Method and apparatus for fusing thermoplastic materials

Abstract

An apparatus and method for attaining fusion temperature at substantially the same time throughout an interface between thermoplastic articles by the controlled application of heat. The method includes providing a sensed temperature signal corresponding with the temperature at the interface, generating a desired temperature signal (such as an analog ramp signal which increases linearly with time) corresponding with a predetermined heat application rate which causes the temperature at substantially all portions of the interface to rise substantially uniformly, providing a heat control signal corresponding with any difference between said signals, and applying heat to the interface at a rate determined by the heat control signal to achieve fusion temperature throughout the interface at the same time. The apparatus includes a heater coil to apply heat to the interface, a sensor to provide the sensed temperature signal, a generator to provide the desired temperature signal, and a differential amplifier to provide the heat control signal. Fault detection circuits stop the process if a heater fault, a temperature sensor fault, or a power supply fault is detected. Testing circuits are included to test the apparatus for proper operation before commencing fusion.