DE102011106135A1 - Method for printing on workpieces and printing device - Google Patents

Abstract

A method for printing workpieces (4) comprises the following steps: - feeding a workpiece (4) to at least one workpiece carrier (7); - Fixing the workpiece (4) on the workpiece carrier (7); - Conveying the workpiece (4) on the workpiece carrier (7) to a printer (14), - Detecting the conveying speed of the workpiece (4) on the workpiece carrier (7), - Controlling the printing speed depending on the detected conveying speed. This allows fluctuations in the actual conveying speed of the workpiece to be compensated.

Description

The present invention relates to a method for printing on workpieces and to a printing device.

When digitally printing workpieces, in particular boards made of wood-based materials, a distinction is made today between the "multipass" method and the "single-pass" method. In the multipass method, the workpiece is at rest while the one or more digital printheads reciprocate over the workpiece. Subsequently, the workpiece advances again for a portion of a printhead width, comes to rest again, and the printing operation with the movement of the printheads is repeated; This process is repeated until complete printing of the workpiece.

In the case of the single-pass method, on the other hand, a row of print heads stops over the full width of the workpiece, while the workpiece passes under the print heads and is printed in one pass ( DE 100 51 088 ). In order to achieve high performance (in printed areas per unit of time) with this "single-pass" process, the workpieces must be conveyed continuously under the print heads. According to the prior art, this is done with tape transports. Despite various modifications to the belt control, it has not been possible to accurately guide a workpiece on a belt transport transversely to the feed direction, which limits the print quality.

In addition, with the known printing devices, an edge accurate printing of workpieces, such as prefabricated door leaves, not possible - either too much is printed, or it remains a white stripe back. In the printing of prepared floor panels, which are already provided on the four side edges with fastening mechanisms results in overprinting in the grooves.

In the prior art, it is common practice in so-called single-pass digital printing devices to let the printheads drop droplets at an internal frequency onto the workpiece moving beneath them. Thus, according to the prior art z. B. a printhead with a predetermined frequency of z. B. Delivering 7 kHz droplets and a suitable conveying device convey the workpiece to be printed at a speed under the printheads, which generates the desired distance from one droplet to the next.

The correct relationship between the frequency at which the droplets are delivered, the so-called internal trigger frequency, and the speed with which the workpiece must be moved, can usually be determined from the distance of the individual nozzles of the digital print head in single-pass digital printing (" Nozzleöffnungen ") calculate transversely to the conveying direction. If z. For example, if an equal resolution in the X and Y directions is to be achieved on the image, for example 600 dpi, then 600 nozzle openings per inch must be present transversely to the conveying direction (600 dpi = 600 nozzle openings per inch = 600 nozzle openings divided by 2, 54 cm: This results in a nozzle to nozzle distance of 25.4 mm divided by 600 = 0.04 mm or 40 μm.

In order to obtain the same distance of the points in the X direction, ie the conveying direction, as in the Y direction, at z. B. a feed rate of 20 m / min. = 333 mm per second a frequency of 8333 droplets per second or a firing frequency of 8.33 kHz can be achieved.

The disadvantage of this prior art is due to the fact that always arise in a conveyor conveyor speed variations in the feed direction. Although these tolerances can be reduced, they can never be completely eliminated.

It is therefore an object of the present invention to provide a method for printing on workpieces and a printing device in which the workpieces can be continuously printed one behind the other with high precision.

The present invention solves this task with a method having the features of claim 1 and a printing device with the features of claim 3 solved.

• – Zuführen eines Werkstückes zu mindestens einem Werkstückträger;
• – Fixieren des Werkstückes an dem Werkstückträger;
• – Fördern des Werkstückes (an dem Werkstückträger zu einem Drucker,
• – Erfassen der Fördergeschwindigkeit des Werkstückes an dem Werkstückträger,
• – Steuern der Druckgeschwindigkeit abhängig von der erfassten Fördergeschwindigkeit.

The method according to the invention for printing on workpieces comprises the following steps:

• - feeding a workpiece to at least one workpiece carrier;
• - Fixing the workpiece to the workpiece carrier;
• Conveying the workpiece (on the workpiece carrier to a printer,
• Detecting the conveying speed of the workpiece on the workpiece carrier,
• - controlling the printing speed depending on the detected conveying speed.

By using a recognizer for detecting the position or speed of the workpieces on the workpiece carriers, it is possible to adjust the printer depending on the actual speed of the workpieces to control. If the transport movement of the workpieces is a little slower, the printer can compensate for the slower transport movement by proportionally slowing down the print speed. Conversely, with a faster transport movement of the workpieces and the printing speed can be increased proportionally, so that as a result, even with changes in the speed of the workpieces an optimal print image with high quality is obtained.

The printing device according to the invention comprises stationary digital printing heads during the printing process, under which at least one workpiece to be printed is continuously moved during the printing process, wherein a detection device is provided for detecting the conveying speed of the workpiece to be printed or a conveying device connected thereto wherein an electronic control device processes the data of the detection device and by means of the data, the printing speed of the print heads is controllable. As a result, fluctuations in the actual conveying speed of the workpiece can be compensated, which then have little or no effect on the print quality.

In order to enable a high-precision control of the printer of the printing device, an accurate measurement of the position and / or the conveying speed of the workpiece via an electronic detection device which passes a trigger signal to the digital printheads of the digital printing device, a so-called external trigger. As a result, a high-precision resolution in the X and Y directions can be achieved uniformly. This is especially important in multicolor printing to avoid color variations by different levels of different colors.

In the printing device, the workpiece carriers are preferably guided along a guide device at least in the region of the printer. As a result, the workpieces conveyed one behind the other can also be guided and printed with high precision transversely to the feed direction, so that a particularly high print quality is achieved. In addition, the problems mentioned above with the printing of the edges or white stripes are avoided at the edges.

The guide device preferably comprises a linear rail aligned with its longitudinal axis parallel to the conveying direction. In this case, one or more ball-bearing rollers may be attached to the workpiece carriers, which are supported on the at least one linear rail, so that a high-precision guidance is obtained. Due to the high-precision guidance, certain parts of the printed image can be placed exactly on the workpiece. In addition, a particularly high printing speed and capacity, for example, more than 1,500 m ² per hour can be achieved by the stationary printheads arranged.

According to a further embodiment of the invention, the workpiece carriers comprise a transverse bar whose longitudinal axis extends substantially perpendicular to the conveying direction. On each workpiece carrier fastening means, preferably suction elements for the fixation of the workpieces can be provided. As a result, the fastening means are simple and have low wear.

By the preferred use of a detection device for detecting the position of the workpieces on the workpiece carriers, it is possible to control the printer depending on the speed of the workpieces, whereby the print quality can be further increased. As a result, movement tolerances of the conveyor can be compensated.

Further advantageous embodiments are described in the subclaims.

The invention will be explained in more detail below with reference to an embodiment with reference to the accompanying drawings. Show it:

1 a view of a workpiece for conveying in the device according to the invention;

2 a plan view of the device for conveying without printer;

3 a partially sectioned front view of the device of 2 ;

4 a front view of a workpiece carrier;

5 a side view of the workpiece carrier of 4 , and

6 a side view of the entire printing device.

A plate-shaped workpiece 4 should in a feed direction 1 be transported. The plane perpendicular to the feed direction is defined by a horizontal axis 2 perpendicular to the feed direction and a vertical axis 3 clamped.

It should be as workpieces 4 For example, coated chipboard with dimensions of about 300 mm to 1,500 mm width, 400 mm to about 3,000 mm length and 2 mm to about 60 mm thickness digitally printed with a decorative image. As decor images woodgrains, tile patterns, photos or other graphic elements can be used. For this purpose, the chipboard (workpieces) are provided on an upstream conventional belt transport continuously at a feed rate of 15 to 25 m / min and a gap of one plate length between each two chipboard. Higher speeds are possible. In addition, other workpieces can 4 For example, be printed from metal, plastic, wood, cardboard, paper or other materials.

In the 2 and 3 a conveyor is shown without the overlying printer, especially the digital printer. The conveying device comprises direct electrical drives 5 and 5 ' , each driving a toothed belt pulleys. Both timing pulleys each drive a circulating toothed belt 10 at. The two parallel toothed belts 10 are with a variety of workpiece carriers 7 connected with the timing belt 10 be moved circumferentially in the manner of a conveyor belt. The rotating workpiece carriers 7 are designed as metallic beams or steel cross members, which edge on the rotating toothed belt 10 are attached.

At the top of each workpiece carrier 7 are several fasteners 12 provided in the form of suction elements, the vacuum deposited on the fasteners plate-shaped workpieces 4 suck in and on the workpiece carriers 7 fix. For this purpose, designed as hollow profiles workpiece carrier 7 with vacuum generating units 6 connected, which within a frame construction 60 and create a negative pressure along channels, which then passes through openings or slots on the toothed belt 10 in the fasteners 12 is fed to the workpieces 4 to fix. The negative pressure on the fasteners 12 is only over a part of the upper path of the workpiece carrier 7 created, so that already printed workpieces 4 be released at the end of the conveyor.

It is also possible, instead of the suction elements shown mechanical or magnetic fastening means for fixing the workpieces 4 use.

Furthermore, one between the timing belt 10 approximately centrally arranged metallic guide rail 8th provided, as in the 5 and 6 is shown. The guide rail 8th is on a longitudinal carrier oriented in the conveying direction 80 fixed, which is designed as a steel profile and is fixed to a frame of the conveyor. For exact guidance of the workpiece carrier 7 grip on opposite sides of the guide rail 8th lateral guide rollers 20 are rotatably mounted to the about a vertical axis. Every leadership 20 can with a certain bias against the guide rail 8th be pressed. In addition, the storage of the guide rollers 20 be adjusted horizontally and perpendicular to the conveying direction, so that each workpiece carrier 7 in horizontal direction on the guide rail 8th is guided.

To the workpiece carriers 7 Also to guide exactly in the vertical direction are on the frame of the conveyor on opposite sides of the guide rail 8th rails 22 assembled. At the bottom of each rail 22 is a role 21 Guided on a vertical roll holder 23 is rotatably mounted. The vertical roll holder 23 is on the workpiece carrier 7 set and can be made adjustable in length to a positioning of the workpiece carrier 7 in a vertical direction.

The leadership roles 20 , the roles 21 , the guide rail 8th as well as the rails 22 are preferably made of metal, in particular steel. The guide rail 8th and the rails 22 are in the area of the raceways of the guide rollers 20 or, the roles 21 provided with machined flat surfaces for an accurate guidance. The guide rail 8th and the rails 22 For example, consist of a hardened steel and are aligned with high precision with a tolerance of less than 0.01 mm across the feed direction.

The conveying and printing of the workpieces 4 is referring to 7 explained in more detail:
The plate-shaped workpieces 4 be from a conveyor belt 30 continuously without speed change on the in 2 and 3 Pass shown conveyor. The workpiece carriers 7 run during the recording of the workpieces 4 to a guide roller 31 , on each of which on opposite sides a toothed belt 10 located. At the takeover, the workpieces 4 from the suction elements of the fastening means 12 , which on the workpiece carriers 7 are fixed, fixed as soon as the suction elements to the vacuum sources 6 are connected. Every workpiece 4 Then, depending on the length of two to four such workpiece carriers 7 taken and fixed by a plurality of suction elements.

On the timing belt 10 are the workpiece carriers 7 attached, which centrally on its underside ball-bearing guide rollers 20 and side rollers 21 have, fixed to the frame of the conveyor guide rail 8th and the rails 22 Thread.

During the conveyance of the workpieces 4 in the transport direction, the individual workpiece carriers 7 right and left of the two timing belts 10 pulled and are on the bottom mounted ball-bearing guide rollers 20 and roles 21 on the guide rail 8th as well as the rails 22 supported, so that they are guided transversely to the feed direction with high precision with a tolerance of less than 0.01 mm.

The timing belt 10 right and left on the conveyor are driven by a gear with rounded edges to prevent a fluctuation of the transport speed (prevention of the "polygon effect"). The two timing belts 10 each have their own electric direct drive 5 respectively. 5 ' , which is flanged to the toothed belt pulley. The toothed belt pulley preferably has a diameter of more than 400 mm. At the end of the transport route is a pulley 32 for every toothed belt 10 in which the payment belt 10 be redirected and be conveyed back on the back below the transport route. The workpiece carriers 7 Run at the end of the transport route, first at a slight angle of about 10 ° down, with the ball-bearing central guide rollers 20 out of the end bevelled guide rail 8th Unlatch, and then from the timing belt 10 taken right and left of the transport route and returned under the transport route back.

The negative pressure or the vacuum in the suction elements is through a rail-shaped opening in the conveyor through the toothed belt 10 through into the workpiece carrier 7 transfer. The individual suction elements are equipped with correspondingly small openings, so that even for the suction elements, not by a workpiece 4 are occupied, only a small outflow of air goes through, which does not cause the vacuum to collapse. Problems with so-called false air are thus excluded.

Above the conveyor is a printer 14 attached, which is designed as a digital printer and the single-pass workpieces 4 printed, which are conveyed via the conveyor. The workpieces 4 are guided so that they are exactly at the given vertical distance to printheads 15 of the printer 14 and exactly to the side in the track under the printheads 15 be continuously fed during the printing process at a constant speed.

For exact placement of the ink, a detection device for the current position of the workpieces 4 be provided, for example, seen for detecting a leading edge of the workpiece for detecting the start of printing and a printing end of a printed image in the conveying direction. In addition, the detection device, for example, one on the workpiece carriers 7 fixed magnetic moving strip, which from a fixed sensor with high frequency of z. B. 10 kHz is sampled. Alternatively, the detection device by a very precise friction wheel on one of the timing belt or by other z. B. optical cameras or laser light barriers can be realized. By using a detection device for detecting the position of the workpieces 4 on the workpiece carriers 7 is it possible to use the printer 14 depending on the speed of the workpieces 4 to control. Is the transport movement of the workpieces 4 a bit slower, the printer can 14 by proportional slowing down of the printing speed compensate the slower transport movement. Conversely, with a faster transport movement of the workpieces 4 Also, the printing speed can be increased proportionally, so that as a result, even with changes in the speed of the workpieces 4 an optimal print image with high quality is obtained.

The detection device for detecting the conveying speed of the workpiece to be printed 4 is in the range of the printer 14 arranged, preferably below the printer 14 , so that the conveying speed of the workpieces 4 measured in this area. Deviations in the conveying speed are passed on to an electronic control device, which processes the data and then the printing speed of the individual print heads 15 controls.

After printing, one or more drying stations for the printed workpieces 4 be provided depending on the type of printing ink used.

It is of course possible to implement a number of different further forms of expression of the device according to the invention. For example, the workpiece carriers can be made larger, so that a workpiece 4 from a single workpiece carrier 7 can be included. The workpiece carriers 7 also do not need a timing belt 10 run back below the transport device again, but can run back side guided on the same plane of the transport device. The possible characteristics of the workpiece carriers 7 and the fasteners are varied, depending on the requirements of the given workpieces 4 , For smaller workpieces, the form of expression becomes the workpiece carrier 7 be correspondingly smaller, so that the workpieces 4 be securely attached and do not fall into the interstices of the workpiece carrier through or come inaccurately to lie down.

The guidance of the workpiece carriers 7 can also be done via a guide device with at least one rail, on the workpiece carriers 7 specified sliding elements are guided. This can be dispensed with the ball-bearing rollers.

LIST OF REFERENCE NUMBERS

1

feed direction

2

horizontal axis

3

vertical axis

4

workpiece

5

drive

6

Unit for vacuum generation

7

Workpiece carrier

8th

guide rail

9

vacuum tube

10

toothed belt

11

frame

12

suction

14

printer

15

printheads

20

guide rollers

21

roll

22

rail

23

roll holder

30

conveyor belt

31

deflecting

32

idler pulley

60

frame construction

80

longitudinal beams

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 10051088 [0003]

Claims (8)

Method for printing on workpieces ( 4 ) with the following steps: - feeding a workpiece ( 4 ) to at least one workpiece carrier ( 7 ); - fixing the workpiece ( 4 ) on the workpiece carrier ( 7 ); - conveying the workpiece ( 4 ) on the workpiece carrier ( 7 ) to a printer ( 14 ), - detecting the conveying speed of the workpiece ( 4 ) on the workpiece carrier ( 7 ), - controlling the printing speed depending on the detected conveying speed. A method according to claim 1, characterized in that when changing the conveying speed of the workpiece ( 4 ) the printing speed of the printer ( 14 ) is adjusted proportionally. Printing device with digital printheads fixed during printing ( 15 ), under which at a predetermined distance at least one workpiece to be printed ( 4 ) is moved continuously during the printing process via a conveyor, characterized in that a detection device for detecting the conveying speed of the workpiece to be printed ( 4 ) or an associated with this conveyor, wherein an electronic control device processes the data of the detection device and by means of the data, the printing speed of the print heads ( 15 ) is controllable. Printing device according to claim 3, characterized in that a conveyor for workpieces ( 4 ) a conveyor belt ( 10 ) and the electronic detection device comprises a friction wheel, which on the conveyor belt ( 10 ) is present. Printing device according to claim 3 or 4, characterized in that the digital printheads ( 15 ) over the entire width of the workpiece ( 4 ) are arranged and at least four printhead rows are provided in succession for four different printing inks. Printing device according to one of the preceding claims 3 to 5, characterized in that the current position of the workpiece ( 4 ) is detected via a rotary encoder which is directly or indirectly connected to the continuous conveyor of the workpiece. Printing device according to one of the preceding claims 3 to 6, characterized in that as fixed printheads ( 15 ) Piezo-controlled inkjet printheads are used, which emit individual droplets with a frequency between 1 kHz and 10 kHz on the continuously moving workpiece. Printing device according to one of the preceding claims 3 to 7, characterized in that the workpiece carrier ( 7 ) at least in the area of the printer ( 14 ) along a guide device ( 8th ) are guided.

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