Controller for electric permanent chuck

摘要

A novel control circuit for magnetizing and demagnetizing an electric permanent chuck includes a single alternating current source with a selected frequency and phase. A circuit that generates electrical pulses is coupled to the alternating current source to produce pulses at a multiple of the frequency of the alternating current source. The pulse generating circuitry also sets the phase of the pulses relative to the phase of the alternating current source at a predetermined value. The pulses are then applied to the gates of one or more silicon controlled rectifiers ("SCRs") which control current flow through the electric permanent chuck. By adjusting the phase of the electrical pulses, the amount of current and average DC voltage applied to a coil of the electric permanent chuck through an SCR can be controlled.