EP1048470A1 - Ink jet printer and method for controlling the ink quality in such a printer - Google Patents

Abstract

A pressure of the ink ejection is related in terms of a speed and temperature in expression P= a asterisk (rn(T) asterisk V<2> + b asterisk (m)T) asterisk V + (rn(T) asterisk g asterisk h. In the expression H is sensed pressure, (rn(T) and (mn(T) are ink jet characteristic curve; a and b characteristic value of ink jet circuit; g - is the acceleration of the mass. Varying the ejection speed the resulting pressure is measured using determined coefficients to achieve corrective actions. A reservoir (10) contains volume of ink (11), the remaining volume (12) is filled of air. A pipe (13) joins the reservoir ( with a printing head (14). Solvent addition devices (16,17) are controlled by valves (26,27) on signals from pressure, temperatu sensors (20-22) and an ejection speed sensor (25) at the exit of the head (14). A control element (18) electrically controls a pressure regulator (23) and electrically controlled condenser (24).

Description

Technical area

The present invention relates to a printer with inkjet and a method for managing the quality of ink from such a printer.

State of the art

In an inkjet printer using the principle of continuous deflected jet, unused ink for printing is recycled. The recovered ink did not, however, not the same properties as the ink emitted in the jet, mainly due to the evaporation of solvent.

Two documents, referenced [1] and [2] at the end of description, describe methods of controlling the derives from the quality of the ink. Evaporation of solvent must, in fact, be compensated by adding exactly the amount of solvent evaporated to keep constant ink quality. To ensure a enslavement of this addition of solvent without fluctuation (pumping), the speed must be taken into account evaporation.

• la situation présente, ou écart instantané entre la consigne et la pression actuelle de fonctionnement (terme proportionnel) ;
• la situation passée, par exemple en tenant compte des écarts enregistrés sur les dernières heures de fonctionnement (terme intégral) ;
• la situation à venir, ou plutôt la tendance de la situation actuelle (terme dérivé).

In the prior art, different types of servo-control (proportional, proportional-integral, proportional-integral-derivative, etc.) can make a decision to add solvent by affecting a weight distribution relating to:

• the present situation, or instantaneous difference between the setpoint and the current operating pressure (proportional term);
• the past situation, for example taking into account the deviations recorded over the last hours of operation (full term);
• the situation to come, or rather the trend of the current situation (derivative term).

These different types of control are good suitable for managing the quality of an ink. In particular a judicious choice of the relative weights of different terms allow you to gain speed and stability while avoiding oscillations (or "Pumping"). The principle of adjustment of these servo is well known to those skilled in the art.

The document referenced [1] takes into account the measurement of the emptying time, by the inkjet, of a calibrated volume. A temperature sensor allows take into account the natural influence of temperature on the quality of the ink. The temperature acts indeed on the viscosity and on the density of the ink. The enslavement carried out uses a drain curve depending on the temperature. A point of reference is established when the machine is started to take into account dispersions between different applications considered. But such a process is only approximate. The theoretical analysis made in this document [1] supposes, indeed, an independence of the viscosity and ink density, which is not correct: in makes 80% of the operating pressure of a printer is associated with the density of ink so that even a small variation of this density cannot be overlooked the evolution of the pressure term due to viscosity. Of more, to keep a constant writing quality, this document [1] considers operating pressure constant. But such constant pressure only ensures not a constant jet speed over a large area Operating. This process is therefore restricted to one reduced range of temperature development around the calibration point. In practice, a float is placed in the pressure tank supplying the jet (accumulator). The measurement of the emptying time is prone to the vagaries of the float (jamming, sticking, oscillations ...). Precision and reproducibility of this type of measurement is not good. Furthermore the measurement rate is very low (ten per hour), so that a servo built with this type of detector is neither precise nor fast.

In the document referenced [2], the machine used is equipped with a specific device (ball viscometer) to know the viscosity of the machine ink. A curve viscosity / temperature translates the setpoint of operation. However, the evolution of mass ink volume is absolutely not taken into account account. This process is independent of inkjet and does not does not involve operating pressure. This machine works at constant pressure and does not provide consistent writing quality on a wide temperature range. Moreover such cost is high due to the use of a solenoid valve, a calibrated tube, a calibrated ball, detectors, piping ...

Another process is described in the document referenced [3]. This is based on the evolution of operating pressure depending on the ink temperature by imposing a jet speed constant. This process not only ensures a ink quality control but also keeps a print quality independent of the temperature, thanks to a constant jet speed. he also performs a measurement of the jet speed. The operating curve, which constitutes the setpoint of ink quality, takes into account both the viscosity and density of the ink. However, the implementation of this process requires know the difference in height between the head and the machine. A error on it, not controlled by the machine, results in a difference in ink quality and a degraded print quality. What's more process requires operator intervention and reference pressure is established by varying the operating temperature by reference machines.

The object of the invention is to overcome the different drawbacks of known art documents by proposing a quality management process for ink from an inkjet printer, which develops itself its operating instruction without operator intervention.

Statement of the invention

The present invention describes a method for managing the quality of the ink in an inkjet printer, in which information relating to the ink pressure P, the temperature T and the jet speed V and d is available. '' a pressure setpoint curve P _setpoint as a function of temperature T and speed V of the type: P deposit = a × ρ not (T) × V 2 + b × µ not (T) × V + ρ not (T) × g × H H being the difference in height between the print head and the pressure sensor, ρ _n (T) and µ _n (T) of the characteristic curves of the nominal ink, a and b being values characteristic of the ink circuit and g the acceleration of gravity, characterized in that, when starting the machine, the jet speed is varied around its nominal value and the resulting pressure is measured P (T) = a × ρ (T) × V ² + b × µ (T) × V + ρ (T) × g × H so as to determine the coefficients a, b, ρ (T), µ (T) and H, and corrective actions are carried out on the quality ink to bring ρ, µ and P close to ρ _n , µ _n and P _{set point} at temperature T.

In a first mode of operation is used five torque values _(funct P, V) Individual to determine the five characteristics a, b, .DELTA.P, ρ and μ with P _tbd = aρV ² + bμV + .DELTA.P, .DELTA.P represents the term of altitude assumed to be constant.

In a second operating mode, using jet speeds V1 and V2, we draw the line (P _funct (V1) - P _funct (V2)) / (V1 - V2) as a function of V1 + V2 using regression linear, we obtain the coefficients (a × ρ) and (b × µ), we then calculate the average of the ΔP associated with all the measures:

Advantageously the coefficients a and b are known in advance with sufficient precision to a given machine configuration from measurements performed on a control machine and are stored in memory of each machine produced.

avec :

T : température de fonctionnement

T₀ : température quelconque sur le domaine de fonctionnement

α : coefficient traduisant la dilatabilité du fluide

β : coefficient traduisant la variation de viscosité du fluide.

Advantageously, the information concerning the ink is stored in machine memory, for example in the form of the following relationships, for operation at constant concentration:

with:

T: operating temperature

T ₀ : any temperature on the operating range

α: coefficient reflecting the dilatability of the fluid

β: coefficient reflecting the variation in viscosity of the fluid.

Advantageously, the values concerning ρ _n (T) and µ _n (T) are tabulated by being obtained from laboratory tests.

et P_consigne(T) = ΔP_calculé + aρ(T) × V² + b × µ(T) × V.In a first variant of a third mode of operation is known the characteristics of the ink circuit a and b, were measured P _diagram parameters V and T and calculating P = ΔPi _diagram (i) -a × ρ (Td ) × Vi ² -b × µ (Td) × Vi for different operating speeds, we obtain

and P _setpoint (T) = _calculated ΔP + aρ (T) × V ² + b × µ (T) × V.

ρ_ref(T) : masse volumique de l'encre de référence

µ_ref(T) : viscosité de l'encre de référence

ρ_encre(T) : masse volumique de l'encre utilisée

µ_encre(T) : viscosité de l'encre utilisée

ρ_encre(T) = ρ_réf(T) + Δρ

µ_encre(T) = µ_réf(T) + Δµ

In a second variant of the third operating mode, we have: ΔP calculated = (ρ ref (T d ) × g × H) + (a × V 2 × (Δρ)) + b × V × (Δµ)) with:

ρ _ref (T): density of the reference ink

µ _ref (T): viscosity of the reference ink

ρ _ink (T): density of the ink used

µ _ink (T): viscosity of the ink used

ρ _ink (T) = ρ _ref (T) + Δρ

µ _ink (T) = µ _ref (T) + Δµ

Advantageously, the information concerning the characteristics of the ink used is contained in an electronic label associated with the container of the ink. The values of Δρ and Δµ are then calculable and allow the value of the difference in height H to be calculated precisely (the only remaining unknown in the equation of _calculated ΔP). These values (Δρ, Δµ) reflect the difference between the reference ink and the ink actually used by the machine. Significant values (Δρ, Δµ) calculated both during a first start-up and for subsequent restarts of the printer can highlight a problem of ink destabilization, it is then interesting to warn the user of the problem observed.

In a third variant of the third operating mode, the height difference is known (Hconnu), the determination of the pressure setpoint is then trivial. P deposit = a × ρ not (T) × V 2 + b × µ not (T) × V + ρ not (T) × g × H unknown A particular case of knowing the elevation corresponds to a zero elevation. This case is useful for determining the hydraulic characteristics of a machine. In the latter case, the measurement of the ink temperature T ₀ and several measurements of the torque (P _funct , V) are carried out by carrying out a scan at jet speed, the ink flowing from the jet is collected and on this ink the measurement of (ρ (T ₀ ), µ (T ₀ )), we then trace (P _funct ) / V as a function of V, we select the best straight line translating the distribution of the couples (P _funct / V, V) in the diagram (P _funct / VV), we obtain the coefficient b by dividing the ordinate at the origin of the straight line by the measured viscosity µ (T ₀ ) of the ink and the coefficient a by dividing the slope from the right by the measured density ρ (T ₀ ) of the ink.

Advantageously, the same sensor is used. pressure for determining the setpoint and for the measurement of the operating pressure, and a temperature sensor located in the print head.

Advantageously, a condenser is used programmable efficiency, varying the period of the capacitor.

Advantageously, the same mode of use is used. operation during all restarts of the machine, we monitor the quality drifts of ink, and we alert the user on an evolution abnormal of it.

The present invention also relates to a inkjet printer including a reservoir of recovery, solvent addition devices and adding ink controlled by a control body thanks to to solenoid valves, pressure sensors, temperature and jet speed at the head outlet connected to this control unit, a electrically controlled pressure regulator and a electrically controlled condenser, both controlled by the control body, and means for modulating the power supply to the condenser.

• L'établissement de la pression de référence n'est pas réalisé, comme dans les dispositifs de l'art antérieur, en faisant varier la température de fonctionnement de machines de référence, les moyens nécessaires pour une telle opération étant importants et coûteux, la dispersion des pertes de charge entre machines ainsi que la différence entre les capteurs utilisés étant de plus sources d'erreur de mesure.
• La pression de fonctionnement et la pression de référence étant issues de mesures effectuées avec le même capteur, on s'affranchit ainsi de l'ensemble des écarts associés à la non reproductibilité des capteurs.
• Les informations caractérisant l'hydraulique de la machine et nécessaires à l'établissement de la pression de référence peuvent être obtenues à n'importe quelle température de fonctionnement car ces caractéristiques sont indépendantes de la température.
• Les informations caractérisant l'encre et nécessaires à l'établissement de la pression de référence, données par le formulateur de l'encre, sont obtenues à partir de mesures de laboratoire.
• L'utilisation partielle du procédé permet un fonctionnement autonome de la machine, qui détermine par calcul la différence de hauteur entre la partie circuit d'encre et la tête d'impression.
• Le procédé est particulièrement bien adapté à des circuits pour lesquels la reproductibilité des caractéristiques hydrauliques des buses est assurée, par exemple en utilisant des buses obtenues par électrodéposition, électroérosion ou par perçage laser. La machine fabrique alors l'encre du formulateur à partir de l'encre contenue dans la réserve (cartouche d'encre). Cet avantage est considérable du point de vue industriel car les tolérances associées à la production des encres sont élargies. On facilite ainsi la production industrielle de l'encre sans pénaliser le fonctionnement de la machine. De plus, la cohérence entre l'information de l'opérateur et le calcul de la machine est contrôlée par le logiciel de la machine. On évite ainsi le risque majeur d'erreur de signe de ce dénivelé tête/circuit.
• Lors d'un changement de type d'encre (couleur, type), il suffit de remplacer les caractéristiques de l'ancienne encre par celles de la nouvelle pour être opérationnel.

The method of the invention therefore uses the relationship between operating pressure and ink quality. In order to obtain a practically invariable writing quality over the whole temperature range of use of the machine (typically from 0 to 50 ° C.), we work with a constant jet speed. The pressure necessary to obtain this jet speed is compared with a reference pressure. This difference between current operating pressure and reference pressure reflects changes in the quality of the ink. Advantageously, the method of the invention makes it possible to establish the reference pressure on the basis of information contained in the memory of the machine and of a start-up sequence consisting of a scanning at jet speed, and a measurement of the various associated pressures. . Thus this reference pressure is established autonomously by the machine, which has many advantages:

• The establishment of the reference pressure is not achieved, as in the devices of the prior art, by varying the operating temperature of reference machines, the means necessary for such an operation being large and expensive, the dispersion pressure losses between machines as well as the difference between the sensors used being moreover sources of measurement error.
• The operating pressure and the reference pressure being taken from measurements carried out with the same sensor, this eliminates all the deviations associated with the non-reproducibility of the sensors.
• The information characterizing the hydraulics of the machine and necessary for establishing the reference pressure can be obtained at any operating temperature because these characteristics are independent of the temperature.
• The information characterizing the ink and necessary for establishing the reference pressure, given by the ink formulator, is obtained from laboratory measurements.
• The partial use of the method allows autonomous operation of the machine, which calculates the difference in height between the ink circuit part and the print head.
• The method is particularly well suited to circuits for which the reproducibility of the hydraulic characteristics of the nozzles is ensured, for example by using nozzles obtained by electrodeposition, electroerosion or by laser drilling. The machine then manufactures the ink of the formulator from the ink contained in the reserve (ink cartridge). This advantage is considerable from the industrial point of view because the tolerances associated with the production of inks are widened. This facilitates the industrial production of ink without penalizing the operation of the machine. In addition, the consistency between operator information and machine calculation is controlled by the machine software. This avoids the major risk of sign error of this head / circuit difference.
• When changing the type of ink (color, type), you only need to replace the characteristics of the old ink with those of the new one to be operational.

Brief description of the drawings

• Figure 1 illustrates a simplified diagram an ink jet printer according to the invention;
• Figure 2 illustrates a simplified diagram of a enslavement of the quality of the ink in the printer illustrated in Figure 1;
• Figure 3 illustrates all of the different embodiments of the method of the invention;
• Figure 4 illustrates a condenser ensuring solvent recovery in the process the invention;
• FIG. 5 illustrates an example of modulation of the condenser of figure 4.

Detailed description of embodiments

In an inkjet printer the relation linking the operating pressure to the quality of the ink is the sum of four terms: a term of kinetic energy aρV ² , a term of viscous friction bµV, a term of energy potential pgh, and a term associated with the surface tension of the fluid. This last term of surface tension is negligible compared to the other terms: it represents less than 2% of the operating pressure and varies little as a function of the temperature.

a :

coefficient de perte de charge singulière du circuit hydraulique

b :

coefficient de perte de charge régulière du circuit hydraulique

ρ :

masse volumique de l'encre

µ :

viscosité dynamique de l'encre

V :

vitesse du jet d'encre

g :

accélération de la pesanteur (environ 10 m/s²)

H :

dénivelé entre le circuit d'encre et la tête d'impression.

The operating pressure can be written P _diagram #a × ρ × V ² + b × μ × V + ρ × g × H, where:

at :

unique pressure drop coefficient of the hydraulic circuit

b:

coefficient of regular pressure drop of the hydraulic circuit

ρ:

ink density

µ:

dynamic viscosity of ink

V:

inkjet speed

g:

gravity acceleration (about 10 m / s ² )

H:

difference in level between the ink circuit and the print head.

The most important term is the kinetic energy term a × ρ × V ² (around 70 to 80% at nominal temperature). The evolution of this term is associated with the evolution of the density ρ as a function of the temperature T, because the jet speed is considered constant, and a independent of the temperature T.

The term viscous friction bµV represents 15 to 20% of the operating pressure P _funct at ambient temperature but its evolution as a function of the temperature T is significant. This change is directly linked to that of the viscosity of the ink as a function of the operating temperature, V and b being independent of the temperature T.

The term of potential energy ρgh represents maximum 10% of pressure over the entire range operation. It varies little depending on the temperature T and, as it represents a percentage low pressure it can be thought of as constant. The error that we make then is limited to a few mBar and is therefore negligible.

• le dénivelé entre le circuit d'encre et la tête d'impression est précisé par l'opérateur ;
• ce terme est calculé par la machine.

We can therefore write: P _funct # a × ρ × V ² + b × µ × V + ΔP, ΔP representing the difference in elevation assumed to be constant and to be known. Two cases are possible:

• the difference in level between the ink circuit and the print head is specified by the operator;
• this term is calculated by the machine.

In the process of the invention, the operating pressure P _funct , the speed of the jet V and the temperature T are measured to obtain the pressure setpoint of the machine used as a function of the working temperature: P _fun = P _fun (T ).

Figure 1 illustrates a simplified diagram of an ink jet printer according to the invention. This includes a reservoir 10 containing a certain ink volume 11, the remaining volume 12 being filled of air, a pipe 13 connecting this tank 10 to the print head 14, adding devices 16 and 17 solvent and ink addition controlled by a control 18 by means of solenoid valves 26 and 27, pressure, temperature and pressure sensors 20, 21 and 22 jet speed 25 at the outlet of the head 14 connected to this control member 18, a pressure regulator 23 to electric control as well as a control condenser electric 24, both controlled by the control 18.

Figure 2 illustrates a simplified diagram of a ink quality control, according to the invention, in such a printer. A comparator 30 creates a difference between the set pressure obtained using the output signal from the temperature 21 and the effective pressure of operation obtained at the output of the pressure sensor 20. This pressure difference is processed by the the control body 18 which, by actions appropriate such as solvent addition, ink addition, modulation of the condenser control, allows limit this pressure difference.

Measuring the ink temperature can be performed at the ink circuit. However the vast majority of pressure drop (more than 90% of the set pressure) being associated with the nozzle, a measurement of the ink temperature at the print head (nozzle support) provides even more precise information.

In the method of the invention when the machine is started for the first time, the jet speed is varied around its nominal speed and the values P _funct , V and T are recorded. This start up step lasts only a few seconds, if although during this short period the temperature of the ink remains practically constant and is worth T _starting (or T _d ). The method of the invention makes it possible to find all of the characteristics a, b, ΔP for the ink circuit and ρ and µ for the ink used.

The method of the invention comprises several embodiments, illustrated in FIG. 3, which will be explained below.

First embodiment (I)

In a first embodiment (I), five independent values of the couple (P _funct , V) are used to determine these five characteristics a, b, ΔP, ρ and µ. Five measurements of the operating pressure P _{funct are made} for five values of the jet speed V centered on the nominal speed speed. We then solve a system of five equations to finally obtain the values a, b, ΔP, ρ and µ. But such an embodiment is very dependent on the precision of the measurements of P _funct and V.

Second embodiment (II)

In a second embodiment (II) statistical calculations are carried out. Using two jet speeds V1 and V2. The relation connecting the two variables (P _funct (V1) -P _funct (V2)) / (V1-V2) and (V1 + V2) is (P _funct (V1) -P _funct (V2)) / (V1-V2 ) = a × ρ × (V1 + V2) + b × µ. We then plot (P _funct (V1) -P _funct (V2)) / (V1-V2) as a function of (V1 + V2) using linear regression (least squares principle). The coefficients of the line thus obtained are then directly (a × ρ) and (bx µ). The calculation of ΔP is then carried out by averaging the ΔP associated with all of the measurements. With (P _funct (Vi), V (i)) for i = 1 to n representing the set of measurements, the ΔP is calculated with the following relation:

The characteristics of the reference ink being known to the machine, this calculated ΔP _stat is necessary and sufficient for establishing the pressure setpoint. This embodiment makes it possible both to limit the demand for precision of the measurement of the jet speed V and to reduce the dispersive effects of all of the measurement errors, thanks to the use of statistics.

The realization of the head nozzle printing by plating or by EDM provides reproducibility remarkable hydraulics. Or 90% of the pressure drop the ink circuit comes from the nozzle; both pressure drop coefficients a and b therefore have a very low dispersion in all machines. These coefficients, independent of the temperature T, can therefore be measured on a sample of machines and their average values are stored in memory of each machine produced.

avec :

T : température de fonctionnement

T₀ : température quelconque sur le domaine de fonctionnement (généralement la température du laboratoire lors de la détermination de la relation)

α : coefficient traduisant la dilatabilité du fluide.

β : coefficient traduisant la variation de viscosité du fluide.

The information concerning the reference ink, also stored in machine memory, can be stored in the form of the following relationships, for operation at constant concentration:

with:

T: operating temperature

T ₀ : any temperature on the operating range (generally the laboratory temperature when determining the relationship)

α: coefficient reflecting the dilatability of the fluid.

β: coefficient reflecting the variation in viscosity of the fluid.

The values for (ρ _n (T), µ _n (T)) can also be tabulated by being obtained from laboratory tests.

For certain inks the low temperature range (typically less than 10 ° C) is associated with a high viscosity of the fluid. Such a viscosity results in a difficulty of recovering the ink not used for printing and in an evolution of the quality of the breakage which can cause a drift in the performance of the printing. To overcome these drawbacks, we can adapt the laws (ρ (T), µ (T)), for example by choosing µ (T) = µ (10) for T <10 ° C. In the T <10 ° C range, the ink concentration at constant concentration is transformed into ink with constant viscosity. We can then determine the pressure setpoint with the following relation: P deposit (T) = ΔPstat + a × ρ not (T) × V 2 + b × µ not (T) × V

The main advantage of this second mode of achievement is the total determination of all settings.

Third embodiment (III)

A third embodiment (III) is possible when we know a part of the parameters, a and b for example. We then measure the parameters P _funct , V and T = T _start = Td. Knowing a and b and the relationships ρ (T) and µ (T), we can calculate: ΔP = P funct - a × ρ (T d ) × V 2 - b × µ (T d ) × V

The calculation is carried out for different operating speeds. For speed values V _i located on either side of the nominal speed, we measure P _{funct (i)} and calculate: ΔPi = P funct (i) - a × ρ (T d ) × V i 2 - b × µ (T d ) × V i

When the machine is started for the first time, the jet speed is varied around the nominal speed and then as many ΔP are calculated as there are torque values (P _funct , V). The average ΔP value obtained by averaging the ΔP (measured) makes it possible to reduce the errors associated in particular with the measurement of the speed V.

In a first variant (III.a) of this third embodiment, ΔP is then obtained with the formula of the average:

For example, for a nominal speed equal to 20 m / s, the operating pressure is measured for speeds V _i = 19 m / s; 19.5 m / s; 20 m / s; 20.5 m / s and 21 m / s (n = 5).

Having calculated ΔP _calculated , the operating curve is easily obtained, by simple calculation, by applying the following relation: P deposit (T) = ΔP calculated + a × ρ ref (T) × V 2 + b × µ ref (T) × V

For managing the quality of the ink is thus measures the operating pressure P _diagram, the temperature T and the jet speed V. The calculation of P _setpoint (T) is immediate and the difference _(funct P - P _setpoint (T)) is directly usable by the control system, whatever its type.

The machine then builds its own pressure setpoint by assimilating its initial start-up ink to the reference ink. the relation, allowing to obtain the _calculated value ΔP, involves (ρ _ref (T), µ _ref (T)) which are information concerning the reference ink developed by the formulator and whose characteristics have been measured in the laboratory . The ink produced in quantity and industrially is, in fact, suitable for the use of a printer but has significantly different characteristics.

The _calculated ΔP value mainly represents the pressure term associated with the difference in level, but it also reflects the difference in characteristics between the reference ink and the ink used by the machine. By assimilating the ink used by the machine to the reference ink, ΔP _calculated directly translates the difference in level.

ρ_ref(T) :

La masse volumique de l'encre de référence

µ_ref(T) :

La viscosité de l'encre de référence

ρ_encre(T) :

La masse volumique de l'encre utilisée (industriellement)

µ_encre(T) :

La viscosité de l'encre utilisée (industriellement)

In a second variant (III.b) of this third embodiment, the differences in characteristics are corrected. For this we note:

ρ _ref (T):

The density of the reference ink

µ _ref (T):

The viscosity of the reference ink

ρ _ink (T):

The density of the ink used (industrially)

µ _ink (T):

The viscosity of the ink used (industrially)

The formulations of the reference ink and the ink used being sufficiently close, their respective coefficients α and β which translate the evolution of their characteristics according to the temperatures are virtually identical.

The machine operating instruction with the reference ink is: P ref setpoint = a × ρ ref (T) × V 2 + b × µ ref (T) × V + ρ ref (T) × g × H

The machine pressure setpoint established with the ink used and defined above is worth: P setpoint = a × ρ ref (T) × V 2 + b × µ ref (T) × V + ΔP calculated

The value ΔP _Calculated is established when the machine is started for the first time. The ink temperature is then T _start = T _d and for each speed V _i of the jet we have: P funct (i) = a × ρ ink (T d ) × V i 2 + b × µ ink (T d ) × V i + ρ ink (T d ) × g × H Gold P funct (i) = a × ρ ref (T d ) × V 2 + b × µ ref (T d ) × V + ΔP i

By identification we therefore have: ΔP i = ρ ink (T d ) × g × H + a × V i 2 × (ρ ink (T d ) - ρ ref (T d )) + b × V i × (µ ink (T d ) - µ ref (T d )).

Since the values of Vi are close and centered on the nominal speed V, the _calculated ΔP value obtained by averaging the ΔP _i can be approximated by: ΔP calculated = ρ ink (T d ) × g × H + a × V 2 × (ρ ink (T d ) - ρ ref (T d )) + b × V × (µ ink (T d ) - µ ref (T d )).

The characteristics of the reference and used inks being close, we can note: ρ ink (T d ) = ρ ref (T d ) + Δρ and µ ink (T d ) = µ ref (T d ) + Δµ

The error on the term in H (difference in level) is very small if we confuse ρ _ink (T _d ) and ρ _ref (T _d ). We can therefore write: ΔP calculated = (ρ ref (T d ) × g × H) + (a × V 2 × (Δρ) + b × V × (Δµ))

The _calculated ΔP value therefore reflects both the difference in altitude between the print head and the ink circuit but also the difference in the characteristics of the ink.

ΔP_H :

Terme traduisant le dénivelé.

ΔP_encre :

Terme traduisant l'écart de caractéristiques entre l'encre utilisée et l'encre de référence.

You can write ΔP _calculated = ΔP _H + ΔP _ink .

ΔP _H :

Term translating the elevation.

ΔP _ink :

Term reflecting the difference in characteristics between the ink used and the reference ink.

The information concerning the characteristics of the ink used, obtained following measurements carried out directly on the production line of the inks, can be contained in an electronic label, as in the document referenced [4] associated with the container of the ink. This electronic label may also contain other relevant information concerning the ink (expiry date, quantity of liquid in the container, ink reference, etc.). The characteristics (ρ _ref (T), µ _ref (T)) and (ρ _ink (T), µ _ink (T)) can be read automatically by the machine. The characteristics of the reference ink being known to the machine, it is then possible to easily calculate ΔP _ink , the calculation of ΔP _calculated remains unchanged. The difference (ΔP _calculated - ΔP _ink ) gives directly ΔP _H. The pressure setpoint is then given by: P deposit = a × ρ ref (T) × V 2 + b × µ ref (T) × V + ΔP H

This setpoint used by the servo-control cancels the value of ΔP _ink . The machine then manufactures a reference ink from a substantially different ink.

In a third variant (III.c) of the third mode of operation, we know the elevation, the operator can for example inform the machine on the exact position of the head relative to the machine at the time of startup, the instruction then being known without any calculation. We have : P deposit = a × ρ ref (T) × V 2 + b × µ ref (T) × V + ρ ref (T) × g × H

This improves the method presented in [3] because we can calculate .DELTA.P _calculated and .DELTA.P _H. The term ΔP _ink is then calculable: ΔP _ink = ΔP _calculated - ΔP _H. This term can be reduced to 0 by servo control, so that the machine will manufacture the reference ink from a similar ink (but not identical). In addition during a restart of the machine with an unchanged elevation condition (no change in the installation of the machine) we can calculate this term ΔP _ink and alert the user if the value of this term exceeds a limit given.

In a particular case, we work at a vertical drop zero (ΔP = 0), the relation giving the pressure of operation thus becoming simpler. The relationship which connects the operating pressure divided by the jet speed is then linear as a function of this jet speed.

For ΔP = 0, we have: P funct (T) = a × ρ (T) × V 2 + b × µ (T) × V, and therefore P _funct (T) / V = a × ρ (T) × V + b × µ (T).

By plotting P _funct (T) / V as a function of V and applying a linear adjustment (with the least squares method for example) the intercept represents (bx µ) and the slope of the line is (ax ρ). The practical realization of this variant is easy and particularly suitable for determining in the laboratory the hydraulic parameters (a, b) of a machine. For a given machine, it suffices to impose a zero difference and to measure the ink temperature T ₀ and several measurements of the torque (P _funct , V) by scanning at jet speed. We then draw (P _funct ) / V as a function of V, we select the best straight line (by applying the least squares method for example) translating the distribution of the couples (P _funct / V, V) in the diagram (P _funct / VV). For an application of the principle in the laboratory, the ink flowing from the jet is collected and the measurement of (p (T ₀ ), µ (T ₀ )) is made on this ink. The coefficient b is easily obtained by dividing the ordinate at the origin of the straight line by the measured viscosity µ (T ₀ ) of the ink. The coefficient a is easily obtained by dividing the slope of the line by the measured density ρ (T ₀ ) of the ink.

• une faible dispersion sur les coefficients a et b ;
• la possibilité de retrouver en quelques minutes les courbes de fonctionnement des machines existantes, alors que dans l'art connu ces courbes de fonctionnement des machines existantes sont établies en plaçant ces machines en étuve, l'établissement de ces courbes en étuve nécessitant de nombreuses heures de travail.

The application of this variant to several machines has shown:

• a low dispersion on the coefficients a and b;
• the possibility of finding in a few minutes the operating curves of existing machines, whereas in the known art these operating curves of existing machines are established by placing these machines in an oven, the establishment of these curves in an oven requiring many hours of work.

Advantageously, in its different modes of operation, the method of the invention allows to obtain maximum autonomy, to calculate the actual elevation between the machine and the print head, and to change the characteristics of the ink used towards those of the reference ink. This process makes it possible to precisely compensate for differences in 1% on density and 10% on viscosity industrially produced ink. The process of the invention makes it possible to establish the setpoint for enslaving the quality of the ink, reducing the difference between the setpoint pressure and that of operation.

On traditional ink circuits the servo can be active to manage properly adding solvent, decreasing the solvent concentration being controlled by natural evaporation. The servo has a limited possibility of adding ink to reduce the solvent concentration but the amount of solvent to evaporate remaining unchanged, only the deviation from concentration decreases. In addition, the internal volume of the circuit being limited, adding ink cannot be done only with a limited and limited amount to avoid the risk of one of the tanks overflowing. In besides the response time of the servo of the ink quality being all the better as the ink quantity is low, adding ink is therefore not in a good way.

To solve such a problem one can use a condenser 24 with programmable efficiency, which allows to recover and reinject into the ink circuit a large part of the solvent evaporated. We do vary the solvent recovery capacity by modulating the power supply to the condenser. The FIG. 4 illustrates the recovery of solvent with a Peltier effect condenser 24, with an effect cell Peltier 35, a cold surface 36, a hot surface (radiator) 37, air outlet 38, solvent outlet recovered 39, pump supply 40, ink return recovered 41, the power supply 42 of the condenser 24.

In Figure 5 is shown the modulation of the power supply of this condenser 24 obtained by varying the Talim period compared during the Tcycle period. Modulation is in this case associated with a food duty cycle electric. It would also be possible to do vary the level of the supply voltage of the condenser 24.

Such a modulation of the effectiveness of the condenser 24 reduces the response time by the enslavement. So to compensate for a solvent concentration too high, you can reduce (and even cancel) the efficiency of the condenser. We thus improves the servo performance of the ink quality. This modulation of efficiency is particularly suitable for start-up phases when the thermal is still in a phase transient. Applications for which observes short thermal cycles also find an advantage with variable efficiency of the condenser.

The different embodiments of the process of the invention allow the establishment of the operating pressure setpoint. This instruction established when the machine is started for the first time. The re-use of the same operating mode when restarting the machine has several advantages. We can in particular verify the characteristics of ink when restarting the machine and, possibly alert the printer user on a drift in the quality of the ink.

There are mainly two types of drifts the quality of the ink. The evolution of the two viscosity and density parameters can be done in parallel and in the natural direction. We note by example an increase in viscosity as well as the density. This first type of evolution, if remains within acceptable limits, does not reflect a ink problem but a natural drift associated by example to storage of the ink under conditions outside limits compared to specifications. It is therefore acceptable by the machine which will be able to compensate these natural deviations. Another possibility for ink relates to an opposite evolution of the density and viscosity. This last type of evolution is abnormal and usually reflects a problem of ink stability (flocculation, deposits ...). The interest of such a characteristic is to be able warn the user as soon as possible drain his machine and restart it with ink correct. So an ink problem doesn't take a catastrophic dimension for the machine and does come not permanently disrupt the production flow of the user. The user is sure of the correct ink quality.

REFERENCES

[1] EP-0 333 325

[2] EP-0 142 265

[3] FR-2 636 884

[4] FR-2 744 391

Claims (22)

Method for managing the quality of the ink in an inkjet printer, in which information relating to the ink pressure P, the temperature T and the jet speed V and a setpoint curve are available pressure _setpoint P as a function of temperature T and speed V of the type: P deposit = a × ρ not (T) × V 2 + b × µ not (T) × V + ρ not (T) × g × H H being the difference in height between the print head and the pressure sensor, ρ _n (T) and µ _n (T) of the characteristic curves of the nominal ink, a and b being values characteristic of the ink circuit and g the acceleration of gravity, characterized in that, when starting the machine, the jet speed is varied around its nominal value and the resulting pressure is measured P (T) = a × ρ (T) × V ² + b × µ (T) × V + ρ (T) × g × H so as to determine the coefficients a, b, ρ (T), µ (T) and H, and corrective actions are carried out on the quality ink to bring ρ, µ and P close to ρ _n , µ _n and P _{set point} at temperature T. The method of claim 1, wherein five values of the torque is used _(funct P, V) Individual to determine the five characteristics a, b, .DELTA.P, ρ and μ with P _tbd = aρV ² + bμV + .DELTA.P, the term representing .DELTA.P elevation assumed to be constant. Method according to Claim 1, in which, using jet speeds V1 and V2, the line is _drawn (P _funct (V1) - P _funct (V2)) / (V1 - V2) as a function of V1 + V2 using a linear regression, we obtain the coefficients (a × ρ) and (bx µ), we then calculate the average of the ΔP associated with all the measures:

Method according to claim 1, in which the coefficients a, b are known in advance with sufficient precision for a configuration of given machine from measurements made on a control machine and are stored in the memory of each machine produced. Process according to claims 1 to 4, in which information about the nominal ink are stored in machine memory. Method according to claim 5, in which this information is stored in the form of the following relationships, for operation at constant concentration:

with: T: operating temperature T ₀ : any temperature on the operating range α: coefficient reflecting the dilatability of the fluid β: coefficient reflecting the variation in viscosity of the fluid. The method of claim 5, wherein the values for ρ _n (T) and µ _n (T) are tabulated by being obtained from laboratory tests. Method according to claim 1, in which, in the laboratory, a zero difference is imposed and the ink temperature T ₀ and several measurements of the torque (P _funct , V) are carried out by scanning at jet speed, we collect the ink flowing from the jet and we measure on this ink the measurement of (ρ (T ₀ ), µ (T ₀ )), we then trace (P _funct ) / V as a function of V, we select the best straight line translating the distribution of the pairs (P _funct / V, V) in the diagram (P _funct / VV), we obtain the coefficient b by dividing the ordinate at the origin of the straight line by the measured viscosity µ (T ₀ ) of the ink and the coefficient a by dividing the slope of the line by the measured density ρ (T ₀ ) of the ink. Method according to claim 1, in which the characteristics of the ink circuit a and b are known, the parameters P _funct , V and T are measured and ρ (Td), µ (Td) and H are calculated; the pressure setpoint is then deduced therefrom: P deposit = a × ρ not (T) × V 2 + b × µ not (T) × V + ρ not (T) × g × H Method according to claim 1, in which the characteristics of the ink circuit a and b are known and the machine ink is assimilated to the reference ink, the parameters P _funct , V and T are measured and calculated ΔPi = P funct (i) -a × ρ not (Td) × Vi 2 -b × µ not (Td) × Vi for different operating speeds, we obtain

and P _setpoint (T) = _calculated ΔP + aρ _n (T) × V ² + b × µ _n (T) × V. Method according to claim 1, in which: ΔP calculated = (ρ ref (T d ) × g × H) + (a × V 2 × (Δρ)) + b × V × Δµ)) with: ρ _ref (T): density of the reference ink µ _ref (T): viscosity of the reference ink ρ _ink (T): density of the ink used µ _ink (T): viscosity of the ink used ρ _ink (T) = ρ _ref (T) + Δρ µ _ink (T) = µ _ref (T) + Δµ Method according to Claim 11, in which the characteristics of the ink circuit are known (a, b) and, the difference in level being entered by the user, the reference pressure is deduced therefrom, the parameters P _funct , V and T and the difference (Δρ, Δµ) between the ink used and the reference ink is calculated. Method according to any one of claims 1 to 12, wherein the information concerning the characteristics of the ink used are contained in an associated electronic tag to the ink container. Method according to any one of claims 1 to 13, in which the same pressure sensor for determining the setpoint and for measuring the operation. Method according to any one of claims 1 to 13, in which a temperature sensor located in the print head. Method according to any one of claims 1 to 14, in which a programmable efficiency condenser. Method according to claim 16, in which we vary the feeding period of the condenser. Method according to any one of claims 1 to 17, in which the same is used operating mode during all restarts of the machine. The method of claim 18, in which we monitor ink quality drifts, and in which we alert the user on a abnormal evolution of it. The method of claim 18, in which we monitor the evolution of the elevation and we can ask the user for confirmation on the evolution observed. Inkjet printer comprising a tank (10), devices (16 and 17) for adding solvent and the addition of ink controlled by a control (18) using solenoid valves (26 and 27), pressure, temperature and pressure sensors (20, 21 and 22) jet speed output from the print head (14) connected to this control member (18), a electrically controlled pressure regulator (23), and an electrically controlled condenser (24), both steered by the control body (18). Printer according to claim 21, comprising means for modulating the supply condenser.

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