Ink-jet printing module for printing robot, magazine for these modules, and ink-jet printing method using this robot

Inkjet printing module (1) capable of being picked up by the arm (111) of a robot (101), characterized in that said module includes: a print head (2); an ink reservoir (3) capable of supplying ink to said print head (2); compressed-gas supply means (4) capable of suppling compressed gas to said print head (2); a mechanical interface (7) capable of engaging removably with a complementary mechanical interface (107) of a robot arm; an electronic interface (6) capable of engaging removably with an electronic interface (106) of said robot arm in order to transfer data between said module and the robot; and at least one fluid interface (5) placed in fluid communication with the compressed-gas supply means or with the ink reservoir.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

This application is a U.S. National Stage Application under 35 U.S.C. § 371 of International Patent Application No. PCT/FR2019/052247, filed Sep. 25, 2019, which claims the benefit of priority of French Patent Application number 1801014 filed Sep. 28, 2018, both of which are incorporated by reference in their entireties. The International Application was published on Apr. 2, 2020, as International Publication No. WO 2020/065208 A1.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to the field of inkjet printing techniques for depositing inks or varnishes onto a surface of industrial parts, in particular on surfaces which are not flat. The purpose of this printing is typically for decoration, protection or functionalization of industrial parts. More particularly, the invention relates to a device and a method for inkjet printing on a surface of industrial parts of decimetric or metric size, using a multi-axis robot.

PRIOR ART

Stylish decoration of visible surfaces is becoming increasingly important in many fields. This is particularly the case in the automotive sector. Nowadays, consumers can design their cars increasingly individually, choosing from a growing range of technical and aesthetic options. This concerns in particular the decoration of visible surfaces inside the passenger compartment.

To respond to this customization trend, special vinyl inks and robotic digital printers capable of printing on curved surfaces, molds or parts, in particular for the decoration of dashboards, door panels and other parts made of molded PVC, intended in particular for automobile passenger compartments, have been developed. This positioned-printing technology makes it possible to print accurately and in color on any type of substrate for the customization thereof.

Movable functional blocks provided with an inkjet print head are already known. These blocks can be mounted on a robot arm, according to the teaching in particular of DE 10 2017 202 195 (Heidelberger Druck-maschinen), EP 3 290 166 (Boeing) and EP 2 887 011 (Hexagon Technology Center). In these arrangements, the inkjet print heads are fed directly by a flexible hose. Similarly, EP 2 644 392 (Heidelberger Druckmaschinen) describes an inkjet print head block which is capable of printing on a curved surface and is fed by a data connection and an ink supply hose.

These known solutions have certain drawbacks, however.

They require the use of numerous supply means connecting the robot and the print head. These supply means, which are in particular fluid supply hoses and power supply cables, are likely to impede the movements of the robot. In addition, data transmission to the print head may require a data line. In any case, the presence of these supply and electronic connection means involves additional assembly and maintenance time when changing the print head. WO 2013/158 310 (Kateeva Inc.) describes a unit including a plurality of inkjet print heads mounted on a gantry which moves the heads in two main orthogonal directions above a planar table. This system may be suitable for printing on a flat surface, but is very complex.

In view of the above, the present invention aims to remedy at least some of the above-mentioned drawbacks of the prior art. In particular, it aims to provide an inkjet printing system which can easily be manipulated by a robot arm having a plurality of axes, allowing precise printing on curved surfaces of industrial parts having a dimension which may exceed one meter, and allowing decoration using a plurality of inks.

Subjects of the Invention

According to the invention, at least one of the above aims is achieved by an inkjet printing module capable of being picked up by the arm of a robot via a quick-coupling mechanical interface, characterized in that said module includes:a print head;an ink reservoir capable of supplying ink to said print head;compressed-gas supply means capable of supplying compressed gas to said print head;a mechanical interface capable of engaging removably with a complementary mechanical interface of a robot arm;an electronic interface capable of engaging removably with an electronic interface of said robot arm in order to transfer data between said module and the robot; andat least one fluid interface placed in fluid communication with the ink reservoir and/or with the compressed-gas supply means.

The invention relates firstly to this module.

Said compressed-gas supply means may include, or may be, an internal compressed-gas reservoir that is integrated into said printing module, or may be represented by the connecting pipes between the print head and the fluid interface, said fluid interface being connected, when the printing module is in a printing configuration, to an external compressed-gas supply.

The printing module according to the invention may include control lines extending between the electronic interface and, respectively, the print head and the ink reservoir. Another optional control line can extend between the fluid interface and the compressed-gas supply means.

The printing module according to the invention may include one or two connecting pipes extending between the fluid interface and/or, respectively, the ink reservoir and the compressed-gas supply means.

The presence of a mechanical interface on said module facilitates its quick connection with the complementary mechanical interface of the robot, which is capable of engaging with the mechanical interface of the module. The presence of an ink reservoir makes the inkjet printing module self-contained for a particular period of time.

The invention also relates to a robot for inkjet printing, including a robot arm, characterized in that said robot arm includes:a complementary quick-coupling mechanical interface capable of engaging with the quick-coupling mechanical interface of an inkjet printing module according to the invention; anda complementary electronic interface capable of engaging with the electronic interface of an inkjet printing module according to the invention.

The robot according to the invention can in particular be a five- or six-axis robot. It can include a central processing unit, as well as at least one control line connecting this central processing unit and the complementary electronic interface.

The invention also relates to a magazine for inkjet printing modules that is capable of accommodating, docked thereon, a plurality of inkjet printing modules according to the invention, said magazine including:a plurality of docking stations for an inkjet printing module, each docking station including at least one complementary fluid interface capable of engaging with the fluid interface of an inkjet printing module according to the invention in order to transfer ink between the head and the docking station and/or to supply compressed gas to the head; as well asat least one complementary mechanical interface capable of engaging with the mechanical interface of an inkjet printing module according to the invention.

This magazine can include at least one compressed-gas supply, which may be a compressed-gas tank. It can include at least one ink tank.

This magazine allows inkjet printing modules to be refilled with ink and compressed air. It facilitates the use of a plurality of modules, which modules differ in nature or in the color of the ink, in order to decorate the same part or the same set of parts.

The magazine according to the invention may include all or some of the following features, insofar as they are technically compatible:each docking station is provided with a particular ink tank;said ink tanks are filled with inks or varnishes of different types;each station further includes at least one complementary electronic interface capable of engaging with the electronic interface of an inkjet printing module according to the invention;each station includes a compressed-gas supply, which may be in particular a compressed-gas reservoir or a hose connected to an external compressed-gas supply;each station includes a frame containing said at least one ink tank and/or said at least one compressed-gas tank;the magazine includes a movable assembly provided with said complementary mechanical interface and, where appropriate, with said complementary fluid interface and/or with said complementary electronic interface;said movable assembly includes a carriage capable of being moved relative to the frame in a first direction, in particular a horizontal direction, as well as a connection block capable of being moved relative to the carriage in a second direction, in particular a vertical direction, said connection block being provided with said complementary mechanical interface and, where appropriate, with said complementary fluid interface and/or with said complementary electronic interface; andeach station further includes an immobilization flange extending from the frame (310), said flange and the frame defining a volume for receiving a module, said flange and/or the frame being provided with means for immobilizing said module.

The invention also relates to an inkjet printing assembly, including a robot according to any of the embodiments of the invention, a magazine according to any of the embodiments of the invention, as well as at least one module according to any of the embodiments of the invention. Advantageously, the mechanical interface and the complementary mechanical interface define a removable quick coupling, in particular of the quarter-turn type.

The invention lastly relates to an inkjet printing method, including the following steps:(i) picking up an inkjet printing module which is located in a docking station of a magazine that can contain a plurality of said modules, said picking up being carried out by means of engagement between said complementary mechanical interface of the robot and said mechanical interface of said module;(ii) connecting the complementary electronic interface of said robot with the electronic interface of said module;(iii) moving the robot arm to a print surface;(iv) printing ink on said surface by moving the robot arm, in one or more passes, said module being controlled by data sent thereto by way of said electronic interface and said complementary electronic interface;(v) at the end of this printing sequence, moving the robot arm to a docking station; and(vi) depositing the print head in said docking station, disconnecting said electronic and mechanical interfaces.

Said method may include the following additional steps:(vii) moving the robot arm to another docking station; and(viii) performing steps (i) to (vi) using another inkjet print head located in this docking station.

Said magazine may be a magazine according to the invention. Said robot may be a robot according to the invention.

The method according to the invention may include at least one of the following technical features, insofar as they are technically compatible with the other steps:said ink reservoir of the module is refilled with ink by connecting the fluid interface of said module and the complementary fluid interface of said station;the ink printing step (iv) is carried out using a first module while at least one other module is being refilled; anddifferent modules are refilled using inks or varnishes of different types.

Finally, the invention relates to the use of the method according to the invention for printing on surfaces that are curved in at least one main direction. Said curved surface may be a visible surface of a trim part of an automobile passenger compartment.

The following reference signs are used in the drawings:

DETAILED DESCRIPTION

The term “ink” is taken here in its broadest sense, in particular in relation to the inkjet printing technique, which is known to a person skilled in the art, and also includes varnishes of all kinds, which may be colored or not colored, transparent or opaque, and also includes protective varnishes.

As shown inFIGS.1to4, the inkjet printing assembly according to the invention essentially comprises:at least one printing module. In the example shown, six printing modules denoted by reference signs1A to1F are provided, it being understood that a different number of these printing modules can be provided;a robot denoted as a whole by reference sign101; anda magazine denoted as a whole by reference sign201, in particular for immobilizing the aforementioned modules, as well as for emptying said modules and refilling them with fluids.

Firstly, the structure of one of the printing modules1A will be described, it being understood that the other modules have an identical structure. With reference toFIG.1(a), this module includes a housing10made of any suitable material, for example steel or plastics material. This housing, which is, for example, of parallelepiped shape, contains the various functional elements of the module.

First, there is a print head, denoted as a whole by reference sign2. This print head, which is of a type known per se, is in particular provided with spray nozzles (not shown in the drawings) for spraying ink onto the work surface. According to the invention, the head2is first placed in communication with an ink reservoir3, via a channel31. It is also placed in communication with a compressed-gas supply, via a particular channel41. Said compressed-gas supply may be a compressed-air reservoir4, as inFIG.1(a). These two reservoirs3and4are also placed in communication with a fluid interface5, the function of which will be described in more detail in the following.51and52denote the respective channels that fluidically connect this interface and these reservoirs.

Alternatively, the compressed-gas reservoir is dispensed with, as shown inFIG.1(b), and the fluid interface5is to be fed by an external compressed-gas supply, as will be explained below. In this case, the duct52communicates directly with the print head2, possibly via a control element (not shown in the figure).

The printing module according to the invention is furthermore provided with an electronic interface6, the function of which will be described in more detail below. Control lines60,61and62connect this interface60to the print head2and the reservoirs3and4, respectively. Finally, this module is provided with a mechanical interface7, the function of will be discussed in more detail in the following.

In an alternative embodiment (not shown in the drawings), the ink reservoir3is removable and can be replaced when it is empty; in this case the ink supply means of the ink reservoir may be dispensed with, specifically the channel51which connects the ink reservoir and the fluid interface5. In yet another alternative embodiment (not shown in the drawings), the ink reservoir and the print head form a single piece which is removable and which can be replaced when the ink reservoir is empty; as in the previous alternative embodiment, the ink supply means of the reservoir may then be dispensed with.

The structure of the robot101will now be described in more detail, with reference toFIG.2. Said robot includes a body110forming a base, of any suitable type, as well as a gripper arm111. The body110optionally comprises at least one additional arm so as to allow movement of the gripper arm in a plurality of spatial directions. Typically, robot101is of the six-axis type; these robots are known as such.

The arm111is provided, near its free end, with a mechanical interface referred to as a complementary mechanical interface107. Said interface is capable of engaging with the mechanical interface7provided on the module1. These two mechanical interfaces, which are of a type known per se, allow in particular removable fastening between the module and the robot. By way of non-limiting examples, these two interfaces define in particular a quick coupling, typically of the quarter-turn type. These quick-coupling mechanical interfaces, or mechanical couplings, are known to a person skilled in the art and are described, for example, in the ISO 11593 standard. In the context of the present invention, the presence of such an interface is essential, but its structure is irrelevant. It is possible, for example, to use a tool changing system for robots from the MPS range marketed by Stäubli.

The arm111is also provided, near its free end, with a complementary fluid interface108capable of engaging with the fluid interface5of the module1. Said complementary fluid interface108is connected to an external compressed-gas supply, which is typically a flexible tube140extending along the arm111of the robot101. This complementary fluid interface108is necessary only in the event that the module1does not have a compressed-gas reservoir and needs an external compressed-gas supply. These quick-coupling fluid interfaces, or fluid couplings are known to a person skilled in the art; their structure is irrelevant.

The robot is also provided with a central processing unit, which is shown schematically and is denoted generally by reference sign161. This central processing unit is connected, via a control line160, to an electronic interface referred to as a complementary electronic interface106, which is capable of engaging with the electronic interface6of the module1. These two electronic interfaces (or couplings), of a type known per se, allow data to be transferred from the unit161to the print head2; these data can be represented by analog and/or digital signals.

It is therefore easy to see that the mechanical interface7of the module1is a coupling, preferably a quick-coupling coupling, designed so as to be able to engage with the complementary mechanical interface107of the arm111of the robot101, and that the fluid interface5of the module1is a coupling, preferably a quick-coupling coupling, designed so as to be able to engage with the complementary fluid interface108of the arm111of the robot101. Likewise, the electronic interface6of the module1is a coupling designed so as to be able to engage with the complementary electronic interface106of the arm111of the robot101. When the two fluid interfaces5,108are coupled, they allow the passage of fluid. In contrast, when these two interfaces are disconnected, each of said interfaces provides a seal for a particular fluid against the ambient air.

FIG.4schematically shows this coupling between the two electrical interfaces106and6, and between the two mechanical interfaces107and7; in this example, the module1has its compressed-gas tank4, and its fluid interface5does not need to be connected to a complementary interface of the arm111of the robot. An example for the structure of these different interfaces will be given below in relation toFIG.9.

The structure of the magazine201will now be described in more detail with reference toFIG.3. As shown in thisFIG.3, this magazine comprises a particular number of stations301for engaging with the modules1described above. Preferably, there are as many stations301as there are modules1, i.e., in other words, each station is dedicated to a particular module. However, in an alternative embodiment, a different number of stations and modules can be provided. In this context, a given module can engage with a plurality of stations and/or a given station can engage with a plurality of modules. In thisFIG.3, a single station301is shown in detail, while stations301′ and301″, located immediately on either side of station301, are shown only very schematically in phantom lines.

The structure of one of the stations will now be described, it being understood that the other stations typically have an identical structure. With reference toFIG.3, this station301firstly includes a frame310, of substantially parallelepiped shape, which contains various functional elements which will be described below. A platform or flange309for immobilizing a particular module projects forward from one of the lateral sides of the aforementioned frame. As shown inFIG.3, the adjacent walls of the frame and of the flange define a volume, denoted by V1, for receiving a particular the module1.

This flange is provided with mechanical means for holding the module in position when said module is immobilized. More precisely, this flange309is provided, for example, with upper and lower edges370and371, respectively, for centering the module when it enters its receiving volume V1. Furthermore, the upper edge370is provided with a pin372for immobilizing the module relative to the flange. To this end, this module is, for example, provided with an opening (not shown) for engaging with the aforementioned pin, for example by resilient snap-fitting.

As shown inFIG.8, a plurality of tanks for receiving different fluids is housed in the frame. There are, respectively, an ink tank303, a compressed air tank304, as well as a tank referred to as a purge tank308, for receiving used ink. This ink tank303and the purge tank308may be dispensed with in the event that the module1uses an ink reservoir which is replaced when empty. Finally, the station301is provided with a central processing unit360which is capable in particular of controlling the activation of the various interfaces of the station, which interfaces will be described below.

The station301is furthermore provided with a movable connection assembly, denoted as a whole by reference sign320. This assembly320firstly includes a carriage321that is movable relative to the frame310in the direction YY. To this end, the upper wall of the frame is provided, for example, with rails322that engage with gliding channels (not shown) provided in the carriage. The carriage is moved along these rails by motor means (not shown) of any suitable type.

The carriage321supports a column324that is stationary relative to this carriage and positioned in front of said carriage, specifically so as to face the storage volume of the module. This column in turn supports a connection block326that is movable relative to this column in the direction ZZ. For this purpose, for example, jacks328are provided, the body of which is rigidly connected to the column and the rod of which is rigidly connected to the block.

The connection block326is provided with a plurality of interfaces. First, there is a fluid interface305that is designed to be able to engage with that,5, of the module1. These two fluid interfaces, which are of a type known per se, allow a quick-coupling detachable connection to be established between the module1and the station301. When these two interfaces are coupled, said connection allows the passage of fluid between this module and this station. In contrast, when these two interfaces are disconnected, each of said interfaces provides a seal for a particular fluid against the ambient air.

The interface305is connected to reservoirs303(if present) and304by respective channels331and341(seeFIG.8). Furthermore, an additional connecting channel381can be provided that connects the print head2and the purge tank308. This channel381, which can be removably coupled to this print head, is associated with a vacuum source (not shown).

The connection block326is also provided with two additional interfaces, respectively electronic306and mechanical307. These interfaces306and307are similar to those106and107described above that are provided on the arm111of the robot. The electronic interface306is connected, via a control line361, to the central processing unit360(seeFIG.8).

FIGS.9and10show, by way of example, one possible embodiment of the various interfaces, provided on the module and the station, respectively.

As shown inFIG.9. the fluid interface5of the module is formed by two female-type coupler elements5′ and5″ for the circulation of compressed gas and ink, respectively. Furthermore, as shown inFIG.10, the fluid interface305of the station is formed by two male-type coupler elements305′ and305″ for engaging with the coupler elements5′ and5″.

In addition, as shown inFIG.9, the electronic interface6of the module is formed by a female-type connector element. Moreover, as shown inFIG.10, the electronic interface306of the station is formed by a male-type connector element for engaging with the female connector6.

Finally, as shown inFIG.9, the mechanical interface7of the module is formed by a female-type quick coupling. Moreover, as shown inFIG.10, the mechanical interface307of the station is formed by a male-type connector element for engaging with the female quick coupling7.

It should be noted that the structure of the electronic interface106and the mechanical interface107provided on the robot have not been described in more detail. Typically, these interfaces are analogous to those306and307provided on the station, as described with reference toFIG.9.

The use of the printing assembly described above will now be described with reference toFIGS.4to8.

Firstly, it is assumed, with reference toFIG.4. that the reservoirs3and4are filled with ink and compressed air, respectively. The two interface pairs,6and106, and7and107, respectively, are brought into engagement. Consequently, the robot and the module are connected electronically, specifically the central processing unit161is capable of controlling the various components of the module via lines160,60,61and62, which is indicated by the arrows f. Moreover, this robot and this module are mechanically rigidly connected to one another due to the interfaces7and107.

The robot thus controls the print head2so as to spray the ink on the target surface, as indicated by the arrows p. In the course of this spraying, additional ink and air are admitted into the head2from the reservoirs3and4, as indicated by the arrows F. During this printing operation, the station301does not engage with the module1. In other words, as shown inFIG.3, the storage volume V1 is empty.

At the end of this printing operation, the reservoirs3and4are now empty. Said reservoirs now need to be refilled, which is shown inFIGS.5to8. The arm111first directs the module1to the storage volume so as to dock this module on the flange309. The module is immobilized, relative to this flange, in particular by the pin372. The interfaces7and107are then disconnected so that the arm can be withdrawn.

When docking the module on the flange, as can be seen inFIG.5, the movable assembly is in a position referred to as an inoperative position, i.e., the connection block cannot engage with the module. This movable assembly is then moved, in two successive stages. The first step is to move the carriage horizontally, toward the storage area, in the direction of the arrow F321. As shown inFIG.6, the connection block326is now located directly above the module, while being spaced apart therefrom.

This block is then moved vertically downward, in the direction of the arrow F326, so as to make the connection block and the module engage. In this operative position of the movable assembly shown inFIG.7, there is mutual engagement between the mechanical interfaces7and307, between the fluid interfaces5and305, as well as between the electronic interfaces6and306.

As shown inFIG.8, which shows only the frame310, the block326and the module1, the central processing unit360thus controls the filling of the reservoirs3and4from the respective tanks303and304, which is indicated by the arrows G. In addition, the purge line381is coupled to the print head2. A cleaning solvent is injected into the inner volume of the head from a solvent reservoir (not shown). The used ink, initially present in this head, is then sucked out of this head in order to be discharged to the reservoir308in the direction of the arrow g. This purging operation prevents the print head1from becoming clogged with dried ink during its inoperative period.

The module1is operational again in readiness for an additional printing operation, which is carried out in a manner analogous to that which has been described above. It may be noted that, during the refilling of the module1, the robot101can pick up another module in order to implement another printing operation. Therefore, the printing assembly according to the invention can work in masked time.

Advantageously, the tanks303belonging to different stations are filled with inks of different types. In this case, each tank is intended for feeding a dedicated print head in order to spray a specific ink on the target surface. Within the meaning of the invention, different types of inks can mean that the inks have different colors and/or different physicochemical characteristics (such as viscosity or density) and/or different appearances (such as gloss).

In the example described and shown, each station is provided with a compressed-gas tank. However, in an alternative embodiment, a single compressed-gas tank having a greater volume can be provided for the entire magazine. In this case, this single tank is connected to the fluid interface of each station, via a particular pipe. It is also possible that neither the stations nor the magazine includes an air tank, but that the compressed-gas supply comes from an external line connected to the magazine.

The invention has many advantages. Owing to the self-contained nature of the ink (and possibly compressed-gas) printing modules1, the movements of the robot101according to the invention are not impeded by the presence of flexible tubes and cables; this simplifies the design, programming and use of the robot.

The robot101according to the invention can be used for the inkjet deposition of protective inks and/or varnishes on the surface of three-dimensional parts. These surfaces can have a decimetric or metric dimension; their largest dimension may thus be, for example, between approximately 2 dm and approximately 2 m. These surfaces can be curved, and can also include a surface structure, for example on a millimeter scale.

By way of example, this robot can be used to decorate trim pieces for the passenger compartment of an automobile. These trim pieces can be, for example, dashboards or door trim pieces; their largest dimension can typically be between 3 dm and 1.5 m. These parts can be manufactured according to methods known as such, for example by forming a PVC coating having a decorative surface appearance on a substrate (core); such a method is described in WO 98/00277 (Elf Atochem S. A.). These parts may have mock seams, the surface of which typically exhibits details at a scale of approximately 0.1 mm to 20 mm. The robot according to the invention allows these details to be decorated by inkjet.

FIG.11schematically shows an inkjet printing assembly according to the invention, including the inkjet printing module1mounted on a five-axis robot101; the axes are denoted by the reference signs A1to A5. The printing module1is moved above the surface to be decorated of the part400to be decorated; in this case, this surface is curved, and the decoration includes a line401which may or may not be straight, and which may or may not be continuous, and which may or may not lie on a ridge of the curved surface. This line may be raised, and/or may comprise raised decorations, as shown inFIG.12.

FIG.12shows a photograph of part of the surface of a part400to be decorated, in this case a trim part for an automobile passenger compartment. This surface includes “artificial leather” graining. It comprises artificial seams arranged along two lines401a,401b, which include raised decoration elements402. The method according to the invention makes it possible in particular to deposit ink of the desired color on these raised decoration elements, excluding the surrounding area; in other words, the ink covers only these raised decoration elements. The positioning precision of the ink on these raised decoration elements can be as much as 0.10 mm, with an ink drop diameter of approximately 80 μm.

The ink can be deposited in one or more passes. Decoration by inkjet can be completed by depositing a transparent varnish, also by inkjet. Since the magazine for inkjet printing modules according to the invention can comprise a plurality of inkjet printing modules each comprising a different ink, it is easy, after the decoration by a jet of ink of a desired color, to deposit a transparent varnish; this can be carried out by exchanging the module comprising the ink for another module comprising the varnish. Likewise, it is easy to use a different ink for the next part to be decorated. The invention thus gives the manufacturer of decorated parts a high degree of flexibility, which responds to customer demand to customize objects.