Planetary Screw And Machine Tool Including Same

Abstract

A planetary screw includes a main screw having an outer threading and a connecting portion. A nut includes a hole extending through two end faces of the nut. The hole includes an inner periphery having an inner threading. A planetary unit includes a supporting mechanism and a plurality of rollers rotatably supported by the supporting mechanism to rotate in a fixed position. The plurality of rollers is identical to each other. Each of the plurality of rollers has an outer threading meshed with the outer threading of the main screw and the inner threading of the nut. The planetary screw can be used in a machine tool.

Claims

1. A planetary screw comprising: a main screw including an outer threading and a connecting portion; a nut including a hole extending through two end faces of the nut, wherein the hole includes an inner periphery having an inner threading; and a planetary unit including a supporting mechanism and a plurality of rollers rotatably supported by the supporting mechanism to rotate in a fixed position, wherein the plurality of rollers is identical to each other, wherein each of the plurality of rollers has an outer threading meshed with the outer threading of the main screw and the inner threading of the nut.

2. The planetary screw as claimed in claim 1, wherein the hole of the nut is a stepped hole, wherein the inner periphery of the hole of the nut includes an intermediate section having a first inner diameter and two end sections respectively on two sides of the intermediate section, wherein each of the two end sections of the stepped hole includes a second inner diameter larger than the first inner diameter and is a sealing portion, and wherein the inner threading is at the intermediate section.

3. The planetary screw as claimed in claim 1, wherein the nut includes at least one through-hole extending from the inner periphery of the nut through an outer periphery of the nut, and wherein a plug is removably received in each of the at least one through-hole.

4. The planetary screw as claimed in claim 3, wherein the at least one through-hole includes two through-holes, and wherein the two through-holes are configured to connect to two oil guiding pipes, respectively.

5. The planetary screw as claimed in claim 1, wherein the supporting mechanism includes two fixing boards and a plurality of fixing rods, wherein each of the two fixing boards includes a central hole at a central portion thereof and a plurality of fixing holes surrounding the central hole, wherein the plurality of fixing holes is located on a circumference having a same radius about a central axis of the central hole, and wherein each of the plurality of fixing rods has two ends respectively mounted in the plurality of fixing holes.

6. The planetary screw as claimed in claim 5, wherein each of two ends of each of the plurality of fixing rods includes an engaging portion protruding beyond an associated one of the two fixing boards, wherein each engaging portion includes an outer threading configured to be in threading connection with an engaging member.

7. The planetary screw as claimed in claim 6, wherein each of the plurality of fixing rods has an outer threading, wherein the plurality of fixing rods is identical, wherein the outer threading of each of the plurality of fixing rods meshes with the outer threading of the main screw and the inner threading of the nut, wherein a gap exists between each engaging member and an associated one of the two fixing boards, wherein each gap is slightly larger than a backlash between the outer threading of each of the plurality of fixing rods and the outer threading of the main screw and another backlash between the outer threading of each of the plurality of fixing rods and the inner threading of the nut.

8. The planetary screw as claimed in claim 6, wherein each engaging member is received in an associated one of the plurality of fixing holes.

9. The planetary screw as claimed in claim 6, wherein each engaging member protrudes beyond an outer face of an associated one of the two fixing boards and does not contact the nut.

10. The planetary screw as claimed in claim 5, wherein each of two ends of the plurality of rollers includes a mounting portion rotatably extending through the fixing hole of an associated one of the two fixing boards.

11. The planetary screw as claimed in claim 10, wherein any two adjacent fixing rods of the plurality of fixing rods has a same quantity of rollers therebetween.

12. The planetary screw as claimed in claim 1, wherein each of the sealing portions at the two end sections of the nut has a sealing member detachably engaged with the nut.

13. The planetary screw as claimed in claim 12, wherein each sealing member is made of an elastic material.

14. The planetary screw as claimed in claim 13, wherein each sealing member is in threading connection with the main screw, wherein each sealing member includes a threading having a pitch and a shape, wherein the pitch or the shape of each sealing member is different from a pitch or a shape of the outer threading of the main screw.

15. A machine tool including the planetary screw as claimed in claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0031] FIG. 1 is a diagrammatic cross sectional view of a conventional planetary screw.

[0032] FIG. 2 is an exploded, perspective view of a planetary screw of a first embodiment according to the present invention.

[0033] FIG. 3 is an exploded, perspective view of a planetary unit of the planetary screw of the first embodiment according to the present invention.

[0034] FIG. 4 is a cross sectional view of the planetary screw of the first embodiment according to the present invention.

[0035] FIG. 5 is an enlarged view of a circled portion A of FIG. 4.

[0036] FIG. 6 is an enlarged view of another circled portion B of FIG. 4.

[0037] FIG. 7 is a cross sectional view of a planetary screw of a second embodiment according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0038] With reference to FIG. 2, a planetary screw of a first embodiment according to the present invention includes a main screw 1, a nut 2, and a planetary unit 3. The planetary unit 3 is disposed in the nut 2 and surrounds the main screw 1, such that the main screw 1 can move axially and linearly relative to the nut 2 and the planetary unit 3 or the nut 2 and the planetary unit 3 can move axially and linearly relative to the main screw 1.

[0039] The main screw 1 includes an outer threading 11. The outer threading 11 can be disposed on an end of the main screw 1. The main screw 1 further includes a connecting portion 12 that can be located on the other end of the main screw 1. The connecting portion 12 can be connected to a power device (not shown) for driving the main screw 1 to rotate.

[0040] The nut 2 includes a hole extending through two end faces of the nut 2. The hole includes an inner periphery that has a uniform diameter. Alternatively, the inner periphery of the hole can have different diameters to form a stepped hole. In this embodiment, the hole is a stepped hole, and the inner periphery of the stepped hole includes an intermediate section having a first inner diameter 2a and two end sections respectively on two sides of the intermediate section. Each of the two end sections of the stepped hole includes a second inner diameter 2b larger than the first inner diameter 2a. Preferably, a third inner diameter portion is provided between each of the two end sections and the intermediate section and has an third inner diameter 2c larger than the first inner diameter 2a but smaller than the second inner diameter 2b. The intermediate section of the inner periphery of the nut 2 having the first inner diameter 2a has an inner threading 21. Each of the two end sections of the nut 2 having the second inner diameter 2b can be a sealing portion 22. Furthermore, each third inner diameter portion having the third inner diameter 2c can be a recessed portion 23. The nut 2 preferably includes at least one through-hole 24 extending from the inner periphery of the nut 2 through an outer periphery of the nut 2. A plug 25 is removably received in each of the at least one through-hole 24. Thus, lubricating oil can be filled into the nut 2 via the at least one through-hole 24. In a case that the nut 2 is positioned and does not rotate, the nut 2 can include two through-holes 24 configured to connect to two oil guiding pipes (not shown), respectively. Thus, the lubricating oil can circulate through the two through-holes 24, providing a better lubricating effect.

[0041] With reference to FIGS. 2-4, the planetary unit 3 includes a supporting mechanism and a plurality of rollers 33 rotatably supported by the supporting mechanism to rotate in a fixed position. In this embodiment, the supporting mechanism includes two fixing boards 31 and a plurality of fixing rods 32 disposed between the two fixing boards 31. Each of the two fixing boards 31 includes a central hole 311 at a central portion thereof. The main screw 1 extends through the central hole 311 of the two fixing boards 31 without contacting inner peripheries of the central hole 311. Each of the two fixing boards 31 further includes a plurality of fixing holes 312 surrounding the associated central hole 311. The plurality of fixing holes 312 is located on a circumference having the same radius and about a central axis of the central hole 311.

[0042] Two ends of each of the plurality of fixing rods 32 are respectively engaged in the two fixing boards 31, such that the plurality of fixing rods 32 and the two fixing boards 31 together form a stable supporting mechanism. The plurality of fixing rods 32 surrounds the main screw 1 without contacting the main screw 1 and the nut 2. In this embodiment, each of the two ends of each of the plurality of fixing rods 32 includes an engaging portion 321 protruding beyond an associated one of the two fixing boards 31. Each engaging portion 321 is securely coupled with an engaging member 322. In this embodiment, each engaging portion 321 has an outer threading, and each engaging member 322 is a nut. Each engaging member 322 can be disposed in an associated one of the plurality of the fixing holes 312. Alternatively, each engaging member 322 protrudes beyond an outer face of an associated one of the two fixing boards 31. The two fixing boards 31 and the engaging members 322 correspond to the third inner diameter portions having the third inner diameter 2c of the nut 2 and do not contact with the third inner diameter portions.

[0043] Each of two ends of each of the plurality of rollers 33 includes a mounting portion 331 rotatably extending through the fixing hole 312 of an associated one of the two fixing boards 31. The plurality of rollers 33 is identical to each other. Each of the plurality of rollers 33 has an outer threading 332 meshed with the outer threading 11 of the main screw 1 and the inner threading 21 of the nut 2. Thus, the two fixing boards 31 and the plurality of fixing rods 32 of the supporting mechanism do not contact the main screw 1 and the nut 2 while permitting each of the plurality of rollers 33 to revolve and rotate relative to the main screw 1 and the nut 2.

[0044] The outer threading 332 of each of the plurality of rollers 33, the outer threading 11 of the main screw 1, and the inner threading 21 of the nut 2 can include a single thread or plural threads. Furthermore, the shape of the outer threading 11 of the main screw 1 is preferably identical to the shape of the inner threading 21 of the nut 2, and the shape of the outer threading 332 of each of the plurality of rollers 33 is preferably different from the shapes of the outer threading 11 of the main screw 1 and the inner threading 21 of the nut 2. As shown in FIG. 5, the outer threading 11 of the main screw 1 and the inner threading 21 of the nut 2 can be mountain-shaped, and the outer threading 332 of each of the plurality of rollers 33 is arcuate. Thus, the contact area between the outer threading 332 of each of the plurality of rollers 33 and the outer threading 11 of the main screw 1 can be reduced to thereby reduce the friction between the outer threadings 11 and 332. Accordingly, noise is reduced, and the rotational smoothness is improved. In alternative embodiments, the outer threading 11 of the main screw 1 and the inner threading 21 of the nut 2 are arcuate, and the outer threading 332 of each of the plurality of rollers 33 is mountain-shaped. The present invention is not limited in this regard.

[0045] The central axes of the plurality of rollers 33 and the plurality of fixing rods 32 are on the circumference of the same radius, are disposed around the main screw 1, and are spaced from each other by regular angular intervals. Preferably, a ratio of the number of the plurality of rollers 33 to the number of the plurality of fixing rods 32 is an integer, such that the number of the plurality of rollers 33 between any two adjacent fixing rods 32 is the same. For example, the total number of the plurality of rollers 33 and the plurality of fixing rods 32 is nine, and the ratio of the number of the plurality of rollers 33 to the number of the plurality of fixing rods 32 is 2:1. Thus, the plurality of fixing rods 32 can uniformly withstand the friction resulting from the revolution of the plurality of rollers 33 relative to the main screw 1 and the nut 2, achieving excellent, balanced load.

[0046] With reference to FIGS. 2 and 4, two sealing members 4 are respectively mounted to two end faces of the nut 2 spaced from each other in the axial direction and are detachably coupled to the sealing portion 22 of the nut 2. The sealing members 4 seal the lubricating oil in the nut 2 to avoid leakage, improving the tidiness of the working environment and preventing ambient dust or alien objects from entering the rotational space, thereby avoiding the rotational smoothness of the nut 2 and the main screw 1 from being adversely affected. In this embodiment, two positioning members 26 extend through the nut 2 to secure the sealing members 4 in place, such that the sealing members 4 and the nut 2 rotate synchronously. Preferably, an anti-leak member 34 is provided between each sealing member 4 and the nut 2 to avoid the lubricating oil from leaking via the engaging portion between the sealing member 4 and the nut 2. Each sealing member 4 includes a through-hole 41 through which the main screw 1 extends. Thus, the main screw 1 extends axially through an interior of the nut 2. The through-hole 41 can include an inner threading 42 threadedly engaged with the outer threading 11 of the main screw 1. The sealing members 4 and the nut 2 jointly move relative to the main screw 1 for use in a machine tool, such as a plastic injection molding machine. The sealing members 4 and the nut 2 can rotate at a fixed position, and the main screw 1 can move linearly relative to the sealing members 4 and the nut 2 to inject plastic material through a nozzle. Alternatively, in other processing machinery, the main screw 1 rotates at a fixed position, and the sealing members 4 and the nut 2 moves axially relative to the sealing members 4 and the nut 2.

[0047] With reference to FIG. 6, the sealing members 4 can be made of an elastic material, such as silicone or rubber, such that the inner threading 42 of each sealing member 4 abuts the outer threading 11 of the main screw 1 to prevent leakage of the lubricating oil during rotation of the main screw 1. In an alternative embodiment, the pitch D1 of the inner threading 42 of each sealing member 4 is different from the pitch D2 of the outer threading 11 of the main screw 1. In another alternative embodiment, the shape of the inner threading 42 of each sealing member 4 is different from the shape of the outer threading 11 of the main screw 1. Thus, the inner threading 42 of each sealing member 4 and the outer threading 11 of the main screw 1 can tightly abut each other. Furthermore, the material of the sealing members 4 is elastic to avoid excessive hindrance to the rotation of the main screw 1, enhancing the sealing effect between the sealing members 4 and the main screw 1.

[0048] FIG. 7 shows a second embodiment of the main screw 1 according to the present invention. In comparison with the first embodiment, each of the plurality of fixing rods 32 in this embodiment has an outer threading 323. The plurality of fixing rods 32 is identical to each other. Each outer threading 323 meshes with the outer threading 11 and the inner threading 21 of the nut 2. Two ends of each of the plurality of fixing rods 32 extend through the two fixing boards 31, such that an engaging portion 321 on each end of each of the plurality of fixing rods 32 protrudes beyond an associated one of the two fixing boards 31 and is coupled with an engaging member 322. Each engaging portion 321 can be an outer threading, and each engaging member 322 can be a nut. A gap G exists between each engaging member 322 and an associated one of the two fixing boards 31. Each gap G is slightly larger than a backlash between the outer threading 323 of each of the plurality of fixing rods 32 and the outer threading 11 of the main screw 1 and another backlash between the outer threading 323 of each of the plurality of fixing rods 32 and the inner threading 21 of the nut 2. Thus, the plurality of fixing rods 32 and the two fixing boards 31 form a stable supporting mechanism while permitting the plurality of fixing rods 32 to slightly move in the axial direction relative to the two fixing boards 31. The engaging members 322 can be mounted in the fixing holes 312. Alternatively, the engaging members 322 extend beyond the outer faces of the two fixing boards 31. Furthermore, the two fixing boards 31 and the engaging members 322 do not contact the third inner diameter portion having the third inner diameter 2c of the nut 2.

[0049] By the above structure, when the planetary screw according to the present invention operates, the main screw 1 can be driven to rotate, such that the plurality of rollers 33 meshed with the outer threading 11 of the main screw 1 and the inner threading 21 of the nut 2 can rotate and can revolve about the main screw 1. Thus, when the nut 2 rotates at a fixed position, the main screw 1 can proceed with relative linear motion. Furthermore, when the main screw 1 rotates in the forward direction and the reverse direction, the main screw 1 can proceed with reciprocating linear motion. Alternatively, when the main screw 1 rotates at a fixed position, the sealing members 4 and the nut 2 proceed with relative axial motion, and the sealing members 4 and the nut 2 can proceed with recirpocating linear motion through forward and reverse rotations of the main screw 1.

[0050] In view of the foregoing, in the planetary screw according to the present invention, the supporting mechanism does not contact the main screw 1 and the nut 2, and only the outer threadings 332 of the plurality of rollers 33 mesh with the outer threading 11 of the main screw 1 and the inner threading 21 of the nut 2 to enable the plurality of rollers 33 to rotate and revolve relative to the main screw 1 and the nut 2. The overall structure is simple, and the friction is reduced. Thus, the processing costs of the planetary screw can be significantly reduced, and the production efficiency and assembly efficiency can be enhanced. Since the supporting mechanism does not directly contact the main screw 1 and the nut 2, the noise resulting from rotation of the planetary screw can be reduced. Furthermore, the planetary screw according to the present invention can be used in a machine tool to permit convenient maintenance and easy filling of the lubricating oil.

[0051] Thus since the invention disclosed herein may be embodied in other specific forms without departing from the spirit or general characteristics thereof, some of which forms have been indicated, the embodiments described herein are to be considered in all respects illustrative and not restrictive. The scope of the invention is to be indicated by the appended claims, rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are intended to be embraced therein.