WO2006067704A1

WO2006067704A1 - Method for determining a constitution of a fluid that is present inside a dosing device

Info

Publication number: WO2006067704A1
Application number: PCT/IB2005/054269
Authority: WO
Inventors: Johan F. Dijksman; Paulus C. Duineveld; Adrianus C. Van Kasteren; Mark T. Meuwese; Maria Van Wely-Dieleman; Alexander J. E. Raaymakers
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2004-12-21
Filing date: 2005-12-15
Publication date: 2006-06-29
Also published as: TW200635786A

Abstract

A characteristic of a resonance behaviour of a pump of a piezo-jet printing head, filled with a fluid, is measured and compared to a pre-determined characteristic. In case the printing head is filled with ink and is involved in a printing process, a moment when a cleaning process of the print head needs to be started is determined by continuously checking whether the measured characteristic is close enough to a pre-determined characteristic of a resonance behaviour associated with an ideal performance of the pump, or not. During a cleaning process, the ink gets replaced by a cleaning fluid, and a moment at which all ink is removed from the print head is determined by checking whether the measured characteristic has come close enough to a pre-determined characteristic of a resonance behaviour of the pump filled with the cleaning fluid only, or not.

Description

Method for determining a constitution of a fluid that is present inside a dosing device

The present invention relates in general to a method for determining a constitution of a fluid that is present inside a dosing device for dosing and emitting droplets of the fluid, which dosing device comprises at least one pump having an inlet for taking in the fluid, a pump chamber for containing the fluid and an outlet for letting out the fluid, and an actuator for generating actuation pulses acting on the fluid in the pump.

A dosing device as mentioned in the preceding paragraph may comprise a print head of an ink-jet printer, or a dispenser for biological fluids, for example. In the following, the present invention will be described in the context of ink-jet printing, which does not alter the fact that the invention is just as well applicable in other technical fields. Printing is a well-known technique for laying down a layer of material on a receiving device consisting of paper, glass, plastic, or another suitable material or mixture of materials. Ink-jet printing is a type of printing technique that involves forming the layer of material on the receiving device by spraying a printing fluid on the receiving device.

For the purpose of carrying out the ink-jet printing technique, ink-jet printers have been developed. These printers comprise a print head in which a large number of miniature valveless pumps are integrated. Each pump is associated with an actuator for influencing the pressure of the printing fluid in the pump. When the actuator is actuated, the pressure in the pump is increased, as a result of which the pump emits a specified amount of printing fluid as one or more droplets, wherein the droplets are given a specified flight direction, speed and size. As the actuators associated with the various pumps may be controlled individually, it is possible to exactly determine when a pump needs to fire a droplet and when the same pump needs to retain the printing fluid on the basis of the characteristics of a desired printing pattern on the receiving device.

The concept of firing and retaining droplets of printing fluid according to a predetermined schedule is often referred to as drop-on-demand (DOD). One type of print head commonly used in processes of DOD ink-jet printing is a so-called piezo-jet print head. In a piezo-jet print head, each pump has its own piezo-electric actuator. When charged, the actuator deforms, causing a pressure rise in the pump that leads to droplet emission. Thus, by controlling the actuators of the pumps in an accurate manner, it is possible to obtain an accurate printing pattern on the receiving device.

DOD ink-jet printing proves to be an enabling technology for the manufacturing of displays comprising a large number of light emitting diodes, which displays are commonly referred to as PoIyLED displays. Each light emitting diode (commonly referred to as LED) comprises a stack of individual layers. A number of these layers is formed by dosing the material of these layers dissolved in a solvent in a pixel, wherein a pixel is a limited area having predetermined dimensions.

The method described above for manufacturing PoIyLED displays can be used for other purposes, such as printing of colour filters for Liquid Crystal Displays and of receptor substrates in biosensors, in a similar manner.

During the manufacturing process of PoIyLED displays, rapidly drying printing fluids are applied, wherein it is important that the print head is cleaned from time to time. The cleaning process involves flushing a pure solvent through the print head. Alternating the printing process with the cleaning process as such does not constitute a problem, but the fact that the printing fluids may be expensive leads to a requirement of avoiding a possible waste of printing fluids. For the purpose of determining whether a certain printing fluid is exclusively present in the pumps of the print head or not, there is a need for a method that is suitable to be applied for determining the constitution of the fluid that is present inside the pumps.

According to the present invention, a method for determining a constitution of a fluid that is present inside a dosing device for dosing and emitting droplets of the fluid, which dosing device comprises at least one pump having an inlet for taking in the fluid, a pump chamber for containing the fluid and an outlet for letting out the fluid, and an actuator for generating actuation pulses acting on the fluid in the pump, comprises the following steps: mechanically actuating the dosing device in order to obtain a vibration of the device; measuring a characteristics of the damped vibration of the pump of the device by means of the actuator of the pump; and comparing the measured characteristics to at least one of a series of predetermined characteristics related to possible constitutions of the fluid.

When the method according to the present invention is applied, the constitution of the fluid in the pumps of the print head is determined by mechanically actuating the print head, measuring a characteristic of the vibration of at least one pump, which follows from actuating the print head, and comparing the measured characteristic to at least one of a series of pre-determined characteristics related to possible constitutions of the fluid. For the purpose of measuring a characteristic of the vibration of the at least one pump, the piezo-electric actuator associated with the pump is applied. The vibration of the pump results in a deformation of the piezo-electric actuator, whereupon the actuator, now acting as a sensor, generates an electric signal, which is indicative of the constitution of the fluid present inside the pump.

In a preferred way of carrying out the method according to the present invention, the viscosity of the fluid in the print head is taken as a measure of the constitution of the fluid. In general, in most cases, the viscosity of fluids changes when the constitution of fluids changes. For example, in the case of a printing fluid for printing a layer of a LED of a PoIyLED display and a cleaning fluid for cleaning the print head, the viscosities of the various fluids are totally different, wherein the viscosity of the cleaning fluid is significantly lower than the viscosity of the printing fluid.

Based on the insight that the nature of a spectrum in the frequency domain of a vibration of a pump of the print head is strongly influenced by the viscosity of the fluid in the pump, and the electric output of the associated piezo-electric actuator is indicative of such a spectrum, it is a practical possibility to use the electric output of the piezo-electric actuator for the purpose of determining whether the viscosity of the fluid in the pump corresponds to a pre-determined viscosity, for example the viscosity of the printing fluid, or not. In such case, it is important that at an earlier stage, tests have been performed in order to determine the electric output of the piezo-electric actuator in case the pump is completely filled with a fluid having the pre-determined viscosity. Another feasible possibility is that a rate at which damping of the vibration of the pump takes place is determined on the basis of a change of the electric output of the associated piezo-electric actuator over time. This rate is also closely related to the viscosity of the fluid, so when the rate associated with a fluid having a pre-determined viscosity is known, it is possible to determine whether an actual rate matches the rate associated with the fluid having the pre-determined viscosity, or not.

The method according to the present invention for determining a constitution of a fluid that is present inside the pumps of a dosing device is not only applicable in cases in which one fluid is replaced by another fluid. For example, this method is also applicable in cases in which it is unknown which fluid is present inside the pumps of a dosing device, and in which it is necessary to identify the fluid before the dosing device is activated to emit droplets of the fluid. Such cases may arise in the field of dispensers filled with a biological fluid. In order to identify the fluid, the dosing device is mechanically actuated, a characteristic of the obtained vibration of at least one pump of the dosing device is measured, and the measured characteristic is compared to a number of pre-determined characteristics, wherein each pre-determined characteristic represents another fluid. When a match between the measured characteristic and one of the pre-determined characteristics is found, it is concluded that the fluid that is present inside the pump of the dosing device is the fluid represented by the matching pre-determined characteristic. It is also possible to use the method according to the present invention for the purpose of determining the state of a fluid that is present inside the pumps of a dosing device. For example, in the case of ink-jet printing of layers of LEDs for the purpose of manufacturing a PoIyLED display, it is important to monitor the state of the printing fluid in the applied print head, so that a right moment for cleaning the print head may be determined. Changes in the state of the printing fluid lead to changes in the characteristics of a vibration of pumps of the print head, which is caused when the print head is mechanically actuated. Only in case a characteristic of the vibration of at least one pump, which is represented by output of the piezo-electric actuator associated with the pump, is outside of a range of allowable values, it is concluded that the print head needs to be cleaned. The printing process may be continued if the measured characteristic of the vibration of the pump is inside the range of allowable values.

Using common frequency measurement techniques, measuring a characteristic of a vibration of a pump of the dosing device does not require much time. The measuring process may be performed so fast, that it is possible to incorporate the measuring process in a printing process, without influencing the speed of the printing process. In such case, a combined process is obtained, in which the process of controlling the pumps of the print head to fire droplets is alternated with the process of checking the state of the printing fluid.

It is noted that a method for determining the viscosity of fluid is known from

US 6 044 694. This known method involves the use of piezo-electric benders in vessels containing fluids, wherein the fluids are intended to be used for the purpose of ink-jet printing, and wherein the vessels are connected to a print head. When the known method is carried out, the piezoelectric benders are driven at a voltage and a frequency which cause the benders to resonate. By monitoring an output voltage of the benders, it is possible to monitor changes in the viscosity of a liquid.

An important difference between the method according to the present invention and the known method is that in the method according to the present invention, the measurements are conducted in the print head itself, wherein the print head is mechanically actuated, and wherein the piezo-elements for sensing characteristics of the obtained vibration of the print head are the same piezo-elements which cause the print head to emit ink droplets, whereas in the known method, the measurements are conducted outside of the print head, namely inside printing fluid vessels, while using separate piezo-electric benders, which are electrically driven such as to resonate.

In particular, the present invention relates to a method for determining a point in time at which a first fluid is completely removed from a dosing device for dosing and emitting droplets of fluids, which dosing device comprises at least one pump having an inlet for taking in a fluid, a pump chamber for containing the fluid and an outlet for letting out the fluid, in case a second fluid is supplied to the dosing device in order to replace the first fluid. Replacing one fluid by another is a complicated process. The main part of the fluid, the core, is effectively replaced. The fluid along the inside walls of the pump is almost stagnant, and can only be removed by diffusion, in principle a slow process.

The method according to the present invention is applicable in various situations, for example in a situation in which cleaning fluid in a piezo-jet print head gets replaced by printing fluid in order to resume a printing process after a cleaning process has taken place. In case the print head is used in a process of printing layers of LEDs of a

PoIyLED display, it is desirable to know the moment when the cleaning fluid is completely flushed away, given the fact that the printing fluid may be expensive, in order to determine the exact moment when the cleaning process may be stopped and the printing process may be started. According to the present invention, this moment can be determined by means of a method comprising the following steps: actuating the dosing device in order to obtain a vibration of the device; measuring a characteristic of the vibration of the pump of the device; and determining whether a value of the measured characteristic is inside a predetermined range of values related to a presence of only the second fluid in the pump. When the method is applied to the above-sketched situation of the piezo-jet print head in which a cleaning fluid is replaced by a printing fluid, the print head is actuated, so that a vibration of the print head and the pumps of the pump head is obtained. A characteristic of the vibration of at least one pump, for example a spectrum in the frequency domain or a rate at which damping of the vibration takes place is measured, after which a value of the measured characteristic is compared to a range of values related to the presence of only the printing fluid in the pump. In case it appears that the measured value is outside of the range, it is concluded that cleaning fluid is still present in the print head. However, in case it appears that the measured value is inside the range, it is concluded that the print head contains only printing fluid, and that the printing process may be resumed.

The present invention is based on the insight that characteristics of a vibration of a pump of a dosing device for dosing and emitting droplets of fluids are closely related to characteristics of the fluid present inside the pump, in particular to the viscosity of the fluid. When the method according to the invention is applied to monitor the content of a dosing device when a first fluid gets replaces by a second fluid, the moment when the first fluid is completely replaced by the second fluid is determined in a convenient manner. All that is needed to find this moment, is a process of causing the dosing device to vibrate, measuring at least one characteristic of the vibration of at least one pump of the device, and checking whether a value of the measured characteristic is inside a range of values associated with the presence of only the second fluid in the pump, which process is continued until the measured value is inside the range of values, indeed. Naturally, the range of values needs to be known before the process is started. This range of values is normally defined on the basis of the results of tests performed on the dosing device when it is filled with no other fluid than the second fluid.

The present invention will now be explained in greater detail with reference to the figures, in which similar parts are indicated by the same reference signs, and in which:

Fig. 1 diagrammatically shows a sectional view of a portion of a piezo-jet print head;

Fig. 2 diagrammatically shows a single pump of the print head shown in figure

1;

Fig. 3 is a flowchart showing a series of steps which are followed in a process of determining when the print head needs to be cleaned; Fig. 4 is a flowchart showing a series of steps which are followed in a process of determining when a printing fluid is completely removed from the print head; and

Fig. 5 diagrammatically shows a device which is suitable for carrying out both the series of steps as shown in the flowchart of figure 3 and the series of steps as shown in the flowchart of figure 4.

Figure 1 shows a portion of a piezo-electrically driven print head 1. The print head 1 may be provided with one or more rows of ink jet pumps 10. In figure 2, a detailed view of one ink j et pump 10 is given.

The pump 10 comprises a pump chamber 11 for containing printing fluid that will hereinafter also be referred to as ink. At one end of the pump chamber 11, which is referred to as outlet end, a nozzle 12 is provided, which extends between the pump chamber 11 and a nozzle front 13 of the print head 1. A diameter of the nozzle 12 is substantially smaller than a diameter of the pump chamber 11. At another end, which is referred to as inlet end, the pump chamber 11 is connected to an ink supply channel 14. The pump chamber 11 of the pump 10 of the print head 1 is indirectly connected to the ink supply channel 14, through a throttle 15. It is also possible that the throttle 15 is omitted, and that a diameter of the pump 10 at the inlet end is substantially equal to the diameter of the pump chamber 11. Each individual pump 10 is associated with an actuator 16 comprising a piezoelectric element. At least a portion of the wall 17 of the pump chamber 11 is flexible, so that the pump chamber 11 contracts when the actuator 16 is actuated and deforms in the direction of the pump chamber 11.

For the purpose of a printing process, the ink supply channel 14 and the pumps 10 are filled with ink. During the printing process, the pumps 10 fire ink droplets in the direction of a carrier (not shown) like a sheet of paper, a glass substrate or a plastic substrate, through the nozzle 12. The ink droplets are generated as a result of an actuation of the actuator 16, which causes the pump chamber 11 to contract. During the contraction of the pump chamber 11, the pressure in the pump 10 is increased, as a result of which a droplet of ink is released through the nozzle 12. The volume of the released droplet is roughly equal to the volume displaced by the actuator 16.

The print head 1 may be applied for printing layers of LEDs in a process of manufacturing a PoIyLED display. In such an application, it is important that the quality of the ink meets certain standards, and that all pumps 11 of the print head 1 function properly. Therefore, the print head 1 is regularly cleaned by flushing a cleaning fluid through the print head 1.

Each of the pumps 11 filled with ink acts as a hydro-acoustic system, with a distinct behaviour in the frequency and time domain. In the following, this behaviour is also referred to as resonance behaviour. It appears that the resonance behaviour of the pumps 11 filled with ink is closely related to the state of the ink. For example, aging of the ink brings about a change in the resonance behaviour. The resonance behaviour is also influenced when the ink gets replaced by a cleaning fluid.

In order to find the exact moment when the cleaning process needs to be performed, i.e. the moment when a deviation between the actual performance of the print head 1 and an ideal performance of the print head 1 exceeds a maximum allowable value, measurements are performed, in a way which will now be explained in the following. Figure 3 serves to illustrate various steps which are taken in performing the measurements.

In a first step, the print head 1 is mechanically actuated, so that a vibration of the print head 1 is obtained. The actual resonance behaviour of the pumps 10 of the print head 1 determines the characteristics of the vibration, such as a spectrum in the frequency domain and a rate at which damping of the vibration takes place. For sake of completeness, it is noted that a spectrum in the frequency domain comprises a collection of resonance frequencies, in particular a key tone frequency and a number of higher resonance frequencies. As a result of the vibration, the actuators 16 of the pumps 10 get deformed harmonically and generate an electric signal varying in time, which is indicative of at least one characteristic of the resonance behaviour of the pumps 10. In order to determine a characteristic of the resonance behaviour of at least one pump 10, the electric signal generated by the associated actuator 16 is interpreted. In this example, a spectrum in the frequency domain is determined on the basis of the electric signal.

The found spectrum in the frequency domain is compared to a pre-determined spectrum, which is associated with an ideal resonance behaviour of the pump 10 filled with ink, i.e. the resonance behaviour of a pump 10 filled with ink of good quality, in which no contaminations or other irregularities are present. In practice, in most cases, it will appear that the found spectrum is shifted with respect to the pre-determined spectrum. The extent to which the found spectrum deviates from the pre-determined spectrum determines whether the print head 1 needs to be cleaned, or not. A maximum allowable deviation has been determined, and in case a comparison between this maximum allowable deviation and the found deviation shows that the found deviation is larger than the maximum allowable deviation, it is concluded that it is necessary to clean the print head 1. In case the comparison between the maximum allowable deviation and the found deviation shows that the found deviation is smaller than or equal to the maximum allowable deviation, the process of cleaning the print head 1 may be deferred, and the routine of the measurements is repeated until a found deviation appears to be larger than the maximum allowable deviation.

When the above-described routine is followed in order to find the moment when cleaning of the print head 1 is necessary, it is possible to perform the cleaning process of the print head 1 right on time. In this way, unnecessary interruption and delay of the printing process, which occurs in case the cleaning process is performed too early, is avoided. Moreover, it is assured that the ink is always of a good quality, and the performance of the print head 1 does always meet high standards.

In principle, it is possible to verify the resonance behaviour of only one pump 10, but it is preferred to verify the resonance behaviour of all pumps 10 of the print head 1, as in that case, local irregularities can not be missed. When a cleaning process is started, cleaning fluid is supplied to the print head

1. In case the print head 1 is applied for printing layers of LEDs in a process of manufacturing a PoIyLED display, the applied ink may be expensive. Therefore, at the start of a cleaning process, it is desirable to know the exact moment when the process of replacing the ink by the cleaning fluid has started in the pumps 10 of the print head 1, so the printing process may be continued until that moment, and a waste of ink is avoided. Furthermore, it is desirable to know the exact moment when the cleaning process has ended, i.e. the moment when all ink is completely flushed away, in order to avoid unnecessary loss of up time of a printer comprising the print head 1.

Based on the insight that the resonance behaviour of a pump 10 filled with the cleaning fluid is different from the resonance behaviour of the same pump 10 filled with ink, mainly due to the fact that the viscosities of the cleaning fluid and the ink are different, it is possible to determine the moment at which the ink is completely removed from the print head 1 on the basis of measurements of a characteristic of the resonance behaviour of at least one pump 10. The way in which these measurements are performed, and the way in which the results of the measurements are interpreted will now be explained in the following. Figure 4 serves to illustrate various steps which are taken in order to find the moment at which the ink is removed from the print head 1, and at which the pumps 10 of the print head 1 are exclusively filled with cleaning fluid. A number of initial steps of the routine for finding the moment at which the ink is removed from the print head 1 corresponds to a number of initial steps of the routine for determining the moment when the print head 1 needs to be cleaned. The routine for finding the moment at which the ink is removed from the print head 1 also starts with actuating the print head 1 in order to obtain a vibration of the print head 1.

As a result of the vibration of the print head 1, the actuators 16 provide an electric signal. An electric signal of at least one actuator 16 is interpreted such as to find a characteristic of the vibration of the associated pump 10. In this example, a spectrum in the frequency domain is chosen, which does not alter the fact that other characteristics of the vibration may be chosen, for example the damping characteristics.

The found spectrum in the frequency domain is compared to a pre-determined spectrum, which is associated with a situation in which the pump 10 is filled with cleaning fluid only. Subsequently, a deviation of the found spectrum with respect to the predetermined spectrum is determined, and compared to a maximum allowable deviation. In case the found deviation is smaller than the maximum allowable deviation, the found spectrum is close enough to the pre-determined spectrum, and it is concluded that all ink has flushed away from the print head 1, and that the process of cleaning the print head 1 needs to be stopped. However, in case the found deviation is larger than the maximum allowable deviation, it is concluded that ink is still present in the print head 1. In that case, the cleaning process is continued, and the above-described routine is repeated until it appears that the resonance behaviour of the pump 10 resembles the resonance behaviour of a pump 10 which is filled with cleaning fluid only.

When the above-described routine is followed in order to find the moment at which the ink is removed from the print head 1, it is possible to stop the cleaning process right on time. In this way, no up time of the printer comprising the print head 1 is lost.

The above-described routine for finding the moment at which all ink has been flushed away from the print head 1 may in a similar manner be applied when the cleaning fluid is replaced by the ink again, in order to find the moment at which all cleaning fluid is removed from the print head 1. In that case, the pre-determined spectrum in the frequency domain, which is used to compare a measured spectrum to, is associated with a situation in which a pump 10 is filled with ink only. In case a deviation of the measured spectrum with respect to the pre-determined spectrum is larger than a maximum allowable deviation, it is concluded that the print head 1 still contains cleaning fluid. However, in case the found deviation is smaller than the maximum allowable deviation, it is concluded that the cleaning fluid is completely removed from the print head 1, and that the printing process may be resumed.

Figure 5 diagrammatically shows an arrangement 20 comprising the print head 1, an actuator 21 for mechanically actuating the print head 1, and a processor 22 for receiving a signal representing a characteristic of the resonance behaviour of at least one pump 10 and for processing the signal according to a routine, which may be the above-described routine for determining the moment when it is necessary to clean the print head 1, or, in case a cleaning process has been started, the above-described routine for determining the moment at which the ink is completely removed from the print head 1, or, in case the cleaning process has been ended, the above-described routine for determining the moment at which the cleaning fluid is completely removed from the print head 1.

In practice, the arrangement 20 may comprise more components, for example amplifiers and converters which are located between the print head 1 and the processor 22, and the processor 22 may be part of a computer. In case the processor 22 is applied for the purpose of determining the moment when it is necessary to clean the print head 1, the processor 22 may be programmed such as to provide a warning signal to a user of the print head 1 when the moment has come. Furthermore, the processor 22 may be programmed such as to provide a signal to a controller 23, in order to let the controller 23 stop the printing process and, in case the cleaning process is performed automatically, start the cleaning process.

In case the processor 22 is applied during a cleaning process in order to determine when the ink is completely flushed away from the print head 1, the processor 22 may be programmed such as to provide a warning signal to a user of the print head 1 when it appears that all ink has gone and/or to provide a signal to the controller 23, in order to let the controller 23 stop the cleaning process. Contrariwise, in case the processor 22 is applied in order to determine when the cleaning fluid is completely flushed away from the print head 1, the processor 22 may be programmed such as to provide a warning signal to a user of the print head 1 and/or to provide a signal to the controller 23, in order to let the controller 23 start the printing process again. It will be clear to a person skilled in the art that the scope of the present invention is not limited to the examples discussed in the foregoing, but that several amendments and modifications thereof are possible without deviating from the scope of the present invention as defined in the attached claims. It is very advantageous to not only use the actuator 16 for the purpose of pushing a droplet of fluid out of the pump 10, but to also use the actuator 16 in the process of measuring a characteristic of the resonance behaviour of the pump 10. In doing so, use is made of the fact that a piezo-electric element can function simultaneously as an actuator and as a sensor. In this way, the measurements can be performed continuously. A common four- points measuring technique may be applied, wherein the actuating and sensing actions may be performed at the same time.

It is not necessary to use the entire piezo-electric element as a sensor. Instead, the piezo-electric element can be split into two portions, wherein one portion is used for actuating the pump 10, and wherein another portion is used for measuring a characteristic of the resonance behaviour of the pump 10.

In the foregoing, a method has been disclosed, in which a characteristic of a resonance behaviour of a pump 10 of a piezo-jet printing head 1, filled with a fluid, is measured and compared to a pre-determined characteristic. In case the printing head 1 is filled with ink and is involved in a printing process, a moment when a cleaning process of the print head 1 needs to be started is determined by continuously checking whether the measured characteristic is close enough to a pre-determined characteristic of a resonance behaviour associated with an ideal p ppeeerrrfffooorrrmmmaaannnccceee ooofft tt mhheee o ppuuummmopp 11 l00υ.,, ooorrr nnnooottt...

During a cleaning process, the ink gets replaced by a cleaning fluid, and a moment at which all ink is removed from the print head 1 is determined by checking whether the measured characteristic has come close enough to a pre-determined characteristic of a resonance behaviour of the pump 1 filled with the cleaning fluid only, or not.

At the end of a cleaning process, the cleaning fluid gets replaced by ink, and a moment at which all cleaning fluid is removed from the print head 1 is determined by checking whether the measured characteristic has come close enough to a pre-determined characteristic of a resonance behaviour of the pump 1 filled with the ink only, or not.

Claims

CLAIMS:

1. Method for determining a constitution of a fluid that is present inside a dosing device (1) for dosing and emitting droplets of the fluid, which dosing device (1) comprises at least one pump (10) having an inlet for taking in the fluid, a pump chamber (11) for containing the fluid and an outlet for letting out the fluid, and an actuator (16) for generating actuation pulses acting on the fluid in the pump (10), the method comprising the following steps: mechanically actuating the dosing device (1) in order to obtain a vibration of the device (1); measuring a characteristic of the vibration of the pump (10) of the device (1) by means of the actuator (16) of the pump (10); and comparing the measured characteristic to at least one of a series of predetermined characteristics related to possible constitutions of the fluid.

2. Method according to claim 1, wherein the measured characteristic of the vibration of the pump (10) comprises a spectrum in the frequency domain.

3. Method according to claim 1, wherein the measured characteristic of the vibration of the pump (10) comprises a rate at which damping of the vibration takes place.

4. Method according to any of claims 1-3, wherein the actuator (16) comprises a piezo-electric element.

5. Arrangement (20) for carrying out the method according to any of claims 1-4, comprising: - an actuator (21) for mechanically actuating the dosing device (1); a processor (22) connected to the actuator (16), which is arranged for receiving a signal representing the measured characteristic from the actuator (16), and which is programmed to compare the measured characteristic to at least one of a series of predetermined characteristics related to a constitution of the fluid.

6. Method for determining a point in time at which a first fluid is completely removed from a dosing device (1) for dosing and emitting droplets of fluids, which dosing device (1) comprises at least one pump (10) having an inlet for taking in a fluid, a pump chamber (11) for containing the fluid and an outlet for letting out the fluid, in case a second fluid is supplied to the dosing device (1) in order to replace the first fluid, the method comprising the following steps: actuating the dosing device (1) in order to obtain a vibration of the device (1); measuring a characteristic of the vibration of the pump (10) of the device (1); and determining whether a value of the measured characteristic is inside a predetermined range of values related to a presence of only the second fluid in the pump (10).

7. Method according to claim 6, wherein the dosing device (1) comprises an actuator (16) for generating actuation pulses acting on the fluid in the pump (10), and wherein the characteristic of the vibration of the pump (10) is measured by means of the actuator (16).

8. Method according to claim 6 or 7, wherein the measured characteristic of the vibration of the pump (10) comprises a spectrum in the frequency domain.

9. Method according to claim 6 or 7, wherein the measured characteristic of the vibration of the pump (10) comprises a rate at which damping of the vibration takes place.

10. Arrangement (20) for carrying out the method according to any of claims 6-9, comprising: an actuator (21) for actuating the dosing device (1); a processor (22) connected to the actuator (16), which is arranged for receiving a signal representing the measured characteristic from the actuator (16), and which is programmed to determine whether a value of the measured characteristic is inside a predetermined range of values related to a presence of only the second fluid in the dosing device (1).