# US 5,708,464 A · Device for direct electrostatic printing (DEP) with "previous correction"

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- Number: US 5,708,464 A
- Document ID: US5708464A
- Status: Granted
- Kind: A
- Application number: 08/743,545
- Filed: 1996-11-04
- Granted: 1998-01-13
- Earliest claimed: 1995-11-09
- Assignees: Agfa-Gevaert
- Inventors: Guido Desie
- Web page: https://patentgrep.com/patent/US5708464A

## CPC

- B41J 2/4155: {for direct electrostatic printing [DEP]}
- G03G 15/346: {by modulating the powder through holes or a slit}
- G03G 2217/0025: where the toner starts moving from behind the electrode array, e.g. a mask of holes
- B41J: TYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
- G03G: ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY

## Abstract

A DEP device adapted for grey-scale printing comprising a back electrode (105), a printhead structure (106), an array of printing apertures (107) in the printhead structure (106) through which a particle flow can be electrically modulated by a control electrode (106a), a toner delivery means (101), at least one control means (111) for applying an electric field to the control electrodes, wherein: (i) the control means controls each single control electrode to enable the printing through each single printing aperture (107) of pixel dots (PD), each of the pixel dots intended to have a density D, and (ii) the control means controls the printing of the pixel dots through the each single printing aperture as a function of both the intended density (D.sub.intend) and the density (D.sub.prev) previously produced through the single printing aperture, i.e. the control means use "previous correction".

## Claims

### Claim 1

A DEP device adapted for grey-scale printing comprising:
a back electrode(105),
a printhead structure(106),
an array of printing apertures(107) in said printhead structure(106) through which a particle flow can be electrically modulated by a control electrode(106a),
a toner delivery means(101),
at least one control means(111) for applying an electric field to said control electrodes, wherein:
(i) said control means controls each single control electrode to enable the printing of pixel dots through each single printing aperture(107) each of said pixel dots intended to have a predetermined density, and,
(ii) said control means controls said printing of said pixel dots using previous electrode parameter characteristics as correction data.

### Claim 2 (depends on 1)

A DEP device according to claim 1, wherein said grey-printing is controlled by said control means by voltage modulation of electrical fields applied to said control electrodes according to the following formula:
V3real=V3intend+(V3prev.times.Kv)
wherein,
V3real is the value of the real blocking voltage V3 at time LTn;
V3intend is the value of the blocking voltage V3 to be used at time LTn when previous correction data is not applied;
V3prev is the value of V3 at time LTn-1;
Kv is a correction constant that is smaller than 1;
LTn is a line time interval used to print an nth line; and,
LTn-1 is a line time interval used to print the n-1th line.

### Claim 3 (depends on 2)

A DEP device according to claim 2, wherein K.sub.v .ltoreq.0.20.

### Claim 4 (depends on 1)

A DEP device according to claim 1, wherein said grey-scale printing is controlled by said control means by time modulation of electrical fields applied to said control electrodes according to the following formula:
WRTreal=WRTintend-((LT-WRTprev).times.Kt)
wherein,
WRTreal is the real value of the write time interval used at time LTn;
WRTintend is the value of the write time interval to be used at time LTn when previous correction data is not applied;
WRTprev is the value of the write time interval at LTn-1;
Kt is a correction constant that is smaller than 1;
LTn is the line time interval used to print an nth line;
LTn-1 is the line time interval used to print the n-1th line; and,
LT is the line time interval for printing a line.

### Claim 5 (depends on 1)

A DEP device according to claim 1, wherein said correction data takes into account the electrical field used to print the density of more than one previous image dot.

### Claim 6 (depends on 1)

A DEP device according to claim 1, wherein said correction data is combined with correction data of neighboring image dots.