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You are an expert at summarizing long articles. Proceed to summarize the following text: 
TECHNICAL FIELD 
     This invention relates to a cable winding drum and more particularly to a cable winding drum for closing a power sliding vehicular door. 
     BACKGROUND OF THE INVENTION 
     Power sliding doors for automotive vehicles such as minivans have seen recent popularity. The use of automatic doors is a great convenience for handicapped people, for young children and for other people who have their hands filled for example with groceries. 
     The use of pull cables have been found to be an expeditious mechanism to both open the door and close the door. When the cable is used to close the door, more torque is need for the cable to close the door against the resisting forces of the seals and door latch. Thus, it is greatly desired to increase the torque exerted by the cable winding drum to overcome the seals and latch mechanism without excessive forces exerted on the cable that may otherwise decrease the durability of the cable. 
     SUMMARY OF THE INVENTION 
     In accordance with one embodiment of the invention, a cable winding drum for closing a vehicle power sliding door includes a first helical outer surface with a first radius about an axis of rotation for taking up cable at a first rate when closing the vehicle door. A second outer elliptically contoured helical surface is tangent with the first helical surface in proximity to a major axis of said second outer elliptically contoured helical surface. The take-up drum when in full closed position has the cable extended out on the second outer elliptically contoured helical surface in proximity to its minor axis at a point substantially closer to the axis of rotation than the first helical outer surface. 
     Preferably, the second outer elliptical contour has an eccentricity of at least 0.5. 
     It is also desired that the second outer elliptical contour has its minor axis intersect the axis of rotation with the axis of rotation interposed between the elliptical contour and the center point for the elliptical contour. 
     In accordance with another aspect of the invention, a first outer surface of the drum has a general first radius about the axis of rotation for taking up cable at a first rate. A second outer facing smoothly contoured surface has a greater bent section tangent to the first outer surface with a decreasing radius with respect to the the axis of rotation and a less bent section of the second outer facing smooth surface about the drum, the maximum tension force of the cable is misaligned and at a different point of the cable from the maximum bending force of the cable. It is preferred that the second outer facing smooth contoured surface has an elliptical contour. 
     In this fashion, the cable have its peak bending forces and peak tensile forces located at different locations along the cable thus lowering the peak combined force load on the cable which increases its durability. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Reference now is made to the accompanying drawings in which: 
     FIG. 1 is a perspective view of a cable drum assembly and a tool for installation; 
     FIG. 2 is an exploded perspective view of the cable drum assembly shown in FIG. 1; 
     FIG. 3 is front plan view of the drums illustrating the take up guide member in its initial position; 
     FIG. 4 is a view similar to FIG. 3 after the take up guide member has been moved to take up cable slack; 
     FIG. 5 is a partially segmented plan view of the drum illustrating its elliptical contour section; and 
     FIG. 6 is a side elevational view of the drum shown in FIG.  5 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to FIGS. 1 and 2, a cable tension assembly  10  includes housing  11  that is constructed to have a section  12  that rotatably houses a first drum  14  and second drum  16  that are connected to rotate together. A tool  15  can be operably mounted to the housing as shown in FIG.  1 . The housing  11  has a body section  18  and cover  20  that are fitted together to retain the two drums within. The two drums snap fit together via prongs  22  fitting into apertures  24 . 
     Both drums are rotatable via a motor not shown which rotates the drums about axis  26 . The motor and controls for the motor are conventional and form no part of this invention. 
     A cable  28  has one end secured  27  onto the second drum  16  at point  30  as shown in FIG.  5  and wraps about the outer surface  32  a plurality of times, extends about tension pulley  34  and out through an aperture  36  to exit the housing and be connected to the door (not shown). 
     Another cable  29  is then attached to the door and has its end  40  return back into the housing through aperture  38  and about a second tension pulley  42  and into the drum  14  through an aperture in the drum that communicates with an arcuate slot  48  within the drum. The end  40  then is connected to a tension take up member  46  that is mounted in the arcuate slot  48  within the drum  14 . The take up member  46  has resiliently mounted ratchet teeth  50  on a cantilevered section  49  that normally engage complementary ratchet teeth  52  about the outer wall  54  of the slot  48 . The cantilevered section  49  has some resilient flex. 
     The take up member  46  is initially positioned in proximity to one end  56  of slot  48  as shown in phantom in FIG.  3 . Furthermore there is sufficient length of cable  29  such that there is plenty of length of cable to easily reach end  40  of cable  29  into the slot  48  and be securely attached to tension take up member  46  without placing any tension onto cable  28 . 
     The take up member  46  is then free to slide in the direction shown by arrow  58  in slot  48  toward the position shown in FIG. 4 with the ratchet teeth  50  on cantilevered section  49  resiliently overriding ratchet teeth  52  in slot  48  until all slack is taken up in cable  29  to a set tension. The teeth  50  and  52  normally prevent the tension take up member from sliding back in a direction opposite arrow  58  toward end  56 . It is also noted that the ratchet teeth  52  progressively become larger away from end  56  and toward end  60  to help retain teeth  50  against larger tension forces placed on cable  29 . 
     A tool  15  and a gear wheel  62  expedite the take up of slack and the tensioning of the cable  28 . The gear wheel  62  is rotatably mounted adjacent the drum  16  and has gear teeth  64  that engage teeth  66  about the perimeter  68  of drum  16 . The gear wheel has an integral hex nut section  69  that can be engaged by tool  15 . The tool  15  socket engaging section  70  is mounted on a distal end of a shaft  72  that is moved by a lever handle  73  that is connected through a ratchet connection  74 . A knob  75  is also mounted on an opposing end of the shaft. A stop assembly  76  is rotatably mounted about the shaft and has one stop member  78  that protrudes through aperture  80  that limits the compression of the spring loaded pulley  34  to about one-half its travel capacity. Tool  15  also has a second stop member  82  that protrudes through aperture  84  and protrudes into slot  86  of take up guide member  46 . 
     In operation, after the cable  28  has been attached to the door, the door is positioned so that the slot  86  is visible through the aperture  84 . The installer then places tool  15  into position and cranks on lever handle  73  to rotate the shaft  72  which in turn rotates the nut  69  and gear wheel  62 . The gear then rotates the drum  14  and drum  16 . The tool simultaneously retains the take up member such that the take up member slides in slot  48  in the direction indicated by arrow  58  with the teeth  50  and  52  causing clicking indicating sounds. The excess cable is taken up onto the drum  16  as both drums rotate. Pulley  42  has its spring fully compressed and pulley  34  is limited by stop member  78 . When the tool is disengaged, the tension on both pulleys  42  and  54  re-balances to provide equal spring resiliency in both pulleys  34  and  42 . The take up guide member  46  remains positioned to be accessed through aperture  84  when the door is in the closed position. 
     If tension in the cable ever needs to be released, the drums  14  and  16  are positioned to align slot  86  with aperture  80 . A screw driver is then placed into slot  86  to flex the cantilevered section to disengage the teeth  50  from teeth  52 . Once the teeth are disengaged from each other the drums are free to rotate to release the tension of the cable system. 
     Drum  16  is used to pull cable  28  such that as the cable  28  wraps about its outer surface  90 , the door is moved to its closed position. As the door is moved to its fully closed position, the driving motor must overcome the higher torque forces cause by sealing members and the closure latch in the last few centimeters of travel. The extra torque is provided by decreasing the effective outer radius of the drum  16  for the last few centimeters of travel. 
     The drum  16  as more clearly shown in FIGS. 5 and 6 has a normal circular first outer surface section  92  normally referred to as a drum helix with a first radius indicated at  94 . A second outer surface helix section  96  has an elliptical contour that is tangent to the first outer surface section  92  at point  99  in proximity to the major axis  98  of the contour. The minor axis  100  of the elliptical contour intersects the axis of rotation  26 . The axis of rotation  26  is interposed between the defined center  102  of the elliptical contour and the elliptical contour surface  96 . The elliptical contour is positioned such that the effective radius continually decreases from the tangent point  99  to the minor axis  100  to it&#39;s minimum radius indicated at  104 . 
     It can be readily seen that the motor thus can provide for more torque to overcome the resisting forces of seals and latches by placing the cable along a smaller radius  104 . 
     In this fashion, when the door is closed and the most tension is placed on the cable, the highest bending stresses occur near the tangent point  99  near the major axis  98  and the highest tensile forces are in proximity of the minor axis  100 . However, the bending stress at the minor axis  100  is lowered due to its flattened elliptical contour. The most bending stress occurs along the major axis  98  where the tensile forces are lower. In this fashion, the location of the highest tensile force and the highest bending stress are displaced from each other along different sections of the cable  28 . By displacing the location of these two highest forces from each other, one lowers the peak stress along any given point along the cable and thus provides for a more durable cable. 
     Variations and modifications are possible without departing from the scope and spirit of the present invention as defined by the appended claims.

Summary:
An automatic sliding door cable mechanism with a take up guide member ( 46 ) mounted in a drum ( 14 ) for taking up slack of a cable during installation of the cable. A second drum ( 16 ) has an elliptical profile drum helix ( 96 ) for increasing durability of the operating cable for the automatic door.