GB2099762A

GB2099762A - Button or key switch

Info

Publication number: GB2099762A
Application number: GB8214932A
Authority: GB
Original assignee: Fujitsu Services Ltd
Current assignee: Fujitsu Services Ltd
Priority date: 1981-06-05
Filing date: 1982-05-21
Publication date: 1982-12-15

Abstract

A button or key switch includes a button or key top 1 supported on a stem 2 which is moveable in a guide means 3 between an operated and unoperated position. A permanent magnet 8 is provided in the stem 2. Further magnets 9a, 9b are provided in the guide means 3, these latter magnets being so positioned with respect to the magnet 8 that a loading force is produced which urges the stem to its rest or unoperated position in the absence of an operating force on the key top 1. The loading force also imparts "feel" to key operation. <IMAGE>

Description

SPECIFICATION Key switch Background of the invention The present invention relates to button or key switches, particularly suitable for incorporation in keyboard assemblies.

It has previously been proposed to provide key switches manually operable by finger pressure to actuate electrical circuits and also to provide assemblies of such switches in a keyboard arrangement simulating, in appearance, for example, the keyboard of a typewriter. In earlier arrangements such key switches have been provided with means for restoring and maintaining their manually operable key top portions in an unoperated position by means of springs. In later examples, key switches have been proposed in which the key tops are held in the unoperated position by means of magnetic attraction between one magnetised member, such as a washer, for example, mounted on a stem of the key top and another mounted on a fixed stop.This form of magnetic retention has the disadvantage that in order to restore the key top the magnets are required to be sufficiently powerful to move the key top over a distance corresponding to its displacement distance between operated and unoperated positions.

Hence, once restored, this magnetic force requires considerable effort to operate the key, while, in operating the key top, once the initial movement is accomplished to separate the magnetic members the magnetic force is very rapidly reduced, with the result that the loading on a key top presented to the switch operator has an undesirable quality or "feel".

Summary of the invention According to the present invention, there is provided a button or key switch, including a button or key top having a stem, means for supporting the stem for movement between an unoperated and an operated position, means for producing a magnetic field having a magnetic axis transverse the direction of movement of the stem, and means for producing distortion of the magnetic field acting on the stem in a direction to provide a loading force on the stem in a predetermined sense along said direction.

Preferably the loading force also being effective to produce movement of the stem towards the unoperated position in the absence of an external operating force.

The magnetic field producing means may be at least one magnet carried by the supporting means, in which case the distortion producing means may be a magnetic member carried by the stem. Alternatively the field may be produced by a magnet carried by the stem, in which case the distortion may be produced by a magnetic member carried by the support means. In either case, the magnetic member may also be a magnet. The distortion of the magnetic field may result in the development of an attractive or a repuisive force between magnetic members carried by the supporting means and the stem, the developed force being effective to act on the stem. The supporting means may be a sleeve embracing the stem and the sleeve may be formed on or supported by a base which may be common to a plurality of key switch structures.

Brief description of the drawings Apparatus embodying the present invention will now be described, by way of example, with reference to the accompanying drawing, in which, Figure 1 is a side view of a key switch operating assembly, Figure 2 is a sectional view of the assembly of Figure 1, and Figure 3 is a section view of an alternative assembly.

Description of the preferred embodiment Referring now to Figures 1 and 2 of the drawing, the operating mechanism of a key switch consists of a key top 1 supported on a stem 2, the stem 2 being moveable in a supporting sleeve 3 which is in turn supported on a base 4. As is indicated in the Figures it is convenient for the foregoing parts 14 to be manufactured as mouldings in a suitable synthetic plastics material. However, it will be understood that the particular form taken by these parts may be modified for manufacture in other materials, for example.

The particular example illustrated is intended for vertical movement, and as shown in Figure 2, the key top is formed with an upper surface 5 suitable for engagement by an operator's finger.

The interior of the key top 1 has a recess 6 to receive one end of the stem 2, the upper end of the stem 2 being secured in the recess 6 of the key top 1 after the stem 2 has been passed through the sleeve 3, in which it is a sliding fit.

The lower end of the stem 2 is formed with a projecting end-piece 7 which abuts the lower end of the sleeve 3 to determine the limit of permissible upward movement of the stem 2 in its unoperated position. As shown, the sleeve 3 and the base 4 are conveniently formed from a single moulding and it will be clear that, if required, for example, a plurality of sleeves 3 could be formed in this manner on a single base member to form a complete keyboard.

As best shown in Figure 2, a permanent magnet 8 is incorporated in the stem 2, for example, by being moulded into the stem 2 during manufacture or, subsequently, by being bonded into a suitable aperture provided in the stem 2. In a somewhat similar manner, a pair of permanent magnets 9a and 9b are incorporated into opposite sides of the sleeve 3. The arrangement of the magnets 8, 9a and 9b is such that their magnetic fields cooperate in the following manner: The magnetic axis of the magnet 8 lies in a direction transverse the direction of movement of the stem 2.Thus, as shown in the Figure 2, in which the stem 2 is moveable in a vertical direction, the magnetic axis of the magnet 8 is horizontal and for the purposes of the present explanation it will be assumed that the magnet 8 is oriented to produce a north-seeking pole at the left-hand side and a south-seeking pole at the right-hand side of the stem 8 as shown. In this case, the magnet 9a supported in the lefthand wall of the sleeve 3 is arranged with respect to the field of the stem magnet 8 to produce an attractive magnetic field also having a horizontal axis, so that in the present example it also produces a north-seeking pole at the left-hand side (facing outwards from the sleeve 3) and a south-seeking pole at the right-hand side (facing towards the stem 2).The magnet 9b in the righthand wall of the sleeve 3 also produces an attractive horizontal magnetic field and also has a north-seeking pole at its left-hand side (facing towards the stem 2) and a south-seeking pole at its right-hand side (facing outwards from the sleeve 3). Thus, the magnetic field of the magnet 9b augments that of the magnet 9a and this combined field is aligned across the stem 2 in the same direction and of the same polarity as the field produced by the magnet 8 in the stem, so that the effect of the combined fields from all the magnets 8, 9a and 9b is to seek to move the stem 2 into a position in which the field of the magnet 8 is aligned with that of the magnets 9a and 9b.

This results in the generation of a force acting to restore the stem 2 into its upper, or unoperated position and to maintain it in this position. To ensure a remanent but positive force in this upward direction when the limit of travel is reached, indicated by the contact of the end piece 7 with the base 4, it is proposed to displace the magnets 9a and 9b slightly upwards with respect to the magnet 8 so that the axis of the magnetic field of the sleeve magnets 9a and 9b is displaced from that of the field of the stem magnet 8 in the direction of stem movement towards the unoperated position. Such displacement results in a permanent distortion of the combined magnetic field resulting from the interaction of the individual fields of all the magnets 8, 9a and 9b.

The degree of this distortion provides the effective initial loading of the key top 1 and it will be apparent that this loading may be controlled by, for example, the field for example, the field strength of the magnets and by the degree of misalignment of the fields produced as the result of the relative displacement of the sleeve magnetic 9a, 9b with respect to the stem magnet 8.

It will also be seen that movement of the-stem 2 resulting from depression of the key top 1 produces a further distortion of the combined magnetic fields which results in a progressive change in the effective load on the key top 1 and provides a force for the restoration of the stem 2 and key top 1 to its initial unoperated position.

This in turn results in a more acceptable "feel" sensed by the operator when using the key switch and is in marked contrast to the sudden change felt in the case of other key switches in which, for example, the initial movement is accompanied by a sharp break in the magnetic attraction of a pair of magnetised members which are mutually attracted into contact with one another by fields acting in a direction parallel to the direction of key top movement.

From the foregoing description of the interaction of the magnetic fields in the present case it will be appreciated that the restoring force on the key top 1 is dependent on the field strengths of the magnets and the degree of field distortion produced by movement of the stem 2 relative to the sleeve 3. In general, it is found that a maximum displacement for the key top 1, usually termed the "key-stroke", of the order of 5mm, is readily obtainable and may be varied by, for example, modifying the relative dimensions of the magnets in the direction of relative movement, the force/displacement characteristic of the arrangement being dependent on the relative positions of the magnets.

The description so far has concentrated upon the control of restoration and loading of the key top 1. It will be realised that in addition to such control, a key switch also requires some means for controlling or switching an electrical circuit.

However, many conventional switching means are known and are used in cooperation with a moving key stem for this purpose and it is proposed that such elements may be used in conjunction with the present key stem controlling arrangement. Such switching devices may therefore include elements such as electrical contacts, reedswitches, Hall effect elements, displaceable contact assemblies, capacitance switches, optical switches or other elements depending, for example, on movement of a coil with respect to a magnet, or vice versa.It will be clear, then, that the precise form of mounting or support assembly for these elements in relation to the moving stem 2 depends upon the exact nature of the switching element to be used, but that the use and mounting of any particular switching element is both irrelevant to the present invention, which is concerned only with the control of stem restoration and loading, and will follow an appropriate conventional practice.

It will be appreciated from the foregoing description with reference, in particular, to Figure 2, that, considered independently, either the magnet 8, or the magnets 9a and 9b will produce a magnetic field acting transverse the direction of movement of the stem 2 relative to the sleeve 3.

In each case the provision of a second magnetic field has the effect of distorting the first field and the loading and restoration of the stem 2 is dependent upon magnetic attraction between the magnets producing these two fields. Thus similar field distortion and magnetic attraction effects may also be obtained by the substitution of a magnetic but unmagnetised material, such as soft iron, for example, for either the magnet 8 or the magnets 9a and 9b. In such a case, the remaining magnetic field producer will continue to function to produce the transverse field, while this field will continue to be distorted due to the presence of the substituted unmagnetised magnetic material.

Because of the inherent attraction between the magnet and the unmagnetised material, a loading and restoring force is developed as described above, although the magnitude of this force will clearly differ from that obtainable if magnetised materials are used in both cases. It also follows that, since a magnetic field may be generated by, for example, an electro magnet, the magnets described need not be of permanently magnetised material. Thus, a form of construction is possible in which, for example, an unmagnetised magnetic element is substituted for the stem magnet 8 and an electromagnet or a pair of electromagnets is or are used to generate the transverse magnetic field in place of the magnets 9a and 9,'; The foregoing descriptions have all assumed that the development of the loading and restoring force is based on the phenomenon of magnetic attraction.It will be understood that a similar force may alternatively be produced, based on the principle of magnetic repulsion. Figure 3 shows such an arrangement. In this case the stem magnet 8 may be oriented as described earlier, with, for example, its magnetic axis horizontal and a north-seeking pole on its left-hand side as shown. The sleeve magnets 9a and 9b, however, although having their combined magnetic axes horizontal, are of reversed polarity as compared with the desciption given above, so that the magnet 9a has its north-seeking pole on the righthand side (facing towards the stem 2) and the magnet 9b has its south-seeking pole on the lefthand side (facing towards the stem 2). Thus, the magnet 8 is so oriented with respect to the magnets 9a and 9b that the respectively adjacent pole-pairs are mutually repellent.The key loading force results from the relative positions of the magnets 8 and 9a and 9b and in this case the stem magnet 8, while the key top 1 is in its unoperated position, is displaced relative to the magnets 9a and 9b in the opposite direction from that in which the stem 2 will move towards the operated position. It will also be realised that the lengths of the magnets in the direction of movement of the stem 2 must be such that, throughout the extent of this movement, there is always present an element of repulsive magnetic force acting to restore the stem 2 to its initial unoperated position. Clearly this form of structure, because it relies upon the phenomenon of the repulsion of like magnetic poles, requires that the magnetic members 8 and 9 are all magnets and non-magnetised elements cannot be substituted.

It is to be understood that while the stem 2 is shown as moveable within a sleeve 3 which is shown and described as a unitary structure entirely embracing the stem 2, the term 'sleeve' is to be interpreted as including any structure which will support the stem 2 and permit the requisite movement. Hence the magnetic members corresponding to the magnets 9a and 9b may be supported in a manner differing from that shown.

Thus, for example, the stem 2 may take the form of a bar or spindle depending from the key top 1 and the supporting means may then consist, say, of a pair of plates carrying apertures through which the bar or spindle passes and in this case the magnetic members could be supported on a separate structure between these plates.

It will also be realised that, while the preceding description deals with the specific key structure shown in the drawings, other ways of fabricating the keys may be employed. For example, it is common in assembling keys merely to press or clip the key top 1 on to a stem which is supported to provide the necessary movement, and this form of construction may clearly be used for the present arrangement. It is also possible to use a construction in which the key top 1 and the stem 2 are a onepiece moulding, a separate travel stop being incorporated at a later stage of assembly of the switch.

It is also apparent that the present invention is applicable to single key switches as well as to arrays of key switches arranged in formation to produce a multi-key structure. Moreover, although the key switch restoring and loading arrangement is described in relation to a key top and stem having downward vertical movement from unoperated to operated positions, it is to be understood that this direction of movement is not to be considered as a limitation on the arrangement, which is suitable for key switches having other directions of such movement.

Claims

1. A button or key switch, including a button or key top having a stem, means for supporting the stem for movement between an unoperated and an operated position, means for producing a magnetic field having a magnetic axis transverse the direction of movement of the stem, and means for producing distortion of the magnetic field acting on the stem in a direction to provide a loading force on the stem in a predetermined sense along said direction.

2. A button or key switch as claimed in Claim 1, wherein said loading force is also effective to produce movement of the stem towards the unoperated position of the button or key top in the absence of an external force on the key top.

3. A button or key switch as claimed in Claim 1 or 2, in which the magnetic field producing means includes at least one magnet carried by the supporting means and in which the distortion producing means is a magnetic member carried by the stem.

4. A button or key switch as claimed in Claim 1 or 2, in which the magnetic field producing means includes at least one magnet carried by the stem, and in which the distortion producing means is a magnetic member carried by the supporting means.

5. A button or key switch as claimed in Claim 4, in which a magnet is provided at opposite sides of the support means, and in which at least one magnetic member is provided on, or in, the stem at such position that when the stem is in its unoperated position the magnets and the magnetic members are relatively offset with respect to each other in the direction of relative movement thereof, the offsetting being such as to produce a remanent amount of said distortion, which serves to hold the stem in its unoperated position.

6. A button or key switch, constructed and arranged to operate substantially as hereinbefore described with reference to the accompanying drawings.