DE20012946U1 - Inkjet printer, in particular for labeling packages - Google Patents

Description

Inkjet printers, especially for labelling shipping items

The invention relates to an inkjet printer, in particular for labelling shipping items, having the features of the preamble of patent claim 1.

Printers used to label shipping items are generally exposed to a harsh environment. In particular, dust, dirt, abrasion in the form of paper particles and the like can impair the quality of the print. Despite these harsh industrial environmental conditions, high demands are often placed on the print result. Especially when, for example, barcodes are to be printed on a shipping item, high print quality is essential, as otherwise the information contained in the barcode will either be evaluated to produce an incorrect result or the evaluation will be impossible. With conventional inkjet printers, however, there is a risk that the print result will be impaired by dust, dirt or the like. Furthermore, a break in printing can lead to the first characters to be printed not being printed correctly because the ink in the nozzles has hardened slightly or its viscosity has increased and the nozzles are only gradually sprayed free. This effect leads to a completely unusable result, especially when printing barcodes.

It is therefore necessary to clean the nozzles of the print head from time to time or to spray them clean after a longer break in printing before the actual printing process begins. To do this, the print head, which can usually be moved horizontally in known printers, is moved from the printing position or the printing area into a service position. In this service position, a service device is provided which

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can carry out several service functions. Such service functions can be spraying the print head nozzles, wiping or doctoring the surface of the metal foil in which the print nozzles are formed or completely closing the nozzles of the print head. A printer of this type is known, for example, from EP-B-O 704 307. This printer has a revolver-like service device, with various service units arranged on the circumference of the "revolver". For example, a closing unit for the nozzles and a wiping unit are provided.

Since cleaning or spraying the nozzles has to be carried out relatively frequently in harsh environments, this leads to a loss of time and thus a detrimental effect on productivity in known printers due to the required transverse movement of the print head into the service position.

In addition, with printers for labeling shipping items, the items to be labeled are usually moved past the print head, with the print head being designed in such a way that all of the information can be printed in one printing process. For this purpose, the nozzles are distributed in the appropriate number over the entire required height of the print (i.e. in the direction perpendicular to the movement of the shipping items). Since this type of printer is often integrated into an overall system with other devices, such as folding and sorting devices, there is also a requirement for the smallest possible size. A service device offset to the side is therefore often only possible with problems.

Based on this state of the art, the invention is based on the object of developing an inkjet printer, in particular for labeling shipping

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pieces, which enables the rapid execution of service functions to ensure a consistently high-quality print result and yet has a simple and space-saving design.

The invention solves this problem with the features of the

saying 1.

By providing a pivoting print head, one or more service units of a service facility can be arranged stationary along the pivoting circle described by the nozzles of the print head. This results in a simple structure of the service facility. Replacing wear parts of individual service units is no problem.

In the preferred embodiment of the invention, the pivot axis of the print head runs parallel to the printing plane in which the nozzles are arranged or parallel to the printing direction. If necessary, the print head can of course also be designed to be movable in addition to being pivotable. This arrangement of the pivot axis enables the service units to be arranged easily along the pivot circle, since the nozzles are moved out of the printing plane.

However, it is also possible to arrange the pivot axis of the print head perpendicular to the printing plane. To increase the space required for arranging the service units, the mail items can be guided along a curved path and bent in the process, if possible (for example in the case of thin letters). In this way, more space is available above and below the printing position for arranging service units.

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The service device can comprise as service units a closure device and/or a stripping device and/or a wiping device and/or an ink collecting device.

The scraping device is primarily used to scrape or doctor off dirt or dried ink residues that have accumulated on the surface of the element (usually a metal foil) in which the nozzles are formed. In contrast, the wiping device is used to suck a small amount of ink up to or onto the surface of the element in which the nozzles are formed and then to wipe off any excess ink that may be present.

The collecting device can be designed, for example, as an ink-absorbing pad or an ink-absorbing sponge. By controlling it in the relevant swivel position, the print head is prompted to release a certain number of ink droplets from each nozzle (or only from certain nozzles). Dried or undesirably highly viscous ink can thus be removed from the nozzles.

In the preferred embodiment of the printer according to the invention, the print head can be moved from a first angular position in which the closure device is arranged, via a second angular position in which the stripping device is arranged, via a third angular position in which the wiping device is arranged, and via a fourth angular position in which the collecting device is arranged, into the angular position corresponding to the printing position and vice versa.

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The printer preferably has a control unit which controls the pivoting movements of the print head, wherein in the case of several service units the print head can preferably be moved into the angular position of a single one or successively into the angular positions of several service units.

Further embodiments of the invention emerge from the subclaims.

The invention is explained in more detail below using an embodiment shown in the drawing. In the drawing:

Fig. 1 is a partially schematic side view of an opened printing unit of a printer according to the invention;

Fig. 2 is a schematic representation of the pivoting movement of the print head of a printer according to the invention and

Fig. 3 is a perspective view of an integrated stripping and wiping device of the printing unit in Fig. 1.

The printing unit of a printer 1 shown in Fig. 1 has a print head 5 pivotably mounted in a housing 3. The pivotable mounting of the print head 5 is carried out by means of a pivotably mounted receiving part 7, in which the print head is exchangeably inserted and held. The print head 5 is designed in the usual way as an integrated unit in which a housing cartridge housing 9 that holds the ink is formed in one piece with or connected to an element 11 in which the actual nozzles for dispensing the ink droplets are formed. This element usually comprises

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a metal foil with the nozzle openings and a controllable device for ejecting the ink droplets.

The print head 5 in the print head shown in Fig. 1 does not have a movable design. This printer is therefore intended for applications in which the material to be printed is moved past the print head.

The receiving part 7 is mounted in the housing 3 with bearing pins 13, with the pivot axis A running parallel to the printing plane E, which is formed by the surface of the element 11 in which the discharge openings of the nozzles are formed. The receiving part has two parallel side walls, between which the print head 5 is inserted. The precise lateral positioning of the print head is carried out by means of spring elements that act on the print head on one side and press it against the inside of the opposite side wall. By means of a pivoting retaining flap 15, the print head is pressed in the direction perpendicular to this against a rear stop and is thus positioned in this direction and at the same time fixed in the correct position.

A drive (not shown in detail) is provided for the pivoting movement of the receiving part 7, which can comprise a stepper motor, for example. The drive can be controlled by a control unit (not shown in detail) in such a way that the receiving part 7 and thus the print head 5 can be moved to a predetermined angular position.

Along the swivel circle K, which the surface of the element 11 describes with the pressure nozzles, several service units of a service facility are provided at different angular positions.

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These are a closure device 17, a stripping device 19, a wiping device 21 and an ink collecting device 23.

The closure device 17 is designed to be pivotable about an axis B and has a driver stop 25. In the closure position, a seal arranged on the side of the closure device 17 facing the element 11 of the print head 5 is pressed against the surface of the element 11 and thus closes the nozzles. The closure position is defined by a stop 27. The driver stop 25 is pressed against this as a result of the impact with the relevant side wall of the element 11 of the print head 5 in the closure position. The fixing of the receiving part 7 in the closure position takes place by means of a locking element 29 which has a locking recess 29a. A complementary locking element (not shown in more detail) engages in the locking recess 29 and can be designed to be controllable to release the pivoting movement of the receiving part 7.

The closure device 17 is preferably acted upon by means of a resilient element such that it assumes the position shown in Fig. 1 until it is moved into the end position defined by the stop 27 during a pivoting movement of the print head 5 into the closure position as a result of the element 11 of the print head 5 coming into contact with the driver stop 25.

The stripping device 19 comprises a stripping lip 31, which is flexible but still sufficiently rigid to ensure that deposits in the form of dirt or ink are stripped or scraped off from the surface of the element 11. The relevant edges on the upper end face of the stripping lip are sharp for this purpose, i.e. they have a very small radius of curvature.

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In contrast, the wiping device 21 has the function of first sucking a small amount of ink from the nozzles up to or onto the surface of the element 11 as the element 11 moves past and then wiping it off. This removes ink with an undesirably high viscosity from the nozzles and cleans the nozzles of dirt particles. The wiping device 21 comprises a wiping element 33 with two wiping lips 35. The two edges on the upper end face of each wiping lip 35 are designed differently: the inner edges facing each other are sharp-edged and serve to scrape off excess ink from the surface of the element 11. The outer edges of the wiping lips 35 facing away from each other, on the other hand, have a relatively large radius. As a result, when the element 11 of the print head 5 moves past, a negative pressure is generated by which ink is sucked up to or onto the surface of the element 11.

Regardless of the direction of the swivel movement, the wiping edge of one wiping lip with a large radius is effective first, i.e. ink is sucked in, and then the sharp wiping edge of the other wiping lip is effective, i.e. ink is scraped off.

In a free spray position, the nozzles are located opposite a collecting device 23, which can be designed as a sponge or the like, for example. In the free spray position, the control device controls the print head 5 so that a predetermined number of ink droplets are emitted from each or from certain nozzles in order to ensure that printing can begin with the required high quality and sufficient amount of ink immediately after the print head is moved into the printing position.

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As shown in Fig. 3, the stripping device 19, the wiping device 21 and the collecting device 23 can be integrated in a common holding device 37. The holding device can be a replacement part and enable the devices in question to be easily replaced at the same time. For fixing in the housing 3 of the printer 1, recesses 39 and 41 are provided in a side wall and a front wall of the holding device 37, which can be designed as a plastic injection-molded part or a bent sheet metal part, into which corresponding holding pins provided in the housing 3 engage.

Fig. 2 illustrates the function of the individual service units with corresponding pivoting movements of the print head 5: At the start of a completely new printing process, the print head 5 is first moved out of the closed position I (in the following this always means an angular position) by a pivoting movement in an anti-clockwise direction. The nozzles are thus released. In the area of the stripping position II, a stripping process is then carried out using the stripping lip 31 of the stripping device. In the area of the wiping position III, a wiping process consisting of a suction and a doctoring process is then carried out using the two wiping lips 35 of the wiping element 33 of the wiping device 21. The nozzles are then sprayed free in the spraying position IV. After these service functions have been carried out, the print head 5 is moved to the printing position V and printing can begin.

Depending on the ambient conditions, the printer's control unit can move the print head to one or more of the positions II to IV after a certain number of printing operations in order to carry out the relevant service function. The print head is preferably initially moved at least to position III in order to carry out a wiping operation.

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(with the wiping device shown in Fig. 2, two wiping processes take place because the print head has to be moved back and forth). However, it can also be moved to position II so that a wiping process, a subsequent stripping process and another wiping process are carried out. Only when the print head is moved back to the printing position V is a free-spraying process carried out in the free-spraying position IV.

Of course, with the configuration shown in Fig. 1 and 2, a spray-cleaning process can also be carried out in isolation or, in the processes explained above, even when the print head is moved from the printing position V to the position III or II.

The closure device 17 can be designed in such a way that a flushing function can also be carried out. In this case, a suction device integrated into the closure device draws a larger amount of ink from the print head in order to clean possibly clogged or contaminated nozzles.

Claims (11)

1. Inkjet printers, especially for labelling packages, a) a print head ( 5 ) having a plurality of nozzles for ejecting ink, and b) with a service facility for executing at least one service function, characterized , a) that the print head ( 5 ) is designed to be pivotable about an axis (A) such that the nozzles can be moved along an imaginary pivoting circle (K) into and out of a printing position (V), and b) that the service device has at least one service unit which is provided at a position (I, II, III, IV) along the pivoting circle (K) at a predetermined angular distance from the printing position (V), wherein the service unit enables one or more service functions to be carried out when the printing head ( 5 ) with the nozzles is in the area of the service unit or is moved with its nozzles past the service unit. 2. Printer according to claim 1, characterized in that the print head ( 5 ) is pivotable about an axis (A) which runs substantially parallel to the printing plane (E) in which the nozzles are arranged. 3. Printer according to claim 1, characterized in that the print head ( 5 ) is pivotable about an axis which is substantially perpendicular to the printing plane in which the nozzles are arranged. 4. Printer according to one of the preceding claims, characterized in that the service device comprises a service unit serving as a closure device ( 17 ) for the nozzles. 5. Printer according to one of the preceding claims, characterized in that the service device comprises a service unit designed as a stripping device ( 19 ) which has a stripping element ( 31 ) with a stripping edge for stripping ink and/or contaminants on the surface of the print head ( 5 ). 6. Printer according to one of the preceding claims, characterized in that the service device comprises a service unit designed as a wiping device ( 21 ) which has one or more wiping elements ( 35 ) for sucking ink up to or onto the surface of the print head ( 5 ) and for subsequently wiping off the excess ink. 7. Printer according to one of the preceding claims, characterized in that the service device comprises a service unit designed as a collecting device ( 23 ) which serves to collect ink which is emitted by the nozzles when carrying out a free-spraying process in the angular position (IV) of the collecting device ( 23 ). 8. Printer according to claims 5 to 7, characterized in that the at least two service units, related to the stripping device ( 19 ), the wiping device ( 21 ) and the collecting device ( 23 ), are designed to be integrated with a common holding device ( 37 ). 9. Printer according to claim 8, characterized in that the holding device ( 37 ) is arranged in the printer (I) so as to be replaceable, preferably without tools. 10. Printer according to one of claims 4 to 9, characterized in that the print head ( 5 ) can be moved from a first angular position (I), in which the closure device ( 17 ) is arranged, via a second angular position (II), in which the stripping device ( 19 ) is arranged, via a third angular position (III), in which the wiping device ( 21 ) is arranged, and via a fourth angular position (IV), in which the collecting device ( 23 ) is arranged, into the angular position corresponding to the printing position (V) and vice versa. 11. Printer according to one of the preceding claims, characterized in that the printer (I) has a control unit which controls the pivoting movements of the print head ( 5 ), wherein in the case of several service units the print head ( 5 ) is preferably movable into the angular position (I, II, III, IV, V) of a single or successively into the angular positions of several service units.