Patent Publication Number: US-2011048157-A1

Title: Mechanical arm assembly

Description:
BACKGROUND 
     1. Technical Field 
     The present disclosure relates generally to mechanical arm assemblies and, more particularly, to a mechanical arm assembly for a robot. 
     2. Description of Related Art 
     An industrial robot generally includes a plurality of connected mechanical arms. An end mechanical arm can support clamping apparatus or detectors to clamp workpieces. A joint mechanism is assembled between a first mechanical arm and a second mechanical arm for rotatably connecting the two mechanical arms. The joint mechanism generally includes a speed reducer with a housing and an output shaft. The housing is fixed in a first assembly hole of the first mechanical arm. The output shaft is fixed to an assembly end of the second mechanical arm. The assembly end of the second mechanical arm is further connected to a bearing received in a second assembly hole of the first mechanical arm. The bearing is opposite to the speed reducer. 
     During assembly of the industrial robot, the output shaft of the speed reducer normally aligns with a rotating axis of the bearing, avoiding damage to the speed reducer and the second mechanical arm during rotation of the second mechanical arm. 
     However, the output shaft of the speed reducer often cannot precisely align with the rotating axis of the bearing, due to machining precision of the described components of the industrial robot. An adjusting ring is generally positioned in the second assembly hole to adjust concentricity of the output shaft of the speed reducer and the rotating axis of the bearing. The adjusting ring is ground many times to achieve a suitable size for the industrial robot. Accordingly, assembly efficiency of the industrial robot is affected. 
     Therefore, there is room for improvement within the art. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The components in the drawings are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the present disclosure. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views. 
         FIG. 1  is an isometric view of an exemplary embodiment of a mechanical arm assembly. 
         FIG. 2  is an exploded, isometric view of the mechanical arm assembly of  FIG. 1 . 
         FIG. 3  is similar to  FIG. 2 , but viewed from another aspect. 
         FIG. 4  is a cross-section of the mechanical arm assembly of  FIG. 1 . 
         FIG. 5  is a sketch-map of a flexible wheel and a rigid wheel of  FIG. 1 . 
         FIG. 6  is a sketch-map of the flexible wheel and the rigid wheel of  FIG. 1 , with a wave generator engaging in the flexible wheel. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIGS. 1 through 4 , an exemplary embodiment of a mechanical arm assembly  100  for a robot (not shown) includes a first mechanical arm  11 , a second mechanical arm  12 , a harmonic speed reducer  13 , and a driving module  21 . The second mechanical arm  12  is rotatably connected to the first mechanical arm  11 . In the illustrated embodiment, the mechanical arm  100  is used for a six-axis robot (not shown). The six-axis robot has a controller (not shown), for controlling movement of the assembly components. The first mechanical arm  11  is positioned on a fifth rotatable axis of the six-axis robot, and the second mechanical arm  12  is positioned on a sixth rotatable axis of the six-axis robot. 
     Referring to  FIGS. 2 ,  3 ,  5  and  6 , the harmonic speed reducer  13  includes a wave generator  131 , a flexible wheel  132 , a rigid wheel  134 , a cross roller bearing  135 , a first side cover  136 , and a second side cover  137 . The wave generator  131  has a rotatable portion  1311 , and the rotatable portion  1311  is substantially elliptic. The flexible wheel  132  includes a hollow cylindrical main body  1321  and a flange  1323  formed on an end of the main body  1321 . The main body  1321  is substantially circular ring shaped. The rigid wheel  134  is substantially circular ring shaped. The flexible wheel  132  forms a plurality of outer teeth  1327  at a periphery of the main body  1321 , and the rigid wheel  134  forms a plurality of inner teeth  1347  at the inner surface. An outer radius of the main body  1321  is shorter than an inner radius of the rigid wheel  134  (as shown in  FIG. 5 ). Therefore, there are less outer teeth of flexible wheel  132  than inner teeth of the rigid wheel  134 . One of the flexible wheel  132  and the rigid wheel  134  is fixed to the first mechanical arm  11 , and the other of the flexible wheel  132  and the rigid wheel  134  is fixed to the second mechanical arm  12 . In the illustrated embodiment, the flexible wheel  132  is fixed to the first mechanical arm  11 , and the rigid wheel  134  is fixed to the second mechanical arm  12 , unilaterally supporting the second mechanical arm  12 . 
     The wave generator  131  is connected to the driving module  21  via the transmission member  22 . When the rotatable portion  1311  of the wave generator  131  is assembled in the main body  1321  of the flexible wheel  132 , the circular main body  1321  can be elastically deformed to an elliptical shape (as shown in  FIG. 6 ). Thus, the outer teeth  1327  of the flexible wheel  132  can partially mesh with the inner teeth  1347  of the rigid wheel  134 . When the rotatable portion  1311  of the wave generator  131  is rotated, the flexible wheel  132  is driven to rotate and partially mesh with different inner teeth  1347  of the rigid wheel  134 , and the rigid wheel  134  is rotated by the flexible wheel  132  at a speed less than that of the flexible wheel  132  because the number of outer teeth  1327  of the flexible wheel  132  is less than the number of inner teeth  1347  of the rigid wheel  134 . 
     The cross roller bearing  135  includes an outer ring  1351 , an inner ring  1353  and a plurality of cross rollers  1354  positioned therebetween. The outer ring  1351  is fixed to the first mechanical arm  11  and the inner ring  1353  is fixedly connected to the second mechanical arm  12 . 
     The wave generator  131 , the flexible wheel  132 , the rigid wheel  134  and the cross roller bearing  135  are positioned between the first side cover  136  and the second side cover  137 . The first side cover  136  is fixed to the first mechanical arm  11 , and the second side cover  137  is fixed to the second mechanical arm  12 . 
     The first mechanical arm  11  includes a main portion  112 , a first support portion  113  and a second support portion  115 . The first and second support portions  113 ,  115  are formed on an end of the main portion  112 , opposite to each other. The main portion  112 , the first support portion  113  and the second support portion  115  cooperatively define a receiving groove  116 . 
     The first support portion  113  includes an assembly base  1131  and an outer cover  1134 . The assembly base  1131  defines an assembly hole  1132 . The wave generator  131  engages the assembly hole  1132  of the first support portion  113 , connected to the driving module  21 . The first side cover  136 , the outer ring  1351  of the cross roller bearing  135 , and the flange  1323  are fixedly connected to the first support portion  113 . The second side cover  137 , the inner ring  1353  of the cross roller bearing  135 , and the rigid wheel  134  are fixed together. The outer cover  1134  is fixed to the assembly base  1131 , thus enveloping the harmonic speed reducer  13  and the driving module  21 . 
     The second support portion  115  includes an assembly base  1150  and a side plate  1154 . The assembly base  1150  defines an assembly hole  1151  aligned with the assembly hole  1132  in a straight line. The assembly base  1150  further forms a positioning portion  1153  surrounding the assembly hole  1151  on a first side surface. A wiper  1158  (shown in  FIG. 4 ) is sleeved on the positioning portion  1153 . The side plate  1154  is fixed to a second side surface of the assembly base  1150 . 
     The second mechanical arm  12  includes a connecting base  121  and a rotating portion  122  formed on an end thereof. The rotating portion  122  is connected to a tool (not shown), such as a cutter or clamp. The rotating portion  122  is rotated by a driving module (not shown) received in the connecting base  121 . The connecting base  121  is received in the receiving groove  116 , and connected to the wave generator  131 . In the illustrated embodiment, the connecting base  121  is substantially a rectangular housing, and includes a first connecting sidewall  1212  and a second connecting sidewall  1213  opposite to the first connecting sidewall  1212 . The first connecting sidewall  1212  defines a circular connecting hole  1215  extending to the second connecting sidewall  1213 . 
     The first connecting sidewall  1212  is fixedly connected to the second side cover  137 , the inner ring  1353 , and the rigid wheel  134 . When the wave generator  131  is rotated by the driving module  21 , the rigid wheel  134  rotates with the wave generator  131 , and then moves the second mechanical arm  12 . The positioning portion  1153  is received in the connecting hole  1215 , and the wiper  1158  is positioned between the positioning portion  1153  and the connecting base  121 . 
     It should be pointed out that the second mechanical arm  12  can also be connected to the flexible wheel  132 , in which case the first mechanical arm  11  is fixedly connected to the rigid wheel  134  and the outer ring  1351  of the cross roller bearing  135 . In addition, in such a case, a load of the second mechanical arm  12  will correspond to that of the harmonic speed reducer  13 , whereby the second mechanical arm  12  can move accurately and stably. The load of the second mechanical arm  12  is preferably less than 30 kilograms. 
     The second mechanical arm  12  is rotatably connected to the first support portion  113  of the first mechanical arm  11  via the harmonic speed reducer  13 , and rotated relative to the first mechanical arm  11  by the driving module  21 . The second support portion  115  only forms a positioning portion  1153  connected to the second mechanical arm  12 . Thus, the mechanical arm assembly  100  is easily assembled, with no need for a bearing positioned on the second support portion  115 . In addition, since the harmonic speed reducer  13  utilizes the cross roller bearing  135 , a load of the harmonic speed reducer  13  can be greatly improved. 
     It is believed that the present embodiments and their advantages will be understood from the foregoing description, and it will be apparent that various changes may be made thereto without departing from the spirit and scope of the disclosure or sacrificing all of its material advantages.