EP3147124A1 - Method for damping the pressure peaks in a circuit for ink of an ink jet printer - Google Patents

Abstract

A method according to the invention for damping pressure spikes in a line for ink of an ink jet printer, the line being connected to a chamber (16, 16) in which a membrane (11, 17) is arranged and which from the membrane into an air-filled first space and an ink-filled second space, and wherein the first space is connected to an air-filled buffer (12, 18) and the buffer is connected to an air pump (13), steps a to c include: a) pumping air into the first space until the chamber is depleted of ink and the membrane abuts a wall of the chamber or the tension of the membrane begins to increase substantially linearly, then b) pumping air from the first space until the chamber is filled with ink and the membrane applies to a wall of the chamber or the voltage of the diaphragm begins to rise substantially linearly, the number of pump cycles being determined, then c) pumping air into the first space, in the western half of the determined number of pump cycles is passed. It is also possible to reverse the order of steps a and b accordingly.

Description

The invention relates to a method for damping pressure peaks in a line for ink of an ink jet printer with the features of claim 1.

State of the art and task

When printing inkjet inks with one or more printheads, it is necessary to provide the printheads with the ink to be printed. For this purpose, usually reservoir, pumps and supply lines (or complex piping systems, so-called manifolds) are provided, wherein in so-called circulating systems, the ink is pumped from the reservoir to the printhead and unprinted ink from the printhead back into the reservoir. In this case, a so-called bypass in the ink supply line may be provided parallel to the print head. Circulating ink supplies are particularly useful when print quality and reliability requirements are high. The advantages of a circulating supply are, on the one hand, the ability to transport trapped air out of the area of the nozzles of the printhead and, on the other hand, to provide and maintain the desired temperature of the ink.

One of the main requirements of ink supply is that of the constancy of the so-called meniscus pressure. This is the pressure of the ink at the orifices of the nozzles of the printhead. This pressure is nominally generally slightly negative to the environment (e.g., between about -5 and about -10 mbar). To ensure this pressure, regulated pumps are often used for certain desired pressures.

The printheads for the different colors are usually connected to a manifold and are parallel to each other. This is usually a manifold for the called supply side and a manifold for the so-called return page provided (ink supply and ink removal). The respective pressure in a manifold is a controlled variable for a pump associated with the manifold. The target pressure in the return or supply manifolds is determined from the desired meniscus pressure, the breakdown of the print head internal resistances (the channels for the ink) and the hydrostatic height of the manifold above the meniscus level. For the calculation of the meniscus pressure, the pressure on the two manifolds can each be regarded as a potential that is divided by the head-internal resistances.

During printing, depending on the image content to be printed and the resulting ink consumption, modulation of the volume flow of the ink in the respective lines and the intra-head ink channels will result in pressure modulation. Since the above-mentioned control variables (the two pressures) are measured at the respective manifolds, these can not detect the pressure drops in the supply lines to the printheads and in particular within the heads.

In addition to these mentioned pressure drops, however, there is also a drop in pressure at the supply lines from the pumps to the manifolds, which is then detected by the pressure sensors but, as a rule, can not be regulated with the necessary bandwidth. The bandwidth results from the image information and the printing speed (i.e., ultimately from the ink consumption). For this reason, it is necessary to damp the pressure modulations on the manifold.

The US 8,042,902 B2 describes the determination of a liquid volume in a liquid chamber of a damper divided by a membrane into two parts. Preferably, this is half of the total volume of the damper, so that the membrane can oscillate within the damper, without applying to a wall of the damper housing. The determination of the volume is made by comparing pressure pulsations, which arise at the damper by the pulsation of liquid pumps. The determination takes place, wherein once the volume of a smaller air chamber behind the membrane is decoupled from a larger buffer volume and at another time the two volumes are coupled. The two measured Pulsation amplitudes can be converted in knowledge of the large volume of air in an air and thus also in a liquid volume in the damper. The described determination can be repeated in printing pauses in order to check the operating point of the membrane.

It is an object of the invention to provide a prior art improved method which makes it possible to reliably damp pressure spikes in a line for ink of an ink jet printer.

Solution of the task

This object is achieved by the method having the features of claim 1.

1. a) Pumpen von Luft in den ersten Raum bis die Kammer von Tinte befreit ist und sich die Membran an eine Wand der Kammer anlegt oder die Spannung der Membran im Wesentlichen linear zu steigen beginnt, danach
2. b) Pumpen von Luft aus dem ersten Raum bis die Kammer mit Tinte gefüllt ist und sich die Membran an eine Wand der Kammer anlegt oder die Spannung der Membran im Wesentlichen linear zu steigen beginnt, wobei die Anzahl der Pumpenzyklen ermittelt wird, danach
3. c) Pumpen von Luft in den ersten Raum, wobei im Westlichen die Hälfte der ermittelten Anzahl der Pumpenzyklen durchlaufen wird,
   oder die Schritte d bis f:
4. d) Pumpen von Luft aus dem ersten Raum bis die Kammer mit Tinte gefüllt ist und sich die Membran an eine Wand der Kammer anlegt oder die Spannung der Membran im Wesentlichen linear zu steigen beginnt, danach
5. e) Pumpen von Luft in den ersten Raum bis die Kammer von Tinte befreit ist und sich die Membran an eine Wand der Kammer anlegt oder die Spannung der Membran im Wesentlichen linear zu steigen beginnt, wobei die Anzahl der Pumpenzyklen ermittelt wird, danach
6. f) Pumpen von Luft aus dem ersten Raum, wobei im Westlichen die Hälfte der ermittelten Anzahl der Pumpenzyklen durchlaufen wird.

An inventive method for damping pressure spikes in a line for ink of an ink jet printer, wherein the conduit is connected to a chamber in which a membrane is arranged and which is separated from the membrane into an air-filled first space and an ink-filled second space, and wherein the first space is connected to an air-filled buffer and the buffer is connected to an air pump, comprising steps a to c:

1. a) pumping air into the first space until the chamber is depleted of ink and the membrane abuts a wall of the chamber or the tension of the membrane begins to increase substantially linearly thereafter
2. b) pumping air from the first space until the chamber is filled with ink and the diaphragm abuts a wall of the chamber or the voltage of the diaphragm begins to increase substantially linearly, the number of pump cycles being determined, thereafter
3. c) pumping air into the first room, in the western half of the determined number of pump cycles,
   or steps d to f:
4. d) pumping air from the first space until the chamber is filled with ink and the diaphragm abuts against a wall of the chamber or the tension of the diaphragm begins to increase substantially linearly thereafter
5. e) pumping air into the first space until the chamber is de-inked and the membrane abuts against a wall of the chamber or the voltage of the membrane begins to increase substantially linearly, the number of pump cycles being determined, thereafter
6. f) pumping air from the first room, in the western half of the determined number of pump cycles is passed.

The method according to the invention makes it possible to reliably damp pressure spikes in a line for ink of an inkjet printer.

The method according to the invention can comprise the further step: g) damping of pressure peaks with the membrane guided to its rest position after steps a to c or d to f.

A preferred embodiment of the invention can be characterized in that the air pressure - in the air pump, in the buffer, in the first room or in a three connecting line - is measured, preferably by means of a pressure sensor.

A preferred embodiment of the invention can be characterized in that step a) or step e) is terminated as soon as the measured air pressure begins to rise significantly, preferably substantially linearly.

A preferred embodiment of the invention may be characterized in that step b) or step d) is terminated as soon as the measured air pressure begins to fall significantly, preferably substantially linearly.

A preferred embodiment of the invention may be characterized in that a peristaltic pump is present as a pump and that the pump cycles are determined by counting the steps of the motor of the pump. The motor of the pump is preferably a stepper motor, wherein the individual steps may be shares of engine revolutions. The counted pump cycles may not be integer, eg rational. Alternatively, you can Also, a motor with timing disc or a motor with gear are used and a count of engine revolutions are performed.

A preferred embodiment of the invention can be characterized in that the pressure of the ink is kept constant.

The invention as such and structurally and / or functionally advantageous developments of the inventions are described below with reference to the accompanying drawings with reference to at least one preferred embodiment. In the drawings, corresponding elements are provided with the same reference numerals.

Figur 1:

eine schematische Darstellung eines Tintenversorgungssystems eines Tintenstrahldruckers bei der Durchführung des erfindungsgemäßen Verfahrens, und

Figur 2:

schematisch jeweils einen Ausschnitt aus Figur 1 in drei verschiedenen Zuständen während der Durchführung des erfindungsgemäßen Verfahrens.

The drawings show:

FIG. 1:

a schematic representation of an ink supply system of an ink jet printer in carrying out the method according to the invention, and

FIG. 2:

schematically each a section of FIG. 1 in three different states during the performance of the method according to the invention.

This in FIG. 1 shown ink supply system or the ink supply device 1 supplies a print head 2 with ink. Conventional printheads have in their interior a variety of smallest channels for the ink. These channels can be understood in a simplified way as flow resistors 2a and 2b. The ink for the print head is initially stored in an ink reservoir 3 and is conveyed from there via an ink line 4, in which a pump 5 is arranged, to the input side of the print head. In the ink conduit 4, a valve 6 is also provided, which can be opened and closed. On the output side, the print head is connected to the ink reservoir 3 via an ink line 7, in which a pump 8 is provided. Also in this return line, a valve 9 is provided, which can be opened and closed. The described constellation allows ink to circulate through the printhead allow unused ink to be pumped back into the ink reservoir. On the so-called supply side of the ink supply device there is also a line system 27 (a so-called manifold), which can form a complex line system and, for the sake of simplicity, is shown only schematically in the figure. On the so-called return side of the ink supply system, a line system or so-called manifold 28 may also be located. This too is simplified in the FIG. 1 shown.

In the two ink lines 4 and 7 or in the two Manifolds 27 and 28, pressure peaks may occur, which are damped by the measures described below. The pressure spikes may be undesirable fluctuations or modulations of the pressure of the ink liquid, for example pressure pulses originating from the pumps or pressure pulses resulting from the start or end of the printing process and the concomitant increased or decreased ink consumption.

The supply side (ink line 4 or Manifold 27) is connected via an ink line 15 with a chamber 10. The chamber 10 has a diaphragm 11 in its interior which divides the chamber into a first space 10a and a second space 10b. Preferably, the chamber is constructed symmetrically and arranged the membrane centrally. Correspondingly, the return side (ink line 7 or manifold 28) is connected to a chamber 16 via an ink line 20. Also in the chamber 16, a diaphragm 17 is provided which divides the interior of the chamber into a first space 16a and a second space 16b.

The respective second space 10b or 16b of the chamber 10 or 16, if the respective membrane 11 or 17 is in its rest position, filled with ink. The two opposite first spaces 10a and 16a, however, are filled with air, provided that the respective membrane is in its rest position. The supply of the first spaces 10a and 16a with air via an air pump 13. From this leads an air line 14 to a buffer 12 and from there to the first room 10a. Between the air pump 13 and the buffer 12, a valve 21 is provided, which is open and can be closed. Between the buffer 12 and the first space 10a, a pressure sensor 25 is provided. Accordingly, an air duct 19 leads via a buffer 18 to the first space 16a. Also in the air line 19, a valve 22, which can be opened and closed, and a pressure sensor 26 are provided.

With a view to FIG. 2 The following is shown: The illustration in the middle shows by way of example the chamber 10 with the two spaces 10a and 10b and the membrane 11 in its rest position. The membrane 11 is in the rest position when the same volume of air or ink is present on both sides of the membrane, that is to say in the first or second space 10a or 10b (if the chamber is symmetrical with respect to the two volumes constructed and the membrane is centrally mounted). The same applies to the chamber 16.

On the left side of the FIG. 2 on the other hand, the following situation is shown. The membrane 11 is deflected from its rest position and is within the chamber 10 at the wall 23 at. At this time, the volume of the second space 10b substantially completely disappears. Accordingly, on the right side of the FIG. 2 illustrated the opposite situation in which the membrane is so deflected from its rest position that the volume of the first chamber 10a substantially completely disappears. In this case, the membrane 11 applies to another wall 24 of the chamber 10. Instead of the walls 23 and 24, it would also be possible to provide stops within the chamber 10, against which the membrane 11 rests in its respective deflected position. The same applies to the chamber 16. The wall 23 or a corresponding stop are preferably constructed so that the ink is not shut off in the operating case by the membrane, ie continue to flow. For this purpose, the wall may preferably be a grid, wherein the membrane rests against the grid and the ink flows behind the grid. It can also be provided not to move the membrane to the respective wall, but only so far until the tension of the membrane begins to increase substantially linearly, for example because the membrane begins to stretch. The slope can be positive or negative. The moment of the transition from essentially constant tension to substantially linearly increasing tension of the diaphragm can be measured via a corresponding change in air pressure with the pressure sensors 25 or 26.

The course of the method according to the invention will now be described below, which can be carried out with the ink supply device described above.

The pressure fluctuations resulting from the modulation of the ink flow affect both the supply and the return side, ie both ink line 4 or manifold 27 and ink line 7 or manifold 28. Depending on the size of the two flow resistors 2a and 2b of FIG Printhead 2, the consumption of ink is composed of an increase in the supply current and a reduction in the return current. For this reason, it is advantageous to provide or to perform damping of possible pressure peaks on both manifolds 27, 28 (or damping means 10 and 16).

The respective damping on the supply or return side is achieved by the two chambers 10 and 16 or their use. The pressure of the ink in the respective second space 10b or 16b is substantially equal to the pressure of the ink in the associated manifold 27 and 28, respectively. However, a slight deviation of the pressure may result from the fact that the respective chamber 10 or 16 on a other height than the respective manifold 27 and 28 is arranged.

The first two spaces 10a and 16a are, as described above, filled with air and connected to a respective buffer 12 and 18, wherein the respective buffer determines the spring rate of acting as a damper chamber 10 and 16 respectively.

The respective membrane 11 or 17 is designed and arranged so that it builds around its rest position around no or only a very small residual stress, so that in the rest position only the air volume of the respective first space 10a and 16a together with the air volume the respectively associated buffer 12 or 18 is responsible for the respective spring rate of the damper on the supply or return side. The air volume in the respective associated air ducts is so small that this can be neglected.

The extreme case of ink flow modulation is the transition from unprinted area to full area at full print speed. In such a transition, the ink consumption increases abruptly by the ejection of ink drops. The required volumetric flow jumps to a maximum value within 10 to 20 milliseconds, which results in a sudden pressure drop in the ink liquid in the supply lines. The damper according to the invention is therefore designed so that the quantity of ink liquid consumed during the reaction time of a control circuit for the ink supply via the pump 5 (about 0.5 second) can be supplied from the second space 10b and / or 16b. By removing ink from the chamber 10 or 16 of the respective damper is to be achieved that the pressure of the ink liquid does not change substantially.

In the following an example of the dimensioning: Assuming a printing speed v of 1 m / s, a printing width b of 1 m, a resolution r of 20 μm and a mass of a pressure drop V of 4 pL, this results in a maximum volume flow at printing of 540 mL / min (v * b * V / r ² ). With a reaction time of the control loop of approx. 0.5 s, this results in a volume of 4.5 mL which the damper must be able to deliver without its diaphragm being deflected so far that it begins to stretch and the spring hardness of the damper thereby would increase suddenly. Assuming that the allowable pressure change due to the consumption of ink from the volume of the damper's ink is allowed to be approximately 5 mbar, the damper's volume of the ink is approximately 1 L (from the context p * V = constant).

So that now the diaphragm of the damper can perform a sufficiently large stroke without their internal stress increases significantly, the membrane must be placed in its central position or rest position and held as possible there, so they can swing freely on both sides.

However, the position of the membrane is generally indeterminate and in its rest position, there is only a balanced pressure balance on both sides of the membrane, that is the air pressure on one side of the membrane is equal to the operating pressure of the ink liquid on the other side of the membrane.

Since the direct measurement of the position of the membrane, for example by a sensor directly scanning the position of the sensor, is not readily possible, it is provided according to the invention to determine the rest position of the membrane as follows and to guide the membrane in this way in its rest position to be able to:

First of all, air is pumped into the first space 10a or 16a until the chamber 10 or 16 or its second space 10b or 16b is freed of ink and the membrane 11 or 17 abuts against the wall 23 of the chamber. The moment the membrane abuts the wall 23, the air pressure begins to increase linearly. This increase takes place according to a characteristic given by the volume of the buffer 12 or 18 and the volume of the first space 10a or 16a. Upon reaching an air pressure that can be measured with commercially available pressure sensors 25 and 26 sufficiently accurate and marks the increase, the pumping of air is terminated in the respective first room. Now, by switching the air pump 13, air is pumped out of the respective first chamber 10a or 16a of the chamber until the chamber or the respective second chamber 10b or 16b of the chamber is filled with ink and the membrane contacts a wall 24 of the chamber invests. Now the air pressure begins to sink in the direction of vacuum. The time of application of the membrane to the wall in turn can be easily determined by means of a pressure sensor 25 or 26, since the pressure then begins to decrease substantially linearly or first linearly. When pumping air from the first space, the number of pump cycles that occurs between the application of the membrane to the wall 23 and to the wall 24 is determined. For this purpose, for example, the steps or revolutions of a motor of the pump can be counted. Finally, air is again pumped into the first chamber 10a or 16a of the chamber 10 or 16, wherein substantially half of the previously determined number of pump cycles is passed through. This applies to the symmetrical construction of the chamber. If the volumes V1 and V2 of the two chambers of the chamber are in a ratio V1 / V2 <> 1 to each other, the number of pump cycles during refilling is adjusted accordingly.

In this way, the membrane can be easily brought into its rest position using existing pumps and using pressure sensors. The positioning of the diaphragm in its rest position is, as already described above, essential for a faultless operation of the damper in order to be able to reliably dampen pressure spikes in the ink conduit.

The operating pressure of the ink preferably remains during the process described above.

The described method may also be performed in a different order, first pumping air from the first space 10a or 16a and then pumping air back into the first space, with the membrane first against the wall 24 and then against the wall 23 applies. In the reverse process, air is eventually pumped out of the first space, with substantially half of the determined number of pump cycles being traversed.

Even after the membrane is once set or centered, i. is in its rest position, it may be necessary to perform a readjustment / recentering: e.g. a) because the temperatures have changed or b) because the ambient air pressure (weather) has changed. Case a is of minor importance because the device 1 is preferably located in a temperate environment. In case b, a permanent air pressure measurement can be provided. Changing the ambient air pressure by a certain predetermined value requires re-centering. For re-centering there are 2 options: either during a printing pause or during printing.

An alternative method can be carried out as follows: The pump 5 is controlled so that the membrane 11 is guided to the wall 24. At this time, the volume V1 of the first space 10a disappears. The buffer 12 (or its volume VP) is in the meantime connected to the atmosphere. Thereafter, the buffer is subjected to an air pressure pLuft, which is dimensioned so that the membrane 11 in its rest position is performed (for a given operating pressure p operation of the ink). The air pressure is calculated according to the formula pAuft = ((VP + V1) / VP) * pOperation.

LIST OF REFERENCE NUMBERS

1

Ink supply means

2

printhead

2a

resistance

2 B

resistance

3

Ink reservoir

4

Ink pipe (supply side)

5

pump

6

Valve

7

Ink line (return page)

8th

pump

9

Valve

10

chamber

10a

First room

10b

Second room

11

membrane

12

buffer

13

air pump

14

air line

15

ink line

16

chamber

16a

first room

16b

second room

17

membrane

18

buffer

19

air line

20

ink line

21

Valve

22

Valve

23

wall

24

wall

25

pressure sensor

26

pressure sensor

27

Line system (manifold)

28

Line system (manifold)

Claims (6)

A method for attenuating pressure spikes in a line for ink of an ink jet printer, wherein the conduit (4, 7, 27, 28) is connected to a chamber (10, 16) in which a membrane (11, 17) is arranged and which of the membrane is separated into an air-filled first space (10a, 16a) and an ink-filled second space (10b, 16b), and wherein the first space is provided with an air-filled buffer (12, 18) and the buffer with an air pump (13) is connected, with the steps a to c: a) pumping air into the first space until the chamber is depleted of ink and the membrane abuts a wall (23) of the chamber or the tension of the membrane begins to increase substantially linearly thereafter b) pumping air from the first space until the chamber is filled with ink and the diaphragm abuts a wall (24) of the chamber or the tension of the diaphragm begins to increase substantially linearly, the number of pump cycles being determined, thereafter c) pumping air into the first room, in the western half of the determined number of pump cycles, or with the steps d to f: d) pumping air from the first space until the chamber is filled with ink and the membrane abuts a wall (24) of the chamber or the tension of the membrane begins to increase substantially linearly thereafter e) pumping air into the first space until the chamber is depleted of ink and the membrane abuts a wall (23) of the chamber or the tension of the membrane begins to increase substantially linearly, the number of pump cycles being determined, thereafter f) pumping air from the first room, in the western half of the determined number of pump cycles is passed. Method according to claim 1,
characterized,
in that the air pressure - in the air pump, in the buffer, in the first space or in one of these three connecting lines (14, 19) - is measured, preferably by means of a pressure sensor (25, 26). Method according to claim 2,
characterized,
that step a) or step e) is terminated as soon as the measured air pressure begins to increase significantly, preferably substantially linearly. Method according to claim 2,
characterized,
that step b) or step d) is terminated as soon as the measured air pressure begins to fall significantly, preferably substantially linearly. Method according to one of the preceding claims,
characterized,
that a peristaltic pump (13) is provided as a pump and that the pump cycles are determined by counting the steps of the motor of the peristaltic pump. Method according to one of the preceding claims,
characterized,
that the pressure of the ink is kept constant.

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