Abstract:
A robot has a gripper for gripping parts and releasing the gripped part at a destination position. The gripped part is vibrated at the destination position to cause the gripper to release the gripped part. The gripped part can be directly vibrated or vibrated by vibrating the mechanical structure of the gripper or by vibrating air in the gripper mechanical structure. The vibrator can connect the gripper to the robot. The vibrator can be inside or attached to the one or more of the articulated fingers of the gripper. The vibrations can be stopped when a sensor detects that the gripped part has been released or after the passage of a preset vibration time.

Description:
FIELD OF THE INVENTION 
       [0001]    This invention relates to robotic gripping of parts and more particularly to the release by the gripper of the picked parts. 
       DESCRIPTION OF THE PRIOR ART 
       [0002]    In robotic gripping and pick and place the part is usually released from a gripper by opening the gripper fingers or turning off suction. This causes gravity force to detach the part from the gripper. However, especially with lightweight parts, gravity may not be strong enough to create a reliable, reproducible detachment. There may be other effects that can make the parts detach in an uncontrolled way or not at all, such as electrostatic adhesion or surface adhesion due to moisture or liquid residuals on the part or on the surface of the gripper finger(s). 
       SUMMARY OF THE INVENTION 
       [0003]    A method of operating a gripper having a mechanical structure for gripping parts: 
         [0004]    vibrates the gripped part when the gripper is at a destination position to cause the gripper to release the gripped part to the destination position. 
         [0005]    An apparatus capable of being operated to grip a part when the apparatus is mounted on a robot has: 
         [0006]    a housing comprising a mechanism operable to grip the part and hold the gripped part when the gripping device is in motion; and 
         [0007]    a device associated with the housing operable to cause a vibration to occur in the gripped part when the gripping device is to release the gripped part at a destination position. 
         [0008]    A system has: 
         [0009]    a robot; 
         [0010]    a gripper connected to the robot for gripping a part, the gripper having a housing comprising: 
         [0011]    a mechanism operable to grip the part and hold the gripped part when the gripper is in motion; and 
         [0012]    a vibrator associated with the gripper operable to cause a vibration to occur to the gripped part when the gripper is to release the gripped part at a destination position. 
     
    
     
       DESCRIPTION OF THE DRAWING 
         [0013]      FIG. 1 a    shows a gripper body with parallel fingers holding a part that is to be placed on destination position on another part or surface. 
           [0014]      FIG. 1 b    shows what happens when the gripper opens to release the gripped part but that part does not detach from both fingers at the same time because the part is sticking onto one of the fingers. 
           [0015]      FIG. 1 c    illustrates in simplified form the method and apparatus that assures for a two finger parallel gripper a reproducible release of the gripped part. 
           [0016]      FIGS. 2 a , 2 b  and 2 c    show three different embodiments of the present method and apparatus for two finger grippers. 
           [0017]      FIG. 3  shows another embodiment of the present method and apparatus for two finger grippers. 
           [0018]      FIG. 4 a    shows a suction cup gripper with one or more suction cups where the grip is caused by a vacuum. 
           [0019]      FIG. 4 b    shows the use of a vibration or buzzing inside the suction channel of the gripper shown in  FIG. 4 a    to ensure uniform and simultaneous detachment of the gripped part from all of the suction cups. 
           [0020]      FIG. 5  shows in block diagram form an example of a six-axis industrial robot manipulator system that has a robot with a gripper to place a gripped part at a destination position. 
       
    
    
     DETAILED DESCRIPTION 
       [0021]    As is well known, robots use grippers to grasp parts and move the grasped part to a predetermined location where the robot held gripper is caused to release the grasped part so that the gripped part is brought into contact with another part or a surface. The receiving part or surface can be on a conveyor that moves the receiving part or surface to the predetermined location. When that happens, the conveyor stops so that the part gripped by the robot can be released by the gripper and thus brought into contact with the receiving part or surface. In a manufacturing environment, the released part should always be brought into contact with the receiving part or surface at the same place. However, that may not happen because for example electrostatic or surface adhesion of the gripped part with the gripper causes the gripped part when released to be not fully seated in the receiving part or surface or not be released. 
         [0022]    Referring now to  FIG. 1   a,  there is shown a gripper body or housing  11  with parallel fingers  12  holding a part  14  that is to be placed on destination position  33  on part or surface  13 .  FIG. 1 b    shows what happens when the gripper opens as indicated by the arrows  21  to release part  14  but part  14  does not detach from both fingers  12  at the same time because the part  14  is sticking onto one finger  12 . As a result and is shown in  FIG. 1   b,  the part  14  is not properly released to destination position  33  and thus part  14  is not fully seated in position  33 . This is a common problem in particular for lightweight parts in the presence of electrostatic adhesion or adhesive surface effects due to moisture or liquid residuals on the part or on the finger surface. 
         [0023]      FIG. 1 c    illustrates in simplified form the method and apparatus that assures for a two finger parallel gripper a reproducible release of the gripped part. In accordance with this method when the fingers  12  start opening as shown by arrows  31  a mechanical vibration  32  is created in both fingers  12 . The vibration  32  makes the gripped part  14  immediately loosen itself from fingers  12  when the fingers  12  are opened further than the size of the part  14 . The part  14  then falls into place precisely where it was positioned at with the gripper  11 , that is, in the destination position  33 . 
         [0024]      FIGS. 2 a , 2 b  and 2 c    show three different embodiments of the present method and apparatus for two finger grippers.  FIG. 2 a    shows an acoustic speaker  41  located on the gripper  11 , close enough to the gripped part  14  that the gripped part is set into vibration from the sound-wave  42  from the speaker. The speaker  41  is activated preferably at the same time the gripper  11  is commanded to release the part.  FIG. 2 b    shows a gripper design where the gripper actuator is a piezo stack  50 . The small displacement  51  of the piezo stack  50  is translated into a large displacement of the gripper fingertips  52 . Since piezo stacks can be actuated with frequencies in the 100s of Hz, the piezo stack  50  when actuated creates vibration of the fingertips  52  that detaches the gripped part  14  from the gripper fingers so that the released part always lands in destination position  33 .  FIG. 2 c    shows another embodiment where there are small free spinning motors  32  with unbalanced mass  34  inside the gripper fingers. When the motors  32  spin, they cause mechanical vibration inside the fingers that detaches the gripped part  14  from the gripper fingers so that the released part always lands in destination position  33 . 
         [0025]      FIG. 3  shows another embodiment of the present method and apparatus for two finger grippers. In this embodiment, a vibrating body  71  is attached to the flange  70  of the robot that holds the gripper. The gripper body  72  is attached to the vibrating body  71 . When the gripped part  14  is released and the gripper fingers open, the vibrating body  71  shakes the entire gripper to reliably detach the gripped part  14  from the gripper fingers so that the released part always lands in destination position  33 . 
         [0026]      FIG. 4 a    shows a suction cup gripper with one or more suction cups  80  where the grip is caused by vacuum  81 . For release of part  14 , the vacuum is turned off and gravity would cause the part  14  to detach. As shown in  FIG. 4 b   , to ensure uniform and simultaneous detachment from all suction cups a vibration or buzzing  82  is created inside the suction channel. The source of vibration of the air could be a piezo disk or a speaker membrane actuating on the air channels of the suction cups. 
         [0027]    While the present apparatus and method has been described for use with a two finger parallel gripper it should be appreciated that the apparatus and method can also be used with other grippers including but not limited as of the earliest claimed filing date of this application to: 
         [0028]    a gripper that has one articulated finger and one or more other fingers that are fixed; 
         [0029]    two finger centric (swiveling finger joint) grippers such as those offered for sale by Schunk GmbH &amp; Co. KG and many other manufacturers as shown as of the first filed application for this invention at http://www.directindustry.com/industrial-manufacturer/gripper-73804.html; 
         [0030]    three finger parallel and three finger centric grippers such as the robot adaptive gripper offered for sale by Robotiq of St. Nicolas, QC, Canada; 
         [0031]    four or more fingers grippers; and 
         [0032]    jamming or coffee grounds gripper such as the gripper described by Brown et al. in “Universal robotic gripper based on the jamming of granular material” published in PNAS, Nov. 2, 2010, vol. 107, no. 44, pages 18809 to 18814. 
         [0033]    Referring now to  FIG. 5 , there is shown in block diagram form an example of a six-axis industrial robot manipulator system  100  that has a robot with a gripper  120  to place a gripped part  140  at a destination position. System  100  also has a vision sensor  110  such as one or more cameras that provide images of the gripped part  140  as the robot with gripper  120  moves the gripped part  140  to the destination position. The images are provided to a computation device  130  which is connected to a controller  150  for robot with gripper  120 . The images from vision sensor  110  can also be provided directly to controller  150  if the controller has sufficient processing capacity for the images. The controller  150  or the computation device  130  controls the vibration that causes the gripper to release the gripped part  140  at the destination position. 
         [0034]    The images from vision sensor  110  can also be used to cause controller  150  or the computation device  130  to stop vibration of the gripped part  140  when those images show that the robot with gripper  120  has released the gripped part  140  at the destination position. 
         [0035]    Instead of using images from the vision sensor  110  the controller  150  or the computation device  130  can be programmed to stop the vibrations after the passage of a preset time. 
         [0036]    It should be appreciated that while a vision sensor is described above to detect the release of the gripped part at the destination position that other forms of sensors such as photoelectric sensors in the gripper that can distinguish between part is present and part is not present and possibly a force sensor can also be used. It should also be appreciated that depending on the type of sensor that the sensor can be mounted in the gripper, on the gripper or fixed on the robot cell at the destination, that is the release, position. 
         [0037]    It is to be understood that the description of the foregoing exemplary embodiment(s) is (are) intended to be only illustrative, rather than exhaustive, of the present invention. Those of ordinary skill will be able to make certain additions, deletions, and/or modifications to the embodiment(s) of the disclosed subject matter without departing from the spirit of the invention or its scope, as defined by the appended claims.