Abstract:
A gripper apparatus for removing and replacing objects such as containers or vials in an array of containers has a gripper head which extends downward from a support arm, a planetary gear assembly mounted in the gripper head including at least three planet gears, and at least one gripping pin extending downward from each planet gear and projecting beyond a lower end of the gripper head. A drive motor drives the planetary gear assembly to rotate the planet gears in opposite directions, moving the pins inward and outward along predetermined paths to grip and carry an object and release the object when in a desired location.

Description:
RELATED APPLICATIONS 
     The present application claims the benefit of U.S. provisional pat. App. Ser. No. 61/253,487, filed Oct. 20, 2009, the contents of which are incorporated herein by reference in their entirety. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to robotic gripping devices. More particularly, the invention concerns a method and apparatus to grasp containers of varied sizes using a plurality of movable fingers. 
     RELATED ART 
     Many industries rely upon automated handling of bottles, vials and tubes of different sizes. In many applications, the ability to handle different size containers is provided by a rotating turret assembly with a number of different size openings arranged on a circular assembly. The turret is rotated to select the opening with a size that matches a selected container size. In other applications, rather than requiring the selection from multiple handlers to accommodate each different size container, attempts have been made to provide adjustable grippers which operate by moving two to more fingers inward and outward relative to a center point at which the container is located. Typically, the fingers are pneumatically actuated. The fingers may either move on fulcrums, like “pincers”, so that the angles of the gripping surfaces change, or they can slide along a single plane so that the fingers remain parallel with the distance between the fingers being adjusted to fit the container diameter. In one example, the gripper mechanism described in U.S. Pat. No. 6,592,324 of Downs et al uses a combination of sliding and rotation of two arms to grip microplates. While such systems may work well with containers of a consistent size, the force applied to the container can vary depending on the size of the container. These failings are particularly pronounced in applications involving the storage of compounds, biological specimens or other samples. Such storage systems hold many thousands of samples which may be in different size glass or plastic vials or tubes and may have different closure means, such as stoppers inserted into the opening and caps or adhesive films covering the edges of the openings. The gripper robotics are often contained within an environmentally-controlled enclosure, making frequent changing of the gripping mechanism to fit a particular container impractical. Since the containers usually hold very small volume samples, these vials and tubes can be small and relatively fragile. One of the problems that can occur with variable force control on current the commercially-available grippers is that sometimes the caps or tubes are broken or are not gripped sufficiently well. These grippers are also incapable of self-adjusting for different cap sizes. Another problem is that pneumatic grippers do not produce sufficient feedback to let the system know if a tube of the expected dimensions was, in fact, picked up. 
     In view of the shortcomings of existing grippers, the need remains for a container gripper that has the ability to adjust to a range of container sizes and surfaces, and which provides feedback to allow control of the force applied to the container. The present invention is directed to such an invention. 
     SUMMARY 
     In an exemplary embodiment, a gripper apparatus has a gripper head extending downward from a gripper support arm. The gripper head comprises a stationary ring gear and a plurality of planet gears which cooperate with the inner teeth of the ring gear. Typically, three or four planet gears are provided. Each planet gear has a pin extending downward from near an outer edge of the planet gear. Each planet gear is rotatably attached to the lower surface of a rotatable gear plate which has a crescent gear disposed on its upper surface in one embodiment. 
     In one embodiment, the pins may be attached to small fingers extending from the edge of each planet gear. The gear plate and crescent gear have a common pivot point. The crescent gear cooperates with a drive gear above the gear plate to rotate the plate so that, as the plate rotates, the teeth of the planet gears cooperate with the teeth of the ring gear. In another embodiment, the crescent gear is replaced by a center gear, and each planet gear has teeth meshing with teeth of the center gear. 
     The rotation of the planet gears causes the pins to move along a radial path relative to the center pivot of the gear plate, thus varying the distance between the pins on adjacent gears and allowing them to adjust to accommodate any container size that is up to the inner diameter of the ring gear, where the pins are straight. If the pins are bent outward, the gripper may be used with containers that have diameters larger than the inner diameter of the ring gear. 
     A stationary bottom plate attaches to the bottom of the gear assembly to enclose the planet gears. Radial slots formed in the face of the bottom plate correspond to the radial path of each pin. 
     The drive gear is connected to a small servo motor mounted above the gripper support arm. The motor gives feedback to a gripper controller, allowing the force applied to the pins to be carefully controlled. Control of the force applied to the pins is a simple matter of increasing or decreasing the range of rotation of the crescent gear. The pins may be covered or coated with a resilient, high friction surface, such as a silicone or elastomer sleeve, to prevent slippage between the pins and the container. In a preferred embodiment, software within the gripper controller will be able to “feel” what is being gripped based on the amount of give as the gripper pins are tightened, allowing the gripper to distinguish between, for example, a metal or hard plastic cap and a rubber stopper. The small diameter of the pins allows the gripper to be used to select vials from high density arrays. Four pin grippers can be configured to define the corners of a square, for use with standard arrays or rectangular, for use with high density arrays. The distal ends of the pins are tapered top facilitate insertion of the pins into a closely packed array of containers. In one embodiment, the pins may be bent outward to permit gripping of containers that have larger diameters than the ring gear. Conversely, if the pins are bent inward, they can come close to touching, thus allowing the smallest diameter object to be gripped. 
     The gripper head of the present invention is particularly useful for handling of the small vials and tubes that are used in biological and chemical compound storage systems. However, upward scaling of the gripper head would allow handling of larger containers, including beverage bottles, food jars and other commonly-used containers. 
     Other features and advantages of the present invention will become more readily apparent to those of ordinary skill in the art after reviewing the following detailed description and accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The details of the present invention, both as to its structure and operation, may be gleaned in part by study of the accompanying drawings, in which like reference numerals refer to like parts, and in which: 
         FIG. 1A  is a diagrammatic perspective view of one embodiment of a gripper apparatus with the grippers or gripping pins holding a small, capped vial; 
         FIG. 1B  shows the gripper apparatus with the grippers fully opened, without the vial; 
         FIGS. 2A and 2B  show arrays of vials or containers in a normal ( 2 A) and high density ( 2 B) arrangement, illustrating the grippers engaged around one of the vials; 
         FIG. 3A  is a bottom view of the apparatus with the gripping pins at their innermost positions to hold a small diameter vial; 
         FIG. 3B  is a bottom view similar to  FIG. 3A , with the bottom plate removed and the gripping pins in the same position as shown in  FIG. 3A ; 
         FIG. 3C  is a bottom view similar to  FIG. 3A , but with the pins moved outwardly from the positions in  FIG. 3A  to define a larger size opening; 
         FIG. 3D  is a bottom plan view similar to  FIG. 3C  but with the bottom plate removed; 
         FIG. 4A  is a bottom perspective view of the apparatus of  FIGS. 1A ,  1 B, and  3 A to  3 D, with the pins in the same position as  FIG. 3A  and the bottom plate attached; 
         FIG. 4B  is a bottom perspective view similar to  FIG. 4A  but with the bottom plate removed; 
         FIG. 4C  is a perspective view similar to  FIG. 4A  but with the pins in the outermost positions to define the largest diameter opening; 
         FIG. 4D  is a view similar to  FIG. 4C  but with the bottom plate removed; 
         FIG. 5  is a side view of a gripper apparatus similar to that of  FIGS. 1 to 4D  but with outwardly bent pins shown in a fully open position; 
         FIG. 6  is a perspective view of another embodiment of a four pin gripper apparatus; 
         FIG. 7  is an exploded view of the gripper apparatus of  FIG. 6 ; 
         FIG. 8A  is a perspective view of a modified gripper apparatus similar to that of  FIGS. 6 and 7 , with the bottom plate removed; 
         FIG. 8B  is a view similar to  FIG. 8A  with the bottom plate attached; 
         FIG. 8C  is a bottom plan view of the gripper apparatus of  FIGS. 8A and 8B  with the bottom plate removed and the pins moved outwardly from the position of  FIG. 8A ; 
         FIG. 8D  is a bottom plan view similar to  FIG. 8C  but with the bottom plate attached; 
         FIG. 9  is a side elevation view of another embodiment of a gripper apparatus having three grippers or gripping pins rather than four; 
         FIG. 10  is a bottom plan view of the apparatus of  FIG. 9 , with the bottom plate removed; 
         FIG. 11  is a bottom plan view similar to  FIG. 10 , with the bottom plate attached; 
         FIG. 12  is a cross sectional view on the lines  12 - 12  of  FIG. 11 ; 
         FIG. 13  is a side elevation view of the gripper apparatus similar to  FIG. 9  but taken from a different direction and with the pins moved outwardly from the position of  FIG. 9 ; 
         FIG. 14  is a cross sectional view on the lines  14 - 14  of  FIGS. 13 ; and 
         FIG. 15  is a block diagram illustrating one embodiment of a control system for the gripper apparatus of any of the preceding embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     Certain embodiments as disclosed herein provide for a robotic gripping method and apparatus for grasping containers of various sizes using a plurality of movable fingers. In one embodiment, the pins depend from respective planet gears of a planetary gear assembly which is driven to rotate the planet gears so that the pins move on radial paths relative to a central pivot axis, and the spacing between the pins can be varied to grip different size containers. 
     After reading this description it will become apparent to one skilled in the art how to implement the invention in various alternative embodiments and alternative applications. However, although various embodiments of the present invention will be described herein, it is understood that these embodiments are presented by way of example only, and not limitation. As such, this detailed description of various alternative embodiments should not be construed to limit the scope or breadth of the present invention. 
       FIGS. 1A ,  1 B and  3 A to  4 D illustrate a gripper apparatus  100  according to a first embodiment, while  FIGS. 2A and 2B  illustrate positioning of the gripping pins  22 ,  23 ,  24  and  26  of apparatus  100  to grip a container in an array.  FIG. 1A  illustrates the pins in gripping and lifting container  110 , while  FIG. 1B  illustrates the apparatus not engaged with a container and with the pins  22 ,  23 ,  24 , and  26  in positions spaced outwardly from those of  FIG. 1A  and defining a large size of opening to engage the rim of a larger container. 
     As shown in  FIGS. 1A and 1B , the gripper apparatus comprises a gripper head extending from support  1  and comprising a support base  2 , a stationary ring gear  3  and a stationary bottom plate  5  attached to the bottom of the ring gear to enclose a planetary gear assembly  35  which is illustrated in  FIGS. 3A to 4D  and which has a central gear axis  30 . The planetary gear assembly  35  basically comprises four planet gears  6 ,  8 ,  10 ,  14  which revolve about parallel planet gear axes, a carrier or gear device  12 ,  13  on which each planet gear is rotatably mounted, and an outer ring gear  3  with inwardly directed teeth  50  with which the teeth of the planet gears mesh, as best illustrated in  FIGS. 3B ,  3 D,  4 B and  4 D. Gripping pins  22 ,  23 ,  24 ,  26  depend from respective planet gears  6 ,  8 ,  10 ,  12  inside ring gear  3  and through respective radial slots  16 ,  17 ,  18  and  19  in bottom plate  5  for engagement with the rim of a container or vial such as container  110 . The planet gears are driven by a motor driven drive gear  4 , as described in more detail below with reference to  FIGS. 3A to 4D . 
     While four planet gears are shown in  FIGS. 3A to 4D , there may be as few as three or more than four. Gripping pins  22 ,  23 ,  24 ,  26  extend downward from near the outer edges of the respective planet gears. In the illustrated embodiment, the gripping pins  22 ,  23 ,  24 ,  26  are each secured to a respective finger  21 ,  25 ,  27  and  28  which extends from the edge of the respective planet gear, to align the finger with the respective slot  16 ,  17 ,  18  or  19  as seen in  FIGS. 3A and 3C . Each planet gear is rotatably attached to the lower surface of a carrier or mounting plate  13  which has a crescent gear  12  disposed on its upper surface (gear plate  13  is cut away in  FIG. 3B  to reveal crescent gear  12 ). Mounting plate  13  and crescent gear  12  are rotatably mounted for rotation about central axis  30  of the gear assembly. 
     The crescent gear  12  cooperates with drive gear  4  above plate  13  to rotate the plate so that, as mounting plate  13  rotates, the planet gears rotate with the gear plate about central axis  30 , and at the same time, the teeth of the planet gears  6 ,  8 ,  10  and  14  cooperate with the teeth of the ring gear  3  to rotate each planet gear about its own pivot axis. The rotation of the planet gears causes the pins  22 ,  23 ,  24  and  25  to move along radial paths relative to the center pivot  30  of the gear plate, thus varying the distance between the pins on adjacent gears and allowing them to adjust to accommodate any container size that is up to the inner diameter of the ring gear.  FIGS. 3A ,  3 B,  4 A and  4 B illustrate the pins  22 ,  23 ,  24  and  26  at their innermost position at the inner ends of the respective slots  16 ,  17 ,  18  and  19 , defining a minimum pin spacing for gripping the smallest diameter vial or container. In  FIGS. 3C and 3D , the planet gears have rotated away from the position of  FIGS. 3A and 3B  so as to move the pins  22 ,  23 ,  24  and  26  outwardly along the respective slots, defining a larger opening for gripping a larger diameter vial. In  FIGS. 4C and 4D , the pins  22 ,  23 ,  24  and  25  are moved to the outermost position in the respective slots, at the largest spacing for gripping the largest diameter vial. As illustrated in  FIG. 4D , for straight pins this corresponds to the inner diameter of ring gear  3 . In an alternative embodiment illustrated in  FIG. 5 , the straight pins of  FIGS. 1 to 4  are replaced by bent pins  22 A,  23 A,  24 A (the bent pin corresponding to pin  25  is not visible in  FIG. 5 ). If the pins are bent outward, as shown in  FIG. 5 , the gripper may be used with containers that have diameters larger than the inner diameter of the ring gear. 
     An opening  34  at the center of bottom plate  5  (see  FIG. 1B ) provides a sight line for an optional optical sensor for detecting the presence of a vial. The drive gear  4  is connected to a small reversible servo motor  7  mounted above the gripper support arm  1 . The motor gives feedback to a gripper controller, allowing the force applied to the pins to be carefully controlled. One embodiment of a control system for the gripper apparatus is illustrated in  FIG. 15  and described in more detail below. The pins are first positioned at a spacing outside the diameter of the container in alignment with the spaces between the selected container and adjacent container in the array, as illustrated in  FIG. 2A  for a standard container array. Once the gripper is lowered so that the pins engage in the gaps between containers, the pins are driven inwards to engage the container as illustrated in  FIG. 1A , and the gripper is then lifted to pick up the container and remove it from the array. The operation is reversed to return a container to an array or place a new container in an array of similar containers.  FIG. 2B  illustrates a high density array with the gripping pins surrounding one container in the array. 
     Control of the force applied to the pins is a simple matter of increasing or decreasing the range of rotation of the crescent gear. The pins may be covered or coated with a resilient, high friction surface, such as a silicone or elastomer sleeve, to prevent slippage between the pins and the container. In one embodiment, software within the gripper controller will be able to “feel” what is being gripped based on the amount of give as the gripper pins are tightened, allowing the gripper to distinguish between, for example, a metal or hard plastic cap and a rubber stopper. The small diameter of the pins allows the gripper to be used to select vials from high density arrays. Four pin grippers can be configured to define the corners of a square, as in  FIG. 2A , for use with standard arrays or rectangular, as in  FIG. 2B , for use with high density arrays. The distal ends  42  of the pins are tapered to facilitate insertion of the pins into a closely packed array of containers. In one embodiment, the pins may be bent outward to permit gripping of containers that have larger diameters than the ring gear, as illustrated in  FIG. 5 . Conversely, if the pins are bent inward, they can come close to touching, thus allowing the smallest diameter object to be gripped. 
     The gripper head of the present invention is particularly useful for handling of the small vials and tubes that are used in biological and chemical compound storage systems. However, upward scaling of the gripper head would allow handling of larger containers, including beverage bottles, food jars and other commonly-used containers. 
     Although the central axis and planet gear axes are all parallel in the embodiment of  FIGS. 1A to 4D , they may be placed at an angle in alternative embodiments to vary the gripping pin movement. 
       FIGS. 6 and 7  illustrate a gripper apparatus  200  according to a second embodiment which has a modified planetary gear assembly. Some parts of the apparatus  200  are identical to the previous embodiment, and like reference numbers are used for like parts as appropriate. As in the previous embodiment, the gripper apparatus has a support base  2  mounted on support  1 , a stationary ring gear  3  and a stationary bottom plate  5  attached to the bottom of the ring gear to enclose planet gears  6 ,  8 ,  10 ,  14  from which respective gripping pins  22 ,  23 ,  24 ,  26  depend. The planet gears mesh with the teeth  50  of the ring gear  3 , while the pins depend from the respective planet gears inside ring gear  3  through respective radial slots  16 ,  17 ,  18  and  19  in bottom plate  5  for engagement with the rim of a container or vial, as in the first embodiment. However, in this embodiment, a center gear  102  replaces the crescent gear of the planetary gear assembly in the previous embodiment for driving the planet gears. Center gear  102  has an upper gear  103  which meshes with drive gear  120 , and a lower, smaller gear  105  which meshes with the teeth of the respective planet gears  6 ,  8 ,  10  and  14 , as illustrated in  FIGS. 7 and 8C . Rotation of the drive gear  120  rotates center gear  102  to rotate the planet gears about their central axes, while the planet gears also rotate about the central axis of the planetary gear assembly to produce the same radial pin movement as the previous embodiment. Rotation of center gear clockwise and anticlockwise moves the pins to their largest and smallest separation respectively. Operation of the apparatus  200  to grip and pick up containers of various sizes is identical to that described above in connection with  FIGS. 1 to 5 , apart from the modified gear assembly between the drive motor and planet gears. 
     The gripper apparatus  202  illustrated in  FIGS. 8A to 8D  has a slightly different configuration from the apparatus of  FIGS. 6 and 7 , in which eccentrically mounted drive gear  120  is eliminated and the center gear  102  is driven directly by the servo motor. In this case, the motor (not visible in the drawings but located immediately above center gear  102 ) is located concentrically with the center gear to drive it directly rather than being located off center, at the corner of the support base, as in the previous embodiment. Other components of apparatus  202  are identical to those of the previous embodiments, and like reference numbers are used for like parts as appropriate. On rotation of the center gear  102  in a clockwise direction, the small lower gear  105  meshes with the teeth of the planet gears in order to drive the planet gears to rotate about their respective central axes in a direction which moves the pins  22 ,  23 ,  25  and  26  radially outwardly along the respective slots, towards the outermost position. On rotation in the opposite direction, the pins are moved radially inwards. The pins are illustrated in a more closely spaced position in  FIGS. 8A and 8B , and are shown at a location spaced outward from that position in  FIGS. 8C and 8D . 
       FIGS. 9 to 14  illustrate a gripper apparatus  300  according to another embodiment, in which a gripper head  302  has three gripping pins  304  rather than four pins as in the previous embodiment. Three pins may be sufficient in many cases to grip and pick up a vial or container from an array or return a container to the array. As in the previous embodiments, gripper head  302  extends from support  303  and includes a planetary gear assembly  303 . Gear assembly  303  comprises three planet gears  308  each having teeth around their outer periphery which engage the internal teeth  309  of ring gear  305 , as illustrated in  FIG. 10 , rotating carrier  307  ( FIG. 12 ) in which the planet gears are each rotatably mounted, and center gear  310 . As in the previous embodiments, gripper head  302  has a support base  301  and a stationary bottom plate  306  attached to the ring gear  305  to enclose the planet gears  308 . 
     Gripping pins  304  depend from respective planet gears inside ring gear  305  and through respective radial slots  312  in bottom plate  306  for engagement with the rim of a container or vial in a similar manner to the four pins of the previous embodiments. As in the embodiment of  FIGS. 6 and 7 , the planet gears are driven by a small lower gear  314  of center gear  310 , which in turn is driven to rotate by drive gear  315  driven by a small reversible servo motor  316  ( FIG. 14 ) under the control of a suitable controller (not illustrated). Center gear  310  has a larger upper gear  318  which meshes with the teeth of drive gear  315 , as illustrated in  FIG. 14 . Alternatively, the center, gear itself may be the drive gear, eliminating the off center drive gear  315 , and the servo motor is then centrally located in the support base  301  of the gripper head. 
       FIG. 15  is a block diagram of one embodiment of a control system for operating the apparatus of  FIGS. 9 to 14 . A similar control system may be used in each of the embodiments described above. As illustrated in  FIG. 15 , a gripper controller  350 , which may be located in the gripper head  302  or the support arm  303 , controls operation of drive motor  7  based on operator input and feedback from drive motor  7 . In some embodiments, feedback may be provided by one or more optional optical sensor(s)  352  in the gripper head, which may be used to detect presence or absence of a container between the gripping pins or fingers  304 . Drive motor  7  drives gear assembly  354  between the drive motor and planet gears  308 . In the embodiment of  FIGS. 9 to 14 , the gear assembly  354  comprises drive gear  315  and center gear  310 , but may comprise only center gear  310  where gear  310  is driven directly by the drive motor, or the crescent gear and gear plate of the first embodiment. As noted above, in order to pick up a container or vial from an array, the gripper head is first moved to a selected position directly above the array, and the gripper controller then controls the drive motor to move the pins inwardly or outwardly until they are at a predetermined spacing from one another defining a predetermined opening of slightly larger dimensions than the container. At this position, the pins are located directly above respective gaps between the selected container and adjacent containers in the array (see  FIG. 2A  for an example of this position for a four pin gripper). The gripper head is then lowered until the lower ends of the pins extend into the spaces or gaps around the selected container. This position may be controlled by an operator or using input from position sensors. 
     Once the pins are located in the space around a selected container, the controller controls drive motor  7  to move the pins inwardly until the container is engaged and grasped between the pins which surround it. The motor continues to apply driving force to the pins so that they grasp the container while the gripper head is raised to lift the container from the array and drive it to the desired location, where it may be released by driving the pins outwardly away from the container. The motor gives feedback to the controller  350  as the container is transported, allowing the force applied to the pins to be carefully controlled. In one embodiment, software within the gripper controller will be able to “feel” what is being gripped based on the amount of give as the gripper pins are tightened, allowing the gripper to distinguish between, for example, a metal or hard plastic cap and a rubber stopper, and the controller then uses this information to control the amount of force applied. 
     The procedure is reversed to return a container to an empty space in an array, with the gripper head driven back to a position above the space in the array and lowered to position the container in the space while the pins grasp the container. The controller than controls motor  7  to drive the pins outwardly away from the container. Once the container is released, the gripper head is raised to move the pins out of the array. 
     The gripper apparatus in each of the above embodiments provides adjustable gripping pins or fingers which are driven by a planetary gear system to move inwardly and outwardly to grip or release a container. 
     The above description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles described herein can be applied to other embodiments without departing from the spirit or scope of the invention. Thus, it is to be understood that the description and drawings presented herein represent a presently preferred embodiment of the invention and are therefore representative of the subject matter which is broadly contemplated by the present invention. It is further understood that the scope of the present invention fully encompasses other embodiments that may become obvious to those skilled in the art and that the scope of the present invention is accordingly limited by nothing other than the appended claims.