Burroughs, Inc.

Flavius A Mathamel

Daniel A Wisner

Truman T Schmalzriedt

Disclosed is a system and method for reducing the level of electromagnetic emission radiated by electrical discharge type printers. Such printers utilize one or more styluses which are scanned across the width of a roll of electrosensitive paper and are selectively energized to vaporize small areas on the paper's coating to thereby form characters. When the coating vaporizes, a spark is produced which generates a broad band of electromagnetic energy which is conducted into the environment due to the conductive coating of the previously printed paper acting as an antenna. In order to reduce the effective antenna length and/or propagation capability to thereby reduce the energy radiated, the present system creates isolation bands at preset intervals as the printing occurs. The isolation bands are produced by continuously energizing all styluses as they scan across the full width of the paper, thereby causing an entire band of the paper's conductive coating to be burned off across the entire width of the paper. Each isolation band severs the conductive surface of the paper, thereby reducing the effective length and/or propagation capability of the antenna created by the printed paper and lowering the level of radiated energy.

Electromagnetic interference suppresion for electrical discharge printers

D.C. power supply having a reactive buck automatic D.C. voltage regulator which directly controls the rectified D.C. output of a loosely coupled transformer thereby providing load regulation from an unregulated alternating current source. The load current passes through the secondary winding of an auxiliary buck transformer and is stepped down to a much lower value in the primary winding of the auxiliary buck transformer. The primary winding of the auxiliary buck transformer is coupled to an isolated winding on the core of a ferroresonant C.V.T. transformer which receives the unregulated alternating current input signal, and the coupling between the isolated winding and the primary winding of the buck transformer effects a bilateral energy transfer between the two transformers which effects a real time reactive compensation which regulates the D.C. output of the power supply for changes in the input voltage and in the load while conserving the energy which would normally be wasted in achieving regulation by transferring it back to the resonant circuit via the bilateral energy transfer between the two transformers. The control system is set up so that the auxiliary buck transformer is normally bucking under all line and load conditions when the frequency is precisely at the resonant frequency of the saturable inductor and capacitor. A frequency shift either above or below resonance simply changes the amount of bucking that takes place in a complimentary manner. It should be noted that little power is consumed during the buck process as the power is returned from the auxiliary buck transformer to the loosely coupled ferroresonant transformer. The operating point of a negative feedback system which determines the point about which the bilateral energy transfer occurs, may be fine-tuned by an error-sensing feedback circuit for altering the voltage level which the coupling network operates to hold constant by controlling the bilateral energy transfer. A capacitor is provided across the primary of the auxiliary buck transformer to reflect capacitance into the secondary winding during conditions of little or no bucking action in order to enhance the stability of the regulator.

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Allen Park, MI, United States of America

Flavius A Mathamel