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ELECTRONIC DRIVE SYSTEM FOR DIRECT ELECTROSTATIC PRINTING

IP.com Disclosure Number: IPCOM000026759D
Original Publication Date: 1993-Aug-31
Included in the Prior Art Database: 2004-Apr-06
Document File: 6 page(s) / 262K

Publishing Venue

Xerox Disclosure Journal

Abstract

Many printing systems print a single row of pixels at a time and require individual drive transistors of high voltage. This is typical of direct electrostatic printing and similar systems. One solution is to use thin film transistors instead of more conventional multiple drivers on a single Silicon chip. However, this has the disadvantages that the speed of TFTs is low and they have a yield problem in fabrication, because of the high voltage, making this solution difficult if not impossible. Although it is possible to affix Silicon driver chips to glass and wirebond them to the pixels, the types of available chips with a voltage rating above 100 volts are generally not conducive to run the capacitive loads of the pixels such as are found in direct electrostatic printing.

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Page 1 of 6

XEROX DISCLOSURE JOURNAL

ELECTRONIC DRIVE SYSTEM FOR DIRECT ELECTROSTATIC U.S. C1.101/489 PRINTING Int. C1. B41m
Joseph F. Stephany
David D. Hoesly
Michael Poleshuk

Proposed Classification

FIG. I

VPP

FIG. 3

FIG. 2

KVPP

XEROX DISCLOSURE JOURNAL - VO~. 18, NO. 4 July/August 1993 351

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Page 2 of 6

ELECTRONIC DRIVE SYSTEM FOR DIRECT ELECTROSTATIC PRINTING(Cont'd)

FIG. 4

NG. 5

I

" 0 N " Pixe I

I

I

4

I I I I

_--_-------

"OFF" Pixel !

I TI I

ALL + w;i;e d ALL 4- 4 OFF ON

352 XEROX DISCLOSURE JOURNAL - VO~. 18, NO. 4 July/August 19%

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Page 3 of 6

ELECTRONIC DRIVE SYSTEM FOR DIRECT ELECTROSTATIC PRINTING( Cont'd)

Many printing systems print a single row of pixels at a time and require individual drive transistors of high voltage. This is typical of direct electrostatic printing and similar systems. One solution is to use thin film transistors instead of more conventional multiple drivers on a single Silicon chip. However, this has the disadvantages that the speed of TFTs is low and they have a yield problem in fabrication, because of the high voltage, making this solution difficult if not impossible. Although it is possible to affix Silicon driver chips to glass and wirebond them to the pixels, the types of available chips with a voltage rating above 100 volts are generally not conducive to run the capacitive loads of the pixels such as are found in direct electrostatic printing.

Conventional high voltage chips, now available, are designed to drive vacuum fluorescent displays and require a resistive load. In order to make these drivers compact and economical, open drain drivers are used, as illustrated in Figure 1. The use of open drain drivers to drive capacitive loads creates two difficulties. First, the capacitance can be charged but not discharged as in the more conventional active pull up or "totem pole" driver illustrated in Figure 2. Unfortunately, totem pole drivers are not generally available above 100 volts. Even if they were available they would be expensive because of the increased space needed for them. Second, the leakage through the "off transistors may cause the capacitive load of the pixel to charge, thus turning "on" all the pixels by using the drivers whether they are "on" or "off. One method of overcoming these difficulties is through the use of pull up resistors R, as illustrated in Figure 3. However, for presently available chips, these resistors must be supplied externally, and present a design complication that is difficult to overcome, particularly when there are more than 3000 in a printbar. A further problem is the power dissipated, which we have calculated to be more than 200 Watts in most cases.

If a method of operating a capacitive load by open drain transistors can be found, it would have great advantages. First of all, it would be unnecessary to use active or resistive pull ups in order to charge and d...