referring now to the drawings , and in particular to fig1 , 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 fig2 , 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 fig1 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 fig2 , 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 fig3 ). referring back to fig2 , 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 fig3 ). 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 fig2 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 fig3 ) 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 fig2 ) 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 . fig3 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 fig5 , 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 fig4 , 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 fig6 . as shown best in fig1 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 fig6 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 .