Method and apparatus for dielectric sensing in a thermoplastic winding process

A thermoplastic filament winding apparatus for consolidating thermoplastic filament using heating and compression of the filament, comprising:

• a. an electrically conductive mandrel around which the thermoplastic filament is wound;
• b. means to apply heat to the portion of the filament being wound;
• c. an electrically conductive roller, juxtaposed with said mandrel and movable radially with respect to said mandrel, to provide for compression of the portion of such thermoplastic filament being wound onto said mandrel, said portion of the thermoplastic filament disposed on said mandrel and said roller disposed on said portion of the thermoplastic filament, such that a dielectric capacitor having two conductive surfaces and a dielectric material disposed therebetween is formed, with said roller and said mandrel comprising the conductive surfaces of the capacitor and the portion of the thermoplastic filament disposed between said roller and said mandrel comprising the dielectric material of the capacitor, the thickness of the dielectric material varying as the filament is wound;
• d. electronic signal generating means for generating a sinusoidal electric signal to be introduced to said mandrel and said roller, said electric signal comprising an input voltage applied across the dielectric capacitor formed between said mandrel and said roller;
• and
• e. electronic monitoring means for continuously measuring said input voltage and an output current, and for determining the permittivity and the loss factor from the measured input voltage and the measured output current of the dielectric capacitor formed by mandrel, roller and thermoplastic filament as the filament is wound onto said mandrel.