WO2005031190A1

WO2005031190A1 - Worm geared speed reducer

Info

Publication number: WO2005031190A1
Application number: PCT/KR2004/002525
Authority: WO
Inventors: Yun Gyu Lee
Original assignee: Yun Gyu Lee
Priority date: 2003-10-02
Filing date: 2004-10-01
Publication date: 2005-04-07
Also published as: KR20050032700A

Abstract

The present invention relates to a worm reducer in which power can be reduced and transmitted smoothly and accurately by means of a plurality of balls interposed between a worm and worm wheel. The worm reducer of the present invention comprises a casing; a worm which is arranged along a Y axis of the casing, connected to a power source and rotatably disposed within the casing; and a worm wheel which is arranged along an X axis of the casing and rotatably disposed within the casing. The teeth of the worm and the teeth of the worm wheel are engaged with each other in a state where they are spaced apart from each other. A plurality of balls mounted to be brought into rolling contact along the teeth of the worm are interposed between the teeth of the worm and the teeth of the worm wheel to transmit a rotating force from the worm to the worm wheel. Further, a cover encloses the worm such that the balls cannot be removed from the teeth of the worm, and an open end through which the teeth of the worm wheel can be inserted into the cover is formed at a lower portion of the cover.

Description

WORM GEARED SPEED REDUCER

Technical Field The present invention relates to a worm reducer, and more particularly, to a worm reducer wherein power can be reduced and transmitted smoothly and accurately by means of a plurality of balls that are interposed between a worm and a worm wheel and brought into rolling contact with the worm and the worm wheel.

Background Art Reducers are devices for reducing rotational speed of power input from a variety of power sources such as motors, actuators and engines and transmitting the reduced power. Reducers are used widely throughout industry including a variety of machines, robots and automobiles. Such reducers are categorized into mechanical reducers and electronic reducers. A reduction gear, a belt pulley and the like are employed in mechanical reducers. A reduction gear of a reducer is composed of a gear pair or gear train in which the angular velocity of a final driven gear is smaller than the angular velocity of an initial driving gear. The reducer is configured in such a manner that mechanical elements such as the gear pair, a shaft and a bearing are assembled within a casing of the reducer. Reducers have been developed to have a variety of structures and usages in the form of a worn reducer, a planetary reducer, a gear box, a geared motor, and the like depending on the shape and kind of gear used therein. A related art worm motor equipped with a worm reducer is disclosed in U.S. Patent No. 6,215,209. This related art worm motor reduces a driving force by means of a worm gear composed of a worm and worm wheel and outputs the reduced driving force. A motor shaft and a worm shaft are interconnected through a coupling to be coaxial with each other. The worm of the worm gear is engaged with the worm wheel. Further, the worm shaft and the worm wheel shaft are supported on the casing through a bearing such that smooth rotation thereof can be maintained. Such a worm reducer of a worm motor has a simple structure, high economical efficiency, and low noise and vibration. Further, the worm reducer has the following advantages: That is, when the reduction ratio is large, a self-locking operation can be performed and thus reverse rotation can also be controlled. In addition, since a moment of inertia is small, it is advantageous in frequent start-up and stop operations thereof. However, the related art worm reducer has disadvantages in that its efficiency is low and that a large amount of heat is generated due to friction between the worm and the worm wheel. In particular, the teeth of worm and worm wheel are precisely machined in consideration of design factors such as the number of teeth, module, pressure angle and ^' undercut. Thus, if the gear teeth of the worm and the worm wheel are worn out and damaged due to the friction therebetween, the worm reducer loses their own function and cannot provide an accurate reduction ratio. Accordingly, there is a problem in that worn and damaged worm gear should be completely exchanged with a new one. Furthermore, there is another problem in that reliability of the worm reducer is reduced since noise and vibration is greatly produced due to the friction between the worm and the worm wheel.

Disclosure of Invention The present invention is conceived to solve the aforementioned problems in the related art. Accordingly, an object of the present invention is to provide a worm reducer wherein an accurate reduction ratio can be obtained and efficiency can also be improved by allowing smooth and accurate power transmission to be made by means of balls serving as transmission elements interposed between a worm and a worm wheel. Another object of the present invention is to provide a worm reducer wherein wear, damage and heat generation can be minimized by greatly reducing friction between the worm and the worm wheel due to the rolling contact of the balls therewith interposed between the worm and the worm wheel, and its reliability can be improved by efficiently preventing noise and vibration from being generated. According to the present invention for achieving the objects, there is provided a worm reducer, comprising a casing; a worm which has teeth and is arranged along a Y axis of the casing, connected to a power source and rotatably disposed within the casing; a worm wheel which has teeth engaged with the teeth of the worm in a state where the teeth of the worm wheel are spaced apart from the teeth of the worm, and is arranged along an X axis of the casing and rotatably disposed within the casing; a plurality of balls which are provided to be brought into rolling contact along the teeth of the worm and interposed between the teeth of the worm and the teeth of the worm wheel to transmit a rotating force from the worm to the worm wheel; and a cover which is fixed to the casing, encloses the worm to prevent the balls to be removed from the teeth of the worm, and is formed with an open end, through which the teeth of the worm wheel can be inserted into the cover, at a lower portion thereof.

Brief Description of Drawings Fig. 1 is a partially cut-away sectional view showing the configuration of a worm reducer according to the present invention. Fig. 2 is a sectional view showing the configuration of the worm reducer according to the present invention as viewed from the right side of the worm reducer. Fig. 3 is a front view showing the configuration of a worm, a worm wheel, balls and a cover employed in the worm reducer according to the present invention. Fig. 4 is a sectional view taken along line IN-IN of Fig. 3. Fig. 5 is a perspective view showing the configuration of a ball circulation guide means employed in the worm reducer according to the present invention. Fig. 6 is a sectional view showing the configuration of a ball circulation guide means employed in the worm reducer according to the present invention. Fig. 7 is a sectional view taken along line NII-NII of Fig. 6. Fig. 8 is a plan view showing the configuration of a ball circulation guide means employed in the worm reducer according to the present invention. Fig. 9 is a perspective view showing the configuration of a modified ball circulation guide means employed in the worm reducer according to the present invention.

Best Mode for Carrying Out the Invention Hereinafter, preferred embodiments of a worm reducer according to the present invention will be described in detail with reference to the accompanying drawings. Referring to Figs. 1 and 2, a worm reducer of the present invention includes a casing 10 in the form of a box, which defines an external appearance of the worm reducer. A first shaft bore 12 in alignment with an X axis (X-X') is formed on the front and rear surfaces of the casing 10, and a second shaft bore 14 in alignment with a Y axis (Y-Y') is formed in the right and left surfaces of the casing. The first shaft bore 12 in alignment with the X axis (X-X') is disposed at an upper portion of the casing 10, and the second shaft bore 14 in alignment with the Y axis (Y-Y') is disposed at a lower portion of the casing 10. Alternatively, the first shaft bore 12 of the casing 10 may be aligned with the Y axis and the second shaft bore 14 may be aligned with the X axis. A plurality of cooling fins 16 for heat radiation are formed on the external surface of the casing 10, and a through-hole 18 is formed at the center of the top surface of the casing. In addition, the worm reducer of the present invention has a worm 20 and a worm wheel 30 which substantially reduce rotational speed of power input from a variety of power sources such as motors, actuators and engines, and transmit the reduced power. Both the worm 20 and the worm wheel 30 are provided within the casing 10. A worm shaft 22 is connected to the power source, and teeth 24 of the worm 20 are formed to be semicircular. Both ends of the shaft 22 are supported by a bearing 26 such that the shaft can be rotated about the shaft bore 12. As shown in Figs. 1 and 3, the worm 20 is formed into a. double enveloping worm called a sandglass-type worm, which is shaped to be similar to a sandglass, in such a manner that a diameter of the worm gradually increases toward both ends thereof from a center portion thereof such that the external shape of the teeth 24 of the worm conforms to the outer periphery of the worm wheel 30. The double enveloping worm can smoothly and accurately transmit power even though it operates at large load and high reduction ratio, because large curvature of the teeth thereof allows contact area to be maximized. The double enveloping worm may be replaced with a cylindrical worm. Referring to Figs. 1, 2 and 4, the worm wheel 30 is supported by a bearing 36 such that both ends of a shaft 32 thereof can be rotated about the second shaft bore 14 of the casing 10. An output means such as a gear, pulley or linkage is connected to the shaft 32 of the worm wheel 30 to output the rotating force. Teeth 34 of the worm wheel 30 are shaped to be semicircular. The bearings 26 and 36 for supporting the shafts 22 and 32 of the worm 20 and the worm wheel 30 are accommodated in bearing housings 28 and 38, respectively, which in turn are fixed into the first and second shaft bores 12 and 14 of the casing 10, respectively. Bearing caps 38a of the bearing housing 38 are attached to the both ends of the shaft 32 by means of screws 38b to fix the bearing 36. Roller bearings or ball bearings may be employed as the bearings 26 and 36. The conventional worm gear is configured in such a manner that the teeth of the worm are engaged directly with the teeth of the worm wheel such that power can be transmitted. On the other hand, the worm reducer of the present invention is configured in such a manner that the teeth 24 of the worm 20 are engaged with the teeth 34 of the worm wheel 30 through balls 40 such that they are spaced apart from each other. Referring to Figs. 1 to 4, the worm reducer of the present invention includes a plurality of balls 40 serving as a power transmission element which is mounted such that they can be brought into rolling contact along the teeth 24 of the worm 20. The balls 40 are interposed between the teeth 24 of the worm 20 and the teeth 34 of the worm wheel 30 to transmit the rotating force from the worm 20 to the worm wheel 30. The balls 40 are designed to have the same curvature as the semicircular teeth 24 and 34. Therefore, the balls 40 and the semicircular teeth 24 and 34 are brought into close contact with each other. Further, a cover 50 encloses the worm 20 such that the balls 40 cannot be removed from the teeth 24 of the worm 20. An open end 52, through which the teeth 34 of the worm wheel 30 can be inserted into the cover, is formed at a lower portion of the cover 50. On the inner surface of the cover 50 are formed helical groove 54 which has the same lead and lead angle as those of the teeth 34 of the worm wheel 30 to allow the rolling motion of the balls 40 to be guided. The cover 50 is fixed to a coupler 60, by means of screws 62, which is already mounted into the through-hole 18 of the casing 10 by means of screws 64. Referring to Figs. 5 to 8, the worm reducer of the present invention includes a ball circulation/guide means 70 that connects starting and terminating ends 54a and 54b of the helical groove 54 such that the balls 40 can circulate along the helical groove 54 of the cover 50. The ball circulation/guide means 70 is composed of a first ball return hole 72, a second ball return hole 74, a ball return groove 76 and an outer cover 78. The first ball return hole 72 is formed to penetrate through the cover 50 in a tangential direction from the starting end 54a such that the starting end 54a of the helical groove 54 and the outer surface of the cover 50 are connected with each other. The second ball return hole 74 is formed to penetrate through the cover 50 in a tangential direction from the terminating end 54b such that the terminating end 54b of the helical groove 54 and the outer surface of the cover 50 are connected with each other. The ball return groove 76 is formed on the outer surface of the cover 50 to connect the first and second ball return holes 72 and 74 with each other. The outer cover 78 is mounted to the outer surface of the cover 50 by means of the screws 62 such that the balls 40 circulating along the first and second ball return holes 72 and 74 and the ball return groove 76 cannot be removed from the ball return groove 76. The screws 62 are screwed into screw holes 56a and 56b via through-holes 78a and 78b of the coupler 60 and outer cover 78, respectively, to fix together the coupler 60, the cover 50 and the outer cover 78. As the worm 20 rotates, each of the balls 40 arriving at the terminating end 54b of the helical groove 54 is returned to the starting end 54a via the second ball return hole 74, the ball return groove 76 and the first ball return hole 72. If the worm 20 rotates in the opposite direction, the ball 40 arriving at the starting end 54a of the helical groove 54 is returned to the terminating end 54b via the first ball return hole 72, the ball return groove 76 and the second ball return hole 74. Fig. 9 shows a modification of a ball circulation/guide means. Referring to Fig. 9, . the ball circulation/guide means 170 of the modification includes first and second ball return holes 172 and 174 that are same as the first and second ball return holes 72 and 74 of the ball circulation/guide means 70. The first and second ball return holes 172 and 174 of the ball circulation/guide means 170 are connected with each other by means of a ball return tube 176 in place of the ball return groove 76. Both ends of the ball return tube 176 are fitted into the first and second ball return holes 172 and 174, respectively. The screws 62 are screwed into the screw holes 56a and 56b via the coupler 60 to fix together the coupler 60 and the outer cover 78. Since the processing of the ball return groove 76 and the mounting of the outer cover 78 can be omitted due to the ball return tube 176 of the ball circulation/guide means 170, the further simplified structure and improved assembly characteristics of the ball circulation/guide means 170 can be obtained as compared with the ball circulation/guide means 70 including the ball return groove 76 and the outer cover 78. Hereinafter, the operation of the worm reducer according to the present invention so configured will be described. Referring to Figs. 1 and 2, the shaft 22 of the worm 20 is rotated about the first shaft bore 12 of the casing 10 by means of the power input from the power source. As the worm 20 rotates, the balls 40 disposed along the teeth 24 of the worm 20 are rotated and engaged with the teeth 34 of the worm wheel 30. At this time, the teeth 24 of the sandglass-type worm 20 causes the balls to be brought into close contact with the teeth 34 of the worm wheel 30 and the contact area of the balls 40 to be kept large. Referring to Figs. 1, 2, 5 and 6, the rolling motion of the balls 40 is guided along the helical groove 54 of the cover 50, and the cover 50 functions to prevent balls 40 from being removed from between the teeth 24 of the worm 20 and the teeth 34 of the worm wheel 30, which are engaged with each other. Each of the balls 40 arriving at the terminating end 54b of the helical groove 54 is returned to the starting end 54a via the second ball return hole 74, the ball return groove 76 and the first ball return hole 72 and then circulates along the helical groove 54. The first and second ball return holes 172 and 174 and the ball return tube 176 of the ball circulation/guide means 170 shown in Fig. 9 guide the circulation motion of the balls 40 in the same manner as the first and second ball return holes 72 and 74 and the ball return groove 76 of the ball circulation/guide means 70. In addition, the rotating force from the worm 20 is transmitted to the worm wheel

30 through the balls 40 engaged with the teeth 34 of the worm wheel 30, and the shaft 32 of the worm wheel 30 is rotated about the second shaft bore 14 of the casing 10 at a rotating speed that is slower than the rotating speed of the worm 20. Accordingly, since the rotating force from the worm 20 is transmitted to the worm wheel 30 via the balls 40 brought into rolling contact with both the teeth 24 of the worm 20 and the teeth 34 of the worm wheel 30, power transmission can be smoothly and accurately made. Thus, the accurate reduction ratio can be obtained and the efficiency can also be improved. Further, since the balls 40 are brought into rolling contact with the teeth 24 and 34, the friction between the teeth 24 and 34 is greatly reduced. Thus, wear and damage of the teeth 24 and 34 can be minimized and the heat generation due to the friction can also be minimized. Power transmission through the rolling contact of the balls 40 with the teeth 24 and 34 efficiently prevents noise and vibration from being produced and thus reliability in power transmission can be improved, as compared with power transmission through the direct engagement of the worm 20 and the worm wheel 30. The heat generated due to the friction between the worm 20 and worm wheel 30 and the balls 40 is radiated through the cooling fins 16 formed on the casing 10. Accordingly, the reduction of performance due to the deterioration of the worm 20, the worm wheel 30 and the balls 40 can be prevented and the life span of the worm reducer can also be greatly extended. The aforementioned embodiments are merely illustrative and do not limit the scope of the present invention. Those skilled in the art can make various changes, modifications or substitutions thereto within the technical spirit and scope of the present invention defined by the appended claims. Such embodiments should be construed as falling within the scope of the present invention.

Industrial Applicability According to the worm reducer of the present invention as described above, the rotating force from the worm is smoothly and accurately transmitted to the worm wheel via the balls that are mounted between and brought into rolling contact with the worm and the worm wheel, the accurate reduction ratio and improved efficiency can be obtained. Further, since the friction between the worm and the worm wheel can be greatly reduced due to the rolling contact of the balls therebetween, the wear and damage of the worm and the worm wheel can be minimized and heat generation due to friction can also be minimized. Furthermore, since the generation of noise and vibration are efficiently prevented, the life span of the worm reducer can be greatly extended and the reduction of performance due to deterioration can also be prevented. Accordingly, the reliability of the worm reducer can be improved.

Claims

1. A worm reducer, comprising: a casing; a worm having teeth, said worm being arranged along a Y axis of the casing, connected to a power source and rotatably disposed within the casing; a worm wheel having teeth engaged with the teeth of the worm in a state where the teeth of the worm wheel are spaced apart from the teeth of the worm, said worm wheel being arranged along an X axis of the casing and rotatably disposed within the casing; a plurality of balls provided to be brought into rolling contact along the teeth of the worm and interposed between the teeth of the worm and the teeth of the worm wheel to transmit a rotating force from the worm to the worm wheel; and a cover fixed to the casing, said cover enclosing the worm to prevent the balls to be removed from the teeth of the worm and being formed with an open end, through which the teeth of the worm wheel can be inserted into the cover, at a lower portion thereof.

2. The worm reducer as claimed in claim 1, wherein the teeth of the worm and the teeth of the worm wheel are shaped as a semicircle having the same curvature as the balls.

3. The worm reducer as claimed in claim 2, wherein the worm is a double enveloping worm.

4. The worm reducer as claimed in claim 1, wherein the worm is a double enveloping worm.

5. The worm reducer as claimed in claim 1, wherein a helical groove along which a rolling motion of the balls can be guided is formed on an inner surface of the cover.

6. The worm reducer as claimed in claim 5, further comprising a ball circulation/guide means for guiding the balls to allow the balls to circulate along the helical groove of the cover.

7. The worm reducer as claimed in claim 6, wherein the ball circulation/guide means comprises: a first ball return hole formed to penetrate through the cover in a tangential direction from a starting end of the helical groove such that the starting end of the helical groove and an outer surface of the cover are connected with each other; a second ball return hole formed to penetrate through the cover in a tangential direction from a terminating end of the helical groove such that the terminating end of the helical groove and the outer surface of the cover are connected with each other; a ball return groove formed on the outer surface of the cover to connect the first and second ball return holes with each other; and an outer cover mounted to the outer surface of the cover such that the balls circulating along the first and second ball return holes and the ball return groove cannot be removed from the ball return groove.

8. The worm reducer as claimed in claim 6, wherein the ball circulation/guide means comprises: a first ball return hole formed to penetrate through the cover in a tangential direction from a starting end of the helical groove such that the starting end of the helical groove and an outer surface of the cover are connected with each other; a second ball return hole formed to penetrate through the cover in a tangential direction from a terminating end of the helical groove such that the terminating end of the helical groove and the outer surface of the cover are connected with each other; and a ball return tube mounted to the outer surface of the cover to connect the first and second ball return holes with each other.