Field of the invention

This invention relates to an armature/actuator for a relay.

Background to the invention

Armature/actuators for relays are known in the form of a generally U-shaped sub-assembly consisting of two magnetisable cheeks or pole pieces of soft iron, such as Swedish iron, bridged by a powerful permanent magnet. It is an object of this invention to provide an armature/actuator for use in place of the aforesaid known sub-assembly.

The invention

According to the invention, there is provided an actuator/armature for a relay comprising a one-piece member of U-shape, formed by shaping with heat treatment from a strip of ductile magnetic material whilst said material is in non-magnetised condition and which in its final heat treated form and after magnetisation is characterised by high remanance and high magnetic energy.

A preferred material for the actuator/armature is a chromium/cobalt/iron alloy, such as Crovac 10 (Trade Mark) supplied by Vacuumschmeltze G.m.b.h.

For assisting mounting of the actuator/armature in a relay, the U-member may be formed with integral external locating projections, such as semi-shear lugs, on the outer faces of the side cheeks.

An important application of the actuator/armature of the invention is in miniature electric relays for mounting to an insulating base above a circuit board. In this case the base may be formed or assembled with upstanding parts for engagement with the locating lugs on the side cheeks of the U-member, thus ensuring its accurate positioning relative to the other parts of the relay, which are also mounted and located by other parts upstanding relative to the insulating base in accurate positional relationship to the first mentioned upstanding parts.

For example, our PCT Application No.88/00445 provides an insulating base on which an electrical device such as a miniature relay can be mounted, the said base being moulded onto a sheet of conductive material which has previously been stamped or otherwise cut away to define elements which, after partial embedding in the base material, can be cut and bent to constitute on the one hand depending conductive pins for attachment to the circuit board and on the other hand upstanding parts for use in mounting the relay. The conductive sheet material may be a sheet metal such as phosphor bronze, copper or brass, and the base injection moulded thereto from plastics material. The invention of our aforementioned PCT Application has the advantage that accurate relative positioning of the relay parts is achieved by means of the accurately formed conductive sheet, and without reliance on the moulded base to determine such positioning.

In a preferred arrangement described in the said PCT Application, a separate sub-assembly is also formed from the conductive sheet/moulded base composite, by attaching pole pieces and a bridging permanent magnet (prior to magnetisation thereof) , to a preformed part of the composite sheet, thereby to form a U-shaped actuator/armature for a relay, the sub-assembly then being cut away from the main portion of the sheet and subsequently re-assembled thereto, after cutting and bending of the latter, in the position required for it to serve as an operative part of the relay. The present invention enables the aforesaid sub-assembly formed from the composite sheet to be dispensed with, replacing it with a U-shaped, integrally formed magnetic element which assembles to the cut and bent composite sheet in analogous manner to the previously employed U-shaped sub-assembly.

Thus, the present invention may also be employed in conjunction with further aspects of the aforementioned PCT Application, according to one of which there is provided a method of constructing an electrical relay having at least one fixed and at least one movable contact, and which is adapted for mounting to a printed circuit board. In the context of the present invention, this method includes the step of bending some of the conductive elements of the stamped conductive sheet upwardly so as to form (or form supports for) fixed and movable switch contacts, wherein the working gap is determined solely by the relative positions of the elements in the original conductive sheet and the bending thereof after moulding of the base material.

Moreover, as also described in the PCT Application, a bobbin sub-assembly for the relay is preferably adapted

for assembly to the base composite by means of tapering spigots on a moulded base of said bobbin sub-assembly, conductive pins passing through the spigots to provide electrical connections to the coil and the spigots sealing into matching tapering holes provided in the base composite.

Wherever a powerful magnet is incorporated, it is a common problem that magnetisable particles will be attracted to the magnet. When very small clearances are provided between components associated with the magnetic field produced by such a magnet, such particles can produce undesirable effects such as preventing a magnetic armature in a relay from fully closing and thereby preventing correct contact pressure between conductive contacts associated with the armature.

According to a preferred aspect of the invention, therefore this problem can be largely obviated by fabricating the component part which is to possess a high level of permanent magnetism, from an alloy which can be permanently magnetised by placing it in a very intense magnetic field, but which is initially demagnetised, and bending and heat treating the alloy component whilst the material is in its unmagnetised state, and thereafter, in a clean environment free of magnetisable particles, assembling the component with its cooperating components to form a complete article, and whilst still in that environment, enclosing the article within a dust-tight housing or casing, and only thereafter causing the complete encapsulated assembly to be influenced by the intense magnetic field needed (and if necessary heated) to magnetise the alloy component. In this way agnetisable particulate material is prevented from reaching the alloy

components (or any magnetised cooperating components) after the component has been magnetised.

Typically the component is formed from a chromium cobalt iron alloy such as Crovac 10 (Trade Mark) as supplied by Vacuumschmeltze GmbH.

The invention thus lies in a method of assembling an article which is to include a strongly magnetised permanent magnet component of an alloy which can be strongly magnetised by inter alia bringing it under the influence of an intense magnetic field, wherein the said component is constructed and assembled with its cooperating components and encapsulated by a cover or casing of non magnetisable material in a clean environment before the component is magnetised so as to prevent the ingress of magnetisable particles which will otherwise be attracted to the magnetised component.

The invention also lies in an article which includes a strongly magnetised permanent magnet component and which is constructed in accordance with the aforementioned method.

Description of drawings

An actuator/armature for a relay in accordance with the present invention is exemplified with reference to the accompanying drawings, in which:-

Figures 1 and 1A show a U-shaped actuator/armature magnet in side view and in plan view, respectively;

Figure 2 is a plan view of a composite base (in the flat) for a relay?

Figure 3 shows the spring contact arrangement of the relay;

Figure 4 shows a bobbin sub-assembly for the relay;

Figure 5 shows the assembled base and relay sub- assemblies; and

Figures 6 and 6A show the actuator/armature magnet in perspective and a detail of its assembly to the formed base.

Description of embodiment

Referring to Figures 1 and 1A, there is shown a U—shaped magnet 300 constituting an actuator/armature for a miniature relay. The U-shaped magnet is formed in one piece by shaping with heat treatment of a ductile magnetic material, more especially a chromium/cobalt/iron alloy such as Crovac 10 (Trade Mark) . Semi-shear locating lugs 302 are formed on the outer faces of the two side cheeks 304, 306. The arrow 308 indicates the direction of the grain, and the N-S poles are marked in Figure 1A. The magnet is formed by shaping alloy strip and magnetisation is effected after final heat treatment to produce a component of high remanance and high magnetic energy.

Figure 2 shows a composite base for the relay, said base being in the flat prior to shaping thereof. It includes a lead or host frame 10 having pairs of indexing sprocket holes 12, 14 and 16, 18 at regular intervals along its

- 7 - length. The lead frame is formed from thin sheet metal such as phosphor bronze, and typically can be coiled.

Intermediate sprocket holes 15 are shown which may be used for indexing but are not necessarily used for locating the lead frame at work stations.

The two pairs of sprocket holes 12 and 14 and 16 and 18 define a square on the lead frame having apertures formed therein as by stamping. Similar patterns of apertures such as large rectangular apertures 20, 22 are formed at regular intervals along the length of the lead frame between corresponding spaced apart pairs of sprocket holes.

Electrical contacts of appropriate metal, typically of a precious metal are formed at 24 and 26 as by riveting or brazing and on the underside at 28 and 30 in a similar way.

The material which has not been cut away in the lead frame comprises conductive links which are to form pins on the one hand, adapted for securing to a printed circuit board or the like, and on the other hand, structural elements or supports for the final device. Such devices require an insulated base and this is most conveniently formed by plastics injection moulding in the central region of the lead frame to form a substantially rectangular plastics base 32.

A second lead or host frame 34 is laid over the first lead frame 10 at right angles to the general direction of the latter so that elongate spring arms 36 and 38 in the second lead frame are correctly positioned relative to

appropriate links in the first lead frame to allow the components to be joined as by riveting, brazing or welding at 40 and 42 respectively. After joining in this way, the arms 36 and 38 can be severed from the remainder of the lead frame 34 by means of cuts at 44, 46, 48 and 50 whereafter the second lead frame 34 can be lifted and indexed relative to the lower lead frame 10. The latter may then also be indexed away from the work station.

Circular holes in the second lead frame 34 are aligned with the sprocket holes 12, 14 and 16, 18 of the first lead frame to enable locating pins 52, 54, 56 and 58 to protrude therethrough and accurately align the two lead frames at the work stations.

The spring arms 36 and 38 also include apertured rectangular lugs 55 and 57 (see Figures 3 and 6A) which are formed by stamping and severing cuts along the lines 44 and 50 shown in Figure 2.

The moulded base 32 includes two tapered circular apertures 60 and 62, the purpose of which will be described later.

By severing and selectively folding some of the links which secure the moulded base assembly 32 to the first lead frame 10, so the sub-assembly of Figure 3 can be formed. By way of illustration the fingers 64 and 66 shown in Figure 2 have been folded down to form two of the pins by which the device can be secured to a printed circuit board or the like, whilst fingers such as 68 and 70 to which the components 36 and 38 are attached, have been folded in an upward sense so as to provide structural elements of the final component.

Although not shown- clearly in Figure 2, the moulded base includes recesses and slots as at 72 and 74 (Figure 3) to facilitate the bending of the severed links such as 68 and 64 to their final positions.

Whilst some of the links joining the moulding to the lead frame are shown as having been severed and bent in Figure 3, others remain as at 76 to 80, by way of example. These remaining links serve to support the moulding within the lead frame for the remaining stages of manufacture and, after the component has been fully manufactured and assembled, these remaining but now redundant links can likewise be severed and as appropriate bent up into slots such as 86 for link 78, so as to be well clear of the edges of the base and enable a lid or cover to be sealingly engaged over the base.

The sub-assembly shown in Figure 3 comprises the spring contact assembly of the miniature relay. Thus the arms 36 and 38 are the springs on which the moving contacts are carried whilst the bent up severed links 68 and 70 provide the supports for the fixed ends of the springs. The bent up severed links 88, 90, 92 and 94 comprise the fixed contact supports which cooperate with the two springs 36 and 38 to form two change-over contact sets.

Within the sub-assembly of Figure 3 is mounted the electromagnetic actuator made up of a coil and magnet assembly and attention is now directed to the manner of manufacture of this internal sub-assembly of actuator and magnet.

Figure 4 is a perspective view of one part of the actuator

sub-assembly. The total sub-assembly comprises a U-shaped yoke 100 (Figure 5) and the armature/actuator 300.

The armature/actuator magnet 300 includes the locating lugs 302 which act on the two elongate spring arms 36 and 38 and, by biasing the armature in one direction opposite to the direction in which it will move when the coil 104 is energised, so the contact sets can be made to change over in response to energisation of the coil.

The electromagnet is formed from the sub-assembly shown in Figure 4. This comprises a bobbin 156 having end cheeks 158 and 160 the latter including legs 162 and 164 having tapering spigots 166 and 168 on their undersides respectively. Conductive pins 170 and 172 protrude through and are embedded in the legs 162, 164. The lower protruding ends of the pins comprise further conductive devices for attaching the component to a printed circuit board or the like, and the upper protruding ends ^" provide terminations for the coil 104, which is wound on the bobbin 156 in a manner known per se and may comprise a single or double wound coil. If the latter, then additional leads and terminations are required.

A magnetisable core is fitted through the rectangular section hollow interior 176 of the bobbin 156 with an exposed central pole at the end remote from the end having the legs 162 and 164.

The U-shaped yoke 100 is fitted around the bobbin after the coil 104 has been wound thereon. The yoke has projecting two pole pieces (not visible in the drawings) which cooperate with the central pole of the core.

Figure 4 clearly shows the two spigots 166 and 168 which are designed to fit into the tapering holes 60 and 62 previously referred to with reference to Figure 2. The location of the spigots in the holes 60 and 62 is sufficiently accurate to position the bobbin and electromagnetic assembly relative to the fixed contacts formed by bending up the severed links 88, 90 etc. as shown in Figure 5. To ensure a good seal, the spigots 166 and 168 are adhesively secured within the holes 60 and 62.

The conductive pins 170 and 172, to which opposite ends of the winding are attached, are themselves a tight fit in the base of the sub-assembly and extend through the spigots 166 and 168 so as to protrude beyond and below the base of the device after assembly. By providing a good tight fit between the pins and the base of the sub- assembly, so there is little chance of any ingress of moisture into the otherwise sealed interior of the relay assembly after construction.

Referring again to Figure 5, the U-shaped armature and actuator magnet 300 is fitted over the central core with the cheeks 304 and 306 between the two pole pieces of the yoke and the central pole.

The manner in which the actuator/armature 300 fits in position is apparent from Figure 5 and Figures 6, 6A. The lugs 302 on the outer faces of the cheeks 304, 306 are received in the apertured rectangular lugs 55 and 57 of the spring arms 36 and 38 via the intermediary of strip- moulded inserts 310. Figure 6A also shows the contact 312 on the end of the spring arm 36.

The assembly of Figure 5 is protected by means of a lid or cover of generally rectangular proportions, denoted by reference numeral 184, the interior of which is generally rectangular but includes pairs of moulded bosses at the upper corners and towards the centre thereof. These extend to a depth within the cover 184 such that the latter is caused to just fit snugly on the base 10 with the lower ends of the bosses contacting the upper edges of the U-shaped yoke 100.

The height of the cover 184, at least internally, is thus controlled so that when fitted the cover prevents the U- shaped yoke 100 from lifting off the base and the armature actuator from lifting relative to the spring arms 36 and 38.

Figure 5 also shows how the unwanted support links can be folded up after severing so as to be wholly contained within the cover 184 when the latter has been fitted. In this way they do not constitute unwanted conductive protrusions on the underside or along the edge of the base. Two of the folded up links are denoted by reference numerals 186 and 188 in Figure 5.

The conductive pins such as 190, 192 and 194 provide electrical connection to the moving contacts and fixed contacts of the nearest contact set shown in Figure 5, whilst a similar set of conductive pins on the other side of the base (of which one can be seen at 196) provide similar contacts to the other contact set on the other side of the assembly.

Since the actuator strip 208 is non-symmetrical, and both of the spring arms 36 and 38 are biased inwardly towards

one another, the insertion of the armature/actuator of Figures 1, 1A will cause the spring arm 36 to be displaced outwardly, leaving spring arm 38 in the position dictated by its natural resilience. Energisation of the coil 104 will result in interaction between the powerful static field due to the permanent magnet and the induced electromagnet field, th.ereby causing the armature assembly to move in the direction of the spring 38 thus allowing spring 36 to relax inwardly and cause spring 38 to be displaced. The contacts on the ends of the springs 36 and 38 will thus change-over, and in the case of the nearest spring set, the spring contact will change-over from being in contact with the outboard fixed contact to the inboard fixed contact, upon energisation of the coil, and vice versa on de-energisation. The opposite is the case with regard to spring 38.

In accordance with the preferred aspect of the invention the U-shaped armature 300 of Figures 1, 1A is constructed by stamping and/or cutting a rectangular piece of material from a strip of Crovac 10 (Trade Mark) alloy, punching or otherwise forming locating lugs 302 on the outer faces of the two side cheeks 304,306, and bending and heat treating the armature and assembling it with other components whilst the alloy is in a demagnetised condition, in a clean environment, fitting the cover 184 to the base 32 and sealing the component assembly therewithin whilst still in the said clean environment and only thereafter causing an intense magnetic field to act on the encapsulated assembly and if required heating the assembly so as to cause the Crovac 10 (Trade Mark) component to become a powerful intensed permanent magnet.