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    • 专利摘要:
    The invention relates to a device for continuous level measurement in a reservoir (10) of a continuous inkjet printer (CIJ), comprising: - first means (24, 26) for measuring the impedance of a first liquid height, predetermined, in said tank; second means (16, 18) for measuring the impedance of any second height of the same liquid in said reservoir; means for comparing the two measured impedances and for calculating said second height.
    公开号:FR3027669A1
    申请号:FR1460138
    申请日:2014-10-22
    公开日:2016-04-29
    发明作者:Jean-Pierre Arpin
    申请人:Dover Europe SARL；
    IPC主号:
    专利说明:

    [0001] TECHNICAL FIELD AND PRIOR ART The invention relates to the field of continuous inkjet (CU) printers. It also relates to a device and a method for measuring a conductive liquid level, in particular ink in a reservoir of such a printer. Continuous inkjet (CIJ) printers are well known in the field of coding and industrial marking of various products, for example to mark barcodes, the expiry date on food products, or references or distance marks on the cables or pipes directly on the production line and at high speed. This type of printer is also found in some areas of decoration where the graphic printing capabilities of the technology are exploited. These printers have several standard subassemblies as shown in FIG. 1. First, a print head 1, generally offset relative to the body of the printer 3, is connected thereto by a flexible umbilicus 2. bringing together the hydraulic and electrical connections necessary for the operation of the head by giving it a flexibility that facilitates the integration on the production line. The body of the printer 3 (also called desk or cabinet) usually contains three subsets: - an ink circuit in the lower part of the desk (zone 4 '), which allows on the one hand, to provide ink at the head, at a stable pressure and of adequate quality, and secondly to take charge of the jet ink, not used for printing, - a controller located at the top of the desk (zone 5 '), capable of managing the sequencing of actions and of performing the processes enabling the activation of the various functions of the ink circuit and the head, - an interface 6 which gives the operator the means of putting the printer in action and to be informed about its operation. In other words, the cabinet has 2 sub-assemblies: in the upper part, the electronics, the power supply and the operator interface, and in the lower part an ink circuit supplying the ink, of nominal quality, under pressure at head and vacuum recovery of ink not used by the head.
    [0002] Figure 2 schematically shows a print head 1 of an ICJ printer. It comprises a drop generator 60 supplied with electrically conductive ink, pressurized by the ink circuit. This generator is capable of emitting at least one continuous jet through a small orifice called a nozzle. The jet is transformed into a regular succession of drops of identical size under the action of a periodic stimulation system (not shown) located upstream of the outlet of the nozzle. When the drops 7 are not intended for printing, they go to a gutter 62 which retrieves them to recycle the unused ink and send them back into the ink circuit. Devices 61 placed along the jet (charge and deflection electrodes) make it possible, on command, to electrically charge the drops and to deflect them in an electric field Ed. These are then deviated from their natural trajectory of ejection of the generator of drops. The drops 9 for printing escape the gutter and will be deposited on the print medium 8. This description can be applied to continuous jet printers (CIJ) called binary or continuous jet multi-deflected. The binary CIJ printers are equipped with a head whose drop generator has a multitude of jets, each drop of a jet can be oriented only to 2 paths: printing or recovery. In multi-deflected continuous jet printers, each drop of a single jet (or a few spaced jets) can be deflected on different paths corresponding to different charge commands from one drop to another, thus performing a scan of the area to be printed in a direction which is the deflection direction, the other scanning direction of the area to be printed is covered by relative displacement of the print head and the print medium 8. Generally the elements are arranged in such that these two directions are substantially perpendicular.
    [0003] An ink circuit of a continuous ink jet printer makes it possible, on the one hand, to supply ink under controlled pressure, and possibly solvent, to the drop generator of the head 1 and, on the other hand, on the other hand, to create a depression to recover fluids that are not used for printing and then come back from the head. It also allows the management of consumables (dispensing of ink and solvent from a reserve) and the control and maintenance of ink quality (viscosity / concentration). Finally, other functions are related to the comfort of the user and the automatic support of certain maintenance operations in order to guarantee a constant operation whatever the conditions of use. Among these functions are the solvent rinse of the head (drop generator, nozzle, gutter), the preventive maintenance aid, for example the replacement of components with limited life, including filters, and / or pumps. These different functions have very different purposes and technical requirements. They are activated and sequenced by the controller of the printer which will be all the more complex as the number and sophistication of the functions will be great. In general, the ink circuit of known ink jet printers capable of projecting inks remains an expensive element, because of the many hydraulic components to be used.
    [0004] There is therefore the problem of performing all or part of the functions of an ink circuit, in a CIJ-type printer, at a lower cost and with a reduced number of components, while guaranteeing a minimum of reliability, or, in In any case, reliability expected by users, particularly related to the homogeneity of inks throughout the consumption. It is therefore sought to implement the simplest possible components, especially for functions such as level measurement in tanks, control and maintenance of the quality of the ink. The latter can be defined in terms of viscosity and / or concentration of the ink. Regarding the level sensors, we know sensors that measure one or more levels, but in a discrete manner. This type of sensor can operate on the basis of a capacitive measurement, or optical, or with floats that trigger on a threshold. This type of device allows to indicate only one or more discrete levels: full, empty, low, intermediate. For example, a known sensor implements level rods that indicate the presence or absence of current between the rods, this current being related to the ink level. Since we are not trying to measure the value of this current, they are independent of the conductivity. EP 0784784 describes such a discrete sensor. Document WO 2011/076810 describes a continuous sensor, but which is complex and expensive.
    [0005] A system for continuous measurement has a dependence on the measurement medium. We must either enslave this environment, or measure the variations to make the necessary corrections. The signal produced by a resistive sensor will depend on the conductivity of the ink, that of a capacitive sensor depends on the capacity; a pressure sensor can be sensitive to density and atmospheric pressure. For an acoustic sensor, the signal level will depend on the speed of propagation in the medium measured. There is therefore the problem of finding a new sensor, continuous type, whose measurement data it provides are independent of the measuring medium and in particular independent of the conductivity of the liquid which is measured level. Preferably, such a sensor is easy to implement, and low cost. SUMMARY OF THE INVENTION The invention relates firstly to a device for continuous level measurement in a reservoir of an inkjet printer. continuous circuit (CU), comprising: first means for measuring the impedance of a predetermined first liquid height in said tank; second means for measuring the impedance of any second height of the same liquid in said reservoir; means for making a comparison of the two measured impedances and for calculating said second height with the aid of said comparison.
    [0006] A device according to the invention allows a continuous and linear measurement, independent of the conductivity of the liquid. This avoids a specific calibration for each liquid, or each ink, or even for each printer. Means, for example of the type of multiplexing means, may be provided to alternatively enable measurements using the first means and the second means. According to one embodiment, the first means for measuring the impedance of a first predetermined liquid height, in said tank, comprise two measuring rods, designed to be mounted parallel in the tank, each having a measuring end made of a conductive material. , to measure an impedance that corresponds to the first liquid height, predetermined, and remains constant for any second height, greater than the first height. The second means for measuring the impedance of a second height of any liquid in said tank may comprise two measuring rods, each also of conductive material, intended to be mounted in parallel in the tank, to measure an impedance which corresponds to a second height of liquid. Preferably, the end intended to be immersed of each of the measuring rods: is offset from the end of the first means by a value greater than or equal to the predetermined height or is covered with an insulating coating or an insulating sleeve, over a length greater than or equal to said first height. Means for supplying the measuring rods of the first impedance measuring means and / or measuring rods of the second impedance measuring means can be provided, to provide an alternative electrical signal of zero average. Preferably, supply means supply a current whose frequency is between 1 kHz and 1 MHz. One end of each measuring rod can be free. It is therefore, during the measurement, intended to be in contact with a liquid whose height is to be measured. According to an advantageous variant, means allow the mechanical maintenance of this end. The two measuring rods of the impedance of a first liquid height may have a geometry, for example a shape and / or a spacing distance between the two rods, different from, or identical to, that of the two rods of measuring the impedance of a second height of liquid. A system for continuously measuring the level of a fluid in a reservoir of a continuous ink jet printer (CU), comprises a device as described above, and means for calculating the height of fluid in said tank. It may further comprise means for storing at least one parameter for calculating the height of a fluid, and / or one or more height correction data calculated to take account of the presence of a wall of the reservoir, and / or the configuration, free or not, of the ends of the electrodes.
    [0007] According to another aspect of the invention, an ink tank, for a continuous ink jet printer (CU), comprises: at least one wall, means for introducing ink into said reservoir and ink evacuation means of said reservoir, - a continuous level measuring device or system according to one of the preceding claims. The wall may be electrically conductive; in this case, means are provided for the tank to be electrically isolated, for example it can be connected to the ground by a very high impedance with respect to the impedances measured, or to be measured, by the system (with a ratio of minus 10 between said very high impedance and the impedances measured or to be measured). Alternatively, the wall may be electrically insulating. Such a reservoir may further comprise means for maintaining the first impedance measuring means and the second impedance measuring means at a minimum distance from said wall at least equal to the spacing between the rods. The invention also relates to a continuous inkjet printer, comprising: an ink circuit comprising a reservoir as described above, a printing head, hydraulic connection means, for bringing, from the ink tank, an ink to be printed at the print head and send, to said ink circuit, an ink to be recovered from the print head, - electrical connection means for supplying said head with power printing. The invention also relates to a method of level measurement in a reservoir of a continuous inkjet printer (CU), implementing a device or a system as described above.
    [0008] The invention also relates to a method for level measurement in a tank of a continuous ink jet printer (GA comprising: a measurement of the impedance of a first liquid height, predetermined in said reservoir a measurement of the impedance of any second height of the same liquid in said reservoir, the comparison of the measured impedances and the calculation of said second height on the basis of this comparison. continuous and linear, independent of the conductivity of the liquid.
    [0009] In such a method: the first means for measuring the impedance of a first predetermined liquid height in said tank may comprise two measurement rods, mounted parallel in the tank, each having a measurement end made of a material conductor, for measuring an impedance that corresponds to the first liquid height, predetermined, and remains constant for any second height, greater than the first height; the second means for measuring the impedance of a second height of any liquid in said tank may comprise two measuring rods, each also made of conductive material, connected in parallel in the tank, for measuring an impedance corresponding to a second height of liquid. According to one embodiment, the measurement rods are electrically powered by an alternating electrical signal of zero average. The measuring rods can be electrically powered by a current whose frequency is between 1 kHz and 1 MHz. Preferably, the end of the rods is maintained with holding means. More preferably, the rods are held at a distance from the tank wall at least equal to the spacing between the rods.
    [0010] In a method and a device according to the invention, the distance between the canes and the tank walls is preferably maintained greater than the distance between the canes. The rods are for example arranged in a square. A correction of the calculated height can be made, to take into account the presence of a wall of the tank, and / or the configuration, free or not, of the ends of the electrodes.
    [0011] The invention also relates to a computer program comprising the instructions for implementing a method according to the invention, in particular as described above. The invention also relates to a data carrier, readable by a computer system, comprising the data, in coded form, for implementing a method according to the invention, in particular as described above. The invention also relates to a software product comprising a program data support means that can be read by a computer system, making it possible to implement a method according to the invention, in particular as described above. BRIEF DESCRIPTION OF THE FIGURES - FIG. 1 represents a known printer structure; FIG. 2 represents a known structure of a printer head of an ICJ type printer; FIGS. 3A and 3C represent embodiments of FIG. a sensor according to the present invention; FIG. 3B shows an electrical diagram of 2 of the electrodes of a sensor according to the present invention; FIGS. 4A and 4B represent test results realized with a sensor according to the present invention; FIG. 5 shows sensitivity curves obtained with a sensor according to the present invention; FIGS. 6A, 6B represent embodiments of another sensor structure according to the present invention, with an electrode holding ring, FIGS. 7A, 7B show results of tests carried out with a sensor according to the present invention, with an electrode holding ring, - FIGS. 8A-8C represent various configurations. electrodes, with free ends (FIG. 8A), or with holding means at the end (FIG. 8B), or with, in addition, a separator (FIG. 8C), FIG. 9 represents the results of tests carried out with sensors according to the present invention, with various electrode configurations, of the type shown in FIGS. 8A-8C; FIG. 10 schematically represents an electrode structure; FIGS. 11A-11C represent tests and test results in FIGS. the case of a wall parallel to measuring rods, - Figures 12A-12C show tests and test results in the case of a wall perpendicular to the measuring rods, - Figures 13A - 13B represent tests and test results to evaluate the influence of the walls on the level measurement, - Figures 14A-14D represent tests and test results to evaluate the influence of a conical shaped tank wall on level measurement, FIG. 15 shows test results for evaluating the influence of cane geometry on the level measurement; FIG. 16 schematically represents an assembly comprising an ink circuit, a controller and user interface means. DETAILED DESCRIPTION OF AN EMBODIMENT An example of a measuring device according to the invention is illustrated in FIG. 3A. It is here arranged in a tank 10. It comprises 2 rods, or electrode, 16, 18 measuring and 2 rods, 20, 22 reference. Each of the reference rods comprises an electrode covered, over a large part of its length, with a coating, or a sleeve, 24, 26, which leaves only an end portion of the corresponding electrode, of IR length . Thus it makes it possible to measure a liquid level, of IR + p depth, p being the distance between the free end of the reference electrode and the bottom of the tank 2.
    [0012] Each of the measuring rods 16, 18 comprises an electrode which is not covered by a sleeve, at least on the portion which lies between the free end of the electrode, intended to be closest to the bottom. of the reservoir, and the maximum level hmax that one wishes to be able to measure. The different electrodes are made of conductive material, for example stainless steel. The pairs of electrodes are supplied with current by means 30 forming a generator. The electrodes of each pair are electrically arranged in series. Preferably, the current supplied is an alternating electric current, at zero average to avoid any electrolysis. The frequency of the current is neither too low (again, to avoid any electrolysis), nor too high (to avoid any displacement current by capacitive coupling between the electrodes). For example, the frequency of the current is between 10 kHz and 50 kHz, it is for example equal to 15 kHz or 20 kHz or 30 kHz. In order to study these phenomena more precisely, we consider the electric diagram, presented in FIG. 3B, of two electrodes 16, 18, partially immersed in a tank 10. The electrical impedance of this system comprises several terms: the real component (resistive ) and an imaginary component (capacity or self). The term self has no physical meaning here and can be omitted. On the other hand, the capacitive coupling between the electrodes can generate a non-negligible displacement current in front of the conduction term, for example if the frequency of the measurement signal is too high. Taking the notations of FIG. 3B, the impedance between two partially immersed cylindrical electrodes is written: in the liquid: Cl - ze oe rhl Log (DI 2r) - in the air: Ca - ns oha Log (DI 2r) The total capacity C is therefore: C = Ca + Cl The total capacity is the sum of the two capacities in parallel. It appears that this parasitic capacitance is reinforced, and penalizing, when the reservoir is full of ink and for liquids with a high dielectric constant. For water, the relative permittivity is 80, whereas it is only a few units in solvents such as alcohol, MEK Capacitive coupling remains negligible if its impedance remains low compared to the electrical resistance between electrodes. Since the electric current flowing between the electrodes is small (preferably small in front of 1 Ampere), for example between 10 .mu.A and 10 mA, the field lines (electrostatic) are coincident with the current lines (electrokinetic); the geometric coupling factors for determining the resistance and the capacitance are identical and therefore simplify by producing the product RC (Zr = Zc). The impedance by capacitive coupling is written: 1 Zc = jo) Cl The impedance of the electrical resistance is written: ZrRa1 Log (D 12r) = = o-ha The frequency for which the impedances are equivalent is therefore written : f 27re oe, The conductivity of the ink a is taken equal to 100011S / cm, the permittivity of the vacuum co equal to 8.8 10-12 F / m and the relative permittivity of the water sr equal to 80. The application digital gives a limit frequency of 22 Mhz for a tank filled with water-based ink. In practice, a working frequency of less than 10 MHz or even 1 MHz or even 100 kHz will be used.
    [0013] Furthermore, at the interface of the electrodes and the conductive liquid, the passage of the electric current is provided by two mechanisms that take turns depending on the interface potential. If the potential drop at the interface remains below the volt, the current that passes is a current of movement through the double layer o-electronic (called "electric double layer"). If the interface potential typically exceeds the volt then the current flow is provided by an electronic exchange which results in electrolysis of the liquid. Diffusion of the chemical species in the vicinity of the electrode governs the current density at the interface of the electrode.
    [0014] So that the measurement does not depend on the chemical species in solution, which offers a freedom of formulation, the current at the interface of the electrode is written: IC dbr7 db f Where Cdb is the capacity of double layer: C db e 0 27r r hl e with e = thickness of the interface defined at the atomic scale. As a first approximation, it is assumed that e = 1 Å (10-10 m) and where Vdb is the double-layer potential = 1 V. The current i flowing between the electrodes is determined by Ohm's law: U = Ri where U is the polarization voltage of the electrodes and R is the electrical resistance between electrodes: R-1 Log (D 12r) o-hl The minimum frequency for which the electrolysis mechanism is not triggered can be determined: UU o- ef -> - R ccib Vcib f - V db 27r r E0 Log (D / 2 r) - - with: U = 5 volts - Vdb = 1 volt and D = 20 mm - 2r = 2 mm. The digital application gives a minimum operating frequency of 390 Hz. We can therefore consider, practically, a minimum frequency of 500 Hz, or even 1 kilohertz. Considering the above results, it will be possible to take a frequency below 10 MHz or even at 1 MHz or 100 kHz and above 500 Hz or at 1 kHz.
    [0015] Means 32 make it possible to measure a voltage Vm between the two measuring rods. For example, these means 32 comprise a resistor which makes it possible at the same time to measure the intensity by measuring the voltage and to limit the current in the circuit.
    [0016] Preferably, these measuring means perform a sampling on the peak values, then an amplification. Means 34, such as multiplexing means, may be provided to perform, alternately, a measurement at the terminals of the two measurement rods and a measurement at the terminals of the two reference rods. Thus, the pair across which no measurement is made is completely disconnected and has no influence on the measurement made across the other pair, and any coupling effect of the electrode pairs is avoided. In this configuration, the same voltage measuring means 32 can be used to measure a voltage VR between the two measuring rods and to measure a voltage VR between the two reference rods.
    [0017] For example, a measurement is carried out for 100 ms with the two measuring rods, then for 100 ms with the two reference rods. The measurement times with the two measuring rods and the two reference rods can be equal or different: for example, the ratio of the measurement time with the two measurement rods to the measurement time with the two reference rods can be between 5 and 10. Measurements of voltage Vm and VR, it is possible to deduce an impedance, respectively a measurement impedance Rm and a reference impedance RR. RR / Rm is then calculated to deduce the hm level of the liquid height by the following formula: hm = K. (RR / Rm) - Ko So RR / Rm is calculated to deduce the ink level. This formula is independent of the conductivity of the liquid, which, as will be seen below, is confirmed by the experimental measurements. Surprisingly, it has been found that the reference resistance, per mm of ink, is different from the measuring resistance, per mm of ink.
    [0018] A good measurement can be performed when the reference electrodes are totally immersed (this is the case in FIG. 3A) and / or the measurement electrodes have a distance p ', with respect to the bottom of the reservoir, equal to p increased a length corresponding to the active part of the reference electrodes (this is also the case in FIG. 3A). In a variant, illustrated in FIG. 3C, the ends of the measurement electrodes may be protected by an insulating coating or insulating sleeves 16 ', 18', of length equal to or greater than the active part IR of the reference electrodes (the other elements of FIG. Figure 3C are identical to those of Figure 3A). In the opposite case, the formula hm = K. (RR / Rm) - Ko is not valid in the bottom of the tank as long as the ends (on the IR distance) of the reference electrodes are not totally immersed (in this case In this case, the measurement and reference impedances are equal, which gives a value of constant hm). But, once the reference electrodes are totally immersed, we can then apply the formula above, the coefficients Ko and K1 being determined experimentally.
    [0019] Electronic means can be programmed, for example in the printer controller, to calculate hm as a function of the values of RR and Rm. The measurement data is transmitted from the ink tank to the controller, which then performs the processing. data and the calculation of the ink or liquid level. If the ink level thus calculated is below a predetermined threshold level, the controller can trigger a filling operation of the reservoir. Test measurements were performed. The device used is very close to that shown in FIG. 3A, with the following particular data: - volume of the tank 10: 1 I, - the ends of the electrodes opposite the free ends are held by a piece of plastic material 35 (shown in FIG. in dashed lines in FIG. 3A) and the 4 electrodes are arranged at the vertices of a square of 20 mm on each side, the electrode of each of the reference rods 24, 26 is covered over a large part of its length, by a coating, or a sleeve, 24, 26, which leaves only a length IR = 10 mm of electrode at its end, the distance p between the bottom of the tank and the free end of each of the electrodes is 20 mm. A lateral rule (not shown in the figure) was mounted on one side of the tank 10 to measure the height of the liquid. With two pumps 37, 39, the test liquid can be transferred from a bottle 41 to the tank 10 and vice versa. The impedance measurement chain has been checked and calibrated. The rod supporting part is set to obtain the same impedance for both pairs of rods with a liquid height of 5 mm. Impedance measurements were made with this device. They consisted in raising the impedances on the 2 pairs of rods for liquid heights, from 5mm to 5mm. They were made with a liquid based on water and salt, with 4 different conductivities, ranging from 410 uS to 1660 uS: 410 uS, 765 uS, 1230 uS, 1660 uS. 2 other series of measurements were made with a pure ink, based on Mek, then with the same very diluted ink, respectively of conductivity 1110 uS and 260 uS. The graphs of FIGS. 4A (water-based liquid and salt) and 4B (Mek-based ink) represent the RR / RM ratio, between the reference impedance (RR) and the measurement impedance (RM), depending on the height of the liquid.
    [0020] All the readings show that the curves with different conductivities are superimposed and are linear. In general, the measurements made according to the invention are independent of the conductivity. In a configuration where the measurement and reference rods are set at the same height (the distance p is the same for the 2 pairs of electrodes), the liquid height (of the ink) is given by the following relation: - in water basis: H = ((RR / RM) * (1 / 0.0572)) - (0.6938 / 0.0572) H = 17.48 (RR / RM) - 12.1 - in base Mek: H = ((RR / RM) * (1 / 0.0572)) - (0.4987 / 0.0572) H = 17.48 (RR / RM) - 8.7 The only difference is in the offset (offset) of the curve , which is explained by the different behavior of the liquid on the electrodes and the tank wall. More specifically, the surface tension of the liquid is not the same for the two inks, which causes a different meniscus. In general, the level of any ink of any conductivity, 50 I.J.S to 20 kg, can be measured using a device and a method according to the invention. This is all the more interesting as the conductivity can vary greatly depending on the temperature. For an amplitude of 50 ° C., the conductivity can be multiplied by a factor of 2 or 3. Because of their independence with respect to the conductivity, the measurements made according to the invention are therefore not, or only slightly, affected by variations. temperature. A method and a measuring device according to the invention can therefore be used to measure a level of conductive liquid, in particular ink or solvent (if it is conductive), in a reservoir, in particular a jet jet printer. continuous ink. Figure 5 shows the sensitivity of the sensor, that is, the variation in height that the system can measure. The curves which are represented are those of AH = f (h), that is to say, for each conductivity, the evolution of the sensitivity as a function of the measured height. The curves shown relate to: for curves I-IV: a liquid based on water and salt, respectively of conductivity 410 g (curve I); 765 I.J.S (curve II); 1660 I.J.S (curve III); for curves V-VI: pure Mek-based ink (260 IJS (curve IV), then diluted at 1110 g (curve V)). It can be seen that the sensitivity of the measurement decreases with the height of the liquid, but also with the conductivity of the liquid. The observed variation can be smaller with better measuring means.
    [0021] Overall, the sensitivity is less than 1/10 mm, or 3/10 mm. It can be even better with, here again, more powerful measuring means. Another embodiment is shown in Figures 6A and 6B. The difference with the previous embodiment lies in the presence of means 50 which allow to hold, integrally, the end of the rods or electrodes. These means 50 make it possible to reinforce the mechanical stability of the assembly and to maintain the spacing between the electrodes. These means 50 therefore contribute to the stability of the measurements. In the embodiment of FIGS. 6A and 6B, these means take the form of a ring 52 which surrounds a cross constituted by 2 diameters 54, 56, or by 4 branches (spokes) 541, 542, 561, 562 of the ring. An orifice 543, 544, 563 (that on the branch 562 is not visible) on each of the branches of the cross accommodates the end of an electrode, measurement or reference. In FIG. 6B, all the electrodes are seen, with the means 50 for holding the ends. We also see the support 35 which holds them at the other end. Impedance measurements were made with this sensor, the electrodes being provided with means 50, the remainder of the system having all the characteristics of that of FIG. 3A. These measurements consisted of raising the impedances on the 2 pairs of rods every 5mm. They were made on a liquid based on water and salt, with the same 4 conductivities as above, ranging from 410 uS to 1660 uS. 2 other series of measurements were made with pure ink, based on Mek, then with the same very diluted ink, respectively of 1110 uS and 260 uS.
    [0022] The graphs of Fig. 7A (MEK-based liquid) and 7B (water-salt ink) represent the RR / RM ratio between the reference impedance (RR) and the measurement impedance (RM). depending on the height of the liquid. Again, the readings show that the curves at different conductivities (Figure 7A: 260 uS and 1110 uS, Figure 7B: 410 uS, 765 uS, 1230 uS and 1660 I.J.S) are superimposed and are linear. The measurement principle is therefore usable for measuring a level of conductive liquid in a tank. In a configuration where the measurement and reference rods are set at the same height (same distance p for the 2 pairs of electrodes), the liquid height (of the ink) is given by the following relation: - in base water: H = ((RR / RM) * (1 / 0.0661)) - (0.3464 / 0.0661) H = 15.12 (RR / RM) -5.24 - based on Mek: H = ((RR / RM) * (1 / 0.0662)) - (0.2248 / 0.0662) H = 15.10 (RR / RM) - 3.39 The only difference between the two lies in the offset ("offset") of the curve , which is explained by the different behavior (by the surface tension which is not the same for the 2 liquids, as already explained above) on the electrodes and the wall of the tank. It can be seen that, for a given configuration (that of FIG. 3A or that of FIGS. 6A and 6B), the coefficient of proportionality is the same, substantially close to 17.5 in the case of FIG. 3A, substantially close to 15, 1 in the case of Figures 6A and 6B.
    [0023] The coefficient of proportionality reflects the influence of the boundary conditions on the distribution of the field lines, as shown in the diagrams of Figures 8A-8C. FIG. 8A shows the two reference electrodes 24, 26, the ends of which are free, and the corresponding field lines of the system.
    [0024] FIG. 8B shows these two reference electrodes 24, 26, in the case where their ends are held by a holding part 50. In FIG. 8C, these two same reference electrodes 24, 26, whose ends are embedded in an infinite plane, a separator 60, in the area defined by the bottom of the sleeves 24, 26; this separator 60 avoids bypassing the field lines from above. These lines are therefore maintained perpendicular to the conductors of the electrodes. Impedance measurements were made with these 3 sensors, the rest of the system having all the characteristics of that of Figure 3A. These measurements consisted in raising the impedances on the 2 pairs of rods with a level of liquid, of 5mm in 5 mm. They were made on a liquid based on water and salt, with a conductivity of 1230 u.S. The graphs of FIG. 9 represent the ratio RR / RM, between the reference impedance (RR) and the measurement impedance (RM), as a function of the liquid height (curve I: configuration of FIG. 8A, ends free curve II: configuration of Figure 8B, semi-free ends, curve III: configuration of Figure 8C, masked ends). The height of liquid is given by the following relationships: Rod with free ends (Figure 8A): H = ((RR / RM) * 17,2) +10.4 Rod with semi-free ends (Figure 8B): H = ((RR / RM) * 15,2) +5.4 Cane with masked tips (Figure 8C): H = ((RR / RM) * 12,2) +3.6 It can be seen that the coefficient of proportionality varies according to the configuration; it is he who translates the influence of the boundary conditions on the distribution of the field lines. In general, data relating to the coefficient of proportionality, as a function of the configuration, and relating to the deviation at the origin, as a function of the ink, can be memorized and used during the operation of the data. measures. It was possible to model the results obtained by considering electrodes distant from d = 20 mm, each being such as that illustrated in FIG. 10, consisting of a cylinder of radius R terminated, at its lower end, by a hemisphere of radius A. More precisely, it has been possible to show the validity of the following law: hm = (hR + B) RR / RM - aB where B = 2R (Ln (d / R) / (1- (R / d) 2) ). B is a constant which depends only on the geometry and which models edge effects: when means make it possible to reduce these edge effects, one modifies the value of B, to take into account this geometrical modification, by means of the factor a between 0 and 1: a = 0 in the absence of edge effect, a = 1 for rounded and free electrode tips, dipping in a large volume of ink. The results of the preceding figures could be compared with values calculated using the formula above. It has been found that the experimental curves have a look close to the straight lines resulting from the analytical calculation and that there is, in addition, a good quantitative agreement between the case "free electrode tips" (a = 1) as well as for "masked electrode tips" cases (a = 0.1). The formula given above can therefore be used for dimensioning a level measurement system, as well as for calculating the height of liquid with the calculation means available in the printer. Whatever the embodiment chosen, a sensor according to the invention will be installed in a tank 10 so that each electrode is at a distance from any wall of the tank, for example at a minimum distance of at least 20 mm from the tank. any wall of the tank. The means 35 for holding the electrodes (FIG. 3A) at their end opposite to that intended to be in contact with the liquid, make it possible to carry out this positioning. This precaution makes it possible to avoid any influence on the part of the walls on the measurement. In the opposite case, it is possible to attempt to correct the measurements by correction data previously stored in printer control means. These correction data may comprise at least one additional coefficient, or consist of such a coefficient, independent of the conductivity, which makes it possible to retain the advantages of the invention and its linearity. We tried to evaluate the influence of the environment, and in particular the presence of the walls, on the canes.
    [0025] As illustrated in FIG. 11A, measurements were first made which consist of raising the impedance between two rods 116, 118, which define a plane parallel to an insulating wall 100, as a function of the distance D between each of the rods and this wall. The rods are immersed 50mm in a 12301iS conductivity fluid. The rods used are without spacers (such as 50, 60, see Figure 8C) at the end to be able to reduce D and go to the contact of the wall. The results are shown in Figure 11 B. It is seen that the wall has a large influence on the impedance, especially when the canes are very close to the wall. This is explained by the fact, illustrated in Figure 11C, that a large part of the conduction lines pass on either side of the axis of the rods. By removing these lines, the impedance is greatly increased when the wall approaches the canes. An attempt has also been made to evaluate the influence of a wall perpendicular to the canes (these define a plane perpendicular to the wall). As illustrated in FIG. 12A, measurements were first made which consist of raising the impedance between two rods 116, 118, parallel to one another, but arranged in a plane perpendicular to an insulating wall 101, as a function of the distance D 'between the rods 116 closest to the wall and the latter. The rods are immersed 50mm in a 12301iS conductivity fluid. The rods used are without spacers (such as 50, 60) at the end to be able to reduce D 'and go to the contact of the wall.
    [0026] The results are shown in Figure 12 B. It is seen that the wall has an influence on the impedance, especially when the rods are very close to the wall. This is explained by the fact, illustrated in Figure 12C, that part of the conduction lines pass through the back of the cane. It can be seen that the influence is less than in the previous case, since the conduction paths are longer and therefore have less influence on the total impedance. We have also tried to evaluate the influence of the walls on the measurement of liquid level. The measurements here consisted in plotting the ratio between the reference impedance and the measuring impedance as a function of the liquid height (for a 12301iS conductivity fluid). As illustrated in FIG. 13A, the two measuring rods 116, 118 are placed: parallel to the wall 102, at a distance D1 from it, which corresponds to an influence of 50% (in parallel position) and perpendicularly at the wall 103 at a distance D2 thereof (D2 is in fact the distance between the rod 116 closest to the wall 103 and the latter) which corresponds to a 50% influence in the perpendicular position. The rods 120, 122 are arranged in a plane parallel to the rods 116, 118.
    [0027] One of the reference rods 120, 122 is also in perpendicular influence to keep the arrangement in square rods. We take D1 # 3mm and D2 # 3mm. The reference rods 120, 122 are naked on 10 mm and lowered by mm with respect to the measuring rods according to the geometry given by the piece 50 (FIG. 6A). The results are shown in Figure 13B. It is noted that the proximity of walls parallel to the rods does not question the measurement system and especially its linearity. On the other hand the slope which makes it possible to connect the ratio of the impedances to the height varies. In our case: H = (24.15 * Ratio) - 3.38. For the same rods, without walls, we had: H = (17.5 * Ratio) - 12 Some tanks having a shape at least partly conical, it was also sought to evaluate the influence of this type of configuration on the measurement liquid level. The measurements here consisted of plotting the ratio between the reference impedance and the measurement impedance as a function of the liquid height. As illustrated in FIGS. 14A (top view) and 14B (side view), the measurement rods 116, 118 are placed in a truncated cone 107 of angle 22 ° and height 150mm (D being the diameter of the cone, D = 20mm at the bottom of the cone, D = 77mm at the top of it). The electrodes are arranged in a square and their ends are in contact with the cone, as can be seen in FIG. 14B, which corresponds to an extreme embodiment. The results are shown in FIG. 14C (for a 1230uS conductivity liquid).
    [0028] It can be seen that the cone generates nonlinearity over the first 10 or 15 millimeters. This deformation is light and comes only from measuring rods 116, 118, which are more influenced by the proximity of the wall. The reference rods 120, 122 influence only the slope, which makes it possible to connect the ratio of the impedances to the height. We went from a coefficient of 17.5, in free medium (see relation above, H = (17.5 * Ratio) - 12), to a coefficient of 13.2, in the cone. This decrease comes from the increase of the reference impedance, as illustrated in FIG. 14D, this is explained by the suppression of conduction lines on the edge but also from below. In the case of a free rod, the reference impedance, measured during measurements, goes from 476 Ohms to 624 Ohms in the cone. We find the same report: (476/624) * 17.5 = 13.3. It can be concluded from these tests that the properties of the invention are preserved, except in the lower part of the cone (linearity). It will therefore be sought, preferably, to respect a minimum distance, for example of about 15 mm, between the electrodes and the wall of the tank. It has been seen that, in all tests, the reference impedance is a constant which serves to compensate for fluid conductivity variations. It has also been investigated whether the geometry (understood as the shape of the rods and their relative spacing) of the reference rods must be identical to those of the measuring rods. The impedance between two rods depends on the conductivity, the question arises as to whether it varies in the same way for two pairs of rods of shapes and / or distances of different spacing. The tests reported below show that this is not the case. Measurements have been made with a reference rod geometry different from that of measuring rods: the reference rods here have a flat surface, while the measuring rods are cylindrical, and the spacing between the reference rods is different of that between the measuring sticks. Under these conditions, the reference impedance / measurement impedance ratio was plotted for 2 different conductivities.
    [0029] The results are shown in Fig. 15 (curve I: conductivity 410 μS, and curve II: conductivity 1660 g). It can be seen that, for the 2 conductivities, impedance reference / impedance slopes are slightly different: H = 19.8 * Ratio + 3.75 (curve II) and H = 21 * Ratio + 3.52 (curve l). So there is a difference, but only 5%. We will therefore seek, preferably, to have the same geometry on the 2 pairs of cane to avoid creating a decrease in the accuracy of measuring the height. Identical geometry where possible simplifies the design of a system independent of conductivity. The above tests show that the proximity of the rods and the walls of the tank modifies the function that links the ratio of the impedances to the height of the liquid. The influence is greater for a wall parallel to the pair of rods considered a perpendicular wall. If the reference rods measure an image of the conductivity and the measuring rods have a geometry, relative to the walls, which is constant in the height, a linear system is kept. On the other hand, the parameters which make it possible to calculate the height can be made dependent on the distance between electrodes and wall. It can be considered that the influence of the walls becomes negligible as soon as the distance canes-wall is greater than the spacing of the rods. Finally, to minimize the errors related to the geometries and the environment on the accuracy of measurement of liquid height by resistive rods, it is preferred to take symmetrical cane geometries, that is to say that the pairs of electrodes have an identical geometry: the distance between the 2 measurement electrodes is the same as that between the 2 reference electrodes and the shape of the 2 measuring electrodes is the same as that of the reference electrodes; it is also preferred, for the same reason, to take a distance between the electrodes and the walls of the largest reservoir possible; preferably, a distance rods - wall greater than the spacing of the rods is selected. An ink circuit of an inkjet printer may comprise an ink tank provided with ink level measuring means according to the present invention. An example of an ink circuit is described for example in WO 2011/076810. Recall that the ink circuit mainly performs the following functions: * supply of ink of adequate quality under pressure to the generator of drops of the head 1, * recovery and recycling of unused fluids to print back of the gutter of the head 1, * suction for purging the drop generator located in the head 1, * supply of solvent to the head 1 for rinsing performed during maintenance operations of the head. A system comprising an ink circuit 4, comprising a reservoir provided with a measuring device as described above, and means for storing and processing the measured data is illustrated in FIG. 16. The ink circuit 4 sends information, including fluid height data in a tank, measured with a sensor according to the invention, to the controller means. These means allow the piloting of the printer. A user interface 6 may be provided to allow the interaction of an operator with the printer. The means 5 may be programmed to: - process the data measured by a sensor according to the invention, - send a filling instruction of the reservoir, for example from a bottle 41 of reserve ink (FIG. 3A), in function of the result of the calculation of the liquid height. If this result gives a value less than a pre-established threshold value, the filling is automatically triggered.
    [0030] The body, or printer console, 3 (FIG. 1) mainly contains the ink circuit 4, the control controller 5 of the printer and a user interface 6 to allow interaction with the printer. The controller 5 may comprise, for example, a microcomputer or a microprocessor and / or one (or more) electronic card and / or at least one embedded software, whose programming ensures (s) the control of the ink circuit 4 and the print head 1. This controller allows to transmit the printing instructions to the head but also to control the motors and valves of the system to manage the circuit power in ink and / or solvent and the recovery of the mixture of ink and air from the head. It is therefore programmed for this purpose. The means 5 may furthermore comprise means for storing at least one piece of calculation data of the height of the fluid (for example one or more of the formulas above), and / or one or more correction data, for example for take into account the presence or the distance of a wall of the tank, and / or the configuration, free or not, of the ends of the electrodes. Instructions for implementing a method according to the invention, in particular as described above, may optionally be implemented in the form of a computer program. The means 5 may comprise means for reading a data medium, comprising the data, in coded form, for implementing a method according to the invention, in particular as described above. In a variant, a software product comprises a program data support means that can be read by a computer system 5, making it possible to implement a method according to the invention, in particular as described above.
    [0031] The invention can be implemented in a continuous inkjet printer (CIJ) such as that described above in connection with FIGS. 1 and 2. This includes in particular a print head 1, generally deported relative to the body of the printer 3, and connected thereto by means, for example in the form of a flexible umbilicus 2, gathering the hydraulic and electrical connections for the operation of the head.
    权利要求:
    Claims (9)
    [0001]
    REVENDICATIONS1. Continuous level measurement device in a reservoir (10) of a continuous ink jet printer (CIJ), comprising: - first means (24, 26) for measuring the impedance of a first liquid height, predetermined, in said reservoir, - second means (16, 18) for measuring the impedance of any second height, of the same liquid in said reservoir, - means for comparing the two measured impedances and for calculating said second height .
    [0002]
    2. Device according to claim 1, further comprising means (34) for allowing multiplexed measurements using the first means and the second means.
    [0003]
    3. Device according to claim 1 or 2, the first means (24, 26) for measuring the impedance of a first liquid height, predetermined, in said tank, comprising two rods, intended to be mounted parallel in the tank, each having a measurement end of a conductive material, for measuring an impedance that corresponds to the first liquid height, predetermined, and which remains constant for any second height, greater than the first height.
    [0004]
    4. Device according to claim 3, the second means (16, 18) for measuring the impedance of a second height of any liquid in said tank, comprising two measuring rods, each also made of conducting material, intended to be mounted in parallel in the tank, for measuring an impedance which corresponds to a second height of liquid.
    [0005]
    5. Device according to claim 4, the end intended to be immersed of each of the measuring rods: - being offset, with respect to the end of the means, by a value greater than or equal to the 1 predetermined height - or being covered with an insulating coating or an insulating sleeve, over a length greater than or equal to said 1 'height.
    [0006]
    6. Device according to one of claims 3 to 5, further comprising means (30) for supplying measuring rods of the first impedance measuring means and / or measuring rods of second measuring means for measuring impedance, to provide an alternative electrical signal of zero average.
    [0007]
    7. Device according to one of claims 3 to 6, further comprising means (30) power supply, whose frequency is between 1 kHz and 1 MHz.
    [0008]
    8. Device according to one of claims 3 to 7, further comprising means (50) for mechanical holding of an end, intended to be in contact with a liquid to be measured in said reservoir, measuring rods of the first means impedance measuring device and / or measuring rods of second impedance measuring means.
    [0009]
    9. Device according to one of claims 3 to 8, the two rods for measuring the impedance of a first liquid height having a geometry, for example a shape and / or a spacing distance between the two rods, different from, or identical to, that of the two rods for measuring the impedance of a second liquid height. System for continuously measuring the level of a fluid in a reservoir (10) of a jet printer. continuous ink (CIJ), comprising a device according to one of claims 1 to 9, and means (5) for calculating the height of fluid in said reservoir. 11. System according to the preceding claim, further comprising means (5) for storing at least one parameter for calculating the height of a fluid, and / or one or more height correction data calculated to take account of the presence of a tank wall, and / or the configuration, free or not, of the ends of the electrodes. 12. Ink tank for a continuous ink jet printer (CU), comprising: - at least one wall (10), - means (37, 38) for introducing ink into said reservoir and means for discharging ink from said reservoir, - a continuous level measuring device or system according to one of the preceding claims. 13. Tank according to the preceding claim: - the first means (24, 26) for measuring the impedance of a first liquid height, predetermined in said tank, comprising two measuring rods (24, 26), intended to be mounted parallel in the tank, each having a measuring end of a conductive material, for measuring an impedance which corresponds to the first liquid height, predetermined, and which remains constant for any second height, greater than the first height, - the second means (16, 18) for measuring the impedance of any second liquid height in said tank, comprising two measuring rods, each also of conductive material, intended to be mounted in parallel in the tank, to measure a impedance corresponding to a second height of liquid, the device further comprising means for maintaining the rods at a minimum distance of said upper wall at each of the spacings between the canes of each pair of rods. 14. Continuous ink jet printer, comprising: an ink circuit comprising a reservoir according to one of claims 12 or 13, a print head (1), hydraulic connection means, for bringing about from the ink tank, an ink to be printed on the print head (1) and sending ink to be recovered from the print head (1) to the ink circuit, - means electrical connection for electrically supplying said print head. 15. A method of level measurement in a tank of a continuous ink jet printer (CU), implementing a device or a system according to one of claims 1 to 11. 16. Method of level measurement in a reservoir (10) of a continuous ink jet printer (CU), comprising: - a measurement of the impedance of a first predetermined liquid height in said reservoir; a measurement of the impedance of any second height of the same liquid in said reservoir; the comparison of the two measured impedances and the calculation of said second height. 17. The method of claim 16, wherein: the first means (24, 26) for measuring the impedance of a first predetermined liquid height in said reservoir (10) comprise two measurement rods (24, 26), mounted parallel in the tank, each having a measuring end of a conductive material, for measuring an impedance that corresponds to the first liquid height, predetermined, and which remains constant for any second height, greater than the first height; the second means (16, 18) for measuring the impedance of a second liquid height, whatever, in said tank (10), comprise two measuring rods, each also made of conducting material, connected in parallel in the tank, to measure an impedance that corresponds to a second height of liquid. 18. The method of claim 17, wherein, in addition, the measuring rods are electrically powered by an alternating electrical signal of zero average. 19. The method of claim 17 or 18, wherein, in addition, the measuring rods are electrically powered by a current, whose frequency is between 1 kHz and 1 MHz. Method according to one of claims 17 to 19, wherein the end of the rods is maintained with means (50) for holding. Method according to one of claims 17 to 20, wherein the rods are maintained at a distance from the wall of the tank (10) greater than each of the spacings between the rods of each pair of rods. 22. Method according to one of claims 17 to 21, wherein the distance between the canes and the tank walls is maintained greater than the spacing between the rods. 23. Method according to one of claims 17 to 22, further comprising a correction of the height calculated to take into account the presence of a tank wall, and / or the configuration, free or not, of the ends of the electrodes. .
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    同族专利:
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    法律状态:
    2015-11-02| PLFP| Fee payment|Year of fee payment: 2 |
    2016-04-29| PLSC| Publication of the preliminary search report|Effective date: 20160429 |
    2016-10-28| PLFP| Fee payment|Year of fee payment: 3 |
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    优先权:
    申请号 | 申请日 | 专利标题
    FR1460138A|FR3027669B1|2014-10-22|2014-10-22|DEVICE FOR MEASURING LEVEL IN A RESERVOIR|
    FR1460138|2014-10-22|FR1460138A| FR3027669B1|2014-10-22|2014-10-22|DEVICE FOR MEASURING LEVEL IN A RESERVOIR|
    US14/919,156| US9701128B2|2014-10-22|2015-10-21|Device for measuring a level in a tank|
    EP15190721.9A| EP3012602A1|2014-10-22|2015-10-21|Device for measuring a level in a tank|
    CN201510696310.6A| CN105538913B|2014-10-22|2015-10-22|Device for the water level in measuring flume|
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