GB2047004A

GB2047004A - A pushbutton electric switch

Info

Publication number: GB2047004A
Application number: GB8012704A
Authority: GB
Original assignee: Societe dApplications des Machines Motrices SAMM SA
Current assignee: Societe dApplications des Machines Motrices SAMM SA
Priority date: 1979-04-24
Filing date: 1980-04-17
Publication date: 1980-11-19
Also published as: FR2455350B1; FR2455350A1; GB2047004B

Abstract

A pushbutton 3 fitted with contact blade-springs 4 and associated with a restoring spring 5 is slidably fitted within a body 1 in which are fixed electric terminals 2 and an insulating base unit 20. Right-angled conductive strips 17 are fixed in position beneath the head 19 of the base unit, bent-back end portions 4a of the blade-springs 4 being applied elastically against bearing surfaces 23,24 on each side of the head 19. When the pushbutton 3 is depressed, the end portions are capable of downward displacement in sliding motion over a "hard point" 5 delimited by the bearing surfaces so as to come into contact with the conductive strips 17. The electric contact thus established in sliding motion has a self-cleaning effect which ensures operational safety in the event of deposition of dust particles on the conductive strips. Potential applications include push-buttons for aircraft control columns. <IMAGE>

Description

SPECIFICATION A pushbutton for closing and opening an electric circuit This invention relates to a pushbutton for closing and opening an electric circuit.

In more precise terms, the invention is directed to a pushbutton which is so designed as to give the operator a tactile or muscular sensation which indicates that the contact has in fact taken place.

Pushbuttons of this type find a large number of potential applications and can be employed especially for equipping control columns of aircraft or helicopters. In this particular application, the pilot's control column is in fact provided with a number of similar pushbuttons for carrying out electrical control of the motion in pitch or the correction of flight of aircraft, or aircraft radio, or of opening a fire of airborne weapons carried by military aircraft or helicopters.

There has thus been disclosed in French patent No 1,063,868 a pushbutton having a cylindrical body within which are fixed electric terminals and within which is slidably mounted a manual pushbutton equipped with two blade-springs, said pushbutton being associated with elastic restoring means consisting of a helical spring.

The range of travel of the pushbutton is suitably limited to the two blade-springs attached to said pushbutton have bent-back end portions which are intended to embrace the hexagonal-section head of a rod which is capable of axial displacement within the pushbutton body and carries a silver washer.

When the pushbutton is depressed, the bent-back end portions of the blade-springs slide over the bearing surfaces of the hexagonal head. As soon as the bent-back ends have passed over the arrises of this section, they exert a resilient tractive force on the movable rod. The silver washer of said rod accordingly establishes an electrical contact between the terminals. As soon as the pushbutton is released, the restoring spring returns the pushbutton to its initial position. After passing over the arrises of the hexagonal head which determines a kind of dead point, the said head and the rod are forced back elastically by the blade-springs to their initial position, thus breaking the contact.

The pushbutton described in the foregoing is of the so-called quick-break or snap-switch type and operates as a circuit-breaker. The operator is warned that the contact is established by the sudden cessation of resistance of the pushbutton to his thumb.

However, it is found at the end of a certain period of service that, if only a few fine particles of dust or dirt are deposited on the metallic strips which constitute the terminals, this is sufficient to interrupt the flow of current which usually has a low value of the order of a few milliamperes.

Furthermore, it may happen that the articulated mechanism constituted by the blade-springs and the movable rod which accompanies the displacements of said blade-springs seizes-up or jams as a result of deposition of dust particles or debris of any kind.

Thus the fact that there exists a movable component between the pushbutton and the electric terminals constitutes an unfavourable factor as regards reliability of operation of the pushbutton.

Operational failures off this type may be attended in some instances by extremely serious consequences, for example in an aircraft or a helicopter which can thus be completely deprived of any means of control.

The aim of the invention is to overcome these disadvantages by providing a pushbutton which offers operational safety and reliability to the full extent required.

In accordance with the invention, the pushbutton comprises means for ensuring that a predetermined displacement of the pushbutton puts the ends of the blade-springs in direct contact with the terminals or, on the contrary, breaks the contact between the blade-springs and the terminals.

Since the movable intermediate component of the known design is consequently dispensed with, the pushbutton in accordance with the invention is no longer subject to the danger of jamming or seizure.

In one embodiment of the pushbutton in accordance with the invention, the terminals comprise conductive strips rigidly fixed to a base unit provided between the strips with a head having bearing surfaces such that divergent portions followed by convergent portions of said surfaces extend from the top end of the said head with separating arrises. The base unit is mounted in such a manner as to ensure that, when the pushbutton is at rest, the head of the base unit is engaged between the bent-back end portions of the blade-springs and that the said bent-back end portions are capable of sliding over the lateral bearing surfaces of the head of the base unit and of passing over the arrises in order to establish the electric current between the strips when the pushbutton is depressed in opposition to its restoring means.The conductive strips extend in a direction parallel to the direction of displacement of the blade-springs in order that these latter may accordingly be permitted to slide along the strips over a predetermined range of travel.

Under these conditions, the peripheral axis of the head of the base unit provides a "hard point" over which the blade-springs pass and which is felt by the user through his sense of touch when he depresses the push-button. This tactile sensation corresponds to the elastic return of the bent-back end portions of the blade-springs against the conductive strips on which a sliding contact takes place and consequently produces a self-cleaning action. Accordingly, if any dust particle is deposited on one of the metallic strips, it is driven away by the blade-spring and cannot prevent the flow of current.

Further distinctive features and advantages of the invention will become apparent from the following detailed description. One embodiment of the pushbutton in accordance with the invention is illustrated in the accompanying drawings which are given by way of example and not in any sense by way of limitation, and in which:: Figure 1 is a view in longitudinai sectional elevation showing one embodiment of the pushbutton in accordance with the invention as shown in the rest position; Figure 2 is a view in sectional elevation, this view being taken along the line I-I of Figure 1; Figure 3 is a transverse sectional view taken along the line Ill-Ill of Figure 1 and showing the insulating base unit in which it is assumed that the bladesprings have been removed; Figure 4 is a view in elevation to a smaller scale showing the pushbutton and its blade-springs; Figures a view in elevation to a smaller scale and showing the insulating base unit of the pushbutton of Figures 1 to 4, looking in the direction K of Figure 1.

The pushbutton shown in Figures 1 to 5 is intended to control the opening and closing of an electric circuit. Although not limited to this application, the electric circuit can serve in particular to control the motion in pitch or the direction of flight of an aircraft or helicopter, in which case the pushbutton is inserted at the top end of the control column of the aircraft in the manner known perse.

The pushbutton has a cylindrical body 1 within which are fixed two electric terminals 2 and in which is slidably mounted a manual pushbutton 3 fitted with two blade-springs 4. The pushbutton 3 is mounted coaxially with the body 1 and capable of axial displacement within this latter in opposition to the elastic restoring action of a helical spring 5, the displacement of the pushbutton 3 being intended to initiate closing or opening of the terminals 2.

The said terminals are set within an insulating base unit 6 fitted in the body 1 and held in position within this latter at the end remote from the pushbutton 3 by means of a snap-ring 7 which is partially engaged within an annular groove of the body 1. The base unit 6 has a peripheral bearing surface 8 against which is applied the base of an insulating ring 9 having a cylindrical portion 9a which is smaller in diameter than the internal diameter of the body 1. The spring 5 is partially housed within the annular space thus formed between the cylindrical portion 9a and the body 1 and is applied against the shouldered portion 9b constituted by the annular base of the ring 9.

The spring 5 thus urges the pushbutton 3 elastically in the direction opposite to the terminals 2, the entrance opening of the body 1 into which the pushbutton 3 is introduced being provided with an annular shoulder 11 which forms a stop for the pushbutton. Furthermore, the range of travel of the said pushbutton in opposition to the restoring action -ofthe spring 5 is limited by a second stop 12 constituted by a transverse locking-pin 12 which passes through the pushbutton 3 and the ends of which are engaged in lateral openings 13 ofthe body 1.As a complementary feature, the locking-pin 12 passes through an axial recess 14formed in the pushbutton 3, the displacement of this latter in the direction of the base unit 6 being stopped when the bottom portion 14a of the recess 14 comes into contactwiththe locking-pin 12.

In known manner, the two blade-springs 4 are set in the insulating pushbutton 3 and have end portions 4a which are bent-back in the shape of a V and are symmetrical with respect to the axial plane of the pushbutton, the vertices of each V-shaped portion being directed towards each other.

Thus, in the embodiment which is illustrated, each blade-spring 4 has two bent-back end portions 4a (as shown in Figure 2) which are separated by a central recess 15.

In accordance with the invention, means are provided for ensuring that a predetermined displace ment of the pushbutton 3 towards the base unit 6 and the conductive terminals 2 has the effect of putting the bent-back ends 4a of the blade-springs in direct contact with the terminals 2 or, on the contrary, breaks the contact between the bladesprings 4 and the terminals 2.

In the embodiment shown in the drawings, the means aforesaid are so arranged as to ensure that a displacement of the pushbutton 3 establishes a direct electric contact between the end portions 4a of the blade-springs and the ends of the terminals 2.

The terminals 2 are each formed by assembling together a conductive pin 16 and a conductive strip 17 which is bent-back at right angles. The short arms 1 7a of the said strip are rigidly fixed to the pins 16 by means of rivets 18. Four terminals 2 as thus constituted are arranged symmetrically in pairs with respect to a longitudinal axial plane of the body 1 as shown in Figure 3.

The insulating base unit 6 comprises a bottom element 20 which is held in position by means of the snap-ring 7, a central partition 19 extending on each side of a plane P which passes through the axis of the cylindrical body 1, and two shouldered portions 21 formed at right angles to the partition 19 on each side of this latter. The partition 19 and its shouldered portions 21 form a cruciform assembly as shown in Figure 3.

In accordance with a particular feature of the invention, the partition 19 has a head 22 on which the bent-back end portions 4a of the blade-springs are applied elastically as shown in Figure 1, and symmetrically with respect to the axial plane P of the pushbutton.

The head 22 is provided with a series of lateral bearing surfaces 23, 24, a pair of bearing surfaces 23, 24 being provided for each bent-back end portion 4a.

The said bearing surfaces 23,24 have respectively a divergent slope and then a convergent slope extending from the top end of the head 19 with separating arrises 25, thus defining a V-shaped cross-section in which the vertices are oriented in opposite directions towards the bent-back end portions 4a of the blade-springs. Furthermore, the convergent bearing surfaces 24 extend over a distance which is distinctly shorter than the length of the bearing surfaces 23 (as shown in Figure 1).

The long arms of the four conductive strips 17 extend over the opposite faces of the partition 19 and on each side of the radial shoulders 21 whilst the ends of the said long arms are located at the level of the lower ends of the convergent bearing surfaces 24.

In the rest position, the bent-back end portions 4a of the blade-springs are elastically applied against the top edges of the bearing surfaces 23 (as shown in Figure 1). In accordance with the invention, provi sion is also made for a head 22 formed of insulating material which is self-lubricating in order to facilitate the displacement of the blade-springs 4 in sliding motion over the bearing surfaces 23, 24. By way of indication, the said seif-lubricating insulating material can be either "Teflon" Registered Trade Mark or insulating material filled with glass microbeads or insulating material filled with molybdenum bisulphide.

The operation of the pushbutton described in the foregoing is as follows: In the rest position shown in Figure 1, the pushbutton 3 is maintained abuttingly applied against the annular shoulder 11 by the spring 5, the bent-back end portions 4a of the blades 4 being applied against the top edges of the bearing surfaces 23. When the operator depresses the pushbutton 3, the blades 4 move away from each other and the bent-back end portions 4a slide over the insulating bearing surfaces 23 while setting up increasing resistance to the downward displacement of the pushbutton 3.The passage of the end portions 4a over the arrises 25 corresponds to the "hard point" which is felt by the operator's finger, whereupon the vertices of the bent-back end portions 4a slide over the convergent bearing surfaces 25 and consequently move towards each other to be applied in sliding contact with the conductive strips 17.

As the operator continues to exert finger pressure on the pushbutton 3, the bent-back end portions 4a continue to slide overthe strips 17 until further displacement of the pushbutton 3 is prevented by the stop 12. To this end, the insulating partition 19 and the conductive strips 17 are so arranged as to permit displacement of the bent-back end portions 4a in sliding contact with these latter over a distance of travel equal to the travel of the pushbutton 3 as determined by the stops 12 and 11.

The end portions 4a which are applied against the strips 17 therefore establish an electric contact between the terminals 2.

The contact just mentioned is of a sliding nature and therefore has a self-cleaning action, with the result that any dust particle deposited on one of the metallic strips 17 is driven away by the end portions 4a of the blade-springs and therefore cannot prevent the flow of current. This accordingly constitutes an essential advantage and achieves considerably improved safety of operation of the pushbutton in accordance with the invention.

Operational safety is further enhanced by the fact that the intermediate movable component is provided in the prior art and placed between the pushbutton and the contact terminals has now been dispensed with. This accordingly removes any danger of jamming or seizure of the articulation between the two members.

When pressure is no longer exerted on the pushbutton 3, the spring 5 which had been compressed during downward displacement of the pushbutton expands and returns this latter to its starting position whilst the bent-back end portions 4a of the blade-springs slide successively over the bearing surfaces 24 and 23 and pass over the hard point defined by the separating arrises 25.

In consequence, the electric contact between the terminals 2 is broken.

The process observed in the pushbutton which is contemplated by the present invention is not really a quick break or "snap" action as the bent-back end portions of the blades pass over the arrises 25, but rather a "hard point" which is felt by the operator through his sense of touch and which warns him that the electric contact is established. A particularly reliable pushbutton of the two-pole type is thus provided by the invention.

In order to ensure that the insulating head 22 is not subject to progressive degradation as a result of successive operations of the pushbutton 3, it is important to make a suitable choice of the insulating material employed in the fabrication of the pushbutton. It will be found in this connection that the insulating materials mentioned earlier are particularly efficacious but any other suitable insulating material could be employed.

The invention is not limited to the form of construction described in the foregoing and can accordingly extend to alternative embodiments.

Thus, the insulating and divergent bearing surfaces 23 can be covered with electrically conductive portions, in which case the strips 17 are dispensed with. Under these conditions, the electric contact is established in the "rest" position of the pushbutton and is broken when the pushbutton is depressed.

Downward displacement of the pushbutton in fact produces the same action as that described earlier, namely the sliding motion of the bent-back end portions 4a over the conductive portions, then beyond these latter up to the convergent and insulating bearing surfaces while breaking the electric contact between the conductive portions, in which case the pushbutton operates as a circuitbreaker.

Claims

1. A pushbutton for closing and opening an electric circuit, comprising a body within which are fixed electric terminals and in which is slidably mounted a manual pushbutton fitted with bladesprings and associated with elastic restoring means, the displacement of the pushbutton being such as to initiate closing or opening of the terminals which are attached to an insulating base unit housed within the said body, characterized in that it comprises means for ensuring that a predetermined displacement of the pushbutton puts the ends of the blade-springs in direct contact with the terminals or on the contrary breaks the contact between the said blade-springs and the said terminals.

2. A pushbutton in accordance with claim 1, characterized in that the terminals comprise conductive strips rigidly fixed to the base unit which is provided between the strips with a head having lateral bearing surfaces such that divergent portions followed by convergent portions of the said surfaces extend from the top end of the said head with separating arrises and that the base unit is mounted in such a manner as to ensure that, when the pushbutton is at rest, the head of the base unit is engaged between bent-back end portions of the blade-springs and that the said bent-back end portions are capable of sliding over the lateral bearing surfaces of the head of the base unit and of passing over the arrises in order to establish the electric current between the strips when the pushbutton is depressed in opposition to its restoring means, the conductive strips being so arranged as to extend in a direction parallel to the direction of displacement of the blade-springs in order that the said blade-springs may be permitted to slide along the strips over a predetermined range of travel.

3. A pushbutton in accordance with claim 1, characterized in that the base unit has a central partition which terminates in the head aforesaid, the conductive metallic strips being mounted on the faces of the said partition and the ends of the said metallic strips being located at the same level as the lower end of the head which is delimited by the divergent and convergent bearing surfaces aforesaid so that the bent-back end portions of the bladesprings close elastically against the conductive strips as soon as they have passed over the arrises of the said head and are capable of displacement along the said strips over a predetermined range oftravel.

4. A pushbutton in accordance with claim 2 or claim 3, characterized in that the length of the divergent bearing surfaces of the head is greater than the length of the convergent bearing surfaces located next to the ends of the conductive strips, the said strips being constituted by right-angled members attached to connector-pins which extend through the bottom element of the base unit, the assembly consisting of connector-pins and rightangled members being intended to form the pushbutton terminals.

5. A pushbutton in accordance with any one of claims 1 to 4, characterized in that the head of the base unit is fabricated from self-lubricating insulating material so as to facilitate sliding displacement of the blade-springs over the bearing surfaces of the head of the said base unit.

6. A pushbutton in accordance with claim 5, characterized in that the insulating material is selected from the group comprising Teflon, insulating material filled with glass microbeads, insulating material filled with molybdenum bisulphide.

7. A pushbutton in accordance with claim 1, characterized in that the base unit has a head provided with lateral bearing surfaces which are first divergent from the top end of the head and then convergent, the said head being positioned in such a manner as to be engaged between the bent-back end portions of the blade-springs, and that the divergent bearing surfaces are covered with electrically conductive portions so that displacement of the pushbutton produces a displacement of the bent-back end portions of the blade-springs in sliding motion over the conductive portions and beyond the said conductive portions up to the insulating convergent bearing surfaces and breaks the electric contact between the conductive portions which form part of the pushbutton terminals.

8. A pushbutton for closing and opening an electric circuit, substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.