GB2238023A

GB2238023A - Colour ink-jet printing methods

Info

Publication number: GB2238023A
Application number: GB9023448A
Authority: GB
Inventors: Joseph Lahut; Joseph Guiles; Dom Corsi
Original assignee: Ricoh Printing Systems America Inc
Current assignee: Ricoh Printing Systems America Inc
Priority date: 1989-11-09
Filing date: 1990-10-29
Publication date: 1991-05-22
Also published as: JPH03208667A; BR9005630A; GB9023448D0; DE4034263A1

Abstract

Color printing is effected in an ink jet printer by projecting dots of two colors to a single location on the substrate in a sequence which proceeds from the darker to the lighter one of the two colors, whereby a wider range of colors may be produced. The method may be effected by a printer in which the print head is movable in a scanning direction and has a row of nozzles for projecting dots of ink onto a sheet which is advanced past the print head in a sheet feed direction which is perpendicular to the scanning direction, the row of nozzles being inclined to the scanning direction and the print head being movable to provide a predetermined minimum distance in the sheet feed direction between dots projected by each nozzle. The nozzles are spaced apart in the sheet feed direction by an integral multiple of the predetermined minimum distance, which integral multiple has a value of 2<n>, wherein n is a positive integer.

Description

INK JET PRINT HEAD NOZZLE STRUCTURE

BACKGROUND OF THE INVENTION

The present invention relates to ink jet print heads, and is particularly concerned with the arrangement of nozzles on such a print head.

In the course of development of ink jet printers, a variety of nozzle arrangements have been proposed. The earliest printers operated with only a single ink color, generally black, and possessed a single nozzle or a rectangular array of nozzle elements. More recently, full color Ink jet printers capable of printing in three different colors in addition to black have found growing popularity and a variety of nozzle configurations has been developed for such printers.

one nozzle arrangement which has previously been proposed for color printers is composed of two rows of nozzles, with each row extending in a direction whibh forms a small angle with the printing direction, i.e., the direction in which the print head moves relative to a sheet being printed. one row of nozzles may be employed to apply drops of black ink to a sheet, while the other row of nozzles Is divided Into three groups, each supplying ink of a respectively different primary color.

one color system which has achieved popularity employs subtractive primary colors such as cyan, magenta and yellow. By superimposing dots of various combinations of these colors, a range of colors can be produced on the sheet. However, with the arrangements proposed thus far, the range of color variation Is somewhat limited.

When printing is produced by applying a pattern of dots to a sheet, the sheet is conceptualized as being made up of a rectangular matrix of points lying 2 1 PATENT PD-9677 at the intersections between vertical columns and horizontal rows and the print head is positionable for applying one or more dots of ink at each point. For sake of the present discussion, columns are considered to extend in the direction in which the sheet is fed past the print head, while rows extend parallel to the travel path of the print head across the sheet. Typically, the sheet is held stationary during each pass of the print head in the row direction and advances incrementally in the column direction between passes.

When a print head is provided with a row of nozzles extending at an angle to the direction of movement of the print head in the row direction, printing can be effected on a band of rows during each pass of the print head and each row In this band Is associated with a particular nozzle. Thus. a certain delay exists between the time when a nozzle associated with a given row arrives at a given column and the time when the nozzle associated with the next succeeding row arrives at the same column. However, the data provided for controlling the energization of each nozzle Is generally arranged according to columns. Therefore, logic circuitry is required to Impart a suitable timing to the delivery of signals associated with a given column to successive nozzles. Heretofore, this has required relatively complex logic circuitry.

It is also known to effect printing by an interlace scanning procedure In which alternate dot rows are printed during each scan.

i C i i 3 PATENT PD-9677 SUMMARY OF THE INVENTION

It is an object of the present invention to increase the range of colors which can be produced in a color printer employing subtractive primary colors.

Another object of the invention is to provide a nozzle configuration which leads to a simplification in the logic circuitry required to deliver control signals to the individual nozzles.

A further object of the invention is to provide a nozzle configuration which facilitates interlace scanning.

The above and other objects are achieved, according to the invention, by a print head and method of operation of the print head for forming colored dots on a substrate with a color Ink jet printer having ineans for projecting dots of ink of a plurality of different primary colors of a subtractive color system, by projecting dots of two colors to a single location on the substrate in a sequence which proceeds from the darker to the lighter one of the two colors.

objects according to the invention are further achieved by a print head in an Ink let printer, the print head being movable in a scanning direction and comprising a row of nozzles for projecting dots of Ink onto a sheet which is advanced past the print head in a sheet feed direction which is perpendicular to the scanning direction, the row of nozzles being inclined to the scanning direction and the print head being operated to provide a predetermined minimum distance in the sheet feed direction between dots projected by each nozzle, wherein the nozzles are spaced apart in the sheet feed direction by an integral multiple of the predeter-mined minimum distance, which integral multiple has a value of 2n, where n Is a positive integer.

1 A PATENT PD-9677 BRIEF DESCRIPTION OF THE DRAWING

The sole Figure is a front elevational view of a print head provided with an array of nozzles according to the present Invention.

t- i J PATENT PD-9677 DESCRIPTION OF THE PREFERRED EMBODIMENTS

The Figure shows the front, or output, surface of a print head which includes a nozzle plate 2 provided with a plurality of nozzles 4, 6, 8 and 10, each nozzle being constituted by a small circular opening whose diameter is selected according to considerations well known in the art.

The nozzle arrangement chosen to illustrate the present invention is constituted by two parallel rows of nozzles, one row being composed of nozzles 4, 6 and 8 connected to sources of cyan, magenta and yellow inks, respectively, and the second row being composed of nozzles 10 all of which are connected to reservoirs containing black ink. in the illustrated embodiment, each row consists of 48 nozzles, with 16 nozzles 4 serving to supply cyan ink drops, 16 nozzles 6 being connected to supply magenta ink drops and 16 nozzles 8 being connected to supply yellow ink drops. However, other numbers of nozzles and nozzle patterns can be employed.

According to the present invention, when single color printing is to be performed, e.g., with black ink, only nozzles 10 will be active and all 48 nozzles will be employed to effect printing along 48 rows on the printing sheet. The vertical spacing between rows corresponds to the vertical spacing, A, between adjacent nozzles 10. Preferably, the nozzle is employed for printing by int-erlace scanning. After the first pass by the print head in Its scanning direction, the sheet will be advanced In the sheet feed direction by a distance equal to a, after which the print head 2 will perform its second pass. At this point, a complete band will have been printed. Before the next pass, the sheet will be advanced by a distance equal to 48XA-A/2 in preparation for printing the next band. If printing 6 PATENT PD-9677 is to be effected in a single direction, the print head must be returned to its starting position before executing the next pass.

on the other hand, when full color printing is to be effected, it is preferred, according to the present invention, to utilize only the 16 black ink nozzles at the right-hand end of the row of black ink nozzles so that the same number of nozzles will be used for printing each of the four colors. This results in a simplification of the circuitry employed for supplying drive signals to the nozzles. Specifically, If data is supplied at the same rate to the nozzles for each ink color, the timing circuitry for controlling the delivery of this information can be simplified.

In accordance with the invention, the range of colors which can be produced by applying dots of ink of different colors upon one another at the same point on the sheet being printed is enhanced by the order in which such dots are applied. Specifically, this can be achieved by applying such dots in the order: black, cyan, magenta, yellow, or essentially the order from the darkest color to the lightest color. If only two or three ink colors are to be applied to a given point on a sheet, they should also be applied according to their positions in the order set forth above.

In effect, it has been determined that, particularly in a subtractive color system, the lightest ink, in this case yellow, can have a noticeable effect on the color of the resulting dot only if it is applied atop the other dots. If, on the other hand, the layer of yellow ink is covered by any of the other inks, they will essentially mask the yellow Ink and minimize, or substantially eliminate, its contribution to the resulting color.

since the black ink would have a similar effect on any one of the three color inks, it should i always be applied first at any location where it is to be applied to contribute to the final ink color.

In order to apply Ink dos of different colors to the same point on a sheet in a simple manner, nozzles 4, 6, 8 and 10 are arranged so that, during color printing, a band of rows on the sheet being printed will receive ink dots from the black ink nozzles 10 employed during the color printing operation during a first pass of the print head. That same band of tows will then be positioned, by advancing the sheet, to receive ink clots from the cyan ink nozzles A during a subsequent pass, followed by ink dots from magenta nozzles 6 during a further print head pass, ending with reception of ink dots from yellow ink nozzles 8 during the next print head pass. Each point on the sheet which is to receive ink dots of only two or three of the colors will nevertheless always receive these ink dos in the preferred sequence, I.e., if black ink is applied, it will always be applied first and if yellow ink is to be applied, it will always be applied last.

While the arrangement illustrated in the Figure appears to produce the best results, It has also been found that substantially similar results would Joe achieved if the locations of the cyan and magenta nozzles are interchanged since these colors are close to one another in lightness.

For each row of nozzles, illustrated in the Figure, adjacent nozzles are spaced apart in the print head scanning direction, i.e., in the row printing direction, by a distance B. As explained earlier herein, the print data which must be converted into nozzle energizing signals is organized with reference to vertical columns of the area to be printed so that when a respective nozzle is assigned to each row of the printing region, the timing of the delivery of nozzle energizing signals to each nozzle must be adjdsted 7 PATENT PD-9677 i PATENT a PD-9677 1 1 according to the magnitude of the spacing B between adjacent nozzles.

Heretofore, this has required relatively complex timing circuitry in view of the values 5 previously employed for the dimension B. According to the present invention, the complexity of such timing circuitry can be substantially reduced by giving spacing B a value which is equal to the product of 2n, where n is a positive integer, and the spacing between columns of the printing matrix, or the horizontal resolution of the printer. The first term of this product may be one of the integers 2, 4, 8, 16, 32, etc. It is Presently preferred that a value of 16 he chosen for this factor.

The horizontal resolution of a print head is deter-mined by the smallest distance which can exist between successive dots along a row being printed. This is determined by the design of the printer and the rate at which driving signals can be supplied to each nozzle. Typically, high quality printers are constructed to have a resolution of 300 dots per Inch, but can he set to have a lower resoldtion, for example 150 dots per inch.

Thus, in a preferred embodiment of the present 1 bl 1 1 invention, the value of dimension 13 would be 16/300=0.0533 inch and dimension A would he 1/150.00666 inch.

As will be appreciated, the inclination of each row of nozzles to the print head scanning direction, or the slope of each row.ot nozzles, will correspond to A/B.

Since the horizontal spacing, B, between successive nozzles of each row has a value equal to the smallest allowable spacing between dots multiplied by a quantity represented by an integral binary number, the delays which must be introduced between the energizing 9 PATENT PD-9677 signals to adjacent nozzles for effecting printing on a single column can be controlled in a simple manner by binary signals, without any additional Interpolation being required for this purpose.

It will further be noted that in the nozzle arrangement illustrated in the Pigure, the uppermost one of nozzles 10 is separated from the lowermost one of nozzles 4 by a distance C. This distance can have any suitable value, one possible value being two times the vertical resolution of the printer and a second possible value being the vertical height of each nozzle row.

The circuitry employed for supplying nozzle driving signals to the print head can be designed in accordance with principles known In the art. The only difference would be that in place of the complex timing circuitry previously employed, use can be made of timing circuitry which supplies Integral binary shifting signals.

With regard to this aspect of the present invention, the nozzle pattern can be other than that illustrated, provided that there Is at least one group of nozzles which extend at an angle to the print head scanning direction and which are each assigned to a given one of a plurality of adjacent rows of a region being printed.

While the description above refers to particular embodiments of the present invention, it will be understood that many modifications may be made without departing from the spirit thereof. The accompanying claims are intended to cover such modifications as would fall within the true scope and spirit of the present invention.

The presently disclosed embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims, rather j PATENT PD-9677 than the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

t- J 11 PATENT PD-9677

Claims

WHAT IS CLAIMED IS:

1. A method for forming colored dot-s on a substrate with a color ink jet printer having means for projecting dots of ink of a plurality of different primary colors of a subtractive color system, comprising projecting dots of two colors to a single location on the substrate in a sequence which proceeds from the darker to the lighter one of the two colors.

2. A method as defined in claim 1 wherein there are three primary colors and said step of projecting is carried out such that at each substrate location where ink of a plurality of primary colors, one of which is the lightest primary color, is projected on a single substrate location, ink of the lightest primary colors is projected last.

3. A method as defined In claim 2 wherein said printer further has means for projecting dots of black ink at selected locations on the substrate, and said step of projecting dots is carried out to project a black ink dot first at each location at which a dot of ink of at least one primary color Is also being J?rojected.

A method as defined In claim 3 wherein the primary colors are cyan, magenta and yellow and when a dot of yellow ink and a dot of Ink of one other primary color are projected at a single location, the dot of yellow Ink Is projected last.

5. A method as defined In claim A wherein the Inks are phase change inks.

4 12 PATENT PD-9677

6. A method as defined in claim 2 wherein the primary colors are cyan, magenta and yellow and when a dot of yellow ink and a dot of ink of one other primary color are projected at a single location, the dot of yellow Ink is projected last.

7. A method as defined In claim 6 wherein the inks are phase change Inks.

S. A method as defined in claim 1 wherein said printer further has means for projecting dots of black ink at selected locations on the substrate, and said step of projecting dots is carried out to project a black ink dot first at each location at which a dot of ink of at least one primary color is also being projected.

9. A method as defined In claim 8 wherein the inks are phase change inks.

10. A print head for an Ink jet printer, said print head having first nozzle means for projecting dots of ink of a first primary color and second nozzle means for projecting dots of ink of a second primary color which is lighter than the first primary color onto a sheet which is advanced past said nozzle means In a sheet feed direction, wherein said nozzle means are located relative to one another such that as a sheet is advanced in the sheet feed direction, each incremental region of the sheet passes said first nozzle means before passing said second nozzle means.

A 1 J PATENT PD-9677

11. A print head as defined In claim 10 further comprising third nozzle means for projecting dots of an ink of a third primary color onto the sheet, said third nozzle means being located, in the sheet feed direction, between said first and second nozzle means.

12. A print head as defined in claim 11 wherein the primary colors are primary colors of a subtractive color system.

13. A print head as defined in claim 12 further comprising fourth nozzle means for projecting dots of black ink onto the sheet, said fourth nozzle means being located such that as a sheet is advanced In the sheet feed direction, each Incremental region of the sheet passes said fourth nozzle means before passing any one of said first, second and third nozzle means.

14. A print head as defined In claim 13 wherein each of said nozzle means Is composed of an equal number of nozzles.

15. A print head In an ink jet printer, said print head being movable in a scanning direction and comprising a row of nozzles for projecting dots of Ink onto a sheet which is advanced past said print head In a sheet feed direction which is perpendicular to the scanning direction, said row of nozzles being inclined to the scanning direction and said print head being movable to provide a predetermined minimum distance in the sheet feed direction between dots projected by each said nozzle, wherein said nozzles are spaced apart in the scanning direction by an Integral multiple of the predetermined minimum distance, which Integral multiple has a value of 2n, wherein n Is a positive integer.

14 PATENT PD-9677

16. A print head as defined In claim 15 wherein n flas a value of four.

17. A print head as defined in clain 16 wherein the predetermined minimum distance is 1/150 1 nch.

11

18. A print head as defined in claim 15 wherein the predetermined minimum distance is 1/150 Inch.

i Published 1991 at'rbe Patent Office. State House. 66/71 High Holbom. londonNVC I R47P. Further copies Triky be obtained from Sales Branch. Unit & Nine Mile Point. Cwmielinfach. Cross Keys. Newport. NPI 7HZ Printed bv Multiplex techniques lid. St Mary Cray. Kent.