Patent Publication Number: US-2006011010-A1

Title: Joint Mechanism For Robot Hand And The Like

Description:
FIELD OF THE INVENTION  
      The present invention relates to a joint mechanism used in a finger unit and the like of a robot hand that can accurately grasp airborne objects or the like at high speeds, and particularly relates to a joint mechanism wherein a drive torque of a joint axle can be increased without increasing a dimension in a direction orthogonal to the joint axle.  
     DESCRIPTION OF THE RELATED ART  
      Finger units used in robot hands commonly have articulated structures, and actuators that are small, lightweight, have high torque, and can drive finger joints with a high degree of precision are required in order to enable these articulated joint units to quickly and accurately grasp, hold, and throw objects. Configuring such an actuator requires a motor capable of instantaneously generating a maximum torque at high speeds within dimensions of the fingers, a reduction gear with minimal backlash at a high reduction ratio, and a precision encoder. However, such actuators are not commercially available, nor are related products that would serve as structural elements to satisfy such specifications. Specifically, the instantaneous maximum output torque of a servomotor is insufficient, a reduction gear has a large backlash of no less than 1° in an output axle even if it has multistage planetary gears, and no products that are sufficiently small and lightweight and have a high enough resolution for an encoder are available.  
      Also, in order to convert a rotation outputted from a rotational output axle of an actuator in an articulated finger unit into rotational movement of a joint axle orthogonal thereto, combinations of screws and locks/pinions, crank mechanisms, worm gears, wires, sheaves, and the like have been used in the prior art. However, all of these are inconvenient in that they increase the dimensions and mass of the joints, cause the speed of switching between operations to be insufficient, and bring about other problems. Using a regular bevel gear also has problems with the backlash and with smooth rotation.  
      In JP-A 2004-122339, the inventors et al. have proposed an articulated finger unit for a robot hand aimed at resolving such problems.  FIGS. 3 and 4  are a plan view and a cross-sectional view showing the articulated finger unit disclosed in this literature. As shown in these diagrams, an articulated finger unit  1  has a mounting flange  2 , an actuator  3  mounted on this mounting flange  2 , and an articulated finger main body unit  5  connected to a rotational output axle  4  of the actuator  3 . The finger main body unit  5  is configured from a finger-base joint part  6  connected to a front end of the rotational output axle  4  of the actuator  3 , a finger base part  7  connected to a front end of the finger-base joint part  6 , a fingertip joint part  8  connected to a distal end of the finger base part  7 , and a fingertip part  9  connected to the front end of the fingertip joint part  8 .  
      The pillar-shaped actuator  3  faces forward while a front end section thereof is fixed in place in a circular opening frame  2   a  of the mounting flange  2 , and the rotational output axle  4  protrudes forward from a front end surface thereof through the circular opening frame  2   a . A drive bevel gear  11  is coaxially fixed in place on a distal end of the rotational output axle  4 .  
      A pair of finger-base side bearing housings  2   b ,  2   c  extend parallel to each other from top and bottom ends of a front surface of the mounting flange  2  through top and bottom positions of the drive bevel gear  11 . A top ball bearing  12  and a bottom ball bearing  13  are respectively mounted so as to be in coaxial positions on distal ends of these finger-base side bearing housings  2   b ,  2   c  that protrude farther forward than the drive bevel gear  11 . These ball bearings  12  and  13  allow a finger-base side joint axle  14  to be supported in a direction orthogonal, or perpendicular in the present example, to an axial direction of the rotational output axle  4 , with top and bottom ends in a rotatable state.  
      A driven bevel gear  15  is coaxially fixed in place on an outer peripheral surface at the top of the joint axle  14  in the axial direction, and this driven bevel gear  15  meshes with the drive bevel gear  11 . An annular boss  16   a  of a connecting member  16  is fixed in place in the middle of the axial direction of the joint axle  14 . The connecting member  16  has the annular boss  16   a , a neck portion  16   b  that extends forward from the annular boss  16   a , and a fork portion  16   c  that extends forward in a shape of a U from a distal end of the neck portion  16   b . A cylindrical base side cover  17  is connected coaxially to the fork portion  16   c.    
      Thus, the finger-base joint part  6  linked to the front end of the rotational output axle  4  of the actuator  3  is configured from the top and bottom finger-base side bearing housings  2   b ,  2   c  formed on the mounting flange  2 , the top and bottom ball bearings  12  and  13 , the finger-base side joint axle  14 , the finger-base side driven bevel gear  15 , and the finger-base side connecting member  16 . Also, the finger base part  7  is formed from the cylindrical base side cover  17  connected to the fork portion  16   c  of the finger-base side connecting member  16 .  
      Next, the fingertip joint part  8  and the fingertip part  9  connected to the distal end of the finger base part  7  have the same structure as the finger-base side joint part  6  and the finger base part  7 . Specifically, a second actuator  21  is coaxially mounted in the hollow part of the base side cover  17 , and a front end of this actuator  21  is rotatably supported by an annular flange  22  mounted in the same manner in the hollow part of the base side cover  17 . An outer peripheral surface of this annular flange  22  is fixed onto an inner peripheral surface of the base side cover  17 .  
      A rotational output axle  23  of the actuator  21  protrudes coaxially forward through a hollow part of the annular flange  22 , and a fingertip side drive bevel gear  24  is coaxially fixed in place on a distal end thereof. A pair of fingertip side bearing housings  22   a ,  22   b  extend parallel to each other from top and bottom ends of a front surface of the annular flange  22  through the top and bottom of the drive bevel gear  24 . A top ball bearing  25  and a bottom ball bearing  26  are mounted on distal ends of the fingertip side bearing housings  22   a ,  22   b  that protrude farther forward than the drive bevel gear  24  so as to be in coaxial positions. These ball bearings  25  and  26  allow a fingertip side joint axle  27  to be supported in a direction orthogonal, or perpendicular in the present example, to an axial direction of the rotational output axle  23 , with top and bottom ends in a rotatable state.  
      A driven bevel gear  28  is coaxially fixed in place on an outer peripheral surface at a top of the joint axle  27  in an axial direction, and this driven bevel gear  28  meshes with the drive bevel gear  24 . An annular boss  29   a  of a fingertip side connecting member  29  is fixed in place in the middle of an axial direction of the driven bevel gear  28 . The connecting member  29  has the annular boss  29   a , a neck portion  29   b  that extends forward from the annular boss  29   a , and a fork portion  29   c  that extends forward in a shape of a U from a distal end of the neck portion  29   b . A cylindrical fingertip side cover  30  whose distal end is closed off in a semispherical shape is coaxially connected to the fork portion  29   c.    
      In the articulated finger unit  1 , the rotation of the rotational output axle  4  is converted to rotational movement in the joint axle  14  via the pair of bevel gears  11  and  15 , and the connecting member  16  fixed in place at one end to the joint axle  14  revolves through an angle of 90° or more to the left and right around the joint axle  14 . The joint parts  6  and  8  can be controlled to bend by an angle of 90° or more forwards and backwards or to the left and right, and a lightweight, fast and highly precise artificial finger that is capable of various operations can be achieved.  
      The actuators  3  and  21  have a servomotor with a high speed, high maximum torque, and short time rating based on a high-density winding and a high-density component arrangement; a wave gear drive unit with a high reduction ratio (for example, 1/50 to 1/100), small dimensions, high torque, and small backlash; and a small, lightweight, and highly responsive encoder with a high resolution. Also, oilless bevel gears with minimal backlash are used as the bevel gears  11 ,  15 ,  24 , and  28 . Such bevel gears are subjected to a surface hardening treatment after teeth are cut, a lapping treatment is performed using a high-precision bevel gear lapping machine in a backlash-free state, a tooth surface is impregnated with a solid lubricant, and the gears are made capable of backlash-free movement without lubrication.  
      This backlash-free movement structure of the bevel gears  11  and  15  and the bevel gears  24  and  28  used in the joint parts is comprised of spring plates. For example, in the finger-base side joint  6 , spring plates  31  and  32  for applying an axial thrust that limits an amount of axial shift in the joint axle  14  in a direction of a conical center of the bevel gears are mounted on a top surface of the top ball bearing  12  and a bottom surface of the bottom ball bearing  13  on which the top and bottom ends of the joint axle  14  are rotatably supported. Spring plates  33  and  34  that function similarly are mounted in the same manner in the fingertip side joint part  8 .  
     SUMMARY OF THE INVENTION  
      In a joint mechanism for a robot hand and the like as described above, it is common to use a higher size (model number) for a motor and a reduction gear constituting an actuator as a method for enhancing torque of joint axles. However, a motor and a reduction gear of a higher model number normally also have larger outside diameter dimensions. Therefore, the dimensions of the joint mechanism itself will inevitably be larger.  
      Increasing the dimensions of the joint mechanism is not preferred because a diameter or thickness of the finger units of the robot hand incorporating these mechanisms will increase. Particularly, sometimes there is no extra space in a horizontal width direction orthogonal to the joint axle in the joint mechanism. In this case, even if there is extra installation space in a vertical direction (axial direction) of the joint axle, a large actuator cannot be used because of restrictions on the installation space in the width direction, and it is difficult to obtain a required drive torque.  
      A main object of the present invention is to provide a joint mechanism for a robot hand and the like wherein a drive torque of a joint axle can be increased, particularly without accompanying increase in dimensions in a direction orthogonal to the joint axle.  
     MEANS OF ACHIEVING OBJECTIVES  
      In order to achieve the above and other objects, a joint mechanism for a robot hand and the like in accordance with the present invention has a joint axle, a supporting member for rotatably supporting the joint axle around a centerline thereof, a revolving member connected to the joint axle and allowed to revolve around the centerline along with the rotation of the joint axle, at least a first and a second actuators mounted on the supporting member, at least a first and a second driven bevel gears fixedly mounted on the joint axle in coaxial manner, a first drive bevel gear that is coaxially connected to a rotational output axle of the first actuator and that meshes with the first driven bevel gear, and a second drive bevel gear that is coaxially connected to a rotational output axle of the second actuator and that meshes with the second driven bevel gear; wherein the first and second actuators are disposed in parallel with a direction of the centerline of the joint axle.  
      In a typical configuration in the present invention, the supporting member has a mounting frame for mounting the first and second actuators, and a pair of support arms extending parallel to each other from both ends of the mounting frame. Also, distal ends of these support arms rotatably support both end sections of the joint axle via bearings, and the first and second driven bevel gears are fixedly mounted at locations inside of the each bearing in the joint axle. Furthermore, the revolving member comprises a connecting arm connected to a center section of the joint axle between the bearings.  
      In the joint structure for the robot hand and the like according to the present invention, the joint axle is rotatably driven using bevel gears, a plurality of actuators are disposed in parallel along the centerline direction of the joint axle, and rotational forces of these actuators can be transmitted to the joint axle via a gear train comprised of bevel gears.  
      Therefore, the drive torque of the joint axle can be increased by driving these actuators simultaneously. Also, since the plurality of actuators are disposed in parallel with the direction of the joint axle, the dimension in the direction orthogonal to the joint axle does not increase even though the dimension in the direction of the joint axle increases. This approach is therefore extremely useful when the dimension of the joint mechanism cannot be increased in the width direction thereof. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a plan view, front view, and side view as seen from the distal end of a joint mechanism according to the present invention;  
       FIG. 2  is a cross-sectional view showing a portion that is cut along a line a-a in  FIG. 1 ;  
       FIG. 3  is a plan view showing an example of an articulated finger unit; and  
       FIG. 4  is a longitudinal cross-sectional view of the articulated finger unit in  FIG. 3 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      Examples of a joint mechanism for a robot hand and the like according to the present invention will be described with reference to the drawings.  
       FIG. 1  is a plan view, front view, and side view as seen from the distal end showing the joint mechanism of a finger unit in a robot hand, and  FIG. 2  is a cross-sectional view of a portion that is cut along the line a-a in  FIG. 1 .  
      A joint mechanism  100  of the present example has a cylindrical vertically extending perpendicular joint axle  101 , and the perpendicular joint axle  101  is rotatably supported by a supporting bracket  102 . The supporting bracket  102  has a mounting frame  103  and a pair of top and bottom support arms  104  and  105  extending horizontally forward from top and bottom sections of the mounting frame  103 . Bearings  106  and  107  are mounted horizontally on distal end sections of these support arms  104  and  105 , and the perpendicular joint axle  101  is rotatably supported via these bearings  106  and  107 . In the mounting frame  103  of the supporting bracket  102 , first and second circular mounts  103 A and  103 B are formed at the top and bottom thereof (in a direction of a centerline  101 A of the perpendicular joint axle  101 ). A front end section of a first actuator  110  is inserted, connected, and fixed in place in the upper first mount  103 A from a rear side. A front end section of a second actuator  120  is inserted, connected, and fixed in place in the lower second mount  103 B from a rear side.  
      A revolving bracket  130  positioned on a front side of the perpendicular joint axle  101  is connected and fixed in place thereon. The revolving bracket  130  has a connecting arm  131  and a pair of mounting arms  132  and  133  that are bifurcated vertically to extend forward parallel to each other from a front end of the connecting arm  131 . The connecting arm  131  is connected and fixed in place at a vertical center section of the perpendicular joint axle  101 . Therefore, the revolving bracket  130  revolves to the left and right integrally with the rotation of the perpendicular joint axle  101  around the centerline  101 A thereof.  
      The first and second actuators  110  and  120  are mounted in the supporting bracket  102  so that axis lines  110 A and  120 A thereof face backward from the centerline  101 A of the perpendicular joint axle  101  and extend in an orthogonal direction (horizontal direction). The first actuator  110  has a coaxially connected motor  111  and a reduction gear  112 , a reducing rotational output axle  113  of the reduction gear  112  protrudes forward from the first mount  103 A of the supporting bracket  102 , and a first drive bevel gear  114  is coaxially connected and fixed in place on a distal end thereof. The second actuator  120  has the same configuration, which has a coaxially connected motor  121  and a reduction gear  122 , wherein a reducing rotational output axle  123  of the reduction gear  122  protrudes forward from the second mount  103 B of the supporting bracket  102 , and a second drive bevel gear  124  is coaxially connected and fixed in place on a distal end thereof.  
      A first driven bevel gear  141  and a second driven bevel gear  142  are fixedly mounted in coaxial manner at locations inside of the top and bottom bearings  106  and  107  in the perpendicular joint axle  101 . The first driven bevel gear  141  meshes with the first drive bevel gear  114 , and the second driven bevel gear  142  meshes with the second drive bevel gear  124 .  
      In the joint mechanism  100  with this configuration, the supporting bracket  102  is fixed in place, and when the first and second actuators  110  and  120  are rotatably driven in this state, the perpendicular joint axle  101  can be rotatably driven by the both actuators  110  and  120 . When the perpendicular joint axle  101  rotates, the revolving bracket  130  connected and fixed thereto revolves to the left and right from a neutral position of the diagram.  
      The joint mechanism  100  of the present example can be applied, for example, to the fingertip joint part  8  in the finger unit  1  of a robot hand shown in  FIGS. 3 and 4 . In this case, the two actuators  110  and  120  are mounted in the finger base part  7 , and the fingertip part  9  is revolved by these two actuators  110  and  120 . It is thereby possible to revolve the fingertip part  9  with essentially two times the drive torque as when the fingertip part  9  is revolved by a single actuator as shown in  FIGS. 3 and 4 . Also, the horizontal dimensions of the joint axle do not increase even though the dimensions of the joint mechanism in the vertical direction of the joint axle do increase. Therefore, the joint mechanism of the present example can be employed in order to increase the drive torque of the joint axle when there is no extra installation space in the horizontal direction. Furthermore, since two actuators are provided, it is possible to design the configuration such that the drive of the fingertip part  9  can be ensured by the other actuator when one of the actuators  110  and  120  fails.  
      In the example described above, two actuators were provided, but the joint mechanism of the present invention can also be used when three or more actuators are provided. It is also apparent that the joint mechanism of the present invention can be used in a device other than an articulated finger unit with the structure shown in  FIGS. 3 and 4 .