Coil winding machines have been in use for many years, and are now fully automated. This automation became practical when molded winding forms having a lead-in slot were developed. The lead-in slot provides a means for protecting the lead-in wire of the electrical coil when the coil is wound automatically. This type of winding slot, in its earliest version, is found in the Brekke et al U.S. Pat. No. 3,131,371. The exact form of the lead-in slot has been extensively modified by changing its contour and slope. Lead-in slots are now used routinely in automatically wound coils for all types of electrical devices.
The typical winding machine mounts a winding form or molded bobbin against an arbor. The winding form or bobbin is then held in place while an initial turn of wire is wrapped around an electrical terminal that is molded or inserted into a flange of the bobbin. The bobbin or winding form is then rotated with the arbor. The wire that was wrapped around the terminal is automatically directed into the lead-in slot and is brought out on the core of the bobbin. The arbor is then rotated rapidly to wind the desired number of turns of wire on the winding form. The wire is automatically led out to a further terminal structure and wrapped
During the manufacture of the coil, it has been found that a strain relief loop in the wire is necessary between the first terminal and the lead-in into the protective slot of the bobbin or winding form. This typically has been accomplished by mounting a pin on the arbor. The pin causes the wire of the coil to be led over the pin prior to its entry in the lead-in slot. This strain relief loop later prevents breakage between the terminal and the lead-in conductor when the coil or electrical device is further handled and processed.
In the winding of electrical coils that use relatively heavy wire, the strain relief pin causes no particular problem. Where the wire being wound is of a small cross section, the pin that is intended to provide the strain relief loop has a tendency to apply a sufficient force against the strain relief loop to cause breakage of the lead-in wire. This in turn causes a relatively high rejection rate of electrical coils wound with small wire in this type of winding environment.