EP2868477B1 - Printing press for printing of hollow bodies that are open on at least one side and method for operating a printing press - Google Patents

Description

The invention relates to a printing machine for printing hollow bodies which are open at least on one side, with a machine frame, on which a workpiece rotary table is rotatably mounted, with a the workpiece rotary table associated drive unit for a rotational positioning of the workpiece rotary table about a rotation axis, with workpiece holders for receiving formed by to be printed hollow bodies and which are each rotatably mounted on the workpiece rotary table, with drive means for a rotational movement of the workpiece holders and at least one machine frame associated with the printing device for printing a peripheral surface of a recorded on the workpiece holder hollow body, wherein the printing device at least one print head with a series arrangement comprising Farbdosierelementen, which are designed for contactless dispensing of ink on a surface of the hollow body to be printed, wherein the drive unit as b The electric motor is formed brushless electric motor and fixed to the machine frame stator and a rotatable relative to the stator formed, coupled to the workpiece rotary table rotor, wherein the drive unit is associated with a control unit, which is designed to provide electrical drive power to the drive unit, wherein the Farbdosierelemente a discharge surface of the printhead are arranged and for dispensing color particles in a discharge direction are formed and wherein the pressure device comprises a cleaning station, which is designed for cleaning the discharge surface and which is arranged to perform the cleaning in the dispensing direction opposite to the delivery surface. Furthermore, the invention relates to a method for operating a printing press.

From the EP 2 574 421 A1 For example, a processing device and a method for operating a processing device are known, wherein the processing device has a plurality of working devices, which are arranged along a conveying path for the container blanks to be processed and wherein at least one of the working devices can be designed as a printing device to make an impression of an outer surface of the container blanks ,

The WO 2012/147695 A1 discloses an ink jet printing apparatus for printing seamless cans having a mandrel wheel on which a plurality of rotatably mounted mandrels are disposed, and ink jet printing stations for ink jet printing images on outer surfaces of the seamless cans held on the mandrels and a method of printing seamless ones Cans using the same device. In each of the ink jet printing stations, a plurality of ink jet heads are arranged to improve the reproducibility of the printing operation and the productivity.

From the WO 2005/025873 A2 For example, a method and apparatus for printing selected information on bottles is known. In the method, the bottles are transported sequentially via a predetermined path with at least one printing station; Actuating an Inkjet Printhead at the Printing Station Provide liquid ink droplets onto a bottle surface and control the printhead at the printing station to remove the liquid ink droplets on the bottle in accordance with the selected information to be printed on it.

The object of the invention is to provide a printing machine and a method for operating a printing press, with which an improved print quality can be ensured.

This object is achieved for a printing machine of the type mentioned with the features of claim 1.

Preferably, the print head is arranged within the printing device such that the discharge surface is opposite to the peripheral surface of the hollow body to be printed. Furthermore, it is advantageous if the ink dosing elements, which are designed in particular as ink nozzles, are aligned with the peripheral surface in such a way that a discharge of ink from the ink dosing elements ensures a preferential impact in the radial direction on the usually cylindrical circumferential surface of the hollow body. Preferably, the Farbdosierelemente are formed such that the dispensing directions the individual Farbdosierelemente a printhead in a common, especially aligned transversely to the discharge surface, discharge plane lie. It is particularly advantageous for the print quality if this discharge plane also includes an axis of rotation of the workpiece holders and thus ensures at least an almost exactly vertical impact of the color particles on the peripheral surface of the hollow body to be printed. By way of example, the colorant particles emitted by the paint dosing elements in the dispensing direction are small droplets of ink, the ink preferably being designed to cure with ultraviolet light. Nevertheless, during use of the printhead around the respective color metering elements, deposits of ink residues may form on the delivery surface of the printhead which may have undesirable effects on the discharge direction and / or the dispensed size of the colorant particles and possibly lead to clogging of the respective ink metering element. To be able to eliminate such deposits at the latest when deteriorations of the printed image produced can be detected on the hollow body, a cleaning station is provided. This cleaning station can be arranged during a cleaning operation opposite to the delivery surface and is preferably arranged during a rest phase away from the delivery surface.

According to the invention, it is provided that the control unit for controlling the drive unit for performing rotary step movements of the workpiece rotary table about the axis of rotation in a freely selectable sequence of at least two different

Angular step sizes is formed. Preferably, further working means are provided on the machine frame of the printing press in addition to the printing device, which are preferably arranged in a constant angular pitch to the axis of rotation. Thus, the hollow bodies to be processed, in particular to be printed, can be moved from one to the next workstation by rotary incremental movements with a first angular increment corresponding to the angular pitch of the arrangement of the workstations. It when the angle division for the workstations and an angular pitch for the circularly arranged about the rotation axis workpiece holders are identical is particularly advantageous. As a result, when the first angular increment for the rotational step movements of the workpiece rotary table is maintained, it is ensured that an advantageous positioning of a plurality of workpiece receptacles with respect to respectively oppositely arranged workstations is always ensured. According to the invention, the control unit is designed at least for carrying out a further rotary step movement, which comprises an angular increment which deviates from the first angular increment. As a result, an at least temporary arrangement of the workpiece holders and the hollow bodies received thereon can be achieved away from the workstations. As a result, for example, the unhindered access to the workstations by a user or by automated maintenance facilities is made possible.

In an advantageous development of the invention, it is provided that the drive unit is associated with a sensor device connected to the control device for determining a rotational position of the rotor and that the control unit is designed for a freely selectable setting of a rotational position of the workpiece rotary table relative to the printing device is. With the aid of the sensor means, which is, for example, an incremental rotary encoder, preferably an encoder, the control device can at any time an exact determination of the angular position of the rotor and the associated workpiece rotary table relative to the stator, which in turn is set on the machine , carry out. In knowledge of this rotary position of the rotor, which is transmitted to the control device based on a sensor signal of the sensor means, the control device can release electrical power to the rotor in order to achieve the desired rotational position of the workpiece rotary table relative to the printing device. This default can be done either in the form of a controlled or controlled control of the drive unit, so that the workpiece rotary table can be positioned exactly opposite the printing device. In a subsequent step, a printing operation can then be carried out with high-precision alignment of the hollow body with respect to the printing device and preferably stationary workpiece rotary table. Preferably, the control device is adapted to bring the drive unit when reaching the predetermined rotational position of the workpiece rotary table relative to the printing device in a braked state, so that no further relative movement between the workpiece rotary table and printing device takes place, could possibly cause an undesirable distortion of the applied print image. For this purpose, a corresponding algorithm is stored in the control unit, which is provided for the coordination of the activities of the drive unit and the printing device and maintains the braking state for the drive means until the printing operation is completed. By way of example, it is possible to provide position deviations occurring between the workpiece rotary table and the printing device during the execution of the printing process to be disregarded or taken into account only proportionally with a high damping factor in order to avoid swinging or other relative movements of the workpiece rotary table relative to the printing device.

Preferably, the cleaning station comprises at least one fluid nozzle for a, in particular contactless, provision of a cleaning fluid to the delivery surface. By way of example, the print head comprises several hundred or even several thousand, in particular straight lined, Farbdosierelemente, which are arranged in particular in a uniform pitch and have a diameter of a few hundredths of a millimeter. To ensure a damage-free cleaning of the print head, it is advantageous if the discharge surface is cleaned with a matched to the chemical composition of the paint particles cleaning fluid. The cleaning fluid is preferably a cleaning fluid which, in particular without contact, is provided with a fluid nozzle to the delivery surface and leads there to eliminate the undesired accumulations of color particle residues.

It is preferably provided that the cleaning station comprises at least one suction means for a suction of the cleaning fluid used for cleaning the discharge surface. With the help of the suction means can be ensured that even with a supply of a large volume of fluid flow to the discharge surface rapid and low-pollution cleaning of the print head can be performed. Preferably, the cleaning station is associated with a storage tank for the cleaning fluid and a storage tank for spent cleaning fluid. By way of example, each of the storage tanks is connected via a fluid line and an intermediate feed pump with the fluid nozzle or a suction mouth in the cleaning station.

In a further embodiment of the invention it is provided that the cleaning station comprises a sealing means for a, in particular edge-side, sealing engagement with the delivery surface. With the aid of the sealant, the cleaning station together with the print head can determine a cleaning volume that is essentially determined by the delivery surface and the sealant. In this cleaning volume, the desired supply and removal of cleaning fluid is made to the discharge surface or from the delivery surface, without contaminating an environment of the print head with cleaning fluid and / or detached ink or paint residues. By way of example, the delivery surface of the print head is rectangular, accordingly, the sealant is also at least substantially rectangular and is sealingly against the delivery surface. Preferably, an edge-sealing contact of the sealant is provided on the delivery surface in order to accept the lowest possible requirements for positioning of the cleaning station relative to the print head. It when the discharge surface is flat, so that the sealing means may include a circumferential, arranged in a plane sealing edge, which is designed for the sealing contact with the delivery surface is particularly advantageous.

In a further embodiment of the invention, it is provided that the cleaning station is arranged with at least one guide means movable on the printing device and that at least one coupled to the control unit actuating means for moving the cleaning station between a rest position away from the printhead and an applied to the print head function position is formed. It is particularly advantageous if the actuating means in a double function as well Guiding means is formed, as may be the case, for example, when using a hydraulic cylinder or pneumatic cylinder or an electric actuator. The guide means serve to ensure a precise alignment of the cleaning station for the system on the printing device, in particular on the print head. The actuating means is provided to perform the desired movement of the cleaning station between a rest position away from the printhead, in which the printhead can be used for printing the hollow body, and a voltage applied to the print head operating position. Depending on the arrangement of the printing device on the machine frame and the spatial conditions for the attachment of the cleaning station, it may be necessary to provide a movement of the cleaning station in more than one direction of movement or on a curved path of movement. For this purpose, more than one adjusting means can be used to perform the desired movement of the cleaning station between rest position and functional positions.

In a further embodiment it is provided that the control device comprises at least one frequency converter, which is designed to provide electrical drive energy to the rotor and which is fixed to the rotor. With the aid of the at least one frequency converter, a circulating magnetic field can be imparted to the rotor in order to produce a rotational movement with respect to the stator. Preferably, the rotor comprises a coil arrangement which, when electric drive energy is provided, generates the required circulating magnetic field and thus can interact magnetically with the stator, which in turn is preferably provided with a permanent magnet arrangement or a further coil arrangement. In an embodiment of the rotor With at least one electrical coil arrangement, it is advantageous if a number of electrical connections which have to be provided by the stationary machine frame to the rotatable rotor are kept small in order to minimize a number of electrical rotary joints. Accordingly, it is advantageous if the electrical drive energy for a plurality of coil arrangements of the rotor can be provided by respectively assigned frequency converters which are fixed to the rotor. In this case, the transmission of a supply voltage and a drive signal from the machine frame to the rotor is sufficient since the distribution of the electrical drive energy takes place only at the rotor by the frequency converter accommodated there.

It is preferably provided that the printing device comprises a plurality of print heads, wherein at least one of the print heads is movably arranged along an extension axis of the Farbdosierelemente on a print head carrier and that the movably mounted print head is associated with an electrically controllable adjusting means for adjusting a relative position relative to the at least one further print head , Preferably, the at least two print heads are provided for the printing of the same hollow body. These printheads can be positioned relative to one another by means of the electrically controllable adjusting device in such a way that arranged from the adjacent printhead ink particles arranged on the peripheral surface of the hollow body to be printed in such a favorable manner that a printed image on the hollow body has a resolution higher than the resolution of each printhead is.

Preferably, the cleaning station is designed to individually the at least two print heads of the printing device to clean, which can be reliably prevented even in a relatively movable arrangement of the print heads to each other a penetration of the cleaning fluid in areas away from the delivery surface. It is advantageous if the cleaning device can be moved relative to the printheads so that they each come in sealing engagement with the printhead to be cleaned.

Alternatively, it may be provided to position the at least two printheads of the printing device so as to perform the cleaning operation relative to one another such that no gaps remain open between the printheads so that the cleaning station can clean all printheads of the printing device in a single cleaning operation. In this way, a time advantage over individual cleaning of the at least two print heads of the printing device can be achieved.

Preferably, the print heads are aligned parallel to each other and arranged directly adjacent to the extension axis of the Farbdosierelemente, in particular slidably adjacent to each other.

The object of the invention is achieved according to a second aspect by a method for operating a printing press, as specified in claim 11. In this case, the printing press comprises a workpiece rotary table mounted rotatably on a machine frame, a drive unit designed as a brushless electric motor for introducing rotary step movements onto the workpiece rotary table, a control unit for providing electrical energy to the drive unit, a plurality of workpiece holders arranged rotatably mounted on the workpiece rotary table for recording, end open hollow bodies and several circular Workstations arranged on a circumference of the workpiece rotary table, wherein at least one of the workstations is designed as a printing device. The method according to the invention comprises the steps of: moving the workpiece rotary table in successive rotary incremental movements with a first angular pitch about an axis of rotation in order to arrange hollow bodies to be printed on the workpiece holders opposite the workstations, printing on a respective hollow body respectively associated with the pressure device, temporarily moving the workpiece rotary table a second angular pitch about the axis of rotation, to ensure an arrangement of the hollow body away from the workstations in a maintenance position and performing a maintenance and / or cleaning operation on the workstations, completion of the rotary step movement for moving the hollow body to the next workstation after completion of the maintenance and / or cleaning process.

In the rotary incremental movements with the first angular division are thus the steps for the workpiece rotary table, with which the workpiece holders are arranged on the workpiece rotary table in each case opposite to the workstations. In this case, at least one hollow body passes into a working area of the printing device and can be printed during the rest phase of the rotary step movement, for which purpose preferably a rotation of the workpiece holder is provided about an axis of rotation of the workpiece rotary table aligned rotation axis. Since in an opposing arrangement of the workstations and the respective workpiece holders accessibility to the workstations is very limited, an intermediate position is driven in the inventive method from the workpiece rotary table, which is based on the working position by movement of the workpiece rotary table with a second angular pitch results. In this intermediate position, the respective workpiece holders are away from the workstations, so that an advantageous accessibility of the workstations is ensured and they can be maintained, for example, or cleaning operations can be performed. By way of example, it is provided to carry out a cleaning process on the printing device with the aid of a cleaning station, in order then to resume the regular machining operation for the printing press by completing the rotary step movement until reaching the first angular graduation.

By way of example, this is provided in the inventive method to carry out a cleaning of the printing device with the cleaning station in the maintenance position, which is arranged with at least one guide means movable on the printing device and by a coupled to the control unit actuating means from a rest position away from the printing device in a the printing device adjacent functional position can be moved.

In a further development of the method it is provided that for cleaning the printing device a sealing system of the cleaning station is occupied at least one print head of the printing device and that a, preferably contactless, supply of a cleaning fluid to a discharge surface of the print head and a discharge of the cleaning fluid from the delivery surface means the cleaning station is made.

In a further embodiment of the method is provided that a determination of a print image quality is performed on the printed hollow body with a sensor device and that a carrying out of the cleaning function of the determined print image quality is made. As a result, a flexible handling of the cleaning operations for the printing device is possible because a cleaning is always provided when the print image quality has fallen below a predetermined minimum level. To determine the print image quality, a sensor device is provided, with the aid of which the entire print image or sections of the printed image on the hollow body can be detected and evaluated in order to draw conclusions about the contamination of the print heads. Alternatively it can be provided that at least one hollow body is printed with a special test pattern and a detection of the print image quality is carried out on the printed test hollow body.

Figur 1

eine schematische Draufsicht auf eine Druckmaschine mit einem drehbeweglich gelagerten Werkstückrundtisch und mehreren Arbeitsstationen zur Bedruckung und Inspektion von zylindrischen Hohlkörpern,

Figur 2

eine Ausschnittvergrößerung der Druckmaschine gemäß der Figur 1 in einer Zwischenstellung für den Werkstückrundtisch,

Figur 3

eine schematische Draufsicht einer als Druckeinrichtung ausgebildeten Arbeitsstation der Druckmaschine,

Figur 4

eine teilweise geschnittene Draufsicht auf den Werkstückrundtisch

Figur 5

eine schematische Vorderansicht der Druckeinrichtung,

Figur 6

eine schematische Darstellung einer Druckeinrichtung und einer gegenüberliegend angeordneten Kombination einer Trocknungsstation mit einer Reinigungsstation in einer ersten Funktionsstellung,

Figur 7

eine schematische Darstellung der Druckeinrichtung und der gegenüberliegend angeordneten Kombination von Trocknungsstation und Reinigungsstation in einer zweiten Funktionsstellung und

Figur 8

eine schematische Draufsicht auf die Reinigungsstation.

An advantageous embodiment of the invention is shown in the drawing. Showing:

FIG. 1

a schematic plan view of a printing press with a rotatably mounted workpiece rotary table and several workstations for printing and inspection of cylindrical hollow bodies,

FIG. 2

a detail enlargement of the printing machine according to the FIG. 1 in an intermediate position for the workpiece turntable,

FIG. 3

FIG. 2 is a schematic top view of a work station of the printing machine designed as a printing device, FIG.

FIG. 4

a partially sectioned plan view of the workpiece turntable

FIG. 5

a schematic front view of the printing device,

FIG. 6

a schematic representation of a printing device and an oppositely arranged combination of a drying station with a cleaning station in a first functional position,

FIG. 7

a schematic representation of the printing device and the oppositely arranged combination of drying station and cleaning station in a second functional position and

FIG. 8

a schematic plan view of the cleaning station.

One in the FIG. 1 illustrated printing machine 1 comprises a rotatable about a perpendicular to the plane of the FIG. 1 Aligned rotation axis 2 mounted workpiece rotary table 3 and a plurality of pairs of examples mounted on the workpiece rotary table workpiece holders 4. The workpiece holders 4 are not shown with drive means to exemplary parallel to the plane of the FIG. 1 aligned rotational axes 5 individually rotatably mounted and provided for receiving sleeve-shaped, in particular designed as aerosol can blanks or tube blanks, at least substantially cylindrical hollow bodies 6.

Preferably, the workpiece holders 4 are designed as mandrels on which the hollow body 6 designed as a hollow body, in particular as a hollow cylinder open at least on one side, can be plugged. In one of the workpiece holders 4 during a rotational movement of the workpiece rotary table 3 about the axis of rotation 2 swept annular region 7, the extends in the radial direction about the workpiece rotary table 3, a plurality of work stations 8 to 18 are arranged, which are designed for processing and / or testing of the transported hollow body 6. Since it is in the view according to the FIG. 1 is a plan view and the workstations 9 to 17 are arranged by way of example in the vertical direction above the workpiece holders 4, the workstations are shown 9 to 17 only in dashed lines.

The work station 8 is a loading station, on which the cylindrical hollow body 6 are exemplarily in pairs on the workpiece holders 4 by a suitable transport device 19, which is coupled to a conveyor system, not shown, for the cylindrical hollow body 6, pushed.

By way of example, a rotary position of the cylindrical hollow body 6 is determined at the workstation 9 by a first optical scanning of the cylindrical hollow body 6, for example to ensure correct rotational alignment of the cylindrical hollow body 6 for a printing operation taking place at the workstation 10. This is particularly important if the surface to be printed on the hollow body 6 is provided with features that are to be in a predetermined manner with the applied print image in a predetermined manner. These features may be, for example, local embossing and / or embossing in and / or out of the surface of the article 6 and / or pre-printed areas, which in turn are to serve as a primer for the subsequent printing. It can preferably be provided to print on a partially reshaped or already completely reshaped article 6, which in particular embosses and / or embossments, so that an alignment of the printed image with respect to the deformed Regions takes place and not, as it was previously known from practice, a deformation of the hollow body 6 based on a pre-applied printed image is made. Preferably, it is provided to print a reshaped aerosol can blank with indentations and / or characteristics locally or over its entire peripheral surface, wherein the aerosol can blank after printing in the printed areas with a protective coating, in particular a transparent varnish, can be coated and then ready for a filling ,

The workstation 10 includes an example in the FIGS. 4 to 7 closer to printing device 20, on which the cylindrical hollow body 6 during rotation about respective axes of rotation 5 using printheads 21, 22, as shown in the FIGS. 4 to 7 are shown in more detail and described below, are printed in a predetermined range. Furthermore, the workstation 10 comprises a cleaning station 23, which is designed to clean the print heads 21, 22 and whose operation is also described in more detail below.

The work station 14 is embodied as an inspection device by way of example and makes it possible to determine a print quality of the print image applied by the printing device 21 to the peripheral surface of the object 6.

The other workstations 11 to 13 and 15 to 17 are used for further processing of the cylindrical hollow body 6, for example, for applying a protective coating on the printing or for mounting components to the hollow body. 6

At the workstation 18 takes place an unloading process in which the cylindrical hollow body 6 by means of a transport device 24 are deducted from the mandrel-like workpiece holders 4 and fed to a not shown further transport system.

The workpiece rotary table 4 is exemplarily designed as an asynchronous machine in the form of an external rotor and comprises according to the illustration of FIG. 4 a radially arranged inside, also at least to be regarded as a component of a machine frame stator 25 to which a plurality of schematically illustrated, circularly arranged magnetic means 26, 27 are mounted. The magnet means 26, 27 are designed to provide magnetic fields oriented in the radial direction in each case and can be designed, for example, as current-carrying coils or permanent magnets. The stator 25 is circularly surrounded by a rotor 28 which is rotatably mounted on the stator 25 by means of a bearing device, not shown, and which forms an air gap 29 with the stator 25. Opposite to the magnetic means 26, 27 coils 30 are arranged on the rotor 28, which can provide a predominantly oriented in the radial direction magnetic field when current is applied. The coils 30 are each arranged in segment-like space sections with kreisringabschnittsförmigem cross-section and electrically connected to frequency converters 31. The frequency converter 31 are used for the coordinated provision of the coil currents to the respective connected coils 30. By way of example, it is provided that each of the frequency converter 31 is connected to two coils. The frequency converter 31 are electrically connected to a control device 32, which in turn via a rotary connection, not shown, electrically connected to a supply voltage terminal and to a higher-level machine control, not shown, in particular a programmable logic controller (PLC) is. The programmable logic controller is used to coordinate all work processes for the printing press 1 and in particular provides movement commands for the drive unit 33 formed by the stator 25, rotor 28, frequency converters 31 and control device 32. By arranging the frequency converter 31 and the control device 32 on the rotor 28 designed as a workpiece rotary table 3, only the provision of a movement command, which is transmitted via a wired or wireless bus connection, for example, and electrical drive energy is required for a rotation of the workpiece rotary table 3 relative to the stator 25 the controller 32 required. As a result, compared with an arrangement of the frequency converter in a control cabinet away from the printing press, a significant reduction in the number of electrical connections can be achieved, which must be provided as rotary joints to the rotor. This applies in particular to the case that only a small number of coils 30, in particular only one or two coils 30, can be driven by the respective frequency converter 31.

Furthermore, it can be provided that the control unit 32 is also designed to control the workstations 8 to 18, in particular also for the control of the pressure device 20 and the cleaning station 23.

In one embodiment, not shown, each coil is associated with an individual frequency converter. Alternatively it can be provided that a plurality of coils are connected to a frequency converter.

In order to determine a rotational position of the rotor 28, the control device 32 is assigned a rotational position sensor 34, whose sensor signal is processed in the control device 32 and evaluated. On the basis of the provided sensor signal, the position of the rotor 28 relative to the stator 25 can be determined in order to make an adapted energization of the coils 30 as a function of a movement command to be executed, which is made available in particular by the programmable logic controller.

For stepwise processing of the hollow body 6 to the respective workstations 8 to 18 formed in the form of the workpiece rotary table 3 rotor 28 performs a rotary step movement by a first angular increment with the angle W, in which the paired workpiece holders 4 from one of the respective workstation 8 to 18 opposite position to be transported to one of the respective subsequent workstation 8 to 18 opposite position. The rotational step movement is hereby carried out as a sequence of an acceleration from standstill, a deceleration from the achieved target speed and a subsequent standstill time, wherein at least the deceleration is performed in a controlled operation of the drive unit 33.

Preferably, the drive unit 33 is designed such that the acceleration and deceleration of the workpiece rotary table 3 are freely adjustable over a wide range and the downtime and can be adapted to the requirements of processing the respective cylindrical hollow body 6 at the workstations 8 to 18. By way of example, provision can be made for a regulation of the rotational position for the rotor 28 relative to the stator 25 during the machining, in particular during the printing, of the hollow body 6 in a manner in which a movement of the rotor 28 is minimized, in particular zero, by one Distortion of the printed image to avoid.

Furthermore, the drive unit 33 for the workpiece rotary table 3 can be controlled in such a way that the workpiece holders 4 execute an intermediate step with a second angular increment, for example at an angle W / 2, ie half the angle W. In this intermediate step, the workpiece holders 4 are not arranged opposite to the workstations 8 to 18, but rather are arranged apart or between the workstations 8 to 18, as shown in the FIG. 2 is shown schematically.

The intermediate step of the workpiece rotary table 3 can thus be used in particular for cleaning or other maintenance of workstations 8 to 18, for example for carrying out a cleaning of the printing device 20 with the cleaning station 23.

The in the FIGS. 4 to 7 schematically illustrated printing device 20 is designed for printing a peripheral surface of an article 6. By way of example, the printing device 20 according to the illustration of FIG. 5 two mutually parallel, linearly movable print heads 21, 22, which are mounted on a serving as a print head carrier body 35 of the printing device 20 in a common guide recess 36. Each of the two print heads 21, 22 can be displaced individually along the guide recess 36 by means of an associated actuating means 37, 38. For this purpose, each adjusting means 37, 38 each comprise a spindle motor 39, 40 and a rotatably mounted in the base body 35, with the respective spindle motor 39, 40 rotatably connected drive spindle 41, 42. The adjusting means 37, 38 are not shown in detail with the control device 32nd electrically connected and can be controlled to perform the printing operation of the controller 32.

The strip-like trained trained print heads 21, 22 have each exemplarily a row of nozzles 43, 44, which is designed as a series of nozzles along a straight line, the nozzles can also be referred to as Farbdosierelemente. In both print heads 21, 22, the rows of nozzles 43, 44 are respectively disposed on discharge surfaces 45, 46 of the print heads 21, 22 and formed to dispense color particles in a dispensing direction 47. By way of example, the dispensing direction is aligned transversely to the discharge surface 45, 46, which is embodied as an example. The nozzles are each associated with individually controllable piezo drives, which are used for a discharge of ink droplets through the nozzles and are electrically connected in a manner not shown electrically connected to the controller 32 so that a stored in the controller 32 print image by selective control of the respective piezoelectric drives and a color discharge caused thereby by the respective nozzles on the, preferably rotating, object 6 can be transmitted. By way of example, in printing machine 1, only one printing device 20 is provided, in which the two printing heads 21, 22 are designed, for example, to emit a single color. In a printing press, not shown, a plurality of printing devices may be provided, with which a multi-color print on the object 6 can take place.

When the printheads 21, 22, as in particular in the FIG. 5 are shown, an arrangement of the nozzles is provided in a predetermined and constant pitch, so that each adjacent nozzles arranged along the respective nozzle row 43, 44 always have the same distance from each other. The pitch for the nozzles sets a resolution along the respective nozzle row 43, 44 for a print image that can be created by the print heads 21, 22. Around To achieve an increase in the resolution in the direction of the extension of the nozzle rows 43, 44, the print heads 21, 22 arranged adjacent to one another can be arranged offset relative to one another by using the respective adjusting means 37, 38 such that ink droplets emitted by the second print head 22 in each case between the print heads first print head 21 ink droplets impinge on the object 6, whereby an increase, in particular a doubling, the resolution of the printed image in the direction of the extension of the nozzle rows 43, 44 can be achieved.

Further, each nozzle of each print head 21, 22 can be driven by the controller 32 at a predetermined frequency, and can discharge ink droplets onto the peripheral surface of the article 6 at the predetermined frequency. Depending on a rotational speed of the object 6 about the axis of rotation, the frequency determines the resolution for the printed image in the circumferential direction. At a low rotational speed results in a high resolution in the circumferential direction, at high rotational speed results in a low resolution in the circumferential direction.

In the FIGS. 6 and 7 By way of example, a functional module 48 is arranged opposite the respective printing device 20. The functional module 48 includes a cleaning station 23 and a drying station 50. The functional module 48 is set by way of example to an actuator arrangement 51 which comprises a horizontal actuator 52 and a vertical actuator 53, which allows movement of the functional module 48 in two mutually perpendicular spatial directions. By way of example, the horizontal actuator 52 and the vertical actuator 53 also serve as guides for the functional assembly 48, see FIG that this can be positioned exactly opposite the printing device 20.

The drying station 50 is exemplarily designed as a source for emitting ultraviolet radiation and is designed for curing the ink droplets dispensed onto the object 6, wherein a radiation direction for the ultraviolet radiation is preferably selected to be parallel to the dispensing direction 47 for the ink droplets.

The cleaning station 23 comprises a dimensionally stable carrier part 54 which serves for mechanical coupling to the drying station 50. On the support member 54, a sealant 55 is attached by way of example cohesively, which is made of an elastic, in particular rubber-elastic material. The sealing means 55 has a cuboid shell geometry and comprises a recess 56, which is bounded by a circumferential sealing lip 57. By way of example, the sealing lip 57 has a in the representation of FIGS. 6 and 7 dashed shown trapezoidal cross section, which tapers with increasing distance from the support member 54. In the support member 54 and the sealant 55 corresponding holes 58, 59 are provided. By way of example, the bores 58 are designed as nozzles with a circular cross-section. The holes 59 are formed as recesses of rectangular cross-section. The bores 58 communicate with a supply channel, not shown, in the carrier part 54 in a communicating connection, so that a cleaning fluid that is introduced into the channel can exit through the bores 58. The inlet channel opens out on a side surface of the carrier part 54 and is connected via a hose connection 62 to a pump 60. The pump 60 is in turn connected via a hose connection 63 to a storage tank 66, is stored in the cleaning fluid. The pump 60 may be activated and deactivated by the controller 32 to force the cleaning fluid through the bores 58.

The holes 59 are connected to a non-illustrated flow channel in the support member 54 in communicating connection. The drainage channel terminates at a side surface of the support member 54 and is connected via a hose connection 64 to a pump 61. The pump 61 is in turn connected via a hose connection 65 to a storage tank 67 in which contaminated cleaning fluid can be stored. The pump 60 may be activated and deactivated by the control device 32 to draw cleaning fluid through the holes 59.

The cleaning station 23 can, with the aid of the actuator assembly 50 from a in FIG. 6 illustrated rest position in a in FIG. 7 shown functional position are brought if the workpiece rotary table 3 is located in the maintenance position, in which the workpiece holders 4 are arranged away from the work stations 8 to 18. To carry out a cleaning operation of the printing device 20, it is provided by way of example that initially the two print heads 21, 22 are positioned exactly next to one another by suitable control of the adjusting means 37, 38. Subsequently, the sealing means 55 of the cleaning station 23 is placed in sealing engagement with the two delivery surfaces 45, 46 of the print heads 21, 22. In a subsequent step, the two pumps 60, 61 are activated, so that cleaning fluid from the first storage tank 66 is conveyed through the bores 58 acting as nozzles on the delivery surfaces 45, 46 and there can wash existing ink residues. The contaminated cleaning fluid can be sucked through the holes 59 and into the storage tank 67 promoted. Alternatively, an alternate operation of the two pumps 60, 61 may be provided.

For the implementation of the cleaning cycle, the workpiece rotary table 3 is controlled such that the respective workpiece holders 4 in the in FIG. 2 shown intermediate position between two workstations 9 to 17 are arranged so that no disturbing hollow body between the printing station 20 and the cleaning station 23 are arranged.

For carrying out the printing, the cleaning station 23 is removed from the printing station 20 by means of the actuator arrangement 50. Subsequently, the workpiece rotary table 3 is controlled such that the respective workpiece holders 4 in the in FIG. 1 opposite position to the workstations reach 9 to 17. In this case, the drying station 50 arrives in a position opposite to the printing device 20, so that print heads 21, 22 can be activated, cured or dried on the object 6 discharged color.

Claims (14)

1. Printing machine for printing on hollow bodies (6) which are open on at least one side, the printing machine comprising a machine frame (25) on which a workpiece rotary table (3) is rotatably mounted, a drive unit (33) assigned to the workpiece rotary table (3) for a rotational positioning of the workpiece rotary table (3) around an axis of rotation (2), workpiece receptacles (4) which are designed for the accommodation of hollow bodies (6) to be printed on and rotatably mounted on the workpiece rotary table (3), drive means for a rotary movement of the workpiece receptacles (4) and at least one printing device (20) assigned to the machine frame (25) for printing on a circumferential surface of a hollow body (6) accommodated in the workpiece receptacle (4), wherein the printing device (20) comprises at least one printing head (21, 22) with a row of ink metering elements (43, 44) designed for the contactless application of ink to a surface of the hollow body (6) to be printed on, wherein the drive unit (33) is designed as a brushless electric motor with a stator located on the machine frame (25) and a rotor (28) which is rotatable relative to the stator (25) and coupled to the workpiece rotary table (3), wherein the drive unit (33) is assigned a control unit (32) designed for a provision of electric drive energy to the drive unit (33), wherein the ink metering elements (43, 44) are located on a dispensing surface (45, 46) of the printing head (21, 22) and designed for dispensing ink particles in a dispensing direction (47), and wherein the printing device (20) comprises a cleaning station (23) which is designed for cleaning the dispensing surface (45, 46) and located in the dispensing direction (47) opposite the dispensing surface (45, 46) for performing the cleaning operation, characterised in that the control unit (32) is designed for controlling the drive unit (33) to perform rotary step movements of the workpiece rotary table (3) about the axis of rotation (2) in a freely selectable sequence with at least two different angle step widths (W; W/2).
2. Printing machine according to claim 1, characterised in that the drive unit (33) is assigned a sensor means (34) connected to the control unit (32) for a detection of a rotary position of the rotor (28), and in that the control unit (32) is designed for a freely selectable setting of a rotary position of the workpiece rotary table (3) relative to the printing device (20).
3. Printing machine according to claim 2, characterised in that the cleaning station (23) comprises at least one fluid nozzle (58) for an, in particular contactless, provision of a cleaning fluid to the dispensing surface (45, 46).
4. Printing machine according to claim 3, characterised in that the cleaning station (23) comprises at least one extraction means (61) for extracting the cleaning fluid used for cleaning the dispensing surface (45, 46).
5. Printing machine according to claim 2, 3 or 4 characterised in that the cleaning station (23) comprises a sealing means (55) for an, in particular edge-side, sealing contact with the dispensing surface (45, 46).
6. Printing machine according to any of the preceding claims, characterised in that the cleaning station (23) is movably located on the printing device (20) with at least one guide means (51), and in that at least one actuating means (52, 53) coupled to the control unit (32) is designed for moving the cleaning station (23) between a rest position at a distance from the printing head (21, 22) and a functional position in contact with the printing head (21, 22).
7. Printing machine according to any of the preceding claims, characterised in that the control unit (32) comprises at least one frequency converter (31) which is designed for the provision of electric drive energy to the rotor (28) and which is fixed to the rotor (28).
8. Printing machine according to any of the preceding claims, characterised in that the printing device (20) comprises a plurality of printing heads (21, 22), wherein at least one of the printing heads (21, 22) is mounted on a printing head support (35) for movement along an extension axis of the ink metering elements (43, 44), and in that the movably mounted printing head (21, 22) is assigned an electrically controllable adjusting device (37, 38) for an adjustment of a position relative to the at least one further printing head (21, 22).
9. Printing machine according to claim 8, characterised in that the printing heads (21, 22) are oriented parallel to one another and arranged directly adjacent to one another, in particular slidably adjoining one another, transversely to the extension axis of the ink metering elements (43, 44).
10. Method for operating a printing machine (1) comprising a workpiece rotary table (3) mounted on a machine frame (25), a drive unit (33) designed as a brushless electric motor for introducing rotary step movements into the workpiece rotary table, a control unit (32) designed for a provision of electric drive energy to the drive unit (33), a plurality of workpiece receptacles (4) rotatably mounted on the workpiece rotary table (3) for the accommodation of open-ended hollow bodies to be printed on and a plurality of work stations (8 to 18) arranged in a circle around the circumference of the workpiece rotary table (3), wherein at least one of the work stations (10) is designed as a printing device (20), the method comprising the steps of: moving the workpiece rotary table (3) in consecutive rotary step movements with a first angular pitch (W) around an axis of rotation (2) in order to arrange hollow bodies (6) to be printed on and held on the workpiece receptacles (4) opposite the work stations (8 to 18), printing on a hollow body (6) placed opposite the printing device (20), temporarily moving the workpiece rotary table (3) with a second angular pitch (W/2) around the axis of rotation (2) in order to ensure a location of the hollow bodies (6) away from the work stations (8 to 18) in a maintenance position and carrying out a maintenance and/or cleaning operation at the work stations (8 to 18), completing the rotary step movement for moving the hollow bodies (6) to the next work station (8 to 18) on completion of the maintenance and/or cleaning operation.
11. Method according to claim 10, characterised in that in the maintenance position for the hollow bodies (6) there is provided a cleaning of the printing device (20) with a cleaning station (23) which is movably located on the printing device (20) with at least one guide means (51) and which is moved by an actuating means (52, 53) coupled to the control unit (32) from a rest position at a distance from the printing device (20) into a functional position in contact with the printing device (20).
12. Method according to claim 10 or 11, characterised in that, for cleaning the printing device (20), a sealing contact is established between the cleaning station (23) and at least one printing head (21, 22) of the printing device (20), and in that a, preferably contactless, delivery of a cleaning fluid to a dispensing surface (45, 46) of the printing head (21, 22) and a removal of the cleaning fluid from the dispensing surface (45, 46) are carried out by means of the cleaning station (23).
13. Method according to claim 10, 11 or 12, characterised in that a detection of a quality of the printed image is carried out on the hollow body (6) with a sensor device (14), and in that the cleaning operation is carried out as a function of the detected quality of the printed image.
14. Method according to claim 10, 11, 12 or 13, characterised in that, for the detection of the quality of the printed image, a presettable region of the printed image on the printed hollow body (6) or a presettable region of a test image on a printed hollow test body is analyzed.

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