Abstract:
A fastening device for fastening a small component, in particular a stud provided with an adhesive flange, to a mounting surface using a heat-activated adhesive that creates an adhesive bond between the component and the mounting surface, has an induction coil to heat the component and/or the adhesive and a holding mechanism which holds the component while the fastening device moves to the bonding position. On the side facing the mounting surface is a bearing surface for the component toward which the component can be brought from outside. The holding device can be advanced to the component by the induction coil and has an electromagnet for generating a holding force that is directed toward the bearing surface.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of International Application No. PCT/EP2005/002295, filed Mar. 4, 2005, which claims priority to German Patent Application No. 10 2004 012 786.7 filed Mar. 15, 2004. The disclosures of the above applications are incorporated herein by reference. 
    
    
     FIELD 
     The invention relates to a fastening device for fastening small components, in particular studs provided with an adhesive flange, to a mounting surface using a heat-activated adhesive that creates an adhesive bond between the component and the mounting surface, wherein the fastening device has an induction coil to heat the adhesive zone and a holding mechanism which holds the component while the fastening device moves to the bonding position. 
     BACKGROUND 
     Fastening devices of the specified type are used to automatically transport small components such as mounting studs, drain plugs, fasteners, pegs and the like to a mounting point on a mounting surface such as a motor vehicle body and hold the component there until the adhesive bond is established, and to heat the heat-activated adhesive to the required temperature. The adhesive providing the adhesive bond may be located either on the component or on the mounting surface. 
     From EP 0,927,091 B1 is known a device of the specified type for automatically setting and bonding mounting studs coated with hot-melt adhesive. The device has a housing with a stud catching station and a stud feed channel which is connected to a feed tube through which the mounting studs are conveyed by compressed air into the housing and the feed channel. Located at the end of the feed channel is a cylinder, equipped with an induction coil, that can be placed on the mounting surface and into which the mounting stud can be introduced with the disk flange first. Provided above the cylinder is a device with a plunger that can move into the cylinder, which presses the mounting studs in the cylinder onto the fastening position on the mounting surface. In one design, the plunger has a conical recess for centering the stud end. In another design, the plunger is provided with a gripper that guides the stud. This known device requires a relatively large amount of clearance at the fastening point since the inside diameter of the cylinder arranged within the induction coil must be larger than the outer diameter of the mounting stud&#39;s disk flange. 
     Also known, from DE 203 00 624 U1, is a portable stud gluing device with a portable electric power supply unit and a hand unit which are electrically connected to one another, wherein the hand unit has an inductor mechanism for generating heat. The hand unit of this device has a stud receiving device that carries a toroidal, cylindrical ferrite core that is enclosed by an induction coil. The shank of the stud is inserted in the stud receiving device and is held therein by a permanent magnet attached to a spring. The stud flange, which is located outside the stud receiving device, rests at a distance from the end face of the ferrite core and is pressed against the ferrite core by force applied manually to the hand unit during the fastening process. 
     SUMMARY 
     An object of the invention is to create an improved fastening device for automatically bonding small components. In particular, the device should require only a small amount of space at the bonding point. Furthermore, the device should permit rapid heating of the bonding zone and be removable from the bonded component without the use of force after the adhesive bond has been established. The fastening device according to the invention has, on its side facing the mounting surface, a bearing surface for the component toward which the component can be brought from outside, and the holding device has means for producing a holding force that is directed toward the bearing surface and is transmitted to the component. 
     The fastening device according to the invention has the advantage that it can be made very compact, since no opening is present for the component to pass through. The device&#39;s space requirement at the fastening point is thus small. An additional advantage is that the part of the component adjacent to the fastening zone that is to be heated can be brought into the immediate vicinity of the induction coil, so that especially effective and thus rapid heating of the fastening zone can be achieved. Using the holding device to press the component against the contact surface achieves secure chucking of the component in the fastening device by simple means, with the result that the component remains in an exactly defined position relative to the fastening device, even when transport motions are rapid, and precisely positioned fastening of the component is ensured. Moreover, this allows for adequate clearance for motion between the fastening device and the component so that the fastening device can be separated from the component after the end of the bonding process without the use of force. 
     It is especially advantageous when the holding device has an electromagnet that creates the holding force to hold the component in place. When the component is to be released from the holding device after bonding, it suffices to turn the electromagnet off. A mechanically simple design of the invention provides that the electromagnet is embodied as part of the holding device through the induction coil, in that the induction coil can be connected to a DC voltage source during the holding phase. In the fastening position, the component can be pressed against the mounting surface by the fastening device itself, so that the induction coil can then be disconnected from the DC voltage source and connected to an AC voltage source. According to the invention, the induction coil has a centrally located through-opening extending in the direction of the coil axis, where the wall of the opening is composed of a magnetically soft material as a shield tube. The shield tube directs the magnetic field toward the area of the stud that is to be heated and protects the portions of the stud located in the opening, for example the stud shank, and the parts of the holding device that consist of electrically or magnetically conductive materials, from inductive heating and/or magnetic oversaturation. Thermocouples for monitoring the temperature of the component can also be located inside the shield tube, protected from the alternating magnetic field of the induction coil. 
     To guide components that project into the opening, such as mounting studs, a guide element that works together with the component can be arranged in the opening. If the induction coil is used as an electromagnet, the guide element can be made of a magnetically soft material and be designed to concentrate the magnetic field that acts on the component during the holding phase. The guide element can preferably be moved out of the shield tube opening by an actuating device. This can be useful to increase the effectiveness of the shield tube during the induction phase or to remove the guide element from the bonded component prior to raising the fastening device away from the component. Movability of the guide element also makes it possible to adapt the position of the guide element to components of different lengths. If the guide element is made of a nonconductive and weakly magnetic material, especially plastic, it can also be arranged at a fixed position in the opening of the induction coil or in the shield tube. 
     According to another embodiment of the invention, the guide element can be designed as an electromagnet so that it can serve to grip and hold the component. In order to move the guide element, it can be fastened to the end of the piston rod of an actuating cylinder that is arranged coaxial to the induction coil and rigidly connected thereto. The actuating cylinder is preferably operated pneumatically. 
     According to another embodiment of the invention, the holding device can have a pincerlike gripper whose gripper arms are designed such that they project into the opening of the induction coil or can be moved through it. The gripper can be arranged on the guide element, and it can be moved along the coil axis together with the guide element by the actuating device. The gripper arms, which move transverse to the coil axis, can be pressed into a chucking position in a simple manner by spring force. However, this has the disadvantage that a force spreading each of the gripper arms apart must be overcome in gripping and releasing the component. Thus, an embodiment according to the invention wherein the gripper arms can be moved back and forth between an open position and a closed position by means of a drive is more advantageous, although costlier. The gripper can then be applied to and removed from the component without the use of force. 
     Another embodiment of the invention provides that the induction coil and the holding device form an assembly that is arranged in a housing and is supported therein so as to be movable along the coil axis between two end positions that are preferably limited by stops. This makes it possible to position the fastening device with the housing and to use the assembly in that position to perform movements suitable for gripping a component or moving a component to the mounting surface. The relative motion of the assembly and the housing can be accomplished either actively using a drive, or passively from outside by moving the housing while overcoming a spring holding the assembly in an end position. The drive can be either an electric or magnetic linear motor. 
     The housing can be either rigidly or movably attached to a robot arm, by which means the fastening device can be moved to various fastening positions. According to the invention, a movable connection between the housing and the robot arm can consist of a carriage fastened to the housing that is movable in a carriage guide parallel to the coil axis, wherein the carriage guide is arranged on the robot arm. 
     An additional advantageous embodiment provides that the housing is supported on the robot arm so as to be rotatable about an axis arranged transverse to the coil axis, and can be moved to different angular positions and locked in those positions by a rotary drive. In this case, a device for feeding components can be provided on the robot arm and the fastening device can be pivoted to a loading position facing the feed device, where one component at a time can be gripped by the holding device. This makes it possible in an especially simple manner to execute a rapid loading operation that can be executed while moving to the next fastening position. 
    
    
     
       DRAWINGS 
       Additional details and features of the invention are evident from the description below of individual example embodiments which are shown in the drawings. Shown are: 
       Figure is a first embodiment of a fastening device according to the invention for automatically bonding studs to a mounting surface, with a housing that is attached to a robot arm in a longitudinally movable manner; 
         FIG. 2  is a second embodiment of a fastening device according to the invention with a housing that is supported on a robot arm in a rotatable manner; 
         FIG. 3  is a first modified embodiment of the inner assembly of a fastening device according to the invention from  FIG. 1  or  2 ; 
         FIG. 4  is a second modified embodiment of the inner assembly of a fastening device according to the invention from  FIG. 1  or  2 ; 
         FIG. 5  is a third modified embodiment of the inner assembly of a fastening device according to the invention from  FIG. 1  or  2 ; 
         FIG. 6  is an embodiment of the fastening device according to the invention with a holding device rigidly arranged on the inductor; and 
         FIG. 7  is a device arranged on a robot arm for feeding adhesive studs to a fastening device according to the invention. 
     
    
    
     DETAILED DESCRIPTION 
     The fastening device shown in  FIG. 1  is comprised of an outer cylindrical housing  1  and, supported therein in a longitudinally movable manner, an assembly  2  that contains an induction coil  3  and a longitudinally movable holding device  4 . The housing  1  is fastened to a carriage  5  that is supported in a longitudinally movable manner on a carriage guide  6  extending parallel to the longitudinal axis of the housing  1 . The carriage  5  can be moved, and also fixed in place at defined locations, by an actuating cylinder  7  arranged on the carriage guide  6  on a robot arm. 
     The assembly  2  consists of an actuating cylinder  8 , a coil carrier  9 , and an intermediate member  10  connecting the two, all of which are rigidly joined together. Located on the intermediate member  10  are two diametrically opposite guide pins  11 , each of which engages a longitudinal slot  12 , parallel to the housing axis, in the wall of the housing  1  and prevents rotation of the assembly  2  relative to the housing  1 . In addition, the guide pins  11  and the ends of the guide slots  12  define the two possible end positions of the assembly  2  in the housing  1 . 
     The actuating cylinder  8  is located on the upper end of the assembly  2  located inside the housing  1 . It contains a piston  13  that separates two working chambers  14 ,  15 . The working chambers  14 ,  15  are connected by pressure connections  16 ,  17 , and by pressure lines that are not shown, to a valve device supplied with compressed air. The working chambers  14 ,  15  can be connected alternately to the compressed air source or the atmosphere by means of the valve device. A piston rod  18  extends from the piston  13  through the wall of the actuating cylinder  8  adjacent to the intermediate member  10  into a chamber  19  enclosed by the intermediate member  10 . At its free end, the piston rod  18  carries a guide element  20  that has a conical recess  21  in its end face. The guide element  20  is designed as an electromagnet and carries a coil  22  that can be connected to a DC voltage source by lines that are not shown. 
     Arranged between the actuating cylinder  8  and a bottom  23  of the housing  1  is a compression spring  24  that is supported on the actuating cylinder  8  by a pressure sensor  25 . The compression spring  24  attempts to push the assembly  2  into its lower position, extended from the housing  1 , where it is held in place by the guide pins  11 . 
     The induction coil  3  is arranged on a coil carrier  9  located outside the housing  1 . The coil carrier  9  is made of a nonconducting insulating material and has the form of a cylinder with two annular walls that extend radially outward, between which the induction coil  3  is held. Located in the cylinder is a shield tube  26  made of magnetically soft material, whose bore  27  serves to accommodate a stud  28 , with an adhesive flange  29 , which is to be bonded. The shield tube  26  has a smaller axial length than the cylinder of the coil carrier  9 , so that the lower end of the coil carrier  9  forms a support ring  30  that extends beyond the shield tube  26  and on which the adhesive flange  29  is supported. The air gap  31  thus created between the shield tube  26  and the adhesive flange  29  improves the effectiveness of the shield tube  26  and provides thermal insulation from the flange  29 . 
       FIG. 1  shows the described fastening device essentially in an operating position, wherein the adhesive flange  29  of the stud located in the fastening device has been heated enough that the adhesive present in an adhesive zone  32  has melted and has been partially forced outward to form an adhesive bead  33 . In this process, the adhesive flange  29  is pushed against a mounting surface  34  of a workpiece  35  by the compression spring  24  via the assembly  2 . The motion toward the workpiece  35  of the carriage  5 , and the housing  1  attached thereto, compresses the compression spring  24  to such a degree that the force measured by the pressure sensor  25  corresponds to the desired pressure on the adhesive flange  29 . The holding device  4  with the guide element  20  and the coil  22  are moved to a position outside the shield tube  26  away from the stud  28  by the application of pressure to the working chamber  15 , so that they are not heated by the alternating magnetic field of the induction coil  3 . 
     Once the heat-activated or heat-reactivated adhesive has hardened sufficiently to hold the stud, the actuating cylinder  7  moves the housing  1  to the opposite position, away from the workpiece  35 , by means of the carriage  5 . During this process the compression spring  24  is released while it holds the assembly  2  in contact with the adhesive flange  29  until it reaches the extended end position in which the guide pins  11  rest at the opposite ends of the guide slots  12 . After that, the motion of the housing  1  carries the assembly  2  along with it, so that the assembly  2  also separates from the workpiece  35 , and the stud  28  exits the bore  27  of the shield tube  26 . The robot can then move the fastening device to a feed device to receive a new stud and subsequently move it to another fastening location. 
     The fastening device shown in  FIG. 2  is the same as the fastening device from  FIG. 1  except for the details described below. For this reason, identical reference numbers are used for identical parts. This also applies to the embodiments shown in  FIGS. 3 through 7 . 
     The housing  1  of the fastening device shown in  FIG. 2  is attached to a robot arm  40  such that no relative motion between the housing  1  and the robot arm  40  is possible along the housing axis. The connection to the robot arm  40  is preferably accomplished by means of a rotary bearing with an axis of rotation perpendicular to the longitudinal axis of the housing, wherein a drive can be provided for defined rotation of the housing  1  relative to the robot arm  40 . Provision can also be made to fix the rotary bearing in a previously defined position of the housing  1 . If motion of the housing  1  relative to the robot arm  40  is not necessary, the housing  1  can also be rigidly attached to the robot arm  40 . 
     The housing  1  in  FIG. 2  has a linear motor  41  located in the closed end of the housing  1  to move the assembly  2 . The linear motor  41  is connected to the actuating cylinder  8  of the assembly  2  by a drive shaft  42 . In addition, located between the linear motor  41  and the actuating cylinder  8  is a spring  43  that attempts to push the assembly  2  toward the linear motor  41 . 
       FIG. 2  shows the fastening device in a position in which a new stud  28  is being moved toward the mounting surface  34  of a workpiece  35 . The stud  28  is located in the bore  27  of the shield tube  26  and is held in this position by the guide element  20 , designed as an electromagnet, of the holding device  4 . The end of the stud  28 , provided here with a pointed tip  44 , engages the recess  21  and is thereby centered in the shield tube  26 . The magnetic force exerted by the electromagnet of the guide element  20  presses the adhesive flange  29  against the support ring  30 . The contact pressure can be further increased if necessary by moderate application of pressure to the working chamber  15 . 
     The linear motor  41  is actuated to press the adhesive flange  29  of the stud  28  against the mounting surface  34 . In so doing, said linear motor overcomes the force of the spring  43  and pushes the assembly  2  downward out of the housing  1  until the surface of the adhesive flange  29  that is coated with adhesive  45  rests against the mounting surface  34 . During the subsequent bonding process wherein the adhesive  45  is heated, the contact pressure of the adhesive flange can be regulated as desired by actuating the linear motor  41 . 
       FIG. 3  shows an assembly  48  that can be used instead of the assembly  2  in a housing  1  of the devices shown in  FIGS. 1 and 2 . The assembly  48  differs from the assembly  2  in that a guide element  49 , consisting here of a permanent magnet, can be moved through the bore  27  of the shield tube  26  in order to grip the pointed end of a stud  28  located outside the bore  27  and draw it into the bore  27  of the shield tube  26  until its adhesive flange  29  rests against the support ring  30 . In this case, the stud  28  is received solely by a movement of the holding device  4 , so that an additional motion of the assembly  48  during stud feeding can be eliminated. 
       FIG. 4  shows an embodiment of an assembly  50  wherein the induction coil  3  can produce the magnetic force needed to hold the adhesive flange  29  of a stud  28 . Here, the shield tube  26  has, on the side facing the intermediate member  10 , an annular flange  51  extending radially that increases the concentration of the magnetic field at the inside end of the shield tube  26 . The annular flange  51  consists of the same magnetically soft material as the shield tube  26 . A magnetically soft guide element  52  is arranged in the bore  27  of the shield tube  26  in the vicinity of the annular flange  51  in order to effectively direct the magnetic field into the stud  28 . The outside diameter of the guide element  52  is dimensioned large enough that the air gap  53  between the shield tube  26  and the guide element  52  is significantly smaller than the resulting air gap  31  between the bottom end of the shield tube  26  and the adhesive flange  29  resting against the support ring  30 . Furthermore, as in the previous example embodiments, the guide element  52  has a conical recess  54  by which the stud end engaging the recess is centered. 
     The induction coil  3  is connected to a DC voltage source to hold a stud  28 . This generates a static magnetic field, which produces a holding force that pulls the stud  28  into the shield tube  26  and holds it in the position shown as a result of the described design of the shield tube  26 , annular flange  51  and guide element  52 . Of course, this requires the stud  28 , including the adhesive flange  29 , to be made of a magnetically conducting material such as steel. 
     As in the previous example embodiments, the guide element  52  is attached to the piston rod  18  of the actuating cylinder  8 . The guide element  52  is withdrawn from the shield tube  26  for heating of the adhesive zone. This restores the shielding effect of the shield tube  26  and prevents the alternating magnetic field from excessively heating the shank of the stud  28 . 
     The assembly  50  is characterized by a simple design, and permits secure holding of studs as well as components of different shapes, since a relatively strong static magnetic field can be produced with the aid of the induction coil. When the assembly  50  is in the fastening position, the adhesive flange  29  of the stud  28  is pressed against the mounting surface of the workpiece by the assembly  50  via the support ring  30  and is held in place by this means. The induction coil  3  can thus now be disconnected from the DC voltage source and connected to an AC voltage source to heat the fastening zone. 
       FIG. 5  shows an assembly  56  for use in the housing  1  wherein the holding device  4  is provided with a gripper  57  to grip and hold a stud  28 . The gripper  57  is arranged on the piston rod  18  that carries the guide element  20 . Within the intermediate member  10 , the gripper has a gripper frame  58  attached to the piston rod  18  on which are hinge-jointed two opposing double-armed gripper arms  59 . The gripper arms  59  extend essentially parallel to the piston rod  18 , and their ends, which form retaining jaws  60 , project past the guide element  20  located at the end of the piston rod  18 . The ends of the gripper arms  59  opposite the retaining jaws  60  are each connected to the gripper frame  58  by a pneumatic or electric drive  61 . 
     In the position shown, the gripper  57  has moved almost all the way down and has gripped a stud  28 . The pointed upper end of the stud  28  is supported on the guide element  20 . The guide element  20  here can be designed advantageously as a proximity sensor in order to be able to detect the presence of the stud  28  in the gripper  57 . Through the application of pressure to the working chamber  15  of the actuating cylinder  8 , the closed gripper  57  is moved upward and the stud  28  is drawn into the bore  27  inside the induction coil  3  until the adhesive flange  29  rests against the support ring  30 . In this holding position, the stud  28  is then transported to the fastening position, where the bonding process is then initiated. Once an adhesive bond has been produced, the gripper  57  is opened so that the assembly  56  can be removed from the stud  28  without transmitting any force to it. 
     A passive gripper that is held in the closed position by spring force can also be used instead of the active gripper  57  to hold a stud. However, with such a gripper it is necessary for the gripper to be pulled off the stud using the actuating cylinder  8  while the support ring of the assembly rests against the adhesive flange. A correspondingly longer travel distance for the gripper is then necessary. 
       FIG. 6  shows an embodiment of a fastening device according to the invention that is characterized by simple construction and small overall length. The housing  1 , which is rotatably arranged on a robot arm  40 , has located within it an assembly  64  that moves in the longitudinal direction of the housing by means of a linear motor  41 . The assembly  64  consists of a coil carrier  9  with an induction coil  3  and a cup-shaped end piece  65  fastened thereto. Located in the center of the end piece  65  is a rod  66 , which carries a gripper  57  with a gripper frame  58  and gripper arms  59 , and at its end a guide element  20 . The gripper arms  59  can be moved by drives  61  that are attached to the wall of the end piece  65 . The retaining jaws  60  of the gripper arms  59  are located within the bore  27  of the coil carrier  9 . 
     In the case of the assembly  64 , the gripper  57  is not movable along the coil axis in the assembly  64 . Therefore, in order to grip a stud  28  the linear motor  41  is used to push the assembly  64  with opened gripper  57  over the stud, which for example rests with its adhesive flange on a support, until the support ring  30  rests against the adhesive flange  29 . Once the gripper  57  is closed to grip the stud  28 , the assembly  64  is retracted into the housing  1  so that it can be extended again at the fastening position to set and press the adhesive flange  29  on the mounting surface  34 . 
       FIG. 7  shows an advantageous fastening device for feeding mounting studs and similar components to a fastening device according to the invention. The housing  1  of the fastening device here is rotatably arranged at the end of a robot arm  40  and can be moved to any of various desired angular positions by means of a drive. Located on the robot arm  40  is a feed device  70  that feeds the studs  28  to a delivery point  71 . Provided at the delivery point  71  is a feed gripper  72 , which is magnetic for example, that can be moved by a pivot drive  73  back and forth between a receiving position  74  and a delivery position  75 . In the receiving position  74 , the feed gripper  72  grips one stud  28  at a time by the adhesive flange  29  and holds it at the delivery position  75  in such an orientation that the free end of the stud  28  points toward the axis of rotation of the housing  1 . 
     In order to feed the stud  28  to the fastening device, the housing  1 , for example with the assembly  56  located therein, is pivoted to the feed position  76 , indicated by dashed lines, where the coil carrier of the assembly  56  is located opposite the stud  28  in the delivery position and is oriented coaxial thereto. The actuating cylinder of the assembly  56  is actuated to extend the gripper  57 , grip the stud  28 , and draw it into the assembly  56  until its adhesive flange rests against the support ring  30 . After this process, the feed gripper  72  returns to the receiving position  74 . At the same time, the robot arm  40  is moved to the fastening position and the housing  1  on the robot arm  40  is pivoted to the fastening position, in which its longitudinal axis is perpendicular to the mounting surface  34  of a workpiece  35 . Moving the assembly  56  to the position  77  shown by dashed lines presses the adhesive flange  29  of the stud against the mounting surface  34 , and the bonding process is then initiated. 
     The feed device shown in  FIG. 7  can also be used in combination with the other assemblies described above. If the holding device cannot be extended from the assembly, the induction coil of the assembly must instead be pushed axially onto the shank of the stud far enough that the holding device can grip and hold the stud.