GB2228830A - Microswitch - Google Patents

Abstract

A method of assembling a microswitch sub unit 4 comprises bringing together an anchor element 8, a carrier element 9 and a spring 10 in directions within a single plane and effecting relative rotation between the carrier element 9 and the anchor element 8 about cooperable means of the elements e.g. a groove, to effect stretching of the spring 10. One end of the spring 10 is hooked into an eyelet in the anchor element 8, the carrier element 9 is brought upwards along a path perpendicular to an arm of the anchor element 8 so that one end engages in a groove in the anchor element 8 and the other end of the spring 10 is hooked into an eyelet in the carrier element 9 whereupon the carrier element 9 rotates into a stable position. Stretching and contraction of the spring 10 occurs only when both ends are attached to the sub-unit 4 under the pivoting action, so that handling of the stretched spring is substantially easier and does not involve any risk of it flying away uncontrollably; moreover, the possibility of overstretching the spring is effectively eliminated. <IMAGE>

Description

MICROSWITCH The present invention relates to a microswitch and to a method of manufacturing a microswitch.

In the manufacture of microswitches, the operation of assembling the parts forming the moveable mechanism and their insertion into the microswitch housing can be fiddly and slow, in part because it is necessary to effect tensioning of the spring. One conventional way of facilitating the situation is to provide an arrangement of anchor, spring and contact carrier which can be put together to form a stable construction which is then inserted into a part of the housing. In one implementation of this feature, the anchor has one or more apertures through which an end of the carrier can pass to provide the stable engagement.

U.S. Patent Specification No. 4673778 discloses a variation wherein the anchor and contact carrier are placed in a mounting fixture with tangs of the contact carrier lying against rests formed on the anchor by lateral recesses. Then a spring is hooked onto the anchor, is stretched and its free end moved into engagement with a slot inclined such as to allow the spring to contact and urge the carrier and anchor together. The contact between the tangs and the rest provides centring of the carrier and anchor and prevents relative rotation therebetween, thereby providing a stable construction. While there is much concern within U.S. Patent 4673778 to reduce the assembly and manufacturing difficulties associated with microswitches, the proposed technique remains slow and cumbersome and the carrier is of a complex shape difficult to manufacture.

An object of the present invention is to provide a form of microswitch sub-unit which allows facilitated assembly as compared to conventional microswitches.

Another object of the present invention is to provide a microswitch sub-unit which is particularly suited to automatic assembly.

Another object of the present invention is to provide a microswitch sub-unit whose components can be readily manufactured at low cost.

According to the present invention, there is provided a microswitch sub-unit comprising an anchor element, a carrier element and spring means, the carrier and the anchor elements having co-operable means for assembly of the elements together with the spring means by bringing them together in directions within a plane which contains the longitudinal axis of the anchor and the longitudinal axis of the sub-unit, the elements and spring means being so assembled into a stable arrangement for subsequent insertion into a microswitch housing part, the co-operable means being arranged to provide relative rotation between the carrier and anchor elements in the direction of the longitudinal axis of the sub-unit thereby to effect stretching of the spring means during assembly of the sub-unit into said stable arrangement.In this way, the sub-unit can readily be assembled together by relative movements of the components in directions in a plane containing the longitudinal axis of the anchor and that of the sub-unit, thereby rendering assembly simple and making it particularly suited to automation.

Preferably, the sub-unit provides relative rotation of the co-operable means with the spring means attached to the carrier and anchor elements to assist urging of the sub-unit towards the stable arrangement and automatic tensioning of the spring means. Accordingly, the spring is only stretched when securely held at both ends by components of the sub-unit, this differing from the prior art wherein the spring is stretched when only one end is hooked to a component of the sub-unit; this distinction ensures that, in the present invention, there is no risk of the free end of the stretched spring being mishandled while hooking it to the carrier, thereby causing it to fly away uncontrollably. Also, the handling of the spring is generally easier when it is unstretched, enabling more precise positioning of the ends in the respective element.

Moreover, the assembly machinery does not directly apply any force to the spring to effect its tensioning, this being achieved as a result of the relative movement of the anchor and carrier, and therefore the risk of overstressing is effectively eliminated. Also, the power output of the assembly machinery does not need to be as great during assembly.

Preferably, the co-operable means comprise groove means in the anchor to accommodate a straight edge of a bifurcated end portion of the carrier. In this way, the design of the carrier can be much simpler than that of U.S. Patent 4673778, ensuring simplified production of both the anchor and the carrier. In addition, maintenance of the press-tool for production of the anchor and the carrier is easier and cheaper and the press operation is simpler.

According to the present-invention, there is also provided a method of manufacturing a microswitch sub-unit in a stable arrangement for subsequent insertion into a microswitch house part, the sub-unit comprising an anchor element, a carrier element and spring means, the carrier and the anchor elements having co-operable means for assembly of the elements together with the spring means, the method comprising bringing the anchor and carrier elements and the spring means together in the directions within a plane which contains the longitudinal axis of the anchor and the longitudinal axis of the sub-unit, and effecting relative rotation between the carrier and the anchor elements about the co-operable means in the direction of the longitudinal axis of the sub-unit thereby to effect stretching of the spring means during assembly of the sub-unit into said stable arrangement.Preferably, the method comprises assisting urging of the sub-unit towards the stable arrangement and effecting automatic tensioning of the spring means by relative rotation of the co-operable means with the spring means attached to the carrier and anchor elements. Advantageously, the co-operable means comprise groove means in the anchor to accommodate a straight edge of a bifurcated end portion of the carrier.

The present invention also embodies a microswitch sub-unit made by a method as hereinbefore defined. Furthermore, the present invention also embodies a microswitch incorporating a microswitch sub-unit as hereinbefore defined.

According to another aspect, there is provided resilient engagement means on a plunger to permit insertion into a microswitch housing but to inhibit detachment from the housing.

Preferably the engagement means comprises a snap-fit rib on the plunger.

In order that the invention may more readily be understood, a description is now given, by way of example only, reference being made to the accompanying drawings, in which: Figure 1 is a cross-sectional view of a microswitch incorporating a sub-unit embodying the present invention; Figures 2 to 5 show stages in the assembly of a microswitch sub-unit embodying the present invention; and Figure 6 is a cross-sectional view of part of the microswitch of Figure 1 being assembled.

In Figure 1, there is shown a microswitch (generally designated 1) which has a housing formed by a base 2 and a cover 3 both of electrically insulative material and containing a sub-unit 4 to provide selective electrical contact with a "normally-open" terminal 5 or a "normally-closed" terminal 6 under the influence of a plunger 7.

The sub-unit 4 comprises an anchor 8, a carrier 9 and a spring 10, and can be assembled together as shown in Figures 2 to 5 to form a stable construction which can then easily be positioned on the base 2 and also allows subsequent stages in the manufacture of the microswitch to be readily performed.

Anchor 8 has a longitudinal axis which is in the vertical direction in the orientation depicted in Figure 2, from which axis there extends a transverse arm 11 at the free end of which carrier 9 can engage. The longitudinal axis of the sub-unit 4 includes arm 11, carrier 9 and spring 10 and is perpendicular to the longitudinal axis of anchor 8.

In the assembly of the sub-unit 4, anchor 8 is located on a mount (not shown) and spring 10 is brought up to the anchor along a path substantially parallel to transverse arm 11 while oriented with its length perpendicular to the arm, so that one end of spring 10 becomes hooked into eyelet 12 of anchor 8 (see Figure 2) and then spring 10 proceeds to rotate downwards until it assumes the position shown in Figure 3. Carrier 9 is brought upwards along a path substantially perpendicular to arm 11, so that one end 13 engages with a groove 14 in anchor 8 and the second end of spring 10 is hooked into an eyelet 15 in carrier 9 (see Figure 4); carrier 9 proceeds to rotate about the point of contact between carrier end 13 and groove 14 until the position of stability for the sub-unit 6 is reached (see Figure 5).In moving between the positions of Figures 4 and 5, some stretching and then contraction of spring 10 occurs and so the sub-unit 6 is inhibited from leaving the position of stability; because such stretching and contraction occurs only when both ends of spring 10 are attached to the sub-unit 6 under the pivoting action, handling of the stretched spring is substantially easier and does not involve any risk of it flying away uncontrollably; moreover, the possibility of overstretching the spring is effectively eliminated. When the carrier is moving from the position shown in Figure 4 to that in Figure 5, it reaches a point at which spring 10 begins to contract, and urge the sub-unit into the position of stability without requiring any additional force exerted on it to effect rotation.

All the assembly steps for sub-unit 6 involve simple movements of components in directions in a single plane containing the longitudinal axis of anchor 8 and the longitudinal axis of the sub-unit 4. Accordingly, the design of sub-unit 6 is particularly suited to simple and fast automated assembly with a low risk of errors occurring.

Moreover, the form of carrier used (much simpler in shape than the complex arrangement of tangs, slots and inclined surfaces of U.S. Patent 4673778) ensures that the carrier can be made quickly, easily and at low cost, the requisite maintenance of the press-tool being substantially less.

Subsequent steps in the manufacture of microswitch 1 include inserting the sub-unit 4 into the base 2 already containing "normally-open" terminal 5, and then inserting "normally-closed" terminal 6 into base 2; correct positioning of this terminal 6 urges contact head 15 of carrier 9 to rotate downwardly a sufficient amount to move back portion 16 of carrier 9 away from contact with the end 17 of anchor 8, so that carrier 9 has a knife-edge contact with anchor 8 in operation of the microswitch. Accordingly, the co-operable means of the anchor and carrier provide the functions of centring and stabilising the sub-unit and of effecting a knife-edge pivot for switching.

After cover 3 has been secured to the base 2, plunger 7 is inserted into the resulant housing through an aperture 18 leading to channel 19. Plunger 7 is of plastics material and has a tapered rib 20, on its periphery, of sufficient resilience and dimensions to allow plunger inwardly along channel 19 but to inhibit withdrawal once the rib has passed through the channel.

In this way, plunger 7 can be easily and quickly inserted (manually or automated) after the housing has been completed.

This is particularly convenient for situations wherein, after assembly of the microswitch housing, it is desirable to delay selection of which particular type of plunger is to be incorporated; in this way, it is possible to build up and hold a stock of microswitch housings and a separate stock of types of plunger, so that the requisite types of plunger are only inserted in the housings upon demand, thereby providing substantial flexibility of supply at low cost and with minimal storage-capacity. Clearly the microswitch housing and its contents are self-contained and robust and are suited to further automated handling, e.g. in additional storage, packing and assembly.

Cover 3 includes a stop 21 to inhibit travel of the plunger 7 within the interior of the microswitch.

In summary, the present invention provides a microswitch which is particularly suited to fast, reliable and simple automated manufacture at low cost.

Claims (10)

1. A microswitch sub-unit comprising an anchor element, a carrier element and spring means, the carrier and the anchor elements having co-operable means for assembly of the elements together with the spring means by bringing them together in directions within a plane which contains the longitudinal axis of the anchor and the longitudinal axis of the sub-unit, the elements and spring means being so assembled into a stable arrangement for subsequent insertion into a microswitch housing part, the co-operable means being arranged to provide relative rotation between the carrier and anchor elements in the direction of the longitudinal axis of the sub-unit thereby to effect stretching of the spring means during assembly of the sub-unit into said stable arrangement.

2. A microswitch sub-unit according to Claim 1, wherein the relative rotation of the co-operable means with the spring means attached to the carrier and anchor elements assists urging of the sub-unit towards the stable arrangement and automatic tensioning of the spring means.

3. A microswitch sub-unit according to Claim 1 or 2, wherein the co-operable means provide pivotal action between the anchor and the carrier elements to provide the movement between the two electrical contacts in the completed microswitch.

4. A microswitch sub-unit according to any one of Claim 1 to 3, wherein the co-operable means comprise groove means in the anchor to accommodate a straight edge of a bifurcated end portion of the carrier.

5. A microswitch sub-unit substantially as hereinbefore described with reference to and as illustrated in any one or more of the accompanying drawings.

6. A microswitch incorporating a microswitch sub-unit according to any one of the Claims 1 to 5.

7. A method of manufacturing a microswitch sub-unit in a stable arrangement for subsequent insertion into a microswitch housing part, the sub-unit comprising an anchor element, a carrier element and spring means, the carrier and the anchor elements having co-operable means for assembly of the elements together with the spring means, the method comprising bringing the anchor and carrier elements and the spring means together in the directions within a plane which contains the longitudinal axis of the anchor and the longitudinal axis of the sub-unit, and effecting relative rotation between the carrier and the anchor elements about the co-operable means in the direction of the longitudinal axis of the sub-unit thereby to effect stretching of the spring means during assembly of the sub-unit into said stable arrangement.

8. A method according to Claim 7 comprising assisting urging of the sub-unit towards the stable arrangement and effecting automatic tensioning of the spring means by relative rotation of the co-operable means with the spring means attached to the carrier and anchor elements.

9. A method according to Claim 7 or 8, wherein the co-operable means comprise groove means in the anchor to accommodate a straight edge of a bifurcated end portion of the carrier.

10. A method of manufacturing a microswitch sub-unit, the method being substantially as hereinbefore described with reference to and as illustrated in any one or more of the accompanying drawings.