Patent Publication Number: US-2011067514-A1

Title: Robot arm assembly and industrial robot using the same

Description:
BACKGROUND 
     1. Technical Field 
     The present disclosure generally relates to robot arm assemblies, and particularly to a robot assembly for an industrial robot with multi-stage gear transmissions. 
     2. Description of Related Art 
     A commonly used industrial robot includes a fixed base, a frame pivotally connected thereto about a first axis, a lower arm, one end of which is pivotally connected to the frame about a second axis, and an upper arm, one end of which is pivotally connected to the other end of the lower arm about a third axis. An end effector, such as a welding device, a gripper, or a cutting tool, is mounted at a distal end of the upper arm of the industrial robot to execute specific tasks. Generally six axes are utilized to achieve maximum movement of the end effectors. 
     In typical robots of this kind, each arm of the robots rotates around a rotating axis driven by a driven unit. Typically, the driven unit includes a motor mounted on a first arm and a speed reducer coupled to the motor to transmit the movement of the motor to a second arm. The speed reducer may be a high gear ratio gear, such as a harmonic gear reducer, a RV reducer (rotary vector reducer), or a planetary reducer. The motor and the speed reducer are arranged along the rotating axis of the arm, rendering the range along the rotating axis relatively large. In a six-axis industrial robot, the fifth axle is rotatably connected to the sixth axle and may be perpendicularly positioned. The fifth and sixth axles are respectively driven by two driven units arranged adjacent to each other, such that the whole size of the fifth and sixth axles is relatively large. As a result, the industrial robots need considerable space to operate freely and safely. 
     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, and all the views are schematic. 
         FIG. 1  is a plan view of one embodiment of an industrial robot, having a robot assembly and six rotating axes. 
         FIG. 2  is an isometric of one embodiment of a robot arm assembly, utilized in an industrial robot, such as, for example, that of  FIG. 1 . 
         FIG. 3  is an isometric lateral cross section of the robot arm assembly of  FIG. 2 . 
         FIG. 4  is an enlarged detail appearing in  FIG. 3 . 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIG. 1 , one embodiment of an industrial robot  100  may be a six-axis industrial robot. The industrial robot  100  includes a base seat  11 , a bracket  12  pivotally connected to the base seat  11 , a first arm  13  pivotally connected to the bracket  12 , a joint portion  15  pivotally connected to the first arm  13 , and a second arm  14  pivotally connected to the joint portion  15 . 
     The industrial robot  100  has six rotating axes. The bracket  12  is rotatable around a first axis  161 . The first arm  13 , the joint portion  15  and the second arm  14 , are rotatable around second, third, and fourth axes  162 ,  163 , and  164 , respectively. The industrial robot  100  further includes a fifth axle  165 , a sixth axle  166 , and a control device  19  to control the movement of the industrial robot  100 . An end effector (not shown), such as a clamp, a cutter, or a detector is generally positioned on a distal end of the sixth axle  166  to complete various operations. 
     Referring to  FIG. 2  through  FIG. 4 , one embodiment of a robot arm assembly  200  is included in an industrial robot, such as the industrial robot  100  described above. The robot arm assembly  200  includes the second arm  14 , the fifth axle  165  pivotally connected to an end of the second arm  14 , the sixth axle  166  pivotally connected to the fifth axle  165 , a first motor  17 , a first gear transmission  21  to drive the fifth axle  165 , a second motor  18 , a second gear transmission  23  to drive the sixth axle  166 , and the control device  19  to control the first and second motors  17 ,  18 . The first and second motors  17 ,  18  may provide rotation of the fifth and sixth axles  156 ,  166  respectively, via the first and second gear transmissions  21 ,  23  respectively. The first and second gear transmissions  21 ,  23  are both multi-stage gear transmissions. 
     The second arm  14  is hollow with a substantially fork-like extension. The second arm  14  includes a connecting portion  141  and a supporting portion  142  connected to an end of the connecting portion  141 . The first and second gear transmissions  21 ,  23 , and the fifth axle  165  can be received in the inner space of the second arm  14 . The connecting portion  141  is substantially cylindrical and has a hollow portion  1412 . The supporting portion  142  includes a first supporting wall  1421  in which the fifth axle  165  is supported, and a second supporting wall  1423  provided at a predetermined distance apart from the first supporting wall  1421 . The first and second supporting walls  1421 ,  1423  extend substantially in parallel and are located on opposite sides of the connecting portion  141 . A connecting base  1424  is formed on the first supporting wall  1421  extending substantially perpendicularly to the first supporting wall  1421 . 
     The fifth axle  165  is pivotally connected to the connecting base  1424  and rotatably supported by a bearing  1425  placed in the second arm  14 . The fifth axle  165  includes an output shaft  1651  whose pivotal axis is substantially perpendicular to the first or second supporting wall  1421 ,  1423 . The output shaft  1651  defines a first shaft hole  1652  and a second shaft hole  1653  substantially perpendicular to and communicating with the first shaft hole  1652 . The center axis of the second shaft hole  1652  and the rotating axis of the fifth axle  165  are substantially aligned along a common axis. 
     The first gear transmission  21  is positioned between the first motor  17  and the fifth axle  165 . The first gear transmission  21  includes a first input gear  212 , a first transmission shaft  213 , a pair of first spur gears  214   a ,  214   b , and a pair of first bevel gears  215   a ,  215   b  combined in series. 
     The first transmission shaft  213  is hollow and substantially cylindrical. The first transmission shaft  213  is rotatably received in the hollow portion  1412  of the second arm  14  and supported by bearings (not labeled) placed in the hollow potion  1412 . The first input gear  212  is mounted at an end of the first transmission shaft  14  away from the fifth axle  165 , and coupled to an output gear  171  of the first motor  17 . The first spur gear  214   a  is secured to an end of the first transmission shaft  213  adjacent to the fifth axle  165 . The first bevel gear  215   a  and the first spur gear  214   b  are aligned along a common axis and rigidly connected. The first bevel gear  215   b  and the output shaft  1651  are aligned along a common axis and rigidly connected, such that the fifth axle  165  can rotate as the first bevel gear  215   b  rotates. 
     The second gear transmission  23  is positioned between the second motor  18  and the sixth axle  166 . The second gear transmission  23  includes a second input gear  232 , a second transmission shaft  233 , a pair of second spur gears  234   a ,  234   b , a pair of third bevel gears  235   a ,  235   b , and a pair of second bevel gears  236   a ,  236   b  combined in series. 
     The second transmission shaft  233  is substantially cylindrical and rotatably received in the first transmission shaft  213  with two ends extending out therefrom. The second transmission shaft  233  is rotatably supported by one or more bearings (not labeled) between an inner circumference of the first transmission shaft  213  and an outer circumference of the second transmission shaft  233 . The second input gear  232  is mounted at an end of the second transmission shaft  233  away from the fifth axle  165 , and coupled to an output gear  181  of the second motor  18 . The first and second input gears  212 ,  232  are offset from each other in an axial direction. The first and second motors  17 ,  18  are positioned on opposite sides of the transmissions  213 ,  233  along the axial direction thereof to couple to the first and second gear transmissions  21 ,  23 . The second spur gear  234   a  is secured to an end of the second transmission shaft  233  adjacent to the fifth axle  165 . The pair of second spur gears  234   a ,  234   b  and the pair of first spur gears  214   a ,  214   b  are offset from each other in an axial direction. The third bevel gear  235   a  and the second spur gear  234   b  are aligned along a common axis and rigidly connected. The third bevel gears  235   a  and the first bevel gear  215   a  may be located on opposite sides of the first transmission shaft  213  along the axial direction. The second and third bevel gears  236   a ,  235   b  are substantially aligned along a common axis. The second bevel gear  236   b  is substantially coaxially aligned with the sixth axle  166  and rigidly connected to an end thereof. The second bevel gear  236   b  can be received in the first shaft hole  1652  of the fifth axle  165 . 
     The first and second input gears  212 ,  232 , the first and second spur gears  214   a ,  214   b ,  234   a ,  234   b , the first bevel gears  215   a ,  215   b , the second bevel gears  236   a ,  236   b  and the third bevel gears  235   a ,  235   b  are received in the second arm  14  and rotatably supported by bearings (not labeled) placed therein, respectively. 
     The first and second motors  17 ,  18  can be mounted at the end of the second arm  14  away from the fifth axle  165  and sixth axle  166 , such that it is unnecessary to arrange the first and second motors  17 ,  18  along the axes of the fifth and sixth axles  165 ,  166 , respectively. Therefore, the extension along both the axes of the fifth and sixth axles  165 ,  166  is minimized, and the robot arm assembly  200  is thus compact. 
     In addition, loads on the fifth axle  165  applied by the second motor and speed reducer weight can be removed to facilitate control of the fifth axle and sixth axles  165 ,  166 . Since the first and second gear transmissions  21 ,  23  each apply a multi-stage transmission, a predetermined gear ratio can be achieved, and the first and second gear transmissions  21 ,  23  can use standard gears, so that costs are conserved. Furthermore, the space occupied by the robot arm assembly  200  is further conserved due to the hollow structure of the second arm  14 , allowing at least a partial reception of the first and second gear transmissions  21 ,  23  therein. 
     The operation of the robot arm assembly  200  is explained with reference to one embodiment. The operations of other motion components of the robot  100 , such as the bracket  12  and first arm  13  are similar to a conventional robot, and description thereof is thus not given. 
     The control device  19  is programmable with control instructions therein. The first gear transmission  21  transmits the movement of the first motor  17  to the fifth axle  165  to rotate the fifth axle  165  around the rotating axis thereof, in response to the control instructions for the first motor  17 . Simultaneously, the sixth axle  166  can follow the rotation of the fifth axle  165  to rotate around the axis of the fifth axle  165 , and rotate around the axis of the sixth axle  166 , because the pair of second bevel gears  236   a ,  236   b  meshes with each other, such that an error is produced (defining the error as a following rotation error here). In order to compensate the following rotation error, the sixth axle  166  rotates synchronously around the axis of the sixth axle  166  driven by the second gear transmission  23 , in response to the control instruction for the second motor  18 . Therefore, the sixth axle  166  can be kept in the current position while the fifth axle  165  is rotating. When independent control of the sixth axle  166  is required, the second motor  18  drives the sixth axle  166  via the second gear transmission  23  to a predetermined angle around the axis of the sixth axle  166 , in response to instructions from the control device  19 . The rotation of the sixth axle  166  does not change the position of the fifth axle  165 , such that the sixth axle  166  can be positioned accurately by the control device  19  as described. 
     It should be understood that the first and second gear transmissions  21 ,  23  can also add or remove one or more gear transmission stages to achieve a predetermined gear ratio. 
     It should also be understood that the robot  100  is not limited to a six-axis industrial robot, and can alternatively be industrial robots with fewer axes, with the above-mentioned three axes well within the scope of the disclosure. 
     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.