Abstract:
A method of monitoring a crimping process is disclosed, which determines whether an actual force stroke progression (Fa)/force time progression is, a) above, or, b) below an ideal force stroke progression (Fi)/force time progression in at least one point. The method shifts an upper border (Bu) and/or the lower border (Bl) of a tolerance band upwards in case a) and downwards in case b). Additionally, there is an absolute upper limit (Lu), at which an upward shifting of the upper border (Bu) is inhibited, and an absolute lower limit (Ll), at which a downward shifting of the lower border (Bl) is inhibited. Moreover, a crimping press and a computer program product for employing the inventive method are disclosed.

Description:
This application is a section 371 national-phase entry of PCT International application no. PCT/IB2010/051530 filed on Apr. 8, 2010 and published as WO2010/116339A1 on Oct. 14, 2010; application no. PCT/IB2010/051530 claims benefit of priority to Swiss application no. 0580/09 filed on Apr. 9, 2009, and claims benefit as a non-provisional of prior U.S. provisional application No. 61/168,212 filed on Apr. 9, 2009; the entireties of PCT International application no. PCT/IB2010/051530, of Swiss application no. 0580/09 and of prior U.S. provisional application No. 61/168,212 are all expressly incorporated herein by reference in their entirety, for all intents and purposes, as if identically set forth herein. 
    
    
     TECHNICAL FIELD 
     The invention relates to a method of monitoring a crimping process, comprising the steps of determination whether an actual force stroke progression/force time progression occurring during crimping is within a tolerance band in at least one point, the tolerance band having an upper border above and a lower border below an ideal force stroke progression/force time progression and qualifying a crimp as passed, for which said condition is true. Furthermore, the invention relates to a crimping press for employing the inventive method, comprising means for determination whether an actual force stroke progression/force time progression occurring during crimping is within a tolerance band in at least one point, the tolerance band having an upper border above and a lower border below an ideal force stroke progression/force time progression and means for qualifying a crimp as passed, for which said condition is true. Finally, the invention relates to a computer program product, which when loaded into the memory of a control for a crimping press performs the function of the crimping method. 
     BACKGROUND OF THE INVENTION 
     Crimping, which is a special kind of beading, is a method for joining parts, in particular a wire with a connector (often having the shape of a plug), by plastic deformation. The resulting permanent joint provides good electrical and mechanical stability and is thus a suitable alternative to other connecting methods such as welding or soldering. Hence, common fields of application for crimping are electric devices (e.g. for telecommunication, electrical equipment for vehicles, etc.). The shape of a crimp should exactly be adapted to the wire so as to provide for a predetermined deformation of the same. Crimping usually is done by a crimping gripper or a crimping press. 
     According to prior art, the force acting during the crimping process can be measured to monitor and/or ensure a constant quality of crimp connections manufactured by a crimping press. For example, pressure sensors are utilized for this reason, which measure the force between the frame and the die ( 14 ) and/or the drive and the plunger ( 15 ) (see  FIG. 5 ). A further possibility is to evaluate the deformation of the frame of a crimping press. 
     For example, U.S. Pat. No. 5,841,675 A discloses a method of monitoring the quality of crimping process. To ensure a particular quality, the peak factor, which is defined as crimp work divided by peak force, is determined. The method includes setting the boundaries based upon the mean and standard deviation of a number of learned samples. 
     Furthermore, U.S. Pat. No. 6,418,769 B1 discloses a method of monitoring a crimping process, wherein a force stroke progression occurring during crimping is measured and compared to a nominal force stroke progression. The evaluation is done above a particular threshold value. 
     In addition, EP 1 243 932 A2 discloses a method of monitoring a crimping process, wherein a force time progression occurring during crimping is measured, the crimping work is calculated, said progression is separated in segments and the actual work of a segment is compared to a nominal work. 
     Moreover, U.S. Pat. No. 5,937,505 A, discloses a method of monitoring a crimping process, wherein a force stroke progression occurring during crimping is measured and checked whether it is within a reference region. Statistical theory is utilized to develop a continuous band of allowable variation in the progression. 
     Furthermore, EP 0 460 441 B1 discloses a method of monitoring a crimping process, wherein a force stroke progression occurring during crimping is measured. A group of data element pairs is selected from said progression in an interesting region. This group of data element pairs is analyzed and compared to a standard group of pairs taken during a known high quality crimp cycle to determine the quality of the present crimped connection. 
     Finally, EP 0 730 326 A2 discloses a method of evaluating a crimped electrical connection, which measures the crimping force over a range of positions of the crimping apparatus ram and derives a statistical envelope of acceptable forces. Each crimp is measured and the force measurements are compared against that envelope to determine the acceptability of the crimp. Acceptable crimps are then further evaluated to determine whether their data should be added to the data base. 
     However, despite all measures, which have been taken to make the decision whether a crimp connection is qualified a good (passed) or bad (failed) “fuzzy”, meaning allowing some variation of the crimps, there is still room for improvement. 
     SUMMARY OF THE INVENTION 
     Thus, the invention provides an improved method of monitoring a crimping process, an improved crimping press, and an improved computer program product, in particular to reduce the need for manual intervention during crimping. 
     This is achieved by a method of monitoring a crimping process of the kind disclosed in the first paragraph, additionally comprising the steps of:
         determination whether said actual force stroke progression/force time progression is a) above or b) below said ideal force stroke progression/force time progression in at least one point and   shifting the upper border and/or the lower border upwards in case a) and downwards in case b), wherein there are an absolute upper limit, at which an upward shifting of the upper border is inhibited, and an absolute lower limit, at which a downward shifting of the lower border is inhibited.       

     Furthermore, the invention enables a crimping press for manufacturing crimp connections of the kind disclosed in the first paragraph, additionally comprising:
         means for determination of whether said actual force stroke progression/force time progression is a) above or b) below said ideal force stroke progression/force time progression in at least one point, and,   means for shifting the upper border and/or the lower border upwards in case a) and downwards in case b), wherein there are an absolute upper limit, at which an upward shifting of the upper border is inhibited, and an absolute lower limit, at which a downward shifting of the lower border is inhibited.       

     The invention also provides a computer program product, which when loaded into the memory of a control for a crimping press performs the function of the inventive method. 
     By means of these features, the tolerance band for passed crimps is adapted to changing conditions. There may be slight variants of the wire and/or the crimps (e.g. thickness of material, material characteristics, etc.), changing temperature, drifts of the force sensor and/or stroke sensor, etc. According to prior art, an operator has to monitor these changes directly or indirectly via their influence on the crimp connection and take according measures. This involves a lot of (ongoing) adjustments which can get cumbersome if, for example, an operator of a crimping press has to counteract the rising temperature in the morning, day by day. The present method enables the crimping press respectively its control to adapt themselves to changing conditions. If, for example, a series of crimps have their respective force stroke progressions or force time progressions systematically above an ideal force stroke progression or force time progression, the upper border and/or lower border are shifted upwards. Thus, crimp connections, whose force stroke progression or force time progression is below the new upper border but above an older upper border, are still considered as passed. In this way, the need for manual intervention may be significantly reduced. 
     Furthermore, there is an absolute upper limit, at which a further upward shifting of the upper border is inhibited, and also an absolute lower limit, at which a further downward shifting of the lower border is inhibited. Apart from dynamically shifting a tolerance band, it is useful for an operator to set absolute limits, beyond which the borders of the tolerance band may not move. Otherwise, it could happen that—as it is the case in EP 0 730 326 A2—a series of bad crimps cause the tolerance band to be shifted far away from that crimp (i.e., its force stroke progression or force time progression) considered to be ideal. In such circumstance, crimps, that are qualified as bad in the beginning of the adaptive algorithm, may be undesirably qualified as good at some point in time because of the drifting of the tolerance band. However, one will easily appreciate that said behavior is undesirable, as crimps could get worse and worse without any alert. 
     The method may be performed for just one point of the force progression or for a plurality of points. Of course it is beneficial for the overview to check points spread over the complete force progression. However, to save computing power, it is advantageous to perform the method above a particular threshold value of the force and to focus to a region in which the actual crimping takes place. 
     Initially, the ideal force progression can be determined during a so-called “teach in process”. Here, the force progressions of several crimps are stored, and if the operator of the crimping press considers the crimps to be good (e.g. based on the height or width of the crimp, electrical characteristics, visual inspection, grinding pattern, etc.), the stored progressions are used to generate an ideal force progression. This can be done based on the least mean square method, for example. 
     The elements of the crimping press, include elements for determination whether an actual force stroke progression/force time progression occurring during crimping is within a tolerance band, means for qualifying a crimp as passed or failed, means for determination whether said actual force stroke progression/force time progression is a) above, or, b) below said ideal force stroke progression/force time progression, and means for shifting the upper border and/or the lower border upwards in case a) and downwards in case b) may be embodied in software or hardware or combinations thereof. Furthermore, these elements may be part of a (separate) control for the crimping press. In a preferred version, the means are embodied in software and are in the form of software functions or software routines which may be programmed in any suitable programming language and are stored in a memory of a crimping press control. As is known per se, said code is loaded into a central processing unit of the crimping press respectively its control for execution. 
     Advantageous versions of the invention are disclosed in the written content and the figures of this application. 
     It is advantageous if there are a first zone above and a second zone below said ideal progression and that
         the upper border and/or the lower border is shifted upwards if the actual progression is within said first zone, and   the upper border and/or the lower border is shifted downwards if the actual progression is within said second zone.
 
Adaptation of the crimping process can take place by means of zones, which control the shift of the tolerance band, i.e. the upper and lower border. In this context it is beneficial, if the first zone and the second zone are spaced from the ideal progression. In this way, the algorithm can be made “slow”. That means that not each and every deviation from an ideal crimp causes a shift of the tolerance band. Hence, a kind of hysteresis is employed.
       

     Furthermore, it is beneficial in this context if the first zone and the second zone are adjacent to the ideal progression. In this way, the algorithm can be made “fast”. It is very unlikely, that a crimp is absolutely identical to an ideal crimp. So, probably many crimps will cause a shift of the tolerance band. 
     Moreover, it is beneficial in this context if the upper border is spaced from the first zone and the lower border is spaced from the second zone. In this way, the algorithm can be made slow again, as crimps, whose force stroke progression or force time progression is far away from the ideal progression, do not influence the adaptation of the tolerance band. 
     Finally, it is beneficial in this context if the upper border is adjacent to the first zone and the lower border is adjacent to the second zone. In this way, the algorithm can be made fast again, as crimps, whose force stroke progression or force time progression is far away from the ideal progression, influence the adaptation of the tolerance band. 
     In another advantageous embodiment of the invention, there are a first zone near above, a second zone near below, a third zone far above, and a fourth zone far below said ideal progression and
         the lower border is shifted upwards if the actual progression is within said first zone,   the upper border is shifted downwards if the actual progression is within said second zone,   the upper border is shifted upwards if the actual progression is within said third zone, and   the lower border is shifted downwards if the actual progression is within said fourth zone.
 
The inventor has found out that such a configuration is of particular advantage as the borders move “smoothly”, meaning not too fast and not too slow. In this way, a particular crimp quality can be ensured over a long period of time and/or a broad range of disturbing influences.
       

     In this context it is beneficial, if the first zone is adjacent to said ideal progression, the third zone is adjacent to the first zone, the second zone is adjacent to said ideal progression, and the fourth zone is adjacent to the second zone. This algorithm is a fast one as many crimps cause a change of the tolerance band. 
     Furthermore, it is beneficial in this context if the first zone is adjacent to said ideal progression, the third zone is spaced from the first zone, the second zone is adjacent to said ideal progression, and the fourth zone is spaced from the second zone. This algorithm is a slower one as few crimps cause a change of the tolerance band. It is suitable for crimping presses very well. 
     Moreover, it is beneficial in this context if the upper border is spaced from the third zone and the lower border is spaced from the fourth zone. Again, the algorithm can be made slow, as crimps, whose force stroke progression or force time progression is far away from the ideal progression, do not influence the adaptation of the tolerance band. This algorithm is suitable for crimping presses very well, too. 
     Finally, it is beneficial in this context if the probability that a crimp is within any one of the first to fourth zone is substantially equal for all zones. In this way, convergence of the upper border and lower border towards the standard derivation 3σ after the inventive method has been performed often enough (e.g. 1000 times) can be achieved. 
     In yet another advantageous version of the invention, instead of or in addition to the force a physical variable derived from the force is used for the method. In addition or alternatively to the force also, for example, the crimping work may be the foundation for the method. Furthermore, the first derivative of the force may be said foundation. 
     Finally, it is advantageous if the mean value of the tolerance band gets the ideal force progression after a predetermined number of cycles of the inventive method. According to this embodiment, not only the tolerance band changes but also the ideal force progression, i.e. the perception of what is an ideal crimp connection. Thus, changing influences on the crimping process can be handled even better. 
     It should be noted at this stage that the versions and variants of the invention as well as the associated advantages discussed for the inventive method are equally applicable to the inventive crimping press and the inventive computer program product. 
     The versions disclosed hereinbefore may be combined in any desired way. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention is discussed hereinafter by means of schematic figures and drawings, which help illustrate the invention. These figures, drawings and embodiments are not, however, intended to limit the broad scope of the invention. The Figures show: 
         FIG. 1  an ideal force stroke progression vs. an actual force stroke progression and a tolerance band; 
         FIG. 2  the ideal progression and a tolerance band after several cycles of the inventive method; 
         FIG. 3   a  an embodiment with two zones for controlling the shift of the tolerance band; 
         FIG. 3   b  similar to  FIG. 3   a  but with the zones being spaced from the ideal force progression; 
         FIG. 3   c  similar to  FIG. 3   a  but with the zones being spaced from the upper and lower border; 
         FIG. 3   d  similar to  FIG. 3   a  but with the zones being spaced from the ideal force progression and the upper and lower border; 
         FIG. 4  an embodiment with four zones for controlling the shift of the tolerance band; 
         FIG. 5  a complete crimping press depicts  15  a plunger and  14  a die. 
     
    
    
     DESCRIPTION 
     In the following description and appended claims, the term “force progression” shall be used to mean both force-stroke progression and force-time progression unless specifically indicated otherwise. 
       FIG. 1  schematically shows an ideal force stroke progression (that means an ideal force stroke diagram or graph of an ideal crimp) Fi, an actual force stroke progression (that means an actual force stroke diagram or graph currently occurring crimping) Fa in dashed lines, an upper border Bu of a tolerance band and a lower border Bl of the tolerance band. Crimps having a force stroke graph Fa within the tolerance band are qualified as passed in this example. As can be seen, the actual force stroke progression Fa is below the ideal progression Fi in a first part of the diagram, above it in a second part of the diagram and again below it in a third part of the diagram. Arrows indicate whereto the tolerance band respectively its borders Bu and Bl move respectively are shifted. 
     One skilled in the art will easily appreciate that the teachings disclosed hereinbefore and hereinafter are equally applicable to force-time progressions though just force-stroke progressions are depicted for simplicity in the Figures. 
       FIG. 2  shows the ideal force progression Fi of  FIG. 1  and a tolerance band after several cycles of the inventive method. One can see that the tolerance band has several dents, which are caused by crimps deviating from the ideal crimp. One can also see that the width of the band is not constant but may increase and decrease during the course of time. Furthermore, the inventive method is executed only above a particular threshold force Ft in this embodiment. Thus, the evaluation is focused to a region of interest as here the crimping actually takes place. In addition, points are depicted, at which the inventive method is executed. However, instead of points, regions or ranges in which the method is executed, are also contemplated. 
       FIGS. 3   a  to  3   d  and  4  show details of force stroke progressions of the kind shown in the  FIGS. 1 and 2 , i.e., particular points or regions/ranges, at which the inventive method is executed. 
       FIG. 3   a  shows a first version, wherein a first zone Z 1  and a second zone Z 2  are used to control the shifting of the upper border Bu or the lower border Bl. If the actual progression Fa is within said first zone Z 1 , the upper border Bu and/or the lower border Bl is shifted upwards. If the actual progression Fa is within said second zone Z 2 , the upper border Bu and/or the lower border Bl is shifted downwards.  FIG. 3   a  shows that the first and the second zones Z 1  and Z 2  are adjacent to the ideal force progression Fi and the upper border Bu respectively the lower border Bl. In addition, an absolute upper limit Lu, at which an upward shifting of the upper border Bu is inhibited, and an absolute lower limit Ll, at which a downward shifting of the lower border Bl is inhibited, is shown in  FIG. 3   a . This algorithm is rather fast, as every crimp that qualifies as “passed” and which is not “totally” ideal by chance, causes a shift of the upper border Bu and/or the lower border Bl. 
       FIG. 3   b  is quite similar to  FIG. 3   a . The only difference is that the first and the second zones Z 1  and Z 2  are spaced from the ideal force progression Fi. This causes the algorithm to respond a bit slower as crimps that are almost ideal (near Fi, between Z 1  and Z 2 ), do not cause a shift of the upper border Bu and/or the lower border Bl. 
       FIG. 3   c  shows another version similar to that shown in  FIG. 3   a . Here the first zone Z 1  is spaced from the upper border Bu and the second zone Z 2  is spaced from the lower border Bl. Again, this causes the algorithm to respond a bit slower as passable crimps that are farther away from being ideal do not cause a shift of the upper border Bu and/or the lower border Bl. 
       FIG. 3   d  finally shows a last version utilizing first Z 1  and second Z 2  zones, similar to that shown in  FIG. 3   a . Here the first and the second zone Z 1  and Z 2  are spaced both from the ideal force progression Fi as well as from the upper border Bu, respectively, and the lower border Bl, respectively. This version is rather slow, but also rather stable. 
       FIG. 4  depicts yet another version. A first zone Z 1  is arranged near above, a second zone Z 2  near below, a third zone Z 3  farther above, and a fourth zone Z 4  farther below relative to ideal force progression Fi. If the actual progression Fa is within said first zone Z 1 , the lower border Bl is shifted upwards. If the actual progression Fa is within said second zone Z 2 , the upper border Bu is shifted downwards. If the actual progression Fa is within said third zone Z 3 , the upper border Bu is shifted upwards and if the actual progression is within said fourth zone Z 4  the lower border Bl is shifted downwards. This version performs particularly smooth changes and is very well suitable for crimping presses. 
     According to this version, the first zone Z 1  is adjacent to and above said ideal progression Fi, the third zone Z 3  is spaced separated above from the first zone Z 1 , the second zone Z 2  is adjacent to and below said ideal progression Fi, and the fourth zone Z 4  is spaced separated below from the second zone Z 2 . Furthermore, the upper border Bu may be spaced from the third zone Z 3  and the lower border Bl may be spaced from the fourth zone Z 4 . This variant is even better suitable for the crimping process. 
     In one real implementation, the force stroke progression is separated into 1024 segments, and in each segment it is determined if the actual force is within one of the zones Z 1  . . . Z 4 . In this way, the crimping process can be monitored and controlled very accurately. 
     If the probability that a crimp is within any one of the first to fourth zone Z 1  . . . Z 4  is substantially equal for all zones Z 1  . . . Z 4 , convergence of the upper border Bu and lower border Bl towards the standard derivation  3   a  can be achieved. Hence 99.73% of all crimps are considered as passed. 
     Generally the ratio between the first and the fourth zone Z 1  and Z 4  defines the limiting value of the lower border Bl and the ratio between the second and the third zone Z 2  and Z 3  defines the limiting value of the upper border Bu. One skilled in the art will easily appreciate that the upper and lower border Bu and Bl do not necessarily have to have the same distance to the ideal force progression Fi, but may be set independently by different ratios between the zones Z 1  . . . Z 4 . While the ratio defines the limiting value, the size of the zones Z 1  . . . Z 4  defines the convergence speed. The bigger the zones Z 1  . . . Z 4  are, the faster the algorithm is as the probability that a crimp connection falls within a zone Z 1  . . . Z 4  is increased. In an advantageous embodiment the outer zones, i.e. the third and the fourth zone Z 3  and Z 4  have a width of 1/18 of the distance between the ideal force progression Fi and the borders Bu and Bl. 
     Note that although the zones Z 1  . . . Z 4  have the same width, the probability that a crimp is within any one of the first to fourth zone Z 1  . . . Z 4  is not equal. By contrast, the probability for the first and the second zone Z 1 , Z 2  is higher as the Gaussian distribution is higher in the center region. Accordingly, the first and the second zones Z 1  and Z 2  have to be smaller than the third and the fourth zones Z 3  and Z 4  if the probability for all zones Z 1  . . . Z 4  shall be equal. Concretely, the area under the Gaussian distribution must be equal for all zones Z 1  . . . Z 4  then. 
     In one real version of a crimp press of the applicant, the operator inputs the percentage of the desired passed (or failed) crimps. Then the control of the crimp press computes the ratio between the zones Z 1  . . . Z 4  associated with said percentage and also determines an absolute size of the zones Z 1  . . . Z 4  depending on a desired convergence speed. In many cases setting a percentage of passed crimps to 99.73% (standard derivation 3σ) and a width of the third and the fourth zone Z 3  . . . Z 4  to 1/18 of the distance between the ideal force progression and the borders Bu and Bl will lead to satisfying results. 
     One skilled in the art will easy perceive that the inventive method as shown in the drawings is equally applicable to physical values derived from the force F as, for example, crimping work or first derivative of the force. 
     In a particular advantageous version, the mean value of the tolerance band gets the ideal force progression Fi after a predetermined number of cycles of the inventive method. For example, this change may take place every 50 crimps. In this way, the zones Z 1  . . . Z 4  can be adapted to a “new” ideal crimp that in turn influences the inventive algorithm. The absolute upper and lower limit Lu and Lo may change as well or may stay. The first alternative, however, involves the risk that the process “drifts away” as itself can change its limitations. All in all it is more useful to keep the absolute upper and lower limit Lu and Lo fixed in most cases. 
     Finally, it should be noted that the above-mentioned explanations illustrate rather than limit the invention, and that those skilled in the art will be capable of designing many alternative embodiments without departing from the scope of the invention as defined by the appended claims. The scope of the present invention is defined by the appended claims, including known equivalents and unforeseeable equivalents at the time of filing of this application. In the claims, any reference signs placed in parentheses shall not be construed as limiting the claims. The verb ‘comprise’ and its conjugations do not exclude the presence of elements or steps other than those listed in any claim or the specification as a whole. The singular reference of an element does not exclude the plural reference of such elements and vice-versa. In a device claim enumerating several means, several of these means may be embodied by one and the same item of software or hardware. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. 
     LIST OF REFERENCES 
     
         
         Bl lower border 
         Bu upper border 
         F force 
         Fa actual force progression 
         Fi ideal force progression 
         Ft threshold force 
         Ll absolute lower limit 
         Lu absolute upper limit 
         s stroke 
         Z 1  . . . Z 4  first to fourth zone 
           14  die 
           15  plunger