Abstract:
A hemming apparatus is provided for use with a robot in performing a hemming operation. The hemming apparatus comprises a support housing which mounts to a machine and has a pressurizable interior chamber having forward and rearward portions. A slide member includes a piston which is disposed in the chamber, and a plunger extends outwardly from the piston. Means are provided for attaching the housing to a nose having a central passageway. A bearing shaft is disposed within the central passageway, and means are provided for connecting the bearing shaft to the plunger. A hem roller is attached at the end of the bearing shaft. The rearward and forward portions of the chamber are connectible to a source of fluid pressure such that adjusting the chamber pressures moves the piston, thereby causing the bearing shaft to drive the hem roller into engagement with a work piece.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of U.S. Provisional Application 61/062,033, which was filed on Jan. 23, 2008, the entire disclosure of which is hereby incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to hemming sheet metal and more particularly to a hemming apparatus and method for forming a generally flat hem between two metal panels. Even more particularly, this invention relates to a roller-type hemming apparatus for edge hemming vehicle closure panels, such as hemming door, hood, trunk, and deck lid panels. 
     2. Description of the Prior Art 
     In the automotive industry, hemming machines are conventionally used to attach two metal panels together. These metal panels include, for example, the metal panels to form the automotive hood, door panels, quarter panels, and the like. 
     Hemming machines are disclosed in the patent prior art, including U.S. Pat. No. 5,267,387, issued Dec. 7, 1993 to Sawa; U.S. Pat. No. 6,425,277, issued Jul. 30, 2002 to Wiens; U.S. Pat. No. 6,983,633, issued Jan. 10, 2006 to Holmgren et al.; and U.S. Pat. No. 7,152,447, issued Dec. 26, 2006 to Toeniskoetter; and U.S. Patent Publication No. 2005/0229666, published Oct. 20, 2005 to Toeniskoetter. 
     A conventional roller hemming apparatus is mounted to a multi-axis controllable robot and may include a hem roller carried by a support. The roller hemming apparatus is adapted for hemming a bent portion of a workpiece, such as a door panel, which is positioned on a hemming die. The workpiece is hemmed by rolling the hem roller, under pressure, along the bent portion. The conventional roller-type hemming apparatus is used for continuous hemming along the contour edge of the workpiece. 
     In order to achieve good hemming with a conventional hemming apparatus, the robot must move the hem roller along the edge of the workpiece at a constant distance from the hemming die. However, a robot is not comprised of a perfectly rigid body. Therefore, when the hem roller is positioned against the edge of the workpiece, the robot may be deflected by its own resiliency or by a resistive force exerted by the edge of the workpiece itself. This results in a fluctuation of the pressing force applied by the hem roller onto the edge of the workpiece, and therefore imperfect hemming of the workpiece. 
     Various approaches to compensate for fluctuating pressing force have been proposed. For example, springs have been used. However it has been observed that springs alone have proven to be inadequate. 
     In addition, traditional hemming rollers having a single roller only enable the user to hem simplistic workpiece such as those having open areas. However single roller hemming apparatuses are not capable of hemming a workpiece with complex configurations. 
     Additionally, certain workpieces having complex geometry may be difficult to hem. It is costly to reconfigure robot-controlled hemming apparatuses because it is time consuming with respect to labor expenses. In addition, customized tooling required to reconfigure the mounting of the robot is expensive. To overcome this problem, some roller hemming apparatuses provide two rollers on a common spindle. The first roller is used for the actual hemming, while the second roller is used to guide the first roller relative to the workpiece. 
     Additionally, as work progresses, oftentimes the circumference of the hemming roller may become nicked, thus resulting in an imperfect hemming. 
     SUMMARY OF THE INVENTION 
     The present invention provides a roller-type hemming apparatus which includes a hemming head. Attached to the hemming head is a hem roller that can accurately follow the configuration of a bent portion of a workpiece to be hemmed. The present invention can more accurately and consistently apply a constant hemming force to the workpiece. 
     The present invention also provides a roller-type hemming head wherein deflection of the hem roller is limited to a settable range limited by an adjustable pressure applied to a slidable guide member that supports the hem roller. The hemming head is air compliant in that the pressure on the hemming roller is the result of a cushion of fluid (air or oil) acting on a piston shaft to maintain the roller in contact with the metal being hemmed. 
     Further, according to this invention, the hemming head is replaceable attached to the end of a robot arm of a conventional robotic system. The hemming head is configured to be rapidly removed from the robot arm. The hemming head includes a spindle upon which two or more hemming rollers of different diameter may be attached, so as to enable hemming in complicated and hard-to-reach areas. The position of each hemming roller is adapted to be reversed relative to the spindle so that the outer circumference on each side of the roller is capable of use. 
     According to this invention, there is provided a roller-type hemming apparatus, comprising: 
     a housing having rearward and forward ends and a pressurizable chamber, a slide member including a piston in said chamber and a plunger projecting forwardly of the forward end of said housing and terminating in an interlockable first connector, said piston dividing said chamber into rearward and forward chamber portions, each of said chamber portions being connectible to a source of pressure for selectively pressurizing each said chamber portion so as to move said piston relative to said chamber; 
     a nose having rearward and forward ends and a central guide passage extending between said ends of said nose, a bearing shaft mounted for sliding movement in said guide passage, said bearing shaft including rearward and forward ends that form an interlockable second connector adapted to connect said first connector with a head portion; 
     a spindle cartridge, said cartridge being removably mountable to said head portion and including a rotatably mounted spindle shaft having opposite ends, each of said spindle shaft ends adapted to receive and mount a hem roller thereto for rigid body rotation with said spindle shaft; 
     first means for releasably mounting said rearward end of said housing to a robot; and 
     second means for releasably mounting said rearward end of said nose to said forward end of said housing. 
     According to another embodiment of this invention, there is provided a roller-type hemming apparatus, comprising: 
     a support member having a slide bore and an interior chamber; 
     a closure plate having a guide bore therethrough, said closure plate being mounted in sealing relation to said support member, allowing said interior chamber to be pressurized, and said guide bore being in fluid communication with said chamber; 
     a slide member including a piston and an axially elongated plunger extending therefrom and terminating in a connectible end, said piston mounted in said pressurizable chamber for axial slidable movement relative to said bore and said plunger extending through said guide bore for axial slidable movement relative thereto, said piston separating said interior chamber into forward and rearward chamber portions with each said chamber portion being adapted to be placed in fluid communication with a pressure source for selectively adjusting the pressure in each of said chamber portions and the force applied against opposite sides of said piston wherein to force said piston towards and away from one side of said closure plate and the connectible end of the plunger away and towards said other side of said closure plate, 
     means for sealing the interface between said plunger and said guide bore; 
     a roller hemming assembly, said roller assembly including a hem roller which is adapted to engage a workpiece; and 
     means for connecting said roller hemming assembly to said plunger; 
     wherein adjusting the pressure in said respective chamber portions causes said plunger to force said hem roller into engagement with said workpiece. 
     According to this embodiment, the plunger is a two-part assembly comprised of a piston shaft and a quick-connect shaft, the assembly is coaxially disposed and extends outwardly from the forward side of the piston. The piston shaft and quick-connect shaft are threadably connected to each other at their respective ends. The piston shaft has a rearward end connected to the piston and the connectible end is formed by the forward end portion of the quick connect shaft. 
     In some applications, the plunger may be a single-piece assembly. 
     The roller hemming assembly includes a spindle cartridge having a spindle shaft with opposite ends. The spindle shaft is rotatably mounted to the spindle cartridge. At least one hem roller is rotatably secured to the spindle shaft. 
     Preferably, a hem roller is secured to each end of the shaft and one hem roller has a diameter greater than the other. The hem rollers are adapted to engage and hem the workpiece at various angles depending on the orientation of the spindle shaft. 
     According to this embodiment, the means for connecting the roller hemming assembly to the plunger comprises a quick connect/disconnect to allow interchangeability or repair when needed. In particular, the means for connecting comprises an axial bearing shaft having forward and rearward end portions, the forward end portion including means for removably mounting the roller hemming assembly. Further, the rearward end portion of the bearing shaft and the connectible forward end portion of the connectible shaft have complementary male and female portions which are adapted to interlock with one another wherein to connect the respective shafts end portions together. 
     Further, the hemming apparatus includes a shaped nose having a rearward end that is connected to the other side of the closure plate, a forward end, and a central passage. The central passage extends between the rearward and forward ends to enclose the interconnected shafts. The central passage has a square cross section, which is complementary to the bearing shaft. 
     The forward end of the bearing shaft is positioned outwardly of the nose and the spindle cartridge is positioned forwardly of the nose. 
     In one application, the bearing shaft has a square cross section and the rearward end portion thereof which is hollowed out to provide a generally cylindrical T-shaped cavity centered along the axis of the bearing shaft. The rearward end face of the nose is formed to include a U-shaped cavity that extends transversely of the central passage, and the forward end portion of the quick-connect shaft (or plunger if one-piece) is T-shaped. 
     In practice, the rearward end face of the nose is positioned in an off-centered relation with the quick-connect shaft. The nose is lowered onto the closure plate, and the T-shaped end portion of the quick-connect shaft is centered over and positioned into the U-shaped cavity of the nose. The nose is then moved laterally so that the T-shaped end portion is moved into the hollowed out T-shaped cavity of the bearing shaft. The nose is fixedly attached to the closure plate and the shafts are thus interconnected for axially guided movement. 
     In a particular application, the hemming apparatus is assembled to be in operable connection with a work-arm of a multi-axis robot, and in particular, to a hand at the forward end of the robot&#39;s work arm. 
     According to another aspect of this invention, the hem rollers are adapted to be connected to the spindle in a manner that the outer circumference engages the workpiece and each roller may be rotated 180° in a manner that the outer circumference becomes the inner circumference. 
     Further and according to another embodiment of this invention there is provided a hemming apparatus for use with a robot in performing a hemming operation on a pair of metal panels, the hemming apparatus comprising: 
     a support housing having a rearward base for mounting said housing to a machine, a forward closure plate having a central guide bore, and a pressurizible interior chamber; 
     a slide member including a piston disposed in said chamber and a plunger extending from said piston and through said guide bore to a connectible end spaced from said closure plate; 
     a nose removably secured to said closure plate; 
     a bearing shaft having forward and rearward end portions; 
     means for connecting said rearward end of said bearing shaft to said connectible end of said plunger; 
     a spindle cartridge having a spindle shaft, said spindle shaft having opposite ends mounted for rotation relative to said spindle cartridge, and a hem roller attached to each end of said spindle shaft for rotation therewith, each hem roller having a particular task in performing the hemming operation; 
     means for connecting said spindle cartridge to said forward end portion of said bearing shaft; and 
     said piston dividing said chamber into rearward and forward portions, said rearward and forward portions being connectible to a source of fluid pressure, whereby adjusting the pressure forces the piston to move either forwardly or rearwardly, causing said bearing shaft to drive said hem roller into engagement with a work piece. 
     In practice of this embodiment of the invention, the hemming apparatus is in operable relation with a fluid control apparatus which maintains control of the chamber pressure. The fluid control apparatus is preferably in synchronized operable control by a control system which directs the robotic arm to complete the hemming operation. 
     Preferably the fluid is air, although in some applications the fluid may by oil or other suitable liquid medium. 
     An array of threaded boltholes are provided in the closure plate. A corresponding array of boltholes is provided in the nose thus enabling the nose, and, in turn the hem rollers, to be indexed or angularly positioned relative to one another and to the center axis of the hemming head. This provides flexibility in rapidly changing the orientation of the spindle cartridge and hem rollers relative to the workpiece. 
     In yet another embodiment according to this invention there is provided a method of hemming a pair of metal panels using a robot, the steps including: 
     providing a housing, a nose, and a spindle cartridge, said housing having a pressurizable chamber and a slide member, said slide member including a piston in said chamber and a plunger projecting forwardly of a forward end of said housing and terminating in an interlockable first connector, said piston dividing said chamber into rearward and forward chamber portions, each said chamber portion being connectible to a source of pressure for selectively pressurizing said chamber portions to move said piston relative to said chamber, and said plunger relative to said forward end of said housing, said nose including a central guide passage extending therebetween and a bearing shaft mounted for sliding movement in said guide passage, said bearing shaft including a rearward end that forms an interlockable second connector adapted to connect with said first connector that forms a head portion, and the spindle cartridge including a rotatably mounted spindle shaft having opposite ends each adapted to receive and mount a hem roller thereto for rigid body rotation with said spindle shaft; 
     mounting said rearward end of said housing to said robot; 
     interconnecting said interlockable first and second portions; 
     mounting said rearward end of said nose to the forward end of said housing; 
     mounting said spindle cartridge to said head and said hem roller to said spindle shaft; whereby said chamber portions are in condition for being pressurized and said hem roller placed in operable hemming engagement with said metal panels. 
     For a more complete understanding of the present invention, reference is made to the following detailed description and accompanying drawings. In the drawings, like reference characters refer to like parts throughout the several views, in which: 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an environmental view of a roller-type hemming machine having a robot hand with a roller-type hemming head mounted thereto in accordance with the present invention; 
         FIG. 2  is an exploded assembly view of the roller-type hemming head shown in  FIG. 1  as seen looking rearwardly from the forward end; 
         FIG. 3  is a side elevation section view of an assembly of a cup-shaped support housing and closure plate that form a chamber, a piston disposed in the chamber, and a two-part plunger that extends from the piston through the closure plate and comprised of a piston shaft and quick-connect shaft; 
         FIG. 4  is an enlarged perspective view of a bearing shaft and a T-shaped recess therein for connection to the forward end of the quick connect shaft of  FIG. 3 ; 
         FIG. 5  is an enlarged perspective view of the rearward end of a nose of the hemming apparatus showing detail of a central passage for guidingly receiving the bearing shaft of  FIG. 4  and a U-shaped recess for receiving the forward end of the quick connect shaft of  FIG. 3 ; 
         FIG. 6  is an elevation view of the hemming head according to the present invention; and 
         FIG. 7  is an elevation view in section of the hemming head taken along line  7 - 7  of  FIG. 6 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the drawings, and in particular to  FIG. 1 , there is shown an environmental view of a hemming operation wherein a roller type hemming apparatus  10 , in accordance with the present invention, is operably connected to a work arm, such as a multi-axis controllable robot hand  12 . The robot hand  12  forms the movable portion of a robot machine. The hemming apparatus  10  is constrained for movement along a predetermined traveling path relative to a workpiece W. 
     The work piece W is, for example, an automotive door panel comprised of an outer panel W o  and an inner panel W i . The outer panel W o  has a peripheral portion preliminarily bent upwardly substantially at right angles, and the inner panel W i  has a peripheral stepped portion extending outwardly. The outer panel W o  and the inner panel W i  are placed on a lower die  14  with the stepped portion of the inner panel W i  arranged along the inside of the bent peripheral portion of the outer panel W o . 
     The lower die  14  and the robot machine are both positioned on a common base  18 . The lower die  14  has an upper surface constituting a forming surface  16 . The hemming apparatus  10  is positioned at a predetermined distance away from the lower die  14 . The workpiece W is placed on the forming surface  16  of the lower die  14  and is secured thereto by fixtures  20 . 
     The above arrangement for hemming a pair of panels is conventional and described herein to provide background for the hemming apparatus  10  according to the present invention. Further, the robot machine, including the robot hand  12 , is also well known in the art. 
     Referring to  FIG. 2 , the hemming apparatus  10 , according to this invention, is shown in exploded assembly. The hemming apparatus  10  includes: a support housing  22  that is mountable to the robot hand  12 ; a slide member  24  that is mounted in the support housing  22 ; a closure plate  26  that connects to the support housing  22  and captivates the slide member  24 ; a shaped nose  28  that is connectable to the closure plate  26 ; a bearing shaft  30  that is slidably disposed in the nose  28  connectible to the slide member  24  and a spindle cartridge  32  mounted to the bearing shaft  30 , the cartridge  32  including a spindle shaft  34  journaled for rotation. 
     As shown in  FIG. 1  and according to this invention, two hem rollers  36  and  38  are mounted to the spindle shaft  34  for rigid body rotation therewith. The hem rollers  36  and  38  are preferably of a different diameter and each of the hem rollers  36  and  38  are used for performing a different hemming operation from each other on a workpiece W. 
     As shown in  FIG. 2 , the support housing  22  is cup-shaped and includes a base member  40  and a cylindrical wall  42  that extends coaxially forwardly from the base member  40  to terminate in a forward end face  42   a  and form a cylindrical slide bore  44  and an interior chamber  46 . The base member  40  includes an array of equiangularly-spaced through holes  48  for receiving bolts to mount the support housing  22  to the robot hand  12 . In addition, the forward end face  42   a  includes an array of six equiangularly-spaced threaded boltholes  50 . 
     The closure plate  26  is generally circular and disc-shaped and has a cylindrical guide bore  52  in the center thereof. The closure plate  26  also includes an array of countersunk through boltholes  56  and an array of threaded countersunk boltholes  54  disposed about an outer annular portion of the closure plate  26 . As shown, each array of holes  54  and  56  are comprised of six equiangularly-spaced holes. The twelve boltholes disposed about the outer annular portion of the closure plate  26  are equiangularly-spaced with respect to each other around the circumference, and the holes of the respective arrays  54  and  56  alternate with one another. 
     The closure plate  26  is mounted in fluid sealing relation to the forward end face  42   a  of the support housing  22  to form a closed pressurizable chamber “C” (as shown in  FIG. 3 ). Referring back to  FIG. 2 , the array of through boltholes  56  in the closure plate  24  is aligned with the array of threaded boltholes  50  in the forward end face  42   a  of the support housing  22 . Matching bolts are provided to secure the closure plate  26  to the forward end face  42   a  and atop the support housing  22 . 
     The slide member  24  is mounted in the pressurizable chamber “C” for axial slidable movement relative to the slide bore  44 . The slide member  24  includes a piston  58  and an elongated generally cylindrical piston shaft  60 . The piston  58  is stepped and includes generally cylindrical rearward and forward piston portions,  58 A and  58 B, respectively, disposed on a central axis “A” corresponding to the central axis of the slide bore  44 . The rearward piston portion  58 A has an outer circumferential wall  62  that is generally complementary to the slide bore  44 . The slide member  24  has oppositely facing rearward and forward end faces,  64  and  66 , respectively. The forward piston portion  58 B extends generally coaxially from the forward end face  66  of the rearward piston portion  58 A and has a forward end face  68  that nests within a complementary recess  70  formed in the rearward side of the closure plate  26 . In this regard the recess  70  helps to form a fluid cushion between the piston  58  and the closure plate  26  as well as a stop to limit the forward movement of the piston  58 . 
     The piston  58  is mounted in the slide bore  44  for axial slidable movement, and separates the pressurizable interior chamber “C” into rearward and forward chamber portions,  72  and  74 , respectively (see  FIG. 3 ). Each chamber portion,  72  and  74 , is adapted to be placed in fluid communication with a pressure source (not shown) to selectively increase the pressure in one of the chamber portions while decreasing the pressure in the other chamber portion. The differential in pressure applies a force against the opposite end faces,  64  and  66 , of the piston  58 , forcing the piston  58  either towards or away from the closure plate  26 . 
     In this regard, and as shown in  FIGS. 2 and 6 , first and second pressure lines,  76  and  78 , respectively, are provided in the support housing  22  to supply pressure to one and the other of the respective chamber portions  72  and  74 . The first pressure line  76  (see  FIG. 3 ) extends radially and axially through the base member  40  and into the rearward chamber portion  72  formed between the base member and the rearward end face  64  of the rearward piston portion  58 A. 
     The second pressure line  78  (see  FIG. 2 ) extends radially through the base member  40  and axially and radially through the wall  42  of the support housing  22  into the forward chamber portion  74  formed between the forward end face  68  of the forward piston portion  58 B and the rearward (interiorly facing) recess side of the closure plate  26 . 
     The piston shaft  60  is axially elongated and extends from the center of the forward end face  68  of the forward piston portion  58 B and through the guide bore  52  of the closure plate  26  for axial slidable movement relative thereto. The piston shaft  60  is coaxially aligned with the piston axis “A” and has rearward and forward end portions,  80  and  82 , respectively. The rearward end portion  80  of the piston shaft  60  is externally threaded to enable threadable connection to a threaded socket  84  provided in the forward end face  68  of the forward piston portion  58 B. The forward end portion  82  is provided with a threaded socket  86  to enable connection with a quick-connect shaft  88 . 
     The quick-connect shaft  88  is generally stepped, cylindrical, and includes a threaded rearward end portion  90  that is connectible to the threaded socket  86 . The quick-connect shaft  88  has a medial cylinder member  92  that abuts the socket  86  to accurately position the forward end of the quick-connect shaft relative to the piston shaft  60 . The quick-connect shaft also has a forward cylinder member  94  and a cylindrical neck portion  96  of reduced diameter that extends between the cylinder members  92  and  94 . The neck portion  96  and forward cylinder member  94  form a male section, which is T-shaped in cross-section and is used in a manner described herein below to form a quick connection with the bearing shaft  30 . 
     The quick-connect shaft  88  allows for a quick connect/disconnect with the bearing shaft  30  to allow interchangeability or repair when needed. 
     Although the slide member  22  is described as having piston shaft  60  and a quick-connect shaft  88 , separately provided and assembled, in some applications the two shafts  60  and  88  could be provided as a single-piece construction to form a common plunger member. 
       FIG. 3  illustrates the assembly of the support housing  22 , the piston  58 , the closure plate  26 , and the plunger (as formed by the piston shaft  60  and the quick connect shaft  88 ). 
     In the assembly, a fluid seal  98 , such as a gasket, O-ring, or the like, is provided to form an air tight fluid seal between the piston shaft  60  and the guide bore  52  so that the rearward chamber portion  74  may be pressurized. 
     The outer geometry of the shaped nose  28  is symmetrical about the central axis “A” and includes a rearward end  100  that is connectible to the closure plate  26 , a forward end  102 , and a central passage  104  that extends between the opposite ends  100  and  102 . The central passage  104  has a generally square shaped cross-section and is adapted to guide and support the bearing shaft  30  and, at least in part, receive and enclose the interconnection between the plunger assembly of the piston shaft  60  and the quick connect shaft  88 . As shown in  FIG. 5 , the rearward end  100  of the shaped nose  28  is formed to include a U-shaped cavity  106  that extends transversely from the central passage  104 . 
     An array of countersunk boltholes  108  extend through the body of the nose  28 . The boltholes  108  are equiangularly positioned and aligned with the array of threaded boltholes  54  in the closure plate  26  to receive threaded fasteners for connecting the nose  28  to the closure plate  26 . Desirably, the set of threaded boltholes  54  in the closure plate  26  enable the nose  28  as well as the bearing shaft  30 , to be positioned angularly without significant changes to the robotic system. Thus the position of the roller spindle cartridge  32  may be angularly indexed or rotated relative to the robot hand of the hemming apparatus. 
     The bearing shaft  30  has a generally square shaped cross-section complementary to the cross-section of the central passage  104  to form a close guiding fitment therewith, and has a central geometric axis that aligns with the axis “A” when disposed in the passage  104 . To increase sliding guided movement relative to the central passage  104 , the outer surface of the bearing shaft  30  may be coated with a lubricant. 
     As shown in  FIG. 4 , the bearing shaft  30  has a rearward end portion  110  which is hollowed out to provide a generally cylindrical T-shaped cavity  112 , which is at least in part, centered along the axis “A” of the bearing shaft  30 . The cavity  112  opens outwardly on an open face  114  of the shaft  30  and includes an enlarged interior chamber  116  and a reduced diameter neck portion  118  that forms an axial passage between the rearward end  110  of the shaft  30  and the chamber  116 . 
     The bearing shaft  30  is dimensioned such that when the bearing shaft  30  is seated within the central passage  104  of the nose  28 , the forward end  119  thereof extends outwardly past the forward end  102  of the nose  28  and terminates in an enlarged head  120 . The head  120  is formed with a cylindrical socket  122  for receiving and mounting the spindle cartridge  32  therein. 
     The spindle cartridge  32  is in the form of a cylindrical casing that has a cylindrical mounting flange  124  provided with an array of boltholes that align with threaded mounting holes provided in the head  120 . The casing is inserted into the socket  122  of the bearing shaft  30  and removably mounted thereto by threaded fasteners. 
     The spindle shaft  34  of the spindle cartridge  32  has opposite ends and is rotatably mounted within the spindle cartridge  32 . The spindle axis of rotation “B” is generally at a right angle to the axis “A,” such as shown in  FIG. 6 . 
     As shown best in  FIGS. 1 and 6 , hem rollers of varying sizes,  36  and  38 , respectively, are removably secured to the end of the spindle shaft  34  for rigid body rotation therewith. Each hem roller,  36  and  38 , is adapted to hem the workpiece W, depending on the orientation of the spindle shaft  34 , as well as which roller,  36  or  38 , is engaged with the workpiece W. The rollers,  36  and  38 , are in the form of cylindrical discs and each is connected to the spindle shaft  34  in a manner that the outer circumference of the roller will engage the workpiece panels being hemmed. Further, each roller,  36  and  38 , may be rotated 180° about the axis “A” so that the outer circumference becomes the inner circumference and vice versa. 
     In the embodiment illustrated, the roller  36  has a diameter that is greater than the diameter of the roller  38 , and each roller is adapted to perform a different specified task of the hemming operation. This arrangement enables the robot hand  12 , to which the hemming apparatus  10  is attached, to rotate the hemming apparatus  1800  about the axis “A” and place either the smaller or larger diameter roller in position for use, thereby enabling hemming operations in complicated or hard to reach areas to be accomplished. 
     In a particular application, the hemming apparatus, so assembled, is adapted for operable connection to a work-arm of a multi-axis robot, and in particular, to a hand at the forward end of the work arm. 
     In one method of use, a first subassembly is formed wherein the slide member  24 , including the piston shaft  60 , is positioned in the slide bore  44  of the support housing  22 , the closure plate  26  is positioned about the piston shaft  60  and secured to the housing  22 , and the quick-connect shaft  88  is connected to the piston shaft  60 . The subassembly is fitted to the robot hand. 
     A second subassembly is formed including the spindle cartridge  32  being fitted into the socket  120  of the bearing shaft  30  and the bearing shaft  30  being fitted for sliding movement relative to the central passage  104  of the nose  28 . 
     The rearward end  100  of the nose  28  is positioned in off-centered relation with the forward end face  42   a  of the support housing  22  and lowered towards and onto the closure plate  26 . The forward cylinder member  94  of the quick-connect shaft  88  is aligned and positioned with, and into, the U-shaped cavity  106  formed in the rearward end face  100  of the nose  28 . The nose is then moved laterally to position the axis of the bearing shaft  30  into alignment with the axis “A.” The forward cylinder member  94  of the quick-connect shaft  88  enters into the T-shaped cavity  112  formed in the open face  114  of the bearing shaft  30 , interlocking the bearing shaft  30  and the quick-connect shaft  88 , whereupon the bearing shaft is axially advanced to captivate the interconnection within the central passage  104  (see  FIGS. 6 and 7 ). 
     The nose  28  is then secured to the closure plate  26  by threaded fasteners which extend through the bolt holes  108  of the nose  28  and into the threaded boltholes  54 . The plunger (the piston and quick-connect shafts  60  and  88 ) and the bearing shaft  30  are thus interconnected for axially guided movement relative to the central passage  104  in the nose  28 . The rollers  36  and  38  are then secured to the spindle shaft  34 . 
     In the practice of this invention, the hemming apparatus  10  is placed in operable relation with fluid control apparatus, which maintains control of the chamber pressure. Further, this fluid control apparatus is preferably in synchronized operable control by the control system that directs the robotic arm to complete a hemming operation. 
     Preferably, the pressurizable fluid is air, although in some applications the fluid may by oil or other suitable liquid medium. 
     The fluid pressure supplied to the hemming apparatus  10  provides a cushion of fluid to maintain the hem roller in contact with the metal panels being hemmed and inhibit the piston  58  from unwanted axial movements either toward or away from the workpiece. 
     Desirably, in operation, should one or both of the hem rollers  36  and  38  need replacement, either for repair or to install a different roller having a different diameter for use in another hemming application, the rollers are easily removable and changed for the desired needs. 
     Further, the hemming apparatus  10  guides the bearing shaft  30  and spindle cartridge  32 , thus obviating the need of the robot to change position to accomplish positioning of the roller and cartridge relative to the workpiece. 
     Although various embodiments of the invention have been disclosed for illustrative purposes, it is understood that one skilled in the art can make variations and modifications without departing from the spirit of the invention.