GB2260597A - Solenoid valve and method for adjusting it - Google Patents

Abstract

A solenoid valve comprises an axially elongated body 1 having an axial bore 3, and a plunger 4 reciprocable in the bore under the influence of a coil 2 carried by the body. The body also defines a chamber 9 at or adjacent one end, the distal end, thereof in which the distal end of the plunger reciprocates. The distal end of the chamber is closed by a transverse wall 10 having an outlet 11 therein with which the distal end of the plunger co-operates to control escape of fluid from the chamber. The extent of axial retraction of the plunger is restricted by a pole piece 6 located in the axial bore; the pole piece 6 is an interference fit within the axial bore 3. The performance of the valve is adjusted by rotating and moving the pole piece 6 axially to achieve the desired axial clearance between the pole and the plunger. The valve is usable in an ink jet printer. <IMAGE>

Description

TITLE: DEVICE AND METHOD FOR ASSEMBLING IT The present invention relates to a device, notably to a solenoid valve, and to a method for assembling it.

BACKGROUND TO THE INVENTION: In one form of an ink jet printer, ink is fed under pressure to a valve means which controls the flow of ink through a nozzle orifice so as to deposit a droplet of ink upon a substrate travelling past the nozzle orifice. By having an array of such nozzles and by controlling the sequence at which the valves are operated, it is possible to deposit the droplets to form a wide range of alpha-numeric characters or other images on the substrate.

Typically, the valve means is a solenoid type valve in which a plunger is journalled within an axial bore in a valve body around which an electrical coil is wound. The plunger is reciprocated by applying a current through the coil so as to induce a magnetic field which acts upon the plunger to move it axially into and out of sealing engagement with an outlet in the end face of the wall of the valve body. Typically, the plunger extends into an ink chamber having an axially directed outlet in the transverse end wall thereof and is biassed by a spring or other bias urging the plunger into the valve closed position at which the end face of the plunger seals against the outlet. This end face of the plunger usually carries a sealing disc or pad so as to provide a sealing seat against the end wall of the body or a raised rib around part or all of the outlet.

The extent of axial movement of the plunger is regulated at one extreme by the fixed end wall of the ink chamber, which may be an extension of the bore in the valve body within which the plunger is jdurnalled or may be provided by a wider bore extension mounted upon the end of the valve body.

The other extreme of the plunger- travel is regulated by the position of an axial end pole piece whose axial position in the bore within which the plunger reciprocates is adjusted to give the desired extent of clearance between the end face of the plunger and the transverse end wall of the ink chamber to allow the desired rate of flow of ink through the outlet. The end pole piece is a clearance fit within the bore in the valve body so that its axial position can be adjusted by means of a screw-threaded end engaging a nut or other screw-threaded means secured to the Valve body.

For convenience, such valves will be denoted hereinafter as solenoid valves.

Whilst such a construction provides a comparatively acurate means for adjusting the throw of the plunger, it does require sealing between the valve body and the end pole piece to prevent the escape of ink from the end of the bore in the valve body. Not only does this require extra sealing o rings or other components, but problems arise where the ink is a solvent based ink due to the agressive nature of the solvents used in such ink compositions. Furthermore, the screw-threaded components are extra components which require additional cost and labour to provide. In addition, the screw mechanism remains accessible to a user when the valve is in use and this can lead to unauthorised readjustment of the meachnism by the user, which can prevent the vlave from operating properly.

We have now devised a form of construction which reduces the above problems.

SUMMARY OF THE INVENTION Accordingly, the present invention provides a solenoid valve characterised in that the end pole piece is an interference fit within the axial bore of the valve body.

By making the pole piece an interference fit in the bore, the pole piece is self sealing within the bore so that no additional sealing means is usually required to prevent escape of ink from the bore past the end pole piece. This reduces the risk of degradation of a sealing ring or the like other sealing element by contact with the solvents in the ink compositions. The axial adjustment of the pole piece is readily achieved by rotating the pole piece and moving it axially to the desired position. The rotation of the pole piece overcomes the static friction between the valve body and the pole piece so that it can readily be moved within the bore of the valve body.Where the static friction between the valve body and the pole piece is sufficiently low, for example when the valve body is made from or the bore is coated with a low friction plastic, for example a ploytetraflurohalohydrocarbon, the axial movement may be achieved without the need for rotation of the pole piece.

The design of the invention provides a simple construction with reduced component parts. Futhermore, the free end of the pole pice does not have an accessible screw end, thus reducing the risk of un-authorised tampering with the setting of the axial position of the pole piece. In a preferred embodiment of the design, the pole piece is provided with an axial bore which serves as the ink inlet to the valve. In this case, the exposed spigot end of the pole piece can be mounted into a suitable recess in a manifold feeding ink to a number of such valves so that the end of the pole piece is further protected against unauthorised tampering. Since the pole piece is not to be accessible during normal use of the valve, the valve can be mounted by means of this end of the valve body, which had not hitherto been considered desible with the earlier forms of valve design.

DESCRIPTION OF THE DRAWINGS: To aid understanding of the invention, it will be described by way of illustration only with respect to a preferred form thereof as shown in the accompanying drawings in which Figure 1 is a diagrammatic axial cross-section through a valve of the invention; and Figure 2 is a diagrammatic cross-section through a manifold having a valve of the invention mounted thereon.

DESCRIPTION OF THE PREFERRED EMBODIMENT: As shown in Figure 1, a typical solenoid valve for a drop on demand ink jet printer comprises a tubular body member 1 moulded from a suitable plastic, fpr example a polyester resin. The body member 1 has wound or mounted upon it a substantially co-axial electrical coil 2. Located within the axial bore 3 of the body member 1 is a magnetisable plunger 4 which moves axially under the influence of a bias spring 5 and the coil 2. The spring 5 is restrained by an end pole piece 6 which also limits the retraction of the plunger 3 when a current is applied to the coil 2.

As shown exaggeratedly in Figure 1, the body member 1 can be formed with a taper, typically from 1 to 2.50, so that the narrow end of the body provides a tapered spigot member which can be plugged into other components, for example an end cap 7 (as shown dotted in Figure 1) or manifold (as shown in Figure 2) to tenable the valve to be modified readily for a wide range of uses using a single valve body member. Alternatively, the taper can be provided only over the forward end of the body, and in this case the taper can be as much as 50 or more.

One end, notably the thicker end, of the body member 1 can be formed with a radial flange 8 as shown which serves as -a shoulder against which the electrical coil buts when it is mounted on the body member 1. The flange can also serve as a mounting means for the valve and can be provided with screw holes or other means by which the valve can be attached to the print head of which it is td form part. The flange can have a circular or polygonal transverse crosssection to suit the mounting into which it is to be located.

However, as described below, the valve is preferably mounted by means of the exposed end of the pole piece.

If desired, the outer face of body 1 can be formed with, be treated with or be coated with a high friction or high stiction material to aid retention of the electrical coil upon body member 1. Alternatively, the outer face of the body member can be cut with one or more helical grooves or carry one or more helical ribs to provide a screw thread type of surface to engage with the internal face of the electrical coil to aid location and securing of the coil on the body member.

Preferably, the body member 1 is formed with a closed end so as to provide an ink chamber 9 in the blind end of the bore 3. The transverse end wall 10 closing the end is conveniently formed during moulding of the body member so that it is an integral part of the body member.

Alternatively, the ink chamber 9 can be formed by a separate end wall, for example provided by an end cap, which is secured and sealed upon the body member. For convenience, the invention will be described hereinafter in terms of a tapered body member 1 having the transverse end wall 10 formed integrally therewith during moulding of the body member from a plastic material.

The transverse end wall 10 forming the blind end to the bore 3 is preferably provided with an axial bore 11 therethrough, which serves as the ink outlet to the ink chamber 9. This bore can be formed during the moulding of the body member or can be formed subsequently. It is preferred that the bore 11 have an axially outward portion of broader diameter so as to form an internal shoulder against which a jewel nozzle orifice 12 buts when it is mounted in bore 11 to form the fine bore nozzle orifice for the valve. Alternatively, the jewel nozzle orifice can protrude into the ink chamber 9 to provide a convex seat against which the free end of the plunger seats to close the out, let to chamber 9. The nozzle orifice can also be provided by a capillary tube inserted into outlet 11.The tube can extend into chamber 9 so that its rim provides an rib 13 against which the free end of the plunger 4 seats to close the outlet to the chamber 9.

Alternatively, the inner face of the transverse wall 10 can carry such an annular rib, as shown in Figure 1.

It is preferred that the nozzle orifice 12 be demountable, for example by being a push fit in outlet 11. Other forms of demountable mounting can be used, for example a screw cap carrying the jewel nozzle or capillary tube orifice can be mounted on an external screw thread on the outer face of the end of the body 1. By making the nozzle orifice 12 demountable, the outlet end of the valve body can be connected to other components which may themselves carry nozzle orifices, as when the valve is connected to a manifold. A demountable nozzle orifice also enables the valve to be flushed out after manufacture to remove dirt and debris before the nozzle orifice is fitted at the factory.

The axial bore 3 within body 1 has journalled for axial reciprocation therein a magnetisable plunger 4 whose free end extends into chamber 9 and seals against the end wall 10, the ribs 13 or the protruding end of the jewel or capillary tube nozzle orifice 12. If desired, the free end of plunger 4 can carry a sealing disc or pad 14 of a suitable rubber or resin to provide the sealing seat against the ribs 13 or their equivalent. The seating of the free end of the plunger on end wall 10 provides the limitation to the movement of the plunger 4 in that direction.

The extent of rearward travel of plunger 4 is restricted by the end pole piece 6. This is an interference fit within the bore 3 so that it will self seal within the bore and will retain its axial position against the ink pressures applied to it during operation of the valve. Preferably, the opposing faces of the bore 3 and pole piece 6 are not polished, so as to provide a high co-efficient of static friction between them. However, the opposed faces can be lubricated to assist relative movement, provided that this lubrication is temporary, as when a thixotropic lubricant or slow setting adhesive is used to provide an interface between the pole piece and the bore wall during insertion of the pole piece 6 into the bore 3.

The pole piece 6 extends into bore 3 to the desired extent to limit the retraction stroke of the plunger 4 when the coil 2 is energised. The optimum position of the pole piece 6 can readily be adjusted to give the desired perfomance of the valve during manufacture of the valve. As indicated above, it is preferred to rotate the pole piece 6 so as to overcome the static friction between the pole piece and the wall of the bore so that the pole piece can then be moved axially. In this way it is possible to achieve an accuracy of adjustment of the pole piece which is at least as good as that achieved with the more complicated screw mechanisms hitherto considered necessary.

The free end of th-e pole piece 6 can take any suitable form, for example a smooth cylindrical end stub (as shown in Figure 1) which a user would find difficult to manipulate during un-authorised re-setting of the pole piece position.

Alternatively, the free end of the pole piece can be given a shape suitable for some other purpose. For example, the free end can be provided with an external screw thread whereby the valve can be mounted on a manifold, support or other device. Such a screw thread can also be used to mount the pole piece on a rotating mechanism during assembly and adjustment of the valve during manufacture.

Plunger 6 is normally biassed into sealing engagement with the outlet to chamber 9 to prevent the flow of ink through chamber 9 by a spring 5 or other bias means acting between the pole piece 6 and the plunger 4. As indicated above, due to the interference fit of the pole piece 6 in bore 3, the end of the body member 1 does not require a separate seal or seals between plug 6 and the side wall of the bore 3 or an end cap as hitherto, thus simplifying the construction of the valve of the invention.

Ink is fed to chamber 9, for example via the radial inlet 15 into the chamber, as shown. However, it is preferred that the pole piece 6 have an axial bore 16 therein through which ink may be fed into bore 3 so that it flows axially past plunger 4 into chamber 9. If desired, the axial wall of plunger 4 can be cut with axial grooves or can have axial flatted portions to assist flow of ink past the plunger 4 and into the chamber 9.

Externally upon body member 1 is mounted an electrical coil 2 which is usually wound upon a plastic or similar bobbin or former 17. Preferably, the inner face of the bobbin or former 17 has a taper corresponding to that of the external face of member 1 so that the former or bobbin seats firmly upon the body member as it is pushed axially onto the body member. The coil and bobbin or former are of conventional construction and design. If desired, means, for example a circumferential rib or snap latch 18, can be provided to retain the coil 2 upon the member 1.

Alternatively, the valve of the invention can be mounted by means of the exposed free end of the pole piece 6, notably where that has a screw thread formed upon its external surface so that the valve is mounted by screwing it into a manifold or other component. Such versatility is of especial use where the pole piece 6 has an axial bore 16 to provide the fluid connection between an ink source such as a reservoir or manifold and the ink chamber. Thus, as shown in Figure 2, a valve of the invention can be mounted by means of the exposed end 40 of the pole piece 41 upon a distribution manifold 42 for ink under pressure. The exposed end 40 can be a push fit into a suitable socket in the wall of the manifold, in which case it may be desired to provide an 0 ring or other sealing member to prevent escape of ink at the interface between the socket and the pole piece. Alternatively, the exposed end of the pole piece can carry a screw thread which co-operates with a similar screw thread in the socket in the wall of the manifold.

The above construction of the valve is encased in a metal shell, not shown, to provide the magnetic return for the magnetic field generated as a current is passed trough the coil 2. Such a shell typically takes the form of a cylindrical pot into which the valve assembly fits and which is then closed by a metal disc through which the free end of the vlave body protrudes so that the nozzle orifice or the adaptor cap or other component can be fitted to the assembled valve.

Claims (9)

CLAIMS:

1. A solenoid valve comprising an axially elongated body member having an axial bore therein in which is journalled a plunger member for reciprocation in the bore under the influence of a magnetic field generated by a coil carried by the body member; the body member also being provided with a chamber at or adjacent one end, the distal end, thereof in which the distal end of the plunger can move during reciprocation thereof, the distal end of the chamber being closed by a transverse wall having an outlet therein with which the distal end of the plunger engages in sealing engagement at one extreme of its travel and from which the distal end of the plunger retracts so as to permit fluid to escape from the chamber, the extent of axial retraction of the plunger being restricted by a pole piece located in the axial bore, characterised in that the pole piece is an interference fit within the axial bore.

2. A valve as claimed in claim 1, wherein the pole piece has an axial bore which is adapted to serve as the fluid inlet to the valve.

3. A valve as claimed in claim 2 wherein the pole piece protrudes axially from the body member and is adapted to serve as a means by which the valve may be mounted upon another article.

4. A valve as claimed in claim 3, wherein that other article is a manifold adapted to feed fluid to a number of valves.

5. A valve as claimed in any one of the preceding claims, wherein the body member has an external taper towards the distal end thereof, the taper having an included angle of from 1 to 2.50.

6. A valve as claimed in claim 1 substantially as hereinbefore described.

7. A valve substantially as hereinbefore described with respect to and as shown in the accompanying drawings.

8. A method for adjusting the performance of a valve as claimed in claim 1, wherein the extent of retraction of the plunger is adjusted by rotating the pole piece and moving it axially in the axial bore to achieve the desired axial clearance between the proximal end of the plunger and the distal end of the pole piece.

9. A drop on demand ink jet printer in which ink is to be fed under pressure to a nozzle orifice via a valve means which is to control the flow of ink to the nozzle orifice, characterised in that the valve is a valve as claimed in any one of claims 1 to 7.