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Patent Searching and Data


Title:
SWITCH
Document Type and Number:
WIPO Patent Application WO/1988/001433
Kind Code:
A1
Abstract:
A mechanical disturbance detection switch comprises a chassis plate (1) and a pendulum member in the form of a disc (3) rotatably mounted upon a shaft (2) projecting from the chassis plate. The pendulum disc (3) has an eccentric weight (7) of lead in one sector, and a plurality of ceramic magnets (6) equally spaced around its periphery. A reed switch (8) is mounted on the chassis plate close to the periphery of the disc (3), so that its contacts (10 and 11) come under the attraction of the magnets as they pass successively by. With the chassis plate mounted substantially vertically, any mechanical disturbance of the switch about the pivot axis of the shaft (2) results in rotation of the disc (3) if that disturbance is greater than a threshold value. Such rotation of the disc (3) is then detected by the passage of a magnet (6) past the reed switch which results in actuation of the reed switch. With the latter connected to an alarm system, an indication of such disturbance is given. The device is operative, no matter what orientation the chassis plate has within the substantially vertical plane thereof.

Inventors:
Walsh
Anthony
Barry
Application Number:
PCT/GB1987/000581
Publication Date:
February 25, 1988
Filing Date:
August 17, 1987
Export Citation:
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Assignee:
Walsh
Anthony
Barry
International Classes:
H01H35/02; (IPC1-7): H01H35/02
Foreign References:
BE843943A1976-11-03
FR2326024A11977-04-22
FR726415A1932-05-28
US3761653A1973-09-25
US3963888A1976-06-15
US3882453A1975-05-06
US3701093A1972-10-24
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Claims:
CLAIMS
1. An electrical switch comprising a chassis (1) and a pendulum member (3,7;23,27;43,47) adapted to cause actuation of switch means (8;33;50) upon mechanical disturbance of the switch, characterised in that the pendulum member (3,7;23, 27;43,47) is pivotally mounted on the chassis (1) for rota¬ tion about a pivot axis, in that the pendulum member carries a plurality of switch actuating elements (6;6 ; 30;46) disposed circularly, or partcircularly, about the pivot axis for movement in a circular, or partcircular, path together with the pendulum member about the pivot axis, and in that the switch means (8;33;50) is mounted on the chassis (1) adjacent the circular, or partcircular, path and is adapted to be switched on and off repeatedly as the elements successively pass the switch means.
2. A switch as claimed in claim 1, characterised in that the switch actuating elements (6;6 ;30;46) are provided around a considerable circular arc on the pendulum member (3,7;23,27; 43,47).
3. A switch as claimed in claim 2, characterised in that the switch actuating elements (6;6 ;30;46) are spaced around the whole periphery of the pendulum member (3,7;23,27;43,47) .
4. A switch as claimed in claim 2 or 3, characterised in that the switch actuating elements (6;6 ;30;46) are equally spaced.
5. A switch as claimed in any one preceding claim, chara¬ cterised in that the switch actuating elements (6;6 ) are permanent magnets carried by the pendulum member.
6. A switch as claimed in claim 5, characterised in that the switch means (8) is a reed switch.
7. A switch as claimed in claim 5 or 6, characterised in that the magnets (6;6 ) are of ceramic magnetic material.
8. A switch as claimed in any one preceding claim, chara cterised in that the pendulum member (3;23;43) is cylin drical and has an accentric weight (7;27; 7) of nonmagnetic material.
9. An alarm system incorporating an electrical switch as claimed in any one preceding claim, having an electrical alarm circuit in which the switch means (8;33;50) is included, and in which the chassis (1) is mounted in a substantially vertical plane.
10. An alarm system incorporating two switches as claimed in any one of claims 1 to 8, and having an electrical alarm circuit in which the switch means (8;33;50) are included, and in which the two chassis (1) are mounted in substan¬ tially vertical planes at right angles to each other.
Description:
SWITCH

THE FIELD OF THE INVENTION

The present invention relates to an electrical switch adapted to change state on mechanical disturbance thereof. THE BACKGROUND OF THE INVENTION

Switches have been proposed, for example in US-A3,701,093, in which tilt is indicated by the displacement of a pool of mercury held in a dish with a central electrical contact and secondary and tertiary contacts around the central contact and outside the pool in the level position. Such switches suffer from the disadvantage that they are very sensitive and must have a horizontal level position to avoid spillage of the mercury. Switches incorporating pendulum members, such as disclosed in US-A-3,761,653, employ contacts carried by these pendulum members, so that electrical connections to the contacts on such members introduce complication and expense. GB-A-1,406,314 discloses apparatus in which a magnet in the shape of a roller is movable in an inverted semi-circular trough mounted on a tractor. Pairs of magnetic reed proxi¬ mity switches are arranged near the ends of the trough, so that if the tractor tilts too much, first one and then the other of the pair are closed to operate successive alarm signals. The arrangement is somewhat complicated and the reed switches require careful adjustment to be at the correct positions in relation to the rest position of the magnet roller. There is a suggestion that the switches could be operated by a pendulum sensitive to the angle of tilt of the apparatus, but no details are given.

US-A-3,882,453 discloses a movement sensitive alarm system in which an enclosure is adjusted to be level and to hold an elongate conductive freely movable pendular member vertical in a non-conductive support in a conductive cylindrical

housing. Engagement of the pendular member with the housing following disturbance of the enclosure results in the completion of an electrical circuit to initiate an alarm. The arrangement is very sensitive to the starting disposi- tion of the parts which must be vertical to avoid the alarm sounding falsely. Further, the pendular member itself carries current, so complicating the electrical connections.

US-A-3,963,888 discloses a tilt switch in which a cylindrical casing has a platform near the upper end, through which extends a rod carried on a disc engaging the platform. The rod has a weight at its lower end in a quantity of damping fluid in the casing. Above the centre of the disc is a contact electrical switch. When the weight swings as the casing is tilted, the disc is tilted by the rod and disc, rod and weight tilt about an edge of the disc on the platform. The upper end of the rod is lifted and contacts the switch to operate it. The arrangement is complicated and limited in its application. THE INVENTION The object of the present invention is to provide a mechanical disturbance detection switch with simple elec¬ trical connections.

An electrical switch according to the invention com¬ prises a chassis and a pendulum member adapted to cause actuation of switch means upon mechanical disturbance of the switch, characterised in that the pendulum member is pivotally mounted on the chassis for rotation about a pivot axis, in that the pendulum member carries a plurality of switch actuating elements disposed circularly, or part-circularly, about the pivot axis for movement in a circular, or part- circular, path together with the pendulum member about the pivot axis, and in that the switch means is mounted on the chassis adjacent the circular, or part-circular, path and is adapted to be switched on and off repeatedly as the elements successively pass the switch means.

The invention enables the chassis to be mounted in different positions or attitudes without the necessity of manual resetting of the switch, because the switch means can be actuated by any one of the plurality of switch actuating elements. This is of particular advantage, and for this purpose it is preferred that the elements be provided around a considerable circular arc on the pendulum member. The best results are achieved if the elements are spaced around the whole periphery of the pendulum member, and preferably the elements are equally spaced so that automatic resetting of the switch occurs even if the switch takes up a different mechanical orientation after the first disturbance.

In the preferred embodiments, the switch actuating elements are permanent magnets carried by the pendulum member. In such case, the preferred form of switch means is a reed switch, in which at least one of the contacts is of magnetic material and is movable upon the passage in prox¬ imity thereto of a magnet into or out of contact with another contact. An advantage of this arrangement is that it is sens¬ itive to mechanical disturbance only above a certain thresh¬ old, because of the attraction between the magnetic contact and the magnet nearest it. However, when the mechanical disturbance of the chassis and switch, by way of angular displacement about the pivot axis or acceleration transverse to the plane defined by the centre of gravity and the pivot axis, exceeds a threshold, the attraction is broken and the movable contact of the reed switch moves, making or breaking contact with the fixed contact. Whilst the magnets could be of solid metal, the pre¬ ferred material is of the so-called "ceramic magnet" type. It will be appreciated that the response of the switch

is greatest to disturbances about the pivot axis and that if the switch, or a body to which it is secured, is tilted about an axis at right angles to the pivot axis, the switch may not react. Accordingly, two such switches may be mounted on the body at right angles to each other. It is even possible to envisage the use of three switches ortho¬ gonal to each other.

The pendulum is preferably cylindrical, having an eccentric weight, conveniently of non-magnetic material. However, where the switch is to be used in applications in which only limited movement is possible, it may be preferred to use a semi-cylindrical or other frustro-cylindrical pendulum member.

Although it is envisaged that the switch means may be a solid state device, such as a Hall effect device, it pre¬ ferably incorporates conventional switch contacts.

In an alternative embodiment, the magnets are replaced by steel or other magnetic, metallic elements and the movable switch contact is magnetised or connected to a magnet. When an element is adjacent the movable contact, or its magnet, magnetic attraction to the element moves the contact towards the element. The element resiliently returns when a space between two elements is adjacent the contact. Again it is envisaged that the magnets could be repla¬ ced by successive cam lobes provided around the circular path of these actuating elements, with a follower being provided for mechanically actuating a conventional switch.

Alternatively the switch actuating elements can be a plurality of metallic contact areas with which a pair of switch contacts together selectively make or break contact.

To help understanding of the invention, various spec¬ ific embodiments thereof will now be described by way of example and with reference to the accompanying drawings in which:-

THE DRAWINGS

Figure 1 is a front view of a switch according to the invention;

Figure 2 is a side view of the switch of Figure 1; Figure 3 is a view similar to Figure 1 of a variant; Figure 4 is a view similar to Figure 1 of another embodiment;

Figure 5 is a view similar to Figure 1 of a third embodiment; and Figure 6 is a side view of the switch of Figure 5.

Referring first to Figure 1, the switch there shown has a chassis plate 1 from which fixedly extends at right angles a shaft 2. On the shaft is freely mounted a plastics material disc 3 which is spaced from the plate 1 by a washer 4 and retained on the shaft by a clip 5. The shaft 2 provides a pivot for the disc 3 to rotate about a pivot axis. The disc 3 has a series, fourteen as shown, of ceramic magnets 6 set into its circumference. The magnets 6 are equally spaced around the entire periphery of the disc 3. In one sector, the disc is weighted eccentrically by a weight 7 of non-magnetic heavy material, suitably lead. Thus the disc constitutes a pendulum member pivotally mounted on the chassis for rotation about the pivot axis.

Mounted on the chassis plate 1, which is of non-magnetic plastics sheet, is a reed switch 8, secured by passing its two leads 9 through apertures in the plate 1. The reed switch is positioned close to the circumference of the disc 3 with a movable one 10 of its contacts movable radially of the disc into and out of contact with a fixed one 11 of its contacts. The movable contact 10 is of ferro-magnetic material.

When one of the magnets 6 is close to the reed switch 8, i.e. the disc 3 is in such a rotary position that one of the magnets is directly opposite the reed switch 8, the

movable contact 10 is attracted towards the disc 3 out of contact with the fixed contact 11. On relative rotation between the disc 3 and the chassis plate 1, as might occur on rotation of the chassis plate if fixed to a body in an alarm, the nearest magnet 6 is moved away from the reed switch, allowing the movable contact 10 to move resiliently back into contact with the fixed contact 11. On further rotation, the next magnet causes the contacts to break again, and so on round the circumference of the disc. Thus the magnets constitute switch actuating elements which operate to switch the reed switch on and off repeatedly as they successively pass the reed switch in a circular path round the pivot axis.

The reed switch could of course be re-arranged to make contact when the magnet is close to it and to break contact in between magnets. Because of the attraction of the movable contacts 10 by the operative magnet 6, very small disturbances will not move the disc with respect to the chassis plate 1. However, as soon as the disturbance is large enough to break the magnet/contact attraction, the switch changes condition from break to make or vice versa. Thus adjustment of sensitivity is so intimately associated with switching that sureness of operation is not compromised in adjusting the sensitivity of the switch. The best arrangement of the switch on a body, whose disturbance is to be detected by the switch and a circuit connected thereto, is with the shaft 2 horizontal in the usual position of the body. This is because with the shaft vertical the pendulum effect of the eccentric weight is minimised and the disc will hardly react to disturbance of the body which does not tilt the shaft 2. With a switch secured to a body with its shaft or pivot axis horizontal, there remains a problem if the body is moved along the direction of the longitudinal axis of the shaft. To overcome this, a second similar switch may be secured to the body

with its shaft horizontal at right angles to that of the first switch. It will be appreciated that the device is operative, no matter what orientation the chassis plate has within the substantially vertical plane thereof. In the variant of Figure 3, the switch actuating elements are provided in the form of teeth. Ceramic magnets 6 are set in the plastics material disc 3 and subsequently machined away to tooth shape whereby the magnets are kept discrete without risk of interfering with each other. Thus a higher density of magnets is possible around the circum¬ ference of the disc. In practice, it is found that a spacing of nearly 10mm between centres of the teeth magnets is the optimum. With a 60mm outside diameter disc this permits the provision of twenty magnets 6 . Figure 4 shows a second embodiment in which a disc 23 with an eccentric pendulum weight 27 is mounted on a suit¬ able bearing shaft 22, and has a scalloped periphery present¬ ing a series of cam lobes 30. On these a cam follower wheel 31 on an arm 32 of a microswitch 33 bears. When the wheel 31 is resiliently urged into a trough between two cam lobes, the microswitch is in one of its ON/OFF conditions. When the wheel is on one of the lobes, following rotation of the disc 23, the microswitch will be in the other of its OFF/ON conditions. Figures 5 and 6 show a third embodiment in which metallic strips 46, for example of copper or brass, are embedded in the periphery of a non-conducting disc 43, with an eccentric pendulum weight 47 insulated from the metallic strips and a shaft 42. A pair of contacts 50 bear at their adjacent ends 51 on the periphery of the disc, being either mutually in contact with one of the metallic strips or not according to the position of the disc 43. The contacts are pivoted and spring biassed towards the disc.

The above switches of the invention can be used with conventional alarm circuitry for switching on an alarm in

the event of disturbance of a body to which the switch is secured. As described above, the switches are best mounted with the pivot axis horizontal and two (or more) switches may be secured to the body in different orientations with advantage.

Within the scope of the appended claims, various modifications may be made to the embodiments which are described herein by way of example, and to their methods of construction. Thus, for example, the pivot shaft need not be secured in the chassis plate but may be mounted in the disc or pendulum member itself. In this case, it may be advantageous to mount the shaft for rotation in a rect¬ angular frame disposed diametrically of the disc and secured to the chassis plate. In the case of the variant of Figure 3, the ceramic magnets may be formed as a single cast body with projecting poles around the periphery constituting the switch actuating elements.