Multistage reverse self-circulation ball screw electric cylinder

Abstract

The invention discloses a multi-stage reverse self-circulation ball screw electric cylinder which comprises a power assembly, a transmission assembly and a lead screw assembly. The lead screw assembly comprises a first-stage nut, a second-stage lead screw nut composite body, a third-stage lead screw and balls which are arranged from bottom to top. The first-stage nut is arranged on the second-stage lead screw nut composite body in a sleeving mode and matched with the bottom of the second-stage lead screw nut composite body through right-hand threads, and a reverse self-circulation ball screw pair is formed. The second-stage lead screw nut composite body is arranged on the third-stage lead screw in a sleeving manner and is matched with the bottom of the third-stage lead screw through a left-hand thread to form another set of reverse self-circulation ball screw pair; when the power assembly drives the second-stage lead screw nut composite body to axially rotate through the spline shaft, the bottom of the second-stage lead screw nut composite body pushes the second-stage lead screw nut composite body to linearly move in the axial direction, the top of the second-stage lead screw nut composite body drives the third-stage lead screw to linearly move in the reverse direction at the same time, and therefore the reverse displacement superimposed effect is formed.

Description

TECHNICAL FIELD

[0001] The present application relates to a ball screw electric cylinder for linear drive, in particular to a compact electric cylinder driven by a multi-stage reverse self-circulating ball screw pair, and belongs to the technical field of electric cylinders. BACKGROUND

[0002] In the prior art, the ball screw electric cylinder is a high-precision transmission device combined with a servo motor and a ball screw into a mechanical and electrical integration, which realizes linear motion by driving with electric energy, greatly meets the precise control requirements of the system on thrust, speed and position, and has been widely used in many important fields such as industry, agriculture and national defense. Moreover, the number of ball screws determines the transmission level of the ball screw electric cylinder. If the number of ball screws capable of telescopic linear motion is two, the ball screw electric cylinder is a two-stage electric cylinder.

[0003] At present, the ball screw electric cylinders on the market can be divided into single-stage electric cylinders, two-stage electric cylinders, three-stage electric cylinders, etc. according to the transmission level. Specifically, the single-stage electric cylinder such as the invention patent: a ball screw electric cylinder (CN110255419A) has high transmission accuracy, but due to the single-stage transmission mechanism, the working stroke is limited by the size of the cylinder itself, and the length of the push rod and the size of the cylinder installation need to be increased to obtain a large working stroke, which often makes the cylinder very heavy and cannot be used in places where the installation size is small but the working stroke is large. The two-stage electric cylinder such as the invention patent: a double-layer ball screw electric cylinder (CN114195037A) and the three-stage electric cylinder such as the invention patent: a three-stage ball screw electric cylinder (CN100541981C) can realize the effects of relatively reducing the overall size of the electric cylinder and relatively increasing the stroke, but the structure is complex, the structure is not good under stress, the reliability is not high, and the transmission efficiency, structural compactness and operation stability cannot be considered, which makes it difficult to meet the transmission requirements under complex working conditions.

[0004] Therefore, it is urgent to research a multi-stage electric cylinder with compact structure, stable operation and large stroke output. SUMMARY

[0005] In view of the above existing technical problems, the present application provides a multi-stage reverse self-circulating ball screw electric cylinder, which realizes long stroke and high precision motion through a multi-stage reverse self-circulating ball screw pair, so as to achieve the technical purpose of compact structure, stable operation and large stroke output.

[0006] To achieve the above technical purpose, the present application provides a multi-stage reverse self-circulating ball screw electric cylinder, which comprises a mounting shell configured with a power assembly and a transmission assembly, and a screw assembly arranged on the mounting shell.

[0007] The lead screw assembly includes, from bottom to top, a first-stage nut, a second-stage lead screw-nut composite, and a third-stage lead screw, as well as balls; wherein, the first-stage nut, the second-stage lead screw-nut composite, and the third-stage lead screw are hollow structures; the bottom end of the first-stage nut is mounted on a mounting shell; the first-stage nut is fitted onto the second-stage lead screw-nut composite and engages with the bottom of the second-stage lead screw-nut composite through a right-hand thread to form a reverse self-circulating ball screw pair; the second-stage lead screw-nut composite is fitted onto the third-stage lead screw and engages with the bottom of the third-stage lead screw through a left-hand thread to form another reverse self-circulating ball screw pair;

[0008] The transmission assembly includes a spline shaft and a spline cap; wherein, the spline shaft is located on the central axis inside the first-stage nut, and its bottom end is connected to the power assembly; the spline cap is fitted on the spline shaft, and its two ends are respectively connected to the bottom end of the second-stage lead screw nut composite.

[0009] When the power assembly drives the second-stage screw-nut composite to rotate axially via the spline shaft, the bottom of the second-stage screw-nut composite pushes itself to move linearly along the axial direction, while its top simultaneously drives the third-stage screw to move linearly in the opposite direction, thus forming a superposition effect of reverse displacement.

[0010] In the above technical solution, when the power component drives the spline shaft to rotate, the motion is transmitted to the second-stage lead screw and nut composite through the spline cap. The special thread structure of the second-stage lead screw and nut composite generates bidirectional motion: the second-stage lead screw and nut composite engages with the first-stage nut through a right-hand thread, pushing the second-stage lead screw and nut composite to move axially upward; the second-stage lead screw and nut composite engages with the third-stage lead screw through a left-hand thread, forcing the third-stage lead screw to move downward in the opposite direction. Thus, if the displacement of the second-stage lead screw and nut composite is S1 and the displacement of the third-stage lead screw is S2, then the output displacement of the third-stage lead screw is the vector superposition of the two, i.e., S = S1 + S2, forming a reverse displacement superposition effect, which can significantly expand the stroke range or achieve precise position compensation.

[0011] Furthermore, the first-stage nut has an open right-hand helical nut raceway on its inner diameter; the second-stage screw-nut composite has a right-hand helical circulation mechanism on its bottom outer diameter; the first-stage nut is fitted onto the second-stage screw-nut composite, and the balls are evenly arranged in the closed channel formed by the thread raceway and the circulation mechanism along the circumferential direction, thereby forming a set of reverse self-circulating ball screw pairs.

[0012] Furthermore, the second-stage screw and nut composite has an open left-hand spiral thread raceway on its inner diameter; the third-stage screw has a left-hand spiral circulation mechanism on its bottom outer diameter; the second-stage screw and nut composite is fitted onto the third-stage screw, and the balls are evenly arranged in the circumferential direction within the closed channel formed by the thread raceway and the circulation mechanism, thereby forming another set of reverse self-circulating ball screw pairs.

[0013] Furthermore, the present invention further includes a first-stage sealing cover, a second-stage sealing cover, and a third-stage sealing cover;

[0014] The first-stage sealing cover is installed on the top surface of the first-stage nut and is arranged around the outer diameter of the second-stage screw nut composite; the second-stage sealing cover is installed on the top surface of the second-stage screw nut composite and is arranged around the outer diameter of the third-stage screw; the third-stage sealing cover is installed on the top surface of the third-stage screw.

[0015] Furthermore, the power assembly of the present invention includes a motor and a reducer disposed outside the mounting housing, and a driving gear, a driven gear two and a driven gear one disposed inside the mounting housing;

[0016] The output end of the motor is connected to the input end of the reducer; the output end of the reducer is connected to the center of the drive gear; the drive gear meshes with the driven gear two; and the driven gear two meshes with the driven gear one.

[0017] Furthermore, the present invention also includes a guide component disposed inside the lead screw assembly; the guide component includes a first-stage guide post, a second-stage guide post, and a third-stage guide post arranged from bottom to top;

[0018] The spline shaft, the first-stage guide post, the second-stage guide post, and the third-stage guide post are all hollow structures. The first-stage guide post is located on the central axis inside the spline shaft, and its bottom end is installed inside the mounting housing. The second-stage guide post is movably fitted onto the first-stage guide post and can move linearly along the axial direction. The third-stage guide post is movably fitted onto the second-stage guide post and can move linearly along the axial direction, and its top end is connected to the top end of the third-stage lead screw.

[0019] Furthermore, the invention includes a keyway on the outer diameter of the top end of the third-stage guide post; a guide ring is installed on the inner diameter of the top end of the third-stage lead screw; and the guide ring and the keyway cooperate with each other to achieve circumferential limiting of the third-stage guide post, so that the rotational motion of the third-stage lead screw can be converted into the linear motion of the third-stage guide post.

[0020] In summary, this invention provides a compact, stable, and long-stroke electric cylinder. It employs a power assembly primarily composed of a motor, reducer, and gears, and a transmission assembly consisting of a splined shaft and splined sleeve. Utilizing a two-stage composite transmission mechanism, one end of the second-stage ball screw-nut composite engages with a fixed first-stage nut via a right-hand thread, while the other end engages with a movable third-stage ball screw via a left-hand thread. This achieves a superposition effect of reverse displacement under single-motor drive. In particular, the application of a reverse self-circulating ball screw-nut structure successfully solves the core challenges faced by multi-stage ball screw electric cylinders in pursuing high compactness (especially minimizing radial dimensions), high rigidity, high reliability, and ease of integration, becoming a key technological support for realizing ultra-thin, high-performance multi-stage electric cylinders.

[0021] Compared with the prior art, the present invention has the following technical advantages:

[0022] (1) It adopts a unique non-independent shell structure. Unlike the traditional electric cylinder design that uses an independent cylindrical shell to enclose the internal transmission mechanism, this invention abandons the independent shell design of the traditional electric cylinder, directly simplifying the overall structure and reducing the number of parts and material consumption.

[0023] (2) An advanced “reverse self-circulating ball screw nut pair” structure is adopted. This structure is completely different from the traditional tube-type or end-cap-type circulation method. Its core design concept is to completely internalize the circulation path of the ball into the nut body, thereby achieving a more compact, more efficient and more reliable ball movement.

[0024] (3) A "second-stage screw-nut composite" structure is adopted. This composite is the central node for motion conversion and force transmission in the entire multi-stage transmission system. Its essence lies in playing two different transmission roles at the same time. That is, the end of the composite facing the third-stage screw has the function of a nut, while the end of the composite facing the first-stage nut has the function of a screw.

[0025] (4) It integrates a high-efficiency guide component. When the first-stage nut or the second-stage screw-nut composite is subjected to lateral force or overturning moment, the guide component actively undertakes the main task of absorbing and transmitting radial load. Attached Figure Description

[0026] Figure 1 This is a perspective view of an embodiment of the present invention;

[0027] Figure 2 This is a top view of one embodiment of the present invention;

[0028] Figure 3 This is a left view of an embodiment of the present invention;

[0029] Figure 4This is a right sectional view of an embodiment of the present invention;

[0030] Figure 5 This is a rear sectional view of an embodiment of the present invention;

[0031] Figure 6 This is a schematic diagram of the structure of the circulation mechanism in one embodiment of the present invention;

[0032] In the diagram: 1. Splined shaft; 3. First-stage nut; 4. Second-stage screw-nut composite; 5. Splined cap; 6. First-stage sealing cover; 7. Third-stage screw; 8. Second-stage sealing cover; 9. Third-stage sealing cover; 10. Ball bearing; 11. Shaft retaining ring one; 12. First-stage guide post; 13. Bearing housing; 14. Second-stage guide post; 15. Third-stage guide post; 16. Guide ring; 17. Angular contact ball bearing; 18. Driven gear one; 19. Deep groove ball bearing; 20. Shaft retaining ring two; 21. 21. Driven gear 2; 22. Drive gear; 23. Reducer; 24. Motor; 25. Cable connector bracket 2; 26. Cable sleeve 1; 27. Connector 1; 28. Cable connector bracket 1; 29. ​​Cable sealing cover 2; 30. Connector 2; 31. Socket head cap screw; 32. Hex nut; 33. Shaft retaining ring 3; 34. Mounting housing; 35. Mounting cavity; 36. Base; 37. Positioning ring; 38. External connector; 39. Connecting bolt; 40. Circulating groove; 41. Bearing raceway. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention.

[0034] In the description of this application, terms such as "connection" or "linked" are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. Those skilled in the art can understand the specific meaning of these terms in this application according to the specific circumstances. Furthermore, terms such as "upper," "lower," "left," and "right" are only used to indicate relative positional relationships; when the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0035] like Figures 1-5 As shown, this embodiment provides a multi-stage reverse self-circulating ball screw electric cylinder, including a power component, a transmission component, a screw component, and a guide component. Its core is that the stroke is multiplied through a reverse transmission mechanism, which is described in detail below.

[0036] Firstly, such as Figure 1 , Figure 3 , Figure 5As shown, the power assembly includes a mounting housing 34, a motor 24 and a reducer 23 disposed outside the mounting housing 34, and a driving gear 22, a driven gear 21, and a driven gear 18 disposed inside the mounting housing 34. The output end of the motor 24 is connected to the input end of the reducer 23; the output end of the reducer 23 is connected to the center of the driving gear 22; the driving gear 22 meshes with the driven gear 21; and the driven gear 21 meshes with the driven gear 18.

[0037] In specific implementation, the mounting housing 34 has a mounting cavity 35 inside. The motor 24 and the reducer 23 are mounted above the mounting housing 34. The driving gear 22, driven gear 21, and driven gear 18 are all mounted inside the mounting cavity 35. The output end of the reducer 23 extends into the mounting cavity 35, is connected to the center of the driving gear 22, and provides power input to the transmission components through driven gear 21 and driven gear 18.

[0038] In other embodiments, such as Figure 5 As shown, a positioning ring 37 is also provided inside the mounting housing 34 and is located below the drive gear 22; the output end of the reducer 23 is inserted into the positioning ring 37, thereby fixing the positions of the reducer 23 and the drive gear 22.

[0039] In other embodiments, such as Figure 5 As shown, the mounting housing 34 also contains a hexagonal head screw 31, a deep groove ball bearing 19, and a hexagonal nut 32. In a specific implementation, the deep groove ball bearing 19 is located above the driven gear 21; the hexagonal nut 32 is located below the driven gear 21; the hexagonal head screw 31 extends into the mounting housing 34, passes through the center of the deep groove ball bearing 19 and the driven gear 21 from top to bottom, and connects to the hexagonal nut 32, thereby fixing the position of the driven gear 21.

[0040] In other embodiments, such as Figure 5 As shown, a second elastic retaining ring 20 for the shaft is also provided inside the mounting housing 34. In a specific implementation, the second elastic retaining ring 20 for the shaft is located between the deep groove ball bearing 19 and the driven gear 21, and is fitted onto the internal hexagon socket head cap screw 31.

[0041] In other embodiments, a base 36 is also mounted on the bottom surface of the mounting shell 34 for fixing the bottom of the mounting shell 34.

[0042] In other embodiments, such as Figure 3 , Figure 4As shown, the power assembly also includes cable connection bracket 1 28 and cable connection bracket 25 respectively installed outside the motor 24, motor cable 1 and motor cable 2 respectively connected to the motor 24, cable sleeve 1 26 and cable sleeve 2 respectively fitted on motor cable 1 and motor cable 2, and cable sealing cap 1 and cable sealing cap 29 respectively installed on the outer ends of cable sleeve 1 26 and cable sleeve 2; cable sleeve 1 26 and cable sleeve 2 are placed on cable connection bracket 1 28 and cable connection bracket 25 respectively; the ends of motor cable 1 and motor cable 2 pass through cable sealing cap 1 and cable sealing cap 29 respectively, and connector 1 27 and connector 2 30 are respectively installed for wiring the motor 24.

[0043] Secondly, such as Figure 4 , Figure 5 As shown, the transmission assembly includes a splined shaft 1 and a splined cap 5; the bottom end of the splined shaft 1 is connected to a power assembly, and the top end of the splined shaft 1 is fitted with the splined cap 5; the splined cap 5 can move axially along the splined shaft 1. In a specific implementation, the bottom end of the splined shaft 1 extends into the mounting cavity 35, connects to the center of the driven gear 18, and drives the splined shaft 1 and the splined cap 5 to rotate synchronously through the driven gear 18, thereby realizing the power transmission to the lead screw assembly.

[0044] In other embodiments, a shaft elastic retaining ring 33 is also provided inside the mounting housing 34; the shaft elastic retaining ring 33 is fitted onto the bottom end of the spline shaft 1 and located between the driven gear 18 and the spline shaft 1, thereby reinforcing the fit between the driven gear 18 and the spline shaft 1.

[0045] Thirdly, such as Figure 5 As shown, the lead screw assembly includes a first-stage nut 3, a second-stage lead screw-nut composite 4, and a third-stage lead screw 7 arranged from bottom to top, as well as ball bearings 10, which are described in detail below.

[0046] The first-stage nut 3, the second-stage lead screw and nut composite 4, and the third-stage lead screw 7 are all hollow structures.

[0047] The bottom end of the first-stage nut 3 is mounted on the mounting housing 34, and its inner diameter has a special open right-hand helical thread raceway. The cross-section of this thread raceway is typically Gothic arched or circular arc-shaped, providing a precise running trajectory for the balls 10. The bottom outer diameter of the second-stage screw-nut composite 4 has a right-hand helical circulation mechanism, such as an end cap type, insert type, or internal circulation structure. The first-stage nut 3 is fitted onto the second-stage screw-nut composite 4, and the two maintain a precise clearance fit, thus forming a reverse self-circulating ball screw pair.

[0048] The inner diameter of the second-stage screw-nut composite 4 is provided with a special open left-hand helical thread raceway. The cross-section of this thread raceway is typically Gothic arched or circular arc-shaped, providing a precise running trajectory for the balls 10. The bottom outer diameter of the third-stage screw 7 is provided with a left-hand helical circulation mechanism, such as an end cap type, insert type, or internal circulation structure. The second-stage screw-nut composite 4 is fitted onto the third-stage screw 7, and the two maintain a precise clearance fit, thus forming another set of reverse self-circulating ball screw pairs.

[0049] Furthermore, numerous precision balls 10 are precisely and evenly arranged along the circumference and fill the closed channel formed by the threaded raceway and the circulation mechanism. This unique arrangement allows the balls 10 to be effectively guided and constrained, rolling forward along the corresponding threaded raceways during the relative rotational motion of the first-stage nut 3 and the second-stage screw-nut composite 4, and the second-stage screw-nut composite 4 and the third-stage screw 7. In this way, the synergistic effect of the open threaded raceway and the circulation mechanism together constitutes a dynamic, closed ball circulation loop.

[0050] When either the first-stage nut 3 or the second-stage screw-nut composite 4, or the second-stage screw-nut composite 4 or the third-stage screw 7, rotates, the balls 10, driven by friction, roll along the corresponding thread raceways, pushing the other to produce precise linear displacement. Simultaneously, when the balls 10 reach the end of the thread raceway on the first-stage nut 3 or the second-stage screw-nut composite 4, they can smoothly change direction via the circulation mechanism on the second-stage screw-nut composite 4 or the third-stage screw 7, returning to the beginning of the corresponding thread raceway, thus forming a continuous, reciprocating, low-friction rolling transmission. This entire precision mechanism, composed of the nut, screw, circulation mechanism, and balls 10, ultimately achieves efficient, smooth, and high-precision conversion between rotary motion and linear motion, constituting the reverse self-circulating transmission mechanism of the ball screw.

[0051] For example, such as Figure 6As shown, according to the existing "reverse self-circulating ball screw pair" structure, in the reverse self-circulating ball screw pair composed of the first-stage nut 3 and the second-stage screw-nut composite 4, the circulation mechanism includes a right-hand helical bearing raceway 41 and a circulation groove 40. The bearing raceway 41 is annular and is arranged along the circumferential direction on the outer diameter of the second-stage screw-nut composite 4. A transition curved surface on the bearing raceway 41 forms the circulation groove 40. Unlike the ball screw structure with a circulator, this reverse self-circulating ball screw pair adopts a circulation mechanism without a circulator, integrating the second-stage screw-nut composite 4 with the circulator. This eliminates the need for separate drilling to install the circulator, improving structural rigidity and avoiding assembly errors at the connection points. Furthermore, there are multiple sets of bearing raceways 41, with the circulation grooves 40 arranged helically on these multiple sets of bearing raceways 41. The number of bearing raceways 41 can be adjusted according to the size of the second-stage screw-nut composite 4 and the first-stage nut 3. The basic design parameters of the multiple sets of circulating grooves 40 on the bearing raceway 41 are designed and machined according to the lead screw lead and the thread helix angle.

[0052] Similarly, such as Figure 6 As shown, according to the prior art, in the reverse self-circulating ball screw pair composed of the second-stage screw-nut composite 4 and the third-stage screw 7, the circulation mechanism includes a left-hand helical bearing raceway 41 and a circulation groove 40; the bearing raceway 41 is annular and is arranged along the circumferential direction on the outer diameter of the third-stage screw 7; the bearing raceway 41 has a transition surface forming the circulation groove 40. Similarly, there are multiple sets of bearing raceways 41, and the circulation grooves 40 on the multiple sets of bearing raceways 41 are arranged helically.

[0053] Furthermore, the spline shaft 1 is located on the central axis inside the first-stage nut 3; the two ends of the spline cap 5 are respectively connected to the bottom ends of the second-stage lead screw and nut composite 4. When the power assembly drives the second-stage lead screw and nut composite 4 to rotate axially through the spline shaft 1, the bottom of the second-stage lead screw and nut composite 4 pushes itself to move linearly along the axial direction, while its top simultaneously drives the third-stage lead screw 7 to move linearly in the opposite direction, thereby forming a superposition effect of reverse displacement.

[0054] In specific implementation, the diameter of the first-stage nut 3 is larger than the diameter of the second-stage screw-nut composite 4, and the diameter of the second-stage screw-nut composite 4 is larger than the diameter of the third-stage screw 7. This facilitates the fitting of the third-stage screw 7 inside the second-stage screw-nut composite 4, and the fitting of the second-stage screw-nut composite 4 inside the first-stage nut 3, forming two nested "reverse self-circulating ball screw pairs" structures. This structure is completely different from the traditional insert-type or end-cap-type circulation method. Its core design concept is to completely internalize the circulation mechanism of the ball 10 into the nut body (i.e., the first-stage nut 3 and the second-stage screw-nut composite 4), thereby achieving a more compact, efficient, and reliable ball movement. Furthermore, since the traditional external circulation components (such as bent tubes and end-cap protrusions) are completely eliminated, the outer diameter of the first-stage nut 3 using the reverse self-circulating structure can be significantly smaller. This is crucial for multi-stage nested ball screw electric cylinders, because each stage of transmission needs to be nested inside the previous stage. Smaller radial dimensions mean that more transmission stages can be accommodated within the same housing inner diameter, achieving a larger overall reduction ratio or thrust amplification factor.

[0055] In particular, the second-stage lead screw and nut composite 4 is the central node for the entire lead screw assembly to realize motion conversion and power transmission. Its essence is a core motion conversion structure that integrates inner and outer raceways, and it plays two different transmission roles at the same time:

[0056] (1) The transmission role to the lower level (third level) is that of a "nut": The end of the second-stage screw-nut composite 4 facing the third-stage screw 7 functions as a nut, and its inner diameter is machined with a left-hand helical thread raceway that matches the third-stage screw 7. Furthermore, the third-stage screw 7 is screwed into the second-stage screw-nut composite 4, and the two form a standard reverse self-circulating ball screw pair via the balls 10. When the second-stage screw-nut composite 4 rotates relative to the third-stage screw 7, it drives the third-stage screw 7 to produce axial linear motion (or vice versa, depending on which end is constrained).

[0057] (2) The transmission role to the upper stage (first stage) is that of a "lead screw": The end of the second-stage lead screw-nut composite 4 facing the first-stage nut 3 acts as a lead screw, and its outer diameter is machined with a right-hand helical circulating mechanism that matches the first-stage nut 3. Furthermore, the first-stage nut 3 is mounted on the second-stage lead screw-nut composite 4, and the two form another standard reverse self-circulating ball screw pair via balls 10. When the second-stage lead screw-nut composite 4 rotates relative to the first-stage nut 3, it drives the second-stage lead screw-nut composite 4 to produce axial linear motion (or vice versa, depending on which end is constrained).

[0058] In other embodiments, such as Figure 5As shown, the lead screw assembly also includes an angular contact ball bearing 17; the angular contact ball bearing 17 is located between the first stage nut 3 and the driven gear 18, and is fitted onto the bottom end of the spline shaft 1, thereby fixing the position of the spline shaft 1 and cooperating with the rotational movement of the spline shaft 1.

[0059] In other embodiments, such as Figure 5 As shown, the lead screw assembly also includes a shaft elastic retaining ring 11; the shaft elastic retaining ring 11 is fitted on the top of the spline shaft 1 and located between the second-stage lead screw nut composite 4 and the spline shaft 1, and is used to reinforce the fit between the second-stage lead screw nut composite 4 and the spline shaft 1.

[0060] In other embodiments, such as Figure 5 As shown, the lead screw assembly further includes a first-stage sealing cover 6, a second-stage sealing cover 8, and a third-stage sealing cover 9; the first-stage sealing cover 6 is installed on the top surface of the first-stage nut 3 and is arranged around the outer diameter of the second-stage lead screw and nut composite 4; the second-stage sealing cover 8 is installed on the top surface of the second-stage lead screw and nut composite 4 and is arranged around the outer diameter of the third-stage lead screw 7; the third-stage sealing cover 9 is installed on the top surface of the third-stage lead screw 7.

[0061] In specific implementation, such as Figure 5 As shown, the first-stage sealing cover 6, the second-stage sealing cover 8, and the third-stage sealing cover 9 are respectively installed on the top surfaces of the first-stage nut 3, the second-stage screw-nut composite 4, and the third-stage screw 7 via connecting bolts 39. In particular, the third-stage screw 7 is the outermost protruding rod, and its top end features a threadless design, working in conjunction with the third-stage sealing cover 9 to achieve dustproof sealing and extend service life. Furthermore, the top end of the third-stage screw 7 can be machined into a smooth section (30mm in length), facilitating the installation of external loads and simplifying the design of the first-stage sealing cover 6. In addition, to expand the scope of protection of this invention, the top end of the third-stage screw 7 or the nut on it can be connected to an output rod or actuator.

[0062] In other embodiments, such as Figure 5 As shown, the lead screw assembly also includes an external connector 38 installed on the outer periphery of the first-stage nut 3 for external connection of the electric cylinder.

[0063] Fourth, such as Figure 5 As shown, the guide assembly is located inside the lead screw assembly and is used to constrain the radial degree of freedom. It includes a first-stage guide post 12, a second-stage guide post 14, and a third-stage guide post 15 arranged from bottom to top, as detailed below.

[0064] The spline shaft 1, the first-stage guide post 12, the second-stage guide post 14, and the third-stage guide post 15 are all hollow structures.

[0065] The first-stage guide post 12 is located on the central axis inside the spline shaft 1, with its bottom end installed inside the mounting housing 34 and its top surface lower than the top surface of the first-stage nut 3.

[0066] The second-stage guide post 14 is movably mounted on the first-stage guide post 12 and can move axially linearly along the first-stage guide post 12.

[0067] The third-stage guide post 15 is movably mounted on the second-stage guide post 14 and can move axially along the second-stage guide post 14. Its top end is connected to the top end of the third-stage lead screw 7, and its bottom surface is higher than the bottom surface of the third-stage lead screw 7.

[0068] In specific implementation, the first-stage guide post 12, the second-stage guide post 14, and the third-stage guide post 15 are all placed coaxially with the first-stage nut 3, the second-stage lead screw and nut composite 4, the third-stage lead screw 7, and the spline shaft 1. Furthermore, the outer diameter of the first-stage guide post 12 is smaller than the inner diameter of the second-stage guide post 14, and the outer diameter of the second-stage guide post 14 is smaller than the inner diameter of the third-stage guide post 15, allowing the three to be sequentially and movably fitted together, enabling telescopic movement. This not only guides the linear movement of the lead screw assembly but also allows it to extend and retract to a matching length as the lead screw assembly moves linearly.

[0069] In particular, when the nut body (i.e., the first-stage nut 3 and the second-stage screw-nut composite 4) is subjected to lateral force or overturning moment, these non-axial forces will intensify the contact stress inside the reverse self-circulating ball screw pair, leading to abnormal wear, decreased accuracy, or even premature failure. At this time, the guide component actively undertakes the main task of absorbing and transmitting radial load, and transmits the radial force to the support structure of the electric cylinder efficiently and with low friction through the internal precision rolling elements (i.e., balls 10).

[0070] In other embodiments, a guide ring 16 is installed on the inner diameter of the top end of the third-stage lead screw 7, and a keyway is provided on the outer diameter of the top end of the third-stage guide post 15; and the guide ring 16 can cooperate with the keyway to achieve circumferential limiting of the third-stage guide post 15, ensuring that the rotational motion of the third-stage lead screw 7 can be converted into the linear motion of the third-stage guide post 15.

[0071] In other embodiments, a bearing seat 13 is also provided inside the mounting housing 34; the bottom end of the first-stage guide post 12 is mounted on the bearing seat 13, thereby fixing the position of the first-stage guide post 12.

[0072] As described above, in the working process of the electric cylinder of the present invention, power transmission begins with the power source of the motor 24. After the power is reduced and increased in torque by the reducer 23, it is precisely transmitted to the drive gear 22, which then drives the drive gear 22 to rotate. The drive gear 22, as an intermediate link in the power transmission, transmits power to the driven gear 18 via the meshing action between the gears, and drives the driven gear 21 and the driven gear 18 to rotate synchronously. Since the driven gear 18 is in a mating state with the spline shaft 1, the spline shaft 1 also rotates synchronously under the drive of the driven gear 18.

[0073] Next, a connection is established between the splined shaft 1 and the second-stage lead screw and nut composite 4 through the splined cap 5, and the splined sleeve 5 can slide linearly along the axial direction of the splined shaft 1. Driven by the rotation of the splined shaft 1, the second-stage lead screw and nut composite 4 rotates synchronously around its own central axis, ensuring effective power transmission. Due to the unique structural design of the second-stage lead screw and nut composite 4, it not only uses a left-hand thread engagement with the first-stage nut 3, but also a right-hand thread engagement with the third-stage lead screw 7. Therefore, based on the transmission principle of thread engagement, when the second-stage lead screw and nut composite 4 rotates axially, it not only causes the second-stage lead screw and nut composite 4 to reciprocate axially along the first-stage nut 3, but also causes the splined sleeve 5 to reciprocate axially along the splined shaft 1, and also creates linkage with the third-stage lead screw 7, causing the third-stage lead screw 7 to reciprocate axially synchronously along the second-stage lead screw and nut composite 4, thereby completing specific linear motion execution actions in the overall operation of the electric cylinder.

[0074] It should be noted that the bottom end of the second-stage lead screw and nut composite 4 is engaged with the fixed first-stage nut 3 via a right-hand thread, while the top end is engaged with the movable third-stage lead screw 7 via a left-hand thread, forming a reverse transmission mechanism. Based on this reverse transmission mechanism, when the spline shaft 1 drives the second-stage lead screw and nut composite 4 to rotate, the right-hand thread end of the second-stage lead screw and nut composite 4 engages with the first-stage nut 3, thereby pushing the second-stage lead screw and nut composite 4 to move axially by a stroke S1. Furthermore, the left-hand thread end of the second-stage lead screw and nut composite 4 engages with the third-stage lead screw 7, thereby driving the third-stage lead screw 7 to move in the opposite direction by a stroke S2. Ultimately, the output displacement of the third-stage lead screw 7 is S = S1 + S2, thus achieving the technical effect of stroke multiplication through the reverse transmission mechanism.

[0075] In summary, the multi-stage reverse self-circulating ball screw electric cylinder provided by this invention has advantages such as compact structure, ability to achieve large stroke output, significantly improved bending rigidity, and low installation difficulty. When used, this invention has the following technical effects:

[0076] 1. By combining power and transmission components, power loss during transmission is reduced, improving overall transmission efficiency. Furthermore, gear transmission enables highly efficient power transfer, while ball screw transmission offers high precision. The combination of these two components results in smoother power transmission and less energy loss.

[0077] 2. The tight connection between the components ensures uniform force distribution during transmission, reducing vibration and noise generation, making power transmission smoother, avoiding component damage caused by uneven force distribution, and extending the service life of the equipment.

[0078] 3. It not only greatly saves installation space and makes the overall structure more compact, making it easy to install and use in various mechanical equipment, but also enables multi-stage power transmission to meet the power transmission needs under different working conditions. It can also adjust the transmission ratio according to actual needs through the sequential transmission between the upper and lower level components to adapt to different load and speed requirements.

[0079] 4. The guide assembly is used to absorb radial loads and ensure that the third-stage lead screw 7 moves only in a straight line along the axial direction, avoiding wear or jamming caused by off-center loads.

[0080] The specific embodiments described above are merely illustrative of the present invention and are not intended to limit the scope of protection of the present invention. Those skilled in the art to which this invention pertains can make various modifications, additions, or equivalent substitutions to the embodiments within the spirit and principles of the present invention. All such modifications, substitutions, or improvements should be included within the scope of protection of the present invention.

Claims

1. A multi-stage reverse self-circulating ball screw electric cylinder, characterized in that, It includes a mounting housing with a power assembly and a transmission assembly, and a lead screw assembly mounted on the mounting housing; The lead screw assembly includes, from bottom to top, a first-stage nut, a second-stage lead screw-nut composite, and a third-stage lead screw, as well as balls; wherein, the first-stage nut, the second-stage lead screw-nut composite, and the third-stage lead screw are hollow structures; the bottom end of the first-stage nut is mounted on a mounting shell; the first-stage nut is fitted onto the second-stage lead screw-nut composite and engages with the bottom of the second-stage lead screw-nut composite through a right-hand thread to form a reverse self-circulating ball screw pair; the second-stage lead screw-nut composite is fitted onto the third-stage lead screw and engages with the bottom of the third-stage lead screw through a left-hand thread to form another reverse self-circulating ball screw pair; The transmission assembly includes a spline shaft and a spline cap; wherein, the spline shaft is located on the central axis inside the first-stage nut, and its bottom end is connected to the power assembly; the spline cap is fitted on the spline shaft, and its two ends are respectively connected to the bottom end of the second-stage lead screw nut composite. When the power assembly drives the second-stage screw-nut composite to rotate axially via the spline shaft, the bottom of the second-stage screw-nut composite pushes itself to move linearly along the axial direction, while its top simultaneously drives the third-stage screw to move linearly in the opposite direction, thus forming a superposition effect of reverse displacement.

2. The multi-stage reverse self-circulating ball screw electric cylinder according to claim 1, characterized in that, The first-stage nut has an open right-hand helical nut raceway on its inner diameter; the second-stage screw-nut composite has a right-hand helical circulation mechanism on its bottom outer diameter; the first-stage nut is fitted onto the second-stage screw-nut composite, and the balls are evenly arranged in the circumferential direction within the closed channel formed by the thread raceway and the circulation mechanism, thus forming a set of reverse self-circulating ball screw pairs.

3. The multi-stage reverse self-circulating ball screw electric cylinder according to claim 1, characterized in that, The second-stage screw and nut composite has an open left-hand spiral thread raceway on its inner diameter; the third-stage screw has a left-hand spiral circulation mechanism on its bottom outer diameter; the second-stage screw and nut composite is fitted onto the third-stage screw, and the balls are evenly arranged in the circumferential direction within the closed channel formed by the thread raceway and the circulation mechanism, thus forming another set of reverse self-circulating ball screw pairs.

4. A multi-stage reverse self-circulating ball screw electric cylinder according to any one of claims 1-3, characterized in that, The lead screw assembly also includes a first-stage sealing cover, a second-stage sealing cover, and a third-stage sealing cover; The first-stage sealing cover is installed on the top surface of the first-stage nut and is arranged around the outer diameter of the second-stage screw nut composite; the second-stage sealing cover is installed on the top surface of the second-stage screw nut composite and is arranged around the outer diameter of the third-stage screw; the third-stage sealing cover is installed on the top surface of the third-stage screw.

5. A multi-stage reverse self-circulating ball screw electric cylinder according to claim 1, characterized in that, The power assembly includes a motor and a reducer disposed outside the mounting housing, and a driving gear, a driven gear two, and a driven gear one disposed inside the mounting housing; The output end of the motor is connected to the input end of the reducer; the output end of the reducer is connected to the center of the drive gear; the drive gear meshes with the driven gear two; and the driven gear two meshes with the driven gear one.

6. A multi-stage reverse self-circulating ball screw electric cylinder according to claim 1, characterized in that, It also includes a guide assembly disposed inside the lead screw assembly; the guide assembly includes a first-stage guide post, a second-stage guide post, and a third-stage guide post arranged from bottom to top; The spline shaft, the first-stage guide post, the second-stage guide post, and the third-stage guide post are all hollow structures. The first-stage guide post is located on the central axis inside the spline shaft, and its bottom end is installed inside the mounting housing. The second-stage guide post is movably fitted onto the first-stage guide post and can move linearly along the axial direction. The third-stage guide post is movably fitted onto the second-stage guide post and can move linearly along the axial direction, and its top end is connected to the top end of the third-stage lead screw.

7. A multi-stage reverse self-circulating ball screw electric cylinder according to claim 6, characterized in that, A keyway is provided on the outer diameter of the top end of the third-stage guide post; a guide ring is installed on the inner diameter of the top end of the third-stage lead screw; and the guide ring and the keyway cooperate with each other to achieve circumferential limiting of the third-stage guide post, so that the rotational motion of the third-stage lead screw can be converted into the linear motion of the third-stage guide post.

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