GB2177259A - Electric switches - Google Patents

Abstract

An electric switch comprises a first normally open contact bridge 11 for bridging a first pair of fixed contacts 7,8, a second normally closed contact bridge 12 for briding a second pair of contacts 27,28 and a reciprocable stem 3 movable by snap action against the bias of resilient means to simultaneously move the contact bridges 11,12 and to move by its inner end 47 the second pair of contacts 27,28, each of which is mounted on a bent resilient contact blade 29,30 which is biased against a fixed stop 41,42 when in the closed position. <IMAGE>

Description

SPECIFICATION Safety switch with forced opening of its break contacts The invention relates to an electric safety switch apparatus comprising in an insulating case equipped with two pairs of fixed longitudinally separated contacts, a break contact bridge and a make contact bridge which cooperate respectively with each of these pairs and are simultaneously moved from an inactive position to an active position by resilient means placed under unstable compression therebetween and a longitudinal pusher, an internal end of which causes forced opening of the circuit passing through the break contact bridge, through a longitudinal movement of the corresponding pair of pseudo-fixed contacts.

Such switches, widely used in control circuits governing the movement or stopping of mobile parts with a guarantee of operation, may be illustrated by the German patent application no 26 18 312. The construction of such a switch requires that particular care be paid not only to the quality of the guiding of a mobile insulating support on which the pseudo-fixed contacts concerned are placed, but also to the additional contact resistance which is introduced between these pseudofixed contacts and connecting parts to which they are not fixed.

The invention proposes consequently making improvements to an electric switch apparatus having the general construction mentioned above which overcome the above-mentioned disadvantages.

In accordance with the invention, the aim sought is attained because the pseudo-fixed contact inserts are each fixed mechanically and electrically to a first resilient blade end, a bent region of which ensures application against a fixed stop of the case with a force greater than that which these inserts receive from the corresponding break contact bridge and a second end of which is connected to an electric connecting piece.

From French patent no 2 317 860 a safety switch apparatus is already known in which an internal end of a pusher causes separation of the contacts of an auxiliary switch placed in series with the main contacts of a break contact bridge; in this apparatus where the separation of the auxiliary contacts is accompanied by progressive reduction of their contact pressure which forms a disadvantage when this seapration takes place in the presence of a current, it was necessary to associate with this auxiliary switch a force transmission spring, a return spring and a very flexible blade for providing the electric connection.

The presence of this additional auxiliary switch and that of the springs constitutes a complication and results in an increase of the technical cost of the apparatus, which are not compensated for by clearly visible advantages.

The invention, as well as two embodiments to which it may more particularly give rise will be better understood from reading the following description with reference to the five accompanying figures in which: Figure 1 shows a first embodiment of the switch apparatus of the invention, in an elevational view in section through a longitudinal plane and comprising on the left a half view in the inactive condition and on the right a half view in the active condition of the mobile assembly; Figures 2 and 3 show with more detail, on the one hand, the form of a resilient blade carrying a pseudofixed contact such as used in figure 1 and, on the other hand, the strokes which are operated by the control pusher relatively to the end of this blade;; Figure 4 illustrates a second embodiment of the switch apparatus in an elevational view in section through a longitudinal plane and comprising on the left a half view in the inactive condition and on the right a half view in the active condition of the mobile assembly; and Figure 5 shows in detail the construction of the parts electrically and mechanically concerned by the operation of a pseudo-fixed contact such as the one used in figure 4.

A safety switch 1 shown in figure 1 comprises, in an insulating case 2, a pusher 3 movable longitudinally along the axis XX' between, on the one hand, an inactive position R which is illustrated in the left-hand half of the figure and which is conferred thereon by a return spring not shown and, on the other hand, an active position T which is communicated thereto by an external action exerted in direction G on the external end of pusher 4.

Two pairs 5, 6 of fixed contacts 7, 8 respectively 9,10 are placed in the case in positions longitudinally staggered so as to be able to cooperate: the first one with a transverse make contact bridge 11 which will close when the pusher is in position T and will open conversely and, the second one with a transverse break contact bridge 12 which will open when the pusher is in position T and conversely.

These switching operations take place simultaneously because of the presence of isolating association means or a frame 13 which joins the two contact bridges together. These two contact bridges and this frame form a mobile assembly 14 which has a pusher passing therethrough, each bridge 11,12 having its central portion recessed.

Between this assembly and this pusher are located, symmetrically with respect to the axis XX', two resilient devices 15,16 bearing under compression on first opposed knives 17,18 belonging to the pusher and on second knives 19,20 of the assembly which are placed facing each other.

These resilient devices which here use helical springs 21,22 could also comprise resilient blades bearing in grooves placed at the same positions as the knives.

The fixed make contact inserts 23,24 are integral with fixed conducting pieces 25,26 ending at a first pair of connection terminals not shown.

The fixed break position contact inserts 27,28 are carried by resilient blades 29,30 which allow them to retract and play the role of pseudo-fixed contact inserts.

These resilient blades each comprise a first free end 31, respectively 32, a second fixed end 33 respectively 34, which is mechanically secured to a connecting piece 35, respectively 36, to which it is electrically connected, and an intermediate portion 37, respectively 38, which has a bent shape, see also figure 2.

The inserts 27,28 are fixed in flat regions 39, respectively 40, which are close to the first ends, whereas bearing portions or surfaces 43,44 of these regions also close to the contacts but opposite the ends, are applied against stops 41,42 integral with the case which defines their axial position, see figure 2.

It will be readily understood that such resilient bearing on the stops is obtained by previous bending of these resilient blades which confers thereon before mounting a smaller radius of curvature so that the blades do not flex when the break contact bridge 12 bears thereon.

Referring to figure 1, it can be seen that the first ends 31,32 are placed respectively in the paths followed by two horns 45,46 belonging to the internal end 47 of the pusher when this latter moves towards position T, and so that, for the inactive position R of the pusher, a certain distance -d- separates them whereas at the end of such travel over the distance -dthese horns come to bear on the first ends for moving the blades away from the stops.

In the inactive condition R of the pusher, the contact inserts of the bridge 12 are applied by the mobile assembly and so by the resilient devices against the pseudofixed inserts 27,28 and the assembly 14 is in an inactive position -I-: such application is made with a force which is not sufficient for separating the resilient blades from stops 41,42 so that the positions of the pseudo-fixed inserts are perfectly determined.

In normal operation of the apparatus, it is sufficient for the pusher to travel from position R in direction G a distance -a- less than d- for the resilient devices 15,16 to pass through unstable maximum compression stages which are immediately followed by sudden rocking movements whose action brings the mobile assembly into the active position -A- illustrated in the right-hand half of figure 1, which causes the make switch 11,5 to close and the break switch 12,6 to open.

Continuing movement of the pusher up to a maximum stroke -1- causes deflection of the blades which only results in increasing the in sulating distance between contact inserts already separated.

If, on the other hand, the inserts of conctact bridge 12 have been accidentally welded with the inserts 27,28 and if, consequently, the mobile assembly 14 is not able to assume an active position -A-, the meeting of horns 45,46 and ends 31,32 will cause this assembly to be driven in the same direction G as that followed by the pusher as far as a position where, for a stroke -s- , the mobile assembly 14 comes into abutment through the contact bridge 11 against cross pieces 48,49 of the case, see figure 2 and figure 3. Continuation of the movement of the pusher in the same direction then causes forced mechanical separation of the welded inserts, and the movement of the assembly in the opposite direction to G, see figure 1 on the right.

Depression of the pusher consequently re sulks, in all cases, in a respective arrangement of the parts which corresponds to the condition T shown in the right-hand half figure 1 whereas the release of an external force exerted on end 4 causes, through the return spring which has not been shown for simplifying the drawings, and accessorily, through the elasticity of the blades, the re-appearance of the break condition R.

In the preferred arrangement which is shown in figure 1, the contact bridge 12 which extends tranversely and parallel to bridge 11 is shorter than this latter, which allows the bent portions of the blade to be housed in an intermediate space of the case 50, substantially between the stops 41,42 and the cross pieces 48,49.

This arrangement confers on this switch apparatus a small height -h1- which is interesting for numerous applications; this arrangement may also be credited with the improvement of the galvanic separation which is provided by the presence of the internal end 47 between the ends 31,32 of the resilient blades 29,30.

In a second embodiment of the invention, see figure 4, where the parts having the same functions bear the same references to which a prime accent has been added, the pseudofixed contact inserts 27',28' are each fixed to a face 61,62 belonging to a flat transverse metal part forming contact support 63,64 which are both placed transversely in the case 2. Each support has a free end 65,66 placed in the path of the horns 67,68 and an edge 70,71 which is opposite this and and which bears in a groove of the case 72, respectively 73.

Each support such as 63, see figure 5, is integral through a face 74 opposite the insert 27' with a first flat portion 75 close to a first flat end 76 of a resilient blade 77, whereas a second end 78 of this blade, which is connected by an intermediate bent portion 79 is mechanically and electrically connected to a connecting piece 80 representing a fastening point -P-.

The position of this fastening point in the transverse bottom 82 of the case and of the groove in the longitudinal sidewall 81 of this case 2', as well as the angular extent of the bent portion of the blade not yet installed in the apparatus, are chosen so that the contact support 63 is subjected, once installed with the blade and for the inactive condition R of the pusher 3, to a force F having, on the one hand, a transverse component f, which applies the edge in the groove and, on the other, a longitudinal component f2 which applies face 61 against a stop 84, respectively 86 of the case, see figure 5.

This stop 84 is here carried by a transverse rib 85 further playing, for the contact bridge 12', the same role as that played before by the dividing wall 48 for the contact bridge 11.

With this second embodiment, which occupies a total volume slightly greater than the preceding one, it is easier to give the resilient blades dimensions capable of lowering the level of the mechanical stresses and the pseudo-fixed inserts 27',28', when they bear on the stops 84,86, can be given positions which do not depend on the manufacturing tolerances of the resilient blades.

Claims (8)

1. Electric safety switch apparatus comprising, in an insulating case equipped with two pairs of fixed longitudinally separated contacts, a break contact bridge and a make contact bridge which cooperate respectively with each of these pairs and are simultaneously moved from an inactive position to an active position by resilient means placed under unstable compression therebetween and a longitudinal pusher, an internal end of which causes forced opening of the circuit passing through the break contact bridge, through a longitudinal movement of the corresponding pair of pseudofixed contacts, characterized in that the pseudo-fixed contact inserts (27,28) are each connected mechanically and electrically to a first end (31,32) of a resilient blade (30,40) a bent region (37, 38) of which ensures the application against a fixed stop (48,49) of the case (2) with a force greater than that which these inserts receive from the corresponding break contact bridge (12), and a second end (33,34) of which is connected to an electric connection piece (35,36).

2. The switch apparatus according to claim 1, characterized in that each of the pseudofixed contact inserts (27,28) is placed in an unbent region (39,40) of the resilient blade (30,29) which is included between a bearing surface (43,44) cooperating with the abutment surface (41, 42) and a free end (31,32) which receives the action of a horn (45,46) carried by the pusher (3).

3. The switch apparatus according to claim 2, characterized in that the resilient blades (29,30) are disposed symmetrically in a region (50) of the case (2) situated substantially between the stops (41,42) and cross pieces (48,49) of the case serving as bearing point for the make contact bridge (11), two opposite ends (31,32) of these blades being isolated by the end (47) of the pusher (3) which is placed therebetween.

4. Switch apparatus according to claim 1, characterized in that each of the contact inserts (27',28') is placed on one of the faces (61) of a rigid transverse metal plate (63,64) which pivots about an edge (70) engaged in a groove (72) close to a wall (81) distant from the longitudinal axis XX', the other opposite face (74) of this plate being integral with the free end (76) of the resilient blade (77).

5. Switch apparatus according to claim 4, characterized in that the resilient blades (77,87) are disposed in a region (50') of the case (2') opposite the one containing the mobile assembly (14') formed by the two contact bridges (11,12) with respect to the stops (85,86) receiving alternately in engagement the plates (63,64) or this assembly.

6. The switch apparatus according to one of claims 4 or 5, characterized in that the resilient blades (77,87) are bent so that a force F, having a component f, perpendicular to the axis XX', and a component f2 parallel to this axis is applied to each of the plates (63,64).

7. Switch apparatus according to one of claims 1 to 6, characterized in that the internal end (47,47') of the pusher (3) respectively (3') has opposite horns (45,46, 67, 68) for the forced simultaneous actuation of the two pseudofixed contacts (27,28), respectively (27',28') and establishes an isolation between two free ends (31,32) respectively (65,66) of resilient blades which face each other.

8. Electric safety switch apparatus substantially as described herein with reference to the accompanying drawings.