Abstract:
A method of manufacturing a ribbon cable, comprising providing a set of insulated wires and aligning said insulated wires in a predetermined arrangement. The insulated wires are warmed sufficiently for said insulation to be become soft and adhesive, are pressed together so that they adhere to one another and allowed to cool, to form a ribbon cable.

Description:
RELATED APPLICATIONS 
     The present application is a continuation of U.S. application Ser. No. 10/347,035 filed Jan. 17, 2003 now U.S. Pat. No. 6,766,578 which is a divisional of U.S. application Ser. No. 09/619,121 filed Jul. 19, 2000 now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to ribbon cable and a method of manufacturing the same. 
     At present, ribbon cable is typically produced by setting wires into a molten or partially molten resin and extruding the resultant combination as the resin cools.  FIG. 1  shows a greatly expanded cross-sectional view of a prior art ribbon cable  2  constructed according to this method. A set of wires  4  are set into a resin coating  6 . Note the misalignment of the wires  4 , with some pairs of wires  4  being closer together than others and some wires  4  being at a different vertical level. This manufacturing procedure is perfectly adequate for most of the purposes for which ribbon cable is used. There are some applications, however, for which the availability of ribbon cable having more precisely positioned wires would be greatly beneficial. 
     In some biomedical equipment applications it is necessary to connect each wire of a ribbon cable to a contact pad on a flex circuit. If the wires of the ribbon cable are not precisely aligned, at least one of them might not be able to contact its corresponding contact pad. Currently, manufacturers know how to produce precisely aligned extruded ribbon cables having a dielectric coating of thermoplastic fluoropolymer, tetrafluoroethylene (“TFE,” most commonly marketed under the TEFLON® trademark) being the most well known. Thermoplastic fluoropolymers tend to be relatively hard materials that are difficult to remove using an ND:YAG laser (typically for the purpose of stripping the wires) than are some other dielectric materials such as polyurethane or polyimide. Moreover, the production of extruded, precisely aligned fluoropolymer ribbon cable requires precise adjustments, resulting in an expensive end product. Unfortunately, when a similar extrusion technique is used with polyurethane or polyimide, the product curls up as it comes out of the extruder. Accordingly, it is desirable to broaden the range of dielectric coatings that can be used to produce ribbon cables beyond those that can be made into an extrudable solution, plasma coating or powder coating. 
     It is also desirable to have accurately and uniformly positioned wires in a ribbon cable for the case in which a stack of ribbon cables must be threaded through a fixed size aperture. This situation occurs in the biomedical field in which tolerances for the transmission of signals within a particular spacing can be very tight. If the wires extend in a straight line in each cable, the cables may be stacked in a more compact form, with the ridges of a first ribbon cable fitting into the valleys of a second ribbon cable. 
     SUMMARY 
     In a first separate aspect the present invention is a method of manufacturing a ribbon cable, comprising providing a set of insulated wires and aligning said insulated wires in a predetermined arrangement. The insulated wires are warmed sufficiently for said insulation to become soft and adhesive, are pressed together so that they adhere to one another and allowed to cool, to form a ribbon cable. 
     In a second separate aspect, the present invention is an apparatus for manufacturing a ribbon cable having precisely placed wires, comprising a guide path assembly adapted to draw a set of insulated wires along a predetermined path, at least one heater along said predetermined path, adapted to warm said insulation of said insulated wires until it is soft and adhesive and to press said insulated wires into one another. 
     In a third separate aspect, the present invention is a ribbon cable comprising a set of wires that are aligned to an accuracy of 10 μm and wherein said wires are set into a layer of dielectric material that is softer than tetrafluoroethylene. 
     In a fourth separate aspect, the present invention is a method of producing a ribbon cable comprising the steps of paying out a set of wires, under substantially their maximum bearable tension, through precise place determiners, into a curable resin to form a resin/wire mix and flash curing the resin directly after the resin/wire mix exits the precise place determiners. 
     The foregoing and other objectives, features and advantages of the invention will be more readily understood upon consideration of the following detailed description of the preferred embodiment(s), taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a greatly expanded cross-sectional view of a prior art ribbon cable. 
         FIG. 2  is a perspective view of an apparatus for producing ribbon cable according to the present invention. 
         FIG. 3  is a side view of the apparatus of  FIG. 2 . 
         FIG. 4  is a greatly expanded view of a roller groove of the apparatus of  FIG. 2 , accommodating insulated wires, according to the method of the present invention. 
         FIG. 5  is a greatly expanded cross-sectional view of a ribbon cable according to the present invention. 
         FIG. 6  is a greatly expanded cross-sectional view of a ribbon cable made up of a set of coaxial cables according to an alternative preferred embodiment of the present invention. 
         FIG. 7  is a side view of an alternative apparatus for producing ribbon cable according to the present invention. 
         FIG. 8  is a greatly expanded cross-sectional view of an alternative embodiment of a ribbon cable. 
         FIG. 9  is a side view of an additional alternative apparatus for producing ribbon cable according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A ribbon cable production assembly  10  includes a pay off wire guide assembly  12  having a pair of rollers  14 . A set of insulated wires  16  is threaded through the pay off wire guide assembly  12  and from there travels through a comb assembly  18 , having a set of precise place determiners  19  that ensure that each wire of set  16  maintains its position relative to the other wires of set  16 . After this the wires  16  travel through a heater assembly  30  having two heated, grooved rollers  32 , and a proximity heater  36 . Rollers  32  both guide and heat wires  16 . Heater  36  on the other hand does not touch wires  16  but merely warms them with its radiant heat. 
     Each insulated wire  16  has a conductive core  20  bearing an inner layer  22  of insulation and an outer layer  24  of insulation. Each inner layer  22  is made of polyurethane or polyimide and each outer layer  24  is a thin, heat sealable layer of nylon material  24 . The nylon outer layer  24  has a melting point of approximately 174° C. (310° F.). Polyimide has a melting point that is considerably higher than that of nylon. As a result, the nylon outer layer  24  softens at the temperature of the rollers, but the polyimide inner coating is left unchanged by the heat. More specifically the exterior surfaces of rollers  32  are controlled to stay at about 174° C. (310° F.), preferably by a PID controller (informed by a temperature measurement device [not shown]), so that they soften the nylon layer  24  as it touches this surface. The softened nylon layers  24  of neighboring insulated wires  16  adhere to one another, thereby forming a ribbon cable out of the individual insulated wires  16 . Wire with dual, concentric coatings of polyimide and nylon can be made to order by Rea Wire of Fort Wayne, Ind. 
     Each roller  32  has a set of grooves or troughs  34 . All of the insulated wires  16  are brought together into a single groove  34  of rollers  32  and are heated and gently pushed together in the single groove  34 . In one preferred embodiment each groove  34  has a different radius of curvature, so that various gauge wires can be accommodated. For insulated wires  16  each having a nominal outer radius of 36.75 μm (1.5 mils), a groove having a radius of curvature of 1 mm works well.  FIG. 4  shows the very bottom of a groove  34  filled with wires  16  for this case. It may be noted that even though a 1 mm radius of curvature may sound like a narrow groove to those unfamiliar with the scale used for ribbon cable of this sort, it is not only ample to accommodate the wires  16  but also represents such a gradual curve that no cross-sectional curvature is imparted to the ribbon cable produced. In another note, it has been found that a wire speed of about 1 inch per second produces a sound product. 
     Rollers  32  each have an exterior covering of nonstick material, such as tetrafluoroethylene (most commonly sold under the trademark TEFLON®). This prevents any insulated wire  16  from sticking to a portion of the roller and thereby failing to move into contact with the other wires  16 . 
     Next, insulated wires  16  pass through a dancer assembly  40 , which measures the tension on wires  16 , so that this information can be used to control a take up assembly  50 , to keep the wires under a constant, acceptable level of tension. Dancer assembly  40  works by passing the wires  16  over a first guide wheel  42 , under a dancer wheel  44  (blocked from view in  FIG. 2 ) and over a second guide wheel  46 . The dancer wheel  44  is urged downwardly and to the side by a spring so that its position is dependent on the tension in wires  16 , which pull the other way. The final result of this entire process is a finished ribbon cable  52 . 
     In one preferred embodiment the insulated wires  16  are gauge 50 AW wires having a nominal outer diameter of 36.75 μm (1.5 mils), so that if 8 wires were used the total width of the ribbon cable would be about 294 μm (12 mils). Wires  16  may be made of the copper alloy that goes by the industry standard designation of CA-108. It should be noted that the example of an 8-wire ribbon cable is used merely for ease of explanation. A more typical number of wires would be 32, although there is no maximum or minimum number of wires that must be used. One preferred embodiment includes at least one wire  16 ′ that has a core  20 ′ made of a high tensile strength material such as high tensile strength steel and is not used for conducting electricity but instead is used to impart strength to the overall ribbon cable  52 . There are many operations where it is necessary to direct a ribbon cable  52  by pulling it or otherwise handling the ribbon cable  52 . The physical strength imparted by a wire having high tensile strength facilitates this type of operation. In an alternative preferred as shown in  FIG. 6 , a set of coax cables,  16 ′ and having an outer dielectric layer  22 ′, an outer conductive layer  20 ′, an inner dielectric layer  22 ″ and an inner conductor  20 ″. 
     A first alternative preferred embodiment is shown in  FIGS. 7 and 8 . In  FIG. 7  features that are identical to features in  FIGS. 2 and 3  are given the same reference numbers. A tape  60  having a backing  62  ( FIG. 8 ) of Kapton® or liquid crystal polymer and a face  64  ( FIG. 8 ) of nylon or a similar polyethylene is fed past a payout roller  66  and past a heated roller  68 , where the face  64  is melted and wires  72  (the same as wire cores  20  but initially without the dielectric layers  22  and  24 ) are accepted into the molten face  64  of tape  60  and further pressed together by TFE coated nip rollers  70 , to form a completed ribbon cable  74  ( FIG. 8 ). In a variant of the first preferred embodiment, comb assembly  18  is moved as close as possible to heated roller  68 . To achieve this end, different styles of comb assemblies may be used, for example, ones having less of a range of adjustment than comb assembly  18  and which, accordingly, could be positioned far closer to heated roller  68 . 
     A second alternative preferred embodiment is shown in  FIG. 9 . In this embodiment, an extruder  71  places molten dielectric extrudate  73  atop wires  72 . The wires and the extrudate  73  are pressed together by nip rollers  70  and flash cured by UV light source  76 . In the lexicography of this patent, this is considered to be directly after the resin/wire mix leaves the precise place determiners  19 . In a variant, there is no UV light source  76  and extrudate  73  and nip rollers  70  are heated to cure extrudate  73 . In this embodiment, and the first alternative preferred embodiment, wires  72  are maintained at close to their maximum bearable tension, in order to maintain them in an extremely straight and unwavering alignment. In a variant of the second alternative embodiment UV source  76  is placed upstream (to the left of [in  FIG. 9 ]) of nip rollers  70  so that the extrudate  73  can be cured as soon as it joins with the wires  72 . Similar to the variant of the first preferred embodiment, extruder  71  may also be moved as close as possible to comb  18 , to help ensure proper spacing of wires  72 . In this manner the extrudate is cured directly after leaving the precise place positioners  19  of comb assembly  18 . In another variant, the wires  72  pass through the extruder  71  and a set of precise place determiners are positioned where the wires  72  exit extruder  71 . 
     The terms and expressions which have been employed in the foregoing specification are used as terms of description and not of limitation, and there is no intention, in the use of such terms and expressions, of excluding equivalents of the features shown and described or portions thereof, it being recognized that the scope of the invention is defined and limited only by the claims which follow.