EP0921009A1 - Apparatus for compensating the tolerance in an ink jet print head - Google Patents

Abstract

The arrangement has a mechanical adjuster, and a memory integrated into the print head in which individual print data for position correction of the printed points are stored. The correction data are externally generated before installation of the head by evaluating sample printouts. The head is mounted to rotate about an axis within a range of adjustment.

Description

The invention relates to an arrangement for tolerance compensation in a Ink printhead, especially for one of several modules the "non-interlaced" principle composite ink printhead.

Such ink printheads are used both in office printers and in small, fast printers - as are required for franking machines and product labeling devices - and generally have a larger number of nozzles.
One component that has a particularly large influence on the reliability of a printer is the ink print head. If the ink print head is composed of several components, the precise arrangement of the same with each other and with each other as well as the ink print head itself has a decisive influence on its safe function.

It is known, see "Third Annual European Ink Jet Printing Workshop October 16-18, 1995 Maastricht / Netherlands" to assemble an ink print head from three modules according to the "non-interlaced" principle, which is usually controlled by a microprocessor.
Equal-length, mutually aligned, sloping parallel slots are made in a front plate, into which the modules with their nozzle area are inserted, see also FIG. 1.
The record carrier is moved past the rows of nozzles in such a way that the printed image is composed of three strips lying one above the other. In the case of a vertical full line, the upper third is therefore generated by the first module, the middle third by the second module and the lower third by the third module.
However, it is also possible, for example in the case of hand franking machines, that the recording medium is at rest and the ink print head is moved, see EP 0 750 277 A2.
Although the slots are usually made with high precision in the front plate and the modules are manufactured as precision parts, tolerance deviations of over a tenth of a millimeter - in a 200 dpi print head with 200 nozzles, this corresponds approximately to the vertical distance between two neighboring nozzles - when changing from one module to the next , not be ruled out. The errors can be distance and parallelism errors as well as deviations from the alignment within a row of nozzles as well as nozzles lying one below the other, compare the simplified example according to FIGS. 1 and 2.
Fig. 1 shows an error-free nozzle field with the associated line print. Three modules 11, 12, 13, each with seven nozzles 111 to 117, 121 to 127, 131 to 137, form an ink print head. The nozzles of a nozzle row of a module are arranged equidistantly in a line. Nozzles of the same atomic number, for example the nozzles 111, 121, 131 of the modules 11, 12, 13 are also arranged equidistantly in a row which is orthogonal to the direction of transport of the recording medium 6. The direction of transport is indicated by the arrow.
In this case, the record carrier 6 is a strip, as is usually used for bulky postal items. The distance Δd of the nozzle with the highest atomic number, for example nozzle 117 of the module 11, to the nozzle with the lowest atomic number, for example nozzle 121, of the next module 12 in the direction orthogonal to the transport direction of the recording medium 6 is set so that it is the same Distance between adjacent nozzles of a row of nozzles in the direction mentioned. Δd is the ideal or standard distance, so to speak.
For the printing of a continuous line 5 orthogonal to the transport direction of the printing medium 6, nozzles of the same atomic number are actuated at the same time. It starts with the nozzles of the highest atomic number 117, 127, 137. When the recording medium 6 has covered a distance which corresponds to the distance Δs to the next nozzles 116, 126, 136 in the transport direction, the same is actuated. For a way s = 6 x Δs all twenty-one nozzles 111 to 137 have been actuated once. At constant speed, Δs would correspond to a fixed time interval Δt.
If the conditions described above are met, the associated imprint is a continuous straight line 5 composed of twenty-one pressure points 501 to 521.
Fig. 2 shows a combination of all possible errors of a faulty nozzle field and the associated so-called line print 5. The causes of these errors can be due to production-related deviations in the length of the individual module - see module 12 - as well as stress-related bending of the same - see module 11 - and on the other hand, there are manufacturing tolerances of the front panel and its slots - see module 13-. There would also be errors due to the installation tolerances of the ink printhead attachment.
Corresponding deviations from a straight continuous line can then be found in the imprint 5.

A method for matching the writing nozzles of an ink print head in ink writing devices is already known, compare EP 0 257 570 A2. The ink print head is moved bidirectionally in front of a recording medium by means of a drive. Individual droplets are ejected from its individually controllable writing nozzles in accordance with the data taken from a character generator during its movement at defined printing times.
According to the method, a printer advance takes place, during which a defined line pattern is printed on the recording medium separately for each writing nozzle for each writing direction - counterclockwise, clockwise rotation.

ein optischer Abtastsensor, eine Vergleichsschaltung, zwei zusätzliche Speicher für die Tröpfchenversatzspeicherung und zwei Bildpunktspeicher.

Das ist ein beträchtlicher zusätzlicher Aufwand für einen Drucker.
Hinzu kommt, daß mit dieser Lösung bei Tintendruckköpfen, die aus mehreren Modulen zusammengesetzt sind, Toleranzen von Modul zu Modul nicht ausgeglichen werden können. Das liegt daran, daß nur ein Ausgleich zeitlich vor- oder nacheilend auf der relativen Bewegungslinie der Schreibdüse möglich ist.A scanning run then takes place during which the line pattern is scanned by an optical sensor which is arranged on the printhead and is synchronized with the printing key raster. The samples are transferred to the central control of the ink writing device in the grid of the printing columns of the character matrix as the "actual" position.
In the central control system, a comparison circuit is used to compare the “actual” positions with “target” positions, which are determined by the corresponding control pulses. The deviations between the two positions indicate the values for the so-called droplet offset in the grid of the printing columns.
For each writing nozzle, the droplet offset values are stored separately in an additional memory of the central control for both writing directions. The droplet offset is forwarded separately for the writing directions as a distortion value to a pixel memory also contained in the central control.
Each time a writing nozzle is activated in normal printing operation, the value of the droplet offset determined for the respective writing nozzle is taken into account depending on the writing direction. For this purpose, pre-distortion is carried out in accordance with the printing direction and the determined droplet offset when preparing the characters.
This solution therefore requires the following for each ink writing device:

an optical scanning sensor, a comparison circuit, two additional memories for droplet offset storage and two pixel memories.

This is a considerable additional effort for a printer.
In addition, tolerances from module to module cannot be compensated for with this solution in the case of ink print heads which are composed of several modules. The reason for this is that only a compensation is possible in advance or lagging on the relative line of movement of the writing nozzle.

A franking machine with an ink print head is also known, see EP 0 702 334 A1 and EP 0 702 335 A1, which has a large number of nozzles. The nozzles are arranged in at least two rows which run transversely to the direction of advance of the print carrier. These two rows are staggered along and across the feed direction so that some first nozzles at the end of one row of nozzles are opposite some second nozzles at the end of the other row of nozzles.
The nozzles in the overlap area are operated alternatively. A correction of the nozzle distance is not possible.

Finally, a computer-controlled ink jet printing device is known, see DE 32 36 297 C2, which consists of several ink printheads.
The ink print heads are arranged one behind the other in the print carrier transport direction and one above the other transversely to the same. In this way, the print image is generated according to the "non-interlaced" principle, see also previous explanations. The image signals are loaded in an external memory device assigned to each individual ink print head. When the same is placed on the ink printheads, a droplet ejection and thus a printing process is triggered. A timing and control system is used to apply the image signals. The control system applies the image signals to the laterally offset ink printheads in a time-coordinated relationship in order to print the different lines in the desired mutual alignment. The controller then stores a new set of image signals for printing the next image.
The inkjet printing device is provided with a programmable microprocessor by means of which the image signals are assembled in buffer memories which are individually assigned to the ink print heads. The storage of the image signals in the buffers and the subsequent application to the ink print heads is carried out by means of a central timing and control device with a coarse and fine delay device. This includes the detection of the print media, such as their leading edge, at a specific location on the transport route and a subsequent time control of the start of the printing process. The distance of the ink printheads from this location is precisely known, so that a buffer associated with the same can be loaded with image signals by an ink printhead during the time interval between print carrier detection and the start of the printing process. The time interval can be varied by means of the control. In this way, the image line generated by each ink print head can be shifted left or right on the print carrier in order to set the desired location of the line. At least the first pressure column can thus be aligned.
Although this allows a tolerance compensation of installation-related tolerances of the ink printheads analogously to the solution according to EP 0 257 570, it is also not possible within an ink printhead from nozzle to nozzle. It is also not possible to correct distance errors between the lines.

The purpose of the invention is to reduce the effort for the improvement the print quality.

The invention has for its object an arrangement for tolerance compensation for ink printheads of the type mentioned at the beginning create with both deviations despite reduced effort within a module as well as from module to module as well as installation tolerances of the ink print head can be compensated.

According to the invention, this object is achieved according to the main claim. Further advantageous features of the invention can be found in the subclaims.
Since each ink print head is provided with an integrated non-volatile read-write memory which contains its individual print data, the ink print head is electronically pre-balanced before it is installed in the printer. The individual print data contain the cycle delay values, either module or single nozzle-related. Since the ink print head is rotatably mounted, a correction from module to module by varying the installation angle of the ink print head to the direction of transport is possible by means of the adjusting device. Here, too, mechanical pre-adjustment is possible even before the ink print head is installed. The maximum rotation is such that nozzles overlap in the connection area from module to module and then one of them is electronically excluded from printing. With larger numbers of nozzles, this cannot be determined in the printed image and is therefore justified.
After installation of the ink print head in the printer, if necessary, slight installation tolerances can still be adjusted using the adjustment device.

The invention is explained in more detail below using the exemplary embodiment explained.

Fig. 1

Ein fehlerfreies Düsenfeld mit dem zugehörigen Linienabdruck,

Fig. 2

ein fehlerbehaftes Düsenfeld mit dem zugehörigen Linienabdruck,

Fig. 3

ein Prinzipbild der erfindungsgemäßen Anordnung,

Fig. 4

ein Prinzipbild des Teils der erfindungsgemäßen Anordnung für den elektronischen Abgleich,

Fig. 5

ein Düsenfeld gemäß Fig. 2 mit dem korrigierten Linienabdruck.

Show it:

Fig. 1

An error-free nozzle field with the associated line print,

Fig. 2

a faulty nozzle field with the associated line print,

Fig. 3

a schematic diagram of the arrangement according to the invention,

Fig. 4

2 shows a basic diagram of the part of the arrangement according to the invention for electronic comparison,

Fig. 5

2 with the corrected line print.

The illustration is for simplification and easier understanding carried out schematically.

According to FIG. 3, the arrangement according to the invention consists of an ink print head 1, a memory 2, an axis 3 and an adjustment device 4.
The ink print head 1 is composed of three modules 11, 12, 13. The modules 11, 12, 13 are arranged one above the other in accordance with the "non-interlaced" principle.
The memory 2 is an integral part of the ink print head 1 and is implemented as a non-volatile read-write memory using an EEPROM. Individual print data of the ink print head 1 are stored in the memory 2. The individual print data are generated externally before the ink print head is installed in a printing device by evaluating sample prints. The individual print data contain corresponding positive or negative delay values for the clocks for controlling the modules as a whole or the nozzles as individual. The individual data can also be such that a nozzle is excluded from printing.
The ink print head 1 is rotatably supported on the axis 3 within an adjustment range. The bearing for the axis 3 can be formed directly on the housing of the ink print head 1 or indirectly contained in a crossmember for receiving the ink print head 1.
The adjusting device 4 consists of a threaded bushing 41, an adjusting screw 42 and a spring 43. It serves to rotate the ink print head 1 within the adjusting area. The ink print head 1 is non-positively against the adjusting screw 42 under the action of the spring 43. The adjusting device 4 can expediently also be fastened on the crossmember mentioned.

4, the memory 2 is connected to the pressure control computer 7 - microprocessor - via an outgoing data line 75 and an incoming data line 76. The first module 11 is connected to the pressure control computer 7 via a clock line 71 and an incoming data line 74. The second module 12 is connected to the pressure control computer 7 via a clock line 72. The third module 13 is connected to the pressure control computer 7 via a clock line 73.
In the case shown, the print data D are entered serially into the modules 11, 12, 13. Therefore, the data line 74 is looped through from the pressure control computer 7 via the module 11 to the module 12 to the module 13. An alternative is to input the print data D directly to each module via a parallel bus.
The ink print head 1 or the modules 11, 12, 13 is / are provided in a manner not shown with a commercially available driver circuit with a shift register and latches in front of logic elements. The actuation circuits for the nozzles are triggered in accordance with the time and image information by means of the logic links on which the assigned clock lines with the corrected clocks T1 to T3 are applied.
The print control computer 7 is connected to a scanner 8 via a signal line 81 for generating the correction data or the individual print data 1. If gaps in the impression 5, such as the height offset v between the dot 514 and 515, which go beyond the standard Δd, are found during a first test print, the ink print head 1 is in this case rotated to the left until the connection is made in the vertical direction. The angle of rotation is already mechanically stored when the adjusting screw 42 is turned.
The newly generated impression 5 is scanned and the scanning signals As are fed to the pressure control computer 7 in relation to the dot or nozzle. The scanning signals As are compared in the pressure control computer 7 with standard values already stored therein and the deviations are converted into signed correction data 1 and entered into the memory 2 via the data line 76 in an address-related manner. However, it is also possible to dispense with the sign part if only delay values are generated in relation to the most lagging dot, for example dot 515 or 521 in FIG. 2. In this case, the offset v in the transport direction from module 13 to module 12 is somewhat smaller than the corresponding nozzle spacing Δs.
The correction data or individual print data I are loaded into the memory 2 via the data line 76. The ink print head 1 is thus also electronically adjusted.
After the final installation of the ink print head 1 in a printing device, the individual print data 1 are retrieved via the data line 75 by the microprocessor 7 from the EEPROM 2 and incorporated in the generation of the clocks T1, T2, T3.

5 is one according to the procedure described above corrected line print of the faulty nozzle field according to FIG. 2 shown. In this case, the nozzle 121 is for printing electronically locked.

Reference symbols used

1

Ink printhead

11

first module

111 to 117

Nozzles of the first module

12th

second module

121 to 127

Second module nozzles

13

third module

131 to 137

Third module nozzles

2nd

Memory, EEPROM, non-volatile

3rd

axis

4th

Adjustment device

41

Threaded bush

42

Adjusting screw

43

feather

5

Footprint

501 to 507

Dots or pressure points from the first module 11 generated,

508 to 51

4 dots or pressure points from the second Module 12 generated,

515 to 521

Dots or pressure points from the third module 13 generated,

6

Record carriers, printing strips

7

Pressure control computer, microprocessor

71

Clock line to the first module 11

72

Clock line to the second module 12

73

Clock line to the third module 13

74

Data line to modules 11, 12, 13

75

Data line from internal print head memory 2 to Microprocessor 7

76

Data line to the print head internal memory 2

8th

scanner

81

Signal line

As

Scan signals from scanner to microprocessor 7

D

Print data for modules 11, 12, 13

Δd

Standard nozzle offset orthogonal to the direction of transport

I.

individual print data, correction data

Δs

Standard nozzle offset in the direction of transport

s

Row length of nozzle in transport direction

T1

Clock for module 11

T2

Clock for module 12

T3

Clock for module 13

v

Module offset in the direction of transport

Claims (5)

Arrangement for tolerance compensation in an ink print head, in particular in an ink print head composed of several modules according to the "non-interlaced" principle, which is controlled by a pressure control computer and wherein the modules are arranged obliquely equidistant from one another and their first effective nozzles in relation to the relative Print carrier transport direction should lie on a line orthogonal to this,
characterized,
that a memory (2) is integrated in the ink print head (1), in which individual print data (I) for correcting the position of the print dots are stored, which are evaluated externally by means of evaluation of sample prints, before the final installation of the ink print head (1) in a printing device, are generated and
that the ink print head (1) is rotatably mounted about an axis (3) within an adjustment range and an adjustment device (4) is provided for mechanical adjustment of the ink print head (2). Arrangement according to claim 1, characterized in
that the individual print data (I) for each individual nozzle (111 to 117, 121 to 127, 131 to 137) are stored in the memory (2). Arrangement according to claim 1, characterized in
that the individual print data (I) for each individual module (11, 12, 13) are stored in the memory (2). Arrangement according to claim 1, characterized in
that the memory (2) is designed as a non-volatile read-write memory by means of an EEPROM. Arrangement according to claim 1, characterized in
that the adjusting device (4) consists of a threaded bushing (41), an adjusting screw (42) guided in the same and a spring (43), the threaded bushing (41) being fastened in the printer and the ink print head (1) under the action of the spring (43) rests non-positively on the adjusting screw (42).

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