EP0795407B1 - Device for the stimulated ejection of material under pressure by means of a closable nozzle - Google Patents

Description

The present invention relates to a device allowing the emission of a stimulated jet of material under pressure by a closable nozzle. Such a device can be used in particular to make heads inkjet printer printing.

Indeed, inkjet printers, as their name suggests, generate jets or drops ink using ejection nozzles. Piloting the ink pressure upstream of the nozzle allows start or stop the flow of fluid through the nozzle opening. The quality of the stops and starts essentially depends on the duration of pressure transients during these phases. A free transition of pressure values allows obtain good directivity of the jet at start-up and prevents the formation of an ink deposit at the outlet nozzle when the jet is stopped.

• la répétitivité des phases transitoires qui est difficile à obtenir avec les moyens classiques de pilotage sur le circuit pression que constituent les électrovannes ;
• l'écoulement du fluide par la buse après l'arrêt perturbe la stabilisation rapide du jet : lorsque la température ambiante évolue, l'encre résidant entre la buse et l'électrovanne peut se dilater et provoquer un écoulement de fluide par la buse qui perturbera le redémarrage du jet ;
• l'utilisation d'encres à séchage rapide conduit au colmatage de la buse à la suite d'un arrêt prolongé.

The transition from stop mode to print mode poses some problems, namely:

• the repeatability of the transient phases which is difficult to obtain with conventional means of piloting on the pressure circuit constituted by the solenoid valves;
• the flow of fluid through the nozzle after stopping disrupts the rapid stabilization of the jet: when the ambient temperature changes, the ink residing between the nozzle and the solenoid valve may expand and cause a flow of fluid through the nozzle which will disturb restarting the jet;
• the use of quick-drying inks leads to clogging of the nozzle after prolonged stoppage.

Different solutions have been proposed for overcome these shortcomings. One of these solutions is to close off the nozzle between two operating phases.

We can summarize the solutions proposed for mitigate the risks of clogging of the nozzles by mentioning the following documents.

Document EP-A-54 905 discloses the use electromagnetic closure means of the nozzle jet emission to prevent ambient air penetrates and applies in case the printing ink is a magnetic fluid. We explain in particular how supply system problems for a fluid magnetic are resolved.

US-A-4,199,767 describes a means nozzle closure consisting of a plate which can move in front of the nozzle thanks to a magnetic field. A similar idea is presented in IBM Technical Disclosure Bulletin, vol. 18, n ° 12, May 1976. In the proposed systems, which bring two solid parts to seal an orifice it is however necessary to provide forces electromagnetic sufficient to take off contacts following a prolonged shutdown, a residue ink around these contacts that may have dried.

Document FR-A-2 540 044 describes a device according to the preamble of claim 1, in which is planned a solution closing the nozzle using equipped solenoid valves a flexible part mounted on the rod of an element of translation. This function is used to generate drops at the frequency of openings and closings nozzle. This solution is included in the document WO 91/00808 in the case of use in technology deflected continuous jet. In this case, the element of electromagnetic drive supports on the nozzle via a flexible part and isolates the ink from the surrounding environment during stops. This solution prevents the ink from spilling and drying thereof at the outlet of the nozzle. Moreover, the nozzle is opened when the cavity ink is in established pressure and thus allows stable and rapid start-up of the jet. Imprisonment air in the cavity at the time of shutdown is avoided and we remove the air / ink spray phenomenon when starting the jet. However, this solution has a serious drawback because of the congestion caused by housing on the one hand of the jet stimulation actuator and, on the other hand, of the shutter assembly. The cavity upstream of the nozzle must receive these two functions either so coaxial, i.e. along two distinct converging axes towards the nozzle.

To overcome the disadvantages of these prior art devices it is proposed according to the present invention the establishment of a nozzle shutter which has the distinction of being associated with the stimulation function of the device. The device according to the invention has the advantage of being compact. It ensures the correct sealing of the nozzle while guaranteeing jet stops and starts correct and repetitive. An additional advantage lies in the reduced number of parts required to its implementation.

• être dans une position d'obturation de la buse lorsque les moyens de commande n'autorisent pas l'émission d'un jet de matière,
• être dans une position de libération de la buse lorsque les moyens de commande autorisent l'émission d'un jet de matière.

The subject of the invention is therefore a device allowing the emission of material in the form of a jet via a nozzle comprising at least one emission orifice, the nozzle being able to communicate with a cavity of the device through which transits said material and where it is pressurized to allow the formation of said jet under the effect of control means, stimulation means being located near the nozzle to split the jet into a succession of elements, obturation of the nozzle in the absence of emission of a jet of material being provided, characterized in that the obturation means consist of a deformable member, placed between the stimulation means and the nozzle and integral with the means of stimulation, the deformable member being designed to react mechanically as a function of the pressure to which said material is subjected in order to have the following bistable operation:

• be in a closed position of the nozzle when the control means do not allow the emission of a jet of material,
• be in a position for releasing the nozzle when the control means authorize the emission of a jet of material.

In the event that the emission of a jet is controlled by the pressure existing in the cavity, the deformable member comprises a part lying between the stimulation means and the nozzle, this part being connected to a bellows allowing movement relative of said part with respect to the nozzle, the bellows, subjected on one of its faces to pressure matter in the cavity, having mechanical characteristics such as for pressure material that does not allow the emission of a jet said part of the deformable member closes off the nozzle, and that for a pressure of the material allowing the emission of a jet said part of the deformable member is moved away from the nozzle.

The stimulation means may include an elongated body, the bellows surrounding the elongated body and being tightly attached to this elongated body so that the space between the elongated body, the bellows and the part of the deformable member contains a gas. This gas can simply be air.

Advantageously, when the emission of a jet is not allowed, said part of the body deformable is pressed onto the nozzle, means sealing being provided between said part and the nozzle.

The control means can, according to a other variant, include an actuator acting on the deformable member for closing or releasing the nozzle. This actuator can also serve as means of jet stimulation.

The actuator can advantageously be an element piezoelectric or electromagnetic comprising means for receiving a DC voltage so to force the deformable member to release the nozzle and a alternating voltage to stimulate the jet.

According to a preferred embodiment of this variant, the nozzle can be contained in a plate with nozzle, the deformable member can be a membrane held in the device by its periphery, the nozzle plate, diaphragm and actuator forming a succession of elements stacked and centered on the nozzle, the nozzle plate having one of these faces main in contact with a supply duct said material and the other of its main faces adjacent to the membrane, communication being provided between the two main faces of the nozzle plate for the passage of said material.

• la figure 1 représente, en vue éclatée, un dispositif de stimulation ou de modulation pour tête d'impression à jet d'encre selon l'art connu,
• la figure 2 représente, vu en coupe longitudinale, le canon du dispositif de modulation équipé de son résonateur et où est mise en oeuvre la présente invention,
• la figure 3 représente un élément d'une autre variante de dispositif de modulation mettant en oeuvre la présente invention.

The invention will now be described by taking the example of an inkjet printer printhead, although it can be applied to the emission of a stimulated jet of another material. The invention will be better understood by means of the appended drawings in which:

• FIG. 1 represents, in exploded view, a stimulation or modulation device for an ink jet print head according to the known art,
• FIG. 2 represents, seen in longitudinal section, the barrel of the modulation device equipped with its resonator and where the present invention is implemented,
• FIG. 3 represents an element of another variant of a modulation device implementing the present invention.

The solution proposed by the invention will now be applied to the modulation device disclosed by document FR-A-2 653 063. This device is shown in exploded view in Figure 1, the elements shown on the right side of the figure normally located in the extension of the part upper left.

The device comprises a support 1 which is intended to be fixed on the mechanical structure of the print head (see Figure 1 of the document FR-A-2 653 063). Support 1 has a part tubular 4 axis coincides with the axis of the inkjet. In this tubular part 4 the body is housed 2 of the barrel 3 which is a part of general shape cylindrical, of axis of revolution coincident with the axis of the tubular part 4. The barrel 3 is drilled through from an axial hole 8.

The body 2 constitutes the lower part of the barrel 3. A shoulder 5 constitutes the separation between the body 2 and the upper part of the barrel 3. The body 2 is provided with an upper groove 6 near of the shoulder 5 and of a lower groove 7. The lower end 9 of the body 2 is threaded to receive the nut 10. Radial holes 11, 12 drilled respectively in grooves 6 and 7 provide the communication between the axial hole 8 and the grooves 6 and 7.

Before engaging the barrel body 2 in the tubular part 4 of the support 1, we thread successively on body 2: the shaped joint 13 ring, tubular spacer 14 and seal 15 also in the shape of a ring. The average diameters of seals 13 and 15 correspond to the diameter of the spacer 14. This makes the seal 13, the spacer 14 and the seal 15 constitute a stack.

The body 2 of the barrel 3, equipped with the seal 13, of the spacer 14 and of the seal 15, being introduced in the tubular part 4, the nut 10 is screwed onto the end 9 of the body 2 through the lower orifice of the tubular part 4. The seal 13 abuts on the shoulder 5 of the barrel and the force exerted by the nut 10, during screwing, on the joint 15 affects joint 13 via the spacer 14. The seals 13 and 15 are seals expandable by force. The tightening of nut 10 therefore causes the application of seals 13 and 15 on the inner wall of the tubular part 4, thus ensuring at the same time the sealing at the level joints and fixing the barrel 3 to the support 1. Note that the nut 10 does not come in support on the tubular part 4 of the support. His action works only on the joint stack 13 - spacer 14 - seal 15.

The spacer 14 is provided with a groove upper 16 and lower groove 17. Holes 18 and 19 are drilled radially and respectively in grooves 16 and 17. During assembly, grooves 16 and 17 of the spacer 14 are located opposite the grooves 6 and 7, respectively, of body 2.

The support 4 is provided with a connector 21 for introducing pressurized ink into the part tubular 4 and a connector 22 for purging of this same tubular part. These fittings 21 and 22 open near the gorges respectively 16 and 17 of the spacer 14.

Resonator 25, which stimulates the inkjet, is introduced through its end 24 in the barrel 3 through the upper hole of the hole 8, through seal 20. The other end of the resonator extends by an electric cable 23 to an organ of external control. Cable 23 goes through the hole axial 27 of flange 28.

The fixing of the resonator in the barrel is done in the following way. The equipped resonator 25 of seal 20 is pressed into hole 8 until the underside of the seal 20 abuts on a shoulder provided in hole 8. A flange 26 of the resonator then comes into abutment on the face upper part of seal 20. The flange is slid along cable 23 and its threaded lower part 29 is screwed in the upper threaded part of hole 8 up to press the seal 20.

The device operates as following. The pressurized ink injected by the connection 21 bathes the outside of the spacer 14 and enters inside through holes 18 to reach the external part of the body 2 of the barrel. Ink passes in the holes 11 of the groove 6, penetrates inside of the barrel by bathing the resonator 25 and goes towards the end 9 of the barrel which is terminated by a washer (not visible in Figure 1) pierced with a axial hole serving as an ink emission nozzle. The purge of the device is done by return of the ink, thanks at the holes 12, in the tubular space between the body 2 and the spacer 14 then, thanks to the holes 19 of the spacer, in the tubular space included between the spacer 14 and the tubular part of the support. The ink is then discharged through the connector 22.

The inkjet stimulated by the resonator 25, is therefore done along the axis of the device as well as the arrow drawn under the nut 10 is shown.

Side holes provided in the nut 10, the barrel 3 and the flange 28 make it possible to carry out adjustments to obtain the correct alignment of the inkjet. These settings are explained in the document FR-A-2 653 063.

Figure 2 shows a cannon 103 of modulation device in which is housed a modulator 125, these elements being of the type shown in Figure 1. The modulator 125 is based on a internal shoulder of the barrel 103 thanks to the collar 126 with interposition of a seal 120. It has an end portion 130 of diameter smaller than the rest of the modulator, which leads the presence of a shoulder 131. A collar 132 connects the end portion 130 to the rest of the modulator.

Between the resonator 125 and the barrel 103 exists a cavity 140 constituting part of the axial hole 108 of the barrel and in which ink can flow introduced through hole 111 and capable of being evacuated through hole 112. In cavity 140, the ink is subjected to the action of the resonator 125.

At the lower end of the barrel 103 is fixed a plate 141 in the shape of a disc and provided a central hole 142 forming the nozzle. The nozzle 142 is found opposite the lower end 124 of the resonator 125.

According to the invention, a deformable member 150 is placed between the resonator 125 and the nozzle 142. The deformable member 150 has a shaped part 151 disc, of diameter corresponding to the diameter of the end part 130 of the resonator, a part annular 152 for connection to the resonator and part intermediate 153 playing the role of bellows and surrounding the end portion 130 of the resonator.

The collar 132 of the resonator makes it possible to center easily the deformable member 150 on the part end 130. This deformable member can be in stainless steel and be fixed by waterproof welding on the resonator. A volume of air is therefore trapped between the deformable member 150 and the end part 130 of the resonator.

An elastomer sealing washer 161 or in Teflon®, fixed on the external side of the part 151 disc-shaped, provides a flexible interface between the deformable member and the plate 141. Instead a washer, you can use a coating, for example of fluoropolymer, on the external side of this part 151.

In the application example shown in Figure 2, the nozzle shutter is of the passive type. It is activated thanks to the different pressures established in the barrel during the stop and start phases. The bellows 153 has a useful stroke which allows bistable operation of the shutter. At a first state, the prestressed bellows rests on the plate 141, which causes the closure of the nozzle.

In a second state, the bellows 153 compresses under the effect of the pressure rise of the ink in the cavity 140 until the part 151 of the deformable member comes to bear against the end 124 of the resonator. This is the phase of start-up. The nozzle 142 is released and the ink can be issued as a jet.

This arrangement allows starting and jet stop at controlled pressure values by acting on the following parameters: stiffness bellows mechanics, value of the prestressing closure, effective surface of the bellows. As example, the bellows can be made from a 20 µm thick stainless steel sheet.

• arrêt du jet : coupure franche du jet à la valeur de pression choisie et chute rapide de la pression dans la cavité 140 par ouverture de l'électrovanne de purge pendant la fermeture de l'électrovanne de pression ;
• rafraíchissement de l'encre : l'ouverture de l'électrovanne de purge puis de l'électrovanne de pression permet de réaliser le rafraíchissement de l'encre, la buse étant obturée (pression de fonctionnement inférieure au seuil d'ouverture du soufflet) ;
• démarrage du jet : la fermeture de l'électrovanne de purge pendant la phase de rafraíchissement provoque une brusque élévation de pression dans la cavité 140 et décolle le soufflet de la plaque à buse 141 à une valeur de pression définie.

The optimal dimensioning of the bellows ensures, according to the open or closed states of the solenoid valves of the ink circuit, the following cycles:

• jet stop: abrupt shutdown of the jet at the selected pressure value and rapid drop in pressure in the cavity 140 by opening the purge solenoid valve while the pressure solenoid valve is closing;
• refreshing the ink: opening the purge solenoid valve and then the pressure solenoid valve makes it possible to cool the ink, the nozzle being blocked (operating pressure below the bellows opening threshold);
• start of the jet: the closing of the purge solenoid valve during the cooling phase causes a sudden increase in pressure in the cavity 140 and takes off the bellows from the nozzle plate 141 at a defined pressure value.

Another variant of the modulation device of an ink jet is shown in Figure 3. This device is attached to a jet printing machine ink through a flange 50 and has a body cylindrical 51 screwed to this flange. As a variant, the device can be fixed to the machine by the body cylindrical 51. A nozzle plate 60 in the form of a disc, obtained for example by chemical cutting and etching is arranged in a housing of suitable shape, provided in the bottom 53 of the body 51. The bottom 53 is pierced with a central hole 52 and has an annular duct ink inlet 54 communicating with a circuit ink equipped with pressure and purge valves not represented. The nozzle plate 60 has a conduit annular 61 directed upwards and is pierced with a central hole 62 forming ejection nozzle as well as holes 63 (only one is visible in the figure) making communicate the annular conduits 54 and 61. The volume constituted by conduits 54 and 61 and by the holes 63 forms the equivalent of a cavity.

The nozzle plate 60 is covered by a metallic membrane 55 acting as a shutter, a flexible film 56 (made of elastomer for example) being interposed between the membrane 55 and the nozzle plate 60 for sealing. The membrane 55 and the flexible film 56 are disc-shaped elements held at their periphery by the resulting tightening screwing the body 51 onto the flange 50.

A piezoelectric actuator 70 is returned integral with the membrane 55 and receives signals from electric controls by electric cable 71. Alternatively, an actuator could be used electromagnetic.

The operation of the device shown in Figure 3 is identical to the device in Figure 2. The stiffness of the assembly ensures the two positions stable at defined pressure values. A tension continuous can be supplied to the actuator 70 for allow the lifting of the membrane 55 and the film flexible seal 56 which adheres thereto, thereby releasing the nozzle to cause the emission of an ink jet. The application of this DC voltage makes it possible to obtain more frank pressure transients. Voltage continuous can be positive or negative to help when opening or closing the nozzle. A tension alternative to which is possibly superimposed the direct tension makes the membrane vibrate metallic 55 and divide the inkjet into one succession of drops. When issuing a jet, direct voltage offers the possibility of modifying the flow of ink thanks to a modification of the value of the voltage. This regulates the jet speed.

This arrangement has the advantage of compactness while limiting the number of parts for perform the function.

• la suppression des instabilités de jet pendant les phases de rafraíchissement et d'arrêt en évitant les à-coups de pression jet en marche,
• la coupure ou la mise en route correcte du jet en assurant l'ouverture et la fermeture de la buse à des valeurs de pression connues et répétitives,
• la suppression au démarrage d'une pulvérisation d'air et d'encre en évitant l'introduction d'air dans la cavité,
• le maintien en état de propreté de la sortie de la buse en évitant les écoulements d'encre à l'arrêt.

Among the advantages provided by the present invention, there may be mentioned:

• the elimination of jet instabilities during the cooling and stopping phases by avoiding pressure jerks when the jet is running,
• the correct cutting or starting of the jet by ensuring the opening and closing of the nozzle at known and repetitive pressure values,
• the suppression at start-up of an air and ink spray while avoiding the introduction of air into the cavity,
• keeping the nozzle outlet clean, avoiding ink spills when stopped.

Claims (11)

1. Device permitting the emission of material in the form of a jet by means of a nozzle having at least one emission orifice (62, 142), the nozzle being able to communicate with a cavity (54, 61, 63; 140) of the device through which passes said material and where it is pressurized to permit the formation of said jet under the action of control means, stimulation means (70, 125) being located in the vicinity of the nozzle in order to split up the jet into a succession of elements, means for sealing the nozzle in the absence of material jet emission being provided, characterized in that the sealing means are constituted by a deformable member (55, 150) positioned between the stimulation means and the nozzle and integral with said stimulation means, the deformable member being mechanically designed to react as a function of the pressure to which said material is exposed, so as to have the following bistable operation:

   being in a nozzle sealing position when the control means do not allow the emission of a material jet,

   being in a nozzle freeing position when the control means allow the emission of a material jet.
2. Device according to claim 1, characterized in that the emission of a jet being controlled by the pressure in the cavity (140), the deformable member (150) comprises a part (151) located between stimulation means (125) and the nozzle, said part (151) being connected to a bellows (153) allowing a relative displacement of said part with respect to the nozzle (142), the bellows (153) exposed on one of its faces to the pressure of the material in the cavity (140), having mechanical characteristics such that for a pressure of the material not allowing the emission of a jet, said part (151) of the deformable member (150) seals the nozzle (142), and for a pressure of the material allowing the emission of a jet, said part (151) of the deformable member is moved away from the nozzle (142).
3. Device according to claim 2, characterized in that the stimulation means (125) have an elongated body (130), the bellows (153) surrounding the elongated body and is tight fixed to said elongated body in such a way that the space between the elongated body, the bellows and the part (151) of the deformable member (150) contains a gas.
4. Device according to claim 3, characterized in that the gas contained in said space is air.
5. Device according to any one of the claims 2 to 4, characterized in that when the emission of a jet is not allowed, said deformable member (150) part (151) is engaged on the nozzle (142), sealing means (161) being provided between said part (151) and said nozzle (142).
6. Device according to claim 1, characterized in that the control means comprise an actuator (70) acting on the deformable member (55) in order to seal or free the nozzle (62).
7. Device according to claim 6, characterized in that said actuator (70) also serves as a jet stimulation means.
8. Device according to claim 7, characterized in that said actuator (70) is a piezoelectric or electromagnetic element having means for receiving a d.c. voltage in order to force the deformable member (55) to free the nozzle (62) and an a.c. voltage permitting the stimulation of the jet.
9. Device according to any one of the claims 6 to 8, characterized in that the nozzle (62) is contained in a nozzle plate (60), the deformable member (55) being a membrane maintained by its periphery in the device, the nozzle plate, membrane and actuator forming a succession of stacked elements centred on the nozzle, the nozzle plate (62) having one of its main faces in contact with a supply pipe (54) for said material and the other of its main faces adjacent to the membrane (55), a communication (63) being provided between the two main faces of the nozzle plate (60) for the passage of said material.
10. Device according to claim 9, characterized in that a flexible sealing film (56) is interposed between the membrane (55) and the nozzle plate (60).
11. Use of the device according to any one of the preceding claims in a printing head for an ink jet printer, ink constituting said material.

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