EP0160019A1

EP0160019A1 - Ink feeding circuit for an ink jet printing head.

Info

Publication number: EP0160019A1
Application number: EP84903715A
Authority: EP
Inventors: Luc Regnault
Original assignee: Imaje SA
Current assignee: Markem Imaje SAS
Priority date: 1983-10-13
Filing date: 1984-10-11
Publication date: 1985-11-06
Also published as: FR2553341B1; IT1179769B; IT8453919V0; US4628329A; FR2553341A1; CA1250486A; DE3470693D1; AU3505284A; EP0160019B1; AU581631B2; WO1985001696A1; JPH0553632B2; JPS61500162A; IT8468012A1; IT8468012A0

Abstract

Il s'agit d'un circuit comportant notamment un premier circuit auxiliaire (R1) dont la fonction est de mesurer la pression de l'encre entre la canalisation d'alimentation (20) et la canalisation d'amenée de l'encre (18) et un second circuit auxiliaire (R2) assurant le débouchage éventuel de l'orifice d'éjection (41) des gouttes d'encre (100). Ce circuit peut également comporter un troisième circuit auxiliaire (R3) fournissant un signal représentatif de la viscosité de l'encre. La mesure de la pression et de la viscosité permet un asservissement des principaux paramètres régissant le fonctionnement de l'imprimante qui en est équipée. L'invention s'applique à toute imprimante à jet d'encre.It is a circuit comprising in particular a first auxiliary circuit (R1) whose function is to measure the ink pressure between the supply line (20) and the ink supply line (18 ) and a second auxiliary circuit (R2) ensuring the possible unclogging of the ejection orifice (41) of the ink drops (100). This circuit can also include a third auxiliary circuit (R3) providing a signal representative of the viscosity of the ink. The measurement of pressure and viscosity allows the main parameters governing the operation of the printer which is equipped with it to be controlled. The invention applies to any inkjet printer.

Description

INK SUPPLY CIRCUIT FOR AN INK JET PRINTHEAD

The invention relates to an ink supply circuit for an ink jet print head. It also relates to any printer which is equipped with it.

Several problems arise in the technique of inkjet printing, the main ones being recalled below. On the one hand, the orifice used for the formation of the jet is of reduced size (of the order of 75 mm) and it can happen that a dust comes to obstruct it. It is important, in this case to have a rapid means allowing the unclogging of this orifice. On the other hand, the printing qualities of such a printer are intimately linked to the speed of ejection of the ink from the orifice. The speed can be altered by a variation in ink pressure in front of the orifice, as well as by a variation in the viscosity of the ink. This can be due to a loss by evaporation of the solvent from the ink which is often very volatile.

The object of the present invention is precisely to solve all these problems and relates to a circuit for supplying ink to a printer having a simple architecture and of very flexible operation which, with a minimum of components (two pumps and four solenoid valves) allows to obtain in particular a control of the pressure and the viscosity of the ink.

The invention relates more precisely to a circuit for supplying ink to an ink jet print head, of the type comprising an ink tank, the bottom of which has a first outlet connected to a supply line. brought ink to a. pressurizing pump supplying the body of the print head through a supply line 20; an inlet connected to a discharge line through which the unused ink passes, taken from a recovery gutter and sucked in by means of a vacuum pump; and a second outlet connected to a mooring line connected to the vacuum pump; power circuit

_ WIPO mentation, characterized in that it further comprises a first auxiliary circuit mounted between the ink supply pipe and the supply pipe, and capable of measuring the pressure existing in the supply pipe. The invention also relates to such an ink supply circuit, further equipped with a second auxiliary circuit comprising a combination of solenoid valves capable of unblocking the ejection orifice of the drops of ink and the clear cut of the inkjet.

It also relates to an ink supply circuit equipped with a third auxiliary circuit comprising means for measuring the viscosity of the ink.

Finally, it relates to such a circuit provided with means for treating solvent vapors before they are discharged into the ambient environment. The invention will be better understood with the aid of the explanations which follow and of the appended figures among which: FIG. 1 schematically represents an embodiment of an ink supply circuit of a print head in accordance with 'invention. FIG. 2 schematically represents an exemplary embodiment of a device capable of measuring the viscosity of the ink, cooperating with the pressurization circuit of FIG. 1.

For the sake of clarity, the same elements are given the same references in all the figures.

FIG. 1 therefore schematically represents an ink supply circuit for an ink jet print head 10. Such a circuit essentially comprises a circuit ensuring the pressurization of the ink and a circuit ensuring a depressurization, intended to suck at the level of the recovery gutter 11 of the ink drops 100 not used. The ink is stored in a sealed reservoir 1 which conformé¬ to the invention comprises an internal partition 22 arranged parallel to the side walls of the reservoir, therefore perpendicular to the bottom (ab) of the latter.

The level 38 of the ink always lower than the height 37 of the internal partition 22 changes from this level to the bottom of the reser¬ see. The low level 21 of the ink is detected by means of a sensor Ψ2. This ink is routed

O PI by means of a supply line 18 passing through the bottom (ab) of the tank 1 to a pump 5 driven by a motor. The flow rate of the pump 5 is proportional to the speed of rotation of the motor. The ink delivered by the pump 5 passes through a filter 8, a two-way pipe 190, one called the supply pipe bearing the reference 20 which routes it to the print head 10, the another called return line bearing the reference 19 which brings the ink through a calibrated leak 17 towards the supply pipe 18. The leak 17 makes it possible to create a pressure drop proportional to the flow of ink circulating in the latter .

In normal operation, the flow in the supply line 20 is completely negligible compared to the flow of the pump 5 which passes through the leak 17. The pressure of the pipe 18, downstream of the leak 17 is close to atmospheric pressure, which implies by the flow generated by the leak 17 and by the pump 5, that the pipes 19 and 20 are at a pressure higher than atmospheric pressure and almost proportional to the speed of rotation of the engine • . According to the invention a pressure sensor 9 is interposed on the pipe 19. This. sensor 9 in an exemplary embodiment includes electrical contacts <** and Ψ3 delimiting the pressure zone to be respected and a probe. This combination makes it possible to obtain a signal and to use an associated electronic device (not shown) which permanently controls the speed of the motor 4 so that the pressure in the pipes 19 and 20 retains a fixed and determined value whatever the variation of the parameters which govern it such as, for example, internal leaks at the pump or improper calibration of the leak 17.

This first auxiliary circuit according to the invention and referenced R2 therefore ensures a stable pressure.

According to another characteristic of the invention, a vacuum circuit cooperates with the pressurization circuit described above, the function of which is to recover at the level of the drop.

- Third, the ink drops emitted by the head 10 and not used for printing.

For this, a so-called vacuum pump 7 of the same type as the so-called pressurizing pump 5 is used. These two pumps 5 and 7 can be connected to the same motor 4.

The pump 7 is a volume pump which normally generates a flow of liquid. It may for example be a gear pump. The ink drops 100, collected at the level of the gutter 11 are sucked through a so-called suction pipe 27. This result can only be obtained if the pump 7 is capable of generating an air flow and this from starting the system, when the suction line 27 is still empty of ink.

This type of pump (geared for example) may have internal leaks. In the case of liquids these are negligible, but they are predominant with gases.

On the other hand, such a pump can function perfectly with a gas if its internal elements remain permanently wetted by a liquid, which then closes the leaks. According to the invention, this result is obtained thanks to the combination of means which is now described. The bottom (a, b) of the tank i is equipped with a so-called wetting pipe 45 which conveys through a leak 25 of the ink taken from this tank 1 to the vacuum pump 7 which has the effect of permanently wet its internal components. Under these conditions, it can fully fulfill its suction function: namely, sucking air through the line 27. The flow of ink from the line 45 is limited by the leak 25 so that it always remains lower than the volume flow generated by the pump 7. In this way the latter can generate a vacuum in the pipe 27, an extension 26 plugged in A is intended to be connected if necessary to a device for measuring the viscosity ink as will be described later. This operation of the pump 7 takes place and therefore this depression is created, even if the pipe 27 and its extension 26 contain air in high proportion. The pump 7, permanently wetted with ink from the reservoir 1 through the leak 25 therefore sucks in air and recovered ink from the recovery gutter I I. The ink and the air is discharged to the sealed tank 1 by a so-called discharge pipe 28 and according to a characteristic of the invention this pipe 28 is connected to a rigid pipe 24 and perpendicular to the bottom (a, b) of the reservoir 1, located inside the compartment C delimited by the partition 22. This repressed ink obviously comes from the gutter 11 but also from the wetting line 45. Also, even if no ink flow n 'is recovered at the level of the gutter 11, a minimum flow rate of ink return to the sealed reservoir i via the rigid pipe 24 is maintained thanks to the ink coming from the wetting circuit 45. This results in obtaining d '' a constant level 37, the ink overflowing at d internal bulkhead 22.

The air is also forced into the sealed tank

1. It is discharged to the outside through a coil 39, a non-return valve 47 and a pipe 46 which plunges into a liquid contained in a tank 3 which traps the solvent contained in the air before being returned to the free air through the orifice 36. In fact, the air recovered from the gutter 11 circulates with the ink in the pipes 27 and

24, and becomes saturated with solvent, especially if the latter is very volatile. The role of the coil is to condense the solvent contained in the air as much as possible, which solvent then joins the reservoir i by gravity. The air which cannot be completely rid of all the solvent vapors therefore passes through the bubbling tank 3 which traps these vapors by dissolution.

If the gutter 11 is blocked, the line 27 reaches the maximum depression that the pump 7 can generate. If the printer is stopped at this time, the line 27 will suck ink from the reservoir 1 which can only be replaced by air from the orifice 36. The non-return valve 47 in this case prevents the "return of bubbling liquid in the ink, which would imply a complete purging of the circuits. The circuit R2 for connection to the print head is now described. The body 10 of this print head supporting the orifice 41 creating the jet 100 can be pressurized at the request of the operator by a solenoid valve 13 connected to the head by a pipe 47. A solenoid valve 12 called purge connects the pipe 27 of the vacuum system to a pipe 48 which is at the same pressure as that of the body 10.

In normal operation the solenoid valve 13 is in the open position and the solenoid valve 12 in the closed position. The latter performs three essential functions. Firstly, after a prolonged shutdown of the machine, the line 20, especially if it is long, may contain degraded ink. It may be useful in this case to replace it with fresh ink coming from the reservoir 1. The flow of the ink jet, cannot allow this operation to be done quickly while the opening of the solenoid valve 12 allows to create a significant flow in the line 20, and in the body 10 and therefore to refresh the ink quickly.

Secondly, the presence of this solenoid valve 12 allows an easy uncorking of the orifice 41, if it is for example closed by a dust. The solenoid valve 13 is closed for this and the solenoid valve 12 is opened so that the body 10 is then in depression. Under these conditions it is possible to suck solvent through the orifice 41 and thus expel the dust towards the pipe 48.

Thirdly, the function of the solenoid valve 12 is to ensure, during the procedure for stopping the printer, a clean stop of the ink jet. In fact, when the jet is operating, the pipes 47 and 48 which are under pressure, swell slightly, especially if they are made of plastic and of great lengths. When the solenoid valve 13 is closed to cut the jet, the persistence of pressure in 47 and 48 means that the jet cannot be cut immediately, given its low flow rate. This inevitably leads to pollution of the environment of the jet, which is to be avoided. The original architecture of the ink supply circuit in accordance with the invention overcomes these drawbacks. When you want to cut the jet, you open the solenoid valve 12 shortly before the closing of the solenoid valve 13. When the closing of the latter occurs, the persistence of pressure in the pipes 47 and 48 cannot subsist as a result of the prior opening of the solenoid valve 12. We then close this shortly after the closing of the solenoid valve 13. The jet cut off frankly and the environment is not soiled. The opening and closing sequence of the solenoid valves is programmed in a known manner.

FIG. 2 schematically represents an example of a device capable of measuring the viscosity of the ink, called a viscometer V in the following description cooperating, in accordance with the invention with the pressurization circuit described previously by means of FIG. 1. It is a third circuit R3.

This viscometer (V) essentially consists of a container

14 connected to compartment C delimited inside the tank 1 positioned by construction at a level higher than that of the container 14.

It should be remembered that the level 37 of the liquid is kept constant in this compartment C. This container 14 has three electrodes

32, 33, 34 which dive into it at different levels and which serve to detect a low level and a high level by electrical conduction. Remember that the ink is conductive. The ink will be above the low level (x) when the electrodes 32 and 33 are in short circuit; on the other hand the ink will be at the high level (y) when the electrodes (32) and (34) are short-circuited.

The flow of ink through line 30 makes it possible to fill the container 14, the pressure balances at the surfaces of liquid 37 in the compartment C and 40 in the container 14 is achieved by means of a pipe 35 containing only l air and solvent vapors. The differences in altitudes between the constant level 37, the end of the electrode 33 (corresponding to the low level) the y end of the electrode 34 (corresponding to the high level), the volume of the container 14 and the diameter of the leak 29 being known, the filling time (tr) between x and y depends only on the viscosity of the ink.

A solenoid valve 15 cooperates with the viscometer (V) as described below. The solenoid valve 15 connects the bottom of the container 14 with point A, that is to say with the pipe

26 of the vacuum circuit described by means of FIG. 1. The ink from the container 14 is then sucked through the line 31, which makes it possible to empty the container 14. This requires that the emptying rate in the line 31 is greater than the filling rate in the inlet pipe 30. When the low level is reached, the solenoid valve 15 is closed, the container 14 is refilled to allow a new measurement.

When the viscosity increases due, in particular, to a loss of solvent in the ink, by evaporation, the filling time (tr) increases. As soon as it reaches a setpoint considered as a limit, the viscosity is then corrected by adding solvent.

For this, a solenoid valve 16 is provided to connect a reserve 2 containing pure solvent with point A, that is to say the line 26 which is in depression. This solvent is then sent

By the pump 7 towards the reservoir 1. It is also possible to permanently slave the operation of the solenoid valves 15 and 16 according to the parameters collected at the level of the electrodes 32, 33 and 34 of the viscometer V and therefore correct in permanently the viscosity of the ink by adding solvent when necessary. The sealed container 2 is connected to the pipe 35 which allows the solvent to be replaced by air without bringing it into contact with the ambient air, which has the great advantage of avoiding the risks of pollution of the environment, including unwanted odors. It should be noted that the air which replaces the liquids used such as the ink in the reservoir 1, and the solvent in the container 2 only comes from the recovery gutter 11. The excess air which must exist, s' escapes through the orifice 36 after bubbling into the reservoir 3. The receptacles 1 and 2 are therefore found in slight excess pressure due to the height of liquid in the receptacle 3. As in the case of FIG. 1, the coupling circuit of the two solenoid valves 12 and 13 is provided and operates as described above.

An ink jet printer equipped with an ink supply circuit according to the invention makes it possible to solve the main problems posed by this type of machine, namely in particular: - obtaining a stable pressure;

- control of the viscosity of the ink;

- the unblocking of the ink jet ejection orifice;

- the free stop of the jet. All these results are obtained by means of a simple device, easy to implement. By means of only two pumps and four solenoid valves.

The invention applies to any type of inkjet printer.

- ^ξj REΛt

WIPO

Claims

1) Ink supply circuit for an ink jet print head of the type comprising an ink tank (i), the bottom (ab) of which has a first outlet connected to a pipe (18) of a¬ led ink to a pump (5) pressurizing, supplying the body (10) of the print head through a supply line (20), an inlet connected to a discharge line (28 ) through which the unused ink passes, taken from a recovery gutter (11) and sucked through a recovery pipe (27) by means of a vacuum pump (7); characterized in that it further comprises a second outlet connected to a wetting line (45) connected to the vacuum pump (7), and a viscometer (V) placed below the ink tank (1) which essentially consists of a container (14) comprising three electrodes (32), (33), (34) which immerse therein at different levels whose function is to detect a high level (y) and a low level (x ) which makes it possible to measure the filling time (tr) between (x) and (y) and therefore the viscosity of the ink, this viscometer cooperating with means for adding solvent when a viscosity set value considered limit has been reached.

2) supply circuit according to claim i, characterized in that these solvent addition means consist of a set of valves (15) and (16) arranged so that when the filling of the container (14) through the pipe (30) is finished, the solenoid valve (15) connects the bottom of the container (14) with the point (A) located on the vacuum pipe (26 -27). The container (14) is then emptied through a drain pipe (31); the solenoid valve (15) then being closed, the container (14) can again be filled.

3) Supply circuit according to one of claims 1 and 2, characterized in that when the set value is reached, the solenoid valve (16) links a reserve (2) containing pure solvent with the point (A) so that solvent is then sent by pump 7 to the tank (1). 4) Supply circuit according to one of the preceding claims; characterized in that the reserve (2) of solvent being sealed is connected to a pipe (35) common to the reservoir (1) and to the container (14) so that the. solvent is replaced by air without it being in contact with the ambient air, this air coming from the gutter by the pump (7).

5) Supply circuit according to one of the preceding claims; characterized in that the excess air escapes through an orifice (36) after bubbling into a tank (3). 6) Supply circuit according to one of the preceding claims; characterized in that it further comprises means capable of unblocking the orifice (41) for ejecting the ink drops and clear cutting of the jet. 7) Power circuit according to claim 6; characterized in that these unclogging means consist of a set of solenoid valves (12) and (13) performing three functions: on the one hand, the opening of the solenoid valve (12) makes it possible to create a large flow in the body (10) and thus ensures a purge of the ink; on the other hand the closing of the solenoid valve (13) and the opening of the solenoid valve (12) allows a suction of solvent added by the operator at the ejection orifice (41), suction which ensures the unclogging of this orifice; finally, when the jet is cut off, the opening of the solenoid valve (12) before the closing of the solenoid valve (13) prevents pressure persistence in the pipes (47) and (48) connecting the set of solenoid valves (12) and (13) to the body (10), thus ensuring a clean cut of the jet.

8) Supply circuit according to one of the preceding claims; characterized in that it further comprises means capable of measuring the pressure existing in the supply line (20).