Abstract:
The invention provides a robotic gripper mechanism having a thin, protrusion-free profile for maneuvering through tight areas, which mechanism includes a finger assembly mounted at the distal end of a gripper arm, which arm extends from a movable housing. The finger assembly is normally biased to a retracted position, but may be moved to an extended operative position by a drive member operating on a slide in the arm through suitable intermediary components. The invention also includes a mechanism for permitting retraction of the arm when an obstacle is encountered during vertical downward movement of the gripper mechanism so as to protect the arm and the finger assembly from damage.

Description:
This invention relates to robotic devices and more particularly to a robotic gripper for use in picking up, transporting and dropping selected objects, particularly where the gripper must pass through tight areas to reach the object. 
     BACKGROUND OF THE INVENTION 
     There are many applications in industry, government, (for example the post office), and other businesses or institutions where robotic mechanisms are used to lift and carry selected objects, for example containers for various items, from one place to another. Frequently, the areas of operation for such robotic mechanisms are very tight and require a mechanism having a thin profile, free of protrusions, in order for the robotic gripper mechanism to be maneuvered into a suitable position to perform the gripping and lifting operation. A simple, inexpensive mechanism capable of performing the gripper function, while still having a thin, protrusion-free profile for maneuvering through tight areas, does not currently exist. 
     Another problem for robotic gripper mechanisms when operating in tight areas is that, even with a thin profile, the mechanism may still strike an object when being lowered into a pickup position. Since the gripper mechanisms are frequently being moved at relatively high speed to achieve good throughput rate, such inadvertent striking of an obstruction in a mechanism path may cause significant damage to the gripper mechanism, resulting in a costly shutdown of the entire system in which it is being utilized, and may also damage the object providing the obstruction. It is therefore desirable that a simple and inexpensive mechanism be provided to protect the gripper mechanism and prevent damage thereto in the event an obstruction is inadvertently encountered when the gripper mechanism is being lowered into an operative position. Again, a such simple and inexpensive protection mechanism does not currently exist. 
     SUMMARY OF THE INVENTION 
     In accordance with the above, this invention provides a robotic gripper mechanism which includes a housing, a gripper arm extending from said housing, a finger assembly mounted at a distal end of the arm, the finger assembly being normally biased to a retracted position, a slide moveable in the arm between a first inoperative position relative to the finger assembly and a second operative position, a drive member having at least a first and second state, and components operated by the drive member and operating on the slide in response to the state of the drive member such that the slide is in its first operative position when the drive member is in its first state and the slide is in its second operative position when the drive member is in its second state, the slide not influencing the position of the finger assembly when in its first position and acting on the finger assembly to move it to an extended operative position when the slide is in its second position. 
     The finger assembly may include at least one finger sized and shaped to, when the assembly is in its extended position, either fit under an object to be lifted, to fit in a corresponding receptacle in a side of the object, and/or to fit into a receptacle extending from the top of the object. The finger assembly may also be sized and shaped to fit through an opening form in the top of the object to be lifted when the assembly is in the retracted position and to grip the top of the object for lifting of the object when the assembly is moved to its operative position after passing through the opening. The finger assembly may also be movable, against its normal bias, when the slide moves from its second to its first position and there is weight on the finger assembly from an object being lifted, to a position where the object is released. Once the object is released, removing weight from the finger, the finger assembly operates under its bias to return to its retracted position. 
     The components between the drive member and the slide may be a mechanical linkage which mechanically attaches the drive member to the slide, the drive member preferably being a pneumatic cylinder. The finger assembly is preferably rotated about a pivot between its retracted and extended position, the mechanism preferably including a bias spring acting on the finger assembly to normally maintain it in its retracted position. At least one component may be provided which facilitates tension adjustment on the spring, and thus the bias force applied to the finger assembly. 
     The components between the drive member and slide may alternatively include a pivot arm and a mechanical linkage between the drive member and the pivot arm, the linkage pivoting the pivot arm out of contact with the slide when the drive member is in its first state and pivoting the pivot arm to bear against the slide in a manner to move and hold the slide in its second position when the drive member is in the second state. A biasing mechanism may be provided which moves the slide to its first inoperative position when the pivot arm is out of contact therewith. 
     The housing, including the gripper arm, may be positionable, at least vertically, to bring the gripper arm into position to perform a gripping operation and a mechanism may be provided which permits retraction of the gripper arm to protect the gripper arm when, during a downward vertical positioning of the housing, an obstacle is encountered by the gripper arm. The mechanism which permits retraction may include a mechanism for frictionally maintaining a vertical position for the gripper arm, friction applied to the gripper arm by such mechanism being sufficiently low that the gripper arm may overcome the friction and move up relative to the housing when an obstacle is encountered. The mechanism may also include an element for selectively removing the friction from the gripper arm when the arm is in a raised position, permitting the gripper arm to return to its normal position relative to the housing, and for then restoring frictional engagement with the arm. Alternatively, gravity alone may maintain the vertical position of the gripper arm, facilitating easy movement of the arm when an obstacle is encountered. A detector may be provided which indicates the position of the gripper arm relative to the housing. While the mechanism which permits retraction is preferably used in conjunction with the alternative component embodiment, it may also be utilized with other embodiments of the invention. 
     In accordance with another aspect of the invention, a robotic gripper mechanism is provided which includes the housing, the gripper arm extending from the housing and the finger assembly mounted at the distal end of the arm. The housing, including the gripper arm and finger assembly, are positionable, at least vertically, to bring the gripper arm into position to perform a gripper operation, and a mechanism is provided which permits retraction of the gripper arm to protect the arm and the finger assembly when, during a downward vertical positioning of the housing, an obstacle is encountered by the gripper arm. The mechanism which permits retraction may include a mechanism for frictionally maintaining a vertical position of the gripper arm with a friction sufficiently low that the gripper arm may overcome the friction and move up relative to the housing when an obstacle is encountered and an element may be provided for selectively removing the friction from the gripper arm when the arm is in a raised position, permitting the gripper arm to return to its normal position relative to the housing, and for then restoring frictional engagement of the arm. A detector may also be provided which indicates the position of the gripper arm relative to the housing. The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention as illustrated in the accompanying drawings, the same or related reference numerals being utilized for common elements in the various figures. 
    
    
     IN THE DRAWINGS 
     FIG. 1 is a side view of a gripper mechanism in accordance with a first embodiment of the invention, shown in its operative position. 
     FIGS. 2 a - 2   c  are side views of all or part of the mechanism shown in FIG. 1 in its retracted or home position, extended or pick up position, and drop position respectively. 
     FIGS. 3 a  and  3   b  are a top view and a front view respectively of a gripper mechanism in accordance with a second embodiment of the invention. 
     FIG. 3 c  is a partial rear view of primarily the finger assembly for the embodiment of FIGS. 3 a  and  3   b  (and also for the embodiment of FIG.  1 ). 
     FIG. 3 d  is an exploded view for the embodiment of FIGS. 3 a  and  3   b.    
     FIGS. 3 e  and  3   f  are sectional views for the embodiment shown in FIGS. 3 a  and  3   b , shown in an operative position and in a retracted position respectively. 
    
    
     DETAILED DESCRIPTION 
     Referring first to FIG. 1, a gripper mechanism  10  is shown having a housing  12  with an extending arm  14 . Housing  12  is mounted, for example by a bolt  16 , to a suitable robotic positioning system, which system is preferably capable of moving in three dimensions to position mechanism  10  over an object to be lifted, to maneuver arm  14  into position to grip the object in manners to be described later, and to lift and reposition the object once it is gripped. The specifics of such robotic positioning systems are not part of this invention and any suitable robotic positioning system, either currently existing or developed in the future, may be utilized for performing the positioning function. A pneumatic cylinder  18  is provided having a projection  20  connected by a pin  22  to a pair of projections  24  from housing  12  (only one of which projections  24  is shown in the figures). A rod  26  extending from the opposite side of piston  18  is connected through a linkage mechanism  28  to a slide  30  in arm  14 . Linkage mechanism  28  includes a bell crank  32  fixed at one corner by a pin  34  to arm  14  to rotate therein. The other two corners of bell crank  32  are connected by a pin  36  to an extension of piston rod  26  and by a pin  38  to a linkage  40  connected by a pin  42  to slide  30 . Slide  30  has a toe  44  which bears against a carrier  46  of a finger assembly  48  rotatably mounted by a pin  50  to the distal end of arm  14 . Finger assembly  48  also includes at least one projecting finger  52  mounted on carrier  46 . Referring to FIG. 3 c , it is seen that for preferred embodiments, a torsion spring  54  is wrapped around shaft  50  and supported at its end by locking spring retainers  56 L and  56 R. The tension on spring  54  may be adjusted by loosening set screw  58  and appropriately rotating retainer  56 L. As will be discussed in greater detail later, torsion spring  54  normally biases finger assembly  48  to the retracted position shown in FIG. 2 a . However, the tension on this spring is sufficiently low to permit a drop operation as described hereinafter in conjunction with FIG. 2 c.    
     In operation, finger assembly  48 , under the influence of spring  54 , is normally in the retracted position shown in FIG. 2 a . In this position, arm  14  has a relatively small footprint or profile and may therefore be easily maneuvered through relatively tight places in order to reach a desired location where gripping is desired. To achieve the position shown in FIG. 2 a , piston  18  is retracted, causing rod  26  to pull back on pin  36 . This pivots bell crank  32  in the clockwise direction, resulting in pin  38  being raised. The raising of pin  38  causes link  40  to move upward, resulting in an upward movement of slide  30  to the position shown in FIG. 2 a , with foot  44  substantially out of contact with finger assembly  48 , and particularly carrier  46  thereof. 
     Once arm  14  has been positioned with finger assembly  48  adjacent the object to be gripped, piston  18  may be operated to extend rod  26 . Rod  26  being extended causes rocker arm  32  to rotate about pin  34  in the counterclockwise direction, thereby moving pin  38 , link  40  and slide  30  in the downward direction. This causes foot  44  to bear against finger carrier  46  as shown in FIG.  1 . This rotates the finger assembly  48  in the clockwise direction, as viewed in the Figures, about shaft  50  to extend finger  52  as shown in FIGS. 1 and 2 b , and to hold finger  52  in this position. Once a finger is extended as shown in FIG. 2 b , the finger may be maneuvered into, for example, a slot  60  in the side of, for example, a mail carrier basket  62 . The length and shape of finger  52  (or fingers  52  as will be discussed later) depends on the specific application, and in particular what is being lifted and where it is being gripped. For example, if the object  62  being lifted has relatively straight side walls, it may be possible to have substantially straight fingers  52 , which are perhaps slightly longer than those shown, which fingers are wedged under the object on opposite sides to lift the object. This may be facilitated by having the object on legs so the finger(s) may more easily fit thereunder. Further, a looped extension  64 , or preferably a plurality of such looped extensions, may be provided on the top of object  62  into which fingers  52  of two or more robotic arms  14  are maneuvered in order to perform a pickup and moving operation. Another option is for there to be two or more holes in the top of object  62  which are big enough for the distal end of arm  14  to pass through when the finger assembly is in the retracted state shown in FIG. 2 a , but small enough so that when the mechanism is operated to its extended position shown in FIG. 2 b , finger  52  engages the underside of the lid of object  62  so as to lift the lid and the object secured thereto. The objects to be lifted may be provided with openings or other suitable receptacles on their top, sides or bottom in various applications so as to permit a suitably shaped finger  52  to interact with the object for purposes of gripping and lifting the object. 
     Once the object has been moved to its desired location, piston  18  may be operated to retract rod  26 , rotating bell crank  32  in the clockwise direction to raise slide  30  so that foot  44  is no longer in contact with finger carrier  46 . If there is no weight on the finger when this occurs, for example the finger has been lowered or moved slightly backward, then finger assembly  48  will retract to the position shown in FIG. 2 a , permitting arm  14  to be raised and moved away from object  62 . However, if object  62  is still being supported by finger  52  when slide  30  is retracted, the weight of the object will cause the finger assembly to move to the drop position shown in FIG. 2 c , the object dropping from the gripper mechanism when the finger(s) are in this position. Alternatively, when the object is resting on the ground when slide  30  is retracted, the finger will remain in the position shown in FIG. 2 b  until arm  14  is moved upward, at which time the finger assembly will be moved by the object to the position shown in FIG. 2 c  to permit fingers  52  to be removed from and ultimately clear object  62 . Once the tip of finger  52  clears object  62 , the finger assembly will be retracted to the position shown in FIG. 2 a.    
     FIGS. 3 a - 3   f  illustrate an alternative embodiment of the invention which differs from the embodiment shown in FIGS. 1 and 2 in two respects. First, the manner in which the pneumatic cylinder is linked to operate the slide is different. The second difference, which is facilitated by the first, is that arm  114  is retractable in order to prevent damage to the mechanism  110 , and in particular to the finger assembly  46  of this mechanism, in the event, when the mechanism is being lowered into position to grab an object, the mechanism encounters an obstacle. More particularly, piston rod  126  from piston  118  is connected through a mechanical linkage  128  to a pivot arm  160  having a button  162  at the distal end thereof. Referring to FIG. 3 f , when the piston  118  is in its inactive or retracted position, arm  160  is pivoted away from arm  114  permitting slide  130  to be raised in arm  114  to the position shown in FIG. 3 f  under the influence of a coil spring  164  or other suitable biasing component. Spring  164  fits in an opening  165  formed in slide  130 , the top of the spring pressing on the upper wall of opening  165  and the bottom of the spring contacting a shelf  167  extending into opening  165  from rear plate  169 . Rear plate  169  is attached by screws or other suitable means to arm  114 . This raising of slide  130  permits finger assembly  48  to be biased to its retracted position as shown in FIG. 3 f . If there were a weight on finger(s)  52  when slide  130  was moved to its retracted position, the finger assembly would move to the position shown in FIG. 2 c  to permit the weight to be shed, before returning to the retracted position shown. 
     Referring to FIG. 3 e , when it is desired to move slide  130  to its downward active position, pneumatic cylinder  118  is operated to extend its piston  126 . Piston  126  operates through linkage  128  to rotate pivot arm  160  in the clockwise direction as viewed in FIG. 3 e , bringing button  162  at the distal end thereof into contact with the top of slide  130 , and moving slide  130  into its operative position shown in FIG. 3 e  as arm  160  continues to pivot to its final position. With slide  130  in its lowered active position, foot  144  operates on carrier  46  as previously discussed to move and hold finger assembly  48  in its extended position. The foot  144  is preferably unitary with slide  130  as shown, but may be a separate component fixed in suitable manner to the slide. 
     Protection of the arm assembly is achieved by having rails  171 L,  171 R on opposite sides of arm  114  which are vertically slidable respectively in slots of left and right slide caps  173 L,  173 R fixed to and extending from opposite slides of block  175 , the arm sliding from a normal operative position as shown in FIG. 3 e  to a retracted position as shown for example in FIG. 3 f  when an obstacle is encountered. A pneumatic cylinder  168  is provided which is mounted in a bracket  170  and has a rod attached to a shaft  172  extending through a portion  174  of the housing. Shaft  172  ends in a block  176  having a pair of shafts  178  extending therefrom, each terminating in a Teflon (synthetic resin polymer)-tipped nipple  180 . Tips  180  may also be of other low friction material. A spring  182  on each shaft  178  bears against slide block  175  to retract block  176 , and thus move nipples  180  out of engagement with arm  114 , when cylinder  168  is released/retracted. A sensor  184  is provided which indicates when arm  114  is in the normal position shown in FIG. 3 e  and a bumper  186  is provided which both controls the position of arm  114  when it is in operative position shown in FIG. 3 e  and cushions the return of the arm to this position. 
     In operation, pneumatic cylinder  168  is normally operated to extend its piston to force the nipples  180  against arm  114  to hold the arm in the position shown in FIG. 3 e . So long as an obstacle is not encountered during a downward motion of arm  114 , the apparatus remains in this position. During a downward motion of the arm  114 , in order to provide as small a profile as possible, piston  118  would normally be retracted to pivot arm  160  and button  162  at the distal end thereof out of contact with slide  130 , and to the position shown in FIG. 3 f , so as to no longer be over slide  130 . If at any time during a downward motion of arm  114 , an obstacle is encountered, the pressure or force applied by such obstacle to the bottom of finger assembly  48  is sufficient to overcome the low friction engagement of nipples  180  with arm  114 , so that the arm may move upward under that force, preventing any damage to the arm and the finger assembly at the distal end thereof. Pivot arm  160 , being pivoted away from arm  114  at this time, does not interfere with such upward movement. The fact that the arm has been moved upward as a result of encountering an obstruction is detected by detector  184 . 
     Detector  184  detecting the upward movement of arm  114 , projecting head  188  of arm  114  no longer being detected as being adjacent to detector  184 , causes a suitable robotic control to lift the entire mechanism, including arm  114 , to be clear of the obstruction. Once this is accomplished, pneumatic piston  168  is released. The release of pressure on piston  168  may either pull back on arm  172  to release the pressure applied to arm  114 , or this may be accomplished by the piston merely relieving the force applied to arm  172  and the retraction of this arm and the nipples  180  affixed thereto being accomplished under control of compression springs  182 . In either event, the deactivation of piston  168  results in nipples  180  no longer applying pressure to arm  114 , permitting the arm to fall under the influence of gravity to its normal position shown in FIG. 3 e , cushions  186  operating on projections  188  to cushion and damp this fall and to control the final position of the arm. Once detector  184  detects that arm  114  has returned to its normal position, pneumatic cylinder  168  is again operated to press nipples  180  against arm  114  to hold the arm in that position. 
     While in the discussion above a piston  168  has been provided which normally presses low friction nipples  180  against arm  114  to maintain the vertical position thereof, this is not a limitation on the invention and, for some embodiments, it may be preferable to either dispense with the entire mechanism for applying holding pressure to the arm  114 , including pneumatic cylinder  168  and all of the components between this cylinder and nipples  180  or to only operate this mechanism under selected conditions such as when the gripper fingers have engaged an object to be moved. In this case, gravity would normally be relied upon to hold arm  114  in its desired operative position and the arm could be easily moved to avoid damaging contact with an obstruction when the arm is being lowered or to permit the arm to move over an obstruction as the arm follows a more complicated travel path. Frictional engagement should normally not be required even when an object is being moved by the arm since the weight of the object should only be sufficient to maintain the arm in its operative position. 
     Fingers  52  may be a single finger of a length and shape appropriate for the application, or may be two or more fingers, two fingers  52 L and  52 R being shown for an illustrative embodiment in FIG. 3 b . Further, while pneumatic cylinders are used as the drive mechanism for the preferred embodiments shown, other suitable drive elements, including hydraulic cylinders, solenoids, servomotors and the like, may be utilized as the drive elements in place of the pneumatic cylinders. In addition, while two different coupling mechanisms have been shown between the drive mechanism and the slide, these are also by way of illustration only, and other suitable coupling mechanisms may be utilized, depending on application and other factors. Other details of construction may also vary with application. It should also be noted that, while only a single gripper mechanism  10 ,  110  is shown in the figures, typically at least two such mechanisms, and sometimes more, operating for example on opposite sides of the object  62 , would generally be required to lift the object. Thus, while the invention has been particularly shown and described above with reference to preferred embodiments, the foregoing and other changes in form and detail made therein by one skilled in the art while still remaining within the spirit and scope of the invention, which is to be defined only by the appended claims.