FR2465528A1 - VIBRATION DEVICE WITH PIEZOELECTRIC ELEMENT FOR LIQUID GUNS FOR EYEING HEAD OF A FRAGMENTED LIQUID - Google Patents

Abstract

THE INVENTION RELATES TO A VIBRATORY DEVICE WITH A PIEZO-ELECTRIC ELEMENT FOR A LIQUID CANNON INTENDED FOR A HEAD FOR EJECTING A FRAGMENT LIQUID. THE COMBINATION OF THE PIEZO-ELECTRIC TRANSDUCER WITH A FRONT RESONATOR AND A DISSYMETRIC REAR RESONATOR IS PIERCED IN ITS CENTER OF AN ORIFICE THROUGH WHICH THE LIQUID SUPPLY TUBE PASSES THROUGHOUT THE SQUID DEVICE WITHOUT VIBRATION THERE IS DIRECT CONTACT BETWEEN THE TRANSDUCER AND THE LIQUID. TIGHTENING NUTS ENSURE THE CONNECTION OF THE VARIOUS PARTS TO A AFFUT ITSELF LOCATED IN A HOLDER. THIS CAN BE MULTIPLE AND INCLUDES MOUNTS OF PIVOTING THE AFFUTS ALLOWING THUS AN ORIENTATION OF THE JET. THE INVENTION APPLIES TO TECHNIQUES INVOLVING THE FRAGMENTION OF LIQUID INTO CALIBRATED DROPS, IN PARTICULAR TO THE TECHNIQUE OF PRINTING BY INKJET.

Description

L! The invention relates to a vibratory device with a piezoelectric element

  for liquid gun for an ejection head of a fragmented liquid such as in particular an ink jet print head. It relates more specifically to excitation means in forced mode of an ejection nozzle for the creation of drops and the arrangement of these means leading to the obtaining of gun to

  liquid such as in particular an inkjet print head.

  An inkjet printer must first produce a stream of drops with well-defined characteristics: the drops must be regularly spaced, the same size and propelled in the same direction, at the same speed. For this we create drops of size calibrated by the breaking of a fluid jet emitted by the nozzle. This break is usually achieved through the action

  of piezoelectric ceramics. Various solutions for exciting these ceramics

  They exist either in longitudinal mode called "thickness mode" by piezoelectric disks, or in transverse mode called "necking mode" by piezoelectric tubes or finally in bending mode for compression of a cavity. Among the main drawbacks that these systems present, mention may be made in particular of the problem of space requirement, due to the difficulties of fixing between them ceramics and the feed tube, that of the adjustment of various parameters such as the orientation of the jet of liquid. which gives rise to the train of drops, finally the problem of fixing the nozzle itself which still presents great difficulties, The present invention aims to overcome these disadvantages and relates to a new architecture of the main means constituting a vibratory device including for an ink jet printer: device of reduced dimensions enabling the production of printing heads with several adjacent nozzles arranged in rows at a periodicity which may be only a few millimeters. This result is achieved through the combination of transducer and resonators whose essential feature is to be drilled in their center to let the liquid supply tube through and through the vibratory device and can be made integral of the nozzle

  in the front part of the resonator.

  One of the main applications of the invention is the ink jet printer but it can be applied to any other system requiring the formation of

trains of calibrated drops.

  The invention more particularly relates to a vibratory device with a piezoelectric element capable of generating propagation of acoustic waves in a liquid to ensure the fragmentation of the liquid into droplets, characterized in that it comprises a first combination of a piezoelectric transducer. electric coupled to a front resonator and a second combination of

  piezoelectric transducer with a rear resonator, this double combination

  its having a central orifice through which passes the liquid supply tube which thus passes right through the vibratory device without the liquid

  in direct contact with the piezoelectric transducer.

  The invention will be better understood with the aid of the following explanations and the attached figures among which: - Figures 1 to 3 show schematically two variants of embodiments of a vibratory device according to the invention; FIGS. 4 to 6 schematically illustrate an arrangement of the devices according to the invention constituting an ejection head whose nozzle is orientable in

different plans.

  For the sake of clarity, the same elements bear the same references

in all the figures.

  As shown in FIG. 1, a vibratory device according to the invention

  vention and the barrel which is equipped with a piezoelectric transducer 7 cooperating with a first and a second mechanical resonator front and rear respectively referenced 3 and 5 thus forming a first and a second transducer-resonator combinations. The two resonators 3 and 5 are interconnected by clamping screws 6 which at the same time ensure the assembly of the

  Piezoelectric transducer 7. This consists of one or more ceramics

  piezoelectric elements for example of prismatic shape of any base (circular, square or rectangular) but which in all cases and according to the invention are drilled from one side in a direction perpendicular to their planar faces which constitute their faces of clamping on the mechanical resonators 3 and 5 to allow the passage of the liquid supply tube 1 which under these conditions passes through the vibratory device without there being contact between it and the liquid. The feed tube terminates at one of its ends by a nozzle or ejection nozzle 4 which may be, for example made of clockwork sapphire

  pierced along its axis of revolution.

  The ceramics are contiguous by their face of the same polarity to an electrical contact 8. A variable and in particular periodic potential is applied across the transducer 7 via the connections 8 and 9. The connection 9 in the example described by means of Figure 1 is connected to the liquid supply tube 1 which is metallic and conductive. In the case where this tube is not conductive, this connection would be taken on the metal resonator 5. The tranducer operates in longitudinal vibratory mode (periodic variation in thickness) which entails the propagation of acoustic waves throughout the device vibratory constituted by the transducer and the mechanical resonators whose result is to ensure a fragmentation of the jet into droplets of equal dimensions. The resonance frequency depends on the nature and shape of the resonators. The vibratory device has maximum efficiency when one gives each of its two halves a length corresponding to a phase shift A Y1 and AW2 equal to W / 2 between the middle part (corresponding substantially to the electrical contact 8) and each both ends, for the excitation wave

  acoustic that propagates there as a result of the vibration of the piezo transducer.

  electric. In the example illustrated in FIG. 1, the lengths AB, CD and EF being equal to 12, 15 and 3 mm, respectively, and the resonator being made of brass, the resonance frequency is of the order of 70 kHz. It should be noted that the resonator 3 disposed at the front (on the side of the nozzle 4) is smaller than that of the resonator 5 disposed at the rear. This configuration has the advantage of allowing on this side an emission in the air which is less than

  the acoustic emission obtained on the nozzle 4 side.

  A second variant embodiment of a vibratory device according to the invention is shown in FIG. 2. The two front and rear resonators 3 and 5 are found to have a configuration different from that of the preceding figure which may be preferable for the subsequent arrangement of this device in a given print head. These two resonators are connected to one another and enclose a piezoelectric transducer 7 by means of two clamping screws 6. As in the previous example, a variable potential is applied to

  Transducer terminals 7 via electrical connections 8 and 9.

  The nozzle or nozzle 4 is integral with the liquid supply tube 1 at the front thereof and at the front resonator 3. This embodiment works

  for example, at a resonance frequency of 120 Khz.

  As in the case of the previous variant, this vibratory device has maximum efficiency when giving each of its two halves a length corresponding to a phase shift a (1 and A 2o'2equal / r / 2.The various parts of the device being composed of different materials, the wavelength of the excitation acoustic wave that propagates there varies according to the nature of the material, which is taken into account in the calculation of the phase-shifts t) 1 and AY 2

  that we get at each end.

  In summary, therefore, according to a first feature, a device con-

  form to the invention comprises in particular the combination of the following means: - a fluid supply tube, corrosion resistant material due to the circulation of the fluid; an ejection nozzle forming the orifice of this tube; at least one ring-shaped ceramic or piezoelectric crystal having a central orifice allowing the passage of the fluid supply tube, it being understood that the use of two piezoelectric elements makes the operation more symmetrical, facilitates the connections and allows to obtain a vibration node in the central part;

  metallic masses located on either side of the piezo element (s)

  electrical and constituting acoustic resonators to increase the efficiency of the system, the masses located on either side may be made of metals of different nature to differentiate acoustic impedances and reduce the power output by the so-called end not active device opposite the so-called active end which is located on the side of the ejection nozzle. Another characteristic of the arrangement according to the invention of the means constituting this vibratory device applied to a liquid gun lies in the fact that it is possible to ensure the fixing of this barrel to the rest of the machine without resorting to a tightening. at the level of the transducer. Indeed, one can use a fastening device of the type said clamping nut 20. It is then the same liquid supply tube 1 which serves as an anchoring pin between the part

  200 and the other inner sliding 22 of this fastener 20.

  Such a clamping nut mounting device may also be chosen for fixing the feed tube and the ejection nozzle to the vibratory device on the active end side. An example of a configuration of a vibratory device according to the invention of this type is shown in FIG. 3. It contains the liquid supply pipe 1, the ejection nozzle 4 and the piezoelectric ceramics 7 connected to it. to the resonators 3 and 5 by means of the clamping screws 6. The feed tube and the nozzle are secured to the device

  vibratory by means of a clamping nut 20.

  In summary therefore, according to a second characteristic, the feed tube is connected according to the invention by means of clamping nuts, on the one hand to the vibratory device at the active end (front) and on the other hand to the at the non-active end (rear), which allows the piezoelectric elements to oscillate freely

  longitudinally along an axis parallel to that of the feed tube.

  FIG. 4, supplemented by FIGS. 5 and 6, illustrates an exemplary arrangement

  mounting of a device according to the invention of a vibratory device described above, leading to obtaining a head, for example a print head for

inkjet printer.

  FIG. 4 is a perspective view of the mounting, on a multiple support, of a carriage carrying a barrel consisting essentially of a connected nozzle.

  to the liquid supply tube and an excitation device.

  FIG. 5 represents, according to two sections (a) and (b), a carriage such that

  shown in Figure 4; (Figure 5b is a section along AA 'of Figure 5a).

  Figure 6 shows in two sections (a) and (b) a device for adjusting the orientation of this carriage by pivoting about an axis. These figures as well as the

  Figure 6 view in two sections (a) and (b) are now described simultaneously.

  The vibratory device comprising the piezoelectric ceramics 7 clamped between the resonators 3 and 5 are mounted on a carriage 200. The feed tube 1 is connected to the vibratory device by a clamping nut 20. This tube carries the ejection nozzle at its end. It can rotate around itself (as shown by the arrow A) which makes it possible to mitigate any centering defects existing at the nozzle and to bring the jet into the plane of the adjusting screws 70 (that is that is, in the plane of Figure 6a). A locking screw 30 holds the tube in the optimum position. At least one carriage 200 as described above is contained in a support 60 which can be simple o multiple capable in the latter case, to receive a plurality of carriages. The lookout or plurality of carriages (only one of which is shown in FIG. 4) is held in place by means of an axis 80 around which each carriage can pivot as shown by the arrow B. Adjustment screws 70 allow the orientation of the jet in the plane of Figure 6a. Given the reduced dimensions of the mechanical resonators and the need to rotate the feed tube to obtain the setting defined above, two conditions are in particular realized. On the one hand, the resonators do not have a symmetry of revolution, but rather a flat shape (more visible in Figure 4) which allows a multiple mounting with a periodicity (a C.2 -) b) which can be for example 4 mm while also allowing mounting and tightening with screws. On the other hand, the resonators are set up using clamping nuts when the feed tube is in the proper position. A notorious advantage of the clamping nuts lies in the fact that they make it possible to easily remove and replace the feed tube and the nozzle in case of bad

  irremediable operation or clogging.

  In the case of a head comprising several ink cannons, an advantage of the invention is to make the vibratory devices associated with each nozzle independent, in particular with regard to the acoustic vibration, which makes the interaction between the guns minimal . Another advantage of the invention is to lead to reduced dimensions of the barrel as the excitation frequency is higher. This is particularly advantageous in the case of inkjet printing where an increase in printing speed generally requires, on the one hand, a high excitation frequency in order to obtain a large number of droplets per second and on the other hand a frequency of nozzles of only a few millimeters to minimize the flight time of

  drops to account for the speed of scrolling paper.

  As has already been said above, the invention applies more particularly to inkjet printing techniques, especially at high speed, but it also applies to techniques involving the creation of liquid droplets of calibrated size. in large numbers such as for example

  fog, aerosol, sprays for the elimination of fumes and dust.

Claims (8)

  1. A vibratory device with a piezoelectric element capable of generating propagation of acoustic waves in a liquid to ensure the fragmentation of the   droplet liquid, characterized in that it comprises a first combination of   a pair of piezoelectric transducers coupled to a front resonator and a second combination of the piezoelectric transducer coupled to a rear resonator, this dual combination having an orificecentral through which the liquid supply tube passes through apart from the vibratory device without the liquid being in direct contact with the piezoelectric transducer. Vibratory device according to claim 1, characterized in that the first and the second combination of the transducer with the front resonator and   with the rear resonator are asymmetrical.   3. vibratory device according to claim 2, characterized in that the dimensioning and the nature of the materials are chosen for the resonators so that there is respectively between the front face of the front resonator, the rear face of the rear resonator and the part Transducer median phase shift and tT 2 2 4. Vibration device according to claim 3, characterized in that the front resonator, placed on the nozzle side is of smaller size than the rear resonator.   5. Liquid gun, characterized in that it is equipped with a device   vibratory device according to one of the preceding claims.   6. ejection head of a fragmented liquid characterized in that it comprises a liquid gun according to claim 5, wherein the liquid supply tube is clamped on the front resonator by means of a clamping nut . 7. ejection head of a fragmented liquid, characterized in that it comprises a liquid gun according to claim 5, characterized in that this gun is mounted on a carriage, so that the feed tube is is fixed on this mount by means of a clamping nut so that it can be turned around himself.   8. ejection head of a fragmented liquid according to claim 7, characterized in that at least one carriage is positioned in a support, the carriage can be pivoted about an axis and clamped in a predetermined position at 3.5 means of clamping screw.   9. ejection head of a fragmented liquid according to claim 8, characterized in that this support is a multiple support capable of receiving a   a plurality of pivotable plates each around a common axis.   10. Head of ejection of a fragmented liquid according to one of claims 6   at 9, characterized in that the liquid is ink fragmenting in the form an inkjet printer.