Mechanical shield to protect magnetic core in xerographic developing apparatus

Claim 1

APPARATUS FOR DEVELOPING ELECTROSTATIC LATENT IMAGES PREVIOUSLY FORMED ON THE SURFACE OF A SUPPORT MEMBER, SAID APPARATUS COMPRISING IN COMBINATION: (A) A MAGNETIC FIELD PRODUCING MEANS; (B) A SHIELD AT LEAST PARTIALLY SURROUNDING SAID FIELD PRODUCING MEANS WITH THE EFFECTIVE MAGNETIC FIELD THEREOF AND CAPABLE OF RETAINING MAGNETIC POWDER DEVELOPER PARTICLES ATTRACTED THERETO BY THE FIELD PRODUCING MEANS FOR PRESENTATION TO THE SURFACE OF AN IMAGE SUPPORT MEMBER, SAID SHEILD INCLUDING: (1) A FIRST LAYER OF ELECTRICALLY INSULATING MATERIAL IN CLOSE SPACED RELATION TO THE MAGNETIC FIELD PRODUCING MEANS; AND, (2) A SECOND LAYER OF ELECTRICALLY CONDUCTIVE MATERIAL OVERLYING SAID FIRST RECITED LAYER; (C) A TERMINAL FOR CONNECTING A REFERENCE POTENTIAL TO SAID ELECTRICALLY CONDUCTIVE LAYER; (D) SWITCH MEANS INCLUDING BIAS POTENTIAL, NEUTRAL, AND GROUND SOURCE CONTACTS TO SELECTIVELY CONNECT SAID TERMINAL; AND (E) MEANS TO SUPPORT A QUANTITY OF MAGNETIC POWDER DEVELOPER PARTICLES FOR SUPPLY TO SAID SHIELD.