NL2021957B1

NL2021957B1 - A Method of 3D Jet Printing

Info

Publication number: NL2021957B1
Application number: NL2021957A
Authority: NL
Inventors: J Van Der Meer René; Filippovych Kateryna; G Ionascu Felicia; M M Koper Robertus
Original assignee: Canon Production Printing Holding Bv
Priority date: 2018-11-08
Filing date: 2018-11-08
Publication date: 2020-05-15

Abstract

A 3D jet printing method for forming a plurality of individualized products (20) which differ from one another in at least one property, wherein the products are formed on a 5 conveyor (10) that is moved past a print head assembly (18), characterized in that the conveyor (10) is a recirculating conveyor on which the products (20) are repeatedly moved past the print head assembly (18), and an electronic control system (32) keeps track of the positions of each product (20) relative to the print head assembly (18). 10 (Fig. 1)

Description

A Method of 3D Jet Printing

The invention relates to a 3D jet printing method for forming a plurality of individualized products which differ from one another in at least one property, wherein the products are formed on a conveyor that is moved past a print head assembly.

3D jet printing is a technology in which three-dimensional products are formed by jetting droplets of a curable liquid onto a substrate in a plurality of superposed layers. The liquid will briefly be designated as an “ink” hereinafter, although any other curable or solidifiable liquids, including molten metal, may be used as well. The liquid is jetted out from a plurality of nozzles of the print head assembly which is controlled to form the layers of ink with the desired shapes, colors and material compositions. Once a layer of ink has been formed, the ink is allowed to cure, which process may be accelerated for example by heating or by irradiating the layer of ink with a suitable radiation, e.g. UV light in case of a UV curable ink. When the ink layer has been cured to a certain extent, a subsequent layer of ink may be applied either with the same print head or with a different print head.

US 2011298881 A1 discloses a method wherein the products are formed on a linear conveyer which moves along a line of print heads. Each print head is controlled to form a layer of ink, so that the product is gradually built-up while it moves along the production line. If the products to be formed differ in a certain property, e.g. in shape, color or material composition, each print head receives a sequence of print jobs that specify the properties of the ink layer to be performed by that particular print head.

In another known method, the print head assembly may perform a reciprocating movement, so that the superposed layers of ink may be formed by means of the same print head or print heads in a plurality of scan passes. In this method, the products may be formed one after the other, and the print head controller or controllers may be reprogrammed whenever a product has been completed.

The method of the first-mentioned type, wherein a plurality of print heads are arranged along a production line has the drawback that a large number of print heads and possibly also a large number of curing devices is required. The method using a

P4055NL01 reciprocating print head assembly has the drawback that the print head assembly and also the curing devices, as the case may be, have to be accelerated and decelerated frequently in the course of the reciprocating movement, which limits the productivity. Moreover, since the curing device must always be arranged to follow the print head, efficient bi-directional printing, wherein the print head is active in both the forward and backward scanning direction, is possible only if curing devices are arranged on either side of the print head, which increases the number of curing devices as well as the mass to be accelerated and decelerated.

It is an object of the invention to provide a 3D jet printing method which requires only a limited number of hardware components such as printheads and curing devices and can nevertheless achieve a high productivity.

In the method according to the invention, in order to achieve this object, the conveyor is a recirculating conveyor on which the products are repeatedly moved past the print head assembly, and an electronic control system keeps track of the positions of each product relative to the print head assembly.

This method has the advantage that the conveyor needs to perform only a unidirectional movement, so that acceleration and deceleration processes are avoided. Nevertheless, the same print head or group of print heads can be utilized for forming a plurality of superposed ink layers, so that the required number of print heads is reduced. In the extreme, only a single print head is sufficient. The same holds true also for any possible curing devices.

When an ink layer of a given product has been formed, it takes a certain time until this product has been recirculated to the print head assembly in order to form the next ink layer. However, it is a particular advantage of the invention that the print head assembly does not have to be idle during this time but may be utilized for forming other products, so that a plurality of products are formed in an interleaved production mode. Even if the products differ in their properties, it can be assured that each print head is controlled to perform the task that is required for each particular product, because the electronic control system keeps track of the movements of the not-yet-completed products on the conveyor.

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More specific optional features of the invention are indicated in the dependent claims.

The print head assembly may comprise a plurality of print heads which are arranged for printing with different inks which may differ not only in color but also in their mechanical properties in the solidified state. In order to increase the productivity, the print head assembly may also comprise several print heads of the same type disposed along the path of the recirculating conveyor.

Optionally, one or more curing devices such as UV lamps may be arranged downstream of each print head in transport direction of the conveyor.

The products may be formed directly on a surface of the conveyor which will then constitute the print substrate. In another embodiment, each product may be formed on a substrate member that is carried on the conveyor. The substrate member may be detachable from the conveyor and may remain connected to the ink body so as to form a part of the product. In another embodiment, the ink body may be releasable from the substrate member which may then be fixed on the conveyor non-detachably.

The recirculating conveyor may for example be formed by a rotating disk or a flexible endless chain that moves along a predetermined path in a horizontal plane. If the ink body adheres to the surface of the conveyor or adheres to the substrate body which itself adheres to the conveyor, the conveyor may also be constituted by an endless belt that is trained around at least two deflection rollers which rotate about parallel horizontal axes.

An ejector, e.g. in the form of a push rod may be provided for detaching the completed products from the conveyor.

In an embodiment the printing system comprises a reader arranged at the conveyor for reading labels each of which moves on the conveyor together with a product to be formed and identifies that product. In a further embodiment, the printing system comprises an applicator arranged at the conveyor and configured to place substrate members, which serve as a substrate for a product to be formed, on an empty place on

P4055NL01 the conveyor.

The products that are formed in the interleaved production mode do not have to have the same number of ink layers. If a product with a smaller number of ink layers is completed earlier than the other products, then the completed product may be ejected and the empty place may be utilized immediately for starting with a new product.

In an embodiment, the print head assembly comprises at least two groups of nozzles, each group spanning a width of a print area , wherein each group is connected to a different one of a plurality of reservoirs for holding different jetting materials. Each nozzle group defines a width perpendicular to the transport direction of the products. Preferably, said width is similar for all groups of nozzles. The nozzles may for example be in arranged in a row or a suitably staggered configuration. Each group of nozzles is configured to eject droplets of a different liquid material by being connected to different reservoirs. As such a multi-material product may be provided.

In an embodiment, the control system is configured to receive a plurality of multilayered, multi-materials print jobs and to control the print head assembly for subsequently printing all individual layers of the products in accordance with the multilayered, multi-materials print job for each product. The print job specifies the different layers making up the product. The layers are stacked in the droplet ejection direction of the print head assembly. Preferably, one layer is printed per product as said product passes the print head assembly until the product is completed. One or more layers are formed of different materials or inks, such as different colors or resins. The different inks are respectively provided by the different groups of nozzles, which nozzles are controlled to jet by the control system in accordance with the print job. Each print job is individually linked to a product. The control system further tracks the iteration of different layers having been printed for each product. The control system controls the print head assembly and the curing station in accordance with the print job and the tracked iteration of the layers of said product, such that a consecutively layer for said product is formed with both the prescribed shape as well as the prescribed distribution of the different materials. As such large quantities of different 3D structures may be formed wherein the material composition varies in all directions.

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The invention is particularly useful for forming a set of products that have a similar size but are slightly different from one another. For example, the set of products may be a set of teeth for a dental prothesis.

Embodiment examples will now be described in conjunction with the drawings, wherein:

Fig. 1 is a schematic perspective view of a printing device suitable for carrying out the method according to the invention;

Fig. 2 is a top plan view of a slightly modified embodiment of the printing device; and

Fig. 3 is a side view of a printing device according to yet another embodiment.

As is shown in Fig. 1, a printing device comprises a recirculating conveyor 10 which, in this example, is constituted by a ring-shaped rotary disk 12 that is driven by a motor 14 so as to rotate about a vertical axis A. A specific peripheral portion of the ring-shaped disk 12 constitutes a print station 16 where an ink jet print head assembly 18 is arranged above the conveyor 10 for forming products 20 by 3D inkjet printing.

The print head assembly 18 may comprise a plurality of print heads or ejection units configured for printing with inks of different colors and/or different material compositions. Each print head may have at least one linear array of nozzles that extends over the entire width of the print station 16 in radial direction of the disk 12. Thus, when the disk 12 rotates about the axis A in the direction indicated by an arrow, a top surface of the product 20 that moves past the print head assembly 18 in the print station 16 is scanned by each of the print heads, so that a continuous or discontinuous layer of ink may be formed on the top surface of the product. Then, when the product has left the print station 16 and the disk 12 has performed one complete turn, the same product will move past the print head assembly 18 again, so that another layer of ink may be formed on top of the layer that has been printed before. In this way, a three-dimensional product 20 that is constituted by superposed layers of ink may be formed in any desired color and with any desired material composition and with an almost arbitrary shape. In the

P4055NL01 simplified example shown here, the products 20 all have a simple cylindrical shape.

In the example shown here, the first (bottom) ink layer of each product 20 is formed on a substrate that is constituted by a flat top surface 22 of the disk 12. The bottom ink layer may stick to the surface 22 with a certain adhesive force which, however, is not strong enough to prevent the completed product from being removed from the disk 12.

The inks used in the print head assembly 18 might for example be solvent-based inks which are cured simply by allowing the solvent to evaporate. In another embodiment, the inks may be hot-melt inks which solidify by cooling down. In these cases, the rotary speed of the disk 12 may be adapted such that the time required for a full turn of the disk is long enough to allow the ink to cure to a sufficient degree, so that the next ink layer may be applied.

In this example, however, it is assumed that the inks used in the print head assembly 18 are UV-curing inks which are cured by being irradiated with ultraviolet light. This is why a curing station 24 is disposed downstream of the print station 16 (in the direction of rotation of the disk 12) and comprises a curing lamp 26 for irradiating the product 20 that passes through the curing station on the conveyor 10.

In the example shown, the printing system is used for printing eight products 20 in an interleaved production mode, Thus, during a full turn of the disk 12, the print head assembly 18 is used for printing a layer of ink on each of the eight products 20.

If the products 20 are evenly distributed on the periphery of the disk 12, as in the example shown, the disk 12 may also be driven intermittently, i.e. with a relatively low speed while a product passes through the print station 16 and another layer of ink is printed thereon and another product passes underneath the curing lamp 26 in order for the ink to be cured, and at a higher speed when the ink layer of the product in the print station 16 has been completed and this product is moved to the curing station 24.

Although the products 20 that are formed in the interleaved production mode are of similar size, they may differ from one another in at least one property. For example, they may differ in color or in their material composition. Further, the products may have

P4055NL01 (slightly) different shapes. As an example of the latter case where the products have different shapes, it may be assumed that the products 20 constitute a set of teeth for a dental prothesis. Then, each tooth will have a slightly different shape. The number of teeth in the prothesis or, more generally, the number of products 20 in a set does not have to be equal to the number (8) of products that are produced simultaneously in the printing device.

It is also possible that the products 20 that are formed (almost) simultaneously on the disk 12 have different heights and are consequently constituted by a different number of ink layers, which means that the products will not be completed at the same time. In the example shown, an ejector 28 is arranged radially inwardly of the crown of products 20 for ejecting the completed products from the disk 12 by extending a push rod 30 that pushes the product to be ejected over the outer edge of the disk 12.

An electronic control system 32 is provided for controlling the operation of the motor 14, the print head assembly 18 and the ejector 28. A memory inside the control system 32 keeps track of the instantaneous angular position of each product 20 about the axis A and is therefore capable of determining not only the exact timing when a given product 20 reaches the print station 16 and the print heads have to be activated for forming a new ink layer, but also of determining the identity of that particular product and the properties that this product is intended to have, so that the print heads may be controlled accordingly.

When the print head assembly 18 has been controlled to print the last (topmost) ink layer of a product, which means that this product is completed, the control system 32 keeps track of the movement of this product and determines the timing at which the completed product reaches the position of the ejector 28. Then, the ejector is activated so as to eject the completed product.

Fig. 2 illustrates some possible modifications of the printing system shown in Fig. 1. In this example, the printing system has two print stations 16 and four curing stations 24. The print stations 16 are disposed at an angular distance of 135° (corresponding to four product positions), and two curing stations 24 are disposed downstream of each print station. Consequently, the productivity is higher because two ink layers of each product

P4055NL01 can be formed during each full turn of the disk 12. Further, the curing time in which each ink layer is irradiated in the two curing stations 24 is twice the time needed for printing the ink layer in the print station 16, so that the printing speed may be increased.

Furthermore, Fig. 2 illustrates an example of a printing method where the products 20 are not formed directly on the surface of the disk 12 but on a separate substrate member 34 that may be placed on the conveyor 10 and may be removed therefrom by means of the ejector 28.

An applicator 36 is provided one product position (45°) downstream of the position of the ejector 28 and is arranged to supply a blank substrate member 34 and to place it on the disk 12 at the empty position where a completed product and its substrate member have been removed by the ejector 28.

Each substrate member 34 carries a label 38 with a machine-readable identifier for the product to be formed on that substrate member. A reader 40 is disposed upstream of each print station 16 for reading the labels 38. Thus, whenever a substrate member 34 arrives at a print station 16, the control system 32 can determine the identity and the intended properties of the product to be formed on the basis of the data read from the label 38. Thus, in this embodiment, the control system 32 can keep track of the positions of the products by reading the labels 38, and it is not necessary to integrate the movements of the conveyor.

Another example of a printing system for carrying out the method according to the invention has been shown in Fig. 3. In this embodiment, the printing system has a recirculating conveyor 10’ in the form of an endless belt 42 trained around two deflection rollers 44 which have respective axes 46 of rotation that extend in a horizontal direction, so that the products 20 move in a vertical plane. The print head assembly 18 is disposed above a top run of the belt 42 and has four print heads 48 each of which extends over the entire width of the belt 42. The curing station 24, constituted by a UVlamp, is disposed downstream of the print head assembly 18.

The print heads 48 are controlled to form the products 20 by printing layers of ink. The first (bottom) ink layer is formed directly on the surface of the belt 42. The print heads

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48, together, will form one layer of each product that passes through the print station. Since the bottom ink layer adheres to the belt 42, the products 20 remain attached to the belt even when they move “head-over” on the bottom run of the belt. Again, the electronic control system (which is not shown here) keeps track of the movements of the products 20 and controls the print head assembly 18 such that each product is formed with the desired properties.

An ejector 28’ is provided near the downstream end of the bottom run of the belt 42.

When a product 20 has been completed and is to be removed from the belt, the ejector 10 28’ extends a scraper 50 for peeling-off the completed product from the belt. When a product that has not yet been completed reaches the position of the ejector 28’, the scraper 50 is withdrawn so that the product can pass through and can recirculated to the print head assembly 18.

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Embodiments

1. A 3D jet printing method for forming a plurality of individualized products (20) which differ from one another in at least one property, wherein the products are formed on a conveyor (10; 10’) that is moved past a print head assembly (18), characterized in that the conveyor (10; 10’) is a recirculating conveyor on which the products (20) are repeatedly moved past the print head assembly (18), and an electronic control system (32) keeps track of the positions of each product (20) relative to the print head assembly (18).

2. The method according to claim 1, wherein an ink layer of a product (20) that has been formed by means of the print head assembly (18) is cured in a curing station (24) downstream of the print head assembly in the direction of transport of the conveyor (10; 10’).

3. The method according to claim 1 or 2, wherein the control system (32) controls an ejector (28) so as to remove a product (20) from the conveyor (10; 10’) when the product has been completed.

4. The method according to any of the preceding claims, wherein the products (20) are formed directly on a surface (22) of the conveyor (10; 10’), or wherein each product (20) is formed on a substrate member (34) that is detachably supported on the conveyor (10).

5. A printing system for carrying out the method according to any of the claims 1 to

4, the printing system comprising a conveyor (10; 10’) and a print head assembly (18) for printing products (20) that are supported on the conveyor, characterized in that the conveyor (10; 10’) is a recirculating conveyor arranged to move the products (20) repeatedly past the print head assembly (18), and an electronic control system (32) is configured to keep track of the positions of each product (20) relative to the print head assembly (18) and to control the print head assembly (18) for printing the products in accordance with individual product specifications for each product.

6. The printing system according to claim 5, comprising a plurality of print head

P4055NL01 assemblies (18) spaced apart from one another along the recirculating conveyor (10).

7. The printing system according to claim 4 or 5, comprising at least one curing station (24) disposed downstream of each print head assembly (18).

8. The printing system according to any of the claims 5 to 7, comprising an ejector (28) arranged to remove completed products (20) from the conveyor (10; 10’).

9. The printing system according to any of the claims 5 to 8, wherein the print head assembly (18) comprises at least two groups of nozzles, each group spanning a full width of a print area , wherein each group is connected to a different one of a plurality of reservoirs for holding different jetting materials.

10. The printing system according to claim 9, wherein the control system (32) is configured to receive a plurality of different multi-layered, multi-materials print jobs and to control the print head assembly (18) for subsequently printing all individual layers of the products in accordance with the multi-layered, multi-materials print job for each product.

Claims

1. Werkwijze voor 3D inkjetprinten voor het vormen van een veelheid individuele producten (20) die van elkaar verschillen in ten minste één eigenschap, waarbij de producten gevormd worden op een transporteur (10; 10’) die bewogen wordt langs een printkopsamenstel (18), met het kenmerk dat de transporteur (10; 10’) een recirculerende transporteur is waarop de producten (20) herhaaldelijk langs het printkopsamenstel (18) worden bewogen en een electronisch besturingssysteem (32) de posities van elk product (20) ten opzichte van het printkopsamenstel (18) bijhoudt.A method of 3D inkjet printing for forming a plurality of individual products (20) that differ in at least one property, the products being formed on a conveyor (10; 10 ') moved along a printhead assembly (18) characterized in that the conveyor (10; 10 ') is a recirculating conveyor on which the products (20) are moved repeatedly along the printhead assembly (18) and an electronic control system (32) positions each product (20) relative to the printhead assembly (18).

2. Werkwijze volgens conclusie 1, waarbij een inktlaag van een product (20) die gevormd is door middel van het printkopsamenstel (18) wordt uitgehard in een uithardstation (24) stroomafwaarts van het printkopsamenstel in de transportrichting van de transporteur (10; ,10’).The method of claim 1, wherein an ink layer of a product (20) formed by the printhead assembly (18) is cured in a curing station (24) downstream of the printhead assembly in the conveying direction of the conveyor (10;, 10). ).

3. Werkwijze volgens conclusie 1 of 2, waarbij het besturingssysteem (32) een uitwerper (28) bestuurt om zodanig een product (20) van de transporteur (10; 10’) te verwijderen wanneer het product voltooid is.The method of claim 1 or 2, wherein the control system (32) controls an ejector (28) so as to remove a product (20) from the conveyor (10; 10 ') when the product is complete.

4. Werkwijze volgens een van de voorgaande conclusies, waarbij de producten (20) direct op een oppervlak (22) van de transporteur (10; 10’) zijn gevormd of waarbij elk product (20) is gevormd op een substraatorgaan (34) dat losmaakbaar ondersteund is op de transporteur (10).A method according to any preceding claim, wherein the products (20) are formed directly on a surface (22) of the conveyor (10; 10 ') or each product (20) is formed on a substrate member (34) is releasably supported on the conveyor (10).

5. Printer voor het uitvoeren van een werkwijze volgens een van de conclusies 1 t/m 4, waarbij de printer een transporteur (10; 10’) en een printkopsamenstel (18) voor het printen van producten (20) die ondersteund zijn op de transporteur omvat, met het kenmerk dat de transporteur (10; 10’) een recirculerende transporteur is die ingericht is om de producten (20) herhaaldelijk langs het printkopsamenstel (18) te bewegen, en waarbij een electronisch besturingssysteem (32) is ingericht voor het bijhouden van de posities van elk product (20) ten opzichte van het printkopsamenstel (18) en voor het besturen van het printkopsamenstel (18) voor het printen van de producten in overeenstemming met individuele productspecificaties voor elk product.A printer for performing a method according to any one of claims 1 to 4, wherein the printer comprises a conveyor (10; 10 ') and a printhead assembly (18) for printing products (20) supported on the conveyor, characterized in that the conveyor (10; 10 ') is a recirculating conveyor adapted to move the products (20) repeatedly along the printhead assembly (18), and wherein an electronic control system (32) is arranged for maintaining the positions of each product (20) relative to the printhead assembly (18) and controlling the printhead assembly (18) for printing the products in accordance with individual product specifications for each product.

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6. Printer volgens conclusie 5, omvattende een veelheid printkopsamenstellen (18) die op afstand van elkaar langs de recirculerende transporteur (10) voorzien zijn.The printer of claim 5, comprising a plurality of printhead assemblies (18) spaced apart along the recirculating conveyor (10).

7. Printer volgens conclusie 5 of 6, omvattende ten minste één uithardstation (24)Printer according to claim 5 or 6, comprising at least one curing station (24)

5 dat stroomafwaarts van elk printkopsamenstel (18) gelegen is.5 located downstream of each printhead assembly (18).

8. Printer volgens een van de conclusies 5 t/m 7, omvattende een uitwerper (28) die voorzien is om voltooide producten (20) te verwijderen van de transporteur (10; 10’).A printer according to any one of claims 5 to 7, comprising an ejector (28) provided to remove finished products (20) from the conveyor (10; 10 ").

10 9. Printer volgens een van de conclusies 5 t/m 8, waarbij het printkopsamenstel ten minste twee groepen spuitmonden omvat, waarbij elke groep een total wijdte van een printgebied bestrijkt, waarbij elke groep verbonden is met een andere van een veelheid reservoiren voor het houden van verschillende inkjetmaterialen.9. A printer according to any one of claims 5 to 8, wherein the printhead assembly comprises at least two groups of nozzles, each group covering a total width of a printing area, each group being connected to another of a plurality of reservoirs for the love different inkjet materials.

15 10. Printer volgens conclusie 9, waarbij het besturingssysteem (32) ingericht is voor het ontvangen van een veelheid van elkaar verschillende multilaags, multimateriaal printopdrachten en voor het besturen van het printkopsamenstel (18) voor het opeenvolgend printen van alle individuele lagen van de producten in overeenstemming met de multilaags, multimateriaal printopdracht voor elk product.10. The printer of claim 9, wherein the control system (32) is adapted to receive a plurality of different multi-layer, multi-material print jobs and to control the printhead assembly (18) for sequentially printing all individual layers of the products. in accordance with the multi-layer, multi-material print job for each product.