GB2219950A

GB2219950A - Manufacturing switch plate

Info

Publication number: GB2219950A
Application number: GB8909544A
Authority: GB
Inventors: Pietro Gindri; Alberto Petrone
Original assignee: Elbi International SpA
Current assignee: Elbi International SpA
Priority date: 1988-06-22
Filing date: 1989-04-26
Publication date: 1989-12-28
Also published as: GB8909544D0; IT1219392B; FR2633442A1; DE3913812A1; IT8867581A0

Description

2219950 "IMPROVEMENTS YEN THE MANUFACTURE OF A BISTABLE PLATE" The

invention relates to a method of manufacturing a bistable plate for a rapid-release switch.

More particularly the invention relates to a method comprising the operations of:

Cutting and thereby shaping an elongate plate of metal material formed with two adjacent longitudinal slots which divide it into two side arms and a central arm, and Prestressing the plate so as to produce a predetermined increase in length of a central arm with respect to the side arms, so that the plate can assume two different stable states.

In the prior art, a bistable plate of the aforementioned kind can be prestressed in various ways. According for example to Italian patent application 67111-A-73 the prestress is applied by bending both side arms of the plate, thus shortening them so that the central arm bends and Is disposed on both sides of the plane of the side arms.

According to German PS 29 19 795, the central arm of the previously aforementioned bistable plate is broken at Its central area and the ends of the two remaining branches of the central arm are soldered to a bearing component after moving them axially apart.

Irrespective of the method used of increasing the length of the central arm relative to the side arms, there is still the problem of accurately calibrating the prestress on the plate, which determines the release characteristic thereof and of the switch in which the plate is incorporated.

2 The object of the invention Is to provide a method for easy and accurate calibration of the prestress on a plate of the aforementioned kind.

This object Is achieved according to the invention by the method of the previous ly-specif led kind, which Is also characterised In that In order accurately to calibrate the prestress a measurement is made of the force necessary for moving the plate from one of Its stable states to the other, and When the force is below a predetermined value, at least one portion of the central arm is locally reduced In area and. compressed so as to Increase the length of the aforementioned central arm, the Increase being determined In dependence on the measured value of the aforementioned force, whereas When the force If above the preset value, both the side arms of the plate are lengthened by local reduction In area and compression of at least one respective portion thereof, the lengthening being determined In dependence on the measured value of the aforementioned force.

Other features and advantages of the Invention will be clear from the following detailed description with reference to the accompanying drawings, given by way of non-limitative example only, In which..

Fig. 1 Is a top view of a bistable plate for a rapid-release switch or circuit-breaker; Fig. 2 Is a side view partly in section of the bistable plate shown In Fig. 1; Fig. 3 Is a view In section along line III-III In Fig. 1; 3 Fig. 4 Is a view corresponding to Fig. 2, showing the bistable plate In Its other stable state, during the process of measuring the force necessary for switching it; Fig. 5 Is a view similar to Fig. 3, showing a part of the central arm of the plate which Is acted upon for the purpose of accurate calibration of the prestress on the plate, and Fig. 6 Is a larger-scale view of the detail Indicated by arrow V1 In F ig. 5.

In Fig. 1, the general reference 1 denotes a bistable plate for a rapid-release switch, e.g. for use In a thrust meter. The plate, which has an elongate shape, Is made e.g. by cutting a metal strip, and has two longitudinal slits 2, 3 which divide It Into two lateral arms 4, 5 and a central arm 6.

The plate is prestressed In known manner, e.g. by one of the previously described methods, by Increasing the length of the central arm 5 and 6 relative to the side arms 4 and 5. The plate Is then capable of taking up two different stable states, In which the central arm 6 curves from one to the other side relative to the plane conta.ining the side arms 4 and 5. The two stable positions of the plate are shown more particularly in Figs. 2 and 4.

An electric contact component 7 is secured in known manner to one end of plate 1.

A metal bearing and electrically connecting component (general reference 8) Is secured to the middle part of the central branch 6.

re Component 8 comprises a shaped plate having a first end 8a in the form of a laminar plug, pin or the like and an opposite end 8b bent and welded to the central arm 6 of plate 1 (Figs. 2 and 3). In the embodiment Illustrated, the middle portion of the central arm 6 is 4 disposed between an abutment 9 and the end 8b of the bearing and connecting component 8. The resulting "sandwich" Is then secured by electric weld spots Indicated by 10 In Fig. 1.

The prestress on the plate Is accurately calibrated by measuring the force necessary for moving it from one of its stable states to the other. This can be done e.g. in the manner Illustrated In Fig. 5. The bearing and connecting component 8 Is clamped In a locking device 11 In a position at which the end of the plate carrying the contact means 7 extends between two stationary components 12 which limit Its possible travel. Plate 1 Is Initially disposed in Its stable state shown in Fig. 4, e.g. under the action of a spring 13 which tends to push up the end la of the plate remote from the end which carries the contact 7 (Fig. 4). End la of plate 1 Is then subjected to a downward force In the direction of arrow F In Fig. 4, using a dynamometric thrust device of known kind, adapted more particularly to determine the force necessary to shift the plate from the state shown In Fig. 4, to the state In Fig. 2.

If the measured value of the force Is below a preset value, a part of the central arm 6 of the plate (Fig. 5) Is subjected to reduction of area and compression, so as permanently to reduce Its thickness and permanently increase its length. At the calibration station, the Increase In length of the central arm Is predetermined In dependence on the previously measured force necessary for switching over the plate. Depending on the shape of the plate, the relation between the measured force and the required elongation of the central arm of the plate can be empirically predetermined by a series of tests.

If on the other hand the measured force Is above the preset value, the prestress on the plate Is accurately calibrated by stretching both side arms 4 and 5 by local reduction of area and compression of at least one respective portion thereof, In a manner completely similar to that described hereinbefore with reference to stretching the central arm. In the case when the side arms are reduced in area, the amount of elongation of the aforementioned arms is, as before, predetermined In dependence on the measured force necessary for releasing the plate.

The previously-described method can be used for extremely accurate calibration of the prestress on the plate, Irrespective of the manner In which the prestress was Initially produced.

Advantageously the Initial prestress on the plate can be obtained by local reduction in area and compression of at least one part of the central arm 6, so as permanently to Increase Its length. This method of producing the prestress has considerable advantages over the prior-art methods previously described. If prestress Is brought about by bending and shortening the side branches of the plate, It varies In time. The shortened side arms are permanently under tension, which tends to spread out the fold, thus altering the prestress.

A series of tests on the fatigue characteristics of plates prestressed by the method of cutting the central arm and moving apart and welding the remaining branches of the central arm, have unexpectedly shown that the resulting prestress Is less constant in time than prestress brought about by reducing the area of the arms of the plate. This may be due to plastic micro-settlement of the welds.

Advantageously the initial prestress on the plate is brought about by reduction In area and compression of an end portion of the central arm 6 adjacent the electric contact 7 as shown In the drawings. Alternatively the middle portion of the central arm 6 can be subjected to reduction In area, after which the bearing and connecting component 8 Is welded to it.

6 Of course, without departing from the principle of the Invention, the embodiments and constructional details can be widely varied from those described and 111lustrated by way of non-limitative example only, without thereby departing from the scope of the Invention.

7

Claims

C L A I M S

1 A method of manufacturing a bistable plate for a rapid-release switch, comprising the operations of:

Cutting and so forming an elongate plate of metal material having two adjacent longitudinal slits which are divided Into two side arms and a central arm so that the plate Is capable of assuming two different stable states, characterised In that after the plate has been prestressed, the prestress Is accurately calibrated by measuring the force necessary for moving the plate from one of Its stable states to the other, and When the force Is below a predetermined value, at least one portion of the central arm Is locally reduced In area and compressed so as to Increase the length of the aforementioned central arm, the Increase being determined In dependence on the measured value of the aforementioned force, whereas When the force Is above the preset value, both the side arms of the plate are lengthened by local reduction in area and compression of at leas t one respective portion thereof, the lengthening being determined In dependence on the measured value of the aforementioned force.

2. A method according to claim 1, characterised In tha t the prestress on the plate is obtained by local reduction In area and compression of at least one portion of Its central arm so as permanently to reduce the thickness and permanently Increase the length of the aforementioned portion of the central arm.

3. A method according to claim 1 or 2, characterised In that In order to measure the force necessary for switching from one to the 8 other stable state of the plate an intermediate portion of the central arm is secured to a bearing structure and one end of the plate Is loaded with a measurable force In the direction In which the plate can change direction.

4. A method according to any of the preceding claims, characterised In that the plate Is prestressed by local reduction in area and compression of an end portion of Its central arm, preferably of -the end portion adjacent which the plate Is provided with an electric contact means.

5. A method according to any of claims 1 to 3, characterised In that the prestress on the plate Is brought about by local reduction In area and compression of an Intermediate portion of Its central arm, which Is then welded to a bearing and connection component.

6. A method according to claim 5, characterised In that the bearing and connection component Is welded to those portions of the central arm of the plate which are adjacent the portion subjected to reduction In area.

7. A method of manufacturing and calibrating a bistable plate for a rapidrelease switch, substantially as hereinbefore described with reference to and as Illustrated In the accompanying drawings.

8. A bistable plate for a rapid-release switch, substantially as hereinbefore described with reference to and as Illustrated In the accompanying drawings.

Published 1989 at The Patent Office. State House, 66171 High Holborn. London WClR 4TP. FVrther copies may be obtained from The Patent Office. Sales Branch, St Mary Cray, Orpington, Kent BR5 3RD. Prmted by Multiplex techniques ltd, St Mary Cray, Kent, Con. 1/87