Abstract:
A method for holding a plastic fastener on a holding device in a position for transfer to an assembly tool, the method comprising the steps of: locating the fastening element in proximity to the holding device and oriented so that a thin wall on the fastener is aligned with the axis of a projecting needle on the holding device; pressing the fastening element and the holding device together; piercing the thin wall with the projecting needle; forming an opening through the thin wall; and frictionally engaging the needle with the thin wall edge that defines the opening to thereby hold the fastener on the holding device in the transfer position.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application is a divisional of U.S. patent application Ser. No. 11/869,963, Filed Oct. 10, 2007 which claims the benefit of German Patent Application No. 10 2006 048475.4 filed Oct. 11, 2006, incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    This invention relates to a method and apparatus for holding parts such as plastic elements in a position for transfer to a receiver, such as a tool that uses the parts. The invention also relates to parts constructed for use in such method and apparatus. 
         [0003]    Plastic fastening elements are frequently used in vehicles to attach cables, conduits, paneling elements, or the like to parts of the vehicle. In this connection, it is frequently desirable for the fastening elements to be installed in an automated fashion, for example with the aid of a robot. For automated installation, it is necessary to place a fastening element at the ready in a definite transfer position in which it can be grasped by the installation tool of the robot so that it can then be installed in the required fashion. In other cases, it can also be necessary to keep the fastening element at the ready in an assembly or installation tool, so that by actuating the tool, the assembly or installation can be executed. Plastic fastening elements are embodied in a wide variety of forms, so that keeping the various fastening elements at the ready is often difficult and requires a variety of holding devices. In addition, it is sometimes a challenge to design the fastening elements so that they can be held and secured by the available holding devices. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0004]    An object of the invention is to provide a method and an apparatus for holding parts such as plastic fastening elements at the ready, more particularly for holding uniquely constructed parts at a transfer position, where the parts can be delivered to a receiver, such as a tool. 
         [0005]    Parts utilized in the invention have a wall with one or more pierceable wall regions, and a holding device for the parts has one or more needles. With a part in a predetermined position, a pierceable wall region is pressed against a needle, so that the needle penetrates the pierceable wall region, and the wall is secured to the needle. 
         [0006]    In an embodiment of the invention, a holding device is in the form of a magazine with multiple sockets provided with needles, each socket holding a corresponding part. A slider pushes a part situated in front of the slider off the needles of the socket, so that the part is transferred to a receiver. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    The invention will be further described in conjunction with the accompanying drawings, which illustrate preferred (best mode) embodiments, and wherein: 
           [0008]      FIG. 1  shows a pierceable wall region of a plastic element and a needle intended for piercing the wall region; 
           [0009]      FIG. 2  shows a holding device according to the invention, with a plastic element held by it; 
           [0010]      FIG. 3  is a view of a round magazine with plastic elements held by it; 
           [0011]      FIG. 4  shows a pierceable wall region comprised of a film; 
           [0012]      FIG. 5  shows a perforated pierceable wall region, and 
           [0013]      FIG. 6  shows a slit pierceable wall region. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0014]      FIG. 1  shows a section of a wall  1  of a plastic fastening element in one embodiment of the invention. In the vicinity of its edge, the wall  1  is provided with a recess  2  that forms a wall region  3  with a significantly thinner wall thickness. The thickness of the wall region  3  is dimensioned so that the wall region  3  can be pierced by a sharp needle  4  without exerting a large amount of force. The needle  4  is part of a holding device that serves to keep the fastening element at the ready for transfer to a receiver, such as a tool for automatic installation or assembly of the fastening element. At its free end, the needle  4  has a tip  5  and, spaced apart from the tip, has a holding recess in the form of an annular groove  6 , or a notch or undercut. 
         [0015]    In the embodiment, the recess  2  is round and has a diameter D. Alternatively to this, however, the recess can also be embodied in an oval or polygonal form. The needle has a diameter d, which is considerably smaller than the diameter D of the recess. This diameter difference means that the center of the recess can have an offset x in relation to the central axis of the needle  4 , which corresponds to half of the difference of the diameters D minus d, without hindering the insertion of the needle  4  into the wall region  3  and without causing constraining forces to act on the needle in a transverse direction. The embodiment of the wall region  3  in relation to the needle  4  consequently permits a fastening of the wall  1  through insertion of the needle  4  into the wall region  3 , even when the fastening element with the wall  1  is not exactly aligned in relation to the needle  4 , but when the needle  4  is inserted in a region that is offset from the needle  4  by an amount determined by the diameters D, d. Thus, manufacturing tolerances are accommodated. 
         [0016]    In order to secure the wall  1 , it is pressed with its pierceable wall region  3  against the sharp end of the needle  4 . The needle  4  penetrates the wall region  3  and elastically and plastically deforms it while forming a hole. In the position of the wall  1  achieved by a stop  7  of the holding device adjacent to the needle  4 , the edge of the opening, which is pierced by the needle  4  and encompasses the needle  4  in an elastic fashion, engages in the material of the annular groove  6 , fixing the wall  1  on the needle  4  in a fashion suitable for temporarily holding it. 
         [0017]    A single needle can sometimes be sufficient to hold a part if the part is small and additional supports can be provided on the holding device. In many cases, however, it is suitable to fix a part with several needles at several points.  FIG. 2  shows one such example. A plate-shaped holding device  10  is provided with three needles  11  spaced uniformly apart from one another, only two of which are visible in the drawing. The needles hold a fastening element  12 , which is designed to be fastened in a circular opening in sheet metal. The fastening element  12  has an annular flange  13 , which has thin-walled, pierceable wall regions  14  spaced the same distance apart as the needles  11 . Oriented so that the wall regions  14  are situated in front of the needles  11 , the fastening element  12  is pressed against the holding device  10 . As a result, the needles  11  pierce the wall regions  14  as shown, forming openings whose edges adhere to the outside surface of the needles  11  in a frictionally engaging fashion (with or without needle recesses). The contact of the fastening element  12  against the holding device  10  defines the final position in the axial direction of the needles  11 . The fastening element  12  is thus placed in readiness in a position in relation to the holding device, which position is defined in all three spatial directions in relation to the holding device, so that a subsequent assembly procedure can start from this position. 
         [0018]      FIG. 3  shows a round magazine  20 , which is composed of a rotatable disk  21  and an annular holding device  22  situated on the rim of the disk  21 . The holding device  22  is coaxial to the rotation axis of the round magazine  20  and on its outside has a multitude of sockets  23  spaced uniformly circumferentially. Each socket  23  is provided with several parallel needles  24  that project outward, each set of which holds a respective fastening element  25  in the above-described manner. In the center of each socket, the annular holding device  22  is provided with a through bore  26 . On the inside of the holding device  22  is situated an actuator  27 , which is equipped with a radially mobile slider  28  that is aligned with a through bore in the depicted position of the round magazine  20  and, when the actuator  27  is triggered, can move outward through the through bore  26 . The socket  23 ′ in front of the slider  28  is situated at a position provided for transferring a fastening element  25  to a receiver such as an assembly tool. If such a tool is situated on the outside, in front of the socket  23 ′, ready for transfer of the fastening element  25 , then the actuator  27  is triggered and the slider  28  pushes the fastening element  25  off of the needles and toward the assembly tool. This simplifies the transfer, so that the assembly tool does not have to be brought snugly against the round magazine  20 . 
         [0019]    After the fastening element is transferred, a stepper motor (not shown) rotates the round magazine  20  by a fraction predetermined by the spacing of the through bores so that the slider can transfer the next fastening element. 
         [0020]      FIG. 4  shows a section through a pierceable wall region  31  composed of a film  30  on a wall  32  of a fastening element. The film covers an opening  33  in the wall  32  and, after the manufacture of the fastening element, can be welded to the wall or stuck to the wall in the form of a self-adhesive film. 
         [0021]    If it is not possible to manufacture the pierceable wall region with a thin enough film, then it is possible, as shown in  FIG. 5 , for the pierceable wall region  35  to be perforated with a hole  36 . The diameter of this hole  36 , however, must be smaller than the diameter of the needle. 
         [0022]      FIG. 6  shows a variant in which the pierceable wall region  38  of a wall  39  is provided with a slit  40 . The width of the slit  40 , too, must be smaller than the diameter of the needle. 
         [0023]    The above-described method, and the apparatus described for executing it are suitable not only for plastic fastening elements, but also for a wide variety of parts that must be kept in readiness for processing steps or between such processing steps. The invention is particularly advantageous when the outer form of the parts does not provide any suitable engagement surfaces for holding mechanisms. 
         [0024]    While preferred embodiments of the invention have been shown and described, it will be apparent that changes can be made without departing from the principles and spirit of the invention, the scope of which is defined in the accompanying claims. For example, a multi-socket magazine may be rod-shaped, rather than round, with needles of adjacent sockets projecting in the same direction from one side of the magazine, and with the slider arranged at the opposite side of the magazine and adjustable along the length of the magazine to different positions at which the slider can eject corresponding parts from the magazine.