Abstract:
A down-hole tool includes a first and second portion that are moveable relative to one another, but are electrically coupled together. A rigid tube formed into a helical coil extends between the first and second portions. The helical coil is expandable and compressible in response to movement between the first and second portions. A conductor is positioned within the helically wound tube and is adapted to pass electrical signals between the first and second portions.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention is generally related to flexible electrical connectors, and, more particularly, to a helical spring shaped electrical connector useable in a high-temperature environment. 
     2. Description of the Related Art 
     Electronic devices are commonly formed from a plurality of parts that may be moveable relative to one another, but need to be electrically joined together. For example, a telephone normally consists of a base unit and a handset joined together by an electrical connector, such as a cable. Ordinarily, the telephone cable is formed in a helical coil so that it is at least somewhat self-storing. That is, telephone cables as long as 20 feet may be useful to provide a limited range of mobility to the telephone user; however, storing 20 feet of cable may be inconvenient and cumbersome. The helical construction of the cable is expandable/compressible so that when not in use, a large quantity of cable can be stored in a relatively small area, and when in use, the cable can be dramatically expanded to extend the range of use of the telephone. 
     Other electronic devices are constructed from multiple moveable parts that would benefit from an expandable/compressible connection, such as that used in a telephone. For example, tools used in the well drilling/logging industry are routinely constructed from multiple moving parts that may need to be electrically connected together. Tools used in the well drilling/logging industry are commonly exposed to high-temperature environments that would adversely impact the materials used to construct ordinary telephone cables. That is, high temperature reduces the ability of the cable to return to a compressed state after being expanded. Moreover, ordinary telephone cables are relatively flexible and tend to sag under their own weight, particularly when installed horizontally. This sagging and failure to return to a compressed state can result in the cable interfering with the movement and operation of the tool, and may even cause damage or destruction of the cable. 
     The present invention is directed to a method and apparatus that solves or reduces some or all of the aforementioned problems. 
     SUMMARY OF THE INVENTION 
     In one aspect of the present invention, a method is provided for forming a helical connection. The method includes inserting a conductor through a rigid tube. Thereafter, the tube is wound in a helical configuration, and then annealed. 
     In another aspect of the present invention, a helical connection is provided. The helical connection includes a rigid tube formed into a helical coil than annealed, and a conductor positioned within the helically wound tube. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention may be understood by reference to the following description taken in conjunction with the accompanying drawings, in which like reference numerals identify like elements, and in which: 
     FIG. 1 is an interior perspective view of a portion of a down-hole tool in a compressed configuration; 
     FIG. 2 is an interior perspective view of the down-hole tool in an expanded configuration; and 
     FIG. 3 is a side view of a helically coiled electrical connector of FIGS. 1 and 2 in a stage of manufacture. 
    
    
     While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the description herein of specific embodiments is not intended to limit the invention to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims. 
     DETAILED DESCRIPTION OF THE INVENTION 
     Turning now to the drawings, and in particular to FIG. 1, an interior perspective view of a portion of a down-hole tool  10  is shown in a compressed configuration. The down-hole tool  10  includes a fixed portion  12  coupled to a moveable portion  14  via a ball-screw device  16 . As is conventional, rotation of the ball-screw device  16  is effected by rotation of a motor (not shown), which causes the moveable portion  14  to translate along a longitudinal axis  18  of the down-hole tool  10 . 
     In the illustrated embodiment, it is useful for an electrical and/or optical connection  20  to exist between the fixed and moveable portions  12 ,  14 . The connection  20  may be used to supply electrical power and/or communication signals between the fixed and moveable portions  12 ,  14 . In the illustrated embodiment, the connection  20  is formed in a helical configuration so that it can expand and contract as dictated by movement of the fixed and moveable portions  12 ,  14 . As shown in FIG. 2, the down-hole tool  10  is configured so that the moveable portion  14  can be translated a significant distance along the longitudinal axis  18 . For example, in one embodiment the helical connection  20  is expandable by about 600% relative to its compressed configuration. 
     For ease of illustration, the ball screw device  16  is shown with only a portion of its longitudinal surface having a helical groove  22  formed therein. In the actual embodiment, the helical groove  22  extends along the entire length of the ball screw device  16  so as to permit movement of the moveable portion  14  along the corresponding length of the ball screw device. The down-hole tool  10  illustrated in FIGS. 1 and 2 is commonly used in horizontal bore-holes. Thus, any sagging in the connection  20 , particularly in the expanded configuration of FIG. 2, can result in the coils of the connection  20  being inadvertently captured and damaged by the helical groove  22 . Likewise, any failure of the helical connection  20  to return to its fully compressed configuration, as shown in FIG. 1, can also result in damage and ultimate failure of the helical connection  20 . The helical connection  20  needs to meet the competing requirements of being capable of substantial non-deforming expansion (600% in the illustrated embodiment) while not experiencing substantial sagging. 
     Turning now to FIG. 3, a side view of one embodiment of the helical connection  20  is shown. A relatively stiff but deformable tube  30  is shown helically wound about a mandrell  31  during a stage of manufacture of the helical connection  20 . Prior to being helically wound about the mandrell  31 , a conductor  32  is inserted through the tube  30 . The conductor  32  can take on any of a variety of configurations, including but not limited to electrically conductive and fiber optic materials. In one embodiment, the conductor  32  includes an electrically conductive metal  34 , such as copper or tin copper, surrounded by an insulator  36 , such as TFE. In one embodiment, the conductor  32  is 26 awg TFE wire. 
     The tube  30  may likewise be constructed of a variety of materials and sizes, as dictated by the particular application. In one embodiment, the tube  30  is constructed from stainless steel. The tube  30  may be constructed having a variety of different inner and outer diameters, which may affect the resulting fatigue life, stiffness, deformation characteristics, and durability of the resultant spring. Table I illustrates the relationship between the wall thickness of the tube  30  and the stress experienced by the tube  30  during movement through its expected range of travel. 
     
       
         
               
               
               
             
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                   
                 % of Ultimate 
                   
               
               
                 Tube OD 
                 Tensile Strength 
                 Tube ID 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 0.04 
                 0.159604 
                 0.038 
               
               
                 0.041 
                 0.167687 
                 0.038 
               
               
                 0.042 
                 0.175973 
                 0.038 
               
               
                 0.043 
                 0.184462 
                 0.038 
               
               
                 0.044 
                 0.193155 
                 0.038 
               
               
                 0.045 
                 0.202052 
                 0.038 
               
               
                 0.046 
                 0.211153 
                 0.038 
               
               
                 0.047 
                 0.220458 
                 0.038 
               
               
                 0.048 
                 0.229967 
                 0.038 
               
               
                 0.049 
                 0.239682 
                 0.038 
               
               
                 0.05 
                 0.249601 
                 0.038 
               
               
                 0.051 
                 0.259725 
                 0.038 
               
               
                 0.052 
                 0.270055 
                 0.038 
               
               
                 0.053 
                 0.28059 
                 0.038 
               
               
                 0.054 
                 0.291331 
                 0.038 
               
               
                 0.055 
                 0.302278 
                 0.038 
               
               
                 0.056 
                 0.313432 
                 0.038 
               
               
                 0.057 
                 0.324792 
                 0.038 
               
               
                 0.058 
                 0.336358 
                 0.038 
               
               
                 0.059 
                 0.348132 
                 0.038 
               
               
                 0.06 
                 0.360113 
                 0.038 
               
               
                   
               
             
          
         
       
     
     To maximize fatigue life of the spring, it is desirable to select a wall thickness that produces a stress level within the range of about 25-30% of the ultimate tensile strength of the tube  30 . As can be seen from Table I, tubes falling within the outer diameter range of about 0.05-0.055 inches should maximize the fatigue life of the spring. It was also observed that this same group of tubes produced springs that were sufficiently rigid that they resisted sagging over the desired range of movement. 
     The conductor  32  is inserted through the tube  30  while the tube  30  is relatively straight, i.e., prior to forming the helical coil. Before inserting the conductor  32  into the tube  30 , the ends of the tube  30  are flared to reduce the possibility of damage to the conductor  32  as it is fed through the tube  30 . A wire (not shown) having a substantially small diameter is fed through the tube  30 . The wire is then used to pull the 26 awg TFE wire  32  through the tube  30 . 
     The assembled tube  30  and conductor  32  are next formed into a helical coil. The tube  30  is helically wrapped under tension around the mandrel  31  to form the spring, as shown in FIG.  3 . In one embodiment, the mandrel  31  has a diameter of about 0.75 inches. A heating process normalizes residual stresses in the tube  30 . Thereafter, the tension is released, and the tube  30  is allowed to unwind slightly. In one embodiment, the coiled tube  30  is heated for a predetermined time and temperature to anneal the tube. 
     The particular embodiments disclosed above are illustrative only, as the invention may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular embodiments disclosed above may be altered or modified and all such variations are considered within the scope and spirit of the invention. Accordingly, the protection sought herein is as set forth in the claims below.