Abstract:
A transfer apparatus for automated parts movement includes a cylinder and a piston assembly slidably positioned within the cylinder. The piston assembly includes an outer piston having a recess in which an inner piston is slidably received. A transfer assembly is attached to the piston assembly and includes an inner rod, a sheath, and a gripper. Introduction of fluid at one port or end of the cylinder moves the piston assembly to extend the gripper and transport a gripped part to a target destination. At the target destination, the transfer assembly is moved via pressurized fluid in the cylinder to cause the gripper to release the gripped part. Introduction of fluid generally at an opposite end of the cylinder moves the transfer assembly and gripper to a retracted position relative to the cylinder.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 09/422,578, filed Oct. 21, 1999 now U.S. Pat. No. 6,367,856, which claims priority from U.S. Provisional Application Ser. No. 60/129,487, filed Apr. 15, 1999, which are hereby incorporated herein by reference. 
    
    
     BACKGROUND OF INVENTION 
     The present invention relates generally to apparatus for holding and transporting articles. In particular, the present invention relates to a fluid actuated, dual-piston transfer apparatus for holding and transporting an article. 
     Automated production line assemblies normally utilize transfer apparatus configured to automatically hold or grasp an article needed for the assembly of a product, and move or transport the article from a first location to a second, remote location. Once the article is transported to the second location, the transfer apparatus releases the article, retracts and subsequently repeats the process. The specific articles transported by these apparatus vary according to the particular industrial application. Frequently, transfer apparatus are used in the automated transportation of bolts, weld studs or nuts. 
     Normally, such apparatus include a transfer arm having a manipulator device or gripper connected to a transfer arm assembly, and an actuation assembly for moving the transfer arm in a preselected direction. The actuation assemblies most often used are electrically or pneumatically powered. The electrically powered apparatus are prone to failure due to the sophisticated electrical circuitry necessary to provide precise timed movement of the article. Consequently, such units require frequent maintenance and parts replacement, thereby increasing the manufacturing costs of a particular product. Pneumatically powered apparatus typically enjoy a greater life span than electrically powered assemblies. However, pneumatically controlled transfer apparatus are rarely used in applications requiring a high degree of positional accuracy because of their inability to accurately and dependably deposit the article in the desired location. 
     This lack of positional accuracy is most often encountered in industrial settings wherein the pneumatically actuated transfer apparatus is used in conjunction with other apparatus actuated by the same fluid pressure line, or where there is a large number of pneumatically operated transfer apparatus connected to the same fluid pressure line. In these situations, it is often difficult to precisely control the fluid pressure. As a result, the transfer apparatus experiences pressure fluctuations. When exposed to these pressure fluctuations, existing transfer apparatus will lose their grip on the article, causing the transfer arm to release the article while in transport. This inability to effectively transfer an article due to pressure fluctuations causes a decrease in efficiency, and often damages the article being transferred, thereby increasing material costs. 
     Additionally, many of these pneumatically controlled transfer apparatus require an additional mechanism to deposit the article once it is transported to its desired location. That is, a first cylinder is used to move the transfer arm from a first location to a second location, while a separately actuated, second cylinder is used to grasp and subsequently release the workpiece. This bifurcated operational sequence increases the complexity of the overall design of the transfer apparatus, and increases the probability of error given the imprecision associated with each cylinder. 
     Another problem confronting existing transfer apparatus is the tendency of the manipulator or gripper to rotate while in motion towards its target destination. This rotational movement of the gripper results in the inability of the transfer apparatus to provide proper placement of an article in applications where article orientation critical. Still another problem associated with existing transfer apparatus is their inability to accommodate parts of varying size without requiring the installation of a different gripper or manipulator. Substituting different grippers to accommodate articles of varying size requires the use of manual labor and necessitates placing the particular transfer apparatus off-line. Thus, in applications where there is a frequent change in article size, the costs associated with operating the particular assembly line are increased. 
     Consequently, there exists a need for a transfer apparatus for automated parts movement capable of reliably grasping and transporting an article, which can maintain the article in the proper orientation, and can accommodate articles of varying size without having to replace the gripper. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention provides a transfer apparatus for automated parts movement which, in preferred form, comprises a cylinder with a pair of coaxial pistons operably attached to a transfer assembly which includes a gripper. The transfer apparatus can be actuated by any fluid commonly utilized in the art, but is preferably pneumatically actuated. One of the pistons is advanced to extend the transfer assembly and grip the article held thereby. The pistons are further advanced to move the transfer assembly, and the article held thereby, to a target destination. Further advancement of one piston causes the transfer assembly to release the article, and thereafter, both pistons are retracted. Consequently, the transfer apparatus of the present invention permits the grasping, transportation and deposition of an article to be accomplished using a pair of cooperating pistons, and thus eliminates the imprecision associated with transfer apparatus employing independent, separately actuated, piston assemblies to accomplish the grasping and transportation procedure. 
     According to one aspect of the invention, the transfer apparatus includes an enclosed cylinder sealed by a first and a second end. A first and a second fluid inlet port, in fluid communication with the interior of the enclosed cylinder, are located proximate to the first and second end, respectively. Slidably positioned within the cylinder is a first, or inner, piston which is slidably received by a second, or outer, piston. Attached to both the inner piston and outer piston is a transfer assembly equipped with a gripper extending through the second end of the cylinder. Introduction of fluid through the first inlet port moves the inner and outer piston axially within the cylinder, enabling the transfer assembly to grasp an article and subsequently move the article to a target destination. Continued introduction of fluid through the first inlet port results in the stripping or removal of the article from the transfer assembly. Once the article is removed from the transfer assembly, fluid is introduced through the second fluid inlet port, causing the retraction of the inner and outer pistons and thus, the transfer assembly to thereby complete the stroke. Employing a cooperating inner and outer piston, both of which are actuated by a single fluid source, maximizes the precision of the transfer apparatus. 
     According to another aspect of the invention, a transfer apparatus includes an enclosed cylinder having a first and a second end, and a pair of pistons slidably positioned within the cylinder. The pistons are operably connected to a transfer assembly. The transfer assembly includes a sheath attached to the piston assembly and extending through an opening in the second end of the cylinder, and an inner rod attached to the piston assembly and contained within the sheath. The rod is attached at its end to a gripper. Introduction of fluid through the first end of the cylinder effects movement of the piston assembly to sequentially extend the gripper beyond the end of the sheath, and move the inner rod, sheath, and gripper away from the second end of the cylinder. Introduction of fluid through the second end of the cylinder retracts the piston assembly, and moves the sheath, inner rod and gripper towards the first end of the cylinder. The transfer assembly of the present invention provides efficient and precise movement of articles to thereby increase the efficiency of the transfer process. 
     In a preferred embodiment, the gripper is a gripper assembly having a spring loaded jaw assembly threadably attached to the end of the inner rod. The use of a spring loaded jaw assembly enables the transfer apparatus of the present invention to be used to grasp articles of varying size without switching jaw assemblies. This in turn reduces the complexity and cost of the manufacturing operation. Additionally, threadably attaching the spring loaded jaw assembly to the inner rod prevents the spring loaded jaw assembly from rotating during transportation of the article. Hence, the article is maintained in the proper orientation to thereby enable its precise placement in the desired location. This feature permits the present invention to be used in applications wherein the orientation of the article must be maintained in order to fall within the clearances required by the particular manufacturing application. 
     These and other objects, advantages and features of this invention will become apparent upon review of the following specification in conjunction with the drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a sectional view of a transfer apparatus for automated parts movement according to the invention; 
     FIG. 2 is a detailed sectional plan view of the gripper in the retracted position according to a preferred embodiment of the invention; 
     FIG. 3 is a detailed sectional side view of the gripper depicted in FIG. 2, shown in the extended position; 
     FIG. 4 is a detailed sectional view illustrating the second cushioning member positioned within the second end cap; 
     FIG. 5 is a sectional end view of the first end cap with the inlet ports and bleed port shown in phantom; 
     FIG. 6 is a sectional end view of the second end cap with the inlet ports and the bleed port shown in phantom; and 
     FIG. 7 is a detailed sectional view of a gripper assembly according to an alternative preferred embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention advances a transfer apparatus for the automated movement of parts which effectively grasps, transports and deposits a workpiece or article to a desired location. The apparatus can be used to transport a variety of articles normally encountered in an industrial setting. For example purposes only, such articles include, but are not limited to, nuts, bolts and weld studs. Furthermore, the apparatus of the present invention may be used to transport articles having varying sizes, without replacing the gripper assembly. 
     The transfer apparatus of the present invention utilizes a pair of cooperating pistons which are coupled to a transfer assembly equipped with a gripper. Introduction of fluid into the cylinder at one end advances the pistons, causing the transfer assembly to sequentially grasp and transport an article. Continued advancement of one of the pistons enables the transfer assembly to deposit the article in a desired location. Introduction of fluid at the opposing end of the cylinder retracts the pistons and the transfer assembly. The fluid employed to actuate the transfer apparatus may be any fluid normally employed in the art. Preferably, the transfer apparatus of the present invention is pneumatically controlled. 
     Referring now specifically to the drawings, and the illustrative embodiments depicted therein, a transfer apparatus for automated parts movement  10  includes a rearward or first end cap  20 , and a forward or second end cap  40 . Inner surfaces  22  and  42  of end caps  20  and  40 , respectively, are each formed with an annular recess  50 , allowing attachment to a cylinder  60 . End caps  20  and  40  may be secured to cylinder  60  by any means common utilized in the industry, for example, by welding. Alternatively, end caps  20  and  40  may be fastened to cylinder  60  by tie rods (not shown) placed in apertures  43  of second end cap  40  (FIG.  6 ), and fastened by nut and bolt assemblies  25  positioned on first end cap  20  and received by threaded apertures  25 ′. 
     Slidably positioned within cylinder  60  is a first, or inner piston  70  and a second, or outer piston  90 . As can be seen in FIG. 1, outer piston  90  includes a main body  92 , integrally attached to an annular flange  94 , extending towards first end cap  20 . The inner diameter of annular flange  94  corresponds approximately to the outer diameter of inner piston  70  to thereby enable inner piston  70  to slidably move within the recess  96  defined by annular flange  94 . A horizontal rod or stop pin  72  is attached to inner piston  70  and extends through an aperture  93  formed in outer piston  90 . Outer piston  90  is further formed with a horizontally disposed through hole  95 , extending from surface  92 ′ through surface  92 ″ of main body of outer piston to  92 , to thereby enable fluid communication between interior  62  of cylinder  60  and recess  96  formed by annular flange  94 . 
     Inner piston  70  and outer piston  90  are connected to a transfer assembly  110  which sequentially grasps, transports and releases an article (not shown) at a particular destination. Transfer assembly  110  includes an inner rod  112 , an outer cylindrical rod or sheath  118  and a gripper  117 . Inner rod  112  of transfer assembly  110  is rigidly connected to inner piston  70  and extends through an opening  98  in outer piston  90 , and central opening  48  of second end cap  40 . Sheath  118  is rigidly attached to outer piston  90  and extends through central opening  48  formed in second end cap  40 . Sheath  118  surrounds inner rod  112 . Inner rod  112  contains at its free end a threaded member  114  which is threadably attached to gripper  117 . As shown in FIG. 2, in the fully retracted position, gripper assembly  117  is positioned within sheath  118 . 
     As shown in FIGS. 1 through 3, in a preferred embodiment, gripper  117  is a spring loaded jaw assembly  120  and includes a main body  122  having an internally threaded recess  123  dimensioned to engage threaded member  114  of inner rod  112 . Spring loaded jaw assembly  120  further includes a pair of jaws  124 , held in a preselected biased position by a tension pin  126  and a spring member  128 . It will be recognized that jaws  124  permit articles of varying sizes to be effectively grasped since the inner surfaces  125  of jaws  124  define a wedge therebetween which allows an article to move lengthwise between jaws  124  until frictional contact is achieved between the article and inner surfaces  125 . 
     Transfer assembly  110  is attached to second end cap  40  and extends therethrough. Attachment between transfer assembly  110  and second end cap  40  may be achieved by any mean normally utilized in the industry. For example purposes only, transfer assembly  110  is positioned in second end cap  40  by means of a cartridge  49  received by enlarged opening  51  formed in second end cap  40 , and removably secured thereto by an O-ring  52  positioned within recess  53  of cartridge  49 . Cartridge  49  is attached to the exterior surface  118 ′ of sheath  118  by flanges  119 , and is positioned a preselected distance from end  118 ″ of sheath  118 . 
     A first cushioning member  74  is attached to surface  71  of inner piston  70  and is dimensioned for receipt by opening  28  formed in first end cap  20 . First cushioning member  74  is formed with an internally threaded through hole  75  dimensioned to receive externally threaded section  112 ′ of inner rod  112  projecting from inner piston  70  and into first end cap  20 . It will be recognized by those with ordinary skill in the art that other means of attaching first cushioning member  74  to inner rod  112  may be utilized without departing from the spirit and scope of the invention. A second cushioning member  100  extends from surface  92 ′ of outer piston  90 , and surrounds a portion of sheath  118 . Second cushioning member  100  is received by an annulus  84  defined by exterior surface  118 ′ of sheath  118  and central opening  48  of second end cap  40 . First cushioning member  74  and second cushioning member  100  serve to reduce the impact stress incurred by transfer apparatus  10  during retraction and extension, as will be discussed in detail below. 
     A fluid inlet port  26 , formed in first end cap  20 , is in fluid communication with opening  28 , and thus enables the introduction of fluid into interior  62  of cylinder  60  (FIG.  5 ). Inlet port  26  is attached to a source of pressurized air or other fluid (not shown). Similarly, inlet port  46 , formed in second end cap  40 , is in fluid communication with annulus  84  of second end cap  40  and is further in fluid communication with interior  62  of cylinder  60  (FIG.  6 ). 
     In operation, apparatus  10  begins a stroke in the retracted position, wherein first cushioning member  74  is positioned within opening  28  of first end cap  20 . As can be seen in FIG. 1, when in the retracted position, there exists a gap  30  between first cushioning member  74  and first end cap  20 , allowing fluid introduction within gap  30  to urge first cushioning member  74  towards interior  62  of cylinder  60 . In the retracted position, inner piston  70  is positioned proximate to first end cap  20  and is held in position about annular flange  94  of outer piston  90  by a spring ball retainer  97  removably positioned within a recess  73  formed in inner piston  70 . Also, lip  94 ′ of annular flange  94  of outer piston  90  abuttingly contacts surface  20 ′ of first end cap  20 . In this position, spring loaded jaw assembly  120  is contained within sheath  118 . 
     Introduction of fluid into inlet port  26  of first end cap  20  results in the movement of inner piston  70  within recess  96  and towards surface  92 ″ of outer piston  90 . As inner piston  70  moves towards outer piston  90 , inner rod  112  moves in the direction indicated by the directional arrow labeled extension, and causes spring loaded jaw assembly  120  to extend beyond end  118 ″ of sheath  118  (FIG.  3 ). When spring loaded jaw assembly  120  extends beyond sheath  118 , jaws  124  move a preselected distance apart to thereby enable jaws  124  to grasp an article. Once inner piston  70  abuts surface  92 ″ of outer piston  90 , continued introduction of fluid into cylinder  60  through first end cap  20  causes the concurrent movement of inner piston  70  and outer piston  90  towards second end cap  40 . The concurrent movement of inner piston  70  and outer piston  90  extends transfer assembly  110  in a direction away from second end cap  40  to thereby enable the article to be transported to its preselected destination. Movement of inner piston  70  and outer piston  90  towards second end cap  40  continues until stop pin  72 , attached to inner piston  70 , abuttingly contacts surface  41  of second end cap  40 . Abutting contact between stop pin  72  and second end cap  40  halts the movement of inner piston  70 , and thus also stops inner rod  112 . Thereafter, outer piston  90  will continue to move toward second end cap  40 . Continued movement of outer piston  90  moves sheath  118  over spring loaded jaw assembly  120  and thus strips or removes the article held between jaws  124 . In the extended position, second cushioning member  100  is received by annulus  84 . As can be seen in FIG. 4, a gap  104  exists between annulus  84  and second cushioning member  100  when apparatus  10  is in the extended position. 
     Retraction of the inner piston  70  and outer piston  90  within cylinder  60  is achieved by introducing fluid through inlet port  46  of second end cap  40 . Fluid injected into second end cap  40  enters gap  104  and urges second cushioning member  100  in the direction indicated by directional arrow labeled retraction (FIG. 1) and effects simultaneous movement of inner piston  70  and outer piston  90  towards first end cap  20 . Inner piston  70  and outer piston  90  continue movement towards first end cap  20  until lip  94 ′ of annular flange  94  of outer piston  90  abuttingly contacts surface  20 ′ of first end cap  20 . Thereafter, continued introduction of fluid into cylinder  60  results in the movement of inner piston  70  towards first end cap  20 . Continued movement of inner piston  70  after outer piston  90  contacts first end cap  20  is achieved by fluid traveling through through hole  95  formed in outer piston  90  and contacting inner piston  70 . Movement of inner piston  70  towards first end cap  20  continues until recess  73 , formed in the periphery of inner piston  70 , contacts a spring loaded ball retainer  97  positioned in inner surface  97  of annular flange  94  to thereby complete retraction of the inner piston  70  and outer piston  90 . As the pistons are retracted, transfer assembly  110 , specifically the inner rod  112  and the sheath  118 , move towards first end cap  20  to thereby enable apparatus  10  to repeat the transfer sequence. 
     First end cap  20  and second end cap  40  are each formed with a bleed valve  27  and  47 , respectively. Bleed valves  27  and  47  enable fluid to be evacuated from cylinder  60  to thereby control the speed at which inner piston  70  and outer piston  90  move between the extended and retracted position. Bleed valve  27  is in fluid communication with opening  28  and interior  62  of cylinder  60  via channel  29  and  29 ′, respectively. Similarly, bleed valve  47  is in fluid communication with both annulus  84  and interior  62  via channel  103  and  103 ′, respectively. 
     Referring now to FIGS. 5 and 6, each end cap  20 ,  40  may be formed with a location port  29 ″ and  45 , respectively. Ports  29 ″ and  45  are each dimensioned to accept a cylindricator switch (not shown) to enable the location of the pistons to be determined. Cylindricator switches are known by those with ordinary skill in the art as electrical devices which utilize a spring ball retainer to determine the absence or presence of an object. Here, the spring ball retainers of the cylindricator switches would come into removable contact with first cushioning member  74  and second cushioning member  100 . 
     Alternatively, the position of inner piston  70  and outer piston  90  within cylinder  60  may be determined by the placement of a circular magnet  55  within an annular recess  54  formed in the periphery of outer piston  90 . When magnet  55  is positioned within annular recess  54 , an inductive proximity switch (not shown) is used to enable the location of the pistons to be monitored. The inductive proximity switch may be fastened to first end cap  20  or on a tie rod (not shown). 
     In order to provide frictionless travel between the moving components of transfer apparatus  10 , such components include recesses dimensioned to accept annular bands of a material having a low coefficient of friction. The annular bands may be any material normally utilized in the industry to provide a frictionless interface between contacting surfaces. Specifically, outer piston  90  has a pair of annular recesses  130  and  132 , each of which is dimensioned to accept an annular band  134 . Also, the inner surface of outer piston  90  is formed with an annular recess  133  dimensioned to accept an annular band  134 . Similarly, an annular recess  140 , formed about the periphery of inner piston  70 , is dimensioned to receive an annular band  134 . Furthermore, an annular recess  136 , positioned on the interior surface  118 ″ of sheath  118  accepts an annular band  134 , thereby reducing friction encountered by inner rod  112  as inner rod  112  moves within sheath  118  during extension and retraction. 
     In an alternative preferred embodiment, as shown in FIG. 7, gripper  117  is a magnetic gripper. Preferably, the magnetic gripper is a magnetic gripper assembly  150 , including a main body  160  and a non-magnetic ring  170 . Main body  160  contains an internally threaded recess  162  attached to threaded member  114  of inner rod  112 . A magnetic material  164  is attached to end  163  of main body  160 . Magnetic material  164  may be any material commonly utilized in the art having the requisite magnetic properties needed to securely hold a particular article. Alternatively, main body  162  may be made of a magnetic material. Non-magnetic ring  170  is attached to end  118 ″ of sheath  118 . Non-magnetic ring  170  has at least approximately the same inner diameter as sheath  118 , but may also be larger. Non-magnetic ring  170  serves to remove a particular article from main body  162  during the extension stroke. Non-magnetic ring  170  may be any non-magnetic material commonly used in the art, for example, stainless steel. 
     The above description is considered that of the preferred embodiments only. Modifications of the invention will occur to those skilled in the art and to those who make or use the invention. Therefore, it is understood that the embodiments shown in the drawings and described above are merely for illustrative purposes and are not intended to limit the scope of the invention, which is defined by the following claims as interpreted according to the principles of patent law, including the doctrine of equivalents.