BACKGROUND

[0001] A printing device like an ink-jet printer may comprise a printhead that is to deposit a printing fluid such as ink on a print medium. The printhead may be mounted on a moveable printhead carriage that is to move the printhead across the print medium to deposit the printing fluid as a stripe or swath across the print medium. The print medium may be advanced before printing an adjacent swath, thereby sequentially building up the image that is to be printed.

BRIEF DESCRIPTION OF DRAWINGS

[0002] In the following, a detailed description of various examples is given with reference to the figures. The figures show schematic illustrations of

[0003] Fig. 1 : a print zone assembly according to an example in top view;

[0004] Fig. 2a: a print zone assembly comprising a linear motor track in accord ance with an example in a cross-sectional side view; [0005] Fig. 2b: the linear motor track of the print zone assembly of Fig. 2a in side view according to an example;

[0006] Fig. 3: a printing device according to an example in top view;

[0007] Fig. 4a: a printing device comprising multiple printhead carriages accord ing to an example in top view;

[0008] Fig. 4b: the printing device of Fig. 4a in a cross-sectional side view in accordance with an example;

[0009] Fig. 5: a method of operating a printing device in accordance an exam ple;

[0010] Fig. 6: a method of operating a printing device according to another ex ample; and

[0011] Fig. 7: a printing process on a continuously advancing print medium in accordance with an example.

DETAILED DESCRIPTION

[0012] A printing device with a scanning printhead may offer high image quality at reasonable cost. Moving the printhead, however, takes time, which may limit the printing speed that can be achieved. To increase the printing speed, a larger printhead may be used to increase the area that can be printed on in one pass across a print medium. Yet, this may lead to a longer downtime between passes since the larger printhead may take longer to accelerate and decelerate. Fur thermore, the distance by which the print medium is moved may increase as well. This may reduce the resulting increase in printing speed and may also cause image quality issues due to media advance errors. [0013] Fig. 1 depicts a schematic illustration of a print zone assembly 100 for use in a printing device (not shown) in accordance with an example. The print zone assembly 100 may for example be used in or may be part of the printing device 300 or 400 described below. The print zone assembly 100 comprises a plurality of printhead carriages, e.g. a first printhead carriage 102A and a sec ond printhead carriage 102B as in the example of Fig. 1. Each of the printhead carriages 102A, 102B may comprise or may be to receive a printhead (not shown) that is to deposit a printing fluid such as ink on a print medium (not shown).

[0014] The print zone assembly 100 further comprises an electric motor assem bly 104 that is to move the printhead carriages 102A, 102B along a common scanning path 106. The scanning path 106 extends along a closed loop across a print zone 108 of the printing device. In the print zone 108, the print medium may be arranged to deposit the printing fluid thereon using the printhead car riages 102A, 102B. The scanning path 106 may for example comprise two straight portions 106A, 106B, which may e.g. extend between opposing edges of the print zone 108 and may be parallel to each other as illustrated in Fig. 1. The scanning path 106 may further comprise two curved portions 106C, 106D connecting the two straight portions 106A, 106B to each other to form the closed loop. In one example, printing fluid may be deposited along the lower straight portion 106A or a part thereof, but not along the upper straight portion 106B and the curved portions 106C, 106D. Accordingly, the lower straight por tion 106A or the part thereof may form a printing portion of the scanning path 106, whereas the other portions 106B-D may form a non-printing portion of the scanning path 106 as illustrated by the broken line in Fig. 1. In other examples, printing fluid may be deposited along both straight portions 106A, 106B.

[0015] The electric motor assembly 104 is to independently move the printhead carriages 102A, 102B along the scanning path 106. The electric motor assem bly 104 may for example be to move the first printhead carriage 102A at a dif ferent speed than the second printhead carriage 102B or may be to move one of the printhead carriages 102A, 102B while the other printhead carriage is stopped. For this, the electric motor assembly 104 may comprise an electric mo tor that is independently coupled to each of the printhead carriages 102A, 102B, e.g. by separate gear drives or worm drives. In some examples, the electric mo tor assembly 104 may comprise a linear motor track that is to independently move a plurality of linear motor sliders, e.g. as in the example of Figs. 2a, 2b described below. In other examples, the electric motor assembly 104 may com prise a plurality of independent electric motors, e.g. one electric motor on each of the carriages 102A, 102B or a plurality of electric motors arranged along the scanning path 106.

[0016] Fig. 2a depicts a schematic illustration of a print zone assembly 200 for a printing device (not shown) according to another example in a cross-sectional side view. The print zone assembly 200 may be similar to the print zone assem bly 100 of Fig. 1. The print zone assembly 200 also comprises a plurality of printhead carriages, one of which is shown in Fig. 2a and labelled with the ref erence sign 102A. The print zone assembly 200 further comprises an electric motor assembly 104 that is to independently move the printhead carriages along a common scanning path, e.g. as illustrated in Fig. 1.

[0017] A printhead 202 is arranged in each of the printhead carriages. The printhead 202 may be part of the respective printhead carriage or may be re movably mounted on the respective printhead carriage, e.g. in a corresponding slot of the printhead carriage. The printhead 202 may comprise a nozzle plate 202A facing the print zone 108, wherein the nozzle plate 202A comprises a plu rality of nozzles for ejecting a printing fluid onto a print medium (not shown) ar ranged in the print zone 108. In some examples, some or all of the printhead carriages may comprise multiple printheads, e.g. multiple printheads for inks of different colors.

[0018] The electric motor assembly 104 comprises a linear motor track 204 that extends along the scanning path. The linear motor track 204 may for example comprise a plurality of magnets 206 that are arranged along the scanning path as illustrated in Fig. 2b, which depicts a schematic illustration of the linear motor track 204 in side view along the Y axis of Fig. 2a according to an example. The magnets 206 may for example be permanent magnets, e.g. rare-earth magnets. Additionally or alternatively, the magnets 206 may be electromagnets, which may e.g. comprise a coil.

[0019] The linear motor track 204 further comprises a guide rail 208 that is to receive linear motor sliders such as the linear motor slider 210 of the printhead carriage 102A described below. The guide rail 208 may for example com prise/define a slot 208A that extends along the linear motor track 204. The slot 208A may be to receive and guide a portion of the linear motor slider as illus trated in Fig. 2a. The magnets 206 may for example be arranged in alternating orientations along each side of the guide rail 208, i.e. such that the orientation of each magnet is rotated by 180° relative to the orientation of the adjacent mag nets as illustrated in Fig. 2b. The magnets 206 may be oriented such that a magnetic pole of each magnet faces the slot 208A. The magnets 206 may be arranged in pairs of magnets arranged on opposite sides of the slot 208A, wherein the magnets in a pair may have the same orientation, i.e. such that the north pole of one of the magnets faces the south pole of the other magnet in the pair as shown in Fig. 2b.

[0020] The slot 208A of the guide rail 208 may for example face sideways as in the example of Fig. 2a, i.e. an opening of the slot 208A may face in a direction perpendicular to the direction of gravity. Accordingly, a main body of the print- head carriages may be arranged at substantially the same height as the guide rail 208. In other examples, the slot 208A of the guide rail 208 may have a dif ferent orientation and may e.g. face upwards or downwards. In some examples, the guide rail 208 may comprise a retaining element (not shown) that is to pre vent the linear motor slider from leaving or falling out of the guide rail 208, e.g. a protrusion or groove extending along the guide rail 208 that is to be engaged with a corresponding element on the linear motor slider. [0021] Each of the printhead carriages comprises a linear motor slider 210 that is to be placed on the linear motor track 204, e.g. by arranging the linear motor slider 210 in the guide rail 208 as illustrated in Fig. 2a. The linear motor slider 210 may for example comprise an inductive element such as a coil 212, wherein the inductive element may be to generate a magnetic field when applying a cur rent through the inductive element. In some examples, the coil 212 may be wound around a magnetic core (not shown) comprising a ferromagnetic or fer romagnetic material to increase the strength of the magnetic field generated by the coil 212. The magnets 206 and the coil 212 may for example be arranged such that end faces of the coil 212 face magnetic poles of the magnets 206 when the linear motor slider 210 is placed in the guide rail 208 as shown in Fig. 2a. In some examples, the linear motor slider 210 may comprise a plurality of inductive elements, e.g. a plurality of coils. The linear motor slider 210 may be part of a main body of the printhead carriage or may be attached to the main body of the printhead carriage.

[0022] The print zone assembly 200 further comprises a controller 214 that is to generate respective drive signals for the inductive elements. The drive signal may e.g. be an electric current through the inductive element, wherein the con troller 214 may supply the current itself or may generate a control signal for a current supply that supplies the current. The drive signal may be such that the coil 212 creates a time-dependent magnetic field, which in the presence of the magnets 206 may result in a force accelerating the linear motor slider 210 along the guide rail 208, thereby moving the printhead carriage 102A along the scan ning path. The printhead carriages may be moved independently along the scanning path by generating an individual drive signal for each of the printhead carriages, which may e.g. allow for moving the printhead carriages at different speeds. In other words, the controller 214 may for example be to generate a first drive signal to move the first printhead carriage 102A, e.g. at a first speed to a first position along the scanning path, and a second drive signal to move the second printhead carriage 102B, e.g. at a second speed to a second position along the scanning path, wherein the second speed and position may be differ ent from the first speed and position, respectively.

[0023] The controller 214 may be implemented in hardware, software or a com bination thereof and may for example comprise a microcontroller with a proces sor and a memory storing instructions that are to be executed by the processor to provide the functionality described herein. In the example of Fig. 2a, the con troller 214 is implemented as a distributed controller comprising a control unit in each of the printhead carriages, e.g. a control unit 214A in the printhead car riage 102A. Additionally or alternatively, the controller 214 may comprise a main control unit (not shown), which may e.g. be fixedly arranged within the printing device. The main control unit may for example provide the drive signals to the printhead carriages or may instruct the control unit or a current supply on the respective printhead carriage to generate the drive signal. The control unit on the respective printhead carriage may further be to control the printhead 202, e.g. by providing control signals for the ejection of printing fluid from the print- head 202.

[0024] In some examples, a different linear motor configuration may be used. For example, the arrangement of magnets and coils may be reversed, i.e. a magnet may be arranged in the linear motor slider 210 and a plurality of coils may be arranged along the linear motor track 204. Accordingly, the controller 214 may be to generate drive signals for the plurality of coils, e.g. a first set of drive signals for a first set of coils in the vicinity of the first printhead carriage 102A to move first printhead carriage 102A and a second set of drive signals for a second set of coils in the vicinity of the second printhead carriage 102B to move the second printhead carriage 102B.

[0025] The print zone assembly 200 also comprises a power supply rail 216 that extends along the scanning path. Each of the printhead carriages comprises a connector 218 that is to be in electrical contact with the power supply rail 216 while the respective printhead carriage moves along the scanning path. The connector 218 may for example comprise a flexible conductive element that is to be in contact with a conductive line extending along the power supply rail. The flexible conductive element may for example comprise a spring that is to press a sliding conductive contact pad against the conductive line when the lin ear motor slider 210 is arranged in the guide rail 208. Additionally or alternative ly, the flexible conductive element may e.g. comprise a conductive wire, e.g. a stranded wire or braid, which may for example slide along a slot in which the conductive line is arranged while the linear motor slider 210 moves along the linear motor track 204.

[0026] The power supply rail 216 may for example be to provide a supply volt age to the printhead carriages, e.g. to power the control unit 214A and other elements of the printhead carriage such as the printhead 202. In some exam ples, the power supply rail 216 may comprise a plurality of conductive lines, e.g. two as in the example of Fig. 2a, wherein one conductive line may for example provide the supply voltage and the other conductive line may be a ground line. In some examples, the power supply rail 216 may also comprise a drive signal line (not shown), which may be to provide the drive signals to the printhead car riages. In one example, the power supply rail 216 may further comprise a data line (not shown) for exchanging data such as control signals with the printhead carriages, e.g. between the controller 214 and a main controller of the printing device or between the control units of the printhead carriages. Additionally or alternatively, some or all of the printhead carriages may comprise a wireless communication chip 220 that is to receive signals from a wireless transmitter of the printing device (not shown). The wireless communication chip 220 may for example be to exchange data with the wireless transmitter via a wireless com munication protocol such as Bluetooth or Wi-Fi. This may for example allow for data exchange between the controller 214 and the main controller of the printing device without connecting any cables to the printhead carriages.

[0027] Some or all of the printhead carriages may further comprise an interme diate ink tank 222 that is to store a printing fluid such as ink and to provide the printing fluid to the printhead 202. This may allow for printing with the printhead carriages without connecting any tubes to the printhead carriages for supplying the printing fluids. The intermediate ink tank 222 may for example be refilled periodically by a user or at an ink refill station (not shown) as detailed below with reference to Fig. 4a. For this, the printhead carriages may comprise an in put port 224 that is in fluid communication with the intermediate ink tank 222 and may for example be to be removably connected to a fluid connector of the ink refill station.

[0028] In some examples, the print zone assembly 200 may comprise additional elements, for example the ink refill station, a capping station, or a maintenance cartridge, e.g. as detailed below for the printing device 400. The print zone as sembly 200 may also comprise an encoder strip extending along the scanning path, e.g. to determine a position of the printhead carriage. Each of the print- head carriage may comprise a position sensor, e.g. an optical sensor, which may be to determine the position of the respective printhead carriage using the encoder strip. The print zone assembly 200 may further comprise a support structure such as a platen that is to support a print medium in the print zone 108 and a media advance system that is to advance the print medium in the print zone 108 along a media advance direction, which may e.g. coincide with the Y direction in Fig. 2a.

[0029] Fig. 3 shows a schematic illustration of a printing device 300 according to an example in top view. The printing device 300 comprises a linear motor track 204 that extends in a loop across a print zone 108 of the printing device 300. The printing device 300 further comprises a printhead carriage 102 that is to be engaged with the linear motor track 204 and a controller 302 that is to generate a drive signal for moving the printhead carriage 102 along the linear motor track 204. Accordingly, the linear motor track 204 may define a scanning path along which the printhead carriage 102 can be moved, wherein the scan ning path may for example be similar to the scanning path 106 of the print zone assembly 100 in Fig. 1. A printhead (not shown) may be arranged in the print- head carriage 102, wherein the printhead may be to deposit a printing fluid on a print medium 304 arranged in the print zone 108. The printing device 300 may for example be an inkjet printer, e.g. a large format inkjet printer. A width of the print zone 108 may for example be between 50 cm and 300 cm, e.g. 100 cm. The print medium 304 may for example be a flexible print medium such as pa per or textile or may be a rigid print medium such as cardboard, plastic, or met al. In some examples, the printing device 300 may comprise the print zone as sembly 100 or 200 described above.

[0030] The linear motor track 204 and the printhead carriage 102 may for ex ample be similar to the linear motor track and printhead carriage, respectively, of the print zone assembly 200 described above with reference to Figs. 2a, 2b. The linear motor track 204 may for example comprise a guide rail that is to re ceive a linear motor slider of the printhead carriage 102.

[0031] The linear motor track 204 may comprise a plurality of magnets that are arranged along the loop of the linear motor track 204. The printhead carriage 102 may comprise an inductive element such as a coil that is to generate a time-dependent magnetic field based on the drive signal, wherein the drive sig nal may for example be a current through the inductive element. In other exam ples, a different linear motor arrangement may be used. For example, a magnet may be arranged in the print head carriage 102, e.g. in a linear motor slider, and a plurality of coils may be arranged along the linear motor track 204. According ly, the controller 302 may e.g. be to generate a plurality of drive signals for the plurality of coils to generate a time-dependent magnet field acting on the mag net in the print head carriage 102.

[0032] The controller 302 may be to generate the drive signal so as to generate a force along the linear motor track 204 for accelerating or decelerating the printhead carriage 102, e.g. to move the printhead carriage 102 to a target posi tion or to accelerate the printhead carriage 102 to a target velocity. In some ex amples, the controller 302 may further be to control a printing process, e.g. by providing the corresponding control signals to the printhead carriage 102 and to a media advance system for advancing the print medium 304. In one example, the controller 302 may be to execute one of the methods 500, 600 described below at least in part.

[0033] The controller 302 may be implemented in hardware, software or a combination thereof and may for example comprise a microcontroller with a processor and a memory storing instructions to be executed by the processor to provide the functionality described herein. The controller 302 may be imple mented as one unit as illustrated in Fig. 3 or may be implemented in a distribut ed manner and may e.g. comprise a plurality of control units as described above with reference to Fig. 2a. In some examples, the controller 302 may be or may comprise the controller 214 of the print zone assembly 200 of Fig. 2a.

[0034] In some examples, the printing device 300 may also be equipped with more than one print head carriage, e.g. with two printhead carriages similar to the print zone assembly 100 of Fig. 1 or three printhead carriages similar to the printing device 400 described below. The controller 302 may be to generate drive signals for independently moving the plurality of the printhead carriages along the linear motor track 204, e.g. as detailed above with reference to Fig. 2a.

[0035] Figs. 4a and 4b depict schematic illustrations of a printing device 400 comprising multiple printhead carriages according to an example. The printing device 400 is shown in top view in Fig. 4a and in a cross-sectional side view in Fig. 4b. The printing device 400 is similar to the printing device 300 of Fig. 3 and also comprises a controller 302 and a linear motor track 204 extending in a loop across a print zone 108. In some examples, the printing device 400 may com prise one of the print zone assemblies 100 and 200 described above.

[0036] The printing device 400 comprises a plurality of printhead carriages, e.g. three printhead carriages 102A, 102B, 102C as in the example of Fig. 4a. The printhead carriages 102A-C may have a similar or the same structure. Accordingly, the following description which uses the printhead carriage 102B depicted in Fig. 4b as an example for illustration purposes may also apply to the other printhead carriages 102A, 102C in some examples.

[0037] The controller 302 is to generate a plurality of drive signals for independently moving each of the printhead carriages 102A-C along the linear motor track 204, e.g. a respective drive signal for each of the printhead carriages 102A-C or a respective drive signal for each of a plurality of coils arranged along the linear motor track 204. The controller 302 may for example comprise a main control unit 302X, which may e.g. be fixedly arranged within the printing device 400, and a respective control unit in each of the printhead carriages 102A-C, e.g. the control unit 302B in the printhead carriage 102B. The controller 302 may be to generate the drive signal by sending a command signal from the main control unit 302X to the control unit of the respective printhead carriage, e.g. to the control unit 302B. The command signal may instruct the control unit 302B to generate a specified time-dependent current through an inductive element in the linear motor slider 210 to move the printhead carriage 102B. The controller 302 may for example comprise a wireless transmitter/receiver 402 for communicating with the control unit 302B of the printhead carriages 102B via the wireless communication chip 220.

[0038] The linear motor track 204 defines a scanning path 106, along which the printhead carriages 102A-C can be moved. The scanning path 106 extends along a closed loop across the print zone 108 of the printing device 400. In the example of Fig. 4a, the scanning path 106 comprises four portions or segments 106-1, 106-11, 106-111, 106-IV, wherein the first and third portions 106-1, 106-111 extend between opposing edges of the print zone 108 and are connected to each other via the second and fourth portions 106-11, 106-IV. In one example, the first and third portions 106-1, 106-111 may be straight and may e.g. be similar to the straight portions 106A, 106B of the scanning path of Fig. 1 or a part thereof. At least a part of the second and fourth portions 106-11, 106-IV may be curved and may e.g. be similar to the curved portions 106C, 106D of the scanning path of Fig. 1. In one example, printing fluid may be deposited along the first portion 106-1, but not along the other portions 106-11 to 106-IV. Accordingly, the first portion 106-1 may form a printing portion of the scanning path 106 as illustrated by the dotted line in Fig. 4a, whereas the other portions 106-11 to 106- IV may form a non-printing portion of the scanning path 106 as illustrated by the broken line in Fig. 4a. In other examples, printing fluid may be deposited along both the first and third portions 106-1, 106-111.

[0039] The controller 302 may further be to determine a position of each of the printhead carriages 102A-C, e.g. based on the generated drive signals or based on a sensor signal, for example using an encoder strip. The controller 302 may be to adjust the drive signals based on the determined positions and may for example perform a closed-loop feedback to control the speed and position of the printhead carriages 102A-C. In some examples, the printing device 400 may further comprise a media sensor (not shown) and the controller 302 may be to determine the presence or position of the print medium in the print zone 108 using the media sensor.

[0040] The printing device 400 further comprises an ink refill station 404 that is arranged along the linear motor track 204, e.g. outside of the print zone 108 adjacent to a curved portion of the linear motor track 204. In the example of Figs. 4a, 4b, the printhead carriage 102B is located at an ink refill position adjacent to the ink refill station 404. The ink refill station 404 is to be removably connected to an input port 224 of the printhead carriage 102B. The ink refill station 404 is to provide a printing fluid to an intermediate ink tank 222 of the printhead carriage 102B via the input port 224. The ink refill station 404 may for example comprise a fluid connector 404A that is to be connected to or inserted into the input port 224 to bring the ink refill station 404 into fluid communication with the intermediate ink tank 222. In some examples, the ink refill station 404 may be to provide a plurality of printing fluids, e.g. inks of different colors, and may comprise a respective fluid connector for each of the printing fluids, e.g. four fluid connectors as in the example of Fig. 4a. The input port 224 may for example be arranged on a top surface of the printhead carriage 102B, e.g. as illustrated in Fig. 2a or 4. The ink refill station 404 may comprise an actuator for moving the fluid connector 404A up and down to connect/disconnect the fluid connector 404A to/from the input port 224.

[0041] In some examples, the printhead carriage 102B may comprise a respec tive main body 102B-I and an extension 102B-II. The main body 102B-I and the extension 102B-II may be formed in one piece. In other examples, the extension 102B-II may be attached to the main body 102B-I, in one example removably attached to the main body 102B-I. This may for example allow for retro-fitting the main body 102B-I for use with the printing device 400. The extension 102B- II may for example provide a fluid connection between the input port 224 and a port on the main body 102B-I, e.g. as illustrated in Fig. 4b. In some examples, the intermediate ink tank 222 may be arranged in the extension 102B-II, in other examples in the main body 102B-I, e.g. similar to printhead carriage of Fig. 2a.

[0042] The linear motor track 204 may for example have an orientation similar to the one shown in Figs. 2a, 2b, i.e. an opening of the guide rail 208 may face sideways and the main body 102B-II of the printhead carriage 102B may be ar ranged at substantially the same height as the guide rail 208. The extension 102B-II may for example extend from the main body 102B-I to above the linear motor track 204 as shown in Figs. 4a, 4b. The printing device 400 may also comprise a power supply rail 216 that is to be in electrical contact with a con nector 218 of the printhead carriage 102B, e.g. similar as described above with reference to Fig. 2a.

[0043] The printing device 400 further comprises a capping station 406 that is arranged along the linear motor track 204, e.g. outside of the print zone 108 adjacent to a curved portion of the linear motor track 204, in one example adja cent to the ink refill station 404 as illustrated in Figs. 4a, 4b. In the example of Figs. 4a, 4b, the capping station comprises a plurality of capping subsystems 406-1, 406-11, 406-111, each of which is to cover a nozzle plate 202A of a print- head 202 on one of the printhead carriages 102A-C when the printhead carriage is placed at a respective capping position along the linear motor track 204. The capping station 406 may comprise a capping subsystem for each of the print- head carriages 102A-C, wherein the capping subsystems 406-I to 406-III may be arranged such that the printhead carriages 102A-C can simultaneously be parked at the respective capping positions. The capping subsystems 406-I to 406-III may be adjacent to each other as in Fig. 4a or may be distributed along the linear motor track 204, e.g. arranged adjacent to opposing end portions of the linear motor track 204.

[0044] The printing device 400 also comprises a maintenance cartridge 408 for performing maintenance operations on the printhead carriages 102A-C. The maintenance cartridge 408 may for example be arranged in a servicing zone outside of the print zone 108, e.g. on a side of the print zone 108 opposing the ink refill station 404 and the capping station as in Fig. 4a. In some examples, the maintenance cartridge 408 may be moveable, e.g. parallel to a media ad vance direction, which in the example of Fig. 4a may for example be aligned with the Y direction. The maintenance cartridge 408 may comprise a wiper 408A, which may be to wipe off contaminants from the nozzle plate 202A. The maintenance cartridge 408 may further comprise a spittoon 408B. The spittoon 408B may be to receive printing fluid ejected from the print head 202, e.g. to prevent clogging of the nozzles on the nozzle plate 202A.

[0045] Fig. 5 shows a flow chart of a method 500 of operating a printing device in accordance with an example. The method 500 may for example be imple mented with a printing device comprising the print zone assembly 100 of Fig. 1 or with the printing device 400 of Fig. 4a, which are used as examples for illus tration purposes in the following. This is, however, not intended to be limiting in any way and the method 500 may also be implemented with other printing de vices, e.g. a printing device comprising the print zone assembly 200 of Fig. 2a or the printing device 300 of Fig. 3 when equipped with two printhead carriages. Furthermore, the method 500 is not limited to the order of execution implied by the flow chart of Fig. 5. As far as technically feasible, the method 500 can be executed in an arbitrary order and parts thereof can be executed simultaneously at least in part.

[0046] The method 500 comprises, in block 502, moving a first printhead car riage 102A along a printing portion of a scanning path 106 to deposit a printing fluid on a print medium. The printing portion extends between opposing edges of the print medium and may for example correspond to the first portion 106-1 of the scanning path 106 shown in Fig. 4a, the straight portion 106A of the scan ning path 106 shown in Fig. 1 or a part thereof. The first printhead carriage 102A may e.g. be moved from a starting position on one end of the printing por tion to an end position on the opposite end of the printing portion. The starting position may for example be at a point connecting the fourth and first portions 106-IV, 106-1 of the scanning path 106 of Fig. 4a, whereas the end position may for example be at a point connecting the first and second portions 106-IV, 106- II. In another example, the starting position may for example be at a point along the straight portion 106A of the scanning path of Fig. 1 or at a point connecting the curved portion 106D and the straight portion 106A, whereas the end position may for example be at another point along the straight portion 106A or at a point connecting the straight portion 106A and the curved portion 106C. Thereby, the first printhead carriage 102A covers a stripe on the print medium, on which a swath may be printed on in block 502. In some examples, the print medium may be advanced in block 502 while depositing printing fluid thereon with the first printhead carriage 102A.

[0047] The method 500 further comprises, in block 504, moving a second printhead carriage 102B along a non-printing portion of the scanning path 106 while the first printhead carriage 102A moves along the printing portion of the scanning path 106. In other words, the two printhead carriages 102A, 102B are moved simultaneously along different parts of the same scanning path 106. The non-printing portion of the scanning path 106 may for example comprise the fourth portion 106-1 V of the scanning path 106 shown in Fig. 4a or the curved portion 106C of the scanning path 106 shown in Fig. 1. In one example, the non-printing portion may also comprise the second and third portion 106-11, 106- IN of the scanning path 106 of Fig. 4a or the straight portion 106B and the other curved portion 106D of the scanning path 106 of Fig. 1 , e.g. when printing in a unidirectional mode.

[0048] The second printhead carriage 102B is moved to the starting position of the printing portion of the scanning path in block 504, e.g. such that the second printhead carriage 102B reaches the starting position before or at the same time when the first printhead carriage 102A reaches the end position of the printing portion. In this way, the second printhead carriage 102B may be ready to print a second swath on the print medium when the first printhead carriage 102A fin ishes printing the first swath.

[0049] The second printhead carriage 102B moves at a speed V _B that is differ ent from a speed V _A of the first printhead carriage 102A. The second printhead carriage 102B may for example move faster than the first printhead carriage 102A, e.g. such that the second printhead carriage 102B can cover a longer distance than the length of the printing portion while the first printhead carriage 102A moves along the printing portion. The second printhead carriage 102B may for example be moved from the end position along the non-printing portion to the start position, e.g. along the portions 106-11, 106-111, 106-IV or 106D, 106B, 106C of the scanning path 106, while the first printhead carriage 102A moves from the start position along the printing portion to the end position, e.g. along the portion 106-1 or 106A of the scanning path 106.

[0050] To allow for such an independent movement of the printhead carriages 102A, 102B, the printhead carriages 102A, 102B may for example be moved using a linear motor, e.g. as detailed above, or may be moved using two inde pendent motors coupled to or arranged in a respective one of the printhead car riages 102A, 102B. [0051] In some examples, the speed VB of the second printhead carriage 102B within the non-printing portion may always be larger than the speed V _A of the first printhead carriage 102A within the printing portion. In other examples, the second printhead carriage 102B may be moved at the same speed or at a lower speed than the first printhead carriage 102A along at least a part of the non printing portion. In one example, one or both of V _A and V _B may be constant.

[0052] In some examples, no printing fluid may be ejected from the second printhead carriage 102B in bock 504. The printing fluid may be deposited on the print medium in a unidirectional printing mode, i.e. the printhead carriages 102A, 102B may always move in the same direction when depositing printing fluid, e.g. from left to right along the portion 106-1 or 106A of the scanning path 106 in Fig. 1 and 4a, respectively. This may for example avoid image quality issues due to hue shift banding, which may arise in bidirectional printing modes due to the different order of ejection of printheads on the printhead carriages 102A, 102B.

[0053] Fig. 6 shows a flow chart of a method 600 of operating a printing device according to another example. The method 600 is similar to the method 500 and may for example also be implemented with a printing device comprising the print zone assembly 100 of Fig. 1 or with the printing device 400 of Fig. 4a, which are used as examples for illustration purposes in the following. This is, however, not intended to be limiting in any way and the method 600 may also be implemented with other printing devices, e.g. a printing device comprising the print zone assembly 200 of Fig. 2a or the printing device 300 of Fig. 3 when equipped with two printhead carriages. Furthermore, the method 600 is not lim ited to the order of execution implied by the flow chart of Fig. 6 As far as techni cally feasible, the method 600 can be executed in an arbitrary order and parts thereof can be executed simultaneously at least in part.

[0054] The method 600 allows for printing on a print medium while continuous ly advancing the print medium, i.e. to deposit printing fluid on the print medium while the print medium is in motion. To account for this, the method 600 com- prises a pre-processing of the image that is to be printed on the print medium in block 602. The image is divided into a plurality of trapezoidal segments, each of which may be printed on the print medium during a respective pass along the printing portion of the scanning path 106 by one of the printhead carriages 102A, 102B. In other words, each of the trapezoidal segments may be printed as one swath 700-1 , 700-2, 700-3, 700-4, ..., 700-n on the print medium 304 as illustrated in Fig. 7, which depicts a printing process on a continuously advanc ing print medium 304 in accordance with an example.

[0055] Block 602 may comprise determining a segmentation angle a for divid ing the image that is to be printed into a plurality of segments. The segmenta tion angle a is determined based on a scanning speed v _sc of the first printhead carriage 102A and a media advance speed v _m of the print medium. The seg mentation angle a may for example be calculated as a = arctan (v _m /v _sc ). The scanning speed may for example be the average speed of the first printhead carriage 102A along the printing portion of the scanning path 106 and may be equal to VA. The media advance speed may for example be between 1% and 10% of the scanning speed, in one example between 2% and 5% of the scan ning speed.

[0056] Subsequently, the image may be divided into trapezoidal segments us ing the segmentation angle a. Each segment may for example have two parallel borders that extend at an angle of 90° - a relative to a direction in the image that corresponds to the media advance direction, which may e.g. be aligned with the Y direction as illustrated in Fig. 7. In some examples, the trapezoidal segments may be parallelograms, i.e. may have two pairs of parallel borders, e.g. as shown in Fig. 7. One pair of borders may extend at an angle of 90° - a relative to the media advance direction. The other pair of borders may be formed by borders of the image and may e.g. be aligned with the media advance direction. In some examples, the segments may also comprise a triangular segment, e.g. the first or last segment that is to be printed on the print medium 304. [0057] In some examples, block 602 may also comprise determining a firing sequence for printing the image, e.g. a respective firing sequence for each of the trapezoidal segments. The firing sequence may for example characterize a plurality of ejection times for a nozzle or a group of nozzles of the printhead 202, at which the respective nozzle or group of nozzles is to eject drops of printing fluid, e.g. to form the image on the print medium 306. Determining the firing se quence may comprise determining a static firing sequence based on the image that is to be printed. The static firing sequence may correspond to a firing se quence for forming the image on the print medium 306 in a static printing mode, in which neither the print medium nor the respective printhead carriage is mov ing while ejecting the printing fluid. Determining the firing sequence may further comprise adjusting the static firing sequence to obtain a corrected firing se quence which accounts for a motion of the print medium and of the printhead carriage while ejecting the printing fluid. The corrected firing sequence may be determined using a first offset characterizing a shift in the scanning direction, e.g. the X direction of Fig. 7, as a result of the motion of the printhead carriage and a second offset characterizing a shift in the media advance direction, e.g. the Y direction of Fig. 7, as a result of the motion of the print medium. The cor rected firing sequence may be transmitted to the control unit of the respective printhead carriage, e.g. via the wireless transmitter/receiver 402 and the wire less communication chip 220.

[0058] In blocks 604 and 606, a first segment of the image is printed on the print medium 304 using the first printhead carriage 102A, for example by depos iting printing fluid in a first stripe or swath 700-1 on the print medium 304 as il lustrated in Fig. 7. For this, the first printhead carriage 102A is moved along the printing portion of the scanning path 106 in block 604, e.g. along the portion 106-1 or 106A of the scanning path 106 in Fig. 1 and 4a, respectively. The first printhead carriage 102A may for example be moved from the starting position to the end position of the printing portion. At the same time, the second printhead carriage 102B is moved along the non-printing portion of the scanning path 106 to the starting position of the printing portion, e.g. as in block 504 of method 500. The second print head 102B may for example be moved along the portions 106-11 to 106-IV or 106B-D of the scanning path 106 in Fig. 1 and 4a, respec tively. While the first printhead carriage 102A moves along the printing portion, the printhead 202 in the first printhead carriage 102A may deposit the printing fluid for printing the first swath 700-1 using the corrected firing sequence.

[0059] The method 600 may comprise advancing the print medium 304 while depositing the printing fluid thereon with the first printhead carriage 102A, e.g. such that the first swath 700-1 extends at the angle a relative to the scanning direction. The scanning direction may for example be the direction of motion of the first printhead carriage 102A along the printing portion and may e.g. be aligned with the X direction. In some examples, the print medium 304 may be advanced at a constant speed, which may for example be between 1 cm/s and 20 cm/s.

[0060] In blocks 608 and 610, a second segment of the image is printed on the print medium 304 using the second printhead carriage 102B, for example by depositing printing fluid for printing a second swath 700-2 on the print medium 304 as illustrated in Fig. 7. For this, the method 600 may further comprise, in block 608, starting to move the second printhead carriage 102B from the start ing position of the printing portion along the printing portion when the first print- head carriage 102A reaches the end position of the printing portion. While the second printhead carriage 102B moves along the printing portion, e.g. from the starting position to end position, printing fluid may be deposited in the second swath 700-2 to print the second segment in block 610. In this way, a continuous printing mode may be implemented, wherein the second printhead carriage 102B starts printing the second swath 700-2 at the same time when the first printhead carriage 102A finishes printing the first swath 700-1. In other words, there may be no downtime during the printing process.

[0061] The print medium 304 may be advanced while depositing the printing fluid thereon with the second printhead carriage 102B in block 610. In some ex- amples, the print medium 304 may be advanced continuously while printing thereon, e.g. during the entire printing process. This may prevent image quality issues due to media advance errors, e.g. due to the print medium 304 slipping when starting to advance the print medium 304 or when stopping the print me dium 304.

[0062] While the second printhead carriage 102B moves along the printing por tion of the scanning path 106 in block 608, the first printhead carriage 102A may be moved along a return portion of the scanning path 106 from the end position of the printing portion to the starting position of the printing portion. The return portion may for example comprise the second to fourth portions 106-11 to 106-IV of the scanning path 106 as shown in Fig. 4 or the straight portion 106B as well as the curved portions 106C, 106D of the scanning path 106 as shown in Fig. 1. The return portion may comprise the non-printing portion of the scanning path 106. In some examples, a unidirectional print mode may be used and no print ing fluid may be ejected from the first printhead carriage 102A along the return portion. Accordingly, the return portion may correspond to the non-printing por tion. In other examples, a bidirectional print mode may be used and printing fluid also be ejected from the printhead carriage 102A along at least a part of the return portion, e.g. while moving along the straight portion 106B of the scanning path 106.

[0063] The first printhead carriage 102A may be moved along the return portion at a higher speed than the speed at which the second printhead carriage 102B is moved along the printing portion. The first printhead carriage 102A may e.g. move along the return portion with VB, whereas the second printhead carriage 102B may move along the printing portion with VA. In some examples, the first printhead carriage 102A may arrive at the starting position of the printing portion before or when the second printhead carriage 102B reaches the end position. Subsequently, blocks 604-610 may be executed repeatedly to print further seg ments of the image, e.g. by printing the swaths 700-3, 700-4, ..., 700-n for ex ample until the entire image is formed on the print medium 304. [0064] In some examples, the method 600 may also comprise refilling the in termediate ink tank 222 of one or both of the printhead carriages 102A, 102B. The intermediate ink tank 222 may for example be refilled prior to or after the printing process. In some examples, the intermediate ink tank 222 may also be refilled during the printing process, e.g. along the return portion after completing a swath on the print medium 304. To refill the intermediate ink tank 222, the re spective printhead carriage may be moved to the ink refill position, which may e.g. be along the second portion 106-11 of the scanning path 106 of Fig. 4a. When the printhead carriage is at the ink refill position, the fluid connector 404A of the ink refill station 404 may be lowered and connected to the input port 224 of the printhead carriage to provide the printing fluid.

[0065] In some examples, the method 600 may also comprise performing a maintenance operation on one or both of the printhead carriage is 102E, 102B. The maintenance operation may for example be performed prior to or after the printing process. In some examples, the maintenance operation may also be performed during the printing process, e.g. along the return portion after com pleting a swath on the print medium 304. Prior to returning to the starting posi tion, the respective printhead carriage may be moved to a servicing position, which may e.g. be located along the fourth portion 106-IV of the scanning path 106 of Fig. 4a, to perform the maintenance operation. The maintenance opera tion may for example comprise wiping the nozzle plate 202A of the printhead 202 using the wiper 408A and ejecting printing fluid from the printhead 202 into the spittoon 408B.

[0066] The methods 500 and 600 may also be adapted to involve more than two printhead carriages, for example three printhead carriages 102A-C as in the printing device 400. For example, the first printhead carriage 102A may be moved along the printing portion of the scanning path 106 to deposit printing fluid for printing the first swath 700-1. At the same time, the second and third printhead carriages 102B, 102C may be moved along the return portion, e.g. such that the second printhead carriage 102B reaches the starting position of the printing portion before or when the first printhead carriage 102A reaches the end position. When the first printhead carriage 102A reaches the end position, the second printhead carriage 102B may start to move along the printing portion to deposit printing fluid for printing the second swath 700-2. While the second printhead carriage 102B moves along the printing portion, the first and third printhead carriages 102A, 102C may be moved along the return portion, e.g. such that the third printhead carriage 102C reaches the starting position of the printing portion before or when the second printhead carriage 102B reaches the end position. When the second printhead carriage 102B reaches the end posi tion, the third printhead carriage 102C may start to move along the printing por tion to deposit printing fluid for printing the third swath 700-3. While the third printhead carriage 102C moves along the printing portion, the first and second printhead carriages 102A, 102B may be moved along the return portion, e.g. such that the first printhead carriage 102A reaches the starting position of the printing portion before or when the third printed carriage 102C reaches the end position. This process may be repeated until the entire image is formed on the print medium 304.

[0067] In some examples, two printhead carriages may also deposit printing fluid on the print medium 304 simultaneously. For example, the second print- head carriage 102B may start moving along the printing portion before the first printhead carriage 102A has reached the end position. In some examples, the printhead carriages may stop at the starting position of the printing portion be fore starting to move along the printing portion, e.g. to wait for another printhead carriage reaching the end position. In other examples, the printhead carriages may not stop at the starting position, but may continuously move from the non printing portion into the printing portion. In one example, the printhead carriag es may be in motion continuously during the printing process, i.e. may not stop during the entire printing process.

[0068] The description is not intended to be exhaustive or limiting to any of the examples described above. The print zone assembly, the printing device, and the method of operating a printing device disclosed herein can be implemented in various ways and with many modifications without altering the underlying basic properties.