EP0389481B1 - Process and arrangement for automatic performance checking of printing ink devices - Google Patents

Abstract

To ensure fully automatic performance checking, a printing ink device has a cleaning and rinsing device (105) and an ink drop sensor (11). When a fully automatic self-check procedure is called before the actual printing operation or after printing for a specified period of time, the printing ink head is cleaned and rinsed in a rest position and its performance is then checked in a spray test by an ink drop sensor (11). If the results of the spray test are satisfactory, the printing operation can be resumed. If the results of two consecutive spray test are unsatisfactory, the printing device is placed in a breakdown position and the printing operation is brought to a halt.

Description

The invention relates to an arrangement for determining the functionality of an ink printing device according to the preamble of patent claim 1.

• Gas- bzw. Lufteinschlüsse in der Tinte;
• Ein- oder Antrocknen bzw. starke Änderung der Viskosität der Tinte;
• Verschmutzung des Düsenbereiches der Tintenköpfe durch Fremdkörperpartikel, z. B. Papierstaub; und
• bei Tintendruckeinrichtungen, die mit Unterdruck arbeiten, die Zerstörung des konkaven Tintenmeniskus am Düsenende, z.B. durch Erschütterung des Druckers beim Transport.

Ink printing devices that work with multi-nozzle ink heads are sensitive to environmental influences. These influences that may cause malfunctions include:

• Gas or air pockets in the ink;
• Drying or drying or a strong change in the viscosity of the ink;
• Contamination of the nozzle area of the ink heads by foreign body particles, e.g. B. paper dust; and
• in the case of ink printing devices which work with negative pressure, the destruction of the concave ink meniscus at the end of the nozzle, for example due to vibration of the printer during transport.

The elimination of all of these malfunctions requires a wide variety of means that must be used by the printer user when a malfunction occurs.

Another problem with ink printing devices that is subject to the functional monitoring of the user is the problem of print image acceptance. The user of ink printing devices must recognize in good time whether the typeface generated is faulty or not. This is particularly difficult with multi-nozzle ink heads of high print resolution, since e.g. B. the failure of one or more nozzles of the ink print head initially only results in a slight deterioration in the printed image.

In general, the proper functioning of the print head is checked by the user himself by visual inspection of special print patterns. It is not easy and requires Because of the relatively small droplet diameter, which is on the order of about 60 µm, a very strenuous observation, which often requires a magnifying glass. The human eye is particularly overwhelmed when the failure affects outlet nozzles that are spaced relatively far apart. Overall, such a review is unsatisfactory.

For other malfunctions of the type described, it is also customary to initiate or carry out procedures manually initiated by the user of the printing device in order to enable trouble-free recommissioning of the writing head and thus of the printing device.

In order to be able to determine malfunctions due to the failure of individual nozzles, it is known from DE-A-36 34 034 to use an ink droplet sensor which comprises a plurality of electrodes, at least the first electrode of which can be brought into a position in which it meets the outlet nozzles opposite of the ink print head at a predetermined distance. The change in resistance between the first electrode and another electrode is detected when conductive ink ejected from the ink print head reaches the first electrode.

DE-A-32 44 112 describes an arrangement for checking nozzle outlet openings on ink writing heads for clogging or contamination in ink writing devices. For this purpose, an ink device for monitoring the droplet ejection is arranged in the range of movement of the ink print head, with a light receiver and a light transmitter. After cleaning the ink print head, a nozzle test is carried out by spraying, the presence of an ink meniscus being checked at the nozzle outlet openings. If the reflection intensity of the meniscus deviates from a comparison intensity, a control signal is generated. This control signal either triggers a flushing of the write head or an optical or acoustic warning signal.

It is also known from DE-B-26 10 518 to clean the ink head and in particular the nozzle surfaces by briefly increasing the ink pressure manually in order to wash away the dirt particles on the nozzle surface due to the emerging ink.

Other known cleaning devices (DE-A-32 07 072) use a pivotably arranged plate which is moved back and forth with an edge over the nozzle surface.

Furthermore, DE-A-29 19 727 describes a device for closing the nozzle surface on an ink writing head, in which a motor-driven, elastic endless band is provided, which rests on the nozzle surface.

To flush the ink print head, it is known from EP-A-0 212 503 to use a hose pump which is arranged in the printer carriage.

The object of the invention is to provide an arrangement of the type mentioned at the beginning, with which an automatic operational security of the ink printing device is possible.

This object is achieved in an arrangement of the type mentioned at the outset according to the characterizing part of patent claim 1.

Advantageous embodiments of the invention are characterized in the subclaims.

According to the invention, when a function test procedure is called up, the ink head in the region of its nozzle surface is first cleaned and flushed through. After the cleaning procedure has been completed, each nozzle of the ink print head is then subjected to a spray test, and then, depending on the result of the spray test, either the printing operation is released or the ink printing device is put into a fault state after one or more unsuccessful cleaning procedures. H. further printing is prevented or the fault status is shown on a display.

This automatic operational security of the ink printing device before the start of the printing operation or automatic control procedure during the printing operation ensures optimal operational reliability and printing quality. The arrangement is inexpensive and inexpensive and relieves the user of the printing device from its own possibly imprecise controls, since the ink printing device checks itself at defined times.

The necessary components are inexpensive and easy to manufacture, and the function test procedure that controls the process can be saved as part of the microprocessor-controlled central control.

The function test procedure can be called up when the printing device is started up or after a predefinable printing time.

• FIG 1 eine Prinzipdarstellung eines Tintentröpfchensensors,
• FIG 2 und FIG 3 ein Ausführungsbeispiel für den als Tintentröpfchensensor vorgesehenen Elektrodenkamm,
• FIG 4 ein zweites Ausführungsbeispiel für den Elektrodenkamm,
• FIG 5, FIG 6 und FIG 7 jeweils Beispiele für eine Auswerteschaltung,
• FIG 8 ein Ausführungsbeispiel für den Aufbau und die Herstellung einer Sensorplatte,
• FIG 9 und 10 ein Ausführungsbeispiel für den praktischen Einsatz der Sensoranordnung,
• FIG 11 eine schematische Darstellung einer Anordnung zur automatischen Betriebssicherstellung,
• FIG 12 eine Schnittdarstellung der Anordnung gemäß FIG 11 entlang der Schnittlinie I-XII,
• FIG 13 eine Schnittdarstellung einer Anordnung gemäß FIG 11 entlang der Schnittlinie II-XIII in Ruheposition und
• FIG 14 eine Darstellung einer Anordnung entsprechend der FIG 13 in Spülposition.

Embodiments of the invention are shown in the drawings and are described in more detail below, for example. Show it

• 1 shows a schematic diagram of an ink droplet sensor,
• 2 and 3 show an exemplary embodiment of the electrode comb provided as an ink droplet sensor,
• 4 shows a second exemplary embodiment for the electrode comb,
• 5, 6 and 7 each show examples of an evaluation circuit,
• 8 shows an exemplary embodiment for the construction and manufacture of a sensor plate,
• 9 and 10 show an exemplary embodiment for the practical use of the sensor arrangement,
• 11 shows a schematic illustration of an arrangement for automatic operational security,
• 12 shows a sectional illustration of the arrangement according to FIG. 11 along the section line I-XII,
• 13 shows a sectional illustration of an arrangement according to FIG. 11 along the section line II-XIII in the rest position and
• 14 shows an arrangement corresponding to FIG 13 in the rinsing position.

In an ink printing device shown here only schematically in FIG. 11, an ink writing head 1 which is arranged on a printer carriage 100 is moved line by line along a recording medium (not shown here) with the aid of a stepping motor 101 in printing operation. The printer carriage 100 is guided on guide rods 102 and is connected to the stepper motor 101 via a toothed belt 103. On the left edge of the range of movement of the printer carriage 100, the components required for automatically ensuring the operational reliability of the ink printer are arranged on the printer chassis 41. These are essentially a cleaning and rinsing station 105 and an ink droplet sensor 11 arranged next to them.

The cleaning and rinsing station shown in particular in FIGS. 11, 13 and 14 consists of a rotating endless belt 107 made of elastic material, e.g. Rubber or elastomer, which is guided by two rollers 108 and the width of which is somewhat larger than the width of the nozzle surface (nozzle plate) 2 of the ink writing head 1. On the endless belt 107, two wedge-shaped wiping lips 109 are arranged. These wiper lips have an approximately triangular cross section, the angle at the front edge may differ from the angle at the rear edge, so that they can form oblique triangular lips. It is essential that the triangular wiper lips are attached to the endless belt 107 in such a way or are designed as a bulge of the endless belt that they cannot flip over during the wiping process.

The endless belt 107 with the wiper lips 109 is arranged at such a distance close to the nozzle surface 2, so that the wiper lips 109 can surely slip over the nozzle surface during the cleaning process. The elasticity and resilience for generating the pressing force necessary for stripping is essentially achieved by the deflection of this band.

In order to prevent drying and soiling of the nozzle surface 2 of the ink print head 1 during breaks in writing, the endless belt has further lips 110 parallel to the belt between the wiping lips 109, so that a corresponding protective hood-like depression results in the endless belt 107. This recess is brought in front of the nozzle surface 2 during pauses and rests elastically on the latter. The lips 109 and 110 are arranged so that they cover the area of the writing nozzles in the sealed state. The side lips 110 are arranged with respect to the wiper lips 109 so that they leave openings in order to ensure pressure and temperature compensation to the environment. It is essential, however, that after positioning this protective hood in front of the nozzle openings in the area of the protective hood, a kind of small climate is established that prevents drying and contamination of the nozzle surface during breaks in writing.

With ink printheads, there is a risk that the ink will thicken in the area of the nozzle openings during longer pauses in writing. Therefore, to achieve an immediate print image after resuming printing, it is necessary to remove this thickened ink or possibly also dirty ink from the nozzle openings. For this purpose it is common to spray the nozzles freely in the cleaning station.

In order to make this free spraying easy, an area 111 is provided on the endless belt 107 in the device shown, which serves for free spraying as a collecting surface for the ink droplets during free spraying. 14, this area 111 is brought in front of the nozzle surface 2 during free spraying, the impinging ink then dripping off the endless belt 107 and being collected by a collecting container 112.

When flushing, the ink is passed through the ink print head 1 with the aid of a hose pump arranged in the printer carriage 100 113 pressed. This hose pump can be designed in accordance with EP-A-0 212 503.

A single motor 106 drives both the cleaning and rinsing station 105 and the hose pump 113, depending on its direction of rotation. For this purpose, a respective first 116 and second locking mechanism 117 are arranged on the drive shaft 115 of the motor 106. This locking mechanism, which is dependent on the direction of rotation, is designed as freewheels, the first freewheel 116 being connected to the rollers 108 of the endless belt 107 via a belt 118. The freewheel 116 is designed in such a way that it freewheels counterclockwise when the drive shaft 115 is driven and is coupled to the endless belt 107 via the belt 118 when the drive shaft is driven clockwise. The second freewheel 117 is designed as a freewheel freewheeling in the clockwise direction of the drive shaft 115 and has toothing 119 on its outside which cooperate with a corresponding toothing 120 of the hose pump 113.

The hose pump 113 is coupled to the motor 106 by moving the printer carriage 100, the coupling being carried out in the position shown on the left in FIG.

The ink droplet sensor 11 arranged next to the cleaning and rinsing device 105 will now be described in more detail below with reference to FIGS. 1 to 10.

In Figure 1, the ink writing head 1 is shown on the right. It has, for example, a nozzle plate 2 with nine outlet nozzles 3, a head part 4 with nine ink channels 5 and drive elements 6 associated therewith, and an ink supply part 7. This is connected via an ink feed 8 to an ink reservoir, not shown here. By individually controlling the drive elements 6, a single ink droplet 9 is ejected from the associated nozzle 3. The nozzles 3 in the sectional view according to FIG. 1 can also be arranged several times, namely in several rows perpendicular to the plane of the drawing. Four such rows would then form a write head with 32 nozzles, the nozzles of the individual rows being offset from one another. The ink droplet sensor 11 according to the invention is arranged at a distance 10 from the write head 1. It essentially consists of a sensor plate 12, designed as an electrode comb, with two connecting electrodes 13 and 14 leading to the outside, and of a layer located behind or below it, which is referred to below as suction block 17 and which serves to absorb and discharge liquid. The electrode comb has, at least in the area of the point of impact of the ink droplets, a multiplicity of conductor tracks 18 and 19 which run in parallel in the outlet area of the ink droplets. The device for removing the liquid supplied by the impact of ink droplets consists of non-conductive porous material; it can be constructed in one layer or preferably from several sub-layers. The connection electrodes 13 and 14 are connected to an evaluation circuit 20 which, as will be discussed in more detail later, depending on the impact of one or more ink droplets on the electrode comb 12, emits a corresponding signal, the sensor signal SM.

The mode of operation of the ink droplet sensor is described below with reference to FIGS. 2 and 3, which show an exemplary embodiment of the electrode comb 12 of the ink droplet sensor in a top view (FIG. 2) and in a sectional illustration (FIG. 3). In the example, the electrode comb is formed by two comb parts 121 and 122, whose tongue-shaped conductor tracks 18,19 lie next to each other in the area of the impact points for the ink droplets and form the comb structure. The comb parts 121 and 122 with the conductor tracks 18 and 19 are applied here to the suction block 17 consisting of the porous, non-conductive layer. Each of these comb parts 121 and 122 is electrically accessible from the outside via the connection electrodes 13 and 14.

festgelegt. Soll der Tintentröpfchensensor bereits einen einzigen Tintentropfen des Durchmessers D detektieren, so muß T ≦ D sein, um eine elektrische Widerstandsbrücke zwischen benachbarten Leiterbahnen 18 und 19 und damit zwischen den Kammteilen 121 und 122 zu bilden. Am Beispiel nach FIG 3 erkennt man, daß ein Tintentropfen 9 beim Auftreffen auf die Oberfläche des Tintentröpfchensensors diese Bedingung erfüllt, also zwischen zwei benachbarten Leiterbahnen eine deutliche Widerstandsreduzierung herbeiführt, die an den Anschlußelektroden 13 und 14 durch die Auswerteschaltung ausgewertet werden kann. Nach dem Auftreffen des Tintentröpfchens 9 wird die Flüssigkeitsmenge zunächst von der oberen porösen Teilschicht 15 aufgenommen, nach unten transportiert und dringt schließlich in die zweite Teilschicht 16 ein. Die elektrisch nichtleitenden porösen Teilschichten 15 und 16 wirken als eine Art Saugpumpe mit kapillarischem Effekt. Der Wirkungsgrad dieser Saugpumpe kann durch die Wahl der Porosität (bzw. Porenweite) und/oder der Anzahl bzw. der Dicke S1, S2 der Teilschichten auf bestimmte Einsatzfälle eingestellt werden. Für das in FIG 3 dargestellte Ausführungsbeispiel haben sich folgende Dimensionierungen als besonders vorteilhaft erwiesen:
   A=B=40 µm
   H (Goldelektrode)=1 µm
   L=50 µm
   S1=5 mm
   S2=1,5 mm
Die Porosität P1 und P2 der beiden Schichten 15 und 16 ist unterschiedlich. Es ist vorteilhaft, wenn die Porosität der einzelnen Schichten mit zunehmendem Abstand vom Elektrodenkamm zunimmt ( P2 > P1). Zunehmende Porosität bedeutet abnehmende Porenweite und damit zunehmende Kapillarität der Schichten. Dadurch wird gewährleistet, daß ein Flüssigkeitstransport bevorzugt von der oberen Teilschicht 15 zur unteren Teilschicht 16 stattfindet. Das hat den Vorteil, daß der Raum in der Nähe des Elektrodenkamms relativ rasch von Tinte entleert wird und daß damit eine in kurzen Zeitabständen eintreffende Folge von Einzeltröpfchen sicher detektiert werden kann. Als Materialien für die einzelnen Teilschichten 15 und 16 mit unterschiedlichen Porositäten eignet sich vorzugsweise Duran-Filterglas für die obere Teilschicht 15 und sog. Millipore-Filterpapier für die untere Teilschicht 16. Die Porenweiten der oberen porösen Teilschicht 15 können dabei zwischen 0,01 und 0,02, die Porenweiten der unteren porösen Teilschicht 16 zwischen 0,005 und 0,01 mm liegen. Die beschriebenen Kammstrukturen können vorteilhaft nach der an sich bekannten Dünnfilm-bzw. Dickschichttechnik hergestellt werden.3 shows the structure in detail. In the example, the suction block 17 consists of two partial layers 15 and 16 of absorbent material with the thicknesses S1 and S2. An insulating layer in the form of a gold-coated insulating film 21 is laminated onto the uppermost partial layer 15, which is then structured according to the division ratio T of the electrode comb and is provided with the conductor tracks 18 and 19. This creates the structure shown in FIGS. 2 and 3. The comb parts 121, 122 with the conductor tracks 18 and 19 have a height L; the conductor tracks 18 and 19 each have a width A and run at a distance B from one another. This is a division ratio $\text{T = A + B}$

fixed. If the ink droplet sensor is to detect a single ink drop of diameter D, then T ≦ D must be formed in order to form an electrical resistance bridge between adjacent conductor tracks 18 and 19 and thus between comb parts 121 and 122. The example according to FIG. 3 shows that an ink drop 9 meets this condition when it hits the surface of the ink droplet sensor, that is to say it brings about a marked reduction in resistance between two adjacent conductor tracks, which can be evaluated at the connection electrodes 13 and 14 by the evaluation circuit. After the ink droplet 9 strikes, the amount of liquid is first absorbed by the upper porous sub-layer 15, transported downward and finally penetrates into the second sub-layer 16. The electrically non-conductive porous sub-layers 15 and 16 act as a type of suction pump with a capillary effect. The efficiency of this suction pump can be adjusted to specific applications by selecting the porosity (or pore size) and / or the number or the thickness S1, S2 of the partial layers. For the shown in FIG 3 In the exemplary embodiment, the following dimensions have proven to be particularly advantageous:
A = B = 40 µm
H (gold electrode) = 1 µm
L = 50 µm
S1 = 5 mm
S2 = 1.5 mm
The porosity P1 and P2 of the two layers 15 and 16 is different. It is advantageous if the porosity of the individual layers increases with increasing distance from the electrode comb (P2> P1). Increasing porosity means decreasing pore size and thus increasing capillarity of the layers. This ensures that a liquid transport preferably takes place from the upper sub-layer 15 to the lower sub-layer 16. This has the advantage that the space in the vicinity of the electrode comb is emptied of ink relatively quickly and that a sequence of individual droplets arriving at short intervals can thus be reliably detected. Duran filter glass for the upper partial layer 15 and so-called Millipore filter paper for the lower partial layer 16 are preferably suitable as materials for the individual partial layers 15 and 16 with different porosities. The pore sizes of the upper porous partial layer 15 can be between 0.01 and 0 , 02, the pore sizes of the lower porous sublayer 16 are between 0.005 and 0.01 mm. The comb structures described can advantageously be based on the known thin-film or Thick film technology can be produced.

When an ink droplet with a predetermined electrical conductivity strikes such a comb structure, the electrical resistance between the conductor tracks of the two comb parts changes suddenly. By removing the ink droplet by capillary suction of the liquid into the interior of the two layers, the resistance that can be measured between the comb parts 121 and 122, which are not galvanically connected, increases again in time, so that after one of the Porosity P1, P2 of the sub-layers 15 and 16 and, depending on the properties of the ink, a new suction time, for example a new ink drop ejected from another nozzle of the print head can be detected in the same way. With the dimensioning values given above, it is possible to reliably detect the impact of individual ink droplets at intervals of approximately 20 ms.

With the arrangement described above, in which the relationship T ≦ D exists between the division ratio T and the diameter D of an ink droplet, the impact of a single droplet can already be measured reliably. It is within the scope of the invention to provide a division ratio T which is greater than the diameter D of a single droplet (T> D). This makes it possible to reliably detect the arrival of a plurality of individual droplets ejected in quick succession from a nozzle of the writing head. If the individual ink droplets hit the electrode comb within a period of time before the liquid applied with a previously arrived ink droplet has been sucked off, the amount of liquid between two adjacent conductor tracks increases with each newly arriving ink droplet until the amount of liquid establishes an electrical connection between the two Produces conductor tracks. In this way it is possible that, for example, a significant abrupt change in resistance is only caused with the third droplet arriving. It is within the scope of the invention to adjust the porosity of the individual layers, which cause capillary suction of the ink liquid, accordingly. In practical terms, this means that with a division ratio T> D and a suction block consisting of several partial layers, the porosity of the individual partial layers is increased from top to bottom or the pore size of the individual layers is selected smaller, as was described in connection with FIG. 3.

In a second embodiment of the ink droplet sensor, the structures of the electrode comb arrangement are bifilar arranged conductor tracks designed, which has the advantage that the conductor tracks of the comb structure are electrically controllable and can be connected to each other, for example, during individual pauses in measurement. FIG. 4 shows an example of this.

The conductor tracks 181 and 191 of the two comb parts 123 and 124 are meandered here on the suction block 17. Its construction and the formation of the conductor tracks 181 and 191 can take place in the manner described with reference to FIG. 3. As before, the conductor tracks run parallel next to each other in the area where the ink droplets meet. In contrast to the previously described embodiment, the embodiment specified here offers the possibility of providing a second pair of connecting electrodes 23 and 24 in addition to the connecting electrodes 13 and 14 which lead to the outside and by means of which the conductor tracks 181 and 191 can be galvanically connected to one another. The connection electrodes 23 and 24 are not connected to one another for the duration of a measurement process, that is to say for the duration during which the impact of ink droplets is detected. The mode of operation of the detection for the impingement of ink droplets then takes place as described with reference to FIGS. 2 and 3. The connections 23 and 24 can now be connected to one another via a switch, not shown here, which is actuated in the measurement pauses, that is to say when no ink droplets are detected. It is thus possible to use the conductor tracks 181 and 191 for heating and thus for evaporating the ink droplets during the measurement pauses with the aid of a current source (not shown here) which can be connected to the connections 13 and 14. This has the advantage that in addition to the capillary action of the suction block, there is also liquid removal by evaporation.

A circuit arrangement is provided for evaluating the impact of ink droplets, which is associated with a sudden reduction in resistance in the course of the conductor tracks of the electrode comb, with each impact of an ink droplet emits the sensor signal SM. An embodiment of this is shown in FIG 5. The circuit shown there essentially consists of a voltage divider, which consists of a fixed resistor 30 and the variable measuring resistor 31. This represents the current resistance value between the conductor tracks 18 and 19 (FIG. 2) and 181, 191 (FIG. 4) of the electrode comb, ie the circuit shown is connected to the connection electrodes 13 and 14 of the electrode comb at this point. The tap between the resistors 30, 31 of the voltage divider is connected to the inputs of a comparator 32. This connection takes place in such a way that the voltage value Um which is established at the tap point of the voltage divider circuit 30.31 is fed as a respective instantaneous value via a resistor 39 directly to one input and via an integrating element 35.36 as a mean value Umm to the other input of the comparator 32. Another resistor 34 is used to generate a bias voltage at one of the two comparator inputs, which produces the interference voltage spacing necessary for the function of the comparator 32. A bistable circuit 37 connected downstream of the comparator 32 forms the sensor signal SM from the output signal of the comparator 32 for a subsequent printer control, which is no longer shown here. The circuit works as follows. If an ink droplet strikes the electrode comb due to an ejection of an ink droplet stimulated by the printer control in the print head, this is associated with a sudden reduction in resistance. The measuring resistor 31 thus becomes smaller, which leads to the instantaneous value Um briefly becoming smaller than the temporal mean value Umm. In the example according to FIG. 5, a brief level change from 1 to 0 occurs at the output of the comparator 32. This transition is temporarily stored in the bistable circuit 37 and further processed by the printer controller. After droplet detection, the bistable circuit 37 is reset via its reset input with the reset signal R and the sensor is thus activated for the impact and evaluation of a next ink droplet from another nozzle of the write head.

By monitoring the time period between the excitation for droplet ejection by the printer controller and the occurrence of the sensor signal, it is possible to check the functionality of the individual nozzles. If there is no sudden change in resistance after a certain period of time, which can be set depending on predetermined parameters, such as printer structure, flight time of the droplets, ink composition, etc., the printer controller recognizes that the excited nozzle is not working.

The circuit arrangement described works with direct current, i.e. the voltage divider circuit is connected between a positive voltage source and ground. When using certain ink liquids, this can lead to decomposition of the ink liquid especially when several ink droplets arriving in quick succession are necessary for the evaluation of ink droplets. In order to bring about a measurable reduction in resistance, the ink liquid in this case is exposed to a current flow for a period of t ≧ 100 ms, which can cause electrolytic changes. For example, the dye precipitates out of the solvent, which leads to solidification, which means that capillary suction is no longer possible.

According to one embodiment of the invention, this problem is solved in that the ink droplet sensor is operated with AC voltage. An exemplary embodiment of this is shown in FIG. 6.

The evaluation circuit shown there also has the voltage divider circuit, consisting of the fixed resistor 30 and a resistor 31 representing the current resistance value between the conductor tracks. However, the voltage divider circuit 30, 31 is here connected to an AC voltage generator 38. In addition, a demodulator 33 is connected between the dividing point of the voltage divider circuit 30, 31 and the comparator 32 and operates in the circuit configuration selected in FIG. 7 as a so-called peak value rectifier. A voltage value is therefore available at its output which corresponds to the corresponds to the current peak value of the voltage at the dividing point. This is fed directly to one input of the comparator 32 via the resistor 39 and to the other input via the integrator 35, 36 as an average over time. The comparison in the comparator 32, the reversal of the bistable circuit 37 and the output of the sensor signal SM in the printer control (not shown) then take place, as described with reference to FIG. 5.

7 shows a detailed circuit structure as an example of an embodiment for the evaluation circuit according to FIG. 6.

An embodiment of the construction of the sensor plate according to the invention is explained with reference to FIG 8. This example is based on an arrangement of the conductor tracks according to the example shown in FIG. 2. To produce the sensor plate 25, an electrically insulating carrier plate 26 is provided with a metal layer. This is preferably done by evaporating a glass plate with a thickness of 0.1 to 0.8 mm with a base metallization made of Ti, Cu.

A photoresist layer is applied to both sides of this. Subsequently, the pattern of the electrode comb structure desired later on the sensor plate 25 with the conductor tracks 18, 19 is generated on one side and this is galvanically reinforced to 10 ... 20 µm Ni. In a subsequent photo-technical step, the area of a spray window 28 is exposed on both sides, and after the base metallization has been etched off, the glass is etched away in this area, so that the conductor tracks 18, 19 span the now glass-free spray window 28. In addition, so-called contacting windows 27 are etched free in this glass etching process.

According to these measures, the sensor plate 25 can be produced with great utility and can be connected and contacted with the suction block in a simple manner. Details are described with reference to FIGS. 9 and 10.

The exemplary embodiment shown in FIG. 9 (in a top view) and FIG. 10 (in a sectional view) consists of only four different parts, namely a housing 29, the suction block 17, the sensor plate 25 and contact springs 42 arranged on both sides Non-conductive plastic injection-molded part housing 29 serves to accommodate these parts and is in turn fastened in the printer chassis 41 with the aid of the locking tongues 40 belonging to the housing. The surface quality of the suction block 17 consisting of electrically non-conductive, open-porous material, such as, for example, suction ceramic, filter glass or foam, is subject only to certain requirements with regard to the side facing the ink writing head 1. The flatness of this surface should be of the order of magnitude of the pore size of the porous suction block 17 in order to ensure that the flat sensor plate 25 is supported on it. As described with reference to FIG. 8, the sensor plate 25 has the comb parts 121, 122, the conductor tracks 18, 19, the spray window 28 and two contacting windows 27.

The mechanical assignment of the sensor plate 25 to the suction block 17, whose side provided with the conductor tracks 18, 19 faces the suction block 17, is done by the multifunctional contact springs 42 arranged on both sides. When the device is installed, the suction block 17 is inserted into the housing 29 and Subsequent placement of the sensor plate 25 on the suction block 17, these metal contact springs 42 are pressed into corresponding insertion openings 43 of the housing 29. The contact springs 42 have latching lugs 44 which securely snap into a recess 45 when inserted into the housing 29. This ensures that the three spring tongues 46 formed at one end of the contact springs 42 resiliently rest on the sensor plate 25. In the example, the two outer spring tongues 46 each press on the support of the sensor plate 25 and guarantee a gap-free support of the sensor plate 25 on the suction block 17. The middle spring tongue 46 in each case lies in the area of the contacting window 27, presses directly on the respective contact surface of the electrode comb structure 18, 19 and thus makes the electrical contact. The respective other end of the contact springs 42 forms the connection electrode 13 or 14. The electrical connection from the electrode comb structure to the electronic evaluation circuit, not shown here, is established via a connection designed as a flat connector 47 for standardized plug sleeves.

As described, the ink sprayed onto the conductor tracks 18, 19 is drawn capillary into the suction block 17. The absorbency of the suction block 17 depends on its suction volume and its material, on the ink and on the frequency of the spray test. In order to increase the suction volume and shorten the time for suction, an opening 48 can be provided in the housing of the device for an additional ink disposal, which is filled with a suction material of higher porosity than that of the suction block 17.

The impact of ink droplets, which is associated with a sudden reduction in resistance in the course of the conductor tracks of the electrode comb, is evaluated in a circuit arrangement (20 in FIG. 1) which emits the sensor signal SM with each impact of one or more ink droplets.

The height of the splash window 28 is adapted to the vertical distance of the outer nozzles of the ink writing head. The width of the spray window 28 depends on the horizontal extension of the nozzle exit area of the ink writing head. In the case of a single-row nozzle arrangement, only a narrow, in the case of multi-row, a correspondingly wider spray window 28 is required. It is also possible to orient the spatially separated nozzle rows one after the other towards the spray window 28. This is more advantageous since the spray test of the individual nozzles only takes place sequentially and not next to one another and a narrow spray window 28 is a narrow design of the device and thus allows for less overall widening of the printer chassis.

The arrangement shown in FIG. 11 for automatic operational security of the ink printer is controlled via the microprocessor-controlled central control ZS of the printing device. It controls via a microprocessor-controlled drive control AS designed in the usual way, the stepper motor 101 for the printer carriage drive 100 and the motor 106 for driving the cleaning and rinsing station. Furthermore, the evaluation circuit 20 described in connection with the ink droplet sensor 11, a display DS and a time control arrangement TS are connected to the central control. This time control arrangement TS is constructed in a conventional manner and detects the printing time of the ink printing device or makes it possible to enter freely selectable time periods after which a function test procedure which is stored in the memory area of the central control system ZS is called. The central control ZS of the printing device is connected to the data output via an interface IF, e.g. of a terminal in connection.

The arrangement for fully automatic operational security of the ink printing device now works as follows.

The ink print head 1 is in the rest position (interface II) FIG 11, FIG 13 at the left outer edge of the printing area before printing and the hose pump 113 is coupled to the motor 106 via the freewheel 117. The nozzle surface 2 of the ink print head 1 is closed by the lips 109 and 110. By rotating the motor shaft 115 in a clockwise direction, the nozzle exit surface of the ink head 1 is wiped or cleaned by means of the upper lip of the wiper lips 109 and the endless belt 107 is brought into the position according to FIG. 14, in which the free-spike region 111 faces the nozzle plate. In this position, by rotating the motor shaft 115 counterclockwise, the ink head nozzles can be rinsed by means of the hose pump 113, and this can also be used as a "STANDBY" position designated position can be used to spray the nozzles freely. The resulting amount of ink drips from the ink head 1 or from the endless belt 107 onto the collecting container 112 and is disposed of in this way. After a rinsing process, the wiping process can be repeated by means of the wiping lips 109 of the endless belt 107 by rotating the motor shaft 115 clockwise again.

The inkjet print head 1 is then driven by the carriage drive over a distance 130 (FIG. 11) into a spray control position (shown in broken lines in FIG. 11), where the individual nozzles are sequentially checked for their functionality.

Depending on the result of the evaluation in the central control ZS, printing operation is then either started on the printing paper to the right of position II-XIII or, if the spray test is not accepted, a new rinsing or wiping procedure is carried out in the STANDBY position and then tested again in the control position. Only after a freely definable number of repeat cycles with a negative spray test result does the ink printer go into the fault state. This fault condition of the printer is shown on the display DS and the printer operation is interrupted.

In normal operation with a positive spray test result, ink print head 1 will print.

By means of the time control TS running with the printer switched on, it is possible to insert free spraying and spraying control cycles into the printing operation after a freely selectable period of time in order to check the functionality of the ink head on all nozzles. If the result is negative, the procedure is as described.

Reference list

1

= Ink printhead

2nd

= Nozzle plate

3rd

= Outlet nozzles

4th

= Headboard

5

= Ink channels

6

= Drive elements

7

= Ink supply part

8th

= Ink supply

9

= Ink droplets

10th

= Distance

12.25

= Sensor plate

13,14,23,24

= Connection electrodes

15.16

= Partial layers

17th

= Suction block

18,19,181,191

= Conductor tracks

20th

= Evaluation circuit

121,122,123,124

= Comb parts

21

= Insulating film

26

= Carrier plate

27

= Contact window

28

= Splash window

29

= Housing

30th

= Fixed resistance

31

= Measuring resistor

32

= Comparator

33

= Demodulator

34.39

= Resistance

35.36

= Integrator

37

= bistable circuit

38

= AC voltage generator

40

= Locking tongues

41

= Printer chassis

42

= Contact element, contact spring

43

= Insertion opening

44

= Locking lugs

45

= Recess

46

= Spring tongues

47

= Flat connector

48

= Disposal opening

A

= Wide conductor track

B

= Distance conductor track

D

= Diameter of ink droplets

L

= Height, comb parts and conductor tracks

P1, P2

= Porosity of the partial layers

R

= Reset input

S1, S2

= Thickness

SM

= Sensor signal

T

= Division ratio

t

= Time

Around

= Voltage value, current

Umm

= Voltage value, averaged over time

100

= Printer carriage

101

= Stepper motor

102

= Guide rods

103

= Timing belt

105

= Cleaning and rinsing station

11

= Ink droplet sensor

106

= Electric motor

107

= Endless belt

108

= Roles

109

= Wiping lips

110

= Sealing lips

111

= Free spray area

112

= Collecting container

113

= Peristaltic pump

115

= Drive shaft

116

= first direction-dependent locking mechanism (clutch)

117

= second direction-dependent locking mechanism (clutch)

118

= Strap

119

= Toothing (coupling piece)

120

= Toothing peristaltic pump (coupling piece)

ZS

= Central control of the printing device

AS

= Drive control of the printing device

DS

= Display

TS

= Timing arrangement

IF

= Interface

130

= Distance (range of motion) between standby position and spray control position

Claims (12)

1. An arrangement for ascertaining the functioning capacity of an ink-jet printer comprising a carriage which bears an ink-jet printing head (1) and a device (11) for monitoring the ejection of droplets which possesses an ink droplet sensor which evaluates the impact of ink droplets, characterised in that in the zone of movement of the ink-jet printing head (1) there is arranged a device (105) for cleaning and closing the ink-jet printing head with a cleaning device with wiper lips (109) which, driven by a motor, sweep over the nozzle surface (2) of the ink-jet printing head (1) and a closing device (109, 110) which covers the nozzle surface (2) when necessary.
2. An arrangement as claimed in Claim 1, characterised in that the device (105) for cleaning and closing the ink-jet printing head (1) and the device (11) for monitoring the ejection of droplets are arranged outside of the printing zone at the periphery thereof.
3. An arrangement as claimed in Claim 1, characterised in that the device (105) for cleaning and closing the nozzle surface comprises a motor-driven, resilient endless band (107) which is guided along the nozzle surface (2), where the endless band (107) is guided at a distance in front of the nozzle surface (2) and possesses wiper lips (109) of wedge-shaped cross-section which are arranged on the endless band (109) so as to be resistant to rotation in such manner that during the operation of the endless band (107) they sweep over the nozzle surface at least with their front edge.
4. An arrangement as claimed in Claim 3, characterised in that the endless band (107) possesses a zone (111) which is free of wiper lips and which when required can be brought in front of the nozzle surface (2) as collector plate for the ink droplets for the free spraying through the nozzles.
5. An arrangement as claimed in Claim 4, characterised in that the endless band (2) comprises a recessed zone (109, 110) which, as a protection against drying up, can be brought in front of the nozzle surface in the manner of a protective hood and which is designed in such manner that a micro-climate which inhibits the drying out of the nozzle forms in the recessed zone.
6. An arrangement as claimed in Claim 1, characterised in that a common stationary motor (106) is provided both for the drive mechanism of the cleaning device (105) and for the drive mechanism of an ink pump (113), with first and second, direction-dependent locking mechanisms (116, 117) which are coupled to the motor (106) and the cleaning device (105) and ink pump (113) in such manner that the ink pump (113) is driven in a first direction of rotation of the motor (106) and the cleaning device (105) is driven in a second direction of rotation.
7. An arrangement as claimed in Claim 6, characterised in that the ink pump (113) is arranged on the printer carriage (100) and comprises a coupling device (120) which, when the printer carriage (100) is positioned in a cleaning position, couples the ink pump (105) to the motor (106).
8. An arrangement as claimed in Claim 1, characterised in that the device for monitoring the droplet ejection comprises a sensor plate (12, 25) with conductor paths structured in a comb-like formation and arranged in a specified division ratio (T), where an analysis circuit (20) detects and evaluates the change in resistance occurring between at least two adjacent conductor paths and that the ink liquid applied during a monitoring or measuring period is discharged from the sensor plate (12, 25) by capillary action.
9. An arrangement as claimed in Claim 1, characterised in that on its surface facing towards the outlet openings (3) the sensor plate (12, 25), which is arranged at a distance (10) in front of the outlet nozzles (3), has the form of an electrode comb, the conductor paths (18, 19; 181, 191) of which, which form the comb structure, possess a division ratio (T) governed by the breadth (A) of, and distance (B) between, the conductor paths (18, 19; 181, 191), that the sensor plate (12, 25) is adjoined by a suction block (17) which is formed by at least one, electrically non-conductive porous layer and which serves to discharge liquid, and that the analysis circuit (20) which is electrically connected to the conductor paths (18, 19; 181, 191) of the sensor plate (12, 25) evaluates the change in resistance between at least two adjacent conductor paths (18, 19; 181, 191) which occurs when at least one droplet strikes the surface of the electrode comb of the sensor plate (12, 25) and emits a sensor signal (SM).
10. An arrangement as claimed in Claim 9, characterised in that the electrode comb consists of two comb members (121, 122) and each comb member (121, 122) comprises a terminal electrode (13, 14) to which the analysis circuit (20) is connected, and that the conductor paths (18) of the first comb member (121) and the conductor paths (19) of the other comb member (122) extend in the manner of tongues into the impact zone of the droplets where they form the comb structure with the division ratio (T).
11. An arrangement as claimed in Claim 9, characterised in that the electrode comb is formed by conductor paths (181, 191) which are arranged in bifilar fashion and which extend in serpentine formation and in the impact zone of the droplets form the comb structure with the division ratio (T), and that the analysis circuit (20) can be connected to two respective terminals (13, 14) of the bifilar conductor paths (181, 191) and the two other terminals (23, 24) are not connected to one another.
12. An arrangement as claimed in Claim 11, characterised in that during the measuring pauses of the analysis circuit (20) a current source can be connected to two respective terminals (13, 14) of the bifilar conductor paths (181, 191) and the two other terminals (23, 24) are connected to one another in this case.

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