Patent Publication Number: US-6983633-B2

Title: Apparatus for roll hemming with zero angle deflection

Description:
BACKGROUND OF INVENTION 
     1. Field of the Invention 
     The present invention relates to a robot manipulated roll hem forming apparatus. 
     2. Background Art 
     Roll hem forming is a production process that is used to join a sheet metal outer panel to an inner panel by forming a hem flange. The hem flange is formed by bending a peripheral flange of an outer panel from a generally perpendicular orientation to a reversely turned orientation over an outwardly extending flange of an inner, reinforcement panel. A robot may be used to manipulate an end effector tool having a roller that is rolled against the peripheral flange of the outer panel to cause it to overlie the outwardly extending flange of the inner panel. In a robotic hemming system, the robot manipulates the roller about the edges to be hemmed. 
     Hard robot systems use precise position control of the location of the roller to press the outer panel peripheral flange against an anvil or solid supporting surface. A principal problem associated with hard robot systems is that they require precise position programming and lack flexibility. The end effector roller must be exactly located within about 0.1 mm or panel quality problems may be encountered due to application of excessive or inadequate force to the hem flange. The range of force applied to properly form an aluminum hem is between 150 and 350 psi. Other materials such as steel or specialized alloys would have different ranges of acceptable force application. A hem may be inadequately formed if insufficient force is applied resulting in a partially formed hem and potential for movement of the inner flange. If excessive force is applied to the hem, the peripheral flange of the outer panel may split or otherwise be distorted. Robots that are capable of meeting these exacting requirements are more expensive than standard robots. 
     Force control robot systems have been proposed in which a force transducer, or spring element, is incorporated into the end effector to address problems associated with hard robotic hemming systems. The force transducer moderates the force applied by the robot arm to the hem by the roller. Force control systems allow for limited misalignment of the hemming roller relative to the anvil. Examples of force transducers used in force control systems include mechanical springs, hydraulic dampers and air springs. A disadvantage associated with conventional force control systems is that the roller must generally be in line with the force transducer and robot arm or an angular deflection error will arise. 
     One example of a force control system is disclosed in U.S. Pat. No. 5,228,190 in which a slide block is incorporated in the end effector to connect the roller to a mechanical spring biasing member. Another example of a force control system is disclosed in U.S. Pat. No. 5,038,597 that discloses an end effector incorporating a parallelogram linkage that engages a resilient biasing element to bias the roller to a starting position. A hydraulic cylinder is provided to extend and retract the roller relative to the workpiece. With either of these prior art systems, only a single roller is provided even though in many hemming operations long straight hems are performed more quickly by a large diameter roller. Tight radius hems and hems in confined locations are preferably formed by means of smaller diameter rollers. It is necessary to change out the end effector to provide large and small rollers to hem panels requiring large and small rollers in such prior art force controlled robotic hemming systems. Changing out an end effector is time consuming and increases the cycle time of the hemming operation. 
     Another disadvantage of conventional systems is that the robot must extensively articulate the end effector to position the roller relative to the anvil surface and flanges to be hemmed. This problem is associated with both hard robotic hemming systems and force controlled hemming systems. Generally, a single roller must be moved by the robot to different angular orientations for a pre-hemming step and a final hemming step. In the pre-hemming step, the peripheral flange of the outer panel is formed to an acute angle of about 45° or may be formed in a two-step process to acute angles of 30° and then 60° to reduce forming stresses applied to the hem. Moving the roller to different angular orientations generally requires complex manipulations of the robot arm that increase cycle time. 
     There is a need for an improved hem roller end effector that includes a force transducer and a plurality of different rollers to provide an appropriately sized roller for different hem areas and that also may provide rollers oriented at different angular orientations relative to the end of the robot arm. The above problems and needs are addressed by Applicants&#39; invention as summarized below. 
     SUMMARY OF INVENTION 
     According to one aspect of the present invention a robot manipulated hem forming roller tool for a robot having an arm with a receptacle for an end effector on one end. The end effector is adapted to be received in the receptacle on the end of the robot arm. A linkage is provided that comprises a bracket extending from the end effector, a tool support member, and two links that connect the bracket and the tool support member together in the manner of a four bar link. A pre-hem roller is disposed on the tool support member at a first angular orientation relative to the tool support member. A final hemming roller is disposed on the arm at a second angular orientation relative to the tool support member that is different than the angular orientation of the pre-hem roller. A force transducer operatively engages the tool support member to limit force supplied by the robot arm to the rollers through the tool support member. 
     According to another aspect of the invention, a roll form hem tool is provided with a linkage comprising a bracket, a tool support arm having a back end and a distal end, and two links that connect the bracket and the back end of the tool support arm together in a four bar linkage. The tool support arm is moveable relative to the bracket and a force transducer engages the tool support arm and the bracket to limit force applied by the tool support arm. A first roller is disposed on the tool support arm at a first angular orientation relative to the tool support arm and a second roller is disposed on the tool support arm at a second angular orientation relative to the tool support arm that is different then the first angular orientation. Additional rollers can also be provided on the tool support arm. 
     According to other aspects of the invention the tool support member arm is supported by the linkage for limited movement and is biased by the force transducer into an extended position. Upon engagement by one of the rollers with a workpiece to form a hem on the workpiece, the force applied to the workpiece is limited by the force transducer. The linkage transfers a spring force from the force transducer in a linear direction to the rollers that engages a workpiece. The rollers are disposed generally in alignment with the end effector adaptor or force transducer so that the force is applied in a linear direction to a hem flange by the roller. Stated another way, the rollers are disposed so that the force applied to a workpiece is in a direction normal to an axis of rotation of one of the rollers wherein the force transducer is displaced in the same linear direction. 
     According to another aspect of the invention more than one final hemming roller and more than one pre-hem roller may be provided on the tool support member or arm. By providing additional rollers, the time required to manipulate the end effector with the robot arm may be reduced. 
     These and other aspects of the present invention are more fully described below with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a side elevation view of a hemming tool end effector attached to a robot arm; 
         FIG. 2  is a perspective view of one embodiment of a hemming tool end effector; 
         FIG. 3  is a side elevation view of an alternative embodiment of the hemming tool end effector; 
         FIG. 4  is a front elevation view of a hemming tool end effector disposed at an angular orientation to pre-hem a hem flange; 
         FIG. 5  is a fragmentary elevation view of a hemming tool forming a 45° pre-hem; 
         FIG. 6  is a fragmentary elevation view of a hemming tool forming a 45° pre-hem; 
         FIG. 7  is a elevation view of the alternative end effector shown in  FIG. 3  being used to form a final hem flange; 
         FIG. 8  is a front elevation view of a hemming tool end effector forming a final hem flange in an alternative approach; 
         FIG. 9  is a side elevation view of another alternative embodiment of the hem tool end effector shown forming a 30° pre-hem on a workpiece; 
         FIG. 10  is a side elevation view of another alternative embodiment of the hem tool end effector shown forming a 60° pre-hem on a workpiece; and 
         FIG. 11  is another alternative embodiment of a roll hem effector forming a final hem on a workpiece. 
     
    
    
     DETAILED DESCRIPTION 
     Referring now to  FIGS. 1 and 2 , an end effector hemming tool  20  is shown connected to a robot arm  22 . While the invention is illustrated in  FIG. 1  secured to a robot arm  22 , other apparatus for manipulating a roll hemming tool could be used in accordance with the present invention. The robot arm  22  has an adapter  24  including a receptacle  26  for receiving a ribbed shaft  28  of the hemming tool  20 . Radial alignment guides  30  are provided on a circular plate  32  of the hemming tool  20 . A tooling plate  36  is attached to the circular plate  32  and supports a stationary bracket  38 . A tool support  40  is shiftably mounted relative to the stationary bracket  38  by means of a pair of links  42 . The stationary bracket  38  comprises a bracket stop  43  formed by an inner surface located between the pair of links  42 , which are connected by bearings  44 . Similarly, a coupler stop  45  is formed in the surface of tool support  40  located between the bearings  44  and adjacent to the bracket stop  43 . The links  42 , tool support  40  and stationary bracket  38  in combination form a four-bar link that permits the tool support  40  to move in a generally linear direction relative to the bracket  38 , as limited by stops  43 , 45 . The bearings  44  also connect the links  42  to the tool support  40  and stationary bracket  38 . 
     A distal roller  46  is provided on one end of the tool support  40 . The distal roller  46  may be used to form a pre-hem or final hem as will be more fully described below. A first coaxial roller  48  and a second coaxial roller  50  are secured to the tool support  40  on a common axis. The first and second coaxial rollers  48  and  50  may have different diameters to perform different hem forming operations as will be more fully described below. A spring  52 , or force transducer, is supported on an arm  54  of the tool support  40 . The force transducer  52 , or spring, may be a mechanical spring, air spring, hydraulic cylinder, or pneumatic cylinder. The force transducer  52  functions to bias the tool support  40  in one direction relative to the bracket  38 . The tool support  40  is resiliently supported relative to the bracket  38  so that forces applied by one of the rollers is moderated or held within an acceptable range of pressure. 
     Referring now to  FIG. 3 , an alternative embodiment of the hemming tool  20  is shown that includes an aft roller  56  that is oppositely oriented relative to the distal roller  46 . The aft roller may be of the same diameter as the distal roller  46  or may be of a different diameter to provide flexibility in selecting a proper size roller for rolling either long flat sections with a larger diameter roller or rolling tighter curved or contoured sections with a smaller diameter roller. The aft roller  56  is secured to the tool support  40  that is supported on links  42  relative to the stationary bracket  38 . Bearings  44  are used to connect the links  42  to the bracket  38  and tool support  40 . 
     As shown in  FIG. 3 , the distal roller  46  is shown engaging a workpiece that is supported on an anvil support  60 . The workpiece is held on the anvil support  60  by means of a work holding clamp  62 . A hem flange  64  is shown as it is initially formed in a pre-hemming operation. The hem flange  64  is part of an outer panel  66  that is to be joined to an inner panel  68  by the hem flange  64 . 
     Referring now to  FIG. 4 , the alternative embodiment of  FIG. 3  is shown wherein a large radius combination roller  70  and a small radius combination roller  72  correspond to the first and second coaxial rollers  48  and  50 , as shown in  FIG. 2 . The combination rollers  70 ,  72  each have a partially conical portion  74  and a cylindrical portion  76  that may be used to form the hem flange  64  to different angular orientations as appropriate to perform pre-hemming and final hemming passes on the hem flange  64  of the workpiece. 
     As shown in  FIG. 4 , the partial conical portion  74  of the large radius combination roller  70  is being used to form a 60° pre-hem pass on the hem flange  64 . 
     Referring now to  FIG. 5 , the distal roller  46  is shown engaging the hem flange  64  of the workpiece that is held in place on anvil  60  by work holding clamp  62 . The distal roller  46  is a cylindrical roller that is supported on the tool support  40 . 
     Referring to  FIG. 6 , the hemming tool  20  is shown with a large radius combination roller  70  engaging the hem flange  64  of the workpiece. This view should be compared to  FIG. 4  wherein a first pre-hemming pass forms the hem flange  64  to approximately a 60° angle with the partially conical portion  74  of the combination roller  70 . To then form a pre-hemming pass forming the hem flange to a 30° angle, the roller must only be indexed slightly by the robot arm so that the cylindrical portion  76  of the combination roller  70  may then be used to form the 30° pre-hemming pass. The large radius combination roller  70  is preferred for long straight hem flanges, while the tool could be reversed in orientation so that the small radius combination roller  72  engages the workpiece as would be preferred for forming a hem in contoured areas or areas where the hem must be formed around a curved portion or corner of the workpiece. 
     Referring to  FIG. 7 , a hemming tool  20  is shown alternatively forming a hem with the distal roller  46  and the aft roller  56 . The tool would be used to form a single hem with a single roller. 
     As shown in  FIG. 7 , the distal roller  46  is engaging the outer panel  66  on the left hand side of the view to perform a final hemming pass on the workpiece.  FIG. 7  also shows the aft roller  56  on the right hand side performing a final hemming pass on the hem flange  64 . As the tool support  40  engages either the workpiece on the right side with the aft roller  56 , or the workpiece on the left side with the distal roller  46 , the force applied by either roller is moderated by means of force transducer  52  that is mounted on the arm  54 . The arm  54 , as illustrated, is located between the two links  42  to assure that there is a zero angle deflection of forces transmitted by the robot arm to the rollers  46  or  56 . This same zero angle deflection is achieved by the coaxial rollers  48 ,  50  (not shown) due to the arrangement of the two links  42  that support the tool support  40  relative to the bracket  38  for linear movement. The arm  54  moves in a linear direction relative to the bracket  38 . In this way, forces applied by the rollers  46 ,  48 ,  50 ,  56  are moderated by the force transducer  52 . 
     Referring now to  FIG. 8 , the end effector  20  is shown with a large radius combination roller  70  and small radius combination roller  72  are provided on the tool support  40 . As described above with regard to  FIG. 7 , the drawing illustrates two hems being alternatively formed. Only one roller would be engaged with the hem flange  64  at one time. The rollers  70  and  72  are selected and manipulated to provide an appropriate radius roller for different hemming applications. 
     Referring to  FIG. 9 , another alternative embodiment of the hemming tool  20  is shown that includes a first roller arm  80  that supports distal roller  46  and a second roller arm  82  that supports aft roller  56 . The roller arms  80  and  82  may be provided to simplify servicing of the rollers and to provide additional flexibility in roller location. The tool support  40  is supported by means of the links  42  relative to the bracket  38 , as previously described, and zero angle deflection is realized even though the aft roller  56  and distal roller  46  are supported on the roller arms  80  and  82 . 
     In  FIG. 9 , roller  56  is shown forming a 60° pre-hem pass on hem flange  64 . The workpiece is held by anvil support  60  and work holding clamp  62  in a vertical orientation. 
     Referring to  FIG. 10 , the tool  20  is shown at a different angular orientation relative to the workpiece and the anvil  60  to perform a 30° pre-hemming pass on the hem flange  64 . The tool must only be moved 30° relative to the workpiece to change from a 60° pre-hem pass, as previously seen in  FIG. 9 , to a 30° pre-hem pass using the cylindrical roller  56 . 
     Referring to  FIG. 11 , an alternative embodiment of the hemming tool  20  is shown that applies a pulling force to the hem flange  64  with distal roller  46 . A spring  84  exerts a biasing force against a reverse orientation extension  86  that is secured to the bracket  38 . The spring  84  is mounted on arm  88  that extends from the tool support  40  between the links  42 . The spring  84  biases the arm  88  away from the extension  86  so that when force is applied by the roller  46  to the hem flange  64  the force is moderated by the spring  84  that functions as a force transducer. The force transducer could alternatively be a mechanical spring, air spring, pneumatic cylinder or hydraulic cylinder. 
     While the best mode for carrying out the invention has been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention as defined by the following claims.