Induction heating apparatus

Claim 1

IN COMBINATION, AN ALTERNATING CURRENT SOURCE, AN INDUCTION HEATER ADAPTED TO RECEIVE AN OBJECT TO BE HEATED, AND A POWER TRANSMISSION COUPLING INTERPOSED BETWEEN SAID SOURCE AND SAID HEATER COMPRISING A MULTI-TERMINAL AUTO-TRANSFORMER HAVING AT LEAST THREE PRIMARY TERMINALS WITH A PRE-SELECTED NUMBER OF COIL TURNS BETWEEN SAID TERMINALS AND AT LEAST A PAIR OF SECONDARY TERMINALS CONNECTED TO SAID HEATER TO ESTABLISH A LOAD CIRCUIT, MEANS FOR CONNECTING SAID AUTO-TRANSFORMER ACROSS SAID SOURCE INCLUDING AT LEAST A PAIR OF SEQUENTIALLY OPERABLE SWITCHING DEVICES OPERABLE WHEN CLOSED TO CONNECT SAID SOURCE TO A PAIR OF SAID PRIMARY TERMINALS WHEREBY THE NUMBER OF TRANSFORMER COIL TURNS CONNECTED ACROSS SAID SOURCE IS VARIED BY A PREDETERMINED MAGNITUDE TO CONTROL THE VOLTAGE INPUT IN SAID LOAD CIRCUIT, AND SELECTOR MEANS FOR ACTUATING SAID SWITCHING DEVICES AND BEING OPERABLE, WHEN ONE OF SAID SWITCHING DEVICES IS IN CLOSED POSITION, TO CLOSE THE OTHER OF SAID SWITCHING DEVICES BEFORE SAID ONE OF SAID SWITCHING DEVICES IS OPENED TO ENABLE THE PRIMARY TO SECONDARY RATIO OF SAID TRANSFORMER TO BE VARIED WITHOUT INTERRUPTION OF POWER TRANSMISSION FROM SAID SOURCE TO SAID HEATER, SAID SELECTOR MEANS COMPRISING MEANS RESPONSIVE TO THE TEMPERATURE OF THE OBJECT IN SAID HEATER FOR AUTOMATICALLY CONTROLLING THE ACTUATION OF SAID SWITCHING DEVICES FOR PERIODICALLY VARYING THE VOLTAGE INPUT IS ACCORD WITH VARIATIONS OF THE IMPEDANCE OF SAID OBJECT.