and a working section; the input section is connected to a servo motor or reducer and serves as the input for the entire mechanism; the working section is the first cylindrical cavity, which is integrated with the input section and extends into the first-stage nut (6); The first-stage nut (6) is a second cylindrical cavity, which is sleeved on the outside of the working section of the first-stage lead screw (1) to form a first annular cavity in the radial direction; Several primary rollers (2) are evenly distributed in the first annular cavity along the circumference, and each primary roller (2) is threadedly engaged with the primary nut (6) and the primary lead screw (1) to form a primary lead screw pair; The adapter shaft (10) is a third cylindrical cavity, including a rod-shaped cavity and a stepped base cavity, which are connected. The rod-shaped cavity extends into the first cylindrical cavity of the first-stage screw (1) and is engaged by a spline. The stepped base cavity includes a stepped part and a base part. The stepped part is sleeved on the inner side of the first-stage nut (6) and forms a second annular cavity in the radial direction. The base part is radially connected to the second-stage nut (14). The tapered roller bearing (12) is located in the second annular cavity, supports the rotational motion of the transfer shaft (10), and transmits the axial motion of the first-stage nut (6) to the transfer shaft (10). The secondary nut (14) is the fourth cylindrical cavity, which is sleeved on the outside of the primary nut (6). It includes the first section, the middle section and the tail section connected in sequence. The inner wall of the first section and the outer wall of the primary nut (6) form a third annular cavity in the radial direction. The inner wall of the middle section and the outer wall of the base of the adapter shaft (10) are connected by spline meshing. The stepped structure of the tail section is axially fixedly connected to the tertiary nut (15). Several secondary rollers (29) are evenly distributed in the third annular cavity along the circumference, and each secondary roller (29) is threadedly engaged with the primary nut (6) and the secondary nut (14) to form a secondary lead screw pair; The three-stage nut (15) has a stepped cavity structure, including a base and a stepped cavity; The base is axially fixed to the tail end of the secondary nut (14); the stepped cavity and the second guide plate (23) form a fourth annular cavity in the radial direction; The second guide plate (23) is provided with a second rectangular key structure, which cooperates with the rectangular groove of the housing (34) to guide the axial movement of the third-stage nut (15) and the second-stage nut (14); An angular contact ball bearing (22) is located in the fourth annular cavity and supports the rotation of the third-stage nut (15) and the second-stage nut (14). The three-stage lead screw (25) has a columnar structure. One end passes through the three-stage nut (15) and extends into the rod-shaped cavity of the adapter shaft (10), forming a fifth annular cavity radially with the three-stage nut (15). The other end is located outside the stepped cavity structure of the three-stage nut (15), and the end is connected to the load. Several tertiary rollers (24) are evenly distributed in the fifth annular cavity along the circumference, and each tertiary roller (24) is threadedly engaged with the tertiary screw (25) and the tertiary nut (15) to form a tertiary screw pair; the tertiary screw pair has the same thread direction as the primary screw pair and the opposite thread direction to the secondary screw pair. The housing (34) is a cylindrical structure, which is sleeved on the outside of the secondary nut (14) and forms a sixth annular cavity in the radial direction; the housing (34) is connected to the bearing seat that fixes the primary lead screw (1).

2. The multi-stage lead screw mechanism according to claim 1, characterized in that, The motion mode of the first-stage lead screw pair is as follows: The primary lead screw (1) meshes with several circumferentially distributed primary rollers (2) to transmit rotational motion, which is then converted into axial motion of the primary nut (6). The axial motion speed is... (mm / s), where, The thread lead of the first-stage lead screw (1) is... (r / min) represents the input rotational speed of the entire mechanism; The distance that the first-stage roller (2) moves on the first-stage lead screw (1) is the stroke of the first-stage lead screw pair. (mm).

3. A multi-stage lead screw mechanism according to claim 2, characterized in that, The motion pattern of the second-stage lead screw pair is as follows: The rotary input of the secondary nut (14) is converted into its own axial motion through the planetary motion of several secondary rollers (29), and the axial motion speed is (mm / s), where For the thread lead of the first-stage nut (6), The rotational speed of the secondary nut (14) is, and (r / min); The distance that the secondary roller (29) moves on the primary nut (6) is the stroke of the secondary lead screw pair. (mm).

4. A multi-stage lead screw mechanism according to claim 3, characterized in that, The motion pattern of the three-stage lead screw pair is as follows: The three-stage nut (15) converts its rotational motion into the axial motion of the three-stage lead screw (25) relative to the three-stage nut (15) through the planetary motion of several three-stage rollers (24). The axial motion speed is... (mm / s), where, (mm) represents the thread lead of the three-stage lead screw (25). The rotational speed of the three-stage nut (15) is, and (r / min); The distance that the third-stage roller (24) moves relative to the third-stage lead screw (25) is the stroke of the third-stage lead screw pair. (mm); The total stroke of the multi-stage lead screw machine is: .

5. A multi-stage lead screw mechanism according to claim 1, characterized in that, The first-stage nut (6) is equipped with a first left internal gear ring (5) and a first right internal gear ring (7) with the same internal tooth phase. The first left internal gear ring (5) is located on the input side of the mechanism, and the first right internal gear ring (7) is located on the other side. Both are connected to the outer teeth of the first-stage roller (2) by meshing with the inner teeth of the inner wall.

6. A multi-stage lead screw mechanism according to claim 5, characterized in that, The first right internal gear ring (7) is divided into 3 or 4 segments by cutting. Each segment of the gear ring is machined with two radial stop pin holes that intersect at an angle, and the cutting arc angle θ of each segment satisfies: in: For the minor diameter of the thread of a first-grade nut (6), The outer radius of the first right internal gear ring (7) is denoted as .

7. A multi-stage lead screw mechanism according to claim 6, characterized in that, The secondary nut (14) is equipped with a second left internal gear ring (30) and a second right internal gear ring (27) with the same internal tooth phase. The second left internal gear ring (30) is located on the input side of the mechanism, and the second right internal gear ring (27) is located on the other side. Both are connected to the secondary roller (29) by meshing with the outer teeth of the secondary roller (29) through the inner teeth of the inner wall. The cutting and segmentation process of the second right internal gear ring (27) is the same as that of the first left and right gear rings (7).

8. A multi-stage lead screw mechanism according to claim 1, characterized in that, Also includes: First guide plate (33), third guide plate (19); The first guide plate (33) is axially fixed to the end of the second cylindrical cavity of the first stage nut (6) located on the input side of the mechanism; the first guide plate (33) is provided with a first rectangular key structure, which cooperates with the rectangular groove of the housing (34) to restrict the rotation of the first stage nut (6) and provide guide support; The third guide plate (19) is fixedly connected to the connecting plate structure (25-3) set on the part of the third-stage screw (25) outside the stepped cavity structure of the third-stage nut (15); the third guide plate (19) is provided with a third rectangular key structure, which cooperates with the rectangular groove of the housing (34) to limit the rotation of the third-stage screw (25) and guide the axial movement.

9. A multi-stage lead screw mechanism according to claim 1, characterized in that, The first cylindrical cavity of the first-stage screw (1) is provided with a first slider (9); one end of the first slider (9) extends into the rod-shaped cavity of the adapter shaft (10) and is fixedly connected to the rod-shaped cavity through a threaded connection structure (10-3); the first slider (9) moves axially along the inner cavity of the first-stage screw (1) under the drive of the adapter shaft (10) and plays a guiding and supporting role for the adapter shaft (10).

10. A multi-stage lead screw mechanism according to claim 1, characterized in that, The rod-shaped cavity of the adapter shaft (10) is provided with a second slider (26); the second slider (26) is fixedly connected to the third-stage lead screw (25), and moves axially along the rod-shaped cavity of the adapter shaft (10) under the drive of the third-stage lead screw (25), and plays a guiding and supporting role for the third-stage lead screw (25).

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