Patent Publication Number: US-2023141065-A1

Title: Speed reducer

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a Divisional application of U.S. patent application Ser. No. 16/585,474 filed on Sep. 27, 2019 and entitled “SPEED REDUCER”, which claims the benefit of U.S. Provisional Application No. 62/756,706 filed on Nov. 7, 2018 and claims the priority to Chinese Patent Application No. 201910250209.6 filed on Mar. 29, 2019. The entire contents of the above-mentioned patent applications are incorporated herein by reference for all purposes. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a speed reducer, and more particularly to a cycloid speed reducer with the benefits of a rotary vector (RV) reducer and a harmonic drive reducer and capable of achieving the high reduction ratio. 
     BACKGROUND OF THE INVENTION 
     Generally, a motor is operated at a high speed and a low torsion force. In other words, it is difficult for the motor to drive a large-sized load. For allowing the motor to drive a heavy object, a speed reducer is used for reducing the rotating speed of the motor and increasing the torsion force. 
     Conventionally, the speed reducers are classified into several types, including RV reducers, harmonic drive reducers and cycloid speed reducers. For example, the RV-E series reducer is a two-stage speed reducer produced by Nabtesco. The RV-E series reducer comprises a first speed reduction stage with a spur gear reduction mechanism and a second speed reduction stage with a differential gear reduction mechanism. The gears of the first speed reduction stage and the second speed reduction stage are made of metallic material. The RV-E series reducer is a two-stage reduction design to reduce vibration and inertia while increasing the reduction ratio. The RV-E series reducer provides high-end performance in highly rigidity and high reduction ratio configurations, and the rolling contact elements of the RV-E series reducer have high efficiency and long life. However, since the RV-E series reducer has larger volume and weight and has many components to be assembled, the cost of the RV-E series reducer is high. 
     The harmonic drive reducer comprises a wave generator, a flexible element (e.g., a flexible spline) and a rigid gear. The elastic deformation of the flexible element can be controlled to result in a pushing action so as to transmit motion and power of mechanical transmission. The harmonic drive reducer has smaller size, lighter weight and higher precision when compared with the RV reducer. However, since the rigidity of the flexible element of the harmonic drive reducer is lower than the metallic element, the harmonic drive reducer is unable to withstand high impact and has a problem of causing teeth difference friction. In other words, the use life of the harmonic drive reducer is shorter. Moreover, since the input speed of the harmonic drive reducer is not high and limited, the reduction ratio of the harmonic drive reducer is lower. 
     Conventionally, a cycloid speed reducer comprises an eccentric shaft and two cycloid wheels. Each of the two cycloid wheels comprises a plurality of teeth. Moreover, the two cycloid wheels are linked with a power input shaft and a power output shaft, respectively. During operations of the cycloid speed reducer, one cycloid wheel is rotated with the power input shaft through the eccentric shaft, and the power output shaft is rotated with the other cycloid wheel. Through the corresponding teeth, the two cycloid wheels are correspondingly rotated. The conventional cycloid speed reducer has many benefits such as high transmission ratio, compact structure, high loading capability and high transmission efficiency. However, the conventional cycloid speed reducer still has some drawbacks. For forming the teeth, it is necessary to form a concave structure in a surface of the main body of the cycloid wheel. Then, the concave structure is machined to form inner teeth. As known, it is difficult to machine the teeth. 
     For overcoming the above drawbacks, there is a need of providing a cycloid speed reducer with the characteristics of a RV reducer and a harmonic drive reducer and capable of achieving high reduction ratio. Moreover, the teeth can be machined more easily. 
     SUMMARY OF THE INVENTION 
     An object of the present invention provides a speed reducer. By the speed reducer of the present invention, the problems of the conventional RV reducer (e.g., high volume, weight and cost) and the problems of the conventional harmonic drive reducer (e.g., unable to withstand high impact, the teeth difference friction problem and the low reduction ratio) will be overcome. Moreover, when compared with the conventional cycloid speed reducer, the teeth of the speed reducer of the present invention can be machined more easily. 
     In accordance with an aspect of the present invention, a speed reducer is provided. The speed reducer comprises a transmission shaft, an eccentric wheel, a first wheel assembly, a rotating wheel and a second wheel assembly. The transmission shaft has a first end and a second end. The eccentric wheel is eccentrically fixed on the second end of the transmission shaft, and the eccentric wheel is driven by the transmission shaft to eccentrically rotate relative to an axle center of the transmission shaft. The first wheel assembly comprises a first wheel disc and at least one first roller. The first wheel disc is disposed between the first end and the second end of the transmission shaft and comprises a first annular body. The first annular body is extended from the first wheel disc in a direction away from the first end of the transmission shaft. The first annular body has an inner wall. The at least one first roller is disposed on the inner wall. The rotating wheel comprises a main body and an axle hole. The eccentric wheel is disposed within the axle hole. The rotating wheel is rotated with the eccentric wheel. The main body comprises an outer ring structure and a concave structure. The outer ring structure is disposed on an outer periphery of the main body and comprises at least one first tooth. The at least one first tooth is in contact with the corresponding first roller. At least one second roller is disposed within the concave structure. The second wheel assembly comprises a second wheel disc and at least one second tooth. The second wheel disc comprises a second annular body. The second annular body is extended from the second wheel disc in a direction toward the first end of the transmission shaft. The at least one second tooth is disposed on an outer periphery of the second annular body. Each of the at least one second tooth is in contact with the corresponding second roller. 
     In accordance with another aspect of the present invention, a speed reducer is provided. The speed reducer comprises a transmission shaft, an eccentric wheel, a first wheel assembly, a rotating wheel and a second wheel assembly. The transmission shaft has a first end and a second end. The eccentric wheel is eccentrically fixed on the second end of the transmission shaft, and the eccentric wheel is driven by the transmission shaft to eccentrically rotate relative to an axle center of the transmission shaft. The first wheel assembly comprises a first wheel disc. The first wheel disc comprises a first annular body and at least one first tooth. The first wheel disc is disposed between the first end and the second end of the transmission shaft. The first annular body is extended from the first wheel disc in a direction away from the first end of the transmission shaft. The first annular body has an inner wall. The at least one tooth is disposed on the inner wall. The rotating wheel comprises a main body and an axle hole. The eccentric wheel is disposed within the axle hole. The rotating wheel is rotated with the eccentric wheel. The main body comprises an outer ring structure and a concave structure. The outer ring structure is disposed on an outer periphery of the main body and comprises at least one first roller. The at least one first tooth is in contact with the corresponding first roller. At least one second roller is disposed within the concave structure. The second wheel assembly comprises a second wheel disc. The second wheel disc comprises a second annular body and at least one second tooth, and the second annular body is extended from the second wheel disc in a direction toward the first end of the transmission shaft. The at least one second tooth is disposed on an outer periphery of the second annular body. Each of the at least one second tooth is in contact with the corresponding second roller. 
     The above contents of the present invention will become more readily apparent to those ordinarily skilled in the art after reviewing the following detailed description and accompanying drawings, in which: 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1 A  is a schematic exploded view illustrating a speed reducer according to a first embodiment of the present invention; 
         FIG.  1 B  is a schematic cross-sectional view illustrating the speed reducer as shown in  FIG.  1 A ; 
         FIG.  2 A  is a schematic exploded view illustrating a speed reducer according to a second embodiment of the present invention; 
         FIG.  2 B  is a schematic cross-sectional view illustrating the speed reducer as shown in  FIG.  2 A ; 
         FIG.  3 A  is a schematic exploded view illustrating a speed reducer according to a third embodiment of the present invention; 
         FIG.  3 B  is a schematic cross-sectional view illustrating the speed reducer as shown in  FIG.  3 A ; 
         FIG.  4 A  is a schematic exploded view illustrating a speed reducer according to a fourth embodiment of the present invention; and 
         FIG.  4 B  is a schematic cross-sectional view illustrating the speed reducer as shown in  FIG.  4 A . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The present invention will now be described more specifically with reference to the following embodiments. It is to be noted that the following descriptions of preferred embodiments of this invention are presented herein for purpose of illustration and description only. It is not intended to be exhaustive or to be limited to the precise form disclosed. 
     The present invention provides a speed reducer. Hereinafter, four embodiments of the speed reducer will be described. The first embodiment of the speed reducer is shown in  FIGS.  1 A and  1 B . The second embodiment of the speed reducer is shown in  FIGS.  2 A and  2 B . The third embodiment of the speed reducer is shown in  FIGS.  3 A and  3 B . The fourth embodiment of the speed reducer is shown in  FIGS.  4 A and  4 B . The structures and operations of the speed reducers  1 ,  2 ,  3  and  4  of the four embodiments are similar to each other. The differences among the speed reducers  1 ,  2 ,  3  and  4  of the four embodiments substantially lie in that the rollers or the teeth are disposed on the inner wall of the first wheel assembly, the rollers or the teeth are disposed on the outer ring structure of the rotating wheel, and the number of the teeth and the number of the rollers. The detailed structures of the speed reducer  1  of the first embodiment of  FIGS.  1 A and  1 B  are described as below. As for the second embodiment, the third embodiment and the fourth embodiment, the elements and features indicated by the numerals similar to those of the first embodiment of  FIGS.  1 A to  1 B  mean similar elements and features, and are not redundantly described herein. Only the differences among the four embodiments are described in the corresponding paragraphs. 
     Please refer to  FIGS.  1 A and  1 B .  FIG.  1 A  is a schematic exploded view illustrating a speed reducer according to a first embodiment of the present invention.  FIG.  1 B  is a schematic cross-sectional view illustrating the speed reducer as shown in  FIG.  1 A . The speed reducer  1  can be applied to motors, machine tools, robotic arms, automobiles, motorcycles or other motive machines in order to provide a speed reducing function. 
     In this embodiment, the speed reducer  1  is a two-stage cycloid speed reducer. The speed reducer  1  comprises a transmission shaft  10 , an eccentric wheel  11 , a first wheel assembly  12 , a rotating wheel  13  and a second wheel assembly  14 . 
     The transmission shaft  10  has a first end  100  and a second end  101 . The first end  100  is a power input end for receiving an input power from a motor (not shown). Moreover, the eccentric wheel  11  has an eccentric hole  110 . The geometric center of the eccentric hole  110  is deviated from the geometric center of the eccentric wheel  11 . The second end  101  of the transmission shaft  10  is penetrated through the eccentric hole  110 . Consequently, the eccentric wheel  11  is eccentrically fixed on the second end  101  of the transmission shaft  10 . When the input power received by the first end  100  of the transmission shaft  10  to result in rotation of the transmission shaft  10 , the eccentric wheel  11  is driven by the second end  101  of the transmission shaft  10 . Consequently, the eccentric wheel  11  is eccentrically rotated relative to an axle center of the transmission shaft  10 . 
     The first wheel assembly  12  comprises a first wheel disc  120  and at least one first roller  123 . A central hole  124  is formed at the geometric center of the first wheel disc  120 . Moreover, a bearing (not shown) is disposed within the central hole  124  of the first wheel disc  120 . An example of the bearing comprises but is not limited to a ball bearing, a needle bearing or an oil-retaining bearing. The second end  101  of the transmission shaft  10  is penetrated through the bearing that is disposed within the central hole  124  of first wheel disc  120 . Consequently, the first end  100  and the second end  101  of the transmission shaft  10  are located at two opposite sides of the first wheel disc  120 . In addition, the first wheel disc  120  further comprises a first annular body  121 . The first annular body  121  is extended from the first wheel disc  120  in the direction away from the first end  100  of the transmission shaft  10  (i.e., in the direction toward the rotating wheel  13 ). Consequently, the first annular body  121  is a hollow structure. The first annular body  121  has an inner wall  122 . The at least one first roller  123  is disposed on the inner wall  122 . The first wheel assembly  12  may be rotated about the axel center of the transmission shaft  10  or not rotated. In case that the first wheel assembly  12  is rotated, the first wheel disc  120  and the at least one first roller  123  are rotated about the axel center of the transmission shaft  10 . 
     At least a portion of the rotating wheel  13  is accommodated within a hollow space of the first annular body  121 . In this embodiment, the rotating wheel  13  comprises a main body  130  and an axle hole  131 . The axle hole  131  is located at the geometric center of the main body  130 . The bearing (not shown) is disposed within the axle hole  131 . Consequently, the eccentric wheel  11  is rotatably disposed within the axle hole  131  of the rotating wheel  13  through the bearing. Consequently, when the eccentric wheel  11  is rotated, the rotating wheel  13  is synchronously rotated with the eccentric wheel  11 . The main body  130  comprises a first surface  1300 , a second surface  1301 , an outer ring structure  1302  and a concave structure  1303 . The first surface  1300  and the second surface  1301  are opposed to each other. The first surface  1300  is arranged beside the first wheel assembly  12 . The second surface  1301  is arranged beside the second wheel assembly  14 . 
     The outer ring structure  1302  is disposed on an outer periphery of the main body  130 . The outer ring structure  1302  comprises at least one first tooth  133 . The at least one first tooth  133  is in contact with the corresponding first roller  123 . The concave structure  1303  is concavely formed in the second surface  1301  of the main body  130 . The concave structure  1303  comprises at least one second roller  132 . At least a portion of the second roller  132  is accommodated within the concave structure  1303 . Moreover, since at least a portion of the main body  130  comprises the concave structure  1303 , the other region of the main body  130 , for example the region between the concave structure  1303  and the outer ring structure  1302 , is defined as a wall region with thicker thickness. 
     The second wheel assembly  14  comprises a second wheel disc  140  and at least one second tooth  142 . The second wheel disc  140  comprises a second annular body  141 . The second annular body  141  is extended in the direction toward the first end  100  of the transmission shaft  10 . The at least one second tooth  142  is circumferentially arranged on the outer periphery of the second annular body  141 . That is, the second tooth  142  is an outer tooth having a blunt teeth profile, a wavy profile or a petal profile. The at least one second tooth  142  is partially accommodated within the concave structure  1303  and is in contact with the corresponding second roller  132 . 
     In an embodiment, the first wheel assembly  12  comprises a plurality of first rollers  123 . The plurality of first rollers  123  are circumferentially and discretely arranged on the inner wall  122  of the first annular body  121  at regular intervals. The rotating wheel  13  comprises a plurality of first teeth  133 . The plurality of first teeth  133  are circumferentially and discretely arranged on the outer ring structure  1302  formed on the outer periphery of the main body  130 . The plurality of first rollers  123  are in contact with the corresponding first teeth  133 . The first teeth  133  are outer teeth formed on the outer periphery of the main body  130 . Due to the first teeth  133 , the main body  130  has a blunt teeth profile, a wavy profile or a petal profile. 
     In some embodiments, the second wheel assembly  14  may be rotated or not rotated. In case that the second wheel assembly  14  is rotated and the rotating wheel  13  is synchronously rotated with the eccentric wheel  11 , the second teeth  142  and the corresponding second rollers  132  are pushed against each other and the second wheel disc  140  is rotated. Consequently, the second wheel assembly  14  is rotated about its axel center. When the first wheel assembly  12  is rotated about the axel center of the transmission shaft  10 , the second wheel assembly  14  is not rotated. When the first wheel assembly  12  is not rotated, the second wheel assembly  14  is rotated about the axel center thereof. 
     In this embodiment, the number of the second rollers  132  is one greater than the number of the second teeth  142 , and the number of the first rollers  123  is one greater than the number of the first teeth  133  (see  FIG.  1 B ). For example, in case that the number of the first teeth  133  is M and the number of the second teeth  142  is N, the number of the first rollers  123  is equal to (M+1) and the number of the second rollers  132  is equal to (N+1). 
     According to the rotating conditions of the first wheel assembly  12  and the second wheel assembly  14 , the speed reducer  1  of the present invention can be designed to have two operating situations with different reduction ratios. In a first operating situation, M+1 first rollers  123  are not rotated relative to the axle center of the transmission shaft  10  (i.e. the first wheel assembly  12  is not rotated), but N second teeth  142  are driven to rotate as the rotating wheel  13  is rotated (i.e. the second wheel assembly  14  is rotated). The reduction ratio of the speed reducer  1  is equal to (M×N)/{M×N−(M+1)×(N+1)}, wherein M and N are integers greater than 1. Meanwhile, the second wheel assembly  14  is the power output end. In a second operating situation, N second teeth  142  are not rotated (i.e. the second wheel assembly  14  is not rotated), but M+1 first rollers  123  are driven to rotate relative to the axle center of the transmission shaft  10  as the rotating wheel  13  is rotated (i.e. the first wheel assembly  12  is rotated). The reduction ratio of the speed reducer  1  is equal to {(M+1)×(N+1)}/{(M+1)×(N+1)−(M×N)}. Meanwhile, the first wheel assembly  12  is the power output end. 
     From the above descriptions, the present invention provides the speed reducer  1 . The rotating wheel  13  comprises at least one first tooth  133  and at least one second roller  132 . The at least one first tooth  133  is in contact with the corresponding first roller  123  of the first wheel assembly  12 . The at least one second roller  132  is in contact with the corresponding second tooth  142  of the second wheel assembly  14 . The pushing action of the speed reducer  1  of the present invention is similar to that of the conventional harmonic drive reducer. Consequently, the speed reducer  1  of the present invention has simplified structure and less number of components, and is easily assembled and cost-effective. Due to the concave structure  1303  of the rotating wheel  13 , the thickness, volume and weight of the overall speed reducer  1  are reduced. Moreover, due to the wall region of the rotating wheel  13 , the overall rigidity of the speed reducer  1  is increased to withstand high impact, and the use life of the speed reducer  1  is prolonged. In other words, the speed reducer  1  of the present invention has the benefits of a RV reducer and a harmonic drive reducer. Moreover, the speed reducer  1  of the present invention can provide a high reduction ratio. Since the second teeth  142  of the second wheel assembly  14  are formed as the outer teeth on the outer periphery of the second annular body  141 , the second teeth  142  can be machined more easily. 
     Please refer to  FIGS.  2 A and  2 B .  FIG.  2 A  is a schematic exploded view illustrating a speed reducer according to a second embodiment of the present invention.  FIG.  2 B  is a schematic cross-sectional view illustrating the speed reducer as shown in  FIG.  2 A . In the speed reducer  2  of this embodiment, the number of the second teeth  142  is one greater than the number of the second rollers  132 , and the number of the first rollers  123  is one greater than the number of the first teeth  133  (see  FIG.  2 B ). For example, in case that the number of the first teeth  133  is M and the number of the second teeth  142  is N, the number of the first rollers  123  is equal to (M+1) and the number of the second rollers  132  is equal to (N−1). 
     According to the rotating conditions of the first wheel assembly  12  and the second wheel assembly  14 , the speed reducer  2  of the present invention can be designed to have two operating situations with different reduction ratios. In a first operating situation, M+1 first rollers  123  are not rotated relative to the axle center of the transmission shaft  10  (i.e. the first wheel assembly  12  is not rotated), but N second teeth  142  are driven to rotate as the rotating wheel  13  is rotated (i.e. the second wheel assembly  14  is rotated). The reduction ratio of the speed reducer  2  is equal to (M×N)/{M×N−(M+1)×(N−1)}, wherein M and N are integers greater than 1. Meanwhile, the second wheel assembly  14  is the power output end. In a second operating situation, N second teeth  142  are not rotated (i.e. the second wheel assembly  14  is not rotated), but M+1 first rollers  123  are driven to rotate relative to the axle center of the transmission shaft  10  as the rotating wheel  13  is rotated (i.e. the first wheel assembly  12  is rotated). The reduction ratio of the speed reducer  2  is equal to {(M+1)×(N−1)}/{(M+1)×(N−1)−(M×N)}. Meanwhile, the first wheel assembly  12  is the power output end. 
     Please refer to  FIGS.  3 A and  3 B .  FIG.  3 A  is a schematic exploded view illustrating a speed reducer according to a third embodiment of the present invention.  FIG.  3 B  is a schematic cross-sectional view illustrating the speed reducer as shown in  FIG.  3 A . Comparing the speed reducer  3  of this embodiment with the speed reducer  1  of the first embodiment as shown in  FIGS.  1 A and  1 B , the first rollers  123  disposed on the inner wall  122  of the first wheel assembly  12  are replaced by first teeth  123 ′, and the first teeth  133  of the outer ring structure  1302  are replaced by first rollers  133 ′. The first teeth  123 ′ are circumferentially and discretely arranged on the inner wall  122  of the first annular body  121  at regular intervals. The first rollers  133 ′ are circumferentially and discretely arranged on the outer ring structure  1302  of the main body  130 . The first teeth  123 ′ are in contact with the corresponding first rollers  133 ′. In the speed reducer  3  of this embodiment, the number of the second teeth  142  is one less than the number of the second rollers  132 , and the number of the first rollers  133 ′ is one less than the number of the first teeth  123 ′ (see FIG.  3 B). For example, in case that the number of the first teeth  123 ′ is M and the number of the second teeth  142  is N, the number of the first rollers  133 ′ is equal to (M−1) and the number of the second rollers  132  is equal to (N+1). 
     According to the rotating conditions of the first wheel assembly  12  and the second wheel assembly  14 , the speed reducer  3  of the present invention can be designed to have two operating situations with different reduction ratios. In a first operating situation, M first teeth  123 ′ are not rotated (i.e. the first wheel assembly  12  is not rotated), but N second teeth  142  are driven to rotate as the rotating wheel  13  is rotated (i.e. the second wheel assembly  14  is rotated). The reduction ratio of the speed reducer  3  is equal to {(M−1)×N}/{(M−1)×N−(M)×(N+1)}, wherein M and N are integers greater than 1. Meanwhile, the second wheel assembly  14  is the power output end. In a second operating situation, N second teeth  142  are not rotated (i.e. the second wheel assembly  14  is not rotated), but M first teeth  123 ′ are driven to rotate as the rotating wheel  13  is rotated (i.e. the first wheel assembly  12  is rotated). The reduction ratio of the speed reducer  3  is equal to {(M)×(N+1)}/{(M)×(N+1)−(M−1)×N}. Meanwhile, the first wheel assembly  12  is the power output end. 
       FIG.  4 A  is a schematic exploded view illustrating a speed reducer according to a fourth embodiment of the present invention.  FIG.  4 B  is a schematic cross-sectional view illustrating the speed reducer as shown in  FIG.  4 A . Comparing the speed reducer  4  of this embodiment with the speed reducer  3  of the third embodiment as shown in  FIGS.  3 A and  3 B , the number of first rollers  133 ′ is one less than the number of the first teeth  123 ′, and the number of the second teeth  142  is one greater than the number of the second rollers  132  (see  FIG.  4 B ). For example, in case that the number of the first teeth  123 ′ is M and the number of the second teeth  142  is N, the number of the first rollers  133 ′ is equal to (M−1) and the number of the second rollers  132  is equal to (N−1). 
     According to the rotating conditions of the first wheel assembly  12  and the second wheel assembly  14 , the speed reducer  4  of the present invention can be designed to have two operating situations with different reduction ratios. In a first operating situation, M first teeth  123 ′ are not rotated (i.e. the first wheel assembly  12  is not rotated), but N second teeth  142  are driven to rotate as the rotating wheel  13  is rotated (i.e. the second wheel assembly  14  is rotated). The reduction ratio of the speed reducer  4  is equal to {(M−1)×N}/{(M−1)×N−(N−1)×(M)}, wherein M and N are integers greater than 1. Meanwhile, the second wheel assembly  14  is the power output end. In a second operating situation, N second teeth  142  are not rotated (i.e. the second wheel assembly  14  is not rotated), but M first teeth  123 ′ are driven to rotate as the rotating wheel  13  is rotated (i.e. the first wheel assembly  12  is rotated). The reduction ratio of the speed reducer  4  is equal to {(M)×(N−1)}/{(M)×(N−1)−(M−1)×N}. Meanwhile, the first wheel assembly  12  is the power output end. 
     From the above descriptions, the present invention provides a speed reducer. The at least one first tooth is in contact with the corresponding first roller. The at least one second roller is in contact with the corresponding second tooth. The rotating wheel, the first wheel assembly and the second wheel assembly cooperate with each other. The pushing action of the speed reducer of the present invention is similar to that of the conventional harmonic drive reducer. Consequently, the speed reducer of the present invention has simplified structure and less number of components, and is easily assembled and cost-effective. Due to the concave structure of the rotating wheel, the thickness, volume and weight of the overall speed reducer are reduced. Moreover, due to the wall region of the rotating wheel, the overall rigidity of the speed reducer is increased to withstand high impact, and the use life of the speed reducer is prolonged. In other words, the speed reducer of the present invention has the benefits of a RV reducer and a harmonic drive reducer. Moreover, the speed reducer of the present invention can provide a plurality of different high reduction ratios. In addition, in the speed reducer of the present invention, the second teeth of the second wheel assembly are formed as the outer teeth on the outer periphery of the second annular body, and the first tooth of the rotating wheel are formed as the outer teeth on the outer periphery of the outer ring structure of the main body, so that the second teeth and the first teeth formed as the outer teeth can be machined more easily. 
     While the invention has been described in terms of what is presently considered to be the most practical and preferred embodiments, it is to be understood that the invention needs not be limited to the disclosed embodiment. On the contrary, it is intended to cover various modifications and similar arrangements included within the spirit and scope of the appended claims which are to be accorded with the broadest interpretation so as to encompass all such modifications and similar structures.