WO2010071432A1

WO2010071432A1 - Printing assembly and method for depositing material on substrates

Info

Publication number: WO2010071432A1
Application number: PCT/NL2009/050778
Authority: WO
Inventors: Petrus Johannes Fransiscus Diepens; Peter BRIËR
Original assignee: Otb Solar B.V.
Priority date: 2008-12-19
Filing date: 2009-12-18
Publication date: 2010-06-24
Also published as: NL2002355C2; TW201033017A

Abstract

A printing assembly and a method for depositing material on discrete substrates including a transport assembly configured to transport substrates along at least one transport path, at least two printers arranged along the at least one transport path, associated with each printer a manipulator assembly that is configured to unload a substrate from the transport assembly and to load that substrate in the associated printer and vice versa, and a controller configured to control the transport assembly and the manipulator assemblies.

Description

Title: Printing assembly and method for depositing material on substrates

Field

The invention relates to a printing assembly and to a method for depositing material on substrates.

Background

In industrial printing processes, more particularly industrial inkjet printing processes, the material that is deposited by printing in most cases has a special function. For example, the material may be electrically conducting, may be light emitting or may be electrically isolating or combinations thereof. Printing material having such a function in many cases include dispersions, for example metal dispersions or organic material dispersions. However, also other liquids with a higher/lower viscosity than ink that is used for graphic printing, such as lacquer, may be deposited by industrial inkjet printers.

Dispersions and liquids that have a viscosity that is higher/lower than conventional printing ink may lead to a disturbed ink jetting process that may result in inaccurate and/or non repeatable prints or no printing at all. For example, a printing nozzle of the printing head may get clogged. In conventional graphic printing this may be acceptable. In industrial applications however, this may lead to a substrate carrying a dysfunctional component, for example a pixel of an organic light emitting diode that does not function properly, a conductive lead pattern in a print plate that is interrupted, or an encapsulation layer that includes a pin hole thus forming a spot of leakage in the encapsulation layer.

Currently, industrial inkjet printers that are part of a component production line in many cases have multiple parallel printing heads for obtaining a high printing capacity in the production line. However, when one of the nozzles of one of these printing heads is clogged, the entire printer needs to be taken out of production for servicing. This leads to a loss of capacity of the entire production line of which the industrial printing head forms a part. The current disclosure aims to alleviate or overcome one or more disadvantages associated with the prior art.

Summary To that end a printing assembly for depositing material on discrete substrates is provided that includes:

• a transport assembly configured to transport substrates along at least one transport path;

• at least two printers arranged along the at least one transport path; • associated with each printer a manipulator assembly that is configured to unload a substrate from the transport assembly and to load that substrate in the associated printer and vice versa; and

• a controller configured to control the transport assembly and the manipulator assemblies. In another aspect, a method of depositing material on discrete substrates is provided that includes:

• providing at least two printers each with an associated manipulator assembly along at least one transport path that is defined by a transport assembly; • providing a number of substrates;

• loading subsequent substrates in the transport assembly and transporting the subsequent substrates along the at least one transport path; and

• repeatedly performing the following series of steps: o unloading a substrate of said number of substrates from the at least one transport path and loading the substrate in a said printer; o processing the substrate in the printer by applying a said material with the printer on the substrate; o unloading the substrate from the printer after processing and replacing the substrate in the transport assembly for further processing.

Such an assembly and method provides the possibility to include some redundancy in the printing process. The capacity of the individual printers, that is the number of substrates that can be processed by a single printer per unit of time, may be less than the capacity of a production line of which the printing assembly may be a part. As a consequence, the necessity to use printers that have a plurality of parallel printing heads may be reduced. For example, an in-line industrial printer having five parallel printing heads may be replaced by five printers each having a single printing head. It is also possible to provide some redundancy by providing some printer over-capacity and, for example, replace an in-line industrial printing having five parallel printing heads with six or seven printers each having a single printing head. When the printing head of one of the printers becomes clogged, only one printer has to be serviced. During servicing of that printer, the production line may go on producing at a somewhat diminished capacity, instead of, as is the case in the prior art, being shut down completely.

In an embodiment each manipulator assembly may have at least one buffer position configured to temporarily store a substrate.

Such a buffer position may provide a greater flexibility with respect to loading and unloading of a printer. When a printer is processing to deposit material on a first substrate a second substrate may be waiting in the buffer position so that, immediately after finishing the processing of the first substrate, the second substrate may be placed in the printer after removal of the first substrate from the printer. The first substrate may be removed from the manipulator assembly to the transport assembly when an empty location on the transport assembly is in front of that manipulator assembly. Thus, the capacity of the printer may be optimally used. In an embodiment, each manipulator assembly may have at least two substrate carriers that are connected to a manipulator. The manipulator may, for example include a central shaft that may rotate and move upwardly and downwardly and to which two diametrically opposed arms are connected. To each arm a substrate carrier may be connected.

In use, at least one of the carriers, not necessarily always the same carrier, may be considered as buffer position. In use, a first one of the carriers may carry a substrate that still needs to be processed by the associated printer and a second one of the carriers may be used to unload a processed substrate from the associated printer. The manipulator may be moved and the non- processed substrate that is carried by the first carrier may be loaded in the printer after which the printer can be started immediately. Subsequently the manipulator assembly may be moved to the transport assembly where the now empty first one of the carriers can be used to pick up an unprocessed substrate from the transport assembly. Subsequently, the manipulator may be moved and a processed substrate that may be carried by the second one of the carriers can be placed on the just created empty space on the transport assembly or on another empty space of the transport assembly.

In an embodiment the transport assembly may be configured to perform subsequent transport steps wherein a time period between starting moments of subsequent transport steps is a tact time, the controller being configured to determine the tact time.

In such an embodiment, an optimal production capacity of the printing assembly may be obtained, even when one of the printers is out of use because of servicing or the like. When determining the tact time, the controller may include in its determination, the processing times of the various printers of the assembly, the number of printers that is active etc.

In an embodiment, in which the transporting along the at least one transport path is done in subsequent transport steps wherein a time period between starting moments of subsequent transport steps is a tact time Ttact, wherein the printers of the assembly that conduct a process of a same type are grouped in printer groups indicated by p(j), wherein j = 1, 2, ...., m and indicates the process type number, wherein each printer of a printer group p(j) performing the same process type has a number i, wherein i = 1, 2, ..., n(j) and n(j) is the total number of printers within a said printer group p(j), wherein the processing time of each printer of the same process type p(j) may vary and is indicated by T(p(j), i), wherein the controller is configured to determine the tact time Ttact on the basis of the printer group p(j) having the longest mean processing time, i.e. by the following formula:

Ttact > max

T (P(l),i) , T (P(2),i) T (P(m),i) i=l...n(l) i_=l...n(2) i=l...n(m

Such a determination of the tact time may also be used in the method described above. As follows from the above formula, the tact time may be equal to maximum of the mean processing times of the printers of the various printing groups or larger. Slightly larger may be advantageous in order to obtain a bit more flexibility in scheduling the substrates over the printer group p(j) that is most intensively used, i.e. that forms the bottleneck. However, the tact time should not be chosen too large because then the capacity of the printing assembly will not be optimally used.

The printer group p(j) having the longest tact time and so the smallest capacity will be the bottleneck of the printing assembly. In view thereof, giving priority to the loading of that printer group is advantageous for obtaining an optimal capacity of the printing assembly. This teaching may also be used with the same advantages in the method described above.

In an embodiment each printer may be an inkjet printer. Each inkjet printer may have a single printing head. Such an embodiment has the advantage that breaking down of a printing head of a printer will lead to a minimal capacity loss of the assembly. However, embodiments are contemplated that include printers having multiple printing heads.

In an embodiment, the transport assembly may be a belt or chain conveyor. Alternatively, the transport assembly may includes a series of manipulators that are arranged along the transport path that is formed by discrete substrate mounting positions, each manipulator being configured to pick up a substrate from an upstream substrate mounting position and to place the picked-up substrate on a downstream substrate mounting position. In yet another alternative embodiments, the transport assembly may include a number of substrate carriers that are moveable along the transport path over a guide or a rotary table that has substrate mounting positions.

Brief Description of the Drawings

Fig. 1 shows a top view of a first embodiment of a printing assembly; Fig. 2 shows a top view of a second embodiment of a printing assembly;

Fig. 3 shows a top view of a third embodiment of a printing assembly;

Fig. 4 shows a top view of the various steps of loading and unloading a printer and an associated manipulator assembly;

Fig. 5 shows a top view and a side view of a first embodiment of a manipulator assembly;

Fig. 6 shows a top view and a side view of a second embodiment of a manipulator assembly; Fig. 7 shows a top view and a side view of a third embodiment of a manipulator assembly;

Fig. 8 shows a top view and a side view of a fourth embodiment of a manipulator assembly;

Fig. 9 shows a top view and a side view of a fifth embodiment of a manipulator assembly; and Fig 10 shows a top view of a fourth embodiment of a printing assembly.

In the drawings, identical reference numbers identify similar elements. The sizes and relative positions of elements in the drawings are not necessarily drawn to scale. For example, the shapes of various elements and angles are not drawn to scale, and some of these elements are arbitrarily enlarged and positioned to improve drawing legibility. Further, the particular shapes of the elements as drawn are not intended to convey any information regarding the actual shape of the particular elements, and have been solely selected for ease of recognition in the drawings.

Detailed Description Fig. 1 shows a first embodiment of a printing assembly 10 for depositing material on discrete substrates S. The printing assembly includes a transport assembly 12 that is configured to transport substrates along at least one transport path 14. The transport assembly may include at least one belt or chain conveyor 16 on which the substrates S are placed and that may move intermittently with a certain tact time Ttact, between the starting moments of the subsequent transport steps. In an alternative embodiment, the at least one conveyor may move continuously. In an embodiment, of which an example is depicted in Fig. 2, the transport assembly 12 may include a number of substrate carriers 18 that are moveable along the transport path 14 over guides 20. In yet another alternative embodiment, of which an example is shown in Fig. 3, the transport assembly 12 may include a series of manipulators 22 that are arranged along the transport path 14 that is formed by discrete substrate mounting positions 24. Each manipulator 22 may be configured to pick up a substrate S from an upstream substrate mounting position 24 and to place the picked-up substrate S on a downstream substrate mounting position 24. In yet another alternative embodiment, the transport assembly 12 may include a rotary table with a number of substrate mounting positions. The transport assembly 12 may also include a loader module 26 for intermittently loading the transport system 12 with substrates S. The embodiments shown in Figs. 1-3 all have a loader module 26. In yet another alternative embodiment, of which an example is shown in Fig. 10, the transport assembly may include a first path 14a and a second path 14b. The first path 14a may, for example, be used for substrates S that still have to be processed by a printer and the second path 14b may, for example, be used for transporting substrates S that have been processed by a printer. In an alternative mode of operation, the first and the second paths 14a, 14b may both transport substrates S that still need printing process steps to be performed thereon as well as substrates S that have had all required printing process steps. The printing assembly 10 includes a number of printers 28. The embodiment depicted in Fig 8 has seven printers that are indicated by reference number 28.1, 28.2, 28.3, 28.4, 28.5, 28.6 and 28.7. Each printer 28 has a substrate position 30 in which a substrate S may be positioned in the printer 28 and in which the printing process may be performed. The number of printers 28 within a printing assembly 10 may vary depending on the number of processes to be performed and on the capacity needed, i.e. the number of substrates that must be processed per unit of time by the printing assembly 10. The printers 28 may be inkjet printers. From a servicing point of view it may be advantageous to use printers with a single inkjet printing head. When an inkjet printing head of a printer 28 needs service, the total capacity of the printing assembly is only reduced a little. For example, in the case of seven single headed printers, the capacity of the printing assembly 10 is reduced by 1/7 when one inkjet printer head need to be serviced. It should be noted, however, that printers with multiple printer heads are not excluded. The fact that more printers are available for performing a process increases flexibility and redundancy so that, when one printer breaks down, the process upstream and downstream from the printing assembly 10 does not have to be stopped.

Each printer 28 has an associated manipulator assembly 32. In the embodiment depicted in Fig. 1 the various manipulator assemblies are indicates by reference numbers 32.1, 32.2, 32.3, 32.4, 32.5, 32.6, 32.7. In the embodiment shown, each manipulator assembly 32 has two substrate carriers 34, 36, that are connected on two diametrically opposite sides of a shaft 38. The shaft 38 may rotate over at least 180 degrees. Additionally, the shaft 38 may be movable in a direction perpendicular to the rotational axis of the shaft 38 so that the shaft 38 with the substrate carriers 34, 36 may be moved towards and away from the transport assembly 12 and towards and away from the associated printer 28. It is contemplated that only one substrate carrier 34 or more than two substrate carriers are also feasible. Instead of being connected to a shaft 38, the carriers may also be connected to another type of manipulator mechanism. In the embodiment shown, a first one of the two substrate carriers 34, 36 in a manipulator assembly 20 may carry a substrate S that still has to be processed. A second one of the two carriers 34, 36 may be used to manipulate a substrate S that has been processed. In such an embodiment, one of the two carriers 34, 36, not necessarily always the same, may have the function of a buffer position. In an embodiment in which the manipulator itself has only one substrate carrier, it may be advantageous to have a stationary buffer position 40 in the manipulator assembly 20. It also feasible that more than one buffer position 40 is available in each manipulator assembly. More buffer positions 40 may increase the flexibility with respect to the routing of substrates S through the printing assembly 10. As is clear from the example shown in Fig. 10, in an embodiment having two or more transport paths 14a, 14b, the manipulator assembly 32 may be configured to load/unload a substrate S from the first path 14a and to load/unload a substrate S from the second path 14b and to load/unload a substrate from an associated printer 28. The printing assembly 10 also includes a controller 42 that is configured to at least partly control the transport assembly 12 and the manipulator assemblies 32. In the case that the transporting along the transport path 14 is done in subsequent transport steps wherein a time period between starting moments of subsequent transport steps is the tact time Ttact, the controller 42 may be configured to determine the tact time Ttact of the transport assembly 12. In case of a continuous transport speed of the transport assembly 12, the controller 42 may control the transport speed of the transport assembly 12. The determination of the tact time Ttact may be done on the basis of the processing times of the at least two printers 28 of the printing assembly 10. The determination may be dynamic as well, meaning that the tact time Ttact may change when one of the printers 28 of the printing assembly 10 is shut down for service, or process parameters are changed influencing the cycle time of one or more separate printers. In an embodiment, the controller 42 may be configured to give priority to loading the printer group p(j) with substrates that has the smallest capacity, i.e the maximum tact time Ttact. In such a manner, the capacity of the bottleneck printer group p(j) may be used optimally and, consequently, the capacity of the printing assembly 10 may be used optimally. The controller 42 may be a computer with a suitable software program or with a read only memory containing a controller program.

Figs. 5-9 show exemplary alternative embodiments of the manipulator assembly 132, 232, 332, 432, 532, a part of the transport assembly 12 and a printer 28. The left hand side of each Fig. shows a top view and the right hand side of each Fig. shows a side elevation view of the manipulator assembly 132, 232, 332, 432, 532.

Fig. 5 schematically shows a manipulator assembly 132 with a single gripper 134 that is connected to an arm 144 that is connected to a vertical shaft 138 that is rotatable as indicated by arrow R. The shaft may also move upwardly and downwardly as indicated by arrow L. At the end of the arm 144 a substrate carrier 134 is provided. This embodiment is simple and therefore advantageous from a cost point of view.

Fig. 6 shows an embodiment of a manipulator assembly 232 that is the same as the embodiment of Fig. 5 with the exception that two static buffer positions 140 have been added. These buffer positions 140 provide the advantage that the process of the printer 28 is not fixedly coupled with the transport movements of the transport assembly 12. This means that the printer 28 may start with a new substrate even when the printed substrate cannot be transferred to the transport assembly 12. The printed substrate may then be temporarily stored in a buffer position 140.

Fig. 7 schematically shows an embodiment of a manipulator assembly 332 with an arm 144 that extends in two directions away from the central shaft 138. On both ends of the arm 144 a substrate carrier 134, 136 is provided. The loading/unloading at the transport assembly 12 and at the printer 28 may be performed simultaneously. Thus a short handling time is feasible.

Fig. 8 schematically shows an embodiment of a manipulator assembly 432 with two arms 144, 146 each being connected to an associated vertical shaft 138, 138'. The shafts 138, 138' may rotate independently. This provides a high degree of flexibility. The printer module 28 may be loaded/unloaded independently of the loading/unloading of the transport assembly 12. Thus the loading/unloading of the printer 28 may be performed simulateously with the loading/unloading of the transport assembly 12. Fig. 9 schematically shows an embodiment of the manipulator assembly 532 that has been described with reference to Figs. 1-4. This embodiment has a single vertical shaft 138 with an arm 144 that extends in two directions away from the central shaft 138. On both ends of the arm 144 a substrate carrier 134, 136 is provided. The rotatable central shaft 138 with the associated motor are moveable along a linear path S over a guide 148. This provides flexibility in that the substrate carriers 134, 136 may be moved downwardly to load or unload the printer 28 without interfering with the transport assembly 12.

It is clear that many more embodiments of manipulator assemblies are feasible. For example, embodiments that use standard available robots are possible.

In the embodiment of Fig. 1, all printers 28.1-28.7 perform a printing process of the same type 1. The processing time T(p(l), i) of each printer is the same, namely x seconds. It will be clear that the processing time T of a printer 28 is a function of the type of process type j and of the characteristics of the individual printer i. The printers 28 of a printing assembly 10 may be grouped into printer groups p(j) within which each printer performs the same process type j. Reference symbol j may indicate a process type number. Within a printer group p(j), the processing time for finishing a printing process may vary from printer to printer. The individual printers within a printer group p(j) may be indicated by reference symbol i. The individual processing time of a printer i in printer group p(j) may be indicated by T(PG), i).

Fig. 2 shows a second embodiment in which the same parts have been given the same reference numbers. A difference between the second embodiment of Fig. 2 and the first embodiment shown in Fig. 1 is that each manipulator assembly 20.1-20.7 has a stationary buffer position 40. As in Fig. 1, the printers 28 of the embodiment of Fig. 2 also perform a process of the same type 1 and, consequently, all printers 28.1-28.7 may be part of a single printer group p(l). However, in this embodiment the processing time of printer 28.1 is x + 1 s, the processing time of printer 28.3 is x + 0.5 s, and the processing time of printer 28.5 is x + 2.5 s for finalizing the printing process of type 1. The other printers 28.2, 28.4, 28.6 have a processing time of x s for finalizing the printing process of type 1.

Fig. 3 shows a third embodiment in which the same parts have been given the same reference numbers. As described above, the transport assembly 12 of the third embodiment includes a series of manipulators 22 and substrate mounting positions 24. The manipulators 22 are configured to pick up a substrate from an upstream substrate S mounting position 24 and to deliver a substrate S to a downstream substrate mounting position 24. The third embodiment performs three types of processes 1, 2, 3. The four printers performing process type 1 may form a first printer group p(l), the one printer performing process type 2 may form a second printer group p(2), and the two printers performing process type 3 may form a third printer group p(3). The total number of printers within a printer group p(j) may be indicated by n(j). Each individual printer within a printer group may be indicated by i. The printers within a single printer group p(j) may need different processing times T(p(j), i) for performing the same process type j. In the example of the third embodiment shown in Fig. 3, for process type 1, the processing time of printer 28.1 is T(p(l), 1) = x+1, the processing time of printer 28.2 is T(p(l), 2) = x, the processing time of printer 28.3 is T(p(l), 3) = x + 0.5 s and the processing time of printer 28.4 is T(p(l), 4) = x s. For process type 2, the processing time of printer 28.5 is T(p(2), 1) = y + 0.1 s. For process type 3, the processing time of printer 28.6 is T(p(3), 1) = z + 0.2 s and the processing time of printer 28.7 is T(p(3), 2) = z s.

Industrial Applicability

The printing assembly 10 may be used for component manufacturing, such as for printing light emitting polymers on substrates for manufacturing organic light emitting diodes, for printing electrically conducting or isolating layers or tracks on substrates for manufacturing electronic components including solar cells, organic light emitting diodes, or other electronic components.

In use, the loader module 26 will be loaded with discrete substrates on which a printing process has to be performed. The loader module 26 will transfer the substrates S to transport assembly 12. The controller 42 will control the transport assembly and transport the subsequent substrates with a desired speed, or with a desired tact time through the transport assembly 12. In case of an intermittent transport in the transport assembly 12, the tact time Ttact may be determined on the basis of the printer group p(j) having the longest mean processing time, i.e. by the following formula:

1 1 1

Ttact > max

T (P(l),i) ,_ T (P(2),i) T (P(m),i) i=l...n(l) i=l...n(2) i=l..n(m)

In the embodiment of Fig. 1 only one printer group p(l) is present all performing the same printing process type 1. Consequently, using the above formula for the embodiment of Fig. 1 leads to:

Ttact ≥

For the embodiment of Fig. 2 using the above formula leads to:

Ttact >

1 1 1 1

- + — + - - + — + - + — + — x + 1 x x + 0.5 x x + 2.5 x x

For the embodiment of Fig. 3 using the above formula leads to:

Ttact >

The controller 42 may be configured to determine tact time Ttact in the manner as described above. The above formula's describe that the tact time is chosen equal to or greater than the maximum of the average processing time of the various printer groups p(j). It is preferred that the tact time is chosen as small as possible to obtain maximum capacity, i.e. equal to the calculated maximum of the average processing time of the various printer groups p(j). However, in order to provide some extra flexibility when scheduling the routing through the printing assembly 10, the tact time may be chosen a little longer. In order to be sure that the capacity of the printing assembly 10 is optimally used, the bottleneck printer group p(j) should be given priority when routing substrates S through the system. The bottleneck printer group p(j) will be the printer group having the maximum tact time.

Fig. 4 shows subsequent processing stages of an embodiment of a single assembly of a printer 28 and a manipulator assembly 32 that may be a part of an embodiment of a printing assembly 10. In this embodiment the manipulator assembly 32 has the configuration that has been described above with reference to Fig. 1. That is, the manipulator assembly 32 has two substrate carriers 34, 36, that are connected on two diametrically opposite sides of a shaft 38. The shaft 38 is rotatable over at least 180 degrees is be movable in a direction perpendicular to the rotational axis of the shaft 38 so that the shaft 38 with the substrate carriers 34, 36 may be moved towards and away from the transport assembly 12 and towards and away from the associated printer 28. The subsequent processing stages or steps are shown in Fig. 4. Step 1:

A substrate Sl was just picked up from printer 28 and replaced by a new substrate S2. A printing start signal has just been given to printer 28. Step 2: Manipulator 32 has been rotated over 180 degrees to get into position with a substrate carrier 36 for picking up a substrate in central logistic system.

Step 3a:

Manipulator 32 has been shifted to the transport assembly 12 and is waiting for a new substrate S3 in the transport assembly 12 that is routed to printer

28.

Step 3b:

New substrate S3 with correct routing information has arrived at the manipulator 32 for printer 28. Step 4:

New substrate S3 has been picked up from the transport assembly and the manipulator 32 has been rotated over 180 degrees. The processed substrate Sl is placed on the empty position in the transport assembly 12.

Step 5: The manipulator 32 has moved away from the transport assembly to the printer 28 into a rotation position.

Step 6:

The manipulator 32 has been rotated to assume a position in which an empty substrate carrier 34 can move into the printer 28. Meanwhile, the transport assembly 12 may continue transportation of ready substrate and bring a new substrate into position.

Step 7:

The manipulator 32 has moved further away from the transport assembly 12 into an swap waiting position at the printer 28, waiting for printer 28 to be ready.

Step 8:

The printer 28 is ready and the processed substrate S2 is picked up by the manipulator 32.

Step 9: The manipulator has been rotated over 180 degrees and has replaced the processed substrate S2 by the new substrate S3. After step 9, the manipulator 32 again moves towards the transport assembly 12 and then the situation depicted in Step 1 is again arrived at. Steps 1-9 may then be repeated. The printing assembly and method of depositing material on a substrate is more flexible and more redundant than the existing multi-headed in-process inkjet printing systems because of the fact that servicing of a part of the printing assembly may be executed without interrupting the processing of substrates in the printing assembly. Due to the buffer possibility in the manipulator assembly 32 an asynchronous running of the printers 28 on the one hand and the transport assembly 12 on the other hand is feasible. The printing assembly 10 may be redundant in the sense that an extra printer 28 with associated manipulator assembly 32 may be present in the printing assembly 10. The controller 42 may provide the correct routing information for each substrate S to be processed so that clogging of the transport assembly 12 is prevented and an optimal throughput of the printing assembly 10 is obtained. The printing assembly 10 even allows continuing production with inkjet print heads that have reduced quality because compensation by additional printing time to compensate for the reduced quality may be absorbed by the printing assembly by increasing the tact time of the transport assembly 12. Thus, the printing assembly 10 may allow maintenance or exchange of inkjet printing heads or printers 28 at a moment that is convenient to the entire operation. For each process, a printer group p(j) may be formed. The number of printers 28 present in such a group may be tuned depending on the requirements of the process. These requirements may include processing speed and cycle time sensitivity, sensitivity of process maintenance etc. If the duration between subsequent process steps is of importance, then the printers 28 in a printing assembly 10 may be grouped so that process type 2 may be performed directly after process type 1. Consequently, the printers 28 of a single printer group do not have to be physically adjacent to each other.

It will be apparent to those having ordinary skill in the art that various modifications and variations can be made to the printing assembly and the printing method as disclosed herein. Other embodiments will be apparent to those having ordinary skill in the art from consideration of the specification.

Specific features that have been described in one embodiment may also be applied in another embodiment that has other specific features and vice versa.

For example, the at least one stationary buffer position 40 in the second embodiment of Fig. 2 is also feasible in the first and the third embodiment of respectively Figs 1 and 3. It is intended that the specification and embodiments are being considered as exemplary only. Other aspects, features and advantages will be apparent upon an examination of the attached drawings and appended claims.

Claims

1. A printing assembly for depositing material on discrete substrates including:

• a transport assembly configured to transport substrates along at least one transport path; • at least two printers arranged along the at least one transport path;

• associated with each printer a manipulator assembly that is configured to unload a substrate from the transport assembly and to load that substrate in the associated printer and vice versa,

• a controller configured to control the transport assembly and the manipulator assemblies.

2. The printing assembly according to claim 1, wherein each manipulator assembly has at least one buffer position configured to temporarily store a substrate.

3. The printing assembly according to claim 1 or 2, each manipulator assembly having at least two substrate carriers that are connected to a manipulator.

4. The printing assembly according to any one of claims 1-3, wherein the transport assembly is configured to perform subsequent transport steps wherein a time period between starting moments of subsequent transport steps is a tact time, the controller being configured to determine the tact time.

5. The printing assembly according to claim 4, wherein the controller is configured to determine the tact time on the basis of the processing times of the at least two printers.

6. The printing assembly according to claim 1, wherein the transporting along the at least one transport path is done in subsequent transport steps wherein a time period between starting moments of subsequent transport steps is a tact time Ttact, wherein the printers of the assembly that conduct a process of a same type are grouped in printer groups of at least one printer indicated by p(j), wherein j = 1, 2, ...., m and indicates the process type number, wherein each printer of a printer group performing the same process type has a number i, wherein i = 1, 2, ..., n(j) and n(j) is the total number of printers within a said printer group p(j), wherein the processing time of each printer of the same process type p(j) may vary and is indicated by T(p(j), i), wherein the controller is configured to determine the tact time Ttact on the basis of the printer group p(j) having the longest mean processing time, i.e. by the following formula:

Ttact ≥ max

T (P(l),i) ,_ T (P(2),i) T (P(m),i) i=l...n(l) i=l..n(2) i=l..n(m)

7. The printing assembly according to claim 7, wherein controller is configured to give priority to loading the printer group p(j) with substrates that has the longest tact time Ttact.

8. The printing assembly according to any of the preceding claims, wherein each printer is an inkjet printer.

9. The printing assembly according to claim 8, wherein each inkjet printer has a single printing head.

10. The printing assembly according to any of the preceding claims, wherein the transport assembly includes at least one belt or chain conveyor or a rotary table.

11. The printing assembly according to any one of claims 1-9, wherein the transport assembly includes a series of manipulators that are arranged along the transport path that is formed by discrete substrate mounting positions, each manipulator being configured to pick up a substrate from an upstream substrate mounting position and to place the picked-up substrate on a downstream substrate mounting position.

12. The printing assembly according to any of claims 1-9, wherein the transport assembly includes a number of substrate carriers that are moveable along the transport path over a guide.

13. The printing assembly according to any of the preceding claims, wherein the transport assembly includes a single transport path.

14. The printing assembly according to any one of claims 1-12, wherein the transport assembly includes two transport paths.

15. A method of depositing material on discrete substrates including:

• providing at least two printers each with an associated manipulator assembly along at least one transport path that is defined by a transport assembly;

• providing a number of substrates;

• loading subsequent substrates in the transport assembly and transporting the subsequent substrates along the at least one transport path; and • repeatedly performing the following series of steps: o unloading a substrate of said number of substrates from the at least one transport path and loading the substrate in a said printer; o processing the substrate in the printer by applying a said material with the printer on the substrate; o unloading the substrate from the printer after processing and replacing the substrate in the transport assembly for further processing.

16. The method of claim 15, wherein the transporting along the at least one transport path is done in subsequent transport steps wherein a time period between starting moments of subsequent transport steps is a tact time Ttact, wherein the printers that conduct a process of a same type are grouped in printer groups indicated by p(j), wherein j = 1, 2, ...., m and indicates the process type number, wherein each printer of a printer group performing the same process type has a number i, wherein i = 1, 2, ..., n(j) and n(j) is the total number of printers within a said printer group p(j), wherein the processing time of each printer of the same process type p(j) may vary and is indicated by T(p(j), i), wherein the tact time Ttact is determined on the basis of the printer group p(j) having the longest mean processing time, i.e. by the following formula:

Ttact > max i ,= . n .1((1l)) ^{T <P<1)i} i= n(2) ^{T (P(2)a} i=tn_(m) ^T

17. The method according to claim 16, wherein priority is given to loading the printer group p(j) with substrates that has the longest tact time

Ttact.