Ink-drop generator and printer assembly

FIELD OF THE INVENTION

The present invention relates to the field of ink-drop generators used in inkjet printers. It also relates to a print head and a printer using said ink-drop generator.

BACKGROUND ART

The principle of the inkjet printer is now well-known and has been described, for example, in the American patent No. U.S. Pat. No. 3,373,437 granted to Richard G. Sweet. In this type of printer an ink-drop generator produces drops of ink that are electrically charged then deflected or not deflected by deflecting electrodes to print or not print a downstream substrate. The technology of deflected continuous jets has been widely used in industrial marking applications where inks incorporate volatile solvents and/or pigments for mediums that are difficult to mark where the atmosphere is rendered difficult due to the presence of dust and a variable temperature. The printed widths are small and the outputs are high. A generator of small drops, such as that described in French patent No. FR 2 653 063 (granted to the present applicant), generally comprises a single inkjet created from a pressurized inkjet cavity that has a jet nozzle on one of its surfaces.

The ink cavity also has an elongated cylindrical transducer on a surface opposite that which comprises the nozzle. Said transducer vibrates at a high frequency according to a longitudinal mode and constantly fragments the jet into regular, identical, equidistant droplets. The assembly consisting of the ink cavity, transducer and nozzle plate is called an ink-drop generator. The ink-drop generator is associated with charge electrodes, deflecting electrodes and possibly an ink collector to constitute a print head. One or more print heads can be mounted on the same printer. One or more ink-drop generators can also be assembled to constitute a single print head. For instance, patent application Ser. No. 2 653 063 referred to above discloses a print head comprising at least two modulation bodies and therefore at least two nozzles equipped with means for adjusting each jet and a single ink-collector module with a single pipe for returning the ink to the common circuit. This type of print head offers the possibility of printing large characters at a higher rate than that provided by a head with only one jet. The detailed embodiment of the invention described below also comprises two modulation bodies, which are also called acoustic-wave generators, shakers, resonators or transducers in documents concerning this technology, but each body actuates several inkjets.

In the description of the prior art contained in European patent EP 0 449 929 B1 it is recalled in col. 1, lines 24-25 and 54-58 that, for chambers comprising several jets, each nozzle is positioned facing either its own acoustic vibration generator or a section of a longitudinal acoustic generator whose measurements extend parallel to the line formed by the jet-nozzle assembly. The acoustic generator is supplied with sufficient power to print a vibration with ink in a direction parallel to the jet. The patent then points out in col. 2, lines 1-8 that this configuration of the vibration generator relative to the nozzle plate is not indispensable provided certain conditions of resonance are met. If the conditions of resonance are complied with a single acoustic generator can stimulate the ink passing through a line of nozzles or part of a line of nozzles that has a length considerably greater parallel to the line of nozzles than the size of the acoustic generator in the same direction, for example 5 to 10 times larger. The condition to be complied with is that the vibrating body vibrates virtually only in a longitudinal mode and at a resonance frequency that differs by −10% of the excitation frequency of the natural resonance vibrations in the ink of the cavity between the end of the body and the nozzle plate, the width of the body being smaller than the length of the series of nozzles or the part of the series of nozzles associated with said body.

In this patent the lateral walls of the ink chamber have a cross-section perpendicular to the line of nozzles disposed in a V shape. The tip of the V is turned towards the line of nozzles. The section of chamber comprising the V-shaped walls may be changed to enable the height of the V to be varied depending on the density of the ink and therefore the speed of the sound in the ink used.

Patent application WO 98 51503 also describes an ink-drop generator for an inkjet printer with the following characteristics: the lateral walls of a cavity containing the ink consist of interior and exterior walls. The resistance component of the acoustic impedance of the external walls is such that the external walls passively dampen the vibrations of the interior walls by dispersing the vibrations. The reactive component of the acoustic impedance of the external walls is such that the external walls actively inhibit the vibrations of the internal walls, said external walls thus ensuring that each inkjet sprays drops of ink at the same predetermined distance from each respective nozzle. This type of configuration is used to prevent the nozzle bearing plate from bending in a direction parallel to the inkjet when the printer is used.

The present applicant has filed European patent application EP 0 532 406 A1 concerning multijet modules and the juxtaposition of several modules positioned side-by-side to obtain a large printing width. Much of the detailed description of the embodiment given below repeats the description of the above-mentioned application, particularly everything that relates to the mechanical fastening of print modules to a module assembly beam.

BRIEF DESCRIPTION OF THE INVENTION

As in the examples of embodiments in European patent applications EP 449 929 B1 or EP 0 532 406 A1 referred to above, the invention relates to a multijet print head, i.e. a head in which a cavity containing pressurized ink delivers several jets that are divided into drops by a single resonator for said cavity. As in the embodiment described in European patent application EP 0 532 406 A1, the invention also relates to a print head capable of being mounted such that it is aligned with other heads to constitute a print assembly comprising a large number of jets equidistant from one another capable of simultaneously printing a wide band, for example two or more meters.

The multijet cavities of the prior art described, for example, in patent applications WO 98/51503 or EP 0 449 929 B1 referred to above, enable a single resonator to actuate several jets. However, the end jets, i.e. those leaving the first and last nozzles of the cavity, spray irregularly, produce distorted drops or are formed at variable distances when said end jets are too close to the walls of the cavity.

The inventor of the present invention has used digital simulations to improve the quality of the end jets, for example by using a particular contour of the lateral wall at the nozzle plate, i.e. where said lateral wall is secant to the nozzle plate. Another factor that affects the quality of the end jets is the angle formed by the lateral wall of the cavity with the nozzle plate. The angle is preferably 90° along the entire contour of the lateral wall.

The relation between the vibrating surface of the resonator and the surface of the nozzle plate should also be taken into consideration. The relation between the surfaces should preferably be approximately 1, for example between 3/4and 4/3. The shape of the transitional surface between a resonator housing and the cavity also plays a role. Finally, the relation of the cavity measurements is also important. Each of the factors mentioned above provides an improvement and the combination of all or some of the factors enables the spray quality of the end jets to be indistinguishable from the quality obtained with the central jets.

It becomes possible to position the end-nozzles very close to the intersection of the lateral wall of the cavity with the axial line joining the nozzles. Under these conditions, even though the distance between consecutive nozzles may be small, it remains possible to create an alignment of several cavities in which all the nozzles are equidistant despite the thickness of the wall separating two consecutive cavities of the same head or two consecutive print heads.

Compared to known embodiments, the present invention also relates to an ink-drop generator suitable for a wide range of inks that does not require the drop generators to be modified and that can be produced in materials capable of withstanding temperatures to which print heads may be exposed in an industrial environment.

To achieve all these aims, the invention relates to an ink-drop generator for an inkjet printer in which an inkjet is sprayed in drops, said generator particularly comprising:

a generator body,

at least one acoustic wave generator with a body elongated in an axial direction to the inkjets, each generator having a vibrating surface perpendicular to the axial direction of the jets, at least one section comprising the vibrating surface of each acoustic generator being housed in a housing of the drop-generator body,

at least one resonance cavity intended to contain ink, the first section only of each cavity possibly being constituted in a main section of said body constituting the main body of the generator and, in this configuration, a second section in a continuation of said main body of the generator connected to be leaktight to the main body of the generator, each cavity having an ink feed and an ink-feed aperture, each cavity being particularly defined by a nozzle plate and a lateral wall secant to the nozzle plate, the intersection of the lateral wall and the nozzle plate defining a first contour line of the lateral wall, the nozzle plate comprising a plurality of nozzles aligned along an axial direction of the nozzles perpendicular to the axial direction of the jets, the axial direction of the jets and the axial line of the nozzles defining a plane of the jets,

a generator characterized in that the lateral wall of each resonance cavity is secant to the nozzle plate perpendicular to said nozzle plate along the entire first contour line of said wall, the first contour line being formed by two equal segments that are parallel to one another and the axial direction of the nozzles, each segment having two ends: a first and a second end, the two first ends of each segment being connected by a first curved line and the two second ends of each segment being connected by a second curved line.

The lateral surface of the cavity therefore consists of two plane walls parallel to one another and, at the axial line of the nozzles, one of the walls containing one of the segments and the other, the other segment, and two curved connecting walls each containing one of the contour curves.

In one embodiment the connecting curved lines of the segment ends are concave towards the inside of the cavity. In general, in order to facilitate manufacture the curved lines are constituted by semicircles the diameter of which is the space between the two segments. Preferably, in order to facilitate a preferred vibration mode in the fluid the largest measurement

1

of the first contour of the cavity lies along the axial line of the nozzles, the distance between the two segments is approximately l/4 and the height of the lateral wall of the cavity is between l/2 and 3l/4, preferably approximately 5l/8. To enable the vibrations produced by the acoustic-wave generator to be transmitted to the ink contained in the cavity it is necessary to connect the acoustic-wave generator housing to the cavity. The connection is achieved by a hollow connector section defined by a lateral connector surface. Said connector surface is intended to connect, for example, a cylindrical shape with a circular base, the diameter of which is the diameter of the acoustic-wave generator, to a cylindrical shape with a more or less flattened rectangular base that is the shape of the lateral surface of the ink cavity. As described above, the space between the two walls of the largest surfaces of the cavity is preferably equal to l/4. The connector surface is preferably obtained as follows: to create the first section of the surface the cylindrical surface with a circular base, the diameter of which is between l/2 and 3l/4 of the acoustic-wave generator, is extended over the section of its periphery that lies between the two planes defined by the largest plane walls of the cavity separated by a distance of l/4 .

Each of the largest walls and/or a continuation of each wall is also hollowed to obtain a hollow the periphery of which is defined by a curved line in the plane of said wall and part of a circle the diameter of which is equal to the diameter of the acoustic-wave generator, said circle being located in a plane perpendicular to the plane wall of the cavity.

The base of the hollow section, which is defined as described above, may be a conical surface, for example, to obtain a progressive junction between the generator housing and the resonance cavity. This junction forms an opening with a more or less rectangular cross-section between the resonator housing and the resonance cavity. The junction of the walls between the resonator housing and the cavity is achieved progressively.

BRIEF DESCRIPTION OF THE DRAWINGS

An example of an embodiment of the invention will now be described with reference to the attached drawings where:

FIG. 1

is an exploded perspective view of an example of an embodiment of the mechanical parts of a print head, the said parts comprising in particular the ink-drop generator body and an ink distributor/collector;

FIG. 2

is a longitudinal cross-section along the plane of the ink-drop generator body and its continuation;

FIG. 3

is a section through the assembled body with its continuation in a plane perpendicular to that of the jets and parallel to the nozzle plate;

FIG. 4

is a transverse cross-section along a plane perpendicular to that of the jets and that of the nozzle plate of the ink-drop generator body and its continuation;

FIG. 5

are in three parts, A, B and C; these three parts of the figure show the shapes of the contours of the intersection of the connection surface between the housing of the sound wave generator and the cavity, the said sections being along planes parallel to the nozzle plate;

FIG. 6

is a cross-section through the generator body along line E—E of

FIG. 2

;

FIG. 7

shows a perspective view of part of a printer comprising an alignment of print heads comprising ink-drop generators of the invention;

FIGS. 8 and 9

show schematic views of cross-section of the part located behind a multijet print module fitted on a supporting beam of a plurality of modules;

FIG. 8

particularly shows a detailed view of the ink feeding pipes;

FIG. 9

particularly shows a detailed view of the ink drainage and recovery pipes;

FIG. 10

shows part of a printer designed to show the shape of the feeding pipes of the various ink generators;

FIG. 11

shows part of a printer comprising several alignments of print heads arranged in series.

FIG. 1

is an exploded perspective view of an assembly of mechanical parts composing part of an ink-drop generator

33

of the invention. It will be seen below that the generator

33

comprises a body

133

, an ink distributor/collector

29

and an ink-drop deflection assembly

32

. In the part discussed here relative to

FIG. 1

the body

133

and distributor/collector

29

will be described.

Body

133

comprises a dual body

1

forming main body

1

and a continuation

2

. Dual body

1

comprises a section with two cavities

6

. Each cavity

6

is partly composed of a hollow in dual body

1

and partly of a hollow in continuation

2

of dual body

1

. Continuation

2

is connected to dual body

1

by means of a sealed connection. The continuation

2

of dual body

1

is mechanically composed of a mechanical assembly of three parts, a housing

4

of a cavity part, a thin strip

3

bearing calibrated holes

36

forming nozzles and a reinforcement plate

5

. The reinforcement plate

5

and strip

3

are fastened by means of a sealed connection, known per se, for example welding, to a base located outside housing

4

of some of the cavities

6

. Holes in part

5

and the base of part

4

allow jets of ink to pass from inside cavity

6

through nozzles

36

. This embodiment of the nozzle-plate, known per se, makes it possible very accurately to calibrate the nozzles, for example by laser-cutting thin strip

3

to form a clean, neat hole with a diameter of a few tens of μm. In the rest of the present text any reference to nozzle plate

39

is understood to refer to an assembly

39

comprising housing base

4

, strip

3

and reinforcement

5

.

Body

133

is divided into two sections, dual body

1

forming the main body and continuation

2

of the body for machining purposes. The opening in body

133

allows machining of the upper section of cavities

6

using a bit that machines the bottom of dual body

1

and that in the lower section of the same cavities via the top of continuation

2

of main body

1

.

Other than the screws, the leaktightness, positioning and fastening means of main body

1

and its continuation

2

are shown in the drawings but not commented upon as they are known per se.

A description of a cavity

6

will now be given with reference to

FIGS. 2 and 3

.

FIG. 2

is a cross-section along the plane of the jets of main body

1

and its continuation

2

mounted together.

FIG. 3

shows a cross-section through body

133

along plane C—C of

FIG. 2

close to the nozzle plate and parallel to the said nozzle plate.

A cavity

6

has the general shape of a rectangular parallelepiped of length

1

, width more or less l/4 and height somewhere between l/2 and 3l/4 but preferably 5l/8. As explained above, these measurements are designed to encourage vibrations propagating along a plane wave parallel to nozzle plate

39

. The shape of this cavity will now be explained in more detail with reference to FIG.

3

. As stated above, this figure shows a section through a plane parallel to the nozzle plate located a very short distance from the nozzle plate. The contour of this cavity consists of two planar segments

7

,

8

that are generally parallel to one another and located at an approximate distance of l/4 from one another. A side of each segment

7

,

8

is illustrated in

FIG. 3

as the trace in the cross-section plane of the parallel segments

7

,

8

that define an inner periphery of a portion of the cavity

6

. Said segments

7

,

8

are connected by arcuate planar portions

9

,

10

a side of each arcuate planar portion

9

,

10

being illustrated in

FIG. 3

as the trace in the cross-section plane of the arcuate planar portions

9

,

10

. It will be seen from this drawing that cavity

6

is not altogether parallelepiped-shaped since a portion of its inner periphery includes arcuate formations causing the cavity

6

in this case the shape of half-cylinders with circular bases. As can be seen from

FIG. 2

or

FIG. 4

, which is a cross-section through body

133

along line B—B, shown in

FIG. 2

, of a cavity, that also passes through the axis of a jet, arcuate planar portions

9

,

10

and segments

7

,

8

of the cavity

6

are joined perpendicularly to nozzle plate

39

. This shape makes it possible to avoid upward reflections of waves on the walls induced by the V-shaped form of these walls as described in the WO patent application cited above in the description of the prior art. This shape therefore makes it possible to obtain more regular vibration of the ink in the cavity

6

.

In each cavity the apertures

11

, shown particularly in

FIG. 2

, provide the cavity with a supply of pressurized ink. The ink flows through the nozzles

36

once the printer is operating. During jet startup, shutdown or maintenance, the ink may also be supplied in large quantities via aperture

12

. This aperture has a cross-section greater than the sum of the cross-sections of the two ink-supply apertures

11

.

The direction of the ink feeding pipes

11

is in the plane of the preferred vibration mode, perpendicular to the direction of the jets in order to minimise vibration disturbance. With the same end in mind they are also directed more or less along the smallest measurement l/4 of the cavity in order to minimise coupling with the main mode of interference vibration, which is that oriented along the largest measurement

1

of the cavity.

The two feed apertures

11

are located symmetrically relative to a central plane of cavity

6

perpendicular to the plane of the jets, and immediately below upper surfaces

107

,

108

of the cavity. Ink outlet aperture

12

is located in a housing

13

of acoustic wave generator

14

. The ink supplied via apertures

11

is intended to keep the cavity filled and under pressure while the ink leaves via the nozzles

36

. The ink outlet aperture

12

is used during startup, shutdown and hydraulic maintenance phases of the print head. The relative disposition and cross-sections of ink inlet aperture

11

and ink outlet aperture

12

are optimized to ensure uniform distribution of the ink to the nozzles, so as to ensure that the ink in the cavity is not disturbed by the ink-flow pulsations coming from the ink circuit, to ensure that the ink in the cavity is replaced rapidly (draining), and to eliminate any air bubbles in the cavity by ensuring that there is a high flow-rate of liquid during hydraulic maintenance sequences. The body also contains housings

13

each provided for an acoustic wave generator

14

already known per se that has the basic shape of a cylinder

15

ending in a surface

16

that is parallel to the plane of the nozzles, said surface

16

constituting the vibrating surface of the acoustic wave generator. The section of the housing

13

of the acoustic wave generator

14

closest to the cavity has the shape of a cylinder

17

.

In

FIGS. 2 and 4

the acoustic wave generator

14

is shown in dotted lines, firstly in a position close to its assembled position, and secondly once in its assembled position. In the assembled position the contour of the acoustic wave generator

14

is practically identical in

FIGS. 2 and 4

with that of the housing of the generator

14

. In the drawings, particularly

FIGS. 2 and 4

, the housing of the acoustic wave generator

14

is located above cavity

6

. This “above” position is in no way compulsory in practice. However, the terms “above” and “below” are used as a convenient spatial reference to describe the position of components relative to one another. In the example shown, the cylinder of the acoustic wave generator

14

is of diameter l/2, i.e. half the length of cavity

6

and its axis lies both in the plane of the jets and equidistant between the ends of cavity

6

. In operation, the vibrating surface

16

of generator

14

is located level with the upper section of the cavity

6

. This arrangement is in no way compulsory and this surface may be disposed slightly higher in the housing

13

of the acoustic wave generator. Given the shape of the acoustic chamber and the shape of the housing of generator

14

, in order for the acoustic waves to be transmitted efficiently and in a preferred vibration mode through the ink in cavity

6

, it is necessary to provide a connection

18

between housing

13

of acoustic wave generator

14

and cavity

6

. This connection

18

, which consists of a hollow in the segments

7

,

8

, will now be described.

It should first be noted that in terms of the width of cavity

6

the connection is provided by the continuation of the cylindrical surface of housing

13

of acoustic wave generator

14

. This point will be explained in greater detail below with reference to FIG.

5

A.

FIG. 5A

shows the shape of the cross-section of cavity

6

as a plane parallel to the plate

39

carrying the nozzles

36

. The projection on the cross-section plane of cylinder

17

forming the housing of acoustic wave generator

14

is also shown in dotted lines on a section outside cavity

6

and in unbroken lines inside cavity

6

. The centre of the circle representing this projection is located on the longitudinal axial line of cavity

6

equidistant between the two ends of this cavity. For the sections of the connection located between the two planar segments

7

and

8

of cavity

6

shown in

FIG. 5A

, the connection surface includes as shown in part A of continuations

19

and

20

, shown by unbroken lines, of the cylindrical section

17

of the housing

13

of acoustic wave generator

14

. In this way, looking at connection

18

along an axial line of a jet, it will be seen to have a shape whose projection onto the cross-section plane shown in

FIG. 5A

will now be explained.

This opening is composed of a closed cylindrical surface comprising, on the one hand, continuations

19

and

20

of the cylindrical surface and, on the other, the flat parts of the surfaces of the planes containing segments

7

and

8

lying between the ends of said continuations

19

and

20

of the cylinders. The shape of that section of the lateral surface of connection

18

that lies between continuations

19

and

20

of the cylindrical surface will now be explained.

In order to define this shape,

FIG. 5B

shows a cross-section through the wall of connection

18

in a plane parallel to the nozzle plate located between a low end section and a high end section of connection

18

. The cross-section of this connection consists of a line comprising, in order, an end of continuation

19

, a straight section

22

that is part of segment

7

, followed by a curved section

21

, and finally another section

23

of segment

7

, an end of continuation

20

and sections

23

′,

21

′,

22

′ that are respectively symmetrical with sections

23

,

21

,

22

relative to a longitudinal axis XX′ of the cavity. We will now consider the variations in the length of said curved section

21

between the low end section of the wall and the high end section. In the low end section of connection

18

the length of curved section

21

, shown in part A of

FIG. 5

, is nil such that the perimeter of the section is composed of sections of continuations

19

and

20

, sections

22

,

23

of segment

7

joining the ends of continuations

19

and

20

and sections

22

′,

23

′ of segment

8

joining the ends of said continuations

19

,

20

. When the cross-section plane located between the low end sections and the high end sections approaches the high end section the measurements of sections

22

,

23

located between curved section

21

and each of continuations

19

,

20

respectively diminish and the length of section

21

increases. As the high end section as shown in part C of

FIG. 5

is reached the length of sections

22

and

23

is nil and curve section

21

consists of a circular section forming a continuous arcuate portion extending between continuations

19

and

20

.

Naturally if housing

13

and generator

14

were not circular cylinders but had a different shape, section

21

at the top would have the shape resulting from an intersection of this shape with a plane parallel to the nozzle plate. In the example described the intersection of high end section of connection

18

with a plane parallel to nozzle plate

39

consists of a circular closed line whose diameter is equal to the diameter of housing

13

of acoustic wave generator

14

, for example l/2. The perimeter of this line is the perimeter of the circle. For an intermediary plane between the high end section and the low end section the perimeter of the straight cross-section of connection

18

by a plane parallel to nozzle plate

39

is formed on the one hand by continuations

19

,

20

of the circle, by sections

22

,

23

of segment

7

, by a curved section

21

, by parts

22

′,

23

′ of segment

8

and by a curved section

21

′. The perimeter of this intermediate cross-section is therefore smaller than the diameter of the circle located at the high end section. Similarly, coming to the low end part, the cross-section of connection

18

by a plane parallel to nozzle plate

39

has the shape shown in part A, i.e. two sections

19

,

20

of a circle and two continuations of segments

7

and

8

located between said two sections of continuations

19

,

20

. The perimeter of the low end part, shown in part A, is therefore smaller than the perimeter of the intermediate lower part shown in part B. Therefore the shape of connection

18

can be characterized by saying that the perimeter of its cross-section by a plane parallel to nozzle plate

39

reduces the further the plane of intersection is from the upper limit and approaches the lower limit.

It will also be noted that the ends of each of sections

21

,

21

′ are located facing one another and thus separated from one another by a distance between segments

7

and

8

of the first contour. In order for good plane propagation of the acoustic waves to occur, the walls of cavity

6

and connection

18

need to have rotational symmetry, i.e. symmetry relative to an axis or to two perpendicular planes passing through the said axis.

In one simple embodiment, part of connection

18

is made using a conical drill bit with an angle at its tip of, for example, 90°. When the bit is conical the different sections

21

are segments of circles of nil diameter at the lower end section and a diameter equal to that of housing

13

of the acoustic wave generator

14

. This embodiment is shown in

FIGS. 2 and 4

. In

FIG. 2

the intersection of the cone with the plane of segment

7

of the cavity results in a segment

24

of a hyperbola while

FIG. 4

, in which the cross-section is along section B—B, i.e. more or less along the axis of housing

13

of acoustic wave generator

14

, the intersection has the shape of two 90° segments

26

. In this example, moreover, the low end section of housing

13

coincides with the high end section of cavity

6

and thus a low end section

25

of connection

18

is positioned at a distance from the top of cavity

6

slightly less than half the diameter of the cylindrical section of housing

13

of acoustic wave generator

14

.

Another important characteristic of the invention will now be explained. As was seen above, because the segments

7

,

8

, and arcuate planar portions

9

,

10

of the cavity are perpendicular to the nozzle plate

39

at the level of said nozzle plate

39

and that the section of connection

18

between the lower surface

16

of acoustic wave generator

14

and cavity

6

is created progressively, a plane wave perpendicular to the axis of housing

13

propagates in cavity

6

. As this wave is plane, no problems are created due to boundary effect. Consequently a nozzle

361

,

362

may be positioned very close to one of arcuate planar portions

9

,

10

without its operation being affected. For example, it will be seen from

FIGS. 2 and 3

that an end-nozzle

361

is located very close to the arcuate planar portion

10

of cavity

6

. Similarly it will be seen that an end-nozzle

362

is located very close to the arcuate planar portion

9

separating two identical cavities of body

133

. The closeness of nozzle

361

to the arcuate planar portion

10

allows the axis of the nozzle to be at a distance less than half the interval between two consecutive nozzles of the cavity even if said interval is small. Similarly the distance between end-nozzle

362

of arcuate planar portion

9

between two cavities

6

allows the distance between this nozzle

362

and the next consecutive nozzle located in the other cavity of body

133

to be less than the distance between two consecutive nozzles in a single cavity. Hence the interval between consecutive nozzles of all the nozzles in the two cavities remains equal, even when it is small. Moreover, due to the fact that the distance between one end-nozzle and the outer surface of the portion where it intersects with the axis of the nozzles is less than half the interval between two nozzles, it becomes possible to place side by side two modules that are, for example, identical or have the same characteristic that the closeness of the nozzle of one cavity relative to the outer surface of the body containing said cavity, without the interval between two consecutive nozzles of the resulting assembly being modified.

To take the best advantage of this fact without the tolerances of an assembly of different bodies

133

resulting from the accumulated effect of the measurement tolerances on each body, each body is fitted with positioning pins

124

that cooperate in a way known per se with positioning holes on a support beam

28

bearing the alignment of the bodies. Clearly the effect would be the same if the pins were on the alignment beam and the bodies fitted with positioning holes.

In the example explained here and shown particularly in

FIG. 1

, the positioning pins

124

are not fastened directly onto main body

1

. Body

1

is fastened onto an ink distributor/collector

29

. The distributor is an intermediate part used to connect body

133

to the ink circuit. For this purpose it has as many ink collection gutters

34

as there are nozzles and ink inlets and outlets known per se to maintain cavity

6

under pressure. Part

29

is connected to body

133

by any fastening means and is positioned by positioning means, for example by continuations of the pins

124

fitting into the holes (not shown) in body

133

.

It will be seen that in the embodiment described above the surface of nozzle plate

39

is

\frac{l^{2}}{16} (3 + \frac{π}{4})

and that the vibrating surface

16

of the resonator is

\frac{π l^{2}}{16}

such that the relation of the values of these two surfaces is

(\frac{3}{π} + \frac{1}{4})

or approximately 1.15.

The location of the ink inlet and outlet apertures will now be described with reference to

FIGS. 2 and 6

.

FIG. 6

is a cross-section through dual body

1

at apertures

11

and

12

in a plane parallel to nozzle plate

39

.

As shown in

FIG. 2

, the ink inlet apertures

11

are each located at one end of cavity

6

more or less directly above end-nozzles

361

,

362

respectively.

Since the diameter of the nozzles is very small (approximately 50 μm), the rate of ink flowing through them is very slight. It follows that the ink-flow supplied to the nozzles is also very small. The cross-section of ink inlet apertures

11

and ink outlet apertures

12

is set at a measurement considerably greater than the diameter of the nozzles such that the speed at which the ink still in the cavity travels is very slight. The ink is therefore subject to the vibrations of the transducer while it is virtually static.

The disposition of the ink inlet apertures

11

on the top ends of cavity

6

and immediately beneath upper surfaces

107

,

108

respectively of cavity

6

, which at this point mask the propagation of acoustic waves, limit the disturbance of vibrations by the ink-low.

During maintenance operations the ink outlet occurs higher through an aperture

12

(shown in

FIG. 2

) located in the cylindrical section

15

of housing

13

of acoustic wave generator

14

. The ink flows towards outlet aperture

12

from cavity

6

through a clearance between the cylindrical section

15

and acoustic wave generator

14

. The use of a single outlet aperture

12

eliminates areas of static fluid and optimizes drainage of the ink cavity. Finally, in normal operation the solenoid valves controlling the print head prevent ink from flowing through outlet aperture

12

; the ink around this aperture is therefore static. It also acts as a lubricant and vibration insulator for the acoustic wave generator

14

.

FIG. 6

shows ink pipes

37

. The outermost sections of these pipes join curved surfaces

9

,

10

such that they are tangential in order to optimise the drainage of the cavity. The two pipes

37

are symmetrical to one another relative to a perpendicular plane of the jet plane. They open into a distribution throat

88

located between dual body

1

and collector/distributor

29

.

The assembly of generators or ink print modules

33

that each comprise a body

133

and an ink collector is described below with reference to

FIGS. 7-9

.

An example of this kind of module mounted on a beam

28

is shown in FIG.

7

.

FIG. 7

is a view showing a printing device comprising an assembly of eight print modules

140

of m=8 print jets

27

that form a continuous row of 64 regularly spaced print jets. The eight print modules are mounted adjacent to one another on a supporting beam

28

common to all the modules. Each print module comprises:

a collector/distributor

29

a multijet deflector assembly

32

a body

133

the collector/distributor, which is a one-piece body

29

comprising gutters

34

for collecting the non-deflected drops of each jet, supports body

133

which is capable of delivering

8

inkjets through

8

nozzles

36

; the eight inkjets are regularly spaced in a plane parallel to beam

28

;

multijet deflector assembly

32

is shown in two positions: in the low, or working position on the modules located the furthest to the left of FIG.

7

and in the high, or maintenance position on the modules located the furthest to the right. The function of this type of deflector assembly and its construction are known in themselves. They will only therefore be described briefly below. When each jet of liquid leaves nozzles

36

it breaks up into micro droplets and passes through multijet deflector assembly

32

where certain drops are electrically charged by charge electrodes then deflected from their initial trajectory towards gutter

34

by deflecting electrodes, said deflecting and charge electrodes belonging to deflector assembly

32

, to create an impact on a printing substrate that scrolls in front of the printing module. This type of multijet deflector assembly

32

to deflect m=8 inkjets is described, for example, described in French patent application No. 91 05475 filed by the present applicant on 3 May 1991.

An actuating part

31

that rotates multijet deflector assembly

32

around an axis

49

is constructed as part of supporting beam

28

.

It will be seen in reference to

FIGS. 8 and 9

that the side of supporting beam

28

opposite that bearing collector

29

of each print module is associated with a single part

30

that creates, in combination with said beam

28

, a tank

62

for collecting or draining the ink from the collector gutters of the eight print modules and, in combination with a single plate

110

, a single cavity

111

for distributing the ink to the eight devices

33

for generating the eight inkjets. Support beam

28

has internal pipes that connect, on the one hand, collector tank

62

and, on the other, gutters

34

of generator devices

33

mounted on supporting beam

28

and the internal supply pipes.

It should be noted that

FIGS. 8 and 9

are essentially schematic cross-sections to support the description and are not actual cross-sections of the device. It is for this reason that pipes in the figures are not always in the cross-section plane but in the parallel planes. The schematic cross-section of

FIG. 8

is mainly of a plane of the feed pipes of a print module

33

and a plane of ink-collector pipes undirected towards a printing substrate from gutters

34

. The pipes used for ink collection are not necessarily in the same plane as those used for the supply.

Similarly,

FIG. 9

mainly shows the plane of the ink drainage and collection pipes but the pipes relative to these two functions are not necessarily in the same plane.

As described above, body

133

is supplied with ink through pipes

37

pierced in body

133

and a collector throat

88

between body

133

and collector

29

. Throat

88

communicates with the rear of collector

29

via a hole pierced through said collector, as shown in

FIG. 1

by an arrow. Similarly, drainage opening

12

communicates with the rear of collector

29

via pipes pierced in body

133

and collector

29

. Gutters

34

for collecting unused ink drops from a jet, i.e. non-deflected drops, provided in the lower section of collector

29

communicate with the rear section of collector

29

via an internal pipe of said collector

29

. The eight internal pipes open into a suction cavity of collector

29

.

FIGS. 8 and 9

show the workings at the rear of collector

29

in terms of the ink circuits.

The ink supply circuit of each print module will now be described with reference to FIG.

8

. This figure is a schematic transversal cross-section through a supporting beam

28

of an assembly of modules and components on the rear section of said beam

28

. A part

30

is assembled onto beam

28

by bolts and impervious seals (not shown). These bolts are also used to assemble a rear plate

110

to the rear of part

30

.

Ink is distributed to all cavities

6

of the eight modules by a pressurized distributor

111

created on the rear surface of part

110

. The distributor communicates with pipes

38

pierced through beam

28

via pipes that are preferably rigid, such as pipe

144

shown in FIG.

8

and solenoid valves

86

called feeding valves. In

FIG. 8

a single connector pipe

144

between distributor

111

and a single solenoid valve

86

are shown. In fact there are as many pipes, solenoid valves

86

and pipes

38

as print modules.

Pressurized cavity

111

communicates with ink pressurizing means (not shown) via a connector

69

.

A tank

62

, shown in

FIGS. 8 and 9

, is created by a first cavity provided in beam

28

and a second cavity provided in part

30

. The collection and drainage circuit will now be described with reference to FIG.

9

.

Tank

62

, called the collector or drainage tank, is connected to a solenoid valve

89

, called a drainage valve, via a pipe

63

of part

30

, a throat

64

between parts

30

and

110

, a pipe

65

pierced in part

110

, an external pipe

120

, a pipe

92

of part

30

, a throat

91

between parts

30

and

110

and a pipe

90

pierced in part

30

. Said solenoid valve

89

is also connected to the rear of collector

29

by a pipe

77

. Said pipe

77

communicates with opening

12

of cavity

6

through collector

29

and body

133

. Tank

62

is common to all the print modules mounted on beam

28

, i.e. the eight modules shown in FIG.

7

. There is a pipe

77

,

90

,

65

,

63

, a throat

91

,

92

and a drainage solenoid valve

89

for each print module. Tank

62

also communicates with the collector gutters of collectors

29

via pipes

59

pierced in beam

28

. The single tank

62

communicates with a suction pump (not shown) via a single

73

pipe pierced through parts

30

and

110

.

During printing the non-deflected ink from gutters

34

is permanently sucked and returned to the ink circuit. In the drainage mode solenoid valves

89

are open and the suction pump sucks ink from tank

62

collected from the gutters and openings

12

of cavities

6

.

Another aspect of the invention will now be described with reference to

FIG. 10

that shows a rear perspective view of a supporting beam

28

. As explained above the rear surface of support

28

is associated with a single part

30

that creates, in combination with said beam

28

, a collector or drainage tank

62

(

FIGS. 8

,

9

) and, in combination with a plate

110

, a cavity

111

for distributing ink to the eight devices

33

for distributing eight inkjets.

The aim of

FIG. 10

is to show a characteristic of pipes

141

-

144

that each supply an ink generator

33

.

The aim of this characteristic is to ensure that the pressure drops are identical in each pipe

141

-

144

joining distribution cavity

111

to each generator

33

, irrespective of the position of the generator relative to cavity

111

.

To this end all pipes

141

-

144

are of the same length.

Moreover, all the pipes include the same number of elbows. The value of an elbow angle of a pipe is identical on all the other pipes.

These characteristics of pipes will now be described in detail in reference to FIG.

10

. As this figure is a semi-cross-section, only four pipes are visible. A pipe that supplies four other pipes symmetrical to pipes

141

-

144

relative to a plan perpendicular to beam

28

is not shown.

Each connector pipe has a start end section

141

a

-

144

a

perpendicular to plate

110

and a finish end section

141

b

-

144

b

also perpendicular to plate

110

. The end sections of a pipe, for example

144

a

,

144

b

, are connected together by a central pipe section

144

c

parallel to plate

110

. The length of this section varies depending on the distance between the supply point of a generator

33

and the starting point of cavity

111

. The sums of the lengths of sections a, b, c of each pipe

141

-

144

are equal. This means, for example, that central section

141

c

of pipe

141

that supplies a generator

33

close to central supply cavity

111

is shorter than central section

144

c

of pipe

144

that supplies a generator

33

further away from cavity

111

. On the other hand end sections

141

a

,

141

b

of pipe

141

are longer than sections

144

a

,

144

b

of pipe

144

. Given the different configurations pipes

141

-

144

are nevertheless equal in length. They each comprise two connector elbows that are at right angles and with the same radius of curvature. All the pipes are rigid, for example metal, to enable them to retain their shape. In the example of

FIG. 10

it was not necessary to include a section of S-shaped piping to absorb the dilations although one could be provided depending on the conditions of use of the printer assemblies. The position of the S-shaped sections in the piping matters little, it being essential however that they are identically shaped and connected to the rest of the piping.

A printer of the invention comprises one or more supporting beams

28

equipped with print heads

32

that enable ink to be sprayed towards a printing substrate. In principle when there are several beams each beam prints a different colour ink such that a colour image is produced. The advantage of a printer configured according to the invention is that an entire width of the substrate may be printed simultaneously. Under these conditions a relative movement of the print heads and the substrate in a parallel direction to beam

28

is no longer necessary because the width that is printed simultaneously can be adapted to the width of the substrate. The only remaining movement is that of the head relative to the substrate in a direction perpendicular to support beam

28

. This may be a continuous, rapid movement.

FIG. 11

shows a printer provided with several support beam assemblies

28

positioned parallel to one another and printing the same substrate scrolling perpendicular to the beams.

FIG. 11

is a schematic perspective view of this type of configuration. A support frame

150

holds a set of beam assemblies

28

a

,

28

b

,

28

c.

Means (not shown) enable substrate

151

to scroll under the inkjets of print modules or heads

14

a

of beam

28

a

, then

140

b

of beam

28

b

and

140

c

of beam

28

c.

The beam

28

a

the furthest upstream relative to the scrolling substrate periodically prints a reset mark, for example on an edge of the substrate. Each downstream beam

28

b

,

28

c

is provided with a position sensor (not shown) to detect these marks and enable the pixel data of the line to be reset virtually continuously. Good superimposition of colours is therefore obtained.

Number	Name	Date	Kind
4138687	Cha et al.	Feb 1979	A
4303927	Tsao	Dec 1981	A
4370662	Hou et al.	Jan 1983	A
5457484	Regnault et al.	Oct 1995	A
5666677	Crawford et al.	Sep 1997	A
6003971	Hanks et al.	Dec 1999	A

Number	Date	Country
0 449 929	Jul 1995	EP
0 869 001	Jul 1998	EP

Ink-drop generator and printer assembly

Information

Patent Number

Date Filed

Date Issued

Inventors

Original Assignees

Examiners

Agents

CPC

US Classifications

Field of Search

US

International Classifications

Term Extension

Abstract

Description

Claims

Priority Claims (1)

US Referenced Citations (6)

Foreign Referenced Citations (2)

Non-Patent Literature Citations (1)