A variable reduction ratio step-by-step telescopic screw transmission mechanism

Abstract

The present invention provides a variable reduction ratio step-by-step telescopic lead screw transmission mechanism, comprising at least two lead screw pairs, each lead screw pair comprising a lead screw and a nut mounted on the lead screw, the lead screw being a hollow structure, and a tubular output portion coaxial with the nut being fixedly connected to the outside of the nut; the multi-stage lead screw pairs are coaxially and nestedly assembled, the next-stage lead screw is assembled on the previous-stage nut through a bearing, the next-stage nut output portion is located inside the previous-stage nut output portion, and the multi-stage nut output portion is provided with an axial guide structure; the lead screws of the adjacent two-stage lead screw pairs are transmitted through a connecting mechanism, so that the multi-stage lead screw pairs are telescoped step by step. The entire transmission mechanism forms a variable reduction ratio structure, and by adopting a variable reduction ratio and step-by-step telescoping, the power density and rigidity of the electric cylinder are improved, the volume and weight of the electric cylinder are reduced, and the efficiency is improved. The transmission mechanism is suitable for electric servo mechanisms such as high-load and large-stroke electric cylinders, and is particularly suitable for heavy-load erecting electric cylinders with a large load variation range within the working stroke.

Description

Technical Field

[0001] The present invention belongs to the technical field of mechanical transmission, and particularly relates to a variable reduction ratio step-by-step telescopic lead screw transmission mechanism. Background Art

[0002] With the development of fully electric weaponry and equipment, electric cylinders are gradually replacing traditional hydraulic cylinders and being applied to erection devices of special vehicles such as launch vehicles. In order to meet the requirements of rapid vertical launch of on-vehicle heavy missiles, electric cylinders are required to have characteristics such as large thrust, long stroke, high stiffness, light weight, and small size. During the erection process, the missile moves from a nearly horizontal state to a vertical state, and the load borne by the electric cylinder varies within a very large range. Existing erection electric cylinders all adopt a ball screw transmission form with a fixed reduction ratio and synchronous telescoping. In order to balance the output force and output speed of the electric cylinder, the fixed reduction ratio transmission mechanism results in an excessive power of the servo motor, which in turn causes problems such as large volume, heavy weight, and non-maximized application of the efficiency of the electric cylinder. At the same time, the synchronous telescoping transmission mechanism makes the stiffness change of the electric cylinder within the full stroke relatively small, resulting in non-optimal distribution of the stiffness of the transmission mechanism under the premise of limited weight, causing a large deformation of the electric cylinder when bearing a large load at the initial stage of erection, which is not conducive to fast and stable erection motion control. Summary of the Invention

[0003] Aiming at the technical problems of large volume, heavy weight, unreasonable stiffness distribution, and low efficiency of the erection electric cylinder caused by a constant reduction ratio and multi-stage synchronous telescoping in the existing transmission mechanism, the present invention provides a variable reduction ratio step-by-step telescopic lead screw transmission mechanism. Through variable reduction ratio and step-by-step telescopic design, the power density and stiffness of the electric cylinder are improved, the volume and weight of the electric cylinder are reduced, the efficiency is increased, and it is applicable to electric servo mechanisms such as electric cylinders with high load and large stroke, and is particularly applicable to heavy-duty erection electric cylinders with a large load change range within the working stroke.

[0004] The technical solution adopted by the present invention to solve the above technical problems is as follows:

[0005] A variable reduction ratio step-by-step telescopic lead screw transmission mechanism includes at least two stages of lead screw pairs. Each stage of lead screw pair includes a lead screw and a nut mounted on the lead screw. The lead screw is of a hollow structure, and a tubular output part coaxial with the nut is fixedly connected to the outside of the nut; multiple stages of lead screw pairs are coaxially and nestedly assembled. The lead screw of the next stage is assembled on the nut of the previous stage through a bearing. The output part of the nut of the next stage is located inside the output part of the nut of the previous stage. A guiding structure along the axial direction is provided on the output parts of multiple nuts; the lead screws between adjacent two stages of lead screw pairs are driven by a connecting mechanism, so that multiple stages of lead screw pairs are telescoped step by step.

[0006] Further, the connecting mechanism includes a permanent magnet, an input rod, and a limiting structure; the permanent magnet is arranged in the inner cavity of the first-stage lead screw or the inner cavity of the input rod of the connecting mechanism assembled with the previous-stage lead screw pair; the limiting structure includes a limiting part A and a limiting part B, and the limiting part A is arranged at one end of the next-stage lead screw; one end of the input rod passes through the limiting part A and extends into the inner cavity of the first-stage lead screw or the inner cavity of the previous-stage input rod to adsorb with the permanent magnet, and a limiting part B matching the limiting part A is arranged at the other end of the input rod; an axial guiding structure is arranged between the input rod and the inner cavity of the first-stage lead screw or between the input rod and the inner cavity of the previous-stage input rod.

[0007] Further, the limiting part A is a connecting seat, the connecting seat includes a positioning ring and a plurality of female blocks uniformly distributed along the inner circumferential surface of the positioning ring, the limiting part B is a plurality of male blocks arranged on the outer edge of one end of the input rod, and the opposite surfaces of the female blocks and the male blocks adopt spiral curved surfaces.

[0008] Further, the axial guiding structure of the input rod is a convex key arranged on the outer surface, and an axial key groove is arranged in a matching manner in the inner cavity of the first-stage lead screw or the inner cavity of the previous-stage input rod; the input rod is made of ferromagnetic material.

[0009] Further, the guiding structure of the nut output part is a guiding rod, at least one guiding rod is arranged, one end of each guiding rod is fixedly connected to the servo mechanism housing, and the other end passes through a round hole on the end surface of each nut close to the servo mechanism housing, and the guiding rod and the round hole form a sliding pair; adjacent nut output parts form a sliding pair along the axis.

[0010] Further, for any two adjacent lead screw pairs, the next-stage lead screw is assembled on the previous-stage nut through deep groove ball bearings and thrust ball bearings; one end of the next-stage lead screw includes a connecting shaft, the connecting shaft includes a first cavity section and a second cavity section, and the inner diameter of the second cavity section close to the end surface is larger than that of the first cavity section; the previous-stage nut is provided with a step with a small outer diameter close to the end surface; the inner ring of the deep groove ball bearing is fixed on the step of the previous-stage nut, and the outer ring is fixed in the first cavity section of the next-stage lead screw; the shaft ring of the thrust ball bearing is fixed on the previous-stage nut, and the seat ring is fixed in the second cavity section of the next-stage lead screw.

[0011] Further, an inner baffle is arranged on the previous-stage nut close to the end surface of the deep groove ball bearing, an L-shaped outer baffle is arranged in the second cavity section of the next-stage lead screw, and the seat ring of the thrust ball bearing is fixed in the inner cavity of the L-shaped outer baffle.

[0012] Further, the lead screw pair is one of a ball screw, a planetary roller screw, and a trapezoidal screw.

[0013] Furthermore, the transmission mechanism includes a three-stage lead screw pair. A first-stage connection mechanism is provided between the first-stage lead screw and the second-stage lead screw, and a second-stage connection mechanism is provided between the second-stage lead screw and the third-stage lead screw; the maximum extended length L of the transmission mechanism 总 = L 1 + L 2 + L 3 , where

[0014] L 1 = l c1

[0015]

[0016]

[0017] where P h1 , P h2 , P h3 are the reduction ratios of the first-stage lead screw pair, the second-stage lead screw pair, and the third-stage lead screw pair respectively, and l s3 is the stroke of the third-stage lead screw pair; l c1 is the axial distance between the mating surfaces of the male block and the female block in the first-stage connection mechanism, and l c2 is the axial distance between the mating surfaces of the male block and the female block in the second-stage connection mechanism.

[0018] Furthermore, the parameters of the transmission mechanism satisfy

[0019]

[0020]

[0021]

[0022]

[0023] Δ DX ≥ L 总

[0024] where l LJ1 represents the maximum axial length of the long axis of the input rod of the first-stage connection mechanism embedded in the inner cavity of the first-stage lead screw, and Δ LJ1 represents the minimum axial length of the long axis of the input rod of the first-stage connection mechanism embedded in the inner cavity of the first-stage lead screw; l LJ2 represents the maximum axial length of the long axis of the input rod of the second-stage connection mechanism embedded in the inner cavity of the input rod of the first-stage connection mechanism, and Δ LJ2 represents the minimum axial length of the long axis of the input rod of the second-stage connection mechanism embedded in the inner cavity of the input rod of the first-stage connection mechanism, and Δ DX is the effective movement length of the guide rod in the third-stage nut along the axial direction;

[0025] Δ LJ1 The value is not less than the diameter value of the major axis of the input rod of the primary connection mechanism; Δ LJ2 The value is not less than the diameter value of the major axis of the input rod of the secondary connection mechanism.

[0026] Advantages of the present invention compared with the prior art:

[0027] The present invention provides a variable reduction ratio step-by-step telescopic ball screw drive mechanism, and the advantages and beneficial effects are as follows:

[0028] 1) Based on the principle of permanent magnet adsorption connection, through the spiral surface connection form between the male and female blocks of the connection mechanism, it realizes the time-sharing and successive driving of multiple screw pairs, with a simple structure and high reliability;

[0029] 2) Adopting the multi-stage screw step-by-step telescopic motion form, it has the transmission characteristics of variable reduction ratio in different motion stages. In the application of electric cylinders, the stiffness of the drive mechanism can be optimally distributed according to the load conditions, the stiffness of the electric cylinder is increased by more than 20%, and the power density is increased by more than 10%, effectively solving the difficult problem of the drive design of heavy-duty erection electric cylinders with a large load change range within the working stroke;

[0030] 3) Under the same working conditions, the variable reduction ratio drive reduces the requirement for the speed range of the drive motor, enabling a low-speed high-torque motor to directly drive the drive mechanism to achieve the output of the electric cylinder, eliminating the transmission links such as intermediate gears, and simplifying the structure of the electric cylinder;

[0031] 4) Applicable to the design of variable reduction ratio step-by-step telescopic drive mechanisms of different transmission types such as ball screws, planetary roller screws, and trapezoidal screws, with a wide range of applications;

[0032] 5) Applicable to the design of step-by-step telescopic screw-type drive mechanisms with two or more levels, and the number of telescopic levels is not limited, with strong versatility. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The included drawings are used to provide a further understanding of the embodiments of the present invention, which form a part of the specification, are used to illustrate the embodiments of the present invention, and together with the written description are used to explain the principles of the present invention. Obviously, the drawings in the following description are only some embodiments of the present invention, and those of ordinary skill in the art can obtain other drawings based on these drawings without creative efforts.

[0034] Figure 1 is an axonometric view of the variable reduction ratio step-by-step telescopic ball screw drive mechanism provided by a specific embodiment of the present invention;

[0035] Figure 2 is an axonometric sectional view of the variable reduction ratio step-by-step telescopic ball screw drive mechanism provided by a specific embodiment of the present invention;

[0036] Figure 3 is an axonometric sectional view of the first-level lead screw pair provided by a specific embodiment of the present invention;

[0037] Figure 4 is an axonometric sectional view of the second-level lead screw pair provided by a specific embodiment of the present invention;

[0038] Figure 5 is an axonometric sectional view of the third-level lead screw pair provided by a specific embodiment of the present invention;

[0039] Figure 6 is a partial sectional view of the transmission mechanism provided by a specific embodiment of the present invention;

[0040] Figure 7 is an axonometric view of the first-level connection mechanism provided by a specific embodiment of the present invention. Figure (a) is a left axonometric view, and Figure (b) is a right axonometric view;

[0041] Figure 8 is an external view of the first-level connection seat provided by a specific embodiment of the present invention;

[0042] Figure 9 is an axonometric view of the second-level connection mechanism provided by a specific embodiment of the present invention;

[0043] Figure 10 is an external view of the second-level connection seat provided by a specific embodiment of the present invention;

[0044] Figure 11 is a half-sectional view of the transmission mechanism provided by a specific embodiment of the present invention.

[0045] Among them, the above-mentioned drawings include the following reference numerals:

[0046] 1. First-level lead screw pair, 2. Second-level lead screw pair, 3. Third-level lead screw pair, 4. Guide rod, 4-1. Long rod, 4-2. Base, 5. First-level connection mechanism, 6. Second-level connection mechanism, 7. First-level lead screw, 7-1. Keyway, 7-2. Multi-threaded spiral raceway, 7-3. Inner cavity, 8. First-level nut, 8-1. Multi-threaded spiral raceway, 8-2. Step, 8-3. Shaft portion, 8-4. Outer side of the output portion, 8-5. Inner side of the output portion, 9. First-level ball, 10. Second-level lead screw, 10-1. Multi-threaded spiral raceway, 10-2. First inner cavity, 10-3. Second inner cavity, 11. Second-level nut, 11-1. Multi-threaded spiral raceway, 11-2. Step, 11-3. Shaft portion, 11-4. Outer side of the output portion, 11-5. Inner side of the output portion, 12. Second-level ball, 13. First deep groove ball bearing, 13-1. Inner ring, 13-2. Outer ring, 14. First inner baffle, 15. First outer baffle, 15-1. Inner cavity, 16. First thrust ball bearing, 16-1. Axial ring, 16-2. Seat ring, 17. Third-level lead screw, 17-1. Multi-threaded spiral raceway, 17-2. Third inner cavity, 17-3. Fourth inner cavity, 18. Third-level nut, 18-1. Multi-threaded spiral raceway, 18-2. Outer side of the output portion, 19. Third-level ball, 20. Second deep groove ball bearing, 20-1. Inner ring, 20-2. Outer ring, 21. Second inner baffle, 22. Second outer baffle, 22-1. Inner cavity, 23. Second thrust ball bearing, 23-1. Axial ring, 23-2. Seat ring, 24. Servo mechanism housing, 25. Round hole, 26. First-level permanent magnet, 27. First-level connection seat, 27-1. Positioning ring, 27-2. First-level female block, 28. First-level input rod, 28-1. Long shaft, 28-2. Convex key, 28-3. First-level male block, 28-4. Inner cavity, 28-5. Keyway, 29. Second-level permanent magnet, 30. Second-level connection seat, 30-1. Positioning ring, 30-2. Second-level female block, 31. Second-level input rod, 31-1. Long shaft, 31-2. Convex key, 31-3. Second-level male block. Detailed implementation mode

[0047] The following will detail the specific embodiments of the present invention. In the following description, for purposes of explanation rather than limitation, specific details are set forth to facilitate a comprehensive understanding of the present invention. However, it will be apparent to those skilled in the art that the present invention may also be practiced in other embodiments without these specific details.

[0048] It should be noted here that, in order to avoid obscuring the present invention with unnecessary details, only the device structures and / or processing steps closely related to the solution of the present invention are shown in the drawings, while other details less related to the present invention are omitted.

[0049] The present invention provides a variable reduction ratio step-by-step telescopic lead screw drive mechanism, which includes at least two levels of lead screw pairs. Each level of lead screw pair includes a lead screw and a nut mounted on the lead screw. The lead screw is of a hollow structure, and a tubular output part coaxial with the nut is fixedly connected to the outside of the nut. The multi-level lead screw pairs are coaxially and nestedly assembled. The lead screw of the next-level lead screw pair is assembled on the nut of the previous-level lead screw pair through a bearing. The nut output part of the next-level lead screw pair is located inside the nut output part of the previous-level lead screw pair. A guiding structure along the axial direction is provided for the multi-level nut output parts. The lead screws between adjacent two levels of lead screw pairs are driven through a connecting mechanism, and the rotation of the lead screw of the previous-level lead screw pair is transmitted to the lead screw of the next-level lead screw pair, so that the multi-level lead screw pairs are telescoped step by step. The entire drive mechanism forms a variable reduction ratio structure. The drive mechanism adopts a variable reduction ratio and step-by-step telescoping. For the same drive mechanism, the variable reduction ratio can increase the load change range, and the step-by-step telescoping can reasonably distribute the stiffness of each level of lead screw pair, thereby improving the power density and stiffness of the electric cylinder, and is applicable to electric servo mechanisms such as electric cylinders with high load and large stroke, and is particularly applicable to heavy-duty erection electric cylinders with a large load change range within the working stroke.

[0050] Further, in order to realize the reliable time-sharing and sequential driving and telescoping of the multi-level lead screw pairs, a connecting mechanism is designed, which includes a permanent magnet, an input rod, and a limiting structure. For two adjacent levels of lead screw pairs, the permanent magnet is arranged at the front end of the inner cavity of the lead screw of the first-level lead screw pair or at the front end of the inner cavity of the input rod of the connecting mechanism assembled with the previous-level lead screw pair. The limiting structure includes a limiting part A and a limiting part B. The limiting part A is arranged at the rear end of the lead screw of the next-level lead screw pair away from the permanent magnet. One end of the input rod passes through the limiting part A and extends into the inner cavity of the first-level lead screw or the inner cavity of the previous input rod to be magnetically adsorbed to the permanent magnet. The other end of the input rod is provided with a limiting part B matching the limiting part A. A guiding structure along the axial direction is arranged in a matching manner between the input rod and the inner cavity of the first-level lead screw or the inner cavity of the previous input rod. The connecting mechanism realizes the rotational transmission between the lead screws through magnetic adsorption and the cooperation of the limiting parts. At the same time, after the limiting parts are assembled, the input rod can perform linear displacement along with the linear movement of the next-level lead screw pair. The connecting rod mechanism realizes the time-sharing and sequential driving of the multi-level lead screw pairs, and has a simple structure and high reliability.

[0051] Further, the limiting part A is a connecting seat, the connecting seat includes a positioning ring and a plurality of female blocks uniformly distributed along the inner circumferential surface of the ring, and the limiting part B is a plurality of male blocks arranged on the outer edge of one end of the input rod. The opposite surfaces of the female blocks and the male blocks adopt spiral curved surfaces, which are convenient for the female blocks and the male blocks to be assembled during rotation.

[0052] Further, the guiding structure arranged along the axial direction of the nut output part is a guiding rod. At least one guiding rod is provided. One end of each guiding rod is fixedly connected to the housing of the servo mechanism, and the other end passes through the round hole on the end face of each stage of nut close to the housing of the servo mechanism. The guiding rod and the round hole form a sliding pair, and adjacent nut output parts form a sliding pair along the axial direction, so that the nut output part makes a linear motion along the axial direction.

[0053] Further, except for the first-stage lead screw, one end of other lead screws is provided with an integrally formed connecting shaft for mating connection with the previous-stage nut. The connecting shaft includes a first cavity section and a second cavity section. The inner diameter of the second cavity section close to the end face is larger than that of the first cavity section. Except for the last-stage nut, the nuts of other-stage lead screw pairs are provided with steps with a small outer diameter close to the end face for connection with the connecting shaft of the next-stage lead screw. For adjacent two-stage lead screw pairs, the next-stage lead screw and the previous-stage nut are connected by deep groove ball bearings and thrust ball bearings. The inner ring of the deep groove ball bearing is fixed on the step of the previous-stage nut, and the outer ring is fixed in the first cavity section of the next-stage lead screw. An inner baffle is arranged on the end face of the previous-stage nut close to the deep groove ball bearing, and an L-shaped outer baffle is arranged in the second cavity section of the next-stage lead screw. The shaft ring of the thrust ball bearing is fixed on the shaft part of the previous-stage nut, and the seat ring is fixed in the inner cavity of the L-shaped outer baffle. The deep groove ball bearing is used to realize the rotation of the next-stage lead screw around the previous-stage nut, the thrust ball bearing is used to provide axial bearing capacity while the secondary lead screw rotates around the previous-stage nut, the inner baffle is used to prevent the axial movement of the deep groove ball bearing, and the outer baffle is used to prevent the axial and radial movement of the first thrust ball bearing.

[0054] In the present invention, the lead screw pair can be one of transmission structures such as ball screw, planetary roller screw, trapezoidal screw, etc.

[0055] Taking the variable reduction ratio step-by-step telescopic lead screw transmission mechanism using a ball screw as an example, the technical solution of the present invention will be elaborated in detail below.

[0056] As Figure 1 、 2 shown, a variable reduction ratio step-by-step telescopic ball screw transmission mechanism includes a first-stage lead screw pair 1, a second-stage lead screw pair 2, a third-stage lead screw pair 3, a guiding rod 4, rolling bearings, a first-stage connecting mechanism 5, a second-stage connecting mechanism 6, etc. Among them, the first-stage lead screw pair 1, the second-stage lead screw pair 2, and the third-stage lead screw pair 3 adopt a coaxial nested layout form.

[0057] As Figure 3As shown in the figure, the first-level lead screw pair 1 includes a first-level lead screw 7, a first-level nut 8, and first-level balls 9. The first-level lead screw 7 is a hollow cylindrical structure that penetrates along the axial direction. Two key grooves 7-1 penetrate along the axial direction on the inner surface. There are multi-start helical raceways 7-2 on the outer surface of the first-level lead screw 7. The first-level nut 8 includes a shaft portion 8-3 and a tubular output portion fixedly connected to the outside of the shaft portion 8-3. One end of the shaft portion 8-3 and one end of the output portion are integrally formed through an annular bottom plate to form a sleeve structure with the same inner and outer axes. There are multi-start helical raceways 8-1 on the inner cavity of the shaft portion 8-3. A number of first-level balls 9 are located in the helical space formed by the raceways of the first-level lead screw 7 and the first-level nut 8. A step 8-2 with a smaller outer diameter is provided near the end face of the shaft portion 8-3.

[0058] As Figure 4 shown in the figure, the second-level lead screw pair 2 includes a second-level lead screw 10, a second-level nut 11, and second-level balls 12. The second-level lead screw 10 is a cylindrical hollow structure. There are multi-start helical raceways 10-1 on the outer surface. One end of the second-level lead screw 10 includes a connecting shaft, and the connecting shaft includes a first inner cavity 10-2 and a second inner cavity 10-3. The inner diameter of the second inner cavity 10-3 is larger than that of the first inner cavity 10-2. The second-level nut 11 includes a shaft portion 11-3 and a tubular output portion fixedly connected to the outside of the shaft portion. One end of the shaft portion 11-3 and one end of the output portion are integrally formed through an annular bottom plate to form a sleeve structure with the same inner and outer axes. There are multi-start helical raceways 11-1 on the inner cavity of the shaft portion 11-3. A number of second-level balls 12 are located in the helical space formed by the raceways of the second-level lead screw 10 and the second-level nut 11. A step 11-2 with a smaller outer diameter is provided near the end face of the shaft portion 11-3. The second-level lead screw 10 is connected to the first-level nut 8 through a rolling bearing, as Figure 6 shown in the figure. Specifically, the inner ring 13-1 of the first deep groove ball bearing 13 is sleeved on the step 8-2 of the first-level nut 8 and fixedly connected thereto. The outer ring 13-2 of the first deep groove ball bearing 13 is embedded in the first inner cavity 10-2 of the second-level lead screw 10 and fixedly connected thereto. The first inner baffle 14 is fixedly connected to the end face of the first-level nut 8. The L-shaped first outer baffle 15 is embedded in the second inner cavity 10-3 of the second-level lead screw 10 and fixedly connected thereto. The shaft ring 16-1 of the first thrust ball bearing 16 is sleeved on the shaft portion 8-3 of the first-level nut 8 and fixedly connected thereto. The seat ring 16-2 of the first thrust ball bearing 16 is embedded in the inner cavity 15-1 of the first outer baffle 15 and fixedly connected thereto.

[0059] As Figure 5As shown in the figure, the three-stage lead screw pair 3 includes a three-stage lead screw 17, a three-stage nut 18, and three-stage balls 19. The three-stage lead screw 17 is a cylindrical hollow structure with multi-start helical raceways 17-1 on its outer surface. One end of the three-stage lead screw 17 includes a connecting shaft, and the connecting shaft includes a third inner cavity 17-2 and a fourth inner cavity 17-3. The inner diameter of the fourth inner cavity 17-3 is larger than that of the third inner cavity 17-2. The three-stage nut 18 includes a shaft portion and a tubular output portion fixedly connected to the outer surface of the shaft portion. The shaft portion and the output portion are integrally formed. There are multi-start helical raceways 18-1 on the inner cavity of the shaft portion, and a number of three-stage balls 19 are located in the helical space formed by the raceways of the three-stage lead screw 17 and the three-stage nut 18. The three-stage lead screw 17 is connected to the second-stage nut 11 through rolling bearings, as Figure 6 shown. Specifically, the inner ring 20-1 of the second deep groove ball bearing 20 is sleeved on the step 11-2 of the second-stage nut 11 and fixedly connected thereto. The outer ring 20-2 of the second deep groove ball bearing 20 is embedded in the third inner cavity 17-2 of the three-stage lead screw 17 and fixedly connected thereto; the second inner baffle 21 is fixedly connected to the end face of the second-stage nut 11, and the L-shaped second outer baffle 22 is embedded in the fourth inner cavity 17-3 of the three-stage lead screw 17 and fixedly connected thereto; the shaft ring 23-1 of the second thrust ball bearing 23 is sleeved on the shaft portion 11-3 of the second-stage nut 11 and fixedly connected thereto, and the seat ring 23-2 of the second thrust ball bearing 23 is embedded in the inner cavity 22-1 of the second outer baffle 22 and fixedly connected thereto.

[0060] As Figures 2 - 5 shown, the outer side surface 8-4 of the output portion of the first-stage nut 8 and the servo mechanism housing 24 form a sliding pair along the axial direction. The inner side surface 8-5 of the output portion of the first-stage nut 8 and the outer side surface 11-4 of the output portion of the second-stage nut 11 form a sliding pair along the axial direction; the inner side surface 11-5 of the output portion of the second-stage nut 11 and the outer side surface 18-2 of the output portion of the three-stage nut 18 form a sliding pair along the axial direction.

[0061] As Figure 2 shown, each of the bottoms of the first-stage nut 8, the second-stage nut 11, and the three-stage nut 18 has two round holes 25 with the same diameter size (preferably, the round holes 25 of the three-stage nut 18 extend to a partial area of the inner surface of the output portion). The two round holes 25 of the three-stage nut are correspondingly located on two straight lines. As Figure 6 shown, the guide rod 4 is a cylindrical stepped shaft, including a long rod 4-1 and a base 4-2 provided at one end of the long rod 4-1. The long rod 4-1 respectively passes through the bottom round holes 25 of the first-stage nut 8, the second-stage nut 11, and the three-stage nut 18. The guide rod 4 and the bottom round holes 25 of the nut form a sliding pair; the base 4-2 of the guide rod 4 is fixedly connected to the servo mechanism housing 24. In other embodiments, the multi-stage nut output portion can also achieve the axial guiding effect on the nut output portion by providing axial grooves and convex keys between the nut output portions, or designing the multi-stage output portion as a regular polygon tubular structure.

[0062] AsFigure 7 , 8 As shown in 8 , the first-level connecting mechanism 5 includes a first-level permanent magnet 26, a first-level connecting seat 27, and a first-level input rod 28. The first-level permanent magnet 26 is cylindrical and is installed at one end of the inner cavity 7-3 of the first-level lead screw 7 and fixedly connected thereto. The first-level connecting seat 27 is installed on the end face of the second-level lead screw 10 and fixedly connected thereto. The first-level connecting seat 27 includes a positioning ring 27-1 and three first-level female blocks 27-2 fixedly connected to the inner circumferential surface of the positioning ring 27-1. The positioning ring 27-1 coincides with the axis of the second-level lead screw 10. The first-level input rod 28 is made of ferromagnetic material and includes a long shaft 28-1 and a stepped shaft section. The outer diameter of the stepped shaft section is slightly larger than that of the long shaft 28-1, and a cylindrical inner cavity 28-4 is provided inside. A keyway 28-5 is provided on the inner surface of the stepped shaft section. The long shaft 28-1 of the first-level input rod 28 and the inner cavity 7-3 of the first-level lead screw form a sliding pair along the axial direction. The convex key 28-2 provided on the outer surface of the long shaft 28-1 and the keyway 7-1 on the inner surface of the inner cavity 7-3 of the first-level lead screw form a sliding pair along the axial direction. There are three first-level female blocks 27-2 evenly distributed around the axis on the first-level connecting seat 27. The first-level female blocks 27-2 are in the form of a spiral concave surface; there are three first-level male blocks 28-3 evenly distributed around the axis on the outer edge of the end of the first-level input rod 28. The first-level male blocks 28-3 are in the form of a spiral convex surface matching the first-level female blocks 27-2. During the working process, the spiral surfaces approach each other, and the female and male blocks are assembled without blockage during rotation.

[0063] As Figure 9 , 10 shown in 10 , the second-level connecting mechanism 6 includes a second-level permanent magnet 29, a second-level connecting seat 30, and a second-level input rod 31. The second-level permanent magnet 29 is cylindrical and is installed at the deepest part of the inner cavity 28-4 of the first-level input rod and fixedly connected thereto. The second-level connecting seat 30 is installed on the end face of the third-level lead screw 17 and fixedly connected thereto. The second-level connecting seat 30 includes a positioning ring 30-1 and three second-level female blocks 30-2 fixedly connected to the inner circumferential surface of the positioning ring 30-1. The positioning ring 30-1 coincides with the axis of the third-level lead screw 17. The second-level input rod 31 is made of ferromagnetic material and includes a long shaft 31-1 and a stepped shaft section. The outer diameter of the stepped shaft section is slightly larger than that of the long shaft 31-1. The long shaft 31-1 of the second-level input rod 31 and the inner cavity 28-4 of the first-level input rod form a sliding pair along the axial direction. The convex key 31-2 provided on the outer surface of the long shaft 31-1 and the keyway 28-5 on the inner surface of the inner cavity 28-4 of the first-level input rod form a sliding pair along the axial direction. There are three second-level female blocks 30-2 evenly distributed around the axis on the second-level connecting seat 30. The second-level female blocks 30-2 are in the form of a spiral concave surface; there are three second-level male blocks 31-3 evenly distributed around the axis on the outer edge of the end of the second-level input rod 31. The second-level male blocks 31-3 are in the form of a spiral convex surface matching the second-level female blocks 30-2.

[0064] In this embodiment, the three-stage lead screw pair can adopt different reduction ratios. Define the leads (or reduction ratios) of the first-stage lead screw pair, the second-stage lead screw pair, and the third-stage lead screw pair as P h1 , P h2 , and P h3 , and the strokes are l s1 , l s2 , and l s3 respectively; when the transmission mechanism is in the contracted state, the axial distance between the mating surfaces of the first-stage male block and the first-stage female block is l c1 , and the axial distance between the mating surfaces of the second-stage male block and the second-stage female block is l c2 . For a variable reduction ratio step-by-step telescopic ball screw transmission mechanism as described above, during the elongation process:

[0065] The first-stage lead screw 7 rotates to drive the first-stage nut 8 to move linearly and extend relative to the servo mechanism housing 24. The second-stage nut 11 and the third-stage nut 18 have no axial movement relative to the first-stage nut 8. The total lead (or reduction ratio) P h of the transmission mechanism is equal to P h1 . The single-stage movement of the first-stage nut 8 can output a length L 1 = l c1 .

[0066] When the first-stage male block 28-3 of the first-stage input rod 28 comes into contact and cooperation with the first-stage female block 27-2, the first-stage input rod 28 synchronously drives the second-stage lead screw 10 to rotate. The first-stage input rod 28 separates from the first-stage permanent magnet 26. The first-stage nut 8 and the second-stage nut 11 extend synchronously and output linear motion. The total lead (or reduction ratio) P h of the transmission mechanism is equal to P h1 + P h2 . The composite output length of the first-stage nut and the second-stage nut

[0067] When the second-stage male block 31-3 of the second-stage input rod 31 comes into contact and cooperation with the second-stage female block 30-2, the second-stage input rod 31 synchronously drives the third-stage lead screw 17 to rotate. The second-stage input rod 31 separates from the second-stage permanent magnet 29. The first-stage nut 8, the second-stage nut 11, and the third-stage nut 18 extend in a composite manner and output linear motion. The total lead (or reduction ratio) P h of the transmission mechanism is equal to P h1 + P h2 + P h3 . The composite output length of the first-stage nut, the second-stage nut, and the third-stage nut

[0068] For a variable reduction ratio step-by-step telescopic ball screw transmission mechanism as described above, the maximum extended length L 总 takes a value of L 总 = L 1 + L 2 + L3 .

[0069] As described above, in the process of contraction, the movement sequence of the ball screw pairs of each stage is opposite to that of the extension process. First, the first-stage nut, the second-stage nut, and the third-stage nut are contracted to output linear motion. When the second-stage input rod contacts the second-stage permanent magnet, the second-stage male block separates from the second-stage female block; then the first-stage nut and the second-stage nut are contracted to output linear motion. When the first-stage input rod contacts the first-stage permanent magnet, the first-stage male block separates from the first-stage female block; finally, the first-stage nut contracts to output linear motion until the movement reaches the contracted state of the transmission mechanism.

[0070] For a variable reduction ratio step-by-step telescopic ball screw transmission mechanism as described above, the transmission mechanism parameters should satisfy the relationship: Δ DX ≥L 总 . Such as Figure 11 As shown in the formula, where l LJ1 indicates the maximum axial length of the long axis of the primary input rod that can be embedded in the inner cavity of the primary screw, Δ LJ1 indicates the minimum axial length of the long axis of the primary input rod embedded in the inner cavity of the primary screw, which is usually not less than the diameter of the long axis of the primary input rod; l LJ2 represents the maximum axial length of the long axis of the secondary input rod that can be embedded in the inner cavity of the primary input rod, Δ LJ2 represents the minimum axial length of the long axis of the secondary input rod embedded in the inner cavity of the primary input rod, which is usually not less than the diameter of the long axis of the secondary input rod; Δ DX It is the effective moving length of the guide rod in the three-stage nut along the axial direction.

[0071] In the above-mentioned variable reduction ratio step-by-step telescopic ball screw transmission mechanism, each stage of the screw pair can adopt a different lead, and the primary connecting mechanism and the secondary connecting mechanism drive the secondary screw pair or the tertiary screw pair to move in a time-sharing and sequential manner, so that the primary screw pair, the secondary screw pair, and the tertiary screw pair can move step by step during the telescopic process of the multi-stage ball screw transmission mechanism, thereby realizing the variable reduction ratio transmission of the transmission mechanism in different movement stages. The above-mentioned variable reduction ratio step-by-step telescopic ball screw transmission mechanism is particularly suitable for heavy-duty vertical electric cylinders with a large load variation range within the working stroke, and the power density and stiffness of the electric cylinders can be improved through system integration.

[0072] The features described and / or shown above for one embodiment may be used in one or more other embodiments in the same or similar manner, and / or combined with features in other embodiments or used in place of features in other embodiments.

[0073] It should be emphasized that the term "comprising / including", as used herein, refers to the presence of features, whole things, steps or components, but does not exclude the presence or addition of one or more other features, whole things, steps, components or combinations thereof.

[0074] Many features and advantages of these embodiments will be apparent from this detailed description, and thus the appended claims are intended to cover all such features and advantages of these embodiments that fall within their true spirit and scope. Further, since many modifications and variations will be readily apparent to those skilled in the art, the embodiments of the present invention are not to be limited to the exact construction and operation shown and described, but may cover all suitable modifications and equivalents that fall within their scope.

[0075] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

[0076] The parts not detailed in the present invention are well-known technologies to those skilled in the art.

Claims

1. A variable reduction ratio step-by-step telescopic screw transmission mechanism, characterized in that: It comprises at least two stages of lead screw pairs, each stage of the lead screw pair comprises a lead screw and a nut mounted on the lead screw, the lead screw is a hollow structure, and the nut is externally fixedly connected with a tubular output portion coaxial with the nut; The multi-stage screw pair is coaxially and nested, the next-stage screw is assembled on the previous-stage nut through a bearing, the next-stage nut output part is located inside the previous-stage nut output part, and the multi-stage nut output part is provided with an axial guide structure; The screws of two adjacent screw pairs are connected by a connecting mechanism, so that the multi-stage screw pair can be extended and retracted step by step. The connecting mechanism comprises a permanent magnet, an input rod, and a limiting structure; the permanent magnet is arranged in the inner cavity of the first-stage lead screw or in the inner cavity of the input rod of the connecting mechanism assembled with the previous-stage lead screw pair; the limiting structure comprises a limiting portion A and a limiting portion B, and the limiting portion A is arranged at one end of the next-stage lead screw; one end of the input rod passes through the limiting portion A, extends into the inner cavity of the first-stage lead screw or the inner cavity of the previous-stage input rod, and is adsorbed by the permanent magnet, and the other end of the input rod is provided with a limiting portion B matching the limiting portion A; An axial guide structure is provided between the input rod and the inner cavity of the first-stage lead screw, or between the input rod and the inner cavity of the previous-stage input rod; The limiting part A is a connecting seat, which includes a positioning ring and a plurality of female blocks evenly distributed along the inner circumference of the positioning ring. The limiting part B is a plurality of male blocks arranged on the outer edge of one end of the input rod. The facing surfaces of the female blocks and the male blocks are spiral curved surfaces. The axial guiding structure of the input rod is a convex key arranged on the outer surface, and the first-stage screw cavity or the previous-stage input rod cavity is matched with an axial keyway; the input rod is made of ferromagnetic material.

2. The variable reduction ratio step-by-step telescopic screw transmission mechanism according to claim 1, characterized in that: The guiding structure of the nut output part is a guiding rod, and at least one guiding rod is provided. One end of each guiding rod is fixedly connected to the servo mechanism housing, and the other end passes through a circular hole on the end face of each stage nut close to the servo mechanism housing. The guiding rod and the circular hole form a sliding pair; adjacent nut output parts form a sliding pair along the axial direction.

3. The variable reduction ratio step-by-step telescopic screw transmission mechanism according to claim 1, characterized in that: For any two adjacent screw pairs, the secondary screw is assembled on the previous nut through a deep groove ball bearing and a thrust ball bearing; one end of the secondary screw includes a connecting shaft, and the connecting shaft includes a first cavity section and a second cavity section, and the inner diameter of the second cavity section close to the end face is larger than that of the first cavity section; a step with a small outer diameter is provided near the end face of the previous nut; the inner ring of the deep groove ball bearing is fixed on the step of the previous nut, and the outer ring is fixed in the first cavity section of the secondary screw; the thrust ball bearing shaft ring is fixed on the previous nut, and the seat ring is fixed in the second cavity section of the secondary screw.

4. The variable reduction ratio step-by-step telescopic screw transmission mechanism according to claim 3, characterized in that: An inner baffle is arranged near the end face of the deep groove ball bearing of the first-stage nut, an L-shaped outer baffle is arranged in the second cavity section of the second-stage lead screw, and the thrust ball bearing race is fixed in the inner cavity of the L-shaped outer baffle.

5. The variable reduction ratio step-by-step telescopic screw transmission mechanism according to claim 1, characterized in that: The screw pair is one of a ball screw, a planetary roller screw and a trapezoidal screw.

6. The variable reduction ratio step-by-step telescopic screw transmission mechanism according to claim 2, characterized in that: The transmission mechanism includes a three-stage screw pair, a primary connecting mechanism is set between the primary screw and the secondary screw, and a secondary connecting mechanism is set between the secondary screw and the tertiary screw; the maximum extension length L of the transmission mechanism 总 =L1+L2+L3, where L1＝l c1 Among them, P h1 , P h2 , P h3 They are the reduction ratios of the first-stage screw pair, the second-stage screw pair, and the third-stage screw pair, respectively. s3 is the stroke of the three-stage screw pair; l c1 is the axial distance between the mating surfaces of the male block and the female block in the primary connection mechanism, l c2 It is the axial distance between the mating surfaces of the male block and the female block in the secondary connection mechanism.

7. The variable reduction ratio step-by-step telescopic screw transmission mechanism according to claim 6, characterized in that: The parameters of the transmission mechanism meet D DX ≥L 总 Among them, l LJ1 Indicates the maximum axial length of the long axis of the input rod of the primary connection mechanism embedded in the inner cavity of the primary screw, Δ LJ1 Indicates the minimum axial length of the major axis of the input rod of the primary connection mechanism embedded in the inner cavity of the primary screw; l LJ2 represents the maximum axial length of the long axis of the secondary connection mechanism input rod embedded in the inner cavity of the primary connection mechanism input rod, Δ LJ2 represents the minimum axial length of the long axis of the secondary connection mechanism input rod embedded in the inner cavity of the primary connection mechanism input rod, Δ DX The effective moving length of the guide rod in the three-stage nut along the axial direction; Δ LJ1 The value is not less than the diameter of the major axis of the input rod of the primary connection mechanism; Δ LJ2 The value shall not be less than the diameter of the major axis of the input rod of the secondary connection mechanism.

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