Patent Document

FIELD OF INVENTION 
     The present invention relates in general to an articulated robot wrist. 
     BACKGROUND 
     A robot wrist is disclosed for example in European patent application EP 1938930 A1 and in European patent EP 2 022 609 B1. 
     SUMMARY 
     Disclosed herein are embodiments of an articulated robot wrist. One embodiment is of the type comprising a first body comprising a first and a second end, said first end of said first body being intended to be mounted on a robot component that is rotatable around a first axis. A second body comprises a first and a second end, said first end of said second body being rotatably mounted on said second end of said first body around a second axis inclined with respect to said first axis. A third body comprises a first and a second end, said first end of said third body being rotatably mounted on said second end of said second body around a third axis inclined with respect to said second axis. Said first and third axes are both substantially orthogonal to said second axis. In at least one position of said robot wrist, said first and third axes are substantially aligned to each other. Said first body comprises a substantially elbow-shaped portion having at its base a first opening which is directed towards said second and third bodies and which is substantially aligned to said first axis in the mounted condition of said wrist. 
     Said elbow-shaped portion carries an offset portion, substantially arranged side by side and spaced apart with respect to the axis of said first opening and on which there is provided said second end of said first body. Said second body comprises a cantilever portion, corresponding to said second end of said second body, which has a second opening substantially aligned to said third axis, in the mounted condition of said robot wrist said first and second openings being traversed by cables and/or tubes for the supply and/or control of a device associated to said third body of the robot wrist. 
     Said robot wrist can further comprise means for driving rotation of said second and third bodies, around said second and third axes, respectively. Said means for driving rotation of said second and third bodies comprises a first and a second motor carried by said offset portion of said first body, first gear means for transmission of the rotation of the output shaft of said first motor to said second body, and second gear means for transmission of rotation of the output shaft of said second motor to said third body. 
     The object of the present invention is that of improving a robot wrist of this type, in particular by providing a more compact structure and a simpler and more reliable kinematic chain. The object is achieved by providing a robot wrist having the features of claim  1 . The claims form integral part of the technical teaching which is provided herein with reference to the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be now described, purely by way of non-limiting example, with reference to the annexed drawings, in which: 
         FIG. 1  represents a perspective view of the robot wrist described herein; 
         FIG. 2  shows a cross-sectional view taken along the longitudinal sectional plane diagrammatically shown by line II-II in  FIG. 1 ; 
         FIG. 3  shows a detail of  FIG. 2  at an enlarged scale; and 
         FIG. 4  shows a further detail of  FIG. 2  at an enlarged scale. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     In the following description various specific details are described in order to provide thorough understanding of the embodiments. The embodiments may be provided for example without one or more of these specific details, or through other methods, components or materials etc. 
     In other cases, known structures, materials or operations are not shown nor described in detail to avoid a bulky description of the various aspects of the embodiments. Therefore, references as used herein are only for convenience and do not define the scope of protection or the scope of the embodiments. 
     In the figures, reference numeral  10  designates an articulated robot wrist. As known in the art, a robot of this type is to be mounted on a robot component and is to be provided with a tool or other operating apparatus which is supplied and/or controlled with cables and/or tubes which are directly associated with the structure of the wrist itself. These cables and/or tubes are shown diagrammatically in the figures and designated by reference C. They define what is called the “harness” of the robot wrist, the robot wrist being defined as being “harnessed” once the cables and/or tubes have been mounted thereon. These aspects will not be discussed herein in detail, since they are per se conventional in the art and will be explained only to the extent which is necessary for describing the wrist of the invention. 
     Wrist  10  comprises a first body  12  including a first end  12 ′ and a second end  32 . The first end  12 ′ is to be mounted on a robot component (not shown) which is rotatable around a first axis IV. 
     Wrist  10  further comprises a second body  14  comprising a first end  42  and a second end  24 . The first end  42  is rotatably mounted on the end  32  of body  12  around a second axis V inclined with respect to the first axis IV. Furthermore, the robot wrist  10  comprises a third body  16  comprising a first end and a second end designated by reference  16 ″. As shown in the figures, preferably the third body  16  is an annular body which is to be traversed by cables and/or tubes of the tool associated to the wrist and whose end  16 ″ have a surface on which there are formed suitable seats for connection of this tool. 
     The first end of body  16  is rotatably mounted on the second end  24  of body  14  around a third axis VI inclined with respect to the second axis V. 
     Axes IV and VI form an angle substantially of 90 degrees with respect to the second axis V (in other words, axes IV and VI are both substantially orthogonal to axis V). As shown in the figures, in given positions in space of the robot wrist, these axes are substantially aligned with each other. In particular, the configuration shown in the figures is maintained for all the positions of the wrist which, with respect to that shown, are displaced only as a result of a rotation of the wrist around axis IV. 
     It is to be noted that in the present description, when reference is made to an orthogonal condition between two axes or straight lines, this may be applied both to the case of lines or axes which intersect each other and are perpendicular relative to each other, and to the case of lines or axes which do not intersect with each other but have their projections on a common plane parallel to them which form an angle substantially of 90 degrees relative to each other. 
     More specifically, the first body  12  comprises a substantially elbow-shaped body  18  which has, at its base, a first opening  20  facing towards the second body  14  and the third body  16 . In the mounted condition of the wrist, the opening  20  is substantially aligned with the first axis IV. Furthermore, the elbow-shaped portion carries an offset portion  22 , substantially arranged side by side, and spaced apart, with respect to the axis of opening  20 . On this offset portion the second body  14  is rotatably mounted around the second axis V. The second body has instead a cantilever portion  24 , corresponding to the above mentioned second end of the second body  14 , which has a second opening  26  substantially aligned with the third axis VI. In the mounted and harnessed condition of the robot, the first opening  20  and the second opening  26  are both traversed by cables and/or tubes C of the tool associated with the third body  16 . As visible from  FIG. 1 , due to the general configuration which is defined by portions  18  and  22 , there is formed a passage for the cables and/or tubes C such that these cables and the tubes are held within the overall lateral dimension of the robot wrist, so as to avoid that they may interfere with the operations of the wrist itself. To this end, portion  22  further has a bracket  23  on its side facing the openings  20 ,  26 , through which the cables and/or tubes are guided. This bracket has the function of constraining the cables and tubes to remain within the overall lateral dimension of portion  22  in the configurations of the wrist in which the second body  14  is rotated so that the opening  26  is displaced away from the condition aligned with opening  20 . Furthermore, in the mounted and harnessed condition of the robot, the cables and/or tubes C extend, for a portion of their length, substantially aligned with axis IV and, for another portion of their length, substantially aligned with axis VI. This condition provides a reduction to a minimum of the torsional and bending stresses to which the cables are subjected during the manoeuvres of the robot wrist. 
     In the robot wrist described herein, the means for driving the rotation of the second body  14  and the third body  16  are mounted directly on the structure of the wrist itself. In particular the driving means comprise a first motor  28  and a second motor  30  which are both carried by the offset portion  22  of the first body  12 . As will be described more in detail in the following, these driving means further comprise first gear means for transmitting the rotation of the output shaft of said first motor to said second body, and second gear means for transmitting the rotation of the output shaft of the second motor  30  to the third body  16 . 
     In the robot wrist described herein, at its end opposite to the elbow-shaped portion  18 , the offset portion  22  of the first body  12  has a fork-shaped portion  32 , corresponding to said second end of the first body. This fork-shaped portion  32  is arranged side by side, and spaced apart, with respect to the axis of opening  20  and the second body  14  is rotatably mounted thereon, around second axis V. 
     As will be seen herein in the following, this configuration of the offset portion enables the use of a kinematic chain for transmitting the movements from motors  28  and  30 , respectively to the second body  14  and the third body  16 , which is very simple and compact, the transmission of movement to the second and the third bodies being obtained through two different “routes”, with a resulting greater reliability of the entire kinematic chain. 
     In various embodiments, as well as in that shown in the figures, the first transmission means comprise a first shaft  34  rotatably mounted within a first arm  32 ′ of the fork-shaped portion  32 . As visible in  FIG. 3 , the first arm  32 ′ has an opening  38  which is engaged by a plate  40  bolted to the edge of this opening, which has a central portion  40 ′ with a hole, adapted to rotatably support shaft  34  around the second rotational axis V, with the interposition of a bearing member  41 . As will be described more in detail in the following, shaft  34  is connected in rotation to the first motor  28  and is adapted to drive in rotation a second body  14 . 
     On their turn, the second transmission means comprise a shaft  36  rotatably mounted on the second arm  32 ″ of the fork-shaped portion, substantially in line with shaft  34 . As will be described more in detail in the following, the second shaft  36  is connected in rotation to the second motor  30  and is adapted to drive the third body  16  in rotation. 
     The second body  14  comprises a base casing  42 , corresponding to said first end of the second body, which is received within the space between the first and second arms of the fork-shaped portion and is rotatably supported thereby. More specifically, casing  42  has two opposite sides with a first opening  44  and a second opening  46  through which shaft  34  and shaft  36  are respectively received and rotatably supported with interposition of bearing members  53  and  56 . In particular, on the side of the second fork arm  32 ″, a bush  50  bolted to casing  42  engages the opening  46  and rotatably supports shaft  36  through bearing members  56 . The same bush  50  is rotatably supported by a bearing member  52  which is arranged on an opening  48  provided in the second fork arm  32 ″, opening  48  being substantially specularly arranged with respect to opening  38  of the first arm. The bearing member  52  acts also as an abutment member on one side of casing  42  and, similarly, a bearing member  55 , mounted on opening  38  of fork arm  32 ′, acts as an abutment member on the opposite side of this casing. 
     Casing  42  is driven in rotation by shaft  34 . In particular, between shaft  34  and casing  42  there is interposed a reducer means  58  which is supported by the bearing member  55  and is adapted to connect in rotation shaft  34  to casing  42 . The reducer means which has been shown in the figures is a harmonic reducer of a specific type which is conventionally used in the field of robots, and therefore it is not described herein in detail. In any case, it is clearly evident that the reducer means shown merely constitutes an example and in place thereof a reducer means of any other type conventionally used in this field may be adopted. 
     Casing  42  further contains transmission means (which will be described more in detail in the following) adapted to transmit rotation of second shaft  36  to further transmission members which are arranged within the cantilever portion  24  and are adapted to drive the third body  16 . 
     In various embodiments, as well as in that shown herein, inside the cantilever portion  24  the second body  14  comprises, a shaft  60  which is freely rotatably mounted around an axis parallel to the third axis VI. Shaft  60  is connected in rotation to said transmission means and on its turn transmits the rotation to the third body  16 . In particular, shaft  60  has a first end which carries a gear wheel  62  which is engaged by said transmission means and a second end opposite to the first end which carries a gear wheel  64  which engages a gear wheel  66  carried by the third body  16 . It is be noted that due to shaft  60  the third body  16  as well as the terminal part of portion  24  supporting the third body  16  can be positioned much forwardly with respect to the fork portion  32 , so as to allow a distance between second axis V and opening  26  of cantilever portion  24  that reduces to a minimum the torsional and/or bending stresses of the cables and/or tubes C through opening  26 , which may be due to the rotation of the second body  14  around second axis V. 
     In various embodiments, as well as in that shown herein, the transmission means indicated above comprise a shaft  68  which is rotatably mounted within casing  42  around an axis parallel to third axis VI and arranged on the opposite side with respect to shaft  60 . Shaft  68  has a first end with a bevel gear wheel  70  engaging a corresponding gear wheel carried by shaft  36 . Furthermore, this transmission means comprise a reducer means  74  which at its input is coupled to a second end of shaft  68  opposite to the above mentioned first end. At its output reducer means  74  is coupled to a gear wheel  76  which engages the gear wheel  62  carried by shaft  60 . The reducer means which has been shown in the figures is a harmonic reducer of a specific type which is conventionally used in the field of robots and therefore is not described in detail herein. In any case, it is clearly apparent that the reducer means shown herein constitutes only an example and in place thereof a reducer means of any other type conventionally used in this field may be adopted. 
     With reference now to  FIGS. 2 and 4 , the first motor  28  and the second motor  30  are mounted inside offset portion  22  and substantially aligned with each other. The output shafts of motors  28  and  30  are connected to shafts  34  and  36  through respective belt transmissions. In particular, a bevel gear wheel  78  is secured to the output shaft of motor  28  and engages a bevel gear wheel  80  carried by a shaft  82  which is rotatably mounted within the offset portion  22  around an axis parallel and spaced apart from the second axis V. Shaft  82  has its end opposite to wheel  80  carrying a pulley  84  which is connected in rotation through a transmission belt  86  to a pulley  88  carried by shaft  34 . Similarly, on the output shaft of the second motor  30  there is secured a bevel gear wheel  90  which engages a bevel gear wheel  92  carried by a shaft  94  which is mounted in the offset portion  22 , on the side of this portion opposite with respect to shaft  82 . Shaft  94  is rotatable around an axis parallel and spaced from the second axis V. Shaft  94  has its end opposite to wheel  92  carrying a pulley  96  which is connected in rotation, through a transmission belt  98 , to a pulley  100  carried by shaft  36 . 
     In view of the foregoing, the transmission of movement to the second and third bodies, respectively in the rotations around axes V and VI, are obtained as described in the following. 
     When the first motor  28  is activated, shaft  82  is rotated, so as to drive rotation of shaft  34  through belt  86 . Shaft  34  transmits its movement to the reducer means  38 , which carries out a multiplication of torque, finally transmitting the rotation directly to the casing  42  of second body  14 . 
     Similarly, when the second motor  30  is activated, shaft  94  is rotated, so as to drive rotation also of shaft  36  through belt  98 . Shaft  36  drives rotation of shaft  68 , which transmits its movement to the reducer means  74 . The latter carries out a multiplication of torque, transmitting the movement to the gear wheel  76 . On its turn, wheel  76  rotates shaft  60  and wheel  64 , which, by engaging gear wheel  66 , finally drives rotation of the third body  16 . 
     It is to be noted that during the rotation of the second body  14 , shaft  68  is caused to oscillate with respect to shaft  36 . Due to the rotational connection between these two shafts, this oscillation would tend to rotate shaft  68  around its axis and then to cause an undesired actuation of the third body. In order to avoid this drawback, during the oscillation of shaft  68  the second motor  30  is controlled to rotate shaft  36  in a manner coordinated with this oscillation, so that shaft  68  does not rotate around its axis. Obviously, in cases in which a simultaneous actuation of the second and third bodies is requested, motor  30  is suitably controlled so that shaft  36  is able to transmit a rotation to shaft  68  corresponding to the desired movement for the third body. 
     It is finally to be noted that the above mentioned motors  28  and  30  have not been described herein in detail, since they can be of any type which is conventionally used in the field of robots. Similarly, some constructional details shown in the figures have not been described, to avoid an unnecessary complicated description, but they will be anyway clearly evident to the persons skilled in the art. 
     Naturally, while the principle of the invention remains the same, the details of construction and the embodiments may widely vary with respect to what has been described purely by way of non limiting example, without departing from the scope of the invention, as defined in the annexed claims.

Technology Category: 4