Roper Corporation

Buddy Julian Austin

Frederick K Uyeda

An induction cooking appliance for operation at ultrasonic frequencies and including an improved work coil coupled in a solid state inverter circuit to generate an ultrasonic frequency magnetic field which is coupled to a metallic utensil through a non-electrically conductive cooktop. Coil losses are minimized, and coupling efficiency increased by forming the coil of solid conductor wound in a loose spiral, with the pitch of the spiral being related to the radial thickness of the conductor by a factor falling within a predetermined range. The loosely wound coil is held in a grooved dielectric support which insures proper turn spacing for the life of the appliance and which is immune to high temperatures which may be developed during operation of the coil. Means are provided under the support to minimize stray radiation and limit inductance variations which might otherwise result from nearby metallic members. Means are provided for holding the coil adjacent the underside of the cooktop for optimum coupling and to utilize heat developed in the coil. The loosely wound configuration is advantageously fabricated by methods including interleaving the coil conductor with an insulative strip. Alternatively, an open coil may be formed by winding the conductor on a frusto-conical mandrel whose degree of taper is related to the desired pitch of the coil, and compressing the coil into a planar configuration.

Work coil for use in an induction cooking appliance

A control circuit for a microwave oven including a main timer for setting the period of operation and having a high power mode in which power is continuously supplied to the microwave generator for the entire timed period, and a defrost or low power mode wherein power is supplied at a reduced duty cycle for the selected time period. The circuit, in addition to the main timer operable in both modes, includes a defrost timer operable only in the defrost mode for periodically interrupting the power circuit for the microwave generator thereby to provide reduced duty cycle operation. The circuit further includes means for automatically resetting the defrost timer after operation thereof to assure that the microwave generator will be instantly energized upon subsequent operation, independently of the subsequently selected mode.

Timer operated control circuit for a microwave oven

A microwave oven in the form of an enclosed cavity having a magnetron and waveguide communicating with the cavity via a hollow conductor penetrating one of the walls. Centrally mounted in the conductor is an antenna having a straight shank portion and a radially extending arm portion, with an angled transitional portion inbetween, the transitional portion bearing an obtuse angle to the shank portion lying within the range of 105.degree. and 165.degree. and having a length at least equal to the radius of the hollow conductor so that the transitional portion and the arm portion radiate a 'guided' wave in a direction different from that of the 'inertial' wave radiated directly from the hollow conductor. The shank portion of the antenna is supported in a rotatable mount in the waveguide, and a motor coupled to the mount rotates the antenna for sweeping the guided wave throughout the cavity for improved energy distribution in the cavity and relative freedom from hot spots. In the preferred form of the invention the radially extending arm portion has a length greater than the transitional portion and the cavity includes a thermal heating element which is arranged substantially in the plane of the arm portion. In an alternate form of the invention only the shank and the angled portion are used so that the rotated antenna is of dogleg shape.

Antenna construction for microwave oven

An induction cooking appliance for heating a metallic utensil by means of an ultrasonic frequency magnetic field. The appliance includes a smooth, substantially non-metallic cooktop for supporting the utensil, and a work coil mounted below the cooktop for coupling the magnetic field to the utensil. The work coil is arranged in a solid state inverter circuit, including a gate controlled thyristor and a commutating capacitor, arranged to convert a d.c. voltage to current pulses of ultrasonic frequency. Simplified inverter protection circuits assure that conditions within the inverter do not exceed the component ratings. The protection circuits include a load sensing circuit for disabling the inverter when unloaded or when improperly loaded. An associated circuit responds to the power operating level of the inverter for varying the sensitivity of the load sensing circuit. Further protection is provided by an over-voltage limit circuit also adapted to disable the inverter. Means are provided for limiting potentially damaging voltage transients which may be generated when the inverter is disabled by the load sensing circuit. User convenience is enhanced by providing, in combination with the on/off inverter operation, a pilot light circuit which operates from a low voltage supply but responds to a small portion of the energy tapped from the inverter ciruit so as to be illuminated only when the inverter is actually operating.

Growing community of inventors

Lafayette, IN, United States of America

Buddy Julian Austin