Patent Publication Number: US-2009235712-A1

Title: Integrated push pull roller head

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims the priority of U.S. Provisional Application No. 61/070,578 filed Mar. 24, 2008. 
    
    
     TECHNICAL FIELD 
     This invention relates to roller hemming, and more particularly to an integrated push pull roller head for robotic roller hemming of a set of panels. 
     BACKGROUND OF THE INVENTION 
     It is known in the art relating to perform roller hemming utilizing a push-type hem roller to generate hemming pressure by pushing the hem roller against a set of nested panels. For example, a push-type hem roller is used to hem an upturned edge of one or more preformed metal panels to form a hemmed joint or closed panel assembly such as automotive vehicle closure panel assemblies including doors, hoods, decklids, liftgates, and tailgates. However, conventional roller hemming work cells typically require multiple hemming tooling stations in order to complete all of the steps required to hem a set of metal panels. 
     Also, replacement of hem rollers on conventional roller hemming apparatus is labor intensive and time consuming. 
     SUMMARY OF THE INVENTION 
     The present invention provides a push pull roller head that generates hemming pressure both by pushing and pulling, allowing for the utilization of a plurality of roller heads in a single station to act on a panel workpiece using push or pull force roller head orientations. For example, if the panel to be hemmed is in a stand up condition, roller hemming robots may be placed behind the flange area to be hemmed and use the “pull” function of the present roller head to hem the panel, and in the same station, additional robots can perform hemming from the front side of the panel using a “push” force. The present invention provides for the reduction of hemming tooling stations, reduction of plant floor use, and increase in system throughput within one station. 
     The present roller head may also have a programmable regulator integrated with the head that allows roller head hemming pressure changes to occur during cycle or as needed when switching between specific model requirements. 
     More particularly, a roller hemming apparatus in accordance with the present invention includes a linear actuator mountable on an end of a multi-axis robotic arm. The linear actuator includes a connector. A roller hemming head is mounted on the linear actuator by the connector. The roller hemming head includes at least one hem roller. The roller hemming head performs both push force and pull force roller hemming operations. 
     In one embodiment, the connector may be a quick release connector. The linear actuator may include a housing assembly and a piston rod assembly slidable within the housing assembly. The piston rod assembly may include a piston rod extending from the housing assembly and including the connector on a distal end thereof. The housing assembly may include an internal spline and the piston rod may include an external spline cooperable with the internal spline to restrict axial rotation of the piston rod and mounted roller hemming head. The roller hemming head may include a plurality of different hem rollers. One of the hem rollers may be a pull-type hem roller and another of the hem rollers may be a push-type hem roller. Also, one of the hem rollers may be configured to fit into smaller clearances than another of the hem rollers. 
     A method of roller hemming in accordance with the present invention includes the steps of mounting a linear actuator on an end of a multi-axis robotic arm, the linear actuator including a connector; mounting a roller hemming head on the linear actuator by the connector, the roller hemming head including at least one hem roller; and performing both push force and pull force roller hemming operations with the roller hemming head. 
     In one embodiment, the connector is a quick release connector, and the method includes the step of exchanging the roller hemming head with another roller hemming head. The method may include the step of restricting axial rotation of the roller hemming head by providing a spline in the linear actuator. The method may include the step of operating the linear actuator to adjust a magnitude of the hemming force applied by the hem roller. The method may include the step of providing a plurality of different hem rollers on the roller hemming head. The method may include the step of mounting a pull-type hem roller on the roller hemming head and mounting a push-type hem roller on the roller hemming head. Also, the method may include the step of mounting a hem roller on the roller hemming head that is configured to fit into smaller clearances than another hem roller mounted on the roller hemming head. 
     These and other features and advantages of the invention will be more fully understood from the following detailed description of the invention taken together with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the drawings: 
         FIG. 1  is an environmental view of a push pull roller hemming head in accordance with the present invention mounted on a multi-axis robotic arm; 
         FIG. 2  is a side, sectional view of the push pull roller hemming head; 
         FIG. 3  is a cross-sectional view of the push pull roller hemming head taken along the line  3 - 3  in  FIG. 2 ; 
         FIG. 4  is an enlarged, partial view of the push pull roller hemming head as viewed from the direction of arrow  4  in  FIG. 2 ; 
         FIG. 5  is an environmental view of the push pull roller hemming head performing a pull force hemming operation; and 
         FIG. 6  is an environmental view of the push pull roller hemming head performing a push force hemming operation. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the drawings in detail, numeral  10  generally indicates a roller hemming apparatus in accordance with the present invention. The roller hemming apparatus can perform both push force type and pull force type hemming operations using a single roller hemming head. The roller hemming apparatus also provides for quick and easy exchange of the roller hemming head. 
     With reference to  FIGS. 1 through 4 , the roller hemming apparatus  10  includes a linear actuator  12  that is mountable on an end  14  of a multi-axis robotic arm  16  by a tool exchanger or similar. The linear actuator  12  includes a housing assembly  18  and a piston rod assembly  20 . The piston rod assembly  20  is movable between a retracted position (as illustrated in  FIG. 2 ) and an extended position (not shown). As discussed in more detail below, the piston rod assembly  20  carries a hemming roller end effector such as roller hemming head  22  or similar. 
     The housing assembly  18  includes a body  24 , an internal spline housing  26 , and a rear end cap  28 . The body  24  of the housing assembly  18  includes a centrally located cylindrical throughbore  30  that extends through the body. 
     The piston rod assembly  20  fits within and slides with respect to the housing assembly  18 . The rear end portion of the piston rod assembly  20  includes an external spline  32  cooperable with the internal spline of the internal spline housing  26 . The external spline  32  fits inside the internal spline housing  26  and slides relative to the internal spline. The cooperation of the internal spline  26  with the external spline  32  prevents axial rotation of the piston rod assembly  20 . This is important for roller hemming, in which axial rotation of the roller head is undesirable. 
     The piston rod assembly  20  includes a piston rod  34  that slides within the throughbore  30  of the body  24 . The piston rod  34  has a distal end portion  36  that includes a connector  38  for securing the roller hemming head  22  thereto as described in more detail below. The piston rod assembly  20  also includes a generally annular piston  40  having a central opening  42  and a collar  44 . The piston rod  34  fits through the central opening  42  and the collar  44 , and is mounted to the piston  40 . The piston  40  carries a pair of circumferential seals  46 . The seals  46  ride against the internal chamber  50  surface of the body  24  so that fluid pressure applied to one side of the piston  40  causes the piston rod assembly  20  to move in one direction or the other without leakage between the piston  40  and the internal surface of the body  24 . The end of the piston rod  34  opposite the distal end portion  36  includes the external spline  32 . 
     The rear end cap  28  forms a sealed chamber  48  surrounding the external spline  32 . When pneumatic pressure is introduced into the chamber  48 , the piston  40  is forced outward (to the right in  FIG. 2 ) to move to its extended position. Opposite the chamber  48 , the throughbore  30  defines a chamber  50  which surrounds the piston rod  34 . When pneumatic pressure is introduced into the chamber  50 , the piston  40  is forced to its retracted position (to the left as shown in  FIG. 2 ) by the action of the pneumatic pressure on the piston. Pneumatic supply lines  52  may be connected to passages  54  and  56  to supply air under pressure to chambers  48  and  50 , respectively. 
     The roller hemming head  22  is mounted to the linear actuator  12 . For example, as shown in  FIG. 4 , the roller hemming head  22  is mounted via the connector  38  located on the distal end  36  of the piston rod  34 . The connector  38  may be a simple attachment, quick release connector that allows the roller hemming head  22  to be quickly mounted on and dismounted from the piston rod  34 . This facilitates quick change of the roller hemming head  22 , either to replace the roller hemming head when the roller(s) become worn or to exchange the roller hemming head for a different roller head (for example, a roller hemming head including a final hem roller may be exchanged for a roller hemming head including a pre-hem roller). In the embodiment shown in  FIGS. 2 and 4 , the connector  38  includes a through hole in the distal end  36  of the piston rod  34 , and the roller hemming head  22  is secured to the piston rod by a keeper  58  and fastener  60  extending through the roller hemming head and the through hole of the piston rod  34 . 
     The roller hemming head  22  may include a plurality of different hem rollers  62 ,  64  for performing different roller hemming operations. For example, one of the rollers  62  may be utilized for push-type roller hemming operations while the other roller  64  may be utilized for pull-type roller hemming operations. Also, one of the rollers  64  may be configured to fit into locations with small clearances, while the other roller  62  may be configured to hem locations having larger clearances. Further, the rollers may be configured to perform different types of hems, such as flat hems and rope hems. The hem rollers  62 ,  64  are mounted on the roller hemming head  22  via bearings to allow for smooth rotation of the rollers. Although, the roller hemming head  22  is shown having two hem rollers, the roller hemming head may have one roller or a plurality of rollers. 
     Turning to  FIG. 5 , the roller hemming head  22  is shown performing a pull force type roller hemming operation. Outer panel  66  and inner panels  68 ,  70  are supported on an anvil  72 . The hem roller  64  engages a bent edge  74  of the outer panel  66  on a side opposite the anvil  72 , and the hem roller  64  is pulled against the outer panel  66  by the roller hemming head  22 . The linear actuator  12  applies a selectable predetermined force exerted on the outer panel bent edge through the hem roller  64  when the chamber  50  is filled with fluid pressure and chamber  48  is exhausted of fluid pressure. This is carried out by toggling a valve that diverts the fluid pressure from passage  54  to passage  56 . When fluid pressure is applied to chamber  50  and chamber  48  is exhausted, the piston rod assembly  20  is moved and held in a retracted position as shown in  FIG. 2 . The robotic arm  16  then positions the hem roller  64  to be in contact with the bent edge  74 . After positioning the hem roller  62 , the robotic arm then moves the linear actuator  12  in a direction along the axis of piston rod assembly  20  causing the piston rod assembly to become extended by a predetermined amount. When the desired amount of hemming force is obtained, the robotic arm  16  moves the roller hemming head along the edge portion of the outer and inner panels  66 ,  68 , and the hem roller  64  pulls the bent edge  74  of the outer panel  66  against the inner panel  68  to hem the outer panel  66 . The hemming force may be regulated as the hem roller  64  moves along the bent edge  74  of the outer panel  66  to provide a generally constant hemming force through the hemming operation. It should also be appreciated that due to the spline construction of the linear actuator, axial rotation of the piston rod  34  is restricted, and therefore the orientation of the hem roller  64  relative to the edges of the outer and inner panels  66 ,  68  is rigidly maintained. 
     Turning to  FIG. 6 , the roller hemming head  22  is shown performing a push force type roller hemming operation on the outer and inner panels  66 ,  70 . The hem roller  62  engages a bent edge  76  of the outer panel  66  on a side opposite the anvil  72 , and the hem roller  62  is pushed against the outer panel  66  by the roller hemming head  22 . The linear actuator  12  applies a predetermined force exerted on the outer panel bent edge  76  through the hem roller  62  when the chamber  48  is filled with fluid pressure and chamber  50  is exhausted, thereby moving and holding the piston rod assembly  20  in the extended position. The robotic arm  16  then positions the hem roller  62  to be in contact with the bent edge  76  of the outer panel  66 . After positioning the hem roller  62 , the robotic arm  16  moves the linear actuator in a direction along the axis of the piston rod assembly  20  to become retracted by a predetermined amount. When the desired amount of hemming force is obtained, the robotic arm  16  moves the roller hemming head  22  along the edges of the outer and inner panels  66 ,  70 , and the hem roller  62  pushes the bent edge  76  of the outer panel  66  against the inner panel  70  to hem the inner and outer panels. The hemming force may be regulated as the hem roller  62  moves along the bent edge  76  of the outer panel  66  to provide a generally constant hemming force through the hemming operation. It should also be appreciated that due to the spline construction of the linear actuator, axial rotation of the piston rod  34  is restricted, and therefore the orientation of the hem roller  62  relative to the edges of the outer and inner panels  66 ,  70  is rigidly maintained. 
     Although the invention has been described by reference to a specific embodiment, it should be understood that numerous changes may be made within the spirit and scope of the inventive concepts described. Accordingly, it is intended that the invention not be limited to the described embodiment, but that it have the full scope defined by the language of the following claims.