Collapsible Mandrel for Precise Winding of a Coil

This invention relates to the field of coil winding and, more particularly to a mandrel enabling the winding of a precision coil from material having a circular cross-section.

Previously coils have been wound from material having a circular cross-section employing a solid mandrel, or a coil winding arbor. Employing these devices, the precision winding of a material of circular cross-section cannot be maintained in coil manufacture.

An object of the present invention is to provide a collapsible mandrel enabling the precise winding of a material having a circular cross-section into a precision-wound coil.

A feature of the present invention is the provision of a collapsible mandrel for precise winding of a material having a circular cross-section into a precision-wound coil comprising a pair of spaced parallel flanges; a core upon which the coil is wound disposed between the pair of flanges perpendicular thereto, coaxial of a longitudinal axis and removably secured to the pair of flanges, the core including a pair of hollow, partially semicircular members extending between the pair of flanges, each of the hollow members having a given arc length less than 180.degree., being disposed on a different side of the axis and having an outer surface containing therein a plurality of spaced grooves substantially parallel to the pair of flanges, each of the plurality of grooves having a radius substantially equal to the radius of the material, and a pair of grooveless transition members extending between the pair of flanges, each of the transition members being disposed on a different side of the axis between adjacent ends of the pair of hollow members and having a selected arc length equal to the difference between 180.degree. and the given arc length; and a shaft disposed coaxial of the axis extending between the pair of flanges internally of the core, the shaft having a thread on one end thereof extending beyond one of the pair of flanges to receive a nut to releasably lock the core and the pair of flanges into an integral unit when the coil is being wound and to enable removal of the nut, the pair of flanges and the pair of transition members to permit removal of the pair of hollow members after the coil has been wound.

The material having a circular cross-section as referred to herein has reference to a single strand of metallic conductor, a cable formed from a plurality of such conductors, an optical fiber and an optical cable formed from a plurality of such optical fibers.

Above-mentioned and other features and objects of this invention will become more apparent by reference to the following description taken in conjunction with the accompanying drawing, in which:

FIG. 1 is an elevational view partially in cross-section of a collapsible mandrel in accordance with the principles of the present invention;

FIG. 2 is an enlarged elevational view of the left-hand end of the mandrel of FIG. 1, illustrating how a multilayer coil is wound on the mandrel in accordance with the principles of the present invention;

FIG. 3 is an end view of the mandrel core taken along line 3--3 of FIG. 2; and

FIG. 4 is a cross sectional view of the transition member taken along line 4--4 of FIG. 3.

Referring to FIGS. 1-4, the collapsible mandrel in accordance with the principles of the present invention includes a pair of spaced parallel flanges 1 and a mandrel core 2 disposed between flanges 1 perpendicular thereto, coaxial of a longtitudinal axis 3 and removably secured to flanges 1 by a dovetail 4 at both ends of core 2.

Core 2 includes a pair of hollow partially semicircular members 5 and 6, both of which extend between flanges 1 and having a given arc length less than 180.degree.. Each of the hollow members 5 and 6 are disposed on a different side of axis 3 and each have an outer surface containing thereof a plurality of spaced grooves 7 and 8 running substantially parallel to flanges 1 with each of the grooves 7 and 8 having a radius substantially equal to the radius of the material having a circular cross-section from which the coil is to be wound. Interposed between adjacent ends of hollow members 5 and 6 are disposed transition members 9 and 10, which are grooveless and have an outer diameter equal to the diameter of the members 5 and 6 at the deepest point of grooves 7 and 8 and an inner diameter equal to the inner diameter of members 5 and 6. Members 9 and 10 are disposed on different sides of the axis 3 and extend between flanges 1. Each of the members 9 and 10 have a selected arc length equal to the difference between 180.degree. and the given arc length of the hollow members 5 and 6.

It has been found that a precision-wound coil can be produced successfully when the arc length of members 5 and 6 is between 160.degree. to 170.degree. long and when the selected arc length of members 9 and 10 is between 10.degree. to 20.degree.. Preferably the arc length of members 5 and 6 is 170.degree. and the selected arc length of members 9 and 10 is 10.degree..

The dovetails 4 employed to removably secure core 2 to both of the flanges 1 includes a flaring tenion 11 on both ends of member 6 and a flaring tenion 12 on both ends of member 5, which conform to the arc and arc lengths of their associated members. Tenions 11 and 12 fit into mortises 13 and 14 in the form of a partially semicircular groove corresponding to the arc configuration and arc length of members 5 and 6, respectively. The members 9 and 10 are likewise removably secured to flanges 1 by a dovetail which includes a tenion 15 formed on both ends of members 9 and 10, which fits into a mortise 16 in the form of a groove in flanges 1 having an arc configuration and arc length of members 9 and 10.

Flanges 1 and core 2 are held in their position illustrated in FIG. 1 to enable winding of a single or multilayer coil on core 2 by a shaft 17 which is disposed coaxial of axis 3 between flanges 1 with the right-hand end of shaft 17 being embedded in the right-hand flange 1 and extending through the left-hand flange 1 as viewed in the drawing. The left-hand end of shaft 17 is threaded at 18 to receive a locking nut 19 which releasably locks core 2 to the pair of flanges 1 in an integral unit to enable the winding of a single or multilayer coil. After the coil is formed, nut 19 is removed from threaded end 18 of shaft 17 to enable the separation of flanges 1 from core 2. Subsequent to this operation, members 9 and 10 are removed from their position relative to members 5 and 6 so that these members can be moved inwardly toward axis 3 and then pulled out from the formed coil, thereby providing the collapsible feature of the mandrel in accordance with the principles of the present invention.

The spacing between flanges 1 and their perpendicularity to core 2, the spacing of adjacent grooves 7 and 8, the amount of displacement between grooves 7 and 8, the transition members 9 and 10 arc lengths, and the distance of the "start" groove, such as groove 20, and the distance of the "end" groove, such as groove 21, from their associated flanges 1 must be precisely machined and maintained to a high level of tolerance in order to effectively manufacture a precision-wound coil. The spacing between the pair of flanges 1 must be maintained at Nd+d/2, where N is the number of turns in the coil and, thus, the number of grooves 7 and 8 and d is the diameter of the material being wound into a coil. As can be seen in FIG. 1, the spacing between adjacent ones of the grooves 7 and 8 is equal to the diameter of the material being formed into a coil and the shift of grooves 7 and 8 with respect to each other is equal to one half the diameter (d/2) of the material being formed into a coil.

The collapsible mandrel in accordance with the principles of the present invention allows a precise control of the material position and spacing as the material is wound on mandrel core 2. The material is held perpendicular to axis 3, which is the axis of rotation of the mandrel, and passes through two discrete arc lengths provided by members 5 and 6. The material being wound is allowed to advance half a cable diameter for every given arc length of the mandrel rotation provided by members 5 and 6, which in the preferred embodiment is 170.degree. of arc length. The material pitch advance occurs during the smooth transition zone provided by members 9 and 10 which have a selected arc length, which in the preferred embodiment is 10.degree.. This advance occurs twice for each 360.degree. rotation of the mandrel. When the material being wound approaches the mandrel flanges 1, it is constrained between the previous coil layer and flange 1 when a multilayer coil is being wound, as is best illustrated in FIG. 2. Because the material being wound is exactly positioned one half of its diameter from flange 1 along the axis 3, this material moves outward from core 2 and starts the second layer of a multiple layer precision-wound coil. By use of a suitable adhesive during the winding process of a multiple layer coil to fill all the coil-matrix interstitial sites 22, a free-standing coil can be manufactured. Upon cure of the adhesive, flanges 1 and core 2 can be collapsed away from the cable-adhesive matrix as described hereinabove resulting in a precision-wound, free standing coil. Two examples of adhesives that have been employed during the manufacture of coils employing the mandrel in accordance with the principles of the present invention are SILGARD 184, available from Dow Corning, and an epoxy resin known as TRANSFLEXGEL, obtainable from Isochem.

The dimensions mentioned hereinabove and illustrated in FIG. 1, which are related to the diameter of the material being wound to provide the coil, is the true diameter of this material with a factor added thereto to account for the diameter fluctuations of the material with this fluctuation parameter being determined for each of the different types of materials that may be employed to provide coils employing the mandrel in accordance with the principles of the present invention.

While we have described above the principles of our invention in connection with specific apparatus it is to be clearly understood that this description is made only by way of example and not as a limitation to the scope of our invention as set forth in the objects thereof and in the accompanying claims.