Abstract:
An apparatus for the formation of a wire loop comprises a wire drive for advancing a wire and a loop layer to grip a first end of the wire and to lay a wire loop. When the wire is advanced, the wire loop is formed into a selected size. The apparatus can also comprise a pull-out gripper and a sensor device, the pull-out gripper being configured to grasp the wire of the wire loop and, after grasping the wire of the wire loop, move relative to the loop layer, thereby tensioning the wire loop in a longitudinal direction. The sensor device can detect a twist in the wire loop.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to European Patent Application No. 10173456.4, filed Aug. 19, 2010, which is incorporated herein by reference. 
       FIELD 
       [0002]    The disclosure relates to an apparatus and a method for forming a wire loop. 
       BACKGROUND 
       [0003]    Typically, in a wire-processing machine  1  such as is shown by reference to an example in  FIG. 1 , the wire  2  is unrolled from a roll or reel, or fed out of a drum (not shown). A wire drive  3  pulls the wire  2  into the wire-processing machine  1 . The corresponding direction of movement is indicated in  FIG. 1  by the arrow P 1 . A loop layer  4  is employed which forms a loop  2 . 1  from a predefined section of the wire  2 . When doing so, the loop layer  4  grasps the leading wire end of the wire  2  and, through a turning movement, forms the loop  2 . 1 , which, through further advance of the wire  2 , is brought to the desired length. The beginning of this process is shown in  FIG. 1 . Here, the loop  2 . 1  is still very small. 
         [0004]    After separation of the loop  2 . 1 , a transfer unit  5 , such as is known, for example, from patent application EP1073163-A1, takes over the two ends of the loop  2 . 1  and, by a transverse movement in direction P 3 , brings them to a so-called de-twisting apparatus  6 . 
         [0005]    Known from patent application EP1691457-A1 is a corresponding wire-processing machine  1  with loop layer  4 , transfer unit  5 , and de-twisting apparatus  6 , which allows the twist to be removed from a wire loop  2 . 1 . Here, this takes place with a de-twisting apparatus  6 , which is equipped with two turnable wire grippers  6 . 1 ,  6 . 2 , which, at the instant shown in  FIG. 1 , hold a second wire-loop  2 . 2 . The twist in this second wire loop  2 . 2  is removed by at least one of the two wire grippers  6 . 1 ,  6 . 2  executing de-twisting turns of a certain value about a horizontal axis counter to the direction of twist of the wire-loop  2 . 2 . 
         [0006]    A potential disadvantage of this approach is that the direction and angle of this de-twisting movement is often previously determined by trials and saved. Another possible disadvantage is that these values are not always constant over the length of the wire  2  that is fed to the wire-processing machine  1  and that long wire loops do not succeed in every case in removing the twist, since the loops can cross multiple times and unfavorably. 
         [0007]    In at least some cases, crossing of the wire-loops is a problem in the relevant processes. 
       SUMMARY 
       [0008]    In some embodiments, crossing of the wire loops is prevented by the wire, during formation of the loop, being held with a pull-out gripper, and optionally also being pulled out. 
         [0009]    According to an embodiment, the pull-out gripper is so embodied that it can recognize the direction of the twist in the loop and/or the twist-free state of the loop. 
         [0010]    According to another embodiment, the twist in the loop and/or the twist-free state is determined by a sensor device. 
         [0011]    A further embodiment contains a pull-out gripper, which can recognize the twist of a loop and/or the twist-free state of the loop, and a sensor device. 
         [0012]    In some cases, with a stretched loop, the two wire ends are transferred to a de-twisting apparatus according to EP1691457-A1, which performs the de-twisting according to the direction determined by the pull-out gripper and/or the sensor device, until the pull-out gripper and/or the sensor device recognizes the twist-free state of the loop. 
         [0013]    At least some embodiments are suitable for a wire-processing machine according to EP1691457-A1. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    The present disclosure is explained in more detail by reference to the attached figures. Shown are in: 
           [0015]      FIG. 1 , a three-dimensional view of a part of a previously known wire-processing machine; 
           [0016]      FIG. 2A , a three-dimensional view of a part of an apparatus with pull-out gripper in a first instantaneous state; 
           [0017]      FIG. 2B , a three-dimensional view of a part of an apparatus with pull-out gripper according to  FIG. 2A  in a second instantaneous state; 
           [0018]      FIG. 3A , a three-dimensional view of a part of the pull-out gripper in an open state when grasping or releasing a wire loop; 
           [0019]      FIG. 3B , a three-dimensional view of the pull-out gripper according to  FIG. 3A  in a closed state with a grasped wire loop; 
           [0020]      FIG. 3C , a side view of the pull-out gripper according to  FIG. 3A  in the closed state, wherein the wire loop is not shown; 
           [0021]      FIG. 3D , a three-dimensional view of the pull-out gripper according to  FIG. 3A  in a diagonal position in a closed state, wherein the wire loop is not shown; 
           [0022]      FIG. 3E , a back view of the pull-out gripper according to  FIG. 3A , in which two optional light barriers are shown; 
           [0023]      FIG. 4A , a greatly simplified sketch of the principle of a wire-processing machine when inserting a wire piece; 
           [0024]      FIG. 4B , a greatly simplified sketch of the principle of the wire-processing machine according to  FIG. 4A  when forming a wire loop and after grasping the wire loop with the pull-out gripper; 
           [0025]      FIG. 4C , a greatly simplified sketch of the principle of the wire-processing machine according to  FIG. 4A  after the wire loop has been pulled out; 
           [0026]      FIG. 4D , a greatly simplified sketch of the principle of the wire-processing machine according to  FIG. 4A  after transfer of the wire loop to a transfer unit; and 
           [0027]      FIG. 4E , a greatly simplified sketch of the principle of the wire-processing machine according to 
           [0028]      FIG. 4A  after the execution of a transfer movement and before transfer of the wire loop from the transfer unit to a de-twisting apparatus. 
       
    
    
     DETAILED DESCRIPTION 
       [0029]    There follows a description of the disclosed technologies by reference to an embodiment which is based on a wire-processing machine  1  according to EP1691457-A1. At least some embodiments of the disclosed technologies can, however, also used with other wire-processing machines. 
         [0030]      FIG. 2A  shows a perspective view of a part of an apparatus  10  with pull-out gripper  20 . The apparatus  10  is designed for the production of a wire-loop  2 . 1  of a wire-piece. 
         [0031]    The apparatus  10  contains means  3 , for example a correspondingly executed wire-drive  3 , to insert and hold a trailing end of the wire-piece. It further contains means  4 , for example in the form of a loop-layer  4  similar to  FIG. 1 . The loop-layer  4  grasps the leading end of the wire  2  and, with a swivel movement (for example a rotation of 180°), lays the wire-loop  2 . 1 . The wire-drive  3  then advances the wire  2  until the desired length of the wire-loop  2 . 1  is attained, or the wire-loop  2 . 1  in the desired size is formed. 
         [0032]    The apparatus  10  additionally contains a so-called pull-out gripper  20 . The pull-out gripper  20  has at least two basic functions. Firstly, the pull-out gripper  20  serves to grasp an area of the wire piece which is located between the leading end and the trailing end of the wire piece. For this purpose, the pull-out gripper  20  has a gripper  21 . Secondly, the pull-out gripper  20  holds the wire loop  2 . 1  taut by applying to it slight tension in lengthwise direction. For this purpose, the pull-out gripper  20  contains a movement apparatus  22  which makes it possible to move the gripper  21  relative to the means  3 ,  4  after grasping has occurred. This movement can take place in the direction of an arrow P 2 , as indicated in  FIG. 2A . The movement apparatus  22  can, however, also execute a movement in another direction, e.g. diagonal to, or along, a curved path in which the relative distance between the loop-layer  4  and the gripper  21  is enlarged. 
         [0033]    In at least some embodiments, the movement apparatus  22  contains a motor  23 , possibly a servomotor  23 . The movement apparatus  22  of the pull-out gripper  20  can, however, also be coupled for movement purposes to another movement apparatus, for example to the wire-drive  3 . In this case, the pull-out gripper  20  needs no motor of its own. 
         [0034]    In some cases, the movement apparatus  22  contains a linear axle  24  and a belt  25  which is driven by the motor  23 , possibly a toothed belt  25 . The belt  25  transfers a rotation movement of the motor  23  to the gripper  21  so that the latter changes its position along the linear axle  24 . 
         [0035]    In further embodiments, the apparatus  10  contains a wire-tray  11 , which is arranged below the movement apparatus  22  so that, after the wire-loops  2 . 1  have been de-twisted, they can be laid in the wire-tray  11 . 
         [0036]    In additional embodiments, the pull-out gripper  20  of the apparatus  10  is designed in such manner that it has a linear axle which contains a longitudinal guide  24 , a servomotor  23 , and a toothed-belt drive with toothed belt  25 , so that the pull-out gripper  20  can be displaced parallel to the wire-transport direction P 1  (i.e. parallel to P 2 ). 
         [0037]    Sometimes with short wire-loops  2 . 1 , when transporting the wire-loop  2 . 1  to the de-twisting apparatus  6 , it can be advantageous if the pull-out gripper  20  slightly retracts in the direction of the loop-layer  4 . Otherwise, under certain circumstances the wire-loop  2 . 1  could be excessively stretched, or even torn out of the pull-out gripper  20 . Retraction of the pull-out gripper  20  possibly occurs shortly before the execution of a lateral movement P 3  of the transfer unit  5 , or during the execution of a lateral movement P 3  of the transfer unit  5 . 
         [0038]      FIG. 2A  shows the closed pull-out gripper  20  while pulling-out the lengthening wire-loop  2 . 1 . 
         [0039]    The pull-out gripper  20  is embodied in such manner that it grasps a piece of the wire  2  without gripping the latter tightly. 
         [0040]    In at least some embodiments the transfer unit  5  is fitted with two wire-grippers  5 . 1 ,  5 . 2  and can be moved on a guide that is arranged perpendicular to the direction of wire-transport (i.e. parallel to P 3 ), so as to thereby transfer the two wire-ends of the loop  2 . 1  to two wire-grippers  6 . 1 ,  6 . 2  of the de-twisting apparatus  6 .  FIG. 2B  shows the situation after the wire-loop  2 . 1  has been transferred from the transfer unit  5  to the de-twisting apparatus  6 . 
         [0041]    Further recognizable in  FIG. 2B  is that the pull-out gripper  20  has so enlarged the relative distance from the position of the loop-layer  4  that the wire-loop  2 . 1  is slightly taut. To maintain tautness, the control of the movement of the apparatus  10  can be designed in such manner that the pull-out gripper  20  constantly exerts on the wire-loop  2 . 1  a slight tensile force in the direction P 2 . 
         [0042]    In the embodiment shown in  FIGS. 2A and 2B , a slightly diagonal position of the wire-loop  2 . 1  results, since, on transfer from the loop-layer  4  to the de-twisting apparatus  6 , the transfer unit  5  relative to the pull-out gripper  20  executes a transverse movement (here, P 3  stands perpendicular to P 2 ). 
         [0043]    The arrangement of the axes can also be different. For example, the linear axis of the pull-out gripper  20  can run diagonally, or the pull-out gripper  20  can follow an arc-shaped path. 
         [0044]    In some embodiments, the pull-out gripper  20  has two gripper-fingers  26 . 1 ,  26 . 2 , which can be closed or opened by turning about a pin  28  that is arranged in a fork-piece  27 . Corresponding details of such embodiments are shown in  FIGS. 3A to 3E . 
         [0045]    In the embodiment shown, closing of the gripper-fingers  26 . 1 ,  26 . 2  is effected by a torsion spring  29  which is arranged on this pin  28  (see, for example,  FIG. 3C ). The torsion spring  29  applies a closing force to the back-ends of the gripper-fingers  26 . 1 ,  26 . 2 . Hence, in the normal state, the gripper-fingers  26 . 1 ,  26 . 2  are closed. 
         [0046]    Opening of the pull-out gripper  20 , i.e. transition into an open state, is effected by the contrary movement of two gripper jaws  31  of a pneumatic, hydraulic, or motor-driven parallel gripper  30 , which is arranged in the area of the fork-piece  27 . The gripper jaws  31  possibly have V-shaped recesses  31 . 1 ,  31 . 2 , which, on closure of the parallel gripper  30 , press on the pins  26 . 3 ,  26 . 4  that are arranged on the ends of the gripper fingers  26 . 1 ,  26 . 2  and thereby effect opening of the pull-out gripper  20 . The parallel gripper  30  possibly contains a guide  33  (see  FIG. 3B ), which serves to linearly guide the gripper jaws  31 . 
         [0047]    The gripper fingers  26 . 1 ,  26 . 2  of the pull-out gripper  20 , and the fork piece  27  to which they are fastened, can turn freely within a certain angle about a longitudinal axis LA (parallel to the direction of the pulling-out movement P 2 ). In at least some embodiments, to prevent crossing of the wire loop  2 . 1 , this angle is less than 90 degrees. 
         [0048]    The V-shaped recesses  31 . 1 ,  31 . 2  of the gripper jaws  31  of the parallel gripper  30  cause the gripper-fingers  26 . 1 ,  26 . 2  in the open state of the pull-out gripper  20  to stand vertical as shown in  FIG. 3A . 
         [0049]    This position can be maintained on closing of the gripper-fingers  26 . 1 ,  26 . 2 , until the wire-loop  2 . 1  exerts no further torque on the pull-out gripper  20 . Should there be twist in the wire-loop  2 . 1 , the gripper-fingers  26 . 1 ,  26 . 2  turn in one direction or the other. In at least some embodiments, at an angle of maximum 90 degrees, this turning movement is stopped. 
         [0050]    For this purpose, turning of the fork-piece  27  is limited by stops  32 . In some embodiments in which the stops  32  are so embodied and positioned, the maximum angle is 70 degrees. 
         [0051]    In further embodiments, fastened at the end of the fork-piece  27  can be a switching-vane  27 . 1 , which can interrupt a first and a second (fork-)light-barrier  41 . 1 ,  41 . 2 . Corresponding details are shown in  FIG. 3D  and  FIG. 3E . The movement of the switching vane  27 . 1  can coupled with the turning movement of the gripper  21  about the axis LA. 
         [0052]    Through this arrangement, the vertical position of the gripper-fingers  26 . 1 ,  26 . 2  (in this vertical position, in at least some cases, none of the (fork-)light-barriers  41 . 1 ,  41 . 2  is interrupted), or one of the two diagonal end-positions, is detected. In each of the two diagonal end-positions, only one of the two light-barriers  41 . 1 ,  41 . 2  is interrupted. Such a diagonal end-position is recognizable in  FIG. 3D . The vertical position is shown, for example, in  FIGS. 3A and 3B . 
         [0053]    A sensor device  40  with the first and second (fork-)light-barriers  41 . 1 ,  41 . 2  can present a particularly inexpensive and also particularly robust variant. Depending on the state (interrupted by the switching-vane  27 . 1  or not), the two (fork-)light-barriers  41  deliver a digital signal which is directly placed at the disposal of a machine-control of the apparatus  10  or wire-processing machine  1  to control the de-twisting apparatus  6 . In some cases, it is a disadvantage of this sensor device  40  that no intermediate values of the twist of the wire-gripper  21  can be measured or determined, and that also the vertical position of the gripper-fingers  26 . 1 ,  26 . 2  can only be determined approximately if both light-barriers  41  are uninterrupted. However, for the present applications, this type of sensor device  40  is, in at least some cases, adequate. 
         [0054]    Other embodiments can be realized if, instead of the light-barriers  41 . 1 ,  41 . 2 , for example capacitive or inductive proximity switches are employed which, for example, in the case of a certain angular position would also emit the presence of the switching vane  27 . 1  as a digital signal. 
         [0055]    If the angular position of the gripper-fingers  26 . 1 ,  262  should be determined more accurately, another sensor device  40  with other sensors can be employed which, for example, can directly measure the twist of the longitudinal axis LA or of the fork-piece  27 . For this purpose, rotation potentiometers, for example, which deliver an analog voltage value that depends on an angle of rotation, can be used, or absolute-value rotation transducers can be employed. This sensor device  40  then delivers the angular value directly as digital output signal to a machine-control of the apparatus  10  or wire-processing machine  1 . 
         [0056]    Independent of whether the sensors  41 . 1 ,  41 . 2  are optical, capacitive or inductive sensors, or a rotary potentiometer, or an absolute-value rotary transducer, they are part of the sensor device  40 . 
         [0057]    In at least some embodiments, the sensor apparatus  40  can be designed and constructed in such manner that it can also register information about the direction of the twist in the wire-loop  2 . 1 . This information can be useful to enable starting of the de-twisting operation in the correct direction. For this reason, the information about the direction of the twist of the sensor apparatus  40  is passed on to a machine-control of the apparatus  10  or wire-processing machine  1 . However, to determine the direction of the twist, a separate sensor apparatus can also be employed, which operates independent of the sensor apparatus  40 . 
         [0058]    The basis of the twist measurement (i.e. the measurement of the twist and/or the determination of the direction of the twist and/or the determination of the twist-free state) can be that in the pull-out gripper  20 , gripper-fingers  26 . 1 ,  26 . 2  are employed that are rotatably borne about the longitudinal axis LA. Bearing of the gripper-fingers  26 . 1 ,  26 . 2  on a rotatable fork-piece  27  is used in some embodiments. 
         [0059]    Depending on the embodiment, either, first a wire-piece is separated from a wire  2  and then grasped by the means  3 ,  4  (e.g. in interplay of a wire-drive  3  and a loop-layer  4 ) and in interaction with the pull-out gripper  20  formed into a loop  2 . 1 ; or, the loop  2 . 1  is simultaneously formed while the wire  2  is pushed, or pulled, by the wire-drive  3  into the apparatus  10 , as shown in  FIG. 2A . 
         [0060]    After the loop has been laid, the gripper  21  grasps the wire  2  of the wire-loop  2 . 1 . 
         [0061]    In further embodiments, the gripper  21  grasps the wire  2  of the wire-loop  2 . 1  at the start of the loop formation, as shown in  FIG. 2A . Such embodiments can deliver particularly good results in relation to reproducibility and productivity, since the wire-loop  2 . 1  can be constantly held under slight tensile force to prevent crossing. When being formed, the wire-loop  2 . 1  is pulled out taut by means of the movement apparatus  22 . 
         [0062]    If the gripper  21  grasps the wire  2  of the wire-loop  2 . 1  before or during the loop-formation, the gripper  21  is moved through the movement apparatus  22  synchronously with formation of the loop  2 . 1 . In some embodiments, the movement apparatus  22  executes a linear movement of the gripper  21  in the longitudinal direction of the loop  2 . 1 , which corresponds to approximately half of the velocity of the wire  2  in the direction P 1 . If the wire  2  has a velocity v 1  in the direction P 1 , the velocity v 2  of the gripper  21  in the direction P 2  is approximately v 1 /2. 
         [0063]    In some cases, there is monitoring of the twist of the loop  2 . 1  (so-called “twist detection”) and/or monitoring that allows a statement to be made as to whether the twist was successfully removed (detection of the so-called “twist-free state”). Twist-detection and/or detection of the twist-free state can take place at the pull-out gripper  20 , possibly at the gripper  21  itself (e.g. with a sensor device  40 , as already mentioned), or it can take place by means of a separate sensor device  40 . 
         [0064]    A separate sensor device  40  can contain, for example, a CCD camera together with a pattern-recognition software, which is able to digitally analyze an image of the CCD camera and, based on the analysis (e.g. by comparison of a pattern with previously saved images), to allow a statement about the instantaneous twist, including the direction of twist. Such a CCD-based sensor device can also detect the twist-free state by reference to such a pattern-comparison. 
         [0065]    Various alternative embodiments of the pull-out gripper  20  are possible, which can be employed in association with the various embodiments that have been described. 
         [0066]    The functionality of the pull-out gripper  20  can, for example, also be obtained through alternative constructions. For example
       closing and opening of the gripper-fingers  26 . 1 ,  26 . 2  can be directly effected pneumatically, hydraulically, or motor-driven;   movement of the gripper-fingers  26 . 1 ,  26 . 2  into the vertical can be effected by a part that is pressed against the side of the fork-piece  27 ;   movement of the gripper-fingers  26 . 1 ,  26 . 2  into the vertical can be effected by tension springs;   movement of the gripper-fingers  26 . 1 ,  26 . 2  into the vertical can be effected by an electromagnet;   the angular position of the gripper-fingers  26 . 1 ,  26 . 2  can be measured by an (angular) encoder.       
 
         [0072]    The apparatus  10  can also be used in association with machines in which the wire-loop  2 . 1  is formed in different manner, as disclosed, for example, in Patent Application EP0883917 for a wire-processing machine according to the swivel-arm principle that was mentioned at the outset. 
         [0073]    Based on the greatly simplified sketch of the principle of  FIGS. 4A to 4E , described below are exemplary details of the method for forming a wire-loop  2 . 1 . 
         [0074]    In a first step, a wire  2  is inserted into an apparatus  10 , which for this purpose contains a wire drive  3  (here symbolized by two rollers). The leading end of the wire  2  can be grasped by the gripper of a loop layer  4 . The loop layer  4  is embodied in such manner that it can execute a swivel movement along a path  34 . On execution of this swivel movement, the gripper of the loop layer  4  executes, for example, a rotation of 180 degrees. In this manner, the wire loop  2 . 1  is laid. 
         [0075]    After laying the wire loop  2 . 1 , the gripper  21  grasps the wire loop  2 . 1 . This state is shown in  FIG. 4B . For this purpose, the gripper  21  of the pull-out gripper  20  is previously transposed into the open state (as shown, for example, in  FIG. 3A ). The gripper  21  then grasps the wire  2  of the wire loop  2 . 1 , and the gripper  21  is then transposed into a closed state in which it loosely grasps the wire area. This state is shown, for example, in  FIG. 3B . 
         [0076]    A relative movement P 2  of the pull-out gripper  20  relative to the wire drive  3  and the loop layer  4  is executed, so as to apply slight tension in longitudinal direction to the wire loop  2 . 1  during formation of the wire loop  2 . 1 . The final state of this pulling-out movement is shown in  FIG. 4C . 
         [0077]    The two ends of the wire loop  2 . 1  are now transferred to the grippers  5 . 1 ,  5 . 2  of the transfer unit  5 . This instant is indicated in  FIG. 4D . 
         [0078]    For the purpose of transferring the two ends of the wire loop  2 . 1  to the grippers  6 . 1 ,  6 . 2  of the de-twisting apparatus  6 , a lateral movement P 3  is then executed. This instant is indicated in  FIG. 4E . 
         [0079]    A method for de-twisting the wire loop  2 . 1  can now be employed. The direction and/or number of de-twisting turns can be derived from the detected twist. The de-twisting turning takes place about the longitudinal axis of the wire. When executing the de-twisting turning, either, only one of the two grippers  6 . 1  or  6 . 2  of the de-twisting apparatus  6  turns, or, the two grippers  6 . 1  and  6 . 2  turn in opposite directions. 
         [0080]    In some cases, to detect the twist-free state of the wire loop  2 . 1 , a sensor device  40  is employed. As soon as the twist-free state is detected, the method for de-twisting can be terminated. Should no detection of the twist-free state occur, the method for de-twisting can be terminated when a predefined number of de-twisting turns has been executed. 
         [0081]    Having illustrated and described the principles of the disclosed technologies, it will be apparent to those skilled in the art that the disclosed embodiments can be modified in arrangement and detail without departing from such principles. In view of the many possible embodiments to which the principles of the disclosed technologies can be applied, it should be recognized that the illustrated embodiments are only examples of the technologies and should not be taken as limiting the scope of the invention. Rather, the scope of the invention is defined by the following claims and their equivalents. We therefore claim as our invention all that comes within the scope and spirit of these claims.