Patent Application
20170225455
The present invention generally pertains to a method for controlling an inkjet print head in order to detect an operating state of an ejection unit having a nozzle.
A piezo actuated inkjet print head is well known in the art. Such an inkjet print head is commonly provided with a number of ejection units. Each of such ejection units comprises a pressure chamber and a fluidly connected nozzle. The pressure chamber may be filled with a liquid such as an ink and a droplet of the liquid may be expelled through the nozzle by application of a suitable pressure wave in the liquid in the pressure chamber by actuating a piezo actuator that is operatively coupled to the pressure chamber for generating such a pressure wave.
It is also known in the art that the ejection units are sensitive and may become malfunctioning due to a gas bubble, commonly an air bubble, entrapped in the nozzle or pressure chamber. Similarly, dirt or debris may enter the nozzle and cause malfunctioning. Other causes for malfunctioning include liquid residues around the nozzle, electrical failures, drying of the liquid in the nozzle resulting in increased viscosity and deposits of dissolved compounds of the liquid and many more.
When an ejection unit malfunctions, it means that a droplet is not formed correctly. Still after generating a pressure wave, either for droplet ejection or not, a residual pressure wave remains in the liquid and then slowly damps. Characteristic properties of such a residual pressure wave are known to provide detailed information on the cause of the malfunctioning. Therefore and as known, sensing and analyzing such a residual pressure wave may provide detailed information on an operating state of an ejection unit.
In particular, analysis of the residual pressure wave may include comparing the sensed residual pressure wave with a residual pressure wave reference. For example, a residual pressure wave detected from a well functioning ejection unit may be used to determine whether a sensed residual pressure wave corresponds to a well functioning ejection unit. Then, if from an analysis a significant difference between the sensed residual pressure wave and the residual pressure wave reference is derived, it may be concluded that the ejection unit is in a malfunctioning state.
A disadvantage of the above-described known analysis method is that the conditions during which the residual pressure wave is sensed need to be identical to the conditions under which the residual pressure wave reference has been detected. In the prior art, it is therefore known to sense a residual pressure wave when all other ejection units are not actuated, for example, as those other ejection units may cause cross-talk thereby disturbing the sensed residual pressure wave. For example and as a consequence, the detection of an operating state is commonly only performed when the print head is in a non-printing state. However, it is desirable to be able to detect an operating state of an ejection unit also when the print head is in a printing state. More in general, it is desirable to have more flexibility in conditions that are suitable for sensing and analyzing a residual pressure wave.
In an aspect of the present invention, a method for detecting an operating state of an ejection unit of an inkjet print head is provided. The inkjet print head comprises a first ejection unit and a second ejection unit and each ejection unit comprises a pressure chamber for holding an amount of liquid; an actuator operatively coupled to the pressure chamber, configured for generating a pressure wave in the amount of liquid; a sensor operatively coupled to the pressure chamber for sensing a residual pressure wave in the amount of liquid; and an orifice operatively coupled to the pressure chamber for ejecting a droplet of liquid upon generation of an ejecting pressure wave. The method comprises the steps of
In the method according to the present invention, there is a set of at least two residual pressure wave references provided. Each respective residual pressure wave reference corresponds to certain sensing conditions. In particular, one of the residual pressure wave references in the set may correspond to the operation condition wherein the second ejection unit is not actuated and another one may correspond to the condition wherein the second ejection unit is actuated, potentially causing cross-talk.
Having such a set of multiple residual pressure wave references available allows performing the residual pressure wave sensing under a corresponding set of sensing conditions. In an embodiment, such sensing conditions are known when performing the actual residual pressure wave sensing. Therefore, in such embodiment, the method according to the present invention provides a step of determining whether a pressure wave—residual or not—is present in another ejection unit. Based on this determination, it is enabled to select a residual pressure wave reference from the set corresponding to the actual sensing conditions. Then, having selected a suitable residual pressure wave reference, a suitable and accurate analysis is enabled.
In another embodiment, the residual pressure wave is compared with each residual pressure wave reference. In such embodiment, the actual sensing conditions do not have to be known a priori. If the residual pressure wave corresponds to any one of the residual pressure wave references, it may be concluded that the ejection unit is in an operative state. Moreover, it may be determined under which sensing conditions the residual pressure wave sensing has been performed.
The above two embodiments may even be combined into a further embodiment. In such embodiment, the conditions during sensing are known and the residual pressure wave is compared to each residual pressure wave references. If the residual pressure wave does not correspond to the residual pressure wave reference of the known sensing conditions, but the residual pressure wave does correspond to another residual pressure wave reference, it may be suspected or concluded that the second ejection unit is not operating correctly.
For obtaining the set of residual pressure wave references, it is noted that a single ejection unit may be probed and its residual pressure wave may be used as a residual pressure wave reference, taking into account the relevant sensing conditions. This requires strict knowledge on the actual status of the ejection unit to prevent that a residual pressure wave reference is based on a mal-functioning ejection unit. Therefore, in such embodiment, the residual pressure wave references are usually predetermined under controlled conditions. However, the operating conditions may change over time, e.g. due to aging of piezo-electric material. In another embodiment, a relatively large number of ejection units may be probed for their residual pressure waves (all having a same relevant condition in accordance with the present invention) and an average of those residual pressure waves may be used as a residual pressure wave reference. In a particular embodiment, a statistical analysis may be used to remove inappropriate residual pressure waves such as those resulting from mal-functioning ejection units, before averaging. Such a method may be performed regularly in a calibration procedure, not requiring specific controlled conditions, while ensuring that the residual pressure wave reference corresponds to the actual conditions.
It is noted that, as used herein, comparing a residual pressure wave and a residual pressure wave reference may be a simple determination of a difference between the two, but it may additionally or alternatively include complex computations and/or a comparison of certain properties, such as frequency, amplitude, phase shifts and the like. The person skilled in the art will readily understand that, in the latter case, the residual pressure wave reference may be a set of properties instead of a fluctuating signal corresponding to an actual residual pressure wave. So, in general, the present invention is not to be limited to any kind of analysis of the sensed residual pressure wave relative to a residual pressure wave reference.
In a practical embodiment of the method according to the present invention, the pressure chamber of the second ejection unit is adjacent to the pressure chamber of the first ejection unit. It has appeared from technical experiments that a cross-talk contribution from pressure generation in pressure chambers that are not adjacent to the ejection unit subjected to an operating state detection method may have such a limited cross-talk contribution, that those may be ignored. Thus, only a cross-talk contribution from an adjacent pressure chamber needs to be taken into account.
In an embodiment, each ejection unit comprises a piezo-electric element, the piezo-electric element having a piezo-electric layer, a first electrode arranged on a first side of the piezo-electric layer and a second electrode arranged on a second side opposite to the first side. The piezo-electric element is configured to function as the actuator when a driving voltage is applied over the first and second electrodes and to function as the sensor when no driving voltage is applied. Upon application of a driving voltage over the electrodes the electric field induces a mechanical deformation of the piezo-electric element, which deformation may be employed to generate the pressure wave in the liquid in the pressure chamber. On the other hand, when no driving voltage is applied, a residual pressure wave in the liquid may mechanically deform the piezo-electric element. As a consequence, a voltage is generated over the electrodes. Sensing this voltage provides a sensing signal corresponding to the residual pressure wave. Thus, such a piezo-electric element may be advantageously employed as both the actuator and the sensor.
The method according to the present invention allows performing the operating state detection also when the print head is printing. For example, in an embodiment, the method may be performed while an image is printed by image-wise ejection of droplets from the inkjet print head, wherein step c) comprises determining the presence of a pressure wave in the second ejection unit based on print data, the print data indicating when an ejection unit is to eject a droplet. Commonly, print data is supplied to a print head indicating which ejection unit needs to expel a droplet and when. Thus, while print head and recording medium, e.g. paper, are controlled to move relative to each other, droplets are expelled with such a timing that the droplets land on the recording medium at a desired position. Thus, an image may be formed on the recording medium.
Detecting an operating state of an ejection unit may be performed based on a residual pressure wave that remains directly after a droplet is expelled after generating an ejecting pressure wave. Similarly, the detection may be performed based on a residual pressure wave that is deliberately generated by generating a non-ejecting pressure wave, i.e. a pressure wave that does not result in a droplet being expelled. Of course, in accordance with the present invention, separate residual pressure wave references may be provided for the potentially different residual pressure waves. Still, and regardless of the method of generating the residual pressure wave, the print data may be used to determine whether a pressure wave is generated in other ejection units, such as in an adjacent ejection unit. Thus, it is enabled to easily and quickly determine which residual pressure wave reference could be used for the subsequent analysis of the sensed residual pressure wave.
In an embodiment, the print data may be provided with state detection data. Thus, the print data will not only indicate when an ejection unit should expel a droplet based on image data, but the print data will also indicate when the operating state of the ejection unit is to be detected based on the state detection data. In this embodiment, for example based on the image data, it may be determined prior to starting a print job when an ejection unit may be probed for its operating state without affecting the resulting image. In a particular embodiment, the state detection data may indicate whether the detection is to be based on an ejecting pressure wave or on a non-ejecting pressure wave (as above elucidated). Additionally or alternatively, the state detection data may include data about the generation of a pressure wave in other ejection units at the time of the state detection of the ejection unit (for example the print data relating to those other ejection units corresponding to the timing of the state detection of the first ejection unit), such as an adjacent ejection unit. Even further, to reduce computations during printing, the state detection data may include a reference parameter indicating which residual pressure wave reference to use or the state detection data may even include the residual pressure wave reference itself. Thus, certain steps of the method according to the present invention may, in such an embodiment, be performed before the print job is actually started.
It is noted that, as used herein, a residual pressure wave reference relates to an operative state of the ejection unit. From the prior art, it is known to derive a cause for a malfunctioning nozzle from the residual pressure wave by comparison with a number of residual pressure wave references corresponding to certain causes such as the presence of an air bubble, dirt, or an electrical failure, for example. These prior art residual pressure wave references do not consider the conditions applicable to the time at which the residual pressure wave is sensed, as suitable conditions were ensured before sensing, usually ensuring that no pressure wave is present in nearby other ejection units.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating embodiments of the invention, are given by way of illustration only, since various changes and modifications within the scope of the invention will become apparent to those skilled in the art from this detailed description.
The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying schematical drawings which are given by way of illustration only, and thus are not limitative of the present invention, and wherein:
The present invention will now be described with reference to the accompanying drawings, wherein the same reference numerals have been used to identify the same or similar elements throughout the several views.
Images are printed on a image receiving member, for example paper, supplied by a roll 28, 30. The roll 28 is supported on the roll support R1, while the roll 30 is supported on the roll support R2. Alternatively, cut sheet image receiving members may be used instead of rolls 28, 30 of image receiving member. Printed sheets of the image receiving member, cut off from the roll 28, 30, are deposited in the delivery tray 32.
Each one of the marking materials for use in the printing assembly are stored in four containers 20 arranged in fluid connection with the respective print heads for supplying marking material to said print heads.
The local user interface unit 24 is integrated to the print engine and may comprise a display unit and a control panel. Alternatively, the control panel may be integrated in the display unit, for example in the form of a touch-screen control panel. The local user interface unit 24 is connected to a control unit 34 placed inside the printing apparatus 36. The control unit 34, for example a computer, comprises a processor adapted to issue commands to the print engine, for example for controlling the print process. The image forming apparatus 36 may optionally be connected to a network N. The connection to the network N is diagrammatically shown in the form of a cable 22, but nevertheless, the connection could be wireless. The image forming apparatus 36 may receive printing jobs via the network. Further, optionally, the controller of the printer may be provided with a USB port, so printing jobs may be sent to the printer via this USB port.
The image receiving member 2 may be a medium in web or in sheet form and may be composed of e.g. paper, cardboard, label stock, coated paper, plastic or textile. Alternatively, the image receiving member 2 may also be an intermediate member, endless or not. Examples of endless members, which may be moved cyclically, are a belt or a drum. The image receiving member 2 is moved in the sub-scanning direction A by the platen 1 along four print heads 4a-4d provided with a fluid marking material.
A scanning print carriage 5 carries the four print heads 4a-4d and may be moved in reciprocation in the main scanning direction B parallel to the platen 1, such as to enable scanning of the image receiving member 2 in the main scanning direction B. Only four print heads 4a-4d are depicted for demonstrating the invention. In practice an arbitrary number of print heads may be employed. In any case, at least one print head 4a-4d per color of marking material is placed on the scanning print carriage 5. For example, for a black-and-white printer, at least one print head 4a-4d, usually containing black marking material is present. Alternatively, a black-and-white printer may comprise a white marking material, which is to be applied on a black image-receiving member 2. For a full-color printer, containing multiple colors, at least one print head 4a-4d for each of the colors, usually black, cyan, magenta and yellow is present. Often, in a full-color printer, black marking material is used more frequently in comparison to differently colored marking material. Therefore, more print heads 4a-4d containing black marking material may be provided on the scanning print carriage 5 compared to print heads 4a-4d containing marking material in any of the other colors. Alternatively, the print head 4a-4d containing black marking material may be larger than any of the print heads 4a-4d, containing a differently colored marking material.
The carriage 5 is guided by guiding means 6, 7. These guiding means 6, 7 may be rods as depicted in
Each print head 4a-4d comprises an orifice surface 9 having at least one orifice 8, in fluid communication with a pressure chamber containing fluid marking material provided in the print head 4a-4d. On the orifice surface 9, a number of orifices 8 is arranged in a single linear array parallel to the sub-scanning direction A. Eight orifices 8 per print head 4a-4d are depicted in
Upon ejection of the marking material, some marking material may be spilled and stay on the orifice surface 9 of the print head 4a-4d. The ink present on the orifice surface 9, may negatively influence the ejection of droplets and the placement of these droplets on the image receiving member 2. Therefore, it may be advantageous to remove excess of ink from the orifice surface 9. The excess of ink may be removed for example by wiping with a wiper and/or by application of a suitable anti-wetting property of the surface, e.g. provided by a coating.
For use with the present invention, the print heads 4a-4d has a number of ejection units, each ejection unit corresponding to one of the orifices 8. An ejection unit comprises a pressure chamber in which a pressure wave may be generated, e.g. by suitably driving a piezo-electric element associated with the ejection unit. The pressure wave may be such that a droplet of marking material is expelled through the corresponding orifice or the pressure wave may be such that no droplet is expelled. The latter is commonly known for vibrating a meniscus of the marking material, for example.
Likewise, a non-expelling pressure wave is known for use with an acoustic sensing method for detecting an operating state of the ejection unit. For example, if an air bubble is entrained in the pressure chamber of the ejection unit, the acoustics in the pressure chamber are different compared to the situation where no air bubble is present. As a consequence, a generated pressure wave will be different, too. Detecting and analyzing the pressure wave, which is referred to herein as the residual pressure wave, allows determining an operating state of the ejection unit. This method is known in the prior art and to the skilled person. Therefore, this method is not further elucidated herein.
A first residual pressure wave A (‘no neighbors’) relates to a condition wherein none of any adjacent ejection units is actuated; a second residual pressure wave B (‘one neighbor’) relates to a condition wherein one adjacent ejection unit is actuated; and a third residual pressure wave C (‘two neighbors’) relates to a condition wherein two adjacent ejection units (one on each side of the probed ejection unit) are actuated. Note that actuating an ejection unit, i.e. generating a pressure wave in the pressure chamber, usually affects any adjacent pressure chamber due to mechanical and/or acoustic cross-talk, thus resulting in a pressure wave in the adjacent pressure chamber. If an ejection unit is probed for determining the residual pressure wave, while an adjacent ejection unit is actuated, for example for expelling a droplet, the resulting residual pressure wave will likewise be affected. Indeed, as apparent from
In order to enable determining an operating state of an ejection unit, while adjacent ejection units are actuated simultaneously, the present invention provides not only a residual pressure wave reference for the condition wherein none of the adjacent ejection units is actuated. Instead, for a number of conditions affecting the residual pressure wave, a corresponding residual pressure wave may be provided. Herein, as an exemplary embodiment, there are three residual pressure wave references corresponding to the first, second and third residual pressure waves A, B, C as presented in
The present invention thus enables to probe ejection units during a print job as the actuation of adjacent ejection units is not limiting the probing.
The print data illustrated in
After probing and detection of the residual pressure wave, a residual pressure wave reference may be selected based on the print data of the adjacent ejection units. For that purpose, referring to
So, based on the table as shown in
In a particular example, the ejection unit having nozzle number ‘6’ (
Using these multiple numbers for state detection data enables selecting the relevant residual pressure wave reference before starting printing. Thus, the controlling means of the print heads are relieved from selecting the residual pressure wave reference during printing and thus less computing power is required during printing, which may allow a simpler or more cost-effective controlling means.
Whether the state detection data is a number ‘2’, ‘3’ or ‘4’ is dependent on the image data (‘0’ or ‘1’) of the adjacent ejection units. An exemplary process of selecting such state detection data is illustrated by
Then, for the selected image data, the image data of their adjacent cells is assessed and a suitable residual pressure wave reference in accordance with
Based on the outcome of the second step S12, a suitable residual pressure wave reference is selected (S13) and an actual residual pressure wave is collected (S14). Based on a comparison of the selected residual pressure wave reference (S15), an operating state of the ejection unit is determined (S16).
In the embodiment of
Thus, it will be determined that the probed ejection unit is not in a good operating state, while in fact the adjacent ejection unit is not operating correctly. So, the method according to
In another embodiment, which is illustrated in
In an additional/optional further step (S25) the residual pressure wave reference is used to trace what the actuation state of the adjacent ejection units was at the time that the relevant ejection unit was probed, e.g. based on the table of
Detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention, which can be embodied in various forms. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present invention in virtually any appropriately detailed structure. In particular, features presented and described in separate dependent claims may be applied in combination and any advantageous combination of such claims are herewith disclosed.
Further, the terms and phrases used herein are not intended to be limiting; but rather, to provide an understandable description of the invention. The terms “a” or “an”, as used herein, are defined as one or more than one. The term plurality, as used herein, is defined as two or more than two. The term another, as used herein, is defined as at least a second or more. The terms including and/or having, as used herein, are defined as comprising (i.e., open language). The term coupled, as used herein, is defined as connected, although not necessarily directly.
The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 14191021.6 | Oct 2014 | EP | regional |
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/EP2015/075059 | Oct 2015 | US |
| Child | 15493960 | US |
