Trip Mechanism

Abstract

A trip mechanism which can be actuated by a magnet, by inertia, by a mechanical movement or by an electrical current, has powerful magnets in mutual repulsion constrained close together by the attraction of a short length of ferromagnetic material; this attraction balances the repulsion and allows energy to be stored in the magnetic field. When the balance is upset -- which can be done in a number of ways -- the magnet previously held by the short length of ferromagnetic material is driven away by the stored energy and may be used to close a pair of circuit contacts.

Description

This invention relates to a trip mechanism, which can be operated by mechanical, electrical or magnetic actuation.

Usually, such devices comprise a spring loaded latch, and a catch which releases the latch when the catch is moved. This mechanical loading decreases the sensitivity of the trip mechanism, and the wear which occurs will affect operation.

Accordingly, it is an object of this invention to provide a trip mechanism in which the latch and catch are not in physical contact; it is another object of this invention to achieve this with a few inexpensive magnets in mutual repulsion and a magnetic catch.

It is a further object of this invention to provide a preset catch and electrical contacts so that the assembly will function as an inertia switch. It is yet another object of this invention to provide a trigger that can be directly operated by electrical, mechanical or magnetic forces .

The invention will best be understood by reference to the drawing which illustrates, by way of example, two embodiments. In this drawing:

FIG. 1 illustrates one embodiment with a preset catch the mechanism being in a cocked position, that is ready to be tripped;

FIG. 2 illustrates the same mechanism after tripping;

FIG. 3 shows a simpler embodiment.

In these figures, items 2, 4 and 6 are magnets which have north and south poles as indicated on FIG. 1; that is to say, they are magnetized through their thickness. These magnets are such that if they are placed with like poles facing one another (and their magnetic axes constrained from turning through 180.degree., so that unlike poles can never attract one another) they will float one above another by mutual repulsion; such magnets are commercially available.

The drawing illustrates constraint of the magnetic axes by using magnets of annular form and using a tube 8 of a non-magnetic material, such as brass, passing through the central hole. The magnet 6 is located by a flange 7 on the brass tube, the upper face of flange 7 giving a datum plane for magnet 6. Both the flange and this magnet are surrounded by a plastic structure, 9, 10 and 11 which forms a supporting base. The upper face of the magnet 6 is thus fixed relative to the datum plane, of flange retaining means, 7.

A short ferromagnetic core, 12, is located within the brass tube 8 at such a distance from the datum face, that, in FIG. 1, it can retain annular magnet 2 closer to magnets 4 and 6 than would be possible without the core 12 (in the absence of any external force). That is, the attraction of core 12 for magnet 2 overcomes the repulsion forces between magnets 2, 4 and 6 if the magnets are squeezed together and then released gently.

To give dimensions by way of example, and not by way of limitations, I have used annular magnets 0.750 inches outside diameter, with a 0.271 inch diameter hole and a thickness of 0.250 inch. I find that the best length for the core 12 is about three-sixteenths inch although there is not much difference if the length is one-fourth inch. However, cores 1/8 inch long or 3/8 inch long will operate satisfactorily as a catch, but the energy stored in the latch system is less. If the core is made either more than 1/2 inch or less than 1/16 inch long the trip mechanism is only marginally operable because it would seem that the attraction between the core 12 (the catch) and the magnet 2 (the latch) is either insufficiently localized or insufficient to overcome the repulsion of the adjacent magnet; this results in so little release of energy from the system that there is very little movement of the latch, magnet 2, when the catch, core 12 releases it.

In the absence of core 12, there is a 1/2 inch gap when one magnet floats above another freely, and the gap between the second magnet and the next beneath it is about 3/8 inch. Thus the overall height of the stack of three magnets, 2, 4, and 6 without the core present is about 15/8 inch.

If now the core 12 is moveable and introduced at the top of tube 8, and moved downwardly as by rod 5, towards the locating flange 7, it will drag magnet 2 with it against the repulsion of the magnetic field until the position shown in FIG. 1 is reached; a 3/16 inch long core will provide enough attraction so that the overall stack height is reduced to about 1 inch (one inch). At this point, if downward movement of core 12 is stopped, the position is stable, but with stored spring-like energy.

However this stable position may be upset by mechanical or even magnetic forces. A light mechanical impulse, such as a shock, a small acceleration, a tilt, or a change in magnetic environment trips the mechanism by upsetting the balance of forces, and magnet 2 is impelled upwardly by the energy, previously stored in the magnetic field, being suddenly released. This upset, or tripping, may also be carried out electromagnetically by passing a current through a coil around latch magnet 2 (this coil is not shown) to upset the balance of magnetic forces. Of course, if movement of the core 12 is continued downwardly this too will trip the mechanism, as will the approach of a permanent magnet of correct polarity. The result of any of these tripping forces, which can be very light, is that the system reverts to the uncocked position shown in FIG. 2.

The effect is increased in some cases (depending on magnetic materials, dimensions, the nature of the tripping impulse and the like) because as magnet 4 is repelled upwardly by magnet 6 it is caught by core 12 and so comes to rest at a point higher than it would naturally assume.

The endpiece, 14, represents the height to which the uppermost magnet 2 will rebound and it is fitted with relay contacts 16 which will actuate a circuit when closed. A coat of conducting silver paint 18 is provided because these magnets are usually non-conducting. I prefer to make contacts 16 close a self holding relay (not shown) but if desired another core (not shown) can be fixed at the top of tube 8 to hold magnet 2 with its conducting coat 18 against contacts 16.

The trip mechanism will work with only two magnets as shown in FIG. 3. Here, core 12 is much closer to the datum face of the retaining flange 7, and the mutual repulsion of magnets 4 and and 6 is balanced by the attraction of core 12 for magnet 4. Although less energy is stored in the "spring" system, the assembly is more convenient if it is desired to have a moveable core.

Although I have used the terms "upwardly" and "downwards", it will be understood that these refer to the illustrated embodiments and that the device is not dependent upon the force of gravity; a slight adjustment may be necessary to the position of the core 12 to achieve maximum energy storage, if the embodiment of FIG. 3 were inverted, but basically the operation is unimpaired. It will also be obvious to those skilled in the art that various other changes and modifications may be made without departing from the invention as defined by the appended claims. For example, in an inertia switch with a horizontal axis, it is possible to omit flange 7, and its physical face; the relay is made double ended by providing two cores 12, each attracting a permanent magnet against the mutual repulsion of a stack. The "datum plane" is halfway between the two cores, and acceleration is sensed, not only in magnitude but also in direction by the magnet which escapes from its core.

Claims

I claim:

1. A trip mechanism comprising,

at least two permanent magnet means, arranged coaxially with like poles facing one another,

a non-magnetic axial constraint means to keep the magnetic axes aligned, thereby maintaining like poles facing while allowing movement of at least one permanent magnet means therealong,

a means for providing a datum plane for another of said permanent magnet means,

a catch means comprising a piece of magnetic material for applying a force to said one moveable permanent magnet means, and

means for locating said catch means adjacent to said datum plane at a position to urge said moveable permanent magnet means towards said datum plane, said position being a predetermined distance from said datum plane,

the predetermined distance between said catch means position and said datum plane being determined so that the force exerted by the catch on the moveable permanent magnet means urging it towards the datum plane is balanced by the mutual repulsion between the two permanent magnet means,

whereby the force on the catch stores energy in the repulsion field for sudden release.

2. A trip mechanism as claimed in claim 1, wherein

said means for locating said catch means is at a position closer to said other permanent magnet means than the position normally occupied by said moveable permanent magnet means in the absence of said catch means.

3. A trip mechanism as claimed in claim 1, wherein

said catch means is of ferromagnetic material having an axial length of about the same dimension as the magnetic length of said moveable permanent magnet means.

4. A trip mechanism as claimed in claim 1, wherein the

said means for locating said catch means comprises means for moving said catch means towards said predetermined distance from said datum plane.

5. A trip mechanism as claimed in claim 1, wherein

said means for locating said catch means comprises means for fixedly securing said catch means at said predetermined distance from said datum plane.

6. A trip mechanism as claimed in claim 1, wherein

said moveable permanent magnet means is annular, said axial constraint is a thin walled tube, and said catch means is a cylindrical core within said thin walled tube.

7. A trip mechanism as claimed in claim 6, wherein

said means for locating said cylindrical core catch means comprises means for moving said catch means towards said predetermined distance position from said datum plane.

8. A trip mechanism as claimed in claim 1, wherein there

are at least three permanent magnet means, and wherein at least two of said permanent magnet means are free to move along said axial constraint.

9. A trip mechanism as claimed in claim 1, wherein said

datum plane providing means is a flange secured to said axial constraint means, to provide a retaining means for the other permanent magnet means.

10. A trip mechanism as claimed in claim 1, wherein

two similar trip mechanisms are arranged symmetrically upon a single axial constraint means, and

said datum plane is provided by the interaction of said two similar trip mechanisms, one with the the other, at a plane midway between the two catch means.

11. A relay comprising a trip mechanism as claimed in claim 1, and further comprising

a pair of contacts, and

wherein a moveable permanent magnet means has a conductive surface, whereby the pair of contacts are connected together when the mechanism trips.