Abstract:
A method and apparatus for feeding fasteners with at least two parallel boundary surfaces to a processing device includes lining up the fasteners in the same orientation by a feeder. The fasteners move through a conveying duct to a loading device arranged on a processing device. Individual conveying steps are separated from one another in time. At each conveying step a column of multiple fasteners in the same orientation, with their parallel boundary surfaces resting on one another, is conveyed by the feeder to the loading device by introducing air into the conveying duct. The loading device has, adjoining a magazine output end, a loading duct extending perpendicular to a magazine longitudinal axis, terminating in a processing device working duct. The loading duct has a conveying mechanism which conveys individual fasteners emerging from the magazine into the working duct one at a time.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application is a continuation of International Application No. PCT/EP2006/050729, filed Feb. 7, 2006, which claims the benefit of German Patent Application No. 10 2005 006 795.6, filed Feb. 14, 2005. The disclosures of the above applications are incorporated herein by reference. 
     
    
     FIELD  
       [0002]     The invention concerns a method for feeding fasteners having at least two parallel boundary surfaces to a processing device, wherein the fasteners are placed in readiness, lined up in the same orientation, by a feeder and are conveyed through a conveying duct to a loading device arranged on the processing device. The invention further concerns an apparatus for feeding fasteners to a processing device having a feeder for placing the fasteners in readiness in a uniform orientation, a loading device arranged on the processing device, a conveying duct connecting the feeder to the loading device, and a magazine associated with the loading device for accommodating a plurality of fasteners lined up one behind the other in the same orientation.  
       BACKGROUND  
       [0003]     A method is known from EP 0,922,538 B1 wherein a fastener in the form of a self-piercing rivet with a head and a shank recessed from the head is fed by a feeder through a conveying duct to a loading device arranged on the self-piercing riveting tool. The conveying duct has a T-shaped cross-section that corresponds essentially to the projected area of the self-piercing rivet. In this context, the self-piercing rivets are fed to the conveying duct with their longitudinal axes oriented perpendicular to the direction of conveyance and are individually transported through the conveying duct to the loading device by means of air. In the loading device, the delivered self-piercing rivet is stopped, and is held by means of movable positioning segments and an arresting element in a suitable starting position for processing. This known method and the devices for this purpose known from the aforementioned document have been proven in use. However, the time required for individual feeding of the fasteners has proven a disadvantage for fast operating cycles and relatively long application-specific conveying distances. Moreover, if the shape of the rivet is unfavorable, increased wear on the walls of the conveying duct can occur.  
         [0004]     In a method known from EP 0,511,093 B1 for conditioning and delivery of small, cylindrical parts, such as screws or rivets, the small parts are arranged facing in the same direction, with the shanks forward, in a column in a cylindrical supply tube. The supply tube has at its top an opening for supplying parts and a compressed air inlet, and at its bottom has an outlet associated with a member for intermittent release of the parts. The cylindrical tube is arranged in the shape of a ring in multiple windings in the interior of a rigid container and forms a magazine in which a large number of parts are stocked. The inner diameter of the tube is larger than the greatest diameter of the parts by a certain ratio so that an air stream which drives the parts toward the outlet can flow along the tube toward the outlet past the parts to the end of the outlet. This known method has the disadvantage that it requires a relatively large installation space in the vicinity of the processing device. Moreover, the energy requirements for transporting the parts are relatively great, since the entire column of many parts must be moved each time one part is dispensed. Short-term changeover between parts of different lengths is likewise not easily possible.  
       SUMMARY  
       [0005]     The object of the invention is to specify a method of the initially mentioned type that permits fast feed times, is characterized by modest energy requirements, and contributes to low wear of the conveying duct. It is a further object of the invention to create an apparatus suitable for carrying out the method.  
         [0006]     This object is attained in accordance with the invention by the method and apparatus claims set forth herein. Advantageous embodiments of the method and apparatus are specified in the dependent claims referring back to each of these claims. In the inventive method, the fasteners are conveyed in individual conveying steps which are separated from one another in time, wherein at each conveying step a column of multiple fasteners in the same orientation, with their parallel boundary surfaces resting on one another, is conveyed by the feeder to the loading device on the processing device through the introduction of air into the conveying duct.  
         [0007]     The inventive method permits fast conveying times between the feeder and the loading device, since multiple fasteners are conveyed in each conveying step. The conveying speed can be varied over a wide range by the choice of the time intervals between conveying steps and the number of fasteners per conveying step. The inventive method further permits comparatively low use of energy in the form of compressed air, since the quantity of air and pressure required for a conveying step encompassing multiple fasteners is not significantly greater than for a conveying step for conveying a single fastener, yet the number of conveying steps is many times smaller than for individual conveying.  
         [0008]     Surprisingly, it has additionally become apparent that the inventive method contributes to a substantial reduction in wear of the conveying duct and also to problem-free conveying of fasteners with an unfavorable diameter-to-length ratio. This can be attributed to the fact that the individual fasteners in the column support one another with their parallel boundary surfaces, thus stabilizing their position. Even when the fasteners are self-piercing rivets, which have a sharp cutting edge at one end, the fasteners can be conveyed using the inventive method with the cutting edge first without this leading to appreciably greater wear on the walls of the conveying duct.  
         [0009]     Another proposal of the invention provides that the column of fasteners fed to the loading device is accommodated in a magazine of the loading device, and the fasteners are removed individually from the magazine by the loading device and fed to the processing device as a function of the processing cycle. The fasteners are preferably conveyed through the conveying duct to the magazine of the loading device as a function of the processing cycle or the fill level in the magazine. A sensor or a counter detects when the quantity of fasteners in the magazine falls below a minimum level, thereby triggering a control process which brings about the conveyance of a new column of fasteners to the magazine.  
         [0010]     An apparatus suitable for carrying out the method according to the invention comprises a feeder that places fasteners in readiness in a consistent orientation, a conveying duct that connects the feeder to a loading device arranged on a processing device, and a magazine associated with the loading device for accommodating a column of multiple fasteners delivered through the conveying duct in the same orientation, with their parallel boundary surfaces resting on one another, wherein the loading device has, adjoining an output end of the magazine, a loading duct that extends perpendicular to the longitudinal axis of the magazine and terminates in a working duct of the processing device, and wherein the loading duct has associated with it a conveying mechanism which conveys individual fasteners emerging from the magazine into the working duct of the processing device one at a time.  
         [0011]     The inventive apparatus is characterized by a simple construction and reliable operation. The loading device design with a loading duct arranged at right angles to the longitudinal axis of the magazine yields a compact construction of the loading device and an advantageous arrangement of the magazine and conveying duct with little interfering contour in the vicinity of the working area of the processing device. Especially in the feeding of self-piercing rivets to a riveting tool, favorable three-dimensional shapes for the loading device with its magazine result when the self-piercing rivets are fed to the magazine with the cutting edge first. In the loading device, the self-piercing rivets can then be transported perpendicular to their axis of rotation from the magazine to the working duct of the riveting tool, which ensures a reliably functioning feed of the individual self-piercing rivets to the riveting tool.  
         [0012]     According to another proposal of the invention, the conveying mechanism of the loading device has a loading slide that can be moved back and forth in the loading duct with the aid of a pneumatically driven piston. According to another proposal of the invention, the loading slide&#39;s path of motion extends over only part of the length of the loading duct, and a pneumatic conveying mechanism activated by the loading slide is provided to convey the fasteners on the section of loading duct not traversed by the loading slide. This embodiment permits a short stroke for the loading slide, and thus a compact construction of the loading device. Moreover, it prevents collisions between the loading slide and tools of the processing device extending into the working duct.  
         [0013]     In an advantageous embodiment, a pneumatic working cylinder with a double-acting piston whose piston rod is connected to the loading slide is provided for moving the loading slide. In order to form the pneumatic feed mechanism, the piston, the piston rod, and the loading slide are traversed by a passage that communicates with a working chamber of the pneumatic working cylinder when the loading slide is in a position advanced toward the working duct. In order to control the pneumatic conveying mechanism, a valve needle is arranged in the working cylinder; in a first position of the piston, the needle projects into the piston end of the passage, thus closing it, and in a second position of the piston, the needle withdraws from the passage, causing the passage to be connected to the working chamber. 
     
    
     DRAWINGS  
       [0014]     The invention is described below on the basis of an example embodiment which is shown in the drawings.  
         [0015]      FIG. 1  shows a riveting tool with a device for feeding self-piercing rivets;  
         [0016]      FIG. 2  shows a section through a conveying duct with a column of self-piercing rivets resting upon one another; and  
         [0017]      FIG. 3  shows a loading device for transporting individual self-piercing rivets from a magazine into the working duct of a riveting tool.  
     
    
     DETAILED DESCRIPTION  
       [0018]      FIG. 1  shows a processing device shown for example as a riveting tool  1  intended to process self-piercing rivets. Self-piercing rivets are used to join components made of sheet metal. They are pressed into the superposed metal sheets from one side with great force by a die, with the metal sheets being supported on an anvil that constitutes a support. The riveting tool  1  has a C-shaped yoke  2  for this purpose, which carries at one end an anvil  3  and at the opposite end a housing  4  in which are arranged a die that can be moved against the anvil  3  and a device for driving the die. For feeding the self-piercing rivets, there is located on the riveting tool  1  a loading device  5  with a magazine  6 , which is supplied through a conveying duct  7  with self-piercing rivets placed in readiness by a feeder  8 . The conveying duct  7  consists of a resilient plastic tube, and in some applications must bridge a gap of several meters between the feeder  8  and the riveting tool  1 .  
         [0019]      FIG. 2  shows a longitudinal section through a portion of the conveying duct  7 . The wall  9  of the conveying duct  7  has an annular cross-section and encloses a hollow space that, depending on the course of the conveying duct  7 , is cylindrical in part and in part forms a segment of a torus. Located in the conveying duct  7  in  FIG. 2  is a column of individual self-piercing rivets  10 . The self-piercing rivets  10  have a rotationally symmetric shape, composed essentially of a cylindrical shank section  11  and a head section  12  in the shape of a truncated cone. The axial ends of the self-piercing rivet  10  are delimited by parallel circular areas  13 ,  14 . The circular area  13  forms, together with the surface contour of the shank section  11 , a cutting edge  15 . The greatest outer diameter of the self-piercing rivet  10  is located at the head section  12  and is somewhat smaller than the inside diameter of the conveying duct  7  so that the self-piercing rivets  10  can slide through the conveying duct  7  without jamming and without much resistance.  
         [0020]     As can be seen in  FIG. 2 , the self-piercing rivets  10  have an unfavorable aspect ratio, since their diameter is greater than their axial thickness. If the self-piercing rivets  10  were to fail to maintain their coaxial position within the conveying duct  7  shown in  FIG. 2  and turn about, they could jam in the conveying duct  7  and prevent further transport to the loading device  5 . This is avoided by the invention in that a column is formed of a number of self-piercing rivets  10  for transport through the conveying duct  7 , with the circular areas  13 ,  14  of each of the individual self-piercing rivets  10  resting one against the other. The back end of the column is then subjected to compressed air introduced into the conveying duct  7 , which drives the column through the conveying duct  7  to the magazine  6  designed in the manner of an end section of the conveying duct  7 . As a result of the propulsive force acting on the back end of the column and the compressive force acting on the front end of the column—generated by the resistance of the air in front of the column in the conveying duct to being forced through a throttling port at the magazine end of the conveying duct—the self-piercing rivets  10  in the column are pressed against one another and prevented from assuming an orientation that would impede their sliding through the conveying duct. Consequently, the self-piercing rivets  10  glide along the wall  9  of the conveying duct  7 , guided by the edge of their head sections  12 , without their cutting edges  15  being able to touch and damage the wall  9  appreciably.  
         [0021]     From the conveying duct  7 , the self-piercing rivets  10  arrive at the magazine  6  one column at a time. As is visible in  FIG. 3 , the magazine  6  has an S-shaped magazine duct  16 , which joins the conveying duct  7  and has essentially the same diameter as the conveying duct  7 . The magazine  6  is rigidly connected to the loading device  5  and the magazine duct  16  terminates at a right angle in a loading duct  17  of the loading device  5 . Unlike the round cross-section of the magazine duct  16 , the loading duct  17  has a rectangular cross-section, with a width corresponding to the diameter of the shank section  11  of the self-piercing rivets  10 . The top edge  18  of the loading duct  17  is extended outward at an angle on both sides to match the truncated cone shape of the head section  12  of the self-piercing rivets  10  so that the head section  12  can be accommodated and held therein. The loading duct  17  extends from the termination of the magazine duct  16  to a working duct  19 , which branches off from the floor of the loading duct  17  at a right angle. Opposite the working duct  19 , a bore  20  terminates in the loading duct  17 ; a die  21  that can move into the working duct  19  is located in said bore  20 . Immediately next to the bore  20 , a detent pawl  22  protrudes into the loading duct  17  from above, which pawl is rotatably mounted and supported by a spring  23  in such a way that it can be pivoted out of the loading duct  17  against the force of the spring  23 . The detent pawl  22  has a detent surface  24  facing the bore  20 , and on the opposite side has a ramp surface  25  that is inclined to the longitudinal axis of the loading duct and that recedes from the floor of the loading duct  17  when viewed in the direction of the termination of the magazine duct  16 .  
         [0022]     Located next to the termination of the magazine duct  16  in the loading duct  17  is a loading slide  26 , which can move into the loading duct  17 . A pneumatic working cylinder  27  with a double-acting piston  28  and a piston rod  29  is provided to move the loading slide  26 . The piston rod  29  is rigidly connected to the loading slide  26 . A passage  30  extends through the piston  28 , the piston rod  29  and the loading slide  26 . A valve needle  31 , which is affixed to the cylinder block, projects into the piston end of the passage  30 , closing the passage  30 . Connecting bores that are not shown in the drawing connect working chambers  32 ,  33 , which are located on both sides of the piston  28 , with a pneumatic valve device for controlling the movement of the loading slide  26 .  
         [0023]      FIG. 3  shows the loading device  5  in an operating position in which the loading slide  26  has returned to its starting position after a loading process, wherein the loaded self-piercing rivet  10   a  is still located in front of the termination of the working duct  19  and is held in this position by the side walls of the loading duct  17  and the detent pawl  22 . In order to set the self-piercing rivet  10   a , the die  21  is moved downward by operating the riveting tool  1 , in which process the side walls of the loading duct  17  move apart to some degree so that the thicker head section of the self-piercing rivet  10   a  can pass through the narrower region of the loading duct  17 . The die  21  then forces the self-piercing rivet  10   a  through the loading duct  19 , which elastically expands, thus guiding the self-piercing rivet  10   a  in a frictional manner to the workpieces resting on the anvil and pressing it into them. Then the die  21  returns to the starting position shown so that the next self-piercing rivet  10   b  can be loaded.  
         [0024]     As the drawing shows, the self-piercing rivet  10   b  is already located in the back end of the loading duct  17  in front of the loading slide  26 . The self-piercing rivet  10   b  has arrived in this position as a result of gravity and compressed air introduced into the magazine duct  16 , which forces the column of self-piercing rivets  10  toward the loading duct  17  even in the event of an overhead arrangement of the riveting tool  1 . In order to bring the self-piercing rivet  10   b  into the working position between the die  21  and the working duct  19 , compressed air is applied to the working chamber  32  of the working cylinder  27  and the working chamber  33  is connected to the atmosphere. This causes the piston  28  to move the loading slide  26  into the loading duct  17 , pushing the self-piercing rivet  10   b  ahead of it and simultaneously closing the outlet of the magazine duct  16 . Before the piston  28  reaches its end position on the floor of the working chamber  33 , the valve needle  31  emerges from the passage  30 , with the result that the compressed air supplied to the working chamber  32  flows through the passage  30  and exits at the end face of the loading slide  26 . The emerging stream of air strikes the self-piercing rivet  10   b  and pushes it under the detent pawl  22 , which deflects upward, and into the end position under the die  21 , where it is held in place by the detent surface  24  of the detent pawl  22  which has sprung back to its initial position. As soon as the piston  28 , and with it the loading slide  26 , have reached their advanced end position, the compressed air supply to the piston  28  is reversed, moving the piston and the loading slide  26  back into the initial position as a result of the compressed air introduced into the chamber  33 . Once the loading slide  26  has exposed the outlet of the magazine duct  16 , the column of self-piercing rivets  10  moves in the direction of the loading duct  17  until the foremost self-piercing rivet reaches the position of the self-piercing rivet  10   b , where its head section is supported against the upper edge of the loading duct.  
         [0025]     Reliable conveyance of the self-piercing rivets into the working duct of the riveting tool is achieved through the design and method of operation of the loading device  5  described above. Rotation of the rivets is not necessary. The combination of mechanical conveyance with the aid of the loading slide and the subsequent pneumatic conveyance of the self-piercing rivet into its working position permits a compact design of the loading device. The interaction of mechanical and pneumatic conveyance is controlled in a simple manner as a function of travel, and thus requires no additional control. The described design of the apparatus additionally has the advantage that self-piercing rivets of different lengths can be fed without the need to make changes in the device. The conveyance of columns of rivets into the magazine arranged on the loading device permits high working speed for the riveting tool and makes for low consumption of compressed air.