BACKGROUND OF THE INVENTION Switches including a switching blade are commonly used in domestic and commercial applications. Such switches are operated by a dolly with an internal protrusion an end of which engages with an upper part of the switching blade. A bridge pivotably supports the switching blade from below. A compression spring is positioned in or in connection with the dolly as a separable component to provide for a force especially operable between the on and off positions of the switching blade to give a snap action. There are a number of configurations of switching blade, in one commercially available form the switching blade is generally held horizontally, with the dolly fitted with a spring and a slidable member the slidable member urged downwardly to engage an upper surface of the switching blade, and moving either side of the bridge to pivot the switching blade in see-saw action. In a second commercially available form the switching blade is held generally vertically, with the lower end of the switching blade having protrusions engaging the switching bridge to pivot thereabout, and a lug at the top end engaging a compression spring placed between the inside of the dolly and the switching blade, the dolly is moved from side to side of the switching blade to urge it to snap from one side to the other in an on off movement.

A problem with these arrangements is that there a several pieces that make up the switch, and in particular because the dolly is made of a finger contacting portion and a separable compression spring, which assembly needs during fitting to bear against the switching blade whilst two spigots of the dolly are located in two sockets of the switch housing.

This assembly of the switch is awkward and is conventionally undertaken manually, which increases the cost of manufacturing such switches, and as a consequence appliances and fittings that have such switches.

It is an object of at least one embodiment of this invention to provide a switch with a simplified dolly assembly whilst retaining a snap action, or at least to provide the public with a useful choice.

It is an object of a specific aspect of this invention to provide a switch with a dolly assembly and switching blade suitable for automated assembly.

SUMMARY OF THE INVENTION In a broad form the invention might be said to reside in an electrical switch including a switch housing, a conducting switching blade supported for pivotal movement about a bridge between an off position and an on position, the bridge supported by the housing, the switching blade adapted to form part of an electric circuit being open when the switching blade is in the off position and closed when the switching blade is in the off position, in the on position a pair of contacts, one on the switching blade and the other supported by the housing are closed, a dolly of unitary construction having a dolly protrusion pivotably engaging the switching blade, said dolly manipulable to drive the switching blade between the off position and the on position, the bridge being resiliently urged against the switching blade, to make unstable a transition between the on position and the off position to thereby provide for a snap action therebetween.

In a first arrangement of the invention the bridge contacts a first surface of the switch blade, and the dolly protrusion engage a second surface of the switching blade at a location opposed to the contact by the dolly protrusion the switching blade is slidable and rotational relative to either the bridge and/or the extremity of the dolly protrusion so that relative position of the dolly protrusion pivot and the bridge pivot on the switching blade translate relate to each other by reason of manipulating the dolly between the first and second positions, when the pivots are generally aligned one opposite another the compression force making the transition unstable.

This first arrangement then provides for a switching mechanism that potentially has less parts and is much easier to assemble than prior switches if only by reason of not having a dolly protrusion supported on a compression spring directly contacting the switching bridge.

The dolly of the first arrangement may thus be of unitary construction perhaps being moulded as a single piece plastics article, comprising a finger contactable portion which includes spigots that can be journalled into suitable sockets in the switch housing so as to be pivotable relative to the switch housing and having an internal dolly protrusion.

Conventionally the internal dolly protrusion is manufactured of metal and this might also be

desirable for the present invention so that the integrity of the pivot of the switching bridge is maintained, thus the internal dolly protrusion may take the form of a metal plate fastened into position, perhaps by a resinous adhesive, or alternatively a metal plate may be integrally moulded into the plastics of the remainder of the dolly. However, because there is no relative movement between the finger manipulable portion of the dolly and the internal dolly protrusion the latter may function equally well as a plastics component. Whilst generally the dolly protrusion in prior art switches provide a pivot by reason of an extremity of the internal protrusion being located within a transverse groove in the switching blade the pivot may be provided in a number of other ways that might minimise the effect of the lack of the hard surface that a metal component provides. The metal component may be provided in the form of a mild steel plate. In any event it is desired to make the dolly of unitary construction such that any parts thereof do not separate on assembly of the switch.

A spigot and socket arrangement might provide the pivotal connection between the internal dolly protrusion and the switching blade, either the switching blade or the internal dolly protrusion having a spigot or complementary socket respectively.

It may be desired in the first arrangement to have a pair of arms extend down from the sides of the dolly protrusion to positively engage with the switching blade and perhaps where the extremity of the dolly protrusion engages a transverse switching blade groove in the upper surface of the switching blade the arms can be snap fitted underneath the switching blade to provide a more secure engagement of the dolly protrusion into the switching blade groove. This is useful for assembly purposes.

In the above described variations of the dolly and its interaction with the bridge for the first arrangement it will be appreciated that the dolly protrusion and the switching blade have a positive engagement and accordingly there is no relative sliding movement between the switching blade and the dolly protrusion, the sliding movement together with rotational movement is thus between the switching blade and the bridge. In an alternative construction however it may be desired to have the combination slidable and rotational movement between the dolly and the switching blade and thus the whilst the extremity of the dolly protrusion provides for a pivot, the location of the pivot changes relative to the switching blade, and the pivot between the bridge and the switching blade may involve a positive engagement such as by a spigot and socket connection. Alternatively, however, neither of the two pivot connection are positive, in this latter embodiment it may be

desirable to have some means for locating the switching blade so that it does not shift from a functional position.

A feature of a switch of the type to which this invention is directed is that there is a resiliently compressible member which is compressed in the transition of the switching bridge between the open and closed positions, to thereby snap the bridge between the open position and the closed position. This resilience is preferably provided by the bridge.

Generally one or both of the electrical contacts are provided in the form of a metal plate, and in one form of the invention either one of the electrical contacts is extended above the housing to provide for a spring as well the bridge. This may take the form of a cantilever spring. In an alternative form the bridge support may take the form of an elastomeric block made from, for example, a synthetic rubber material which is thus compressible and provides the necessary spring for instability of the transition between the open and the closed position of the switching bridge. The electrical connection being otherwise provided for.

In an alternative form of the first arrangement the present invention might also be said to provide an electrical switch including a switch housing, a first electrical contact and a second electrical contact supported by the housing, and a switching bridge pivotably and resiliently supported by a bridge support said bridge support supported by said housing, a dolly pivotably attached to said frame said dolly being externally finger manipulable from a first pivot position to a second pivot position, said dolly having an internal dolly protrusion, an extremity of the dolly protrusion having pivotal contact with said switching bridge at a position opposed to the pivotal support provided by the bridge support, said internal protrusion being fixed with respect to the dolly, said switching bridge slidable and rotational relative to either the bridge support and/or the extremity of the dolly protrusion so that relative position of the dolly protrusion pivot and the bridge support pivot on the switching bridge exchange by reason of manipulating the dolly between the first and second positions passing through an unstable transition whereby the resilient bridge support is compressed so that the bridge is snapped between an open position and a closed position, the bridge contacting the first contact only in the open position and both the first and second contact when in the closed position.

In a second arrangement of the invention the bridge contacts one end of the switch blade and the dolly protrusion engages an opposite end of the switch blade, the switch blade

being rotational relative to the bridge and the dolly protrusion, the on and off positions being located on either side of the direction of compressional force. It will be understood from the above discussion relating to the first arrangement of the present invention that some of these variations will also be applicable to the second arrangement.

BRIEF DESCRIPTION OF THE DRAWINGS For a better understanding the invention will now be described with reference to an illustrated embodiment wherein, Figure 1 is a somewhat schematic cross sectional view of a prior art switch showing a switching blade in an"off"position, that is, having an open circuit, Figure 2 is a somewhat schematic cross sectional view of a prior art switch showing a switching blade in an"on"position, that is, having a closed circuit, Figure 3 is a diagrammatic illustration of the principle of one embodiment of the first arrangement of the present invention, Figure 4 is a diagrammatic illustration of the principle of a second embodiment of the first arrangement of the present invention, Figure 5 is a diagrammatic illustration of the first arrangement of the invention showing the switching blade in a transition position Figure 6 is a diagrammatic illustration of the first arrangement of the invention showing the switching blade in the"on"position, Figure 7 is a diagrammatic illustration of the first arrangement of the invention showing the switching blade in the"off position, Figure 8 is a diagrammatic illustration of a second arrangement of the invention showing the switching blade in a transition position.

Figure 9 is a diagrammatic illustration of a second arrangement of the invention showing the switching blade in an"on"position,

Figure 10 is a diagrammatic illustration of a second arrangement of the invention showing the switching blade in an"off"position, Figure 11 is partial view showing one form of a connection between the switching blade and internal dolly protrusion of the first arrangement of the invention, Figure 12 is a partial view showing a second form of a connection between the switching blade and an internal dolly protrusion of the first arrangement of the invention, Figure 13 is a partial view showing a third form of switching blade, dolly and bridge of the first arrangement of the invention, Figure 14 is a partial view of a fourth form of switching blade, dolly and bridge of the first arrangement of the invention, Figure 15 is a partial view of a fifth form of switching blade, dolly and bridge of the first arrangement of the invention, Figure 16 is a diagrammatic view of a first arrangement of the invention showing a first form of bridge, and Figure 17 is a diagrammatic view of the first arrangement of the invention showing a second form of bridge and an alternative pivotal connection with the switching blade.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENT Similar reference characters indicate corresponding parts throughout the several views of the drawings.

Dimensions of certain of the parts shown in the drawings may have been modified and/or exaggerated for the purposes of clarity or illustration.

Figures 1 and 2 show, in general format, a prior art switch using a switching blade. The switch is supported on a housing (1) and includes a first contact (3) and a bridge (4)

comprises an edge of a lobe (2) of a conductive plate. This is held rigidly in position as indicated by vertical post (5) extending upwardly from the housing. A switching blade (6) in the form of an inflexible elongate rectangular conductive metal strip pivots about the bridge support (4). An actuator in the form of a dolly (7) is used to operate the switch.

This is a finger operated actuator, and comprises a button shaped finger contact portion (8) which comprises an upper web for finger contact with a peripherally depending skirt.

Spigots (not shown) extend outwardly from the skirt into sockets of a surrounding housing or frame so that a fixed dolly pivot is provided as indicated at (9). An internal dolly protrusion (10) is provided in the form of a metal plate extending inwardly into the housing and an extremity (11) of the dolly protrusion engages a transverse groove (12) in the switching blade. The metal plate is slidably moveable and guided in that movement by a pair of guides (13,14), and biased in an extended position by a compression spring (15).

The working of this prior art switch is that by reason of finger manipulation of the dolly from a first position (shown in figure 1) to a second position (shown in figure 2) the switching blade is pivoted around a first pivot, namely the extremity (11) of the dolly protrusion, but in addition it can be seen that there is a degree of slidable movement of the switching blade to one side or other of the bridge support (4) together with rotation thereabout. The spring (15) biases the position of the switching blade to either the off position or the on position by making a transition therebetween unstable.

Whilst this arrangement, and other similar arrangements, functions quite satisfactorily and are used very widely in domestic and commercial power and light switches it suffers from the disadvantage of having a large number of parts, and moreover there is some awkwardness in assembly especially as a result of the requirement to place the sprung metal plate (10) in position on the switching blade at the same time as locating both spigots of the skirt of the dolly in corresponding sockets in the frame or housing. Such assembly is difficult if not impossible to automate and is therefore carried out manually.

At least some forms of the present invention provide the possibility of reducing the number of parts for use in such switches, and also reduces difficulties associated with assembly especially those associated with the sprung metal plate.

The general principle of a first embodiment of the first arrangement of the present invention is shown in figure 3. A finger manipulable dolly (7) is pivotably rotatable about the dolly pivot (9) which is fixed relative to the frame or housing (1) of the switch. The dolly is pivotably connected with a switching blade (6) at a pivot shown at (20) the pivot being fixed relative to the dolly and the switching blade. The switching blade is pivotably

supported on a resiliently compressible bridge (21) which is fixed in relation to the housing. The switching blade is also slidable on the bridge support in like manner to that as discussed in relation to the prior art switch. Thus when the dolly is pivoted to the right as illustrated the left of the switch blade will god own and the right of the switch blade will go up so that the pairs of contacts (23,24) are open, and the switch blade is thus in the off position. With movement of the dolly in the opposition direct the reverse will occur and the two pairs of contacts will close so that the switch blade is thus in the on position It can be seen that the dolly is of unitary construction, and does not have a slidable or sprung dolly protrusion but rather have one that is fixed. In the illustration it is evident that the dolly is made of one piece however all that is required is that it be unitary to the extent that any component parts that it is made of are not readily separable during assembly of the switch. The resilient compression of the bridge provide for an unstable transition of the switching bridge between and"on"position and an"off'position to thereby give snap to switching therebetween. It will be appreciated that Figure 3 is merely to illustrate the relationship of various kinematic pairs in the switch and is not intended to provide specific working instruction. A person skilled in the art will readily be able to device a working model of this principle.

The general principle of a second embodiment of the first arrangement of the invention is shown in figure 4. The arrangement of the kinematic pairs and working of this embodiment is identical in principle as that of the first embodiment except that there is a kinematic inversion with respect to the two of the pairs namely the dolly and switching blade on the one hand and the bridge and switching blade on the other hand. Thus a fixed bridge support pivot (25) is provided in place of the sliding bridge pivot of the first embodiment. The sliding pivot is in this instance provided by an extremity of the dolly which in this second embodiment does not register particularly in a location on the switching blade. Thus on pivoting the dolly, the extremity of the internal protrusion of the dolly bears against the switching blade initially to one side of the bridge support pivot (25) the switching bridge is moved into a transition position as shown in figure 4, which transitional position is transient because the energy requirement of maintaining the transition is high and once the extremity of the dolly protrusion moves over centre of the bridge support pivot the switching bridge snaps over to the opposite position. The toggling of the dolly results in the see saw action referred to for the first embodiment as illustrated in figure 3.

A third embodiment is not illustrated however reference will be made to figures 1 and 2.

This type of switch can readily be converted to a switch of the present invention. A resiliently compressible support can be provided under the bridge by removal of any vertical posts (5) for support of the first electrical contact. The lobe (2) of the conductive plate is made of a metal that has sufficient resilience that it may be adequate to rely on this alone for resilient compression. Alternatively it might be desirable to provide a spring support for the first electrical contact, and that might be provided by an elastomeric block.

Having provided a suitable means that can be resilient compressible by pressure on the switching bridge it is no longer necessary that the metal plate (10) forming the dolly protrusion be sprung by a compressible coil spring. Thus the coil spring can be discarded from the arrangement and the metal plate can be fixed in place for example by adherence using a settable resin. Alternatively it might be feasible to no longer have a metal plate but to have a unitary moulded internal dolly protrusion that is made of a similar plastics material.

For a better understanding, the first arrangement of the invention will be described by reference to figures 5,6 and 7. These figures are generally the same but illustrating different positions of the switching blade, dolly and bridge.

The housing (100) is schematically depicted as a base member (101), an upright member (102) and a transverse dolly supporting member (103). The dolly (104) is supported from the dolly supporting member (103) by a fixed pivot (105). The dolly is shown as a single piece elongate member, a lower portion of which might be considered to be a dolly protrusion, an extremity (106) of the dolly protrusion contacts switching blade (107). The switching blade is an elongate flat conductive member, typically made of copper. The dolly on the other hand is non-conductive, a finger contacting portion at least being of insulative material. The extremity (106) of the dolly protrusion is preferably (but not illustrated) tapered so that engages a groove (not shown) positioned generally centrally on a first surface of the switching blade. This then also provides a generally fixed pivot point.

A first metal plate (110) of conductive material making up part of an electrical circuit or potential electrical circuit is supported by the base (101) of the housing. The metal plate ends in an upwardly extending lobe (111) an upper edge (112) of which acts as the bridge about which the switching blade is supported from below. It will be appreciated that contact between the bridge and the switching blade is conductive contact.

A second metal plate (113) of conductive material makes up a second conductive element.

A contact pair (114) is carried by the second surface of the switching blade (107) and the second metal plate.

When held in the transition position illustrated in figure 5 a compressive force is exerted by the upwardly extending lobe with resiliently compressibly bears against the second surface of the switching blade, to thereby make the transition position unstable. It can be seen when comparing the lobe of figures 5 on the one hand and figures 6 and 7 on the other that the lobe in the transition portion is compressed. This transition position is generally unstable and there is a tendency for the switch to snap between the on position shown in figure 6 with the contact pair (114) being closed and the off position in figure 7 where the contact pair is open.

As indicated above in describing this embodiment the position of the dolly extremity and the switching blade is fixed, however the position of the upper edge (112) of lobe is not fixed in relation to its position on the dolly. Accordingly the relative position of those two pivots change rapidly and this change in position assists with the snap action of the switch.

Referring now to figures 8,9 and 10 and the second arrangement of the invention. The general principle of the invention remains the same as described for the first arrangement except that the switching blade is held generally upright instead of generally horizontally.

The housing (200) is schematically depicted as a base member (201), an upright member (202) and a transverse dolly supporting member (203). The dolly (204) is supported from the dolly supporting member (203) by a fixed pivot (205) The dolly is shown as a single piece elongate member, a lower portion of which might be considered to be a dolly protrusion, an extremity (206) of the dolly protrusion contacts switching blade (207). The switching blade is an elongate flat conductive member, typically made of copper. The dolly on the other hand is non-conductive, a finger contacting portion at least being of insulative material. The extremity (206) of the dolly protrusion has features (208) that engage the upper end of the switching blade to thereby provide for a fixed pivot point. The features shown are downwardly extending arms fitting either side of the switching blade.

It will be understood that other features might also be provided for example by an arcuate tab which curves so as to engage a slot in the end of the switching blade to thereby allow for relative pivotal movement.

A first metal plate (210) of conductive material making up part of an electrical circuit or potential electrical circuit is supported by the base (201) of the housing. The metal plate ends in an upwardly extending lobe (211) an upper part of which acts as the bridge about which the switching blade is supported from below. It will be appreciated that contact between the bridge and the switching blade is conductive contact. The upper part of the bridge and the lower end of the switching blade are fitted together to also provide for a fixed pivot. The illustrated embodiment shows schematically a slot (212) in the upwardly extending lobe into which a downwardly extending tab of the switching blade is fitted.

An conductive post (213) extends upward from a second conductive plate (214) which together make up a second conductive element. A contact pair (215) is carried by the second surface of the switching blade (207) and the conductive post. A stop (216) is carried by a transverse post (217) extending from the upright member (202) to limit movement of the switching blade on a first side of a virtual axis (218) drawn between the dolly pivot (205) and the bridge generally located at slot (212). The conductive post (213) limits movement of the switching blade towards the second side of the virtual axis.

When held in the transition position illustrated in figure 8 a compressive force is exerted by the upwardly extending lobe with resiliently compressibly bears against the lower of the switching blade and the dolly when generally in line with the virtual axis (218), to thereby make the transition position unstable. It can be seen when comparing the lobe of figures 8 on the one hand and figures 9 and 10 on the other that the lobe in the transition position is compressed. This transition position is generally unstable and there is a tendency for the switch to snap between the on position shown in figure 9 with the contact pair (114) closed and where the position is made stable by the bridge being stopped by post (213) and the off position in figure 7 where the position of the bridge is stopped by stop (216) and the contact pair is open.

Variations of the assembly of various component parts of one or other of the two principle embodiments of the first arrangement of this invention are shown in figures 11 through to 15 but it will be understood that other variations will exist.

Turning then to Figure 11 which illustrates an arrangement between the dolly protrusion and the switching blade that falls within the principle of the mechanism shown in figure 3.

In this arrangement the fixed pivot is not by reason simply of engagement of an extreme edge of the dolly protrusion and a transverse groove in the switching blade, rather a spigot and socket arrangement is provided, spigots (30) extend from the switching blade and can

be fitted into the dolly protrusion which in this instances takes the form of two legs (32, 33) with sockets (31) allowing for pivoting of the spigots therein. It will be understood that this is an embodiment that is suitable for use where the dolly is of unitary construction, being entirely plastics moulded, which moulding accordingly dispenses with two of three parts and particularly awkward assembly methods. In this arrangement the dolly and switching bridge would be assemble first and then positioned into the switch housing against the force exerted by the bridge. It will be appreciated that this lends itself to automated assembly processes.

Figure 12 illustrates another arrangement between the dolly protrusion and the switching blade that falls within the principle of the mechanism shown in figure 3. In this arrangement the switching blade can take on an identical form as in the prior art illustrated in figures 1 and 2 having a transverse groove therein into which is positioned an extremity (11) of the dolly protrusion. The dolly protrusion is as with the embodiment shown in figure 5 formed of plastics, and thus there may be an issue of maintaining positive placement of the extremity of the dolly over an extended period of use. In this embodiment two arms (35,36) are extended on either side of the dolly protrusion and these hook underneath the switching blade to assist with the positive location of the extremity of the dolly protrusion within the groove. It is anticipated that this will help to secure the switching blade during the assembly operations so that the dolly and the switching blade may be inserted into a switch assembly together. During assembly it is usually difficult to locate the extremity of the dolly protrusion into the groove once the switching blade is in position within the housing an as will the embodiment illustrated in figure 11 this embodiment assists with assembly and will assist with automation of assembly.

Figure 13 illustrates an arrangement between the dolly protrusion, the switching blade and the bridge this time falling within the principle of the mechanism shown in figure 4. The extremity (11) of the dolly protrusion in this embodiment has a curved surface that contacts the upper surface of the switching blade. In this embodiment the switching blade does not have a lateral groove and therefore the dolly protrusion does not positively engage with any particular location on the switching bridge. In this instance the bridge includes two upright members (40,41) both having aligned sockets (42,43), into which are fitted corresponding spigots extending from the switching blade. The compressible resilience may be imparted by the two upright members, which may be made of a resiliently compressible material, and accordingly the illustration shows them in a compressed, transitional state.

A further embodiment falling within the principle of the mechanism shown in figure 4 is shown in figure 14. The arrangement of the switching bridge and the extremity (11) of the dolly protrusion is as for figurel3, however in this further embodiment the bridge takes the form of an elastomeric block (45) with an upper ridge (46) that positively locates within a lateral groove (47) located on what is shown in the illustrations as a lower surface of the switching bridge. This provides for the appropriate instability in transition position of the switching bridge, which transition position is shown in figure 8. This embodiment also has means to locate the switching in place during assembly so as to facilitate assembly.

Thus two switching blade locating members (50,51) extend upwardly from a base (52) of the housing. An apex of the both of the switching blade locating members has an inwardly protruding lug (53,54) which rest on top of two switching blade flanges (55,56) extending outwardly from the switching blade at a medial location during assembly operation. It is thus easier to locate the upper ridge (46) within lateral groove (47) than would otherwise be possible.

Figure 15 shows as further embodiment of this first arrangement of the invention. The dolly consists of a slidable button (60) that is slidable within a guide, the dolly protrusion (61) is fixed to the slidable button. The remainder of the invention is similar to those already illustrated for the first arrangement. The switching blade (62) is pivoted about a fixed pivot with respect to the dolly protrusion. The bridge (63) takes the form of a parabolic elastomeric block. The switch is shown in the on position whereby two contacts on either end of the switching blade contact two respective contacts (64,65) in the housing that are or are adapted for connection with an electrical circuit. It will be understood that the dolly when moved over the parabolic elastomeric bridge will be in an unstable transitional position, and will then to snap over the other way to the off position.

Variation of bridges and pivot arrangements pertinent to the first arrangement are shown in figures 16 through 18.

The embodiment illustrated in figure 16 is very similar to that shown in part perspective view in figure 15, except that the dolly is pivotable relative to the housing instead of being slidable. The bridge is illustrate as a parabola which is indicative that the bridge has support from both sides of the apex (70).

The embodiment illustrated in figure 17, has a somewhat different arrangement of pivots connecting to the bridge to that shown in other figures. The primary constructional difference is that the pivotal connection (250) between the dolly (251) and the switching

blade (252) is space above the switching blade. Additionally the pivot connection (253) between the bridge (254) and the switching blade is a fixed pivot. The translational movement of the two pivots (250,253) is not achieved therefore by one of the pivot connections sliding over the surface of the bridge, but rather by reason of the arcuate traverse by reason of the fixed pivot between the dolly protrusion and the switching blade being space at sufficient of a distance from its opposing fixed pivot. The degree of translation traverse required will depend somewhat on the rotation required. The bridge shown is represented differently to that in other figures however the bridge is still supported to be resiliently compressible, some depth is shown to indicate that a fixed pivot can be accommodated into the body of the bridge. It will be appreciated that figure 17 indicates that the bridge is supported from one side only.

It will also be understood that it is relative translational traverse that allows for the snap action between the on an off positions, and therefore both or either of the opposed pivot might be spaced apart from a respective switching blade surface to have the same effect.