WO1998056585A1

WO1998056585A1 - Valve assembly for ink jet printers

Info

Publication number: WO1998056585A1
Application number: PCT/SE1997/001007
Authority: WO
Inventors: Ulf Mielke
Original assignee: Jetline Ab
Priority date: 1996-04-15
Filing date: 1997-06-10
Publication date: 1998-12-17
Also published as: SE9601403D0; SE9601403L; AU3468197A; SE507821C2

Abstract

In an ink jet printer, a valve assembly (1) having a reciprocating (A) valve member (5) formed with a front end face (10) which is arranged to be moved to and away from a position of abutment against the valve seat (11) around an outlet (12, 14) for drop-by-drop discharge of the ink (2) on a recording medium (4) in order to create characters thereon. The valve member (5) has a rear armature part (17) of a soft-magnetic material forming the movable armature (9) of the electromagnet (7) in co-operation with the fixed coil (8) of the electromagnet. In addition, the valve member (5) is formed with a front plunger part (18) of light metal, plastics or other light-weight material, which plunger part is formed with said front end face (10) and which is connected to the rear armature part (17) by means of a joint (23).

Description

VALVE ASSEMBLY FOR INK JET PRINTERS

The present invention concerns a valve assembly for ink jet printers for applying ink in the form of droplets to a recording medium and thus making characters thereon, said valve assembly comprising an elongate valve member having a front end face and being axially reciprocable in a tubular compartment by means of an electromagnet, said front end face being moveable into alternatingly closing and opening co-operation with a valve seat around an outlet for drop-by-drop discharge of the ink for said application to the recording medium.

A valve assembly of the kind defined above is in principle known from SE-C-8700544-3, wherein the axially reciprocable valve member is made entirely of a magnetic or a magnetisable material so as to form the movable armature of the electromagnet.

In reality, the valve member of the valve assembly above has a length of 10 mm and a crosswise dimensional size/diameter of about 1 mm. Consequently, the valve member is an extremely small object and may have an operational frequency of several thousands of Hz.

In order to above all reduce the mass of the valve member and thus its inertia for the purpose of considerably increasing the operational frequency and as a result thereof the performance of the jet ink printer, the valve member in accordance with the invention is formed on the one hand with a rear armature part of a magnetic or magnetisable material, which rear armature part constitutes the movable armature of the electromagnet in co-operation with the fixed coil of the electromagnet, and on the other with a front plunger part, said front plunger part, which is formed with the front end face co-operating with the valve seat, being fixedly connected to the rear armature part by means of a joint and being made of an essentially lighter material than said rear armature part, said front plunger part of the valve member being essentially at least as long as but preferably longer than the rear armature part thereof.

The front plunger part of the valve element suitably has a length that is at least essentially equal to that of its rear armature part but preferably is considerably longer. In principle, for a given size, the armature part made from the heavier material should be as small as possible whereas the lighter material plunger part should be as large as possible, thus ensuring that the total mass of the valve body will be as small as possible.

The invention will be described in closer detail in the following with reference to the accompanying single drawing figure which is a longitudinal section view that schematically illustrates a part of a valve assembly and an associated valve member conceived in accordance with a presently particularly preferred embodiment. The valve assembly, part of which is shown schematically in the drawing figure, is generally designated by reference 1 and is one of several such assemblies incorporated in an ink jet printer of otherwise conventional design, not shown in more detail. Each valve assembly 1 of the ink jet printer serves to apply ink 2 in the form of droplets 3 to a recording or print-receiving medium 4, such as paper, cardboard, plastics, cloth or any similar substrate in order to produce characters and/or graphic images thereon. In the preferred embodiment the valve assembly comprises a valve member 5 of elongate shape, which is arranged for axial reciprocating movements in a tubular compartment 6 in the direction indicated by double arrow A. An electromagnet 7 causes the valve member 5 to per- form the reciprocating movement inside the compartment 6. The stationary coil 8 of said electromagnet 7 forms part of the housing 16 of the assembly 1 whereas the moveable electromagnet armature 9 forms part of the valve member 5, as will be described in closer detail in the following.

The valve member 5 is formed with a front, preferably flat end face 10. Upon the reciprocating movements of the valve member 5, said end face is moveable into alternatingly closing and opening co-operation with a preferably slightly domed valve seat 11 formed in a valve plate 13. The seat 11 surrounds an outlet channel 12 formed in the valve plate 13, the latter in any suitable, conventional manner being connected to the valve housing 16, and the outlet channel 12 communicates with a dis- charge nozzle 14 formed in a nozzle plate 15, the latter, likewise in any conventional manner, being connected to the valve plate 13. The co-operation referred to above between the end face 10 of the valve member 5 and the valve seat 11 in the valve plate 13 causes the sought- after drop-by-drop discharge of the ink 2 through the outlet channel 12 and the discharge nozzle 14 onto the recording medium 4.

In order to achieve the sought-after increase of the operational frequency of the valve body 5 to which reference is made in the introduction hereto, and in consequence thereof increase of the performance of the ink jet printer by reduction of the valve member mass and therefore of its inertia, the valve body 5 in accordance with the preferred embodiment, more specifically com- prises on the one hand a rear armature part 17 of a magnetic of magnetisable material, preferably a soft- magnetic metal, which thus forms the movable armature 9 of the electromagnet 7 in co-operation with the stationary coil 8 of the electromagnet, and on the other a front plunger part 18 which is formed with said front end face 10 that co-operates with the valve seat 11. The plunger part is connected to the rear armature part 17 and is made of an essentially lighter material than the latter. When choosing the material of the front plunger part 18, light metals and their alloys, plastics (reinforced and non-reinforced) of different kinds, composite materials, carbon fibres, etcetera, may be considered.

The proportions of the rear armature part to the front plunger part are variable but as mentioned pre- viously, for a given valve-member size, the valve member should be made as light as it could possibly be and still retain its intended function, which may be achieved by making the armature part, made of the heavier material, as small as possible and the plunger part, made of the lighter material, as large as possible. In practical terms this means that the front plunger part 18 of the valve member 5 could have a length essentially equalling, but preferably even exceeding, that of its rear armature part 17. The rear armature part 17 of the valve member 5 in accordance with the embodiment described and illustrated herein is formed with a recess 19 the opening of which is turned towards the front plunger part 18 in order to receive therein the plunger part end 20 that is situated in front of the recess. The disposition could, however, equally well be the reverse one, i e. the recess could be formed in the front plunger part 18 and the end facing the recess be formed on the rear armature part 17.

In either case the recess 19 preferably is given an essentially axial orientation while at the same time the end 20 disposed opposite said recess preferably is configured as an essentially axially directed pin 21 which is insertable into the recess. For manufacturing reasons and also for other reasons the recess 19 as well as the pin 21 advantageously are given a circular cylindrical shape but they are not limited to this configuration but could equally well be given an oval or polygonal shape. The circular cylindrical shape or other shape could be used also for the valve member 5 as a whole, i.e. the rear armature part 17 as well as the front plunger part 18 could be thus configured and in that case preferably be arranged in coaxial relationship.

In order to reduce eddying flows that counteract the movements of the moveable armature 9 of the electro- magnet/of the rear armature part 17 of the valve member 5 upon activation of the electromagnet 7, a cavity 22 preferably is made in the rear armature part 17 of the valve member 5, which cavity 22 may be formed by one or several apertures or recesses in the armature part 17. In accordance with the shown embodiment the cavity 22 is configured as an axially directed bottom hole in the armature part, said bottom hole being an extension of the recess 19, for reception therein of the pin 21. Alternatively, the cavity 22 may be configured as a through hole, likewise arranged as a prolongation of recess 19. As mentioned previously in this description, the rear armature part 17 and the front plunger part 18 of the valve member are interconnected, more specifically by means of a joint 23 of a suitable kind. In accordance with the preferred embodiment of the invention, the joint 23 preferably is a fixed joint formed by a glue joint, a contraction joint or some other kind of joint between the recess 19 in the rear armature part 17 and the pin 21 on the front plunger part 18. Other possible types of joints could be riveted or welded joints, depending on the material chosen for the armature part 17 and the plunger part 18.

Alternatively, the joint 23 between the recess 19 of the armature part 17 and the pin 21 of the plunger part r O

18 could be a separable joint, for instance in the form of a screw joint, a snap-in joint or similar joint.

As already mentioned, the front plunger part 18 of the valve member 5 is made of a considerably lighter material than the rear armature part 17 of the valve member 5. As examples of materials that have been tested so far and proved to meet the basic requirements is light metal, particularly aluminium, or alloys thereof, but light-weight plastics are of particular interest in this context. These plastics could be reinforced or non- reinforced, depending on the requirements that the material should satisfy. Composite materials, which could per se also contain plastics, are likewise possible alternatives as are also, although expensive, materials based on carbon fibres.

For weight-saving and/or space saving reasons or other reasons, the very structure of the front plunger part 18 in accordance with the preferred embodiment of the invention preferably comprises a connecting part 24 which is provided with the pin 21 and which is formed with a peripheral shoulder 25 on which bear the outer free end of the recess 19 of the rear armature part 17 and, if any, the delimiting jacket wall 26 of the cavity 22. At its forwards end, the front plunger part 18 is provided with a plunger head 27 on which is formed the front end face 10 that co-operates with the valve seat 11 on the valve plate 13. Between the connecting part 24 and the piston head 27 extends a "thinner" plunger rod 28, i.e. a rod having a smaller diameter size than the corresponding dimensions of the connecting part 24 and the plunger head 27, respectively. To a large extent, the degree of the size reduction is a question of strength. In order to ensure that the rear armature part 17, and thus the entire valve member 5, be efficiently pulled upwards as seen in the drawing figure, upon activation of the electromagnet 7, a counter-acting armature 29 is disposed in the stationary coil 8 of the electromagnet in a position at a predetermined distance from the rearmost end 30 of the armature part 17. This counter-acting armature 29 thus creates a magnetic field having a pulling effect and in addition, it forms a back-up or stop means preventing the valve member 5 from rising too far.

Reversely, in order to ensure that upon deactivation of the electromagnet 7 the valve member 5, by means of the front end face 10 formed on the plunger head 27 of the front plunger 18, be urged into closing abutment against the valve seat 11 in the valve plate 13 while simultaneously causing droplets 3 of ink 2 to be ejected from the discharge nozzle 14, a spring 34, preferably a conical helical compression spring or similar means, is held between an annular bearing face 31 on the rear face of the plunger head 27 and a corresponding bearing face 32 formed in an enlarged portion 33 of the annular chamber 6.

It should be appreciated that the invention obviously should not be considered to be limited to the embodiment illustrated in the accompanying drawing figure but that several modifications thereto are possible within the scope of the claimed protection.

Claims

1. A valve assembly for ink jet printers for applying ink (2) in the form of droplets (3) to a recording medium (4) and thus making characters thereon, said valve assembly (1) comprising an elongate valve member (5) having a front end face (10) and being axially reciprocable in a tubular compartment (6) by means on an electromagnet (7), said front end face (10) being raove- able into alternatingly closing and opening co-operation with a valve seat (11) around an outlet (12,14) for drop-by-drop discharge of the ink (2) for said application of the recording medium (4), ch a r a c e r i s e d in that the valve member (5) is formed on the one hand with a rear armature part (17) of a magnetic or magneti- sable material, which rear armature part constitutes the moveable armature (9) of the electromagnet (7) in co-operation with the fixed coil (8) of the electromagnet, and on the other hand with a front plunger part (18), said front plunger part, which is formed with the front end face (10) co-operating with the valve seat (11), being fixedly connected to the rear armature part (17) by means of a joint (23) and being made of an essentially lighter material than said rear armature part (17), said front plunger part (18) of the valve member

(5) being essentially at least as long as but preferably longer than the rear armature part (17) thereof.

2. An assembly as claimed in claim 1, c h a r a c t e r i s e d in that the rear armature part (17) of the valve member (5) is made of a soft-magnetic metal and has a cavity (22) which reduces the eddying flow and the mass and which is formed of an essentially axially oriented bottom hole or through hole.

3. An assembly as claimed in claim 1 or 2, ch a r a c t e r i s e d in that the rear armature part (17) of the valve member (5) has a recess (19) which is open to the front plunger part (18) thereof an which is adapted to recieve the front plunger part end (20) opposing the same or vice versa.

4. An assembly as claimed in any one of the preceding claims, c h a r a c t e r i s e d in that the recess (19) is essentially axially oriented, and that the opposing end (20) has the shape of an essentially axially oriented pin (21) which is insertable into the recess (19).

5. An assembly as claimed in any of the preceding claims c h a r a c t e r i s e d in that the joint (23) between the rear and front armature and plunger parts (17, 18) of the valve member (5) is a glue joint, shrink joint or similar fixed joint between the recess (19) and the pin (21) .

6. An assembly as claimed in any one of claims 1-4, c h a r a c t e r i s e d in that the joint (23) between the rear and front armature and plunger parts (17,18) of the valve member (5) is a thread joint, snap-in joint or a similar joint between the recess (19) and the pin (21).

7. An assembly as claimed in any one of the preceding claims, c h a r a c t e r i s e d in that the front plunger part (18) of the valve member (5) is made of a material such as light metal, plastic, composite material, carbon fibre etc.

8. An assembly as claimed in any one of the preceding claims, ch a r a c t e r i s e d in that the front plunger part (18) if the valve member (5) comprises a connecting part (24) provided with the pin (21), a plunger head (27) formed with the front end face (10) in co-operation with the valve seat (11), and a plunger rod (28) extending between the connecting part (24) and the plunger head (27) and having a smaller transverse dimen- sion than the connecting part and/or the plunger head.

9. An assembly as claimed in any one of the preceding claims, c h a r a c t e r i s e d in that the rear armature part (17) and the front plunger part (18) of the valve member (5) are essentially circular- cylindrical and coaxial.