Abstract:
A gripper apparatus for grasping an object such as a specimen holder. The gripper apparatus comprises two arms. In one embodiment the arms are pivotable, and in a second embodiment, each arm includes a pivotable member. The arms are moveably coupled to each other and are structured to grasp the object therebetween.

Description:
FIELD OF THE INVENTION 
     The present invention generally relates to robotic gripping devices. More particularly, the invention concerns a method and apparatus to grasp an object using a pair of arms. In a preferred embodiment, the present invention grasps and transports specimen plates employed in a high throughput screening system. 
     BACKGROUND OF THE INVENTION 
     Robotic devices of myriad shapes and sizes have been constructed to perform tasks considered either too dangerous or too dreary to be performed by a person. Simple repetitive tasks, which drive human operators to distraction and error, can be performed faultlessly and quickly by robots. However, constructing a robotic system to seamlessly perform the grasping and precise positioning of objects is not a trivial task. 
     Many industrial fields require the precise positioning of an object for automated processing. In particular, the biotechnology field is making rapid advances by transitioning from traditional laboratory bench top processes to more automated systems. These automated systems typically perform assays or screens using a specimen or sample plate. Each sample plate has many individual sample wells, ranging from hundreds to more than a thousand wells. Because a discrete test can be conducted in each sample well, hundreds, or thousands, of tests can be performed using a few plates. 
     Sample plates are used in several industries, such as the biotechnology and biomedical industries. A sample plate typically has multiple sample wells on its top surface into which one or more samples can be placed, although a particular plate may have only a single well for the entire plate. Each of the wells forms a container into which a sample is placed. For example, some commonly used sample plates have 96, 384, or 1,536 wells. Such plates are available from, for example, Greiner America Corp. of Lake Mary, Fla., U.S.A. These plates may be handled manually or robotically. 
     For a robotic or automated system to perform with a high degree of reliability and repeatability, the system needs to accurately, quickly, and reliably position individual sample plates for processing. For example, sample plates must be placed precisely under liquid dispensers to enable the liquid dispenser to deposit samples or reagents into the correct sample wells. A positioning error of only a few thousandths of an inch can result in a sample or reagent being dispensed into a wrong sample well. Such a mistake can not only lead to a failed test, but such a mistake can lead to incorrect test results which others may rely upon for critical decision making, such as a medical treatment path for a patient. Further, even a minor positioning error may cause a needle or tip of the liquid dispenser to crash into a wall or other surface, thereby damaging the liquid dispenser. 
     Current, conventional automated or robotic devices are not known to operate with sufficient positioning accuracy to reliably and repeatably position a high-density sample plate for automated processing. For example, typical conventional robotic systems generally achieve a positioning tolerance of about 1 mm. Although such a tolerance is adequate for some low density sample plates, such a tolerance is unacceptable for high density plates, such as a plate with 1536 wells. Indeed, a positioning error of 1 mm for a 1536 well sample plate could cause a sample or reagent to be deposited entirely in the wrong well, or cause damage to the system, such as to needles or tips of the liquid dispenser. 
     Therefore, there exists a need for a robotic or otherwise automated gripper mechanism that can accurately, reliably, and quickly position an object for processing in an automated system. 
     SUMMARY OF THE INVENTION 
     In order to overcome the deficiencies with known, conventional robotic devices, a robotic gripping mechanism is provided. Briefly, the gripper mechanism includes a first arm having a first pivotable member and a second arm also having a second pivotable member, with the second arm moveably coupled to the first arm. The first and second pivotable members are structured to grasp an object therebetween. In an alternative embodiment, the pivotable members are removed, and the first and second arms are pivotable so that the edges of an object, such as a sample plate, contacts the first and second arms. 
     The robotic gripper mechanism according to the invention provides an accurate, extremely precise automated system for grasping, moving and positioning objects. The gripper mechanism accomplishes the accurate positioning of objects by positively locating the grasped object in all three translational coordinate axes. For example, one method employed by the present invention comprises grasping the object with two arms that include pivot members. During the grasping process, the x-axis, or side-to-side position of the object is determined. The z-axis, or vertical position of the object is also determined during the grasping process. Finally, the object is then pushed against a surface to determine a y-axis, or fore-and-aft position the object. 
     The gripping mechanism of the present invention affords its users with a number of distinct advantages. First, unlike prior robotic grippers, the present gripping mechanism accurately determines the three translational axes of an object with extreme accuracy. Moreover, the determination of the position of the object is performed quickly, thereby enabling high throughput processing of a large quantity of objects. 
     In one aspect, the present invention features a robotic gripper apparatus. The gripper apparatus includes a grasping mechanism coupled to a controller. The grasping mechanism includes a first arm and a second arm. The gripper apparatus determines the position of an object in all three translational coordinate axes with an accuracy of about 0.1 millimeters in each direction and the gripper apparatus also grasps the object. 
     In a preferred embodiment the robotic gripper apparatus includes: (a) a first arm including a first pivotable member; and (b) a second arm including a second pivotable member, the second arm moveably coupled to the first arm; wherein the first and second pivotable members are structured to grasp the object therebetween. 
     In another aspect, the invention provides a robotic gripper apparatus for grasping an object that includes: (a) means for providing first and second arms; (b) means for grasping the object with the first and second arms; and (c) means for pushing the object against a surface to position the object relative to the first and second arms. 
     In yet another aspect, the invention features a method of grasping an object. The method involves the steps of using a robotic gripper apparatus to determine all three translational coordinate axes of the object with an accuracy of about 0.1 millimeters in each direction and of using the robotic gripper apparatus to grasp the object. The gripper apparatus includes a grasping mechanism coupled to a controller, and the grasping mechanism includes a first arm and a second arm. 
     In a preferred embodiment, the method involves the steps of: (a) providing first and second arms; (b) grasping the object with the first and second arms; and (c) pushing the object against a surface to position the object relative to the first and second arms. 
     Finally, another aspect of the invention provides a method of moving an object. The method involves the steps of: (a) approaching the object with a robotic gripper apparatus; (b) grasping the object with the gripper apparatus; (c) removing the object from an initial position with the gripper apparatus; (d) pressing the object against a push surface with the gripper apparatus; and (e) placing the object in a new position with the gripper apparatus. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The nature, goals, and advantages of the invention will become more apparent to those skilled in the art after considering the following detailed description when read in connection with the accompanying drawing in which like reference numerals identify like elements throughout wherein: 
     FIG. 1 is an elevation view of a robotic arm gripper mechanism constructed according to one embodiment of the present invention; 
     FIG. 2 is a perspective view of the gripper mechanism illustrated in FIG. 1; 
     FIG. 3 is an elevation view of the gripper mechanism illustrated in FIG. 2; 
     FIG. 4 is a plan view of the gripper mechanism illustrated in FIG. 2; 
     FIG. 5 is a perspective view of the gripper mechanism and sample plate illustrated in FIGS. 1 and 2; 
     FIG. 6 is an elevation view of the pivot members and sample plate illustrated in FIG. 5; 
     FIG. 6A is an elevation view of the pivot members and sample plate illustrated in FIG. 6; and 
     FIG. 7 is a block diagram illustrating one method of grasping an object with the gripper mechanism illustrated in FIG.  1 . 
     Some or all of the Figures may be schematic representations for purposes of illustration and do not necessarily depict the actual relative sizes or locations of the elements shown. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In the following paragraphs, the present invention will be described in detail by way of example with reference to the attached drawings. Throughout this description, the preferred embodiments and examples should not be considered as limitations on the present invention. As used herein, “the present invention” and “the invention” refers to any one of the herein described embodiments. 
     I. A Robotic Gripper Apparatus 
     In accordance with the present invention, a robotic gripper apparatus (also referred to herein as a robotic gripper mechanism) is provided. Although this disclosed example is designed to be employed with a specific high throughput system, other uses for the present invention are contemplated. In particular, other high throughput systems may utilize the robotic gripper mechanism. Also, the robotic gripper mechanism can be employed to assemble components requiring precise positioning such as electronic devices, medical devices or other devices. 
     Referring to FIG. 1, the robotic gripper mechanism in accordance with one embodiment of the invention is illustrated and designated generally by the numeral  10 . The robotic gripper mechanism  10  is an automated and robotic gripper for grasping, moving and positioning objects. The preferred embodiment is constructed to grasp sample plates, but other types of objects can be grasped by the robotic gripper mechanism  10 . For example, petri dishes, test tubes, vials, crucibles, reaction vessels or flasks, or any type of object that is employed in a process requiring accurate positioning. 
     In the preferred embodiment illustrated in FIG. 1, the robotic gripper  10  comprises a grasping mechanism  20  movably connected to a boom  12  that is movable relative to a base  14 . Controller  15 , comprising a general purpose computing device, controls the movements of the grasping mechanism  20  and the boom  12  in a work perimeter that includes one or more stations  30  that can receive sample plates  25 . The grasping mechanism  20  is designed to grasp the sample plates  25  and move them from one station  30  to another station  30  or to other locations within the work perimeter of the robotic gripper mechanism  10 . Although the disclosed example has one work perimeter, more work perimeters, each employing a robotic gripper mechanism  10 , may be utilized, depending upon the specific application. 
     Referring again to FIG. 1, the boom  12  is capable of about 360 degrees of rotation. In addition, the boom  12  can move vertically and horizontally to align the grasping mechanism  20  with higher or lower stations  30 . In a preferred embodiment, a Stäubli RX-60 robot provided by Stäubli Corporation of South Carolina, U.S.A. comprises the boom  12  and base  14 , but any type of robot can be used by the robotic gripper mechanism  10 . 
     The boom  12  is configured to extend and retract from the base  14 . This defines the work perimeter for the robotic gripper mechanism  10 . Stations  30  are positioned within the work perimeter of the boom  12  as are hand-off areas or other areas that are configured for receiving objects grasped and moved by the grasping mechanism  20 . For example, sample plate  25  is positioned on station shelf  33  and can be grasped by grasping mechanism  20  and moved to another position by boom  12 . In a preferred embodiment, the sample plate  25  comprises several individual wells, with each well configured to hold a sample. For example, a sample plate  25  may contain 384, 967, or 1,536 wells. The grasping mechanism  20  can grasp many other types of sample plates. Other types of devices, such as semiconductor wafers, CDs, medical devices and other items, may be grasped and moved by the grasping mechanism  20 . 
     Referring to FIGS. 2-3, the grasping mechanism  20  is illustrated. Grasping arm A and grasping arm B extend from gripper mechanism body  22 . The body  22  is connected to a breakaway  60  that is deflectably coupled to the boom  12 . The breakaway is structured to detect angular, rotational and compressive forces encountered by the grasping mechanism  20 . The breakaway acts a collision protection device that greatly reduces the possibility of damage to components within the work perimeter by the accidental impact of the grasping mechanism  20  or grasping arms A and B with objects. For example, when the grasping mechanism  20  impacts an object, the breakaway  60  will deflect, thereby also causing the grasping mechanism  20  to deflect. When the controller  15  detects the deflection, it stops movement of the robotic gripper mechanism. In a preferred embodiment, the breakaway is a “quickstop” collision sensor manufactured by Applied Robotics of Glenville, N.Y., U.S.A. The breakaway  60  is a dynamically variable collision sensor that operates on an air pressure system. Other types of impact detecting devices could be employed and they can be operated hydraulically, magnetically, or by other means known in the art. 
     Body  22  connects the grasping arms A and B to the breakaway  60 . When directed by the controller  15 , the body  22  moves the grasping arms A and B, away from or toward each other, to grasp and release objects. In a preferred embodiment, the body  22  is a gripper manufactured by Robohand of Monroe, Conn., U.S.A. In a preferred embodiment, the gripper is pneumatically driven, but other means for operating the gripper can be employed, such as magnetics and hydraulics. 
     Referring to FIG. 2, grasping arms A and B extend from the body  22  and include pivot members  35 . Positioned adjacent to the pivot members  35  are sensors  55  and stops  50 . The sensors  55  communicate with the controller  15  and determine the location of objects adjacent to the arms A and B. In a preferred embodiment, the sensors  55  are optical sensors, but photoelectric, infrared, magnetic, or other suitable sensors can be employed. 
     Referring to FIGS.  4  and  6 - 6 A, the pivoting members  35  are pivotally mounted to the arms A and B. A channel  37  extends along a long axis of each pivot member  35  and, as shown in FIG. 6, includes a horizontal surface  40  and an angled surface  45 . In a preferred embodiment, the pivot members  35  comprise separate pieces which are pivotally mounted to the arms A and B. An alternative embodiment robotic gripper mechanism  10  may employ grasping arms A and B that include channels  37  in the arms A and B. The arms A and B would pivot with respect to the body  22 , thereby eliminating the need for separate pivot members  35 . The grasping arms A and B and pivot members  35  preferably are constructed from a metal or alloy, such as aluminum, but dielectric materials, such as plastic or other types of materials, can be employed. 
     II. Method of Using a Robotic Gripper Apparatus 
     Referring to FIGS. 5-7, the operation of the robotic gripper mechanism  10  will now be described. In a preferred embodiment, the robotic gripper mechanism  10  grips, transports and positions sample plates  25  from a station  30  to another station  30  or to a hand-off area or to another location within the work perimeter of the robotic gripper mechanism  10 . As shown in FIG. 5, the sample plate  25  comprises a plurality of closely arranged sample wells. Each well in the sample plate  25  is square with each side of the well having a length of about 2 millimeters. During a high throughput process, discrete fluid samples may be deposited in each well, requiring positioning accuracy to within 0.1 millimeters. The robotic grasping mechanism  10  of the present invention is capable of this positioning accuracy. 
     When employed in a high throughput process, the controller  15  instructs the robotic gripper mechanism  10  to move the boom  12  toward a station  30 . In a preferred embodiment, the sample plates  25  are vertically arranged on station shelves  33 . When instructed by controller  15 , the boom  12  extends the grasping mechanism  20  toward the station  30  and between the station shelves  33 . Sample plates  25  are located on the station shelves  33  and the sensor  55  detects the station shelf  33  as the grasping mechanism  20  moves closer to the station shelf  33 . As shown in FIG. 5, when the station shelf  33  is detected, the grasping arms A and B move up and contact the sample plate edge  27  with the pivot members  35 . A preferred embodiment sample plate  25  is substantially rectangular with at least two substantially straight sample plate edges  27 . Other objects may be grasped by the grasping mechanism  20 . The objects preferably will have straight sections that can engage the pivot members  35 . The pivot members  35  alternatively may be curved to include a curved channel  37 , suitable for grasping curved objects. 
     Referring to FIGS. 6 and 6A, the pivot members  35  comprise a substantially horizontal surface  40  and an angle surface  45  that combine to form a channel  37 . As the pivot members  35  approach the sample plate  25 , the vertical position of the sample plates  25 , defined by the z-axes, may not correspond with the pivot members  35 . In this case, when the pivot member  35  engages the sample plate edge  27 , the edge  27  may contact the angled surface  45 . As the grasping arms A and B continue to compress together, the grasping arms A and B pivot slightly, pushing the sample plate  25  against the horizontal surface  40 . By including the angled surface  45  on the pivot members  35 , the vertical position, as defined by the z-axis, is always known because the angled surface  45  forces the sample plate  25  to engage the horizontal surface  40 . This is in contrast to conventional gripping devices that do not define the vertical position of the grasped object. In addition, with conventional grasping devices, an object that is misaligned relative to the x-axes, that is, angled relative to the conventional grasping device, will be grasped at an angle, thereby only establishing a single point of contact on each side of the object. 
     As illustrated in FIGS. 5 and 6A, the present invention employs pivot members  35  that pivot to align themselves with the sample plate edge  27 , thereby establishing a line of contact  29  with the sample plate edge  27 . By including pivot members  35  on the grasping arms A and B, the present invention establishes an extremely accurate side-to-side position, or x-axis position of the sample plate  25 . Grasping angled plates with the subsequent mispositioning of the angled plate is thereby eliminated. 
     The next step of positioning the sample plate  25  comprises removing the sample plate  25  from the station shelf  33 . Because of the unique geometry of the channel  37  located in the pivot members  35 , the position of the sample plate  25  on the x-axis and the z-axis is known. The y-axis, or fore-and-aft position of the sample plate  25 , however, is not known. To determine the y-axis of the sample plate  25 , the body  22  and boom  12  of the robotic gripper mechanism  10  are moved to position the sample plate  25  next to the push surface  65 . 
     Shown in FIGS. 1 and 3, the push surface  65  is positioned on the base  14  of the robotic arm gripper mechanism  10 . The push surface  65  can be located in other locations such as on the station  30  or on other locations that are within the work perimeter of the robotic gripper mechanism  10 . The boom  12  pushes the sample plate  25  against the push surface  65  pushing the sample plate  25  against the stops  50  located on the grasping arms A and B. By pushing the sample plate  25  against the stops  50 , the fore-and-aft position of the sample plate is now known. 
     The above-described process of grasping the sample plate  25  with the pivot members  35  so that the sample plate is forced against the horizontal surface  40  and then removing the sample plate from the work stations  30  and pushing it against the push surface  65  ensures that all three translational axes of the sample plate can be determined to within about 0.1 millimeters. In addition, the channel  37  reduces the amount of gripping force required to grasp the sample plate  25  because the sample plate  25  rests on the substantially horizontal surface  40 . Moreover, because the angled surface  45  traps the sample plate  25  against the horizontal surface  40 , thereby preventing the tilting of the sample plate  25 , only the end section of the sample plate  25  is grasped. This allows the easy insertion of the sample plate  25  into constrained locations, because the grasping arms A and B only engage a small section of the sample plate  25 . 
     An apparatus and method for grasping and positioning an object, such as the robotic gripper mechanism, are thus provided. One skilled in the art will appreciate that the present invention can be practiced by other than the preferred embodiments, which are presented in this description for purposes of illustration and not of limitation, and the present invention is limited only by the claims that follow. It is noted that the practice of various equivalents for the particular embodiments discussed in this description is also within the scope of the invention.