Ink jet printer having liquid communicated traveling wave stimulation

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FRENCH REPUBLIC

NATIONAL INSTITUTE OF INDUSTRIAL PROPERTY @ Publication number: 2 401 774

IA use only for reproduction orders).

PARIS

REQUEST

PATENT OF INVENTION ® N ° 78 21514 @ Recording head for inkjet printer.

International classification (Int. CL²).

B 41 J 3/04.

Filing date ............................. July 20, 1978, 3:16 p.m.

Priority claime d: Patent application filed in the United States of America on August 29, 1977 n. 828.274 in the names of Charles L. Cha and John A. Robertson.

(4î) Date of making the request available to the public ............ BOPI - "Lists" n. 13 of 30-3-1979.

[rp Applicant: Company known as: THE MEAD CORPORATION, residing in the United States of America.

(72) Invention of:

@ Holder: idem (7l) @ Agent: Rinuy, Santareili.

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Sale of booklets at IMPRIMERlE NATIONALE, 27, rue de la Convention - 75732 PARIS CEDEX JS

The present invention relates to recording heads with ink drops and more precisely to recording devices in which ink drops are formed by mechanical stimulation.

In the recording apparatus or printers described in U.S. Patents 3,373,437 and 3,560,641, one or more lines of ports receive an electrically conductive recording fluid, for example a water-based ink from a pressurized dispenser and project the fluid into parallel streams of drops. Graphic reproduction is carried out by selective loading and deflection of drops in each of the streams and by depositing at least some of the drops on a moving and continuous sheet of printing material.

Each stream of drops is formed when the conductive fluid flows through an orifice and forms a fluid filament.

The drops form at the end of the filaments. When a charge electrode is placed near the end of the filament, a potential applied to the electrode causes a charge build-up at the end of the filament. When the drop breaks at the end of the filament, it causes part of this induced charge. Then, the drop passes into an electrostatic field and it is deflected by this field by a distance which is proportional to the value of the charge of the drop. In an advantageous embodiment, the drops are loaded binary so that they undergo an impression or not; some drops are charged and diverted to a collecting device while others are not charged and pass unaffected by the electric field to a printing sheet.

It should be noted that the formation of the drops must be regulated in such a recording device, with great precision. When the filaments of fluid undergo natural disturbances of stimulation, they tend to break erratically in drops of various sizes, at irregular intervals. Selective loading and deflection cannot be performed uniformly and therefore images of acceptable quality cannot be printed. Thus, it is known that it is necessary to apply a stimulation disturbance of constant amplitude and of fixed frequency to all the fluid currents. As a result, uniformly spaced streams of droplets of uniform size are formed, and the recording can be reasonably good, as described in U.S. Patent No. 3,586,907 which relates to a device in which the entire print bar is mechanically stimulated by an acoustic vibrator.

Drop stimulation techniques in which the entire printing bar or fluid supply vibrates allow the formation of uniform drops of ink, but the stimulation of the drops has a phase which varies in an unregulated and unpredictable from one current to another. This phenomenon causes a certain uncertainty as regards synchronization, of the order of half of a drop repetition period. An error in the placement or placement of drops causes an error equal to the movement of the print sheet during half the repetition period of the drops. In addition, stimulation of this type causes an unpredictable change in the amplitude of the stimulation energy between the drop currents and a corresponding change in the length of the fluid filaments. This variation in length of the filaments can correspond to a distance as large as + 3 times the distance separating the drops. It is therefore very difficult for the charging electrode to occupy a suitable point close to the end of the filaments. Synchronized variations are also introduced between the different drop currents since the drop drop distance before striking the printing sheet varies from one current to another. The flight times of the drops thus differ and the position of the drops on the printing sheet is adversely affected.

U.S. Patent No. 3,759,595 describes a drop stimulation technique which eliminates a number of the problems presented by this stimulation.

According to this patent, a stimulation arrangement ensures stimulation of the jets by a wave which propagates along the plate comprising the orifices. Bending waves are transmitted at each orifice and cause a disturbance of the drops of the associated jet. This technique removes erratic variations in the length of the fluid filaments and causes good quality stimulation.

A difficulty presented by this technique is that the bending waves are attenuated when they propagate along the orifice plate. As a result, the jet filaments gradually lengthen, with the filament at the end furthest from the orifice plate possibly being much longer than those near the source of the bending wave stimulation. . U.S. Patent No. 3,882,508 describes a jet recording apparatus, having an orifice plate and a head which has a shape of variable section, the active width of the orifice plate gradually decreasing along the bending wave path so that this unwanted attenuation is compensated. As the vibrating mass is gradually reduced, the energy available for application to the filaments is more uniform and the length of the filaments tends to remain more uniform.

Although the formation of drops by stimulation by a propagating wave in the orifice plate has significant advantages compared to stimulation by vibration of the whole head, the construction of the orifice plate is necessarily determined , in such a printer, by the necessary vibrational characteristics. The orifice plate must be flexible enough so that it can be stimulated by a transducer. However, certain materials cannot be used in its construction, although it can be easily machined or worked to form a plate of precise shape, size and spacing of holes corresponding to the desired values.

Although reducing the width of the orifice plate in a device in which waves which. spread feels applied to this plate could give a more uniform amplitude of stimulation there. there are still maximum and minimum plate widths that are acceptable, when these maximum and minimum dimensions are exceeded, the orifice plate may vibrate with undesirable transverse vibrational modes, and the waves may be reflected along the plate as shown in the aforementioned United States patent

42401774 no.5,882,508.

The maximum length of the printing bar can therefore be lengthened by stimulation of the plate at a central point with waves which propagate in both directions along the plate, the latter having a width which decreases in both directions. . The difficulty presented by this technique is however that the real point of macanic stimulation must be slightly offset from the lines of orifices. Stimulation of the orifice plate at a point which is not on the longitudinal central axis causes undesirable flexion. The last cited patent suggests the use of an orifice plate which thickens near the point of excitation so that these undesirable modes of bending are eliminated. However, the realization of a plate having such a design seems difficult to a certain extent.

The invention relates to a head for recording by drops from jets, having a plate with orifices arranged in a line. A common distributor is associated with the orifices and a device ensures the fixing of the steps of the plate on the distributor. A flexible plate device communicates with the distributor and defines a fluid reservoir with the distributor and the orifice plate. The flexible plate is placed along the length of the tank parallel to the orifice plate. A device is intended to transmit the ink to the reservoir at a pressure which is sufficient for the ink to be expelled through the orifices and forms a line of jets of liquid. A stimulator is intended to create a series of flexion waves qdi which propagate along the flexible plate so that the jets are stimulated and break up into streams of drops formed regularly. A device is intended to load and deflect the drops so that they give intelligible patterns.

the stimulator can be arranged so that it provides mechanical stimulation of the first end of the flexible plate, so that the bending waves induced at the first end propagate along the flexible plate towards a second end. A damping device can be placed at both ends of the flexible plate so that the bending waves do not reflect at the ends and that the standing waves which may form as a result of this reflection are minimal. The width of the flexible plate can decrease towards the second end so that the attenuation of the bending waves along the plate can be compensated. Alternatively, the stimulator may be arranged to apply mechanical stimulation at a point which is between the two ends of the flexible plate. In such an arrangement, the distributor can define a fluid reservoir in the form of a boat in which the widest width is in the center, this width decreasing towards the two ends.

The invention therefore relates to a head for recording by drops coming from jets, having a stimulator configuration in which waves which propagate along a part of the reservoir remote from the orifice plate are coupled by liquid to the orifices of plate with orifices and constitute a source of disturbances inducing the formation of drops in the fluid; this recording head is such that the waves which propagate are bending waves which propagate along a flexible plate delimiting a part of the fluid reservoir. The invention also relates to such a recording head in which the flexible plate has a variable width and mechanical stimulation is applied in a wide part of the plate so that the attenuation of the waves is minimal. It also relates to a device in which stimulation is applied to the central zone of the plate, waves propagating from the point of stimulation, in both directions along the plate.

Other characteristics and advantages of the invention will emerge more clearly from the description which follows, given with reference to the appended drawings in which:

Figure 1 is an exploded perspective view of a recording head according to the invention;

Figure 2 is an enlarged section of the assembly of Figure 1;

Figure 3 is an exploded perspective view of part of a variant of the recording head according to the invention;

Figure 4 is a plan view showing an orifice plate and a dispenser of another embodiment of the invention;

5 shows the active part of the flexible plate used with the orifice plate and the dispenser of Figure 4? and FIG. 6 schematically represents three different modes of resonance of a plate with orifices, transverse to this plate.

FIG. 1 represents an advantageous embodiment of a recording head according to the invention, in exploded form, the various elements of the head are assembled by fixing on a support structure 12, mounting is carried out by fixing the elements to the using screws and pliers (not shown).

the recording head comprises a plate 18 with orifices which is welded with or without addition or otherwise fixed to a distributor 20 for supplying fluid, the plate 18 can be formed from any material which can be drilled or machined so that it has the desired configuration for the orifices. the plate 18 preferably defines two lines of orifices 26. the distributor 20 delimits a central cavity 28 forming an ink reservoir, having upper and lower orifices, these orifices being clearly elongated, the plate 18 is mounted so that it covers the lower orifice of the distributor, the lines of orifices being substantially parallel to the length of the dispenser orifices. A flexible plate 30 is mounted above the upper orifice in the distributor 20. A tube 32 allows ink to be transmitted to the fluid reservoir at a pressure which is sufficient for the ink to be expelled through the orifices 26 and forms several lines of ink jets. A tube 34 allows the evacuation of the tank.

A stimulator 36 is mounted in a support bar 12 and is in contact with the flexible plate 30 so that it ensures the mechanical stimulation of this plate 30. Bending waves move along the plate 30, parallel to the length of the orifices of the distributor 20. the bending waves of the plate 30 are coupled to the jets by the fluid in the reservoir 28 so that the jets are stimulated and break up into streams of drops formed regularly. Two wedge-shaped acoustic dampers 23 are mounted at the ends of the plate 30.

These shock absorbers 25 are for example formed from polyurethane rubber or a similar material and their role is to absorb bending waves. These latter are therefore not generally reflected and there are no standing wave patterns. The lines of ink drops formed regularly are loaded and deflected so that they form the desired patterns as described below.

A plate 50 of charge rings, a ribbon 52 conductive of electricity, intended to ensure the deflection, and two collecting devices 54 constitute the elements necessary for the charge and the deflection of the drops allowing the creation of intelligible drawings, the 54 collection devices are carried by supports 56 which are directly attached to the distributor 20. Spacers 58 and 60 pass through orifices 62 and 64 of the plate 50 so that they hold the supports 56 without applying stress or force to the plate 50. the deflection tape 52 is also held by the supports 56 and it is elongated without play between these supports, thanks to the clamping block 66, the ribbon 52 is disposed between the collecting devices 54 as clearly indicated in FIG. 2.

the collecting devices 54 are adjustable laterally with respect to the ribbon 52. the adjustment can be obtained by mounting the head and the devices 54 resting in slots 68 of the supports 56, and by mutual return towards the interior under the action of two elastic bands 70. Adjustment blocks 72 are arranged upwards in cavities 74 and 76 so that they bear against faces 78 of the collecting devices 54 and adjustment screws 80 are intended to move the adjustment blocks 72 and the collecting devices 54 outwards, despite the force applied by the elastic band 70. the supports 56 are formed of an insulating material which can consist of any available wafer of reinforced plastic.

the fully assembled recording head is shown in section in FIG. 2. Thus, a coating fluid 82 flows downwards through the orifices 26 and forms two lines of currents which break into droplets 84. These pass in two lines of load rings 86 of the plate 50 and towards one of the collecting devices 54 or on the movable sheet of paper

88. The switching of the drops between the collection and deposition paths is ensured by charging and electrostatic deflection as described below. The coordinated printing is obtained by shifting the two stream lines according to the techniques described in US Patent No. 5,560,640. As described in the continuation of the present memo, the drops of the front line of current (that is to say the line which is furthest forward in the direction of movement of the sheet) are switched in a time frame of reference delayed with respect to those of the rear line, by a time d / V, d representing the line spacing and V the speed of the sheet. There is thus a coherence between the two lines of currents which plays the role of a single line having an effective spacing equal to half of the real spacing of the real lines.

The formation of the drops 84 is precisely adjusted by applying a stimulation disturbance having a constant frequency and a controlled amplitude, to each of the fluid streams coming from the plate 18. The disturbances used for this purpose are created by a transducer 56 which vibrates the flexible plate 30 with a constant frequency and amplitude. A continuous series of bending waves is thus formed which propagate along the plate 30 · These waves are transmitted by the fluid 82 present in the reservoir to the fluid which forms the filaments of the orifices 26. Dampers 28 are mounted at the upper face of the plate 30 and prevent the reflection of these waves. It should however be noted that damping devices 38 can be mounted under the plate 30 in the tank 28.

During the formation of each of the drops 84, this is exposed to the charge influence of one of the rings 86.

An electric charge is thus induced at the end of the filament of fluid and driven by the drops. An electrostatic field is established between the deflection ribbon 52 and the faces of the collecting devices 54. When the drop 84 passes through this field, it is deflected and strikes the face of the suitable collecting device. Then, the drop descends along the face of the collecting device, is removed and then entrained. The collection of the drops can be promoted by applying a suitable vacuum at the ends 90 of the collecting devices 54 · In the case of the drops which must be deposited on the sheet 88, no electrical charge is applied to the corresponding charging ring so that the gout does not charge.

Charges suitable for the desired drops are induced by establishing a difference in electrical potentials between the orifice plate 18 (or any other conductive structure in electrical contact with the coating fluid reserve) and each charging ring 86, the differences in potentials are created by grounding the plate 18 and applying properly synchronized voltage pulses to the wires 92 and connectors 94 (a single connector is shown), the connectors 94 are plugged into the housings 96 of the end of the plate 50 of the rings and they transmit the indicated pulses of voltage by the lines 98 of printed circuits which join the rings 86. the plate 50 is formed of an insulating material and the rings 86 are simple coatings of a conductive material formed on the surface of the orifices of the plate of the load rings. Voltage pulses useful for this purpose are created by circuits of the type described in the aforementioned United States Patent No. 3,560,640. and the wires 92 which receive the pulses must be adapted to the rings, in a one-to-one manner. In addition, the voltage pulses can be multiplexed so that the number of wires and connectors is reduced. Alternatively, semiconductor demultiplexing circuits can be used for demultiplexing signals and for routing pulses to suitable rings. Such semiconductor circuits are manufactured by known methods in the form of a permanent part of the plate 50.

As indicated in the preceding description, the use of coupling by the printing fluid between the plate 30 which receives the stimulation by the propagating waves, and the orifices 26 allows the implementation of a stimulation technique. in which the flexibility of the orifice plate 18 does not matter. When each bending wave travels in front of a point on the plate 30, a compression wave is transmitted downwards from this point to the fluid towards the orifices which are located below. The resulting variation in fluid pressure causes the formation of a drop, according to the well known phenomenon of rupture of Rayleigh jets.

Figure 5 is an exploded perspective view of the upper part of a variant ink jet printer according to the invention. As in the embodiment of Figures 1 and 2, a transducer 3.6 applies mechanical stimulation to a flexible plate 30 so that a series of bending waves propagates along the plate. This is stimulated at point 100 which is in the middle of the plate. The bending waves are transmitted in both directions along the plate 30 and are absorbed at the ends by damping devices 38.

The distributor 20 can delimit a tank 102 of fluid in the form of a boat, having a greater width in its center and narrowing towards the ends. A groove 104 surrounds the reservoir and houses a gasket 106 which forms a tight seal between the distributor 20 and the plate 30. the bending waves are transmitted in both directions, along the plate 30. As the width thereof gradually decreases towards the extremities, the stimulation remains practically constant along the reservoir. Although the flex wave is slightly attenuated, the effective width of the plate 30 and the angle volume in the reservoir 102 which receives the stimulation wave, are sufficiently reduced. It should be noted that the orifices 26 are placed over the entire length of the reservoir 102 and that these orifices may be located just below the mechanical stimulator 13 · The maximum length of the print bar by ink jets using central stimulation is therefore double that obtained with a bar providing stimulation at one end only.

We now refer to Figures 4 and 5 which show another embodiment. FIG. 4 is a plan view of the plate 108 with orifices and of the distributor 110 and it can be noted that the latter delimits a reservoir which has a width which decreases from left to right. FIG. 5 diagrammatically represents the active part of the flexible plate 112 which is used with the distributor 110 of FIG. 4 · The circle

114 in broken lines represents the point of contact of the stimulator with the plate. It should be noted that this arrangement, analogously to that which has been described with reference to the central stimulation of FIG. 3, compensates to a certain extent the reduction in the amplitude of the flexion wave which is compulsory given that the waves are transmitted along the plate 112.

FIG. 6 schematically represents the flexible plate 30 and the stimulator 36_s observed from one end of the plate. As indicated in the aforementioned U.S. Patents 3,739,393 and 3,882,508, it is desirable that the bending waves which propagate along the orifice plate are such that the plate is stimulated in mode first order transverse resonance. Similarly, it is desirable, with the stimulation according to the invention, that the flexion waves which propagate along the plate 30 are also in first order transverse resonance mode as indicated by the dashed line I in the figure. 6. When the flexible plate 30 is sufficiently large, a series of waves in second order transverse resonance mode can also form as indicated by the dashed line II in FIG. 6. A wider plate 30 allows the creation of bending waves in transverse resonant mode of the third order as indicated by the broken line III. There is also a minimum width of the active surface of the flexible plate necessary for the maintenance of the bending wave in first order transverse resonant mode. Consequently, the width of the reservoir and of the active area of ​​the flexible plate, as indicated by P in FIGS. 4 and 5>, must be chosen so that the width is at least equal to the minimum necessary for the maintenance of second order bending waves. The width of the reservoir and the active surface of the flexible plate, as indicated by the reference G, is necessarily at least equal to the width necessary for the maintenance of first order bending waves. It can therefore be seen that the reduction in width between the plates P and G is limited by these considerations. Consequently, the length of the printing bar which allows effective compensation by reducing the width of this material is also limited.

It appears that the stimulation device according to the invention has a certain number of very clear advantages compared to known devices which use stimulation by waves which propagate along the orifice plate. The latter plate and the flexible plate can each be formed from a material best chosen according to the necessary functions. More specifically, the flexible plate can be formed by a single layer of a metal sheet chosen so that it minimizes bending waves, the orifice plate must not be formed by a thin and elastic material but it can s 'Act glass or ceramic for example, without regard to its flexibility which may be arbitrary. As the stimulator is not placed in the ink tank, the problems posed by this arrangement, in particular the formation of a turbulent stream of ink and corrosion of the stimulator, are eliminated.

It is understood that the invention has only been described and shown as a preferential example and that any technical equivalence may be provided in its constituent elements without going beyond its ambit.