1. US5053596 - Apparatus and method of induction-hardening machine components with precise power output control

An induction-hardening machine for the contour hardening of machine components such as gears includes a system processor which controls thyristor power switching circuits which supply high-power signals to an RF generator. Power switching circuits include silicon controlled rectifiers of SCR's. In order to overcome the variable "on time" characteristics of SCR devices, a zero crossing detector is implemented and time periods are calculated so that the system processor activates the SCR circuits to supply power to the RF generator at predetermined times. The system processor 12 will deactivate the SCR circuits at or just prior to a zero crossing referenced from the predetermined activation time thereby effectively controlling the one time of the SCR circuits with an accuracy of up to five ten thousandths of a second. The signal produced by the RD generator is supplied to an induction heater coil which is used to case harden the gear teeth of a machine component or gear.