GB2185854A - Push button multi-contact electric switches - Google Patents

Abstract

An electric switch comprising a base member 1 supporting a pair of contact sets each including at least one fixed contact and a movable contact which is biassed to one position by means of a spring 7 and which is actuatable to another position by applying a force to the spring by means of an actuating plunger 19 extending through a hole in a cover 2 for the switch mechanism. The actuating plunger is provided with two laterally extending actuating arm 19a each of which is arranged to engage with one spring 7 to cause actuation of one of the pair of contact sets and the plunger also includes a bifurcated portion defining two legs 19c which closely straddle a guide portion 21 on the base member. The actuating surface 19b of one arm 19a may be lower than the actuating surface of the other arm if sequential operation of the two contact sets is required rather than simultaneous operation. The springs engage the movable contacts with one end, the other end of each spring engaging a metal pin of a diameter chosen, to provide the required spring tension, from a set of different diameter pins. The fixed contacts are held in place by projections on the cover 2, which includes other projections engaging in or through the base 1 for cover and switch location. <IMAGE>

Description

SPECIFICATION Electric switches The present invention relates to electric switches.

The invention is more particularly concerned with so-called miniature electric switches which comprise a base member supporting one or more contact sets, each contact sets consisting of a movable contact and one or more fixed contacts and wherein the movable contact is biassed to one position by means of a spring and is actuatable to another position by applying a force through an actuating member to act against the spring. Each contact set may therefore form a normally open, or a normally closed, or a changeover contact set; according to the number and disposition of the fixed contacts in relation to the moving contact. Such electric switches usually also include a cover which fits over the base to enclose the contact set or sets and protect them from dust and the atmosphere.The switch actuating member may project through an aperture in the cover and connecting pins or the like to the switch contacts may extend through the base member.

As will be understood, the nature, size and characteristics of the spring are of importance in ensuring positive, rapid, reliable and consistent operation of the movable contact and firm engagement of the movable contact with the fixed contact or contacts. To this end it is often preferred to use coiled or helical springs of which one end is anchored to the movable contact and the other end is anchored to a fixed point, such as a lug or spigot on the base member.However, it has been found with such an arrangement that the dimensional tolerances which occur with mass production both in the springs and in the overall distance between the anchoring point on the movable contact and the anchoring point on the base member can give rise to undesirable variations in the effective length of the fitted spring in its static condition and hence variations in the operating characteristics of the switch. In this connection it is emphasised that the invention is concerned with so-called miniature switches where both the dimensions and the mass of components is very small whereby small changes in dimensions assume greater importance than in the case of larger and more massive components.

It is an object of the present invention to alleviate this problem.

According to the present invention, that end of the coiled or helical spring which is anchored relative to the base member is provided with a hook or eye through which passes a pin which is disposed in a location in the base member such that the axis of the pin is substantially normal to the longitudinal axis of the spring. By this means it is possible to use pins of different diameter so as slightly to vary the overall effective length of the spring in order to give fine adjustment of the spring tension under rest conditions. In other words the length of and hence the tension in the spring can be calibrated by appropriate selection of the pin diameter so as to compensate for any undesirable variations in the operating characteristics of the switch.

Preferably the pins are made of a metal so that they are resistant to wear.

Furthermore with miniature electric switches of the type with which the present invention is concerned it is often desired to arrange two or more contact sets so that they can be actuated by a common actuating member, either simultaneously or else sequentially. In order to achieve this actuator is formed as a plunger extending through a hole in the cover and provided, below the cover, with two laterally extending actuating arms each of which is arranged to cause actuation of the movable contact of one of the two contact sets.It has however been found that it is relatively easy for the plunger to cant or tilt as it is depressed, thereby causing unreliable operation of the switch due to the correspondingly canted actuating arms acting on the movable contact at other than the intended instant or, in the case of an upwardly canted arm, possibly not effecting actuation of the corresponding movable contact at all.

It is a further object of the invention to alleviate the problem discussed above.

Accordingly, from another aspect of the invention, the switch includes an actuating plunger extending through a hole in the cover and provided with two laterally extending actuating arms each of which is arranged to cause actuation of the movable contact of one of a pair of contact sets carried by the base member and the actuating plunger also includes a bifurcated portion defining two legs which closely straddle a guide portion on the base member whereby the plunger is prevented from canting over or tilting as it is depressed. In this way more reliable operation of the contact sets can be achieved.

The two actuating arms, which are preferably diametrically disposed, may be provided with spring actuating surfaces at the same level so as to effect simultaneous operation of the two contact sets or with spring actuating surfaces at different levels whereby two contacts sets are operated sequentially, that is to say the movable contact of one set is operated before the movable contact of the other set.

The invention will now be further described by way of example with reference to the accompanying drawings, in which: Figure 1 is a plan view of the base portion of one embodiment of miniature electric switch according to the invention; Figure 2 is a plan view of the inside of the switch cover, Figure 3 is a section along the line Ill-Ill in Fig. 1, Figure 4 is a section along the line IV-IV in Fig. 1, Figure 5 is a section along the line V-V in Fig. 1, and Figure 6 is a perspective view of one embodiment of actuating plunger.

Referring to the drawings, the miniature electric switch illustrated comprises a base member 1 and a cover 2, both of which are formed as mouldings of any suitable insulating plastics material. In each of the sectional views the cover 2 is shown in position on the base member 1. The base member 1 carries two contacts sets S1, S2 respectively located to either side of a central partition 1 a extending along the length of the base member.

Each contact set comprises a movable contact 4 which can engage with either of two fixed contacts 5 and 6, respectively situated in locations formed in the base member. As shown in Fig. 4, the movable contact 4 normally engages the upper fixed contact 5 and is maintained in this position by means of a coil or helical spring 7 having a hook 7a at one end anchored to the contact and a hook 7b at its other end anchored relative to the base member by a pin 8. As can be seen, the pin 8 for each contact set extendstransversely to the longitudinal axis of the helical spring 7 and, as shown in Fig. 4 each pin is located in a recess defined between a portion of the base member and the cover.This recess is of a sufficient size to accommodate pins of different diameter over a limited range and therefore, as explained above, the overall effective length of the spring can be varied choosing pins of different diameter so as to give fine adjustment of the spring tension under rest conditions. In this way undesirable variations due to manufacturing tolerances can be compensated. The movable contact 4 is of forked form and its two limbs 4a,4b extend on either side of the spring 7 and terminate in knife edges engaged in a vee location 9 formed in a contact support 10 extending through the base member 1. The external portion 1 0a of the support 10 forms a connecting pin to the movable contact 4. Similar connecting pins 11 and 12 are provided to the fixed contacts 5 and 6 respectively.

The inside of the cover 2 is formed with two pairs of fixed contact-engaging spigots 13 and 14. The shorter spigots 13 are dimensioned and arranged to engage firmly on the fixed contacts 5, whilst the longer spigots 14 are dimensioned and arranged to engage firmly with a part of the fixed contacts 6, as seen in Fig. 3. By means of this arrangement, when the cover 2 is correctly positioned on the base member the fixed contacts are held firmly in their location against displacement due to the impact of the movable contact striking against them as the switch is actuated.

The inside of the cover also carries two further spigots, 15 and 16 which respectively pass into holes 15a,16a formed through the central partition 1 a of the base member and assist in locating and securing the cover in position.

The cover 2 is also formed with a rim 17 which engages a seating 18 around the edge of the base member 1.

The switch is actuated by means of a plunger 19 extending through a hole 20 in the cover and which has two diametrically spaced laterally extending actuating arms 1 9a respectively resting on each of the springs 7. As can be seen in Figs. 5 and 6 the actuating surface 19b of one arm 19a is lower than that of the other arm, whereby on depression of the plunger one spring 7 and associated moving contact will be operated before the other, thereby giving sequential operation of the contact sets. If the two actuating surfaces 1 9b were at the same level, then the two contact sets would be operated simultaneously.As will be understood depression of the plunger 19 presses the arms 1 9a against the springs 7 and thereby causes the associated movable contact 4 to pivot about its knife edge and move away from fixed contact 5 into engagement with fixed contact 6 to effect a changeover action. Release of pressure on the plunger causes both the movable contact 4 and the plunger 19 to return to their rest positions under the action of the spring 7.

In order to prevent canting or tilting of the plunger during its depression and hence malfunctioning of the contact sets S1 and S2, the actuating plunger includes a bifurcated portion defining two legs 19c which closely straddle a guiding web 21 formed in the central partition 1 a. In this way as the plunger moves up or down during its operation, it is constrained against canting or tilting movement and the correct operation of the contact sets is maintained. By reason of the abutting surfaces of the partition la at the ends of the web 21, the legs 19c are also constrained against longitudinal movement with respect to the web, thereby ensuring that the plunger arms 1 9a always engage the springs at virtually the same point and thus helping to ensure consistent and reliable switch operation.

Although the switch as illustrated is a changeover switch, it will be readily understood that either or both of the contact sets could be constructed as a normally-open or normally-closed switch which becomes closed or open upon operation.

Claims (16)

1. An electric switch comprising a base member supporting a pair of contact sets, each contact set consisting of a movable con tact and one or more fixed contacts and wherein each movable contact is biassed to one position by means of a spring and is actuatable to another position by applying a force through an actuating member to act against the spring and including a cover which fits over the base member to enclose the contact sets wherein the actuating member is formed as an actuating plunger extending through a hole in the cover and provided with two laterally extending actuating arms each of which is arranged to cause actuation of the movable contact of one of the pair of contact sets carried by the base member and the actuating plunger also includes a bifurcated portion defining two legs which closely straddle a guide portion on the base member whereby the plunger is prevented from canting over or tilting as it is depressed.

2. An electric switch as claimed in claim 1, wherein the two actuating arms are provided with spring actuating surfaces at the same level so as to effect simultaneous operation of the two contact sets.

3. An electric switch as claimed in claim 1, wherein the two actuating arms are provided with spring actuating surfaces at different levels whereby the two contact sets are operated sequentially.

4. An electric switch as claimed in claim 1, 2 or 3, wherein the two legs are also constrained against longitudinal movement with respect to the web.

5. An electric switch as claimed in any preceding claim, wherein the two actuating arms are diametrically disposed.

6. An electric switch as claimed in claim 1 and substantially as hereinbefore described with reference to the accompanying drawings.

7. An electric switch comprising a base member supporting one or more contact sets, each contact set consisting of a movable contact and one or more fixed contacts and wherein the movable contact is biassed to one position by means of a spring and is actuatable to another position by applying a force through an actuating member to act against the spring and wherein the spring is a coiled or helical spring having one end anchored relative to the base member, said end being provided with a hook or eye through which passes a pin which is disposed in a location in the base member such that the longitudinal axis of the pin is substantially normal to the longitudinal axis of the spring.

8. An electric switch as claimed in claim 7, in combination with a plurality of pins each of a different diameter and any one of which can be selected to anchor the spring so as slightly to vary the overall effective length of the spring in order to give fine adjustment of the spring tension under rest conditions.

9. An electric switch as claimed in claim 7 or 8, wherein the or each pin is a metal pin.

10. An electric switch as claimed in claim 7, and substantially as hereinbefore described with reference to the accompanying drawings.

11. An electric switch as claimed in any preceding claim, including a cover which is provided on its inside with one or more projections which are respectively so dimensioned and arranged that when the cover is correctly in position on the base member, the or each of said projections engages with a part of a fixed contact of a contact set thereby to hold said fixed contact against displacement from its proper location.

12. An electric switch as claimed in claim 11, wherein the or each projection is in the form of a spigot extending from the inside of the cover and which-is of such a length that it rests firmly on its associated fixed contact when the cover is correctly in position on the base member.

13. An electric switch as claimed in claim 11 or 12, wherein the inside of the cover also includes one or more further projections each of which cooperates with a recess or hole formed on the base member in order to locate the cover in position on the base member.

14. An electric switch as claimed in claim 13, wherein at least one of said further projections is of a length such that it projects from the underside of the base member, when the cover is in position, and thereby forms a locating peg for locating the switch in position on a printed circuit board or other component receiving surface.

15. An electric switch as claimed in claim 13 or 14, wherein said one or more further projections are also in the form of spigots.

16. An electric switch as claimed in any preceding claim 11 to 15, wherein the movable contact is arranged to pivot relative to a contact support mounted on the base member and the free end of said contact support is located against a shoulder formed inside the cover when the cover is correctly in position.