Abstract:
Joining apparatus for joining joining elements onto workpieces, comprising a joining element holding device, which is configured to radially hold a joining element, and comprising a loading pin arrangement, which is configured to slide a joining element axially into a holding position in the joining element holding device, and/or to axially support the joining element during a joining process, wherein the loading pin arrangement has a loading pin, which is slidable by means of a loading pin actuator arrangement in the direction of the joining element holding device. The loading pin arrangement is here designed to variably establish a loading pin stroke of the loading pin between at least two stages, so that in a first stage the loading pin is displaceable less far in the direction of the joining element holding device than in a second stage.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority from German Patent Application No. 102016112372.2, filed on Jul. 6, 2016, the disclosure of which is incorporated herein by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    The present invention relates to a joining apparatus for joining joining elements onto workpieces, comprising a joining element holding device, which is configured to radially hold a joining element, and comprising a loading pin arrangement, which is configured to slide a joining element axially into a holding position in the joining element holding device, and/or to axially support the joining element during a joining process, wherein the loading pin arrangement has a loading pin, which is slidable by means of a loading pin actuator arrangement in the direction of the joining element holding device. 
         [0003]    In addition, the present invention relates to a method for loading a joining element into a joining element holding device of a joining apparatus, in particular of the type previously described, wherein the joining apparatus has a loading pin which is alternately transferable into a feed position and into a joining position. 
         [0004]    In the field of joining apparatuses which are configured to join joining elements onto workpieces, for instance by way of so-called stud welding or by way of stud gluing, etc., it is known to feed joining elements in an automated manner to a joining head or a joining gun. 
         [0005]    On the joining head is provided a holding device, at which a joining element is held radially or on its outer periphery. In stud welding, a welding current can be conducted into the joining element via a holding apparatus of this type. The holding apparatus therefore generally has a high radial clamping force. 
         [0006]    In joining apparatuses of this type, the feeding is effected such that joining elements are introduced by means of a joining element receiver from radially into an axial feed channel, via which joining elements are fed from the rear into the holding apparatus. The joining elements then come to rest in the region of the holding apparatus, since they are braked by clamping jaws of the holding apparatus. After this, a loading pin is forced by means of a loading pin actuator out of a feed position, in which the feed channel is freed, from the rear against the joining element, in order to press the latter into a holding position in the joining element holding device. The position of the loading pin can then be maintained during the joining process in order to axially support the joining element during such a process. 
         [0007]    As the loading pin actuator, a pneumatic cylinder, which is transferable between two axial positions in a manner which is known per se, is frequently used. 
         [0008]    In the holding position, the joining elements generally protrude in relation to an axial end of the holding apparatus. Joining elements of different length can therefore protrude by different distances in relation to the axial end of the holding apparatus. The different lengths of joining elements are herein limited, however. 
         [0009]    Document DE 100 18 239 C1 discloses a welding shaft for a stud welding head, wherein a loading pin is manoeuvrable by means of a drive mechanism into a plurality of end positions by means of a spindle arrangement, in order to load parts of different length which are to be welded together. 
         [0010]    Document DE 10 2005 009 950 A1 discloses a stud welding device in which, instead of a rigid loading pin, there is provided a flexible loading pin, which is mounted for guidance purposes on a circular track so as thereby to be able to work different-sized studs with a welding device. 
       BRIEF SUMMARY OF THE INVENTION 
       [0011]    Against this background, it is an object of the invention to define an improved joining apparatus, and an improved method for loading a joining element into a joining element holding device of a joining apparatus. 
         [0012]    The above object is achieved in the joining apparatus stated in the introduction by virtue of the fact that the loading pin actuator arrangement is designed to variably establish a loading pin stroke of the loading pin between at least two stages, so that in a first stage the loading pin is displaceable less far in the direction of the joining element holding device than in a second stage. 
         [0013]    In contrast to the prior art, it is hence proposed not to be able to bring the loading pin steplessly into different positions, but rather to be able to transfer the loading pin into at least two specific different joining positions. 
         [0014]    It is here of particular benefit if the loading pin actuator arrangement is a pneumatic loading pin actuator arrangement. 
         [0015]    A loading pin arrangement of this type can be realized in a constructively comparatively simple and cost-effective manner. In particular, preferably no position sensors are necessary to establish the different stages of the loading pin stroke. 
         [0016]    It is here possible to slide into the holding position of the joining element holding device joining elements which have markedly different lengths. For instance, these can, on the one hand, be studs having a length of 14 mm and, on the other hand, ball studs having a diameter of 6.35 mm. 
         [0017]    In a further variant, studs of different length can be worked, for instance studs having a length of 10 mm or studs having a length of 30 mm. The difference between the two stages of the loading pin stroke can here range from 2 mm to 50 mm, in particular range from 5 mm to 25 mm. 
         [0018]    In the method according to the invention, the joining apparatus hence has a loading pin which is alternatively transferable into a feed position, into a first joining position and into at least a second joining position, with the step of detecting whether a supplied joining element has a first axial length or a second axial length, and with the further step of displacing the loading pin into the first joining position if the supplied joining element has the first axial length, or displacing the loading pin into the second joining position if the supplied joining element has the second axial length. 
         [0019]    The detection of whether the joining element has a specific axial length can here relate to specific axial lengths. In this case, only two different joining elements, for instance, are joined by means of the joining apparatus. 
         [0020]    Obviously, however, the detection of whether a supplied joining element has a specific axial length includes detecting whether the supplied joining element has an axial length within a specific axial length range. For instance, joining elements having very many different axial lengths can thereby be joined, wherein the joining elements are then divided into two groups, a first group, in which the loading pin is transferred into the first joining position, and a second group, in which the loading pin is transferred into the second joining position. 
         [0021]    The loading pin actuator arrangement is, as stated, preferably a pneumatic loading pin actuator arrangement, with which at least two, in particular precisely two, defined joining positions can be established. The transport speed in the loading pin actuator arrangement can be definedly set, at least in one direction, by means of outlet air restrictors. 
         [0022]    A loading pin cylinder can be supplemented by a guide system, whereby distortion can be avoided. 
         [0023]    The object is thus fully achieved. 
         [0024]    It is of particular benefit if the loading pin is coupled with a loading pin piston of a loading pin cylinder which defines a first piston stroke for the loading pin piston. 
         [0025]    The loading pin can here preferably pass through an axial end of the loading pin cylinder, so that sealing is easily possible. 
         [0026]    According to a preferred embodiment, the loading pin piston is here displaceable in a first cylinder chamber of the loading pin cylinder. 
         [0027]    The loading pin actuator arrangement preferably has two sealed cylinders arranged one behind the other, which are connected in series in order thereby to be able to set two defined joining positions. 
         [0028]    It is of particular benefit overall if the above-described loading pin cylinder is displaceable on a housing of the loading pin arrangement, by means of a second piston, between at least two different axial positions. 
         [0029]    It is hereby possible to achieve in a constructively simple manner that a second piston stroke, which, for the establishment of a—first—loading pin stroke, can be added onto the first piston stroke or is not incorporated in the—second—loading pin stroke, is established by means of the second piston. 
         [0030]    It is here of particular benefit if the second piston is fixed in relation to the housing. 
         [0031]    Here, a piston rod of the second piston preferably extends through a further, opposite axial end of the loading pin cylinder and is connected to the housing. 
         [0032]    The piston rod of the second piston hence likewise extends axially through a cover arrangement of the loading pin cylinder and can hence be easily sealed. 
         [0033]    All in all, it is further advantageous if the second piston is displaceable in a second cylinder chamber of the loading pin cylinder. 
         [0034]    In this case it is possible to establish the two stages by means of a single cylinder, in which two pistons are displaceable. 
         [0035]    In this respect, it is of particular benefit if a loading pin piston coupled with the loading pin and the second piston have the same diameter. 
         [0036]    In addition, it is herein advantageous if a first cylinder chamber, in which a loading pin piston coupled with the loading pin is displaceable, and a second cylinder chamber, in which the second piston is displaceable, are mutually separated by a partition. 
         [0037]    This makes it possible to define in a loading pin cylinder two mutually separated cylinder chambers. These two cylinder chambers can in this way be established in a constructively simple manner. In addition, outlet air restrictors can be integrated in a simple manner into both cylinder chambers. Also the supply of compressed air is easily realizable. In particular, the two cylinder chambers can respectively be subjected to same pressure levels, so that it is not necessary to provide compressed air with more than two different pressures (for instance a relief pressure of 0 bar, for instance, and a loading pressure &gt;0). 
         [0038]    It is here further of advantage if the loading pin arrangement is configured such that, in a feed position of the loading pin in which the loading pin frees a feed channel for a joining element which is to be fed into the joining element holding device, the loading pin piston and the second piston are disposed adjacent to the partition. 
         [0039]    In other words, a first and a second cylinder chamber are mutually separated in the feed position by the pistons and the intervening partition. 
         [0040]    In a further embodiment, it is advantageous if a variable cylinder chamber is arranged between a loading pin piston coupled with the loading pin and the second piston. 
         [0041]    In this case, different axial positions of the loading pin piston and of the second piston can be effected by the setting of different pressures in the various cylinder chambers. In this embodiment, the formation of a partition between the pistons is not necessary. 
         [0042]    In elongate joining elements in the form of studs, the holding position within the holding apparatus axially with comparatively large tolerance is acceptable. Insofar as the joining elements, however, are configured in the form of joining balls, for instance, it is advantageous if the axial holding position of such a joining ball is adjustable within the holding apparatus precisely and with narrow tolerances. 
         [0043]    In this case, it is of particular benefit if the loading pin arrangement has, for the second stage of the loading pin stroke, a stroke fine adjustment device. 
         [0044]    Obviously, the loading pin arrangement in a further alternative embodiment can have, at least for the first stage of the loading pin stroke, a stroke fine adjustment device. 
         [0045]    In this embodiment, the loading pin stroke can hence be precisely adjusted via the fine adjustment device. 
         [0046]    It is here of particular benefit if a loading pin cylinder is axially displaceable on a housing of the loading pin arrangement, wherein a stroke-limiting stop between the housing and the loading pin cylinder has a screwing element. 
         [0047]    A screwing arrangement of this type can be easily used to realize a stroke fine adjustment device. 
         [0048]    The above invention is further achieved by a loading pin arrangement of a joining apparatus of the type described above. 
         [0049]    Obviously the above-stated features and the features yet to be described below are usable not only in the respectively stated combination, but also in other combinations or in isolation, without departing from the scope of the present invention. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0050]    Illustrative embodiments of the invention are represented in the drawing and explained in greater detail in the following description, wherein: 
           [0051]      FIG. 1  shows a schematic representation of a joining system comprising an embodiment of a joining apparatus according to the invention, wherein a loading pin is in a feed position; 
           [0052]      FIG. 2  shows the joining apparatus of  FIG. 1 , wherein a loading pin is in a first joining position; 
           [0053]      FIG. 3  shows the joining apparatus of  FIG. 1 , wherein a loading pin is in a second joining position; and 
           [0054]      FIG. 4  shows an alternative embodiment of a joining apparatus, wherein a loading pin is in a first joining position. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0055]    In  FIG. 1 , a joining system for joining joining elements onto workpieces is represented schematically and denoted in general terms by  10 . 
         [0056]    The joining system  10  has a joining head  12 , which forms a joining apparatus. The joining head  12  is movable three-dimensionally in space, by way of example by means of a robot  14 , wherein the joining head  12  is guided on one end of an arm  16  of the robot  14 . 
         [0057]    The joining system  10  further contains a feed device  18 . The feed device  18  has a separating device  20 , in which the joining elements are separated and are then conveyed via a feed system, for instance in the form of blow air, via a feed tube  22  to the joining head  12 . 
         [0058]    The joining head  12  contains a joining element receiver, which contains an inlet opening  28 , via which separated joining elements are fed. The inlet opening  28  is connected via a feed channel  30  to a joining element holding device of the joining head  12 . The joining element holding device  32  has a plurality of holding tongues  34  arranged distributed over the periphery. The joining element holding device  32  is connected to the joining element receiver  26  by means of a fastening system in the form of a cap nut  36 . 
         [0059]    The holding tongues  34  define a conical portion  38 , which passes from an inner diameter, which corresponds to a maximum diameter of a joining element, to an inner diameter, which is smaller than a minimum diameter of the joining elements to be worked. 
         [0060]    The feed channel  30  extends from the inlet opening  28  in a curved path out of a radial feed direction into an axial feed direction and is connected to the rear end of the joining element holding device  32  in order hence to be able to feed joining elements via the feed channel  30  from the rear into the joining element holding device  32 , until these come to a halt in the region of the conical portion  38  in the joining element holding device  32 . 
         [0061]    In order to transfer a thus supplied joining element subsequently into a holding position, which in  FIG. 1  is shown schematically at H, a loading pin arrangement  40  is provided. 
         [0062]    The loading pin arrangement  40  contains a housing  42 , which is fixedly connected to the joining element receiver  26 . In addition, the loading pin arrangement  40  has a loading pin  44 , which extends along a joining axis  46 , i.e. coaxially to the holding device  32 . The loading pin  44  is movable between a feed position SP and two joining positions. 
         [0063]    In  FIG. 1 , the loading pin  44  is shown in the feed position SP. In this, the loading pin  44  is so far withdrawn from the joining element holding device  32  in the axial direction that it frees with its front end the feed channel  30 , so that a joining element can be freely conveyed from a side of the loading pin  44  into the holding device  32 . 
         [0064]    After this, the loading pin  44  can be transferred into one of the joining positions shown in  FIGS. 2 and 3 . As a result, a joining element  48  is pressed from the rear further into the joining element holding device  32  and finally into a holding position H, in which a part of the joining element  48  protrudes in relation to an axial end of the holding device  32 , as is represented in  FIG. 1 . 
         [0065]    In  FIG. 1  is shown that the joining element  48  has a shank portion  50 , which in the holding position H is held on the outer periphery by the holding tongues  34 , and a flange portion  52 , which in the holding position H protrudes axially in relation to the holding device  32 . 
         [0066]    For the performance of a joining operation, the flange portion  52  can then be mounted onto a workpiece  54  such as a metal sheet. After this, a welding current  56  can be conducted into the holding device  32 , so that an electric current flows from the joining element  48  into the workpiece  54 . Next the joining element  48  can be lifted off the workpiece  54  in order to draw an arc which fuses the mutual joining surfaces, after which the joining element  48  can be lowered onto the workpiece  54  in order to end the stud welding operation. The welding current is then short-circuited and shut off. 
         [0067]    The movements of the joining element  48  can here be effected by movements of the joining head  16  as a whole, either via a motor (not described in detail) on the joining head, or directly by means of the robot  14 . 
         [0068]    Instead of a welding operation, a gluing operation or another joining operation can also be performed, however, with a joining apparatus according to the invention. 
         [0069]    In order to move the loading pin  44  between the feed position SP shown in  FIG. 1  and one of the two joining positions SP 1 , SP 2  which are represented in  FIGS. 2 and 3 , a loading pin actuator arrangement  60  is provided. 
         [0070]    The loading pin actuator arrangement  60  has a loading pin cylinder  62 , within which a loading pin piston  64  is disposed, to be precise within a first cylinder chamber  65  of the loading pin cylinder  62 . The first cylinder chamber  65  defines a first piston stroke  66  for the loading pin cylinder  62 . 
         [0071]    The loading pin itself or a therewith associated piston rod passes through a first axial end  68  of the loading pin cylinder  62  and is sealed at this place. The first cylinder chamber  65  is delimited by this first axial end  68  and by a partition  70  within the loading pin cylinder  62 . 
         [0072]    The loading pin cylinder  62  itself is mounted in an axial displaceable manner within a bore  72  of the housing  42 . 
         [0073]    Within the loading pin cylinder  62  is established a second cylinder chamber  74 , which extends between the partition  70  and a second axial end  78  of the loading pin cylinder  62 . Within the second cylinder chamber  74  is disposed a second piston  76 , which is rigidly connected to the housing  42  via a piston rod (not described in detail) which passes through the second axial end  78 . 
         [0074]    The second cylinder chamber  74  is hence delimited by the partition  70  and by the second axial end  78  and establishes a second piston stroke  80 , which is preferably smaller than the first piston stroke  66 . 
         [0075]    As illustrated, the second piston  76  is connected to the housing  42  via a second piston rod  82 , which passes through the second axial end  78 . The second piston rod  82  is here fixed to an end cap  84  of the housing  42 , which closes off an opening via which the loading pin cylinder  62  can be introduced into the bore  72  of the housing  42 . 
         [0076]    A diameter of the cylinder chambers  65 ,  74  is shown in  FIG. 1  at  86 . The diameters are identical. 
         [0077]    In the feed position SP, the second axial end  78  bears against the end cap  84 . In addition, the pistons  64 ,  76  bear against opposite axial sides of the partition  70 . 
         [0078]    The axial mobility of the loading pin cylinder  62  within the housing  42  is adjustable via a fine adjustment device  90 . 
         [0079]    The fine adjustment device  90  has a screw bolt  92 , which protrudes from the first axial end  68  of the loading pin cylinder  62  in the direction of the holding device  32 . Onto the screw bolt  92  is screwed a nut  94 . The nut  94  can here form a stroke-limiting stop in relation to a stop face  96  of the housing  92 . 
         [0080]    Hence a loading pin cylinder stroke  98  can be finely adjusted by twisting of the nut  94 , which forms a screwing element. The loading pin cylinder stroke  98  is here preferably smaller than/equal to the second piston stroke  80 . 
         [0081]    Starting from the feed position SP shown in  FIG. 1 , a first joining position FP 1  can be established, as is represented in  FIG. 2 . To this end, compressed air is fed between the partition  70  and the loading pin piston  64 , so that the loading pin piston is displaced to the fore in the measure of the first piston stroke  66 , such that a front end of the loading pin  44  presses a joining element  48 , such as the stud shown in  FIG. 2 , out of a position within the holding device  32  into the holding position H shown in  FIG. 1  and  FIG. 2 . 
         [0082]    During the joining process, the loading pin can remain in the position to axially support the joining element. 
         [0083]    The hereby established first loading pin stroke  100  is preferably identical to the first piston stroke  66 . 
         [0084]    This first loading pin stroke  100 , corresponding to the first joining position SP 1 , is established when a joining element  48  has a first joining element length  102  which can lie within a specific first joining element length range. 
         [0085]    The position of the loading pin cylinder  62  within the housing  62  here remains unaltered in relation to the feed position SP shown in  FIG. 1  and is shown schematically in  FIG. 2  at  104 . 
         [0086]    Insofar as a joining element  48 ′ having a second joining element length  108  which is smaller than the first joining element length  102  and which can lie within a second joining element length range is to be joined, such as, for instance, the spherical joining element  48 ′ shown in  FIG. 3 , the second stage of the loading pin actuator arrangement  60  is activated, in which stage compressed air is fed into the region between the partition  70  and the second piston  76 , whereby the loading pin cylinder  62  is transferred out of the axial position  104  shown in  FIG. 2  into the second axial position  110  shown in  FIG. 3 , which latter position is established by the fine adjustment device having the nut  94  and the stop face  96 . 
         [0087]    The hereby established second loading pin stroke  106  is larger than the first loading pin stroke  100 . 
         [0088]    In  FIG. 4  is represented an alternative embodiment of a joining apparatus  12 ′, which in terms of structure and working method corresponds generally to the joining apparatus  12  of  FIGS. 1 to 3 . Same elements are therefore identified by same reference symbols. The differences are substantially set out below. 
         [0089]    In contrast to the joining apparatus of  FIGS. 1 to 3 , the loading pin cylinder  62  has no partition between the loading pin piston  64  and the second piston  76 . The ranges of movement of these pistons can be established in the same way as in the embodiment of  FIGS. 1 to 3 . 
         [0090]    For the establishment of the first joining position FP 1 , which is shown in  FIG. 4 , a cylinder chamber between the loading pin piston  64 ′ and that axial end of the loading pin cylinder  62 ′ which is facing the loading pin  44  is pressureless (P 1 =0). In the further cylinder chamber  74 ′ between the second piston  76 ′ and that axial end of the loading pin cylinder  62 ′ which is facing away from the loading pin  44  is contained fluid with a pressure P 2 . 
         [0091]    Finally, in a variable cylinder chamber  112  which is present between the pistons  64 ′,  76 ′ a pressure P 3  is present. In the first joining position FP 1 , P 2  is greater than P 3 . When the second joining position FP 2  is due to be established, the second cylinder chamber  74 ′ is pressurelessly connected, so that the loading pin cylinder  62 ′ is transferred still further to the left in relation to the position shown in  FIG. 4  until the second axial end  78  of the loading pin cylinder  62 ′ butts against the second piston  76 ′. 
         [0092]    Thus in the first joining position FP 1 : P 2 &gt;P 3 &gt;P 1 . 
         [0093]    In the second joining position FP 2 : P 3 &gt;P 1  AND P 3 &gt;P 2 . 
         [0094]    In the feed position (corresponding to  FIG. 1 ), the following applies: 
         [0000]      P 2 &gt;P 1 &gt;P 3 . 
         [0095]    The said pressures apply to uniform impact surfaces or cross sections of the respective cylinder chambers. Insofar as the impact surfaces are different, the pressures shall be adapted accordingly. 
         [0096]    Although exemplary embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that changes may be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.