Browse Prior Art Database

CONTROLLABLE CURRENT SOURCE FOR IONOGRAPHIC HEADS

IP.com Disclosure Number: IPCOM000026560D
Original Publication Date: 1992-Oct-31
Included in the Prior Art Database: 2004-Apr-06
Document File: 4 page(s) / 189K

Publishing Venue

Xerox Disclosure Journal

Abstract

An ionographic print head, similar to that described in U.S. Patent No. 5,081,475 to Frank et al. (Issued Jan. 14, 1992) typically employs a wire corotron ion source and an array of voltage controlled nibs that modulate ion current flowing through a slit or outlet channel to a receiving surface. The output ion current at each slit is a function of nib voltage, air velocity, geometry and the corotron emission level. When the corotron is operated from a voltage source the corotron emission current is a steep function of applied voltage over threshold, and is very sensitive to small changes in the discharge gap geometry, including the changes caused by mechanical vibrations of the corotron wire.

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Page 1 of 4

XEROX DISCLOSURE JOURNAL

CONTROLLABLE CURRENT SOURCE FOR IONOGRAPHIC HEADS
Frank C. Genovese

Proposed Classification
U.S. C1.3461159 Int. C1. GOlD 15/06

-2700V

FIG. I

XEROX DISCLOSURE JOURNAL - Vo1.17 No. 5 SeptembedOctober 1992 313

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Page 2 of 4

CONTROLLABLE CURRENT SOURCE FOR IONOGRAPHIC HEADS(Cont'd)

-2700V

FIG. 2

314 XEROX DISCLOSURE JOURNAL - Vo1.17 No. 5 September/October 1992

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Page 3 of 4

CONTROLLABLE CURRENT SOURCE FOR IONOGRAPHIC HEADS(Cont'd)

An ionographic print head, similar to that described in U.S. Patent No. 5,081,475 to Frank et al. (Issued Jan. 14, 1992) typically employs a wire corotron ion source and an array of voltage controlled nibs that modulate ion current flowing through a slit or outlet channel to a receiving surface. The output ion current at each slit is a function of nib voltage, air velocity, geometry and the corotron emission level. When the corotron is operated from a voltage source the corotron emission current is a steep function of applied voltage over threshold, and is very sensitive to small changes in the discharge gap geometry, including the changes caused by mechanical vibrations of the corotron wire.

The short and long tenn variations in the wire operating current can be eliminated by substituting a current source in place of the voltage source typically used to drive the corotron wire. A current sensing circuit in the high- voltage return path may be used to control the applied potential in order to maintain the current at a specified level. However, the effective capacitance of the floating power source to system ground, via the control and power input lines, limits the response of these systems. Moreover, the output voltage ripple which is produced may also pose a problem.

Accordingly, the present disclosure proposes a constant current power supply that is suitable for reducing variations in the corotron wire operating current in order to provide a uniform charge density across the surface of the electroreceptor drum. As illustrated in Figure 1, a common base transistor constant current power supply, 8, is used. The bias of the base of transistor 10 defines the voltage drop across resistor 14 which establishes the collector- emitter current, ice. The bias voltage, represented by reference numeral 12, may be a battery or any suitable voltage source providing approximately 6 volts potential. Transistor 10 is illustrated as a high-voltage PNP transistor, although a depletion mode p-channel field-effect transistor may be used in place of the PNP transistor, thereby eliminating the need for bias voltage source 12. The high voltage power supply, 16, at a potential of approximately -2700 volts, is typically one or two hundred volts above the breakdown potential of corotron wire 18, so that a small excess may be absorbed by collector 20 at the chosen operating current. The current is inde...