Patent Publication Number: US-2009235713-A1

Title: Magnetically actuated roller head

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims the priority of U.S. Provisional Application No. 61/070,551 filed Mar. 24, 2008. 
    
    
     TECHNICAL FIELD 
     This invention relates to robotic roller hemming, and more particularly a robotic roller head used for robotic roller hemming such as hemming of vehicle closure panels. 
     BACKGROUND OF THE INVENTION 
     It is known in the art relating to actuation of a roller hemming head that conventional actuators typically require one or more of the following: hydraulics, pneumatics, electric cylinders, gas spring charge, monitoring of air or gas pressure, and oil disposal. These requirements may elevate the cost, size, and complexity of a conventional roller hemming head. 
     SUMMARY OF THE INVENTION 
     The present invention provides a magnetically actuated roller hemming head that utilizes magnetic and/or electromagnetic force to actuate a roller hemming head and to provide a hemming force through a hem roller of the roller hemming head. The present invention may allow for variable force control on the roller head with instantaneous response time to roller head force changes. The present invention also may eliminate the need for some or all of the following: hydraulics, pneumatics, electric cylinders, gas spring charge, monitoring of air or gas pressure, and oil disposal. 
     More particularly, a magnetically actuated roller head 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 slide, a magnet operably connected to the slide and operable to urge the slide in a linear direction, and a connector disposed on a distal end of the slide. A roller hemming head is mounted on the linear actuator by the connector. The roller hemming head includes at least one hem roller. 
     Optionally, the magnet may be a rare earth magnet. Alternatively, the linear actuator may include a rare earth magnet disposed between two opposing magnets. The polarity of one of the opposing magnets may be disposed in the same direction as the polarity of the rare earth magnet, and the polarity of the other of the opposing magnets may be disposed in an opposite direction to the polarity of the rare earth magnet. Optionally, the two opposing magnets may be rare earth magnets. Alternatively, the linear actuator may include an electromagnet disposed on each of opposite sides of the magnet. The electromagnets control and assist a force transmitted by the magnet. 
     Also, the slide may include an anti-rotate feature. 
     In another embodiment, a magnetically actuated roller head includes a housing having an internal bore. The housing is mountable on an end of a multi-axis robotic arm. A pair of opposing actuator members are fixedly mounted within the inner bore. A shaft extends through the actuator members. A magnet is mounted on the shaft and is moveable within the inner bore. The magnet is disposed between the actuator members. A slide is connected to the shaft and extends outwardly from the housing. A connector is disposed on a distal end of the slide. A roller hemming head is mounted on the connector. The roller hemming head includes at least one hem roller. The actuator members control and assist a hemming force applied by the roller hemming head through the magnet. 
     Optionally, the magnet may be a rare earth magnet. Also, the actuator members may be rare earth magnets. The polarity of one of the actuator members may be disposed in the same direction as the polarity of the rare earth magnet, and the polarity of the other of the actuator members may be disposed in an opposite direction to the polarity of the rare earth magnet. Alternatively, the actuator members may be electromagnets. 
     The housing may include an anti-rotate linear guide, and the slide may include an anti-rotate feature cooperable with the linear guide. The anti-rotate feature may be one of a spline, a ball spline, and a square linear bearing. 
     A method of roller hemming in accordance with the present invention includes mounting a linear actuator on an end of a multi-axis robotic arm, the linear actuator including a slide, a magnet operably connected to the slide and operable to urge the slide in a linear direction, and a connector disposed on a distal end of the slide; and mounting a roller hemming head on the linear actuator by the connector, the roller hemming head including at least one hem roller. The linear actuator provides a hemming force for performing roller hemming operations with the hem roller. 
     Optionally, the magnet may be a rare earth magnet. The method may also include disposing the magnet between a pair of opposing actuator members. The actuator members may be rare earth magnets. Alternatively, the actuator members may be electromagnets. 
     The method may also include restricting axial rotation of the roller hemming head by providing a spline on the slide. Also, the method may include providing a plurality of different hem rollers 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 a sectional view of a magnetically actuated roller head in accordance with a first embodiment of the present invention; 
         FIG. 2  is a sectional view of a magnetically actuated roller head in accordance with a second embodiment of the present invention for push type roller hemming; 
         FIG. 3  is a sectional view of a magnetically actuated roller head similar to the embodiment of  FIG. 2  for pull type roller hemming; 
         FIG. 4  is a sectional view of a magnetically actuated roller head in accordance with a third embodiment of the present invention for push type roller hemming; and 
         FIG. 5  is a sectional view of a magnetically actuated roller head similar to the embodiment of  FIG. 4  for pull type roller hemming. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the drawings in detail, numeral  110  generally indicates a magnetically actuated roller head in accordance with the present invention. The magnetically actuated roller head utilizes magnetic and/or electromagnetic force to actuate a roller hemming head and to provide a hemming force through a hem roller of the roller hemming head. 
     With reference to  FIG. 1 , in a first embodiment the magnetically actuated roller head  110  includes a linear actuator  112  mountable on an end of a multi-axis robotic arm (not shown). A roller hemming head  114  is mounted on the linear actuator  112 . The linear actuator  112  provides a hemming force for performing roller hemming operations with the roller hemming head  114 . 
     The linear actuator  112  includes a housing  116  that has an inner bore  118  that generally extends through the housing. An end cap  120  is mounted on an end of the housing  116  and closes an end of the inner bore  118 . The end cap  120  may include a feature such as a mounting surface for mounting the linear actuator  112  on a robotic arm. 
     A pair of opposing actuator members  122  are fixedly mounted within the inner bore  118 . A shaft  124  extends through the actuator members  122 . A magnet  126  is mounted on the shaft  124  and is moveable within the inner bore  118 . The magnet  126  is disposed between the actuator members  122 . More specifically, in the first embodiment the actuator members  122  may be electromagnetic coils and the magnet  126  may be a polarized magnet having its north and south poles disposed in an axial direction relative to the shaft  124 . Further, a pair of moveable yokes  128  made of a soft magnetic material sandwich the polarized magnet  126 . The polarized magnet  126  and yokes  128  are fixedly mounted on the shaft  124  and are disposed between and within the electromagnetic coils  122 . The magnetic field of the polarized magnet  126  forms a magnetic circuit that passes through the polarized magnet  126 , the moveable yokes  128 , and the electromagnetic coils  122 . 
     An end  130  of the shaft  124  is supported by the end cap  120 . For example, the end  130  may include a bushing engaged with a bushing hole  132  in an inner surface of the end cap  120 . An opposite end  134  of the shaft  124  is connected to a slide  136 . The slide  136  is slidable within an anti-rotate linear guide  138 . The linear guide  138  is mounted on an end of the housing  116  opposite the end cap  120 , and the slide  136  extends outwardly from the housing through the linear guide. The slide  136  includes an anti-rotate feature  140  such as a spline, a ball spline, a square linear bearing or similar that is cooperable with an inner surface  142  of the linear guide  138 . The cooperation of the anti-rotate feature  140  and the guide inner surface  142  allows the slide to move in a linear direction along its axis in and out of the housing  116  while preventing the slide from rotating about its axis. 
     A distal end  144  of the slide  136  includes a connector  146  such as a quick release connector or similar. The roller hemming head  114  is connected to the slide  136  by the connector  146 . For example, the connector  146  may include a through hole  148  in the slide distal end  144 , and the roller hemming head  114  may be secured to the slide  136  by a fastener  150  extending through the roller hemming head  114  and the through hole in the slide  136 , and a keeper  152  engaged with the fastener. 
     The roller hemming head  114  includes at least one hem roller, and may include a plurality of different hem rollers  154 ,  156  for performing different roller hemming operations. For example, one of the rollers  154  may be utilized for push-type roller hemming operations while the other roller  156  may be utilized for pull-type roller hemming operations. Also, one of the rollers  154  may be configured to fit into locations with small clearances, while the other roller  156  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  154 ,  156  are mounted on the roller hemming head  114  via bearings to allow for smooth rotation of the rollers. Although, the roller hemming head  114  is shown having two hem rollers, the roller hemming head may have one roller or more than two rollers. 
     When current is applied to the electromagnetic coils  122 , the coils are subjected to a force (in either a left or right direction as viewed in  FIG. 1 ) that is dependent upon the direction of current flow and the resultant electromagnetic field. The electromagnetic coils  122 , being fixed, do not move, and the electromagnetic field generated by the coils acts upon the moveable yokes  128  in an opposite direction, causing the moveable yokes  128  and attached shaft  124  to travel axially. The axial movement of the shaft  124  causes the slide  136  to move into or out of the housing  116 . Movement of the shaft  124  to the right causes the slide  136  to move outwardly relative to the housing  116 , while movement of the shaft  124  to the left causes the slide  136  to move inward. In turn, the movement of the slide  136  acts upon the connected roller hemming head  114 . Outward movement of the slide  136  provides a push force when the hem roller  154  is engaged with a panel to be hemmed. Likewise, inward movement of the slide  136  provides a pull force when hem roller  156  is engaged with a panel. Further, the amount of push or pull force exerted by the hem rollers  154 ,  156  can be adjusted by varying the amount of current applied to the electromagnetic coils  122 , which varies the amount of inward or outward force acting on the slide  136 . As the magnitude of the current is increased or decreased, the hemming force also increases or decreases. 
     With reference to  FIG. 2 , in a second embodiment of the present invention a magnetically actuated roller head  210  includes a linear actuator  212  and a roller hemming head  214  mounted on the linear actuator. Reference numbers similar to those of the first embodiment indicate similar features, and unless otherwise noted below, the second embodiment has features similar to the first embodiment. 
     The linear actuator  212  includes a pair of opposing actuator members  258  fixedly mounted within the inner bore  218  of the housing  216 . Each actuator member  258  may be an electromagnet including a cylindrical bobbin  260  mounted in the inner bore  218 . A magnetic material  262  is disposed within the bobbin  260 , and a coil  264  is wound on the bobbin  260 . The shaft  224  extends through openings  266  in the bobbins  260  and is freely moveable therethrough. A rare earth magnet  268  is disposed between the opposing actuator members  258  and is fixed to the shaft  224 . The rare earth magnet  268  is a strong, permanent magnet made from alloys of rare earth elements (lanthanides). Examples of rare earth magnets include but are not limited to neodymium magnets and samarium-cobalt magnets. The rare earth magnet  268  is polarized and has its north and south poles disposed in an axial direction relative to the shaft  224 . For example, in the embodiment of  FIG. 2 , the north pole of the rare earth magnet  268  points to the right towards the roller hemming head  214 , and the south pole points to the left towards the end cap  220  of the housing  216 . 
     Based upon the polarity of the rare earth magnet  268 , the magnetically actuated roller hemming head  210  is arranged for push type roller hemming operations in which the hem roller  254  pushes against a panel to be hemmed. Due to the strength of the magnetic field of the rare earth magnet  268 , the linear actuator  212  applies approximately 330 pounds of force in a linear direction at steady state with no external power/force (zero current) applied to the actuator members  258 . The actuator members  258  control and assist the actuation force of the rare earth magnet  268 . More specifically, the linear force transmitted by the linear actuator  212  is adjustable in an increasing or decreasing manner by varying a current applied to the coils  264 . When a current of greater than approximately 1 Amp is applied to the coils  264 , the force exerted increases relative to the input value as follows: 1 Amp=360±10 pounds of force, 2 Amps=390±10 pounds of force, and 4 Amps=440±10 pounds of force. When a current of less than −1 Amp is applied to the coils  264  (i.e., less than 1 Amp in an opposite flow direction), the force exerted decreases relative to the input value as follows: −2 Amps=280±10 pounds of force, and −4 Amps=230±10 pounds of force. 
     Alternatively, as shown in  FIG. 3 , the polarity of the rare earth magnet  268  can be reversed, i.e. the rare earth magnet may be disposed such that the south pole of the rare earth magnet points to the right towards the roller hemming head  214 , and the north pole points to the left towards the end cap  220  of the housing  216 . In this arrangement, the magnetically actuated roller hemming head  210  is arranged for pull type roller hemming operations in which the hem roller  256  is pulled toward a panel to be hemmed. At steady state, the amount of pull force is approximately 330 pounds, and the pull force can be varied from the steady state value by application of current to the coils  264 . 
     With reference to  FIG. 4 , in a third embodiment of the present invention a magnetically actuated roller head  310  includes a linear actuator  312  and a roller hemming head  314  mounted on the linear actuator. Reference numbers similar to those of the first embodiment indicate similar features, and unless otherwise noted below, the third embodiment has features similar to the first embodiment. 
     The linear actuator  312  includes a pair of opposing actuator members  370 ,  372  fixedly mounted within the inner bore  318  of the housing  316 . Each actuator member  370 ,  372  may be a polarized rare earth magnet disposed in a non-magnetic cylindrical shell  374  that is mounted in the inner bore  318 . The shaft  324  extends through openings  376  in the shell  374  and is freely moveable therethrough. A rare earth magnet  368  is disposed between the opposing actuator members  370 ,  372  and is fixed to the shaft  324 . A gap exist between the rare earth magnet  368  and the inner bore  318  of the housing  316 . The rare earth magnet  368  is polarized and has its north and south poles disposed in an axial direction relative to the shaft  324 . For example, in the embodiment of  FIG. 4 , the north pole of the rare earth magnet  368  points to the right towards the roller hemming head  314 , and the south pole points to the left towards the end cap  320  of the housing  316 . Also, the north pole of the actuator member  370  points to the left and the south pole points to the right, and the north pole of the actuator member  372  points to the right and the south pole points to the left. Therefore, the polarity of the actuator member  370 , rare earth magnet  368 , and actuator member  372  as viewed from left to right in  FIG. 4  is north-south, south-north, south-north. 
     Based upon the polarity of the actuator members  370 ,  372  and rare earth magnet  368 , the magnetically actuated roller hemming head  310  is arranged for push type roller hemming operations in which the hem roller  354  pushes against a panel to be hemmed. The interactions (attraction and repulsion) of the magnetic fields of the actuator members  370 ,  372  and rare earth magnet  368  result in approximately 330 pounds of outward force being applied to the slide  336  and in turn the hem roller  354 . The distance between the actuator members  370 ,  372  and the rare earth magnet  368  provides compliance for the hem roller  354  (i.e., allows the hem roller  354  to travel small distances to the left and right as viewed in  FIG. 4 ). Also, the opposing polarities of the rare earth magnet  368  and the actuator member  372  aid in maintaining a constant hemming force through a stroke of the hem roller  354 . 
     Alternatively, as shown in  FIG. 5 , the polarity of the rare earth magnet  368  can be reversed, i.e. the rare earth magnet may be disposed such that the south pole of the rare earth magnet points to the right towards the roller hemming head  314 , and the north pole points to the left towards the end cap  320  of the housing  316 . Therefore, the polarity of the actuator member  370 , rare earth magnet  368 , and actuator member  372  as viewed from left to right in  FIG. 5  is north-south, north-south, south-north. In this arrangement, the magnetically actuated roller hemming head  310  is arranged for pull type roller hemming operations in which the hem roller  356  is pulled toward a panel to be hemmed. The amount of pull force is approximately 330 pounds, and the opposing polarities of the rare earth magnet  368  and the actuator member  370  aid in maintaining a constant hemming force through a stroke of the hem roller  356 . 
     In the third embodiment, the housing  316  and shaft  324  may be non-magnetic so as to not interfere or interact with the magnetic field of the rare earth magnets. 
     Although the invention has been described by reference to specific embodiments, 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 embodiments, but that it have the full scope defined by the language of the following claims.