1. Field of the Invention.
The invention relates to a method of manufacturing an electric coil deviating from a circular shape, in which a circular coil is deformed by a bending operation performed transversely to the coil axis, and a coil manufactured by this method.
A circular coil is to be understood to mean herein a coil the turns of which are circular or substantially circular. A coil deviating from a circular shape on the contrary contains turns having, for example, a polygonal, in particular a rectangular, variation from a circle.
2. Description of the Prior Art.
A method known from German Pat. No. 264,676 relates to the manufacture of rectangular coils. Such coils are used for transformers, measuring instruments, and the like. Starting material in this method is a coil which is wound on a circular core and which is compressed to form a rectangular coil by means of a number of members movable transversely to the coil axis. This method requires large forces so as to give the adjoining turns the desired rectangular shape. A drawback of this known method is that the wire is easily damaged during the compression process.
The advantage of a rectangular coiled shape has been sufficiently obvious to those making transformers, ballast coils such as those used for gas discharge lamps, and the like, so that techniques have been developed by which rectangular coil shapes can be wound directly. Known machines drive the bobbin at a constant speed, so that the wire undergoes sharp cyclical variations in tension and undergoes a jerking effect when passing around corners of the bobbin. These problems become particularly significant when it is desired to wind the coil orthocyclically.
Orthocyclically coils, each of whose turns lies in a plane perpendicular to the coil axis except for a short, oblique transition portion between adjacent turns, have the planar portions of each turn of each next outer layer nestled in grooves between the adjacent turns of the preceding layer, as described in U.S. Pat. No. 2,930,014 and in "Philip's Technical Review", Vol. 23, no. 11, pp 365-379 (Oct. 16, 1962). Such coils offer a particularly high space factor and therefore are advantageously used with conventional rectangular lamination stacks.
Techniques for successful winding of orthocyclical coils in a rectangular shape have been developed. When winding an orthocyclic rectangular coil, however, the lengths of the transitions between the turns is not constant, independent of the uniformity of the wire used. Also, known orthocyclic windings have provided all transitions only along one side of the rectangular coil. Further, winding orthocyclical coils in a rectangular shape while using relatively fine wire, such as number 25 AWG or finer, has proved to present great difficulties, when a rectangular shape is desired. Because of the small diameter of the wire it is not possible to wind these fine wire sizes at relatively high speed, because the aforementioned variation in tension and jerking effect tend to destroy the orthocyclical winding.