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Switch Regulation of High Voltage Corona Supplies

IP.com Disclosure Number: IPCOM000052689D
Original Publication Date: 1981-Jun-01
Included in the Prior Art Database: 2005-Feb-11
Document File: 3 page(s) / 83K

Publishing Venue

IBM

Related People

Gliebe, RJ: AUTHOR [+2]

Abstract

A multiple corona system is driven by a single high voltage power supply having multiple outputs. The regulation feedback source can be fixed or switchable between the outputs.

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Switch Regulation of High Voltage Corona Supplies

A multiple corona system is driven by a single high voltage power supply having multiple outputs. The regulation feedback source can be fixed or switchable between the outputs.

The xerographic apparatus in Fig. 1 includes a photoconductor, shown as drum 10, which is precharged to a rough negative level by transfer corona 11. As drum 10 passes under positive corona 12, its charge is smoothed. Ultimately a light pattern of an original document is imaged onto drum 10 by means (not shown) so that white areas are discharged and black areas remain charged. Toner is attracted to these image-reflecting charged areas. Drum 10 is cleaned of toner subsequent to transferring the image to a copy sheet. The photoconductor 10 must be as close to ground potential as possible during this cleaning process. The quality of photoconductive copying is a function of the level of regulation of the ionic currents at the coronas.

The Fig. 1 system employs a single pulse-width modulated AC power supply 15 which feeds multiplier 16. Multiplier 16 increases the voltage amplitude, rectifies the AC input, and produces both positive and negative voltage outputs of equal magnitude at 17 and 18. To reduce photoconductor 10 to ground potential, it is desirable to terminate the negative current in corona 11 and allow contribution from the positive corona 12 only. The case supply goes to its highest positive level in corona 12 to bleed off all negative current from corona
11. The negative wire 18 then provides more current so as to maintain the same voltage amplitude or tracking as the positive side 17.

In the Fig. 1 regulation system, tight control of positive current during precharging and tight control of negative current during copy and clean modes are obtained with optimum results. A microprocessor (not shown) switches the regulation current to the appropriate side at the correct time. Negative current regulation exists at two levels: a high level during transfer to enhance toner transfer from the photoconductor to paper, and a low level during clean to allow case bias control and, thus, no contribution of negative ions from the negative wire 18 during cleaning. The microprocessor provides control signals at terminals 20, 21 and 22, with the latter two always being complements of each other and input 20 being the transfer signal. In an exemplary operation, these signals are 10 volts in the "logic 1" state and open in the "logic Phi" state. A high signal disables its respective error amplifier 24 or 25 in the amplifier module 26, which is typically a TL494CN. The following truth table explains the signals appropriate durin...