Printing head assembly and printer comprising said printer haed assembly

Abstract

 A printing head assembly (100) for printing a UV curable ink on a substrate (200) comprising: a base plate (18) with an array of nozzle orifices (16), an ink supply (20; and an array of nozzle assemblies (10), each nozzle assembly comprising: a pin (14); a piezo actuator (12), wherein said pin (14) is arranged in relation to said piezo actuator (12) so that in the resting position of the piezo actuator (12), the pin (14) is caused to close said nozzle orifice (16) and so that in the actuated position, the pin (14) is caused to open the nozzle orifice (16) so as to allow said ink to be released through the nozzle orifice (16) onto said substrate (200). The printing head assembly (100) being connectable to a UV light source (30) for curing said ink released onto the substrate (200).

Description

FIELD OF THE INVENTION

[0001] The present invention relates to a printer head assembly and to a printer comprising said printer head assembly.

BACKGROUND OF THE INVENTION

[0002] Presently known so-called ink-jet printer heads and printers comprising these printer heads have the major disadvantage that quite often the ink reservoirs are integral parts with the printer heads, also called disposable print heads. These print heads are supplied as a part of a replaceable ink cartridge. Every time a cartridge is exhausted, the entire cartridge and print head are replaced with a new one. This adds to the cost of consumables and makes it more difficult to manufacture a high-precision head at a reasonable cost. For a typical OEM cartridge priced at CHF15, containing 5 mL of ink, the ink effectively costs CHF3000 per liter, whereas the price of the pure ink is actually only a very small fraction of this price.

[0003] This disadvantage has been partially addressed by an intermediate solution wherein a disposable ink tank connected to a disposable head, which is replaced infrequently. However the print quality degrades gradually and the print head still needs to be replaced quite often. This is partly due to ink required by current ink-jet printers. Most common ink-jet printers are thermal inkjet printers, wherein inside each partition of the ink reservoir is a heating element with a tiny metal plate or resistor. In response to a signal given by the printer, a low current flows through the metal or resistor making it warm, and the ink immediately surrounding the heated plate is vaporized into a tiny air bubble inside the nozzle. As a consequence, the total volume of the ink exceeds that of the nozzle. An ink droplet is forced out of the cartridge nozzle onto the paper. However, the printing depends on the smooth flow of ink, which can be hindered if the ink begins to dry at the print head, as can happen when an ink level becomes low or the printer is not used for an extended period of time. Furthermore, the required thermal characteristics pose serious limitations to the ink used, which might affect print quality. The lifetime of inkjet prints produced by inkjets using aqueous inks is limited; they will eventually fade and the color balance may change. Also since the ink used in most consumer inkjets is water-soluble, care must be taken with inkjet-printed documents to avoid even the smallest drop of water, which can cause severe "blurring" or "running."

[0004] This problem has been partially addressed by piezoelectric printers, which use a piezoelectric crystal in each nozzle instead of a heating element. When current is applied, the crystal changes shape or size, forcing a droplet of ink from the nozzle by squeezing together capillary tubes. This allows use of inks which react badly when heated, and can produce a smaller ink drop in some situations than thermal inkjet schemes. A particular type of printer based on the so-called "piezo drop-on-demand inkjet technology", a technology patented by US 2009/0289984A1, and employing UV-curable ink is the VUTEk PV200 from EFI. The "piezo drop-on-demand inkjet technology" is based on the concept of causing a piezo element to squeeze (when activated) capillary tubes with ink, thereby forcing droplets out of these tubes. The capillary forces prevent ink from dripping out of the tubes once the extra pressure form the piezo element is stopped. Therefore this printer eliminates some of the disadvantages of the thermal ink-jet printers such as strict limitations as to the ink composition (required thermal characteristics). However due to the fact that the tubes are open in the resting position of the printer, this solution does not solve the problem of prolonged idle times, requiring drainage of the printer heads and removal of ink is needed to avoid dried ink to clog the piezo openings. The use of UV-curable ink does reduce this problem, but fails to completely eliminate it, since after prolonged exposure to ambient air, the ink will still dry.

[0005] Thus piezoelectric printer heads based on this technology have several disadvantages:

• they are significantly more expensive than thermal printer heads;
• the problem of ink clogging the printer head are still not completely eliminated since continued exposure to ambient air causes the ink to dry within the capillary tubes;
• the piezo technology is limited in number of nozzles making them inherently slow;
• due to the limited density of nozzles, current printer heads with piezo technology have a limited resolution.

TECHNICAL PROBLEM TO BE SOLVED

[0006] The objective of the present invention is therefore to provide an ink jet printer head that:

• is relatively cheap to produce;
• is not affected by prolonged idle times, i.e. neither does the print quality deteriorate, nor does the printer head become unusable due to dried ink
  • therefore requiring no drainage ok ink;
• can achieve high printing speeds;
• is capable of producing high resolution prints.

SUMMARY OF THE INVENTION

[0007] The above-identified objectives of the present invention are solved by a printing head assembly for printing a UV curable ink on a substrate comprising: a base plate with an array of nozzle orifices arranged in one or more rows, said array being arranged transversal to a path of said substrate; an ink supply for supplying the ink to said nozzle orifices; and an array of nozzle assemblies. According to the present invention, each nozzle assembly comprises a pin aligned with a corresponding nozzle orifice of said base plate; a piezo actuator having a rest position and an actuated position, wherein said pin is arranged in relation to said piezo actuator so that: in the resting position of the piezo actuator, the pin is caused to close said nozzle orifice and in the actuated position of the piezo actuator, the pin is caused to open the nozzle orifice so as to allow said ink to be released through the nozzle orifice onto said substrate. The assembly further comprises a UV light source, arranged upstream of the array of nozzle assemblies on the path of said substrate, for curing said ink ejected onto the substrate.

ADVANTAGEOUS EFFECTS

[0008] The main advantage of the present printer head assembly is that due to the arrangement of the nozzle assemblies, wherein a pin connected to the piezo actuator closes/ opens the nozzle orifices, a self cleaning function is achieved. Even if some amount of ink remains would tend to dry in the area of the nozzles, these remains would become loose as soon as the pin is actuated by the piezo actuator.

[0009] Furthermore as opposed to prior art piezo actuated printer heads, where a piezo element squeezes capillary tubes to thereby force ink droplets out of these tubes and where these tubes are open in the resting position of the printer head, the nozzle orifices of the printer head of the present invention are closed in the resting position, therefore ensuring that ambient air does not contact the ink within the nozzle assembly. Therefore the printer head assembly of the present invention does not need to be drained from ink even for prolonged idle times.

[0010] An additional advantage of the present invention in comparison with known consumer ink-jet printers is that the printer head assembly is a separate functional unit form the ink reservoirs, therefore offering an easy and cost efficient printing solution, allowing independent refilling of the ink reservoirs or ink be supplied continuously. A further advantage due to the independent ink supply is that the printing operation must not be interrupted during refilling of the ink reservoirs, thus allowing continuous printing using large amounts of ink as long as the ink supply is not interrupted.

[0011] All these features together provide a maintenance-free operation of the printer head assembly.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Further characteristics and advantages of the invention will in the following be described in detail by means of the description and by making reference to the drawings.

Fig. 1A

shows a cross-section of a nozzle assembly according to the present invention in its closed position;

Fig. 1B

shows a cross-section of a nozzle assembly according to the present invention in its open position as ink is ejected through the nozzle orifice onto the substrate;

Fig. 2A

shows a cross-section of a printing head assembly according to the present invention;

Fig. 2B

shows a cross section of a printing head assembly according to the present invention along lines A-A' on figure 2A depicting closed and opened nozzle orifices of the nozzle assembly;

Fig. 2C

shows a cross section of a printing head assembly according to the present invention along lines B-B' on figure 2A depicting closed and opened nozzle orifices of the nozzle assembly;

Fig. 3

shows a perspective view of a piezo board carrying n rows of piezo actuators with the corresponding pins;

Fig. 4

shows a perspective view of a base plate with n rows of nozzle orifices;

Fig. 5A

shows a simplified top view of a base plate with n rows of nozzle orifices, according to a first embodiment of the present invention, wherein each row of nozzle orifices is arranged with an offset transversal to the path of said substrate in relation to the preceding row of nozzle orifices;

Fig. 5B

shows an illustration of dots producable on the substrate by corresponding nozzle orifices of successive rows of nozzle orifices at a virtual resolution of n times the transversal density of nozzle orifices;

Fig. 6

shows a simplified diagram of a single-ink printer comprising a printer head according to a first embodiment of the printer head of the present invention shown on fig. 5A;

Fig. 7

shows a simplified diagram of a four-ink printer comprising multiple printer heads according to a first embodiment of the printer head of the present invention shown on fig. 5A, each being supplied form a separate ink reservoir;

Fig. 8A

shows a simplified top view of a base plate according to a second embodiment of the present invention, wherein a transversal piezo actuator is arranged in relation to said base plate, so that when activated, to transversally shift said base plate by an offset transversal to the path of the substrate;

Fig. 8B

shows a simplified top view of the base plate of figure 8A in three consecutive positions corresponding to three different lateral offsets by the transversal piezo actuator and a magnified illustration of the dots producable by the same nozzle orifice in each of these three positions, at a virtual resolution of n times the transversal density of nozzle orifices;

Fig. 9

shows a simplified diagram of a single-ink printer comprising a printer head according to the second embodiment of the printer head of the present invention shown on fig. 8A and 8B;

Fig. 10

shows a simplified diagram of a four-ink printer comprising multiple printer heads according to a second embodiment of the printer head of the present invention shown on fig. 8A and 8B, each being supplied form a separate ink reservoir;

Fig. 11

shows a side view of a single-ink printer comprising a printer head according to the present invention;

Fig. 12

shows a side view of a four-ink printer comprising multiple printer heads according to the present invention, each being supplied form a separate ink reservoir.

Note: The figures are not drawn to scale, are provided as illustration only and serve only for better understanding but not for defining the scope of the invention. No limitations of any features of the invention should be implied form these figures.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0013] Certain terms will be used in this patent application, the formulation of which should not be interpreted to be limited by the specific term chosen, but as to relate to the general concept behind the specific term.

[0014] The term substrate shall be used in its broad sense, meaning any substrate to be printed. It shall be understood that the nature of the substrate does not affect the concept of the present invention. The substrate could be a flexible substrate such as paper, cardboard, etc. or a stiff substrate such as metal plates, plastic surfaces, etc.

[0015] When referring to the "path of the substrate" reference is made to the path of the substrate within the printer during the printing operation. Upstream the path of said substrate shall mean a subsequent position on said path as the position compared to. Transversal to said path of the substrate shall mean any direction which transverses said path, i.e. a direction that crosses said path.

[0016] The term well shall be used to refer to a deepening forming a cavity with a well-like shape for temporarily receiving a certain amount of ink.

[0017] Fig. 1A shows a cross-section of a nozzle assembly 10 according to the present invention in its closed position. The nozzle assembly 10 comprises a pin 14 aligned with a corresponding nozzle orifice 16 of a base plate 18 and a piezo actuator 12 having a rest position and an actuated position. The pin 14 is preferably a needle-like member configured to be able to close the nozzle orifice 16, preferably in an airtight manner to prevent ambient air form contacting ink within nozzle assembly 10. In a preferred embodiment a well 19 is formed by a nozzle orifice 16 in the base plate 18 and an appropriate cross section of the base plate around the nozzle orifice 16. The well 19 is provided for temporarily receiving a certain amount of ink.

[0018] The nozzle arrangement 10 further comprises a piezo actuator 12 having a rest position and an actuated position. The piezo actuator 12 assumes these rest position and an actuated position according to an electrical current being applied through lead lines 13 from a control circuitry (not shown). In the preferred embodiment depicted, the piezo actuator 12 is of a type that is expanded in its rest position, i.e. when no electrical current is applied. In its activated position, when an electrical current is applied, the piezo actuator 12 shrinks by a displacement Δz. The pin 14 is arranged in relation to the piezo actuator 12 so that this displacement Δz is transmitted to the pin 14, so that in the resting position of the piezo actuator 12, the pin 14 is caused to close said nozzle orifice 16 and in the actuated position of the piezo actuator 12, the pin 14 is caused to open the nozzle orifice 16 so as to allow ink (temporarily stored in the well 19) to be released through the nozzle orifice 16.

[0019] Fig. 1B shows a cross-section of the nozzle assembly 10 in its open position as ink is ejected through the nozzle orifice 16 onto the substrate 200. As electrical current is applied to the piezo actuator 12, this instantaneously assumes its actuated position, thereby causing the pin 14 to open the nozzle orifice 16 allowing ink to be ejected therethrough. The duration of this phase is defined by the amount of time while electrical current is applied to the piezo actuator 12. This is in turn set by control electronics to which the piezo actuator 12 is connected to. As the duration of the electrical pulse on the piezo actuator 12 is short, the ejection of ink through the nozzle orifice 16 results in a dot on the substrate 200 with a diameter approximately equal to the diameter φ of the nozzle orifice 16. As soon as electrical current is no longer supplied to the piezo actuator 12, this reverts to its resting position thereby closing the nozzle orifice 16.

[0020] According to the present invention, an array of nozzle arrangements 10 such as the one shown on figures 1A and 1B are arranged in one or more rows as depicted on Fig. 2A which shows a cross-section of a printing head assembly 100. As seen on this figure and also on figure 3, the piezo actuators 12 with the pins 14 connected are arranged on a piezo board 112. This piezo board 112 is then placed on the base plate 18 with the corresponding nozzle orifices 16 to thereby form the array of nozzle assemblies 10. With each piezo actuator 12 connected to a control unit by control lines 13, each can be independently actuated to apply ink according to a desired pattern thereby producing a print on the substrate.

[0021] In the preferred embodiment of the present invention depicted on figure 2A, the side walls of the base plate 18 form an ink bath 17 being flooded with ink from an ink supply 20.

[0022] Fig. 2B shows a cross section of a printing head assembly 100 according to the present invention along lines A-A' on figure 2A depicting the closed and opened nozzle orifices 16 of the nozzle assembly 10. When a piezo actuator 12 is in its resting position, then the nozzle orifice 16 is closed, therefore only the pin 14 is seen on this cross section, whereas if a piezo actuator 12 is activated, then ink fills the nozzle orifice 16.

[0023] Fig. 2C shows a cross section of the printing head assembly 100 according to the present invention along lines B-B' on figure 2A depicting the closed and opened nozzle orifices 16 of the nozzle assembly 10. On this figure it can be well seen as the ink fills the entire ink bath 17 and each individual well 19 around the nozzle orifices 16. The figure further illustrates that ink is allowed to enter the well 19 in both the resting and actuated positions of the piezo actuators 12 thus irrespective of the position of the pins 12.

[0024] Fig. 3 shows a perspective view of a piezo board 112 carrying n rows of piezo actuators 12 with the corresponding pins 14. The figure also shows the grid of control lines 13 leading to each piezo actuator 12 allowing individual actuation of each.

[0025] Fig. 4 shows a perspective view of a base plate 18 with rows of nozzle orifices 16 corresponding to the pins of the piezo board 112 shown on figure 3.

[0026] Figures 3 and 4 therefore show an exploded view of the print head assembly 100, the base plate 18 and the piezo board forming a single unit in the final assembled printer head.

[0027] To achieve a high resolution exceeding the limit imposed by the lowest technically possible minimum distance between adjacent nozzle assemblies, two alternative embodiments are proposed.

[0028] The first alternative achieves a higher resolution by providing a base plate 18 with multiple rows of nozzle orifices 16, wherein each row of nozzle orifices 16 is arranged with an offset Δq transversal to the path of said substrate 200 in relation to the preceding row of nozzle orifices 16. Fig. 5A shows a simplified top view of a such a base plate 18 with multiple rows of nozzle orifices

[0029] In the preferred embodiment of the present invention, the base plate 18 comprises n rows of nozzle orifices 16, where

where ΔX is the distance between two consecutive nozzle orifices 16 within a row, and φ is the diameter of the nozzle orifices 16. Furthermore, each row i, where i=2 to n, is preferably arranged with an offset

transversal to the path of said substrate 200 in relation with the row i-1 of nozzle orifices 16.

[0030] As illustrated on figure 5B, the rows 1 to n are activated one after the other as the substrate 200 moves along said path by a longitudinal offset ΔL ≅ Δq into one of the virtual positions (illustrated by positions a), b) and c) of the substrate 200). Therefore a virtual resolution of n times the transversal density of nozzle orifices 16 is achieved, a dot being producable by any one of the corresponding n nozzle orifices 16 (illustrated by nozzles i), ii) and iii)) of any of the n rows of orifices at n distinct positions (illustrated by virtual dot positions A), B) and C)).

[0031] Fig. 6 shows a simplified diagram of a single-ink printer 1 comprising a printer head 100 according to a first embodiment of the printer head of the present invention shown on fig. 5A. The printer 1 further comprises a feed arrangement 50 of a known type for moving said substrate 200 along its path within the printer 1. An ink reservoir 52 is provided for supplying ink through said ink supply 20. The ink reservoir 52 is preferably provided with a UV reflecting coating/ layer to prevent curing of the ink within. In a further embodiment of the present invention, the ink reservoir 52 is pressurized to ensure a greater supply of ink to the printer head assembly 100. A UV light source 30 is provided upstream of the array of nozzle assemblies 10 on the path of said substrate 200, for curing said ink released onto the substrate 200. The UV light source is preferably a UV LED or an array of UV LEDs arranged to ensure that the entire printed width of the surface is illuminated.

[0032] The printer 1 further comprises a control unit 300 for controlling the printer 1 connected to said printer head assembly 100, the feed arrangement 50, the UV light source 30 and ink reservoir 52.

[0033] Fig. 7 shows a simplified diagram of a four-ink printer 1 comprising multiple printer head assemblies 100 according to a first embodiment of the printer head of the present invention shown on fig. 5A, each being supplied form a separate ink reservoir 52.1 to 52.4.

[0034] The number of ink reservoirs can vary freely according to the particular requirements. In the depicted embodiment, the printer comprises four printer head assemblies 100 supplied by four ink reservoirs 52.1 to 52.4, corresponding to the common colors used for printing, i.e. black, cyan, magenta and yellow. The printing process for a multi-colored printer 1 is similar to the mono-color process wherein the multiple printer head assemblies 100 work parallel in a synchronized manner to produce the color print on the substrate 200.

[0035] The other alternative of achieving a resolution exceeding the resolution limited by the lowest technically possible minimum distance between adjacent nozzle assemblies is illustrated on figures 8A and 8B.

[0036] Fig. 8A shows a simplified top view of a base plate 18 according to a second embodiment of the present invention, wherein a transversal piezo actuator 22 is arranged in relation to said base plate 18, so that when activated, to transversally shift said base plate 18 by an offset ΔQ transversal to the path of the substrate 200. The transversal piezo actuator 22 is preferably arranged on the side of the base plate 18 being configured to expand as electrical current is applied to it, thus laterally shifting the base plate 18 by the offset ΔQ transversal to the path of the substrate 200.

[0037] In the preferred embodiment of the present invention, the transversal piezo actuator 22 is configured so that it can transversally shift said base plate 18 by said offset ΔQ in increments of Δq = φ , where φ is the diameter of the nozzle orifices 16. In an even further preferred embodiment, said offset ΔQ = ΔX-φ, where ΔX is the distance between two consecutive nozzle orifices 16 within a row. Therefore the transversal piezo actuator 22 is configured so as to transversally shift said base plate 18 by said offset ΔQ in

increments of Δq = φ.

[0038] Therefore this method allows an increase of n times the printing resolution as compared to the highest resolution limited by the minimum distance between two consecutive nozzle orifices 16. At the same time this method does not require an increase of the number of nozzle orifices to achieve higher resolutions. The n different dimensions of the transversal piezo actuator 22 are achieved by n different electrical current levels applied to it.

[0039] Fig. 8B shows a simplified top view of the base plate 18 of figure 8A in three consecutive positions a), b) and c) corresponding to three different lateral offsets by the transversal piezo actuator 22 and a magnified illustration of the dots A), B) and C) producable by the same nozzle orifice 16 in each of these three positions a), b) and c). This illustration shows an example where ΔX=3*φ, therefore n=2. Figure 8B depicts the base plate 18 in its three positions A), B) and C) which the base plate 18 assumes as it is laterally shifted by the transversal piezo actuator 22. The position a) of the base plate 18 corresponds to the resting position of the transversal piezo actuator 22 where the lateral offset is 0. By this embodiment, the printing resolution can be tripled without the need for additional nozzle orifices 22.

[0040] According to this alternative of resolution improvement, the substrate 200 halts temporarily for a period allowing the base plate 18 to assume all its lateral positions so that the nozzle orifices 16 may print all virtual dot locations.

[0041] In order to increase the printing speed, in addition to the transversal piezo actuator 22 employed for improving resolution, multiple rows of nozzle orifices 16 may be provided which work parallel to each other. In this embodiment, after the above-mentioned temporary halt, the base plate 18 advances by multiple rows equal to the number of rows of nozzle orifices 16.

[0042] Fig. 9 shows a simplified diagram of a single-ink printer 1 comprising a printer head 100 according to a second embodiment of the printer head 100 of the present invention shown on fig. 8A, 8B. The printer 1 further comprises a feed arrangement 50 of a known type for moving said substrate 200 along its path within the printer 1. An ink reservoir 52 is provided for supplying ink through said ink supply 20. The ink reservoir 52 is provided with a UV reflecting coating/ layer to prevent curing of the ink within. In a further embodiment of the present invention, the ink reservoir 52 is pressurized to ensure a greater supply of ink to the printer head assembly 100. A UV light source 30 is provided upstream of the array of nozzle assemblies 10 on the path of said substrate 200, for curing said ink released onto the substrate 200. The UV light source is preferable a UV LED or an array of UV LEDs arranged to ensure that the entire printed width of the surface is illuminated.

[0043] The printer 1 further comprises a control unit 300 for controlling the printer 1 connected to said printer head assembly 100, the feed arrangement 50, the UV light source 30 and ink reservoir 52. The feed arrangement 50 is precisely synchronized with the control of the lateral piezo actuators 22 so that the substrate 200 halts temporarily for a period allowing the base plate 18 to assume all its lateral positions so that the nozzle orifices 16 may print all virtual dot locations. In the example depicted on figure 9, the two rows of nozzle orifices 16 are provided which work parallel to each other. In this embodiment, after the above-mentioned temporary halt, the base plate 18 advances by two rows. Therefore the printing speed is easily doubled.

[0044] Fig. 10 shows a simplified diagram of a four-ink printer 1 comprising multiple printer head assemblies 100 according to a further embodiment of the printer head 100 of the present invention shown on fig. 8A and 8B, each being supplied form a separate ink reservoir 52.1 to 52.4.

[0045] The number of ink reservoirs can vary freely according to the particular requirements. In the depicted embodiment, the printer comprises four printer head assemblies 100 supplied by four ink reservoirs 52.1 to 52.4, corresponding to the common colors used for printing, i.e. black, cyan, magenta and yellow. The printing process for a multi-colored printer 1 is similar to the mono-color process wherein the multiple printer head assemblies 100 work parallel in a synchronized manner to produce the color print on the substrate 200.

[0046] Fig. 11 shows a side view of a single-ink printer 1 for example as depicted on figures 6 or 9, comprising a printer head 100 according to the present invention. The path of the substrate 200 is indicated by the arrow P. The arrangement of the UV light source 20 "upstream" of the base plate 18 can be clearly seen.

[0047] Fig. 12 depicts a side view of a four-ink printer 1 for example as sown on one of the figures 7 or 10, comprising multiple printer heads 1001 to 100.4 according to the present invention, each being supplied form a separate ink reservoir 52.1 to 52.4.

[0048] It will be understood that many variations could be adopted based on the specific structure hereinbefore described without departing from the scope of the invention as defined in the following claims.

REFERENCE LIST:

[0049] 

printer	1
printing head assembly	100
piezo board	112
control line	13
nozzle assembly	10
piezo actuator	12
pin	14
nozzle orifice	16
ink bath	17
base plate	18, 18.1-18.4
well	19
ink supply	20, 20.1-20.4
transversal piezo actuator	22
UV light source	30
feed arrangement	50
ink reservoir	52, 52.1-52.4
substrate	200
control unit	300

Claims

1. A printing head assembly (100) for printing a UV curable ink on a substrate (200) comprising:

- a base plate (18) with an array of nozzle orifices (16) arranged in one or more rows, said array being arranged transversal to a path of said substrate (200),

- an ink supply (20) for supplying the ink to said nozzle orifices (16);

- an array of nozzle assemblies (10), each nozzle assembly comprising:

- a pin (14) aligned with a corresponding nozzle orifice (16) of said base plate (18);

- a piezo actuator (12) having a rest position and an actuated position,

wherein said pin (14) is arranged in relation to said piezo actuator (12) so that:

- in the resting position of the piezo actuator (12), the pin (14) is caused to close said nozzle orifice (16) and

- in the actuated position of the piezo actuator (12), the pin (14) is caused to open the nozzle orifice (16) so as to allow said ink to be released through the nozzle orifice (16) onto said substrate (200);

the printing head assembly (100) being connectable to a UV light source (30), arranged upstream of the array of nozzle assemblies (10) on the path of said substrate (200), for curing said ink released onto the substrate (200).

2. A printing head assembly (100) according to claim 1
characterized in that in the resting position of the piezo actuator (12), the pin (14) closes the nozzle orifice (16) airtight.

3. A printing head assembly (100) according to claim 2
characterized in that in said array of nozzle assemblies (10) is airtight and said ink supply (20) is configured such as to prevent ambient air to enter the array of nozzle assemblies (10).

4. A printing head assembly (100) according to one of the claims 1 to 3
characterized in that:

- said base plate (18) comprises n rows of nozzle orifices (16);

- and each row of nozzle orifices (16) is arranged with an offset Δq transversal to the path of said substrate (200) in relation to the preceding row of nozzle orifices (16).

5. A printing head assembly (100) according to claim 4
characterized in that:

-

where ΔX is the distance between two consecutive nozzle orifices (16) within a row, and φ is the diameter of the nozzle orifices (16); and

- each row i, where i=2 to n, is arranged with an offset

n transversal to the path of said substrate (200) in relation with the row i-1 of nozzle orifices (16).

6. A printing head assembly (100) according to one of the claims 1 to 3
characterized in that a transversal piezo actuator (22) is arranged in relation to said base plate (18), so that when activated, to transversally shift said base plate (18) by an offset ΔQ transversal to the path of said substrate (200).

7. A printing head assembly (100) according to claim 6
characterized in that said transversal piezo actuator (22) is configured so that it can transversally shift said base plate (18) by said offset ΔQ in increments of Δq = φ , where φ is the diameter of the nozzle orifices (16).

8. A printing head assembly (100) according to claim 7
characterized in that said offset ΔQ = ΔX - φ, where ΔX is the distance between two consecutive nozzle orifices (16) within a row.

9. A printing head assembly (100) according to claim 8
characterized in that said transversal piezo actuator (22) is configured so as to transversally shift said base plate (18) by said offset ΔQ in


increments of Δq = φ.

10. A printing head assembly (100) according to one of the preceding claims
characterized in that said base plate (18) comprises an array of wells (19) corresponding to said array of nozzle orifices (16) for temporary receiving ink, wherein each well (19) is arranged essentially concentrically with respect to the corresponding nozzle orifice (16).

11. A printing head assembly (100) according to one of the preceding claims
characterized in that said piezo actuator (12) is a discharge piezo, which is expanded in its rest position and is compressed by ΔZ in its actuated position when exposed to an electrical field.

12. A printing head assembly (100) according to one of the preceding claims
characterized in that it comprises further base plates (18.1, 18.2, 18.3, 18.4) each connected to a corresponding further ink supply (20.1, 20.2, 20.3, 20.4) for supplying identical and/or different types of ink such as differently colored inks.

13. A printer (1) comprising:

- a printer head assembly (100) according to one of the preceding claims 1 to 12

- a feed arrangement (50) for moving said substrate (200) along said path;

- an ink reservoir (52) for supplying ink through said ink supply (20);

- a UV light source (30), arranged upstream of the array of nozzle assemblies (10) on the path of said substrate (200), for curing said ink released onto the substrate (200);

- a control unit (300) for controlling the printer, connected to said printer head assembly (100), the feed arrangement (50), the UV light source (30) and ink reservoir (52).

14. A printer (1) according to claim 13,
characterized in that said printer head assembly (100) is a printer head assembly (100) according to claim 12; and in that the printer further comprises:

- further ink reservoirs (52.1, 52.2, 52.3, 52.4) for supplying identical and/or different types of ink through said further ink supplies (20.1, 20.2, 20.3, 20.4) of the base plates (18.1, 18.2, 18.3, 18.4).

Drawing