GB2274743A

GB2274743A - Electrical tilt switch

Info

Publication number: GB2274743A
Application number: GB9302011A
Authority: GB
Inventors: James L Weaver; Robert P Romano
Original assignee: ASSEMTECH EUROP Ltd
Current assignee: ASSEMTECH EUROP Ltd
Priority date: 1993-02-02
Filing date: 1993-02-02
Publication date: 1994-08-03
Anticipated expiration: 2013-02-02
Also published as: GB2274743B; GB9302011D0

Abstract

An electrical tilt switch has a body which defines a cavity 11 with a generally dish-shaped base wall 13 and aside wall 12, at least the inner surface of the base wall 13 being electrically conducting. An electrode 16 projects substantially centrally into the cavity but is insulated from the body. A ball 17 with a conducting outer surface is disposed within the cavity 11 and normally interconnects the electrode 16 and the base wall 13. On tilting of the switch, the ball 17 may roll away from the electrode 16 to open the circuit between the base wall 13 and the electrode 16. <IMAGE>

Description

ELECTRICAL TILT SWITCH This invention relates to an electrical tilt switch.

There have been numerous proposals for electrical tilt switches, able either to open or make an electrical circuit, depending upon the angle of inclination of the switch. One common design of tilt switch employs a bead of mercury disposed within a glass phial containing two electrodes in close juxtaposition, whereby appropriate tilting of the phial causes the mercury bead to flow to the location of the electrodes and make simultaneous electrical contact therewith, so closing the circuit between the two electrodes. Conversely, oppositely tilting the phial causes the bead to flow away from the electrodes, so opening the switch.

A mercury switch as described above is sensitive to the direction of tilting of the switch. Moreover, mercury is a highly toxic material and the regulations controlling the use of mercury make the manufacture of such switches relatively expensive. In addition, such switches may be employed only in environments where the risk of breakage of the phial is very small, in order to minimise the likelihood of an unwanted mercury spillage, for example by the end-user of the switch.

It is a principal aim of the present invention to provide a tilt switch which is robust and, at least in preferred embodiments, insensitive to the direction of tilt of the switch, and which does not suffer from the problems associated with the use of mercury.

According to one aspect of the present invention, there is provided an electrical tilt switch comprising: a switch body defining a cavity having a generally dished base wall and a side wall, at least the surface of the base wall being electrically conducting; an electrode projecting substantially centrally within the cavity defined by the body but insulated therefrom; and a ball having a conducting outer surface and disposed within said cavity so as normally to interconnect the electrode to the conducting surface of the base wall of the cavity, but which ball may roll away from said electrode upon tilting of the body beyond some predetermined angle.

Most preferably, the cavity of the switch is of substantially circular cross-sectional shape with the electrode disposed coaxially within that cavity. Such a switch is intended to be mounted with the cavity axis substantially vertically disposed and with the base wall lowermost; the ball then rests on the base wall and bears against the electrode so as to inter-connect the base wall and electrode. On tilting of the switch away from the vertical through a sufficiently great angle, in any direction, will cause the ball to roll away from the electrode, so opening the circuit between the electrode and the conducting surface of the base wall.

The sensitivity of the switch to tilt may be controlled by an appropriate selection of the shape of the base wall of the cavity. The greater the gradient of the base wall in the contact region, when the ball also contacts the electrode, the greater must the switch be tiled in order to cause the ball to roll away from the electrode.

Advantageously, the cavity is defined by a substantially cylindrical side wall upstanding from a base wall the central region of which is axially displaced from the edge region of the base wall, in the direction away from the side wall. The dished base wall may be of a substantially conical form, or of a generally concave form, when viewed from within the cavity, and in the latter case may have a constant or variable radius of curvature.

In a preferred construction of tilt switch of this invention, a cap may be provided for the cavity, in which case the electrode may be mounted on the cap to project downwardly into the cavity, towards the base wall. The cap may fit to the body in an hermeticallysealed manner, whereby the cavity may contain an inert gas so as to minimise corrosion of the ball or the conducting surfaces of the walls defining the cavity.

This may serve to ensure a good electrical contact is obtained between the ball and the electrode and base wall of the cavity, simultaneously, even with prolonged periods of use.

Advantageously, the switch body is made of a corrosion-resistant material, such as stainless steel, or a plated steel. The body may be made in one piece, by a pressing or deep-drawing operation. Equally, the ball preferably comprises a metallic ball of a corrosion resistant metal, such as stainless steel or a plated steel.

By way of example only, one specific embodiment of tilt switch constructed and arranged in accordance with the present invention will now be described in detail, reference being made to the accompanying drawings, in which: Figure 1 is a side view of the embodiment of tilt switch; Figure 2 is a plan view of the switch of Figure 1; and Figure 3 is a vertical section through the tilt switch of Figure 1.

The embodiment of tilt switch shown in the drawings has a plated steel cup-shaped main body 10 formed by a drawing or pressing operation on a steel sheet, which is then plated. The body 10 defines a cavity 11 which has a cylindrical side wall 12 and a conical lower base wall 13. Around the periphery of the side wall 12, there is an outwardly directed flange 14.

A cap 15 formed of an insulating material is sealed to the flange 14 and closes the cavity 11. An electrode 16 is mounted in the cap 15 and projects into the cavity, towards the base wall 13, but does not make electrical contact therewith.

A metallic ball 17, for example of stainless steel or of a plated steel, is disposed within the cavity and, when the switch is disposed in its normal position as illustrated in Figures 1 and 3, makes electrical contact with both the base wall 13 and the electrode 16 so completing an electric circuit therebetween. The cavity may contain an inert gas, to minimise the likelihood of corrosion of the components, within the cavity.

The switch is used by being suitably mounted within apparatus the tilting of which is to be detected. For example, the switch may be held by a clamp surrounding the side wall 12, which clamp is in electrical communication with the body 10 and may serve to connect the body to electrical ground of the apparatus. The normal disposition of the switch when mounted within the apparatus is with its axis vertical, as shown in Figures 1 and 3, and so with the ball 17 completing the circuit between the electrode 16 and the body 10. The electrode 16 is connected externally of the cap -15, to the circuit to be switched by the switch.

When the switch is in its normal position, the conical base wall 13 causes the ball to roll towards the switch axis, until the ball contacts the electrode 16. The contact pressure against the electrode 16 is governed by the conical angle of the base wall 13: the smaller that angle, the better the contact pressure against the electrode.

When the switch has been tilted through more than the conical angle of the conical base wall 13, away from the vertical, the ball will roll away from the electrode 16 towards the side wall 12, so opening the circuit between the electrode and the side wall. It will be appreciated that the direction in which the switch is tilted is not significant, in view of the symmetry of the switch about the vertical axis thereof, containing the electrode 16. The ball will simply roll round the electrode during the initial stage of tilting so that the ball lies on the line of the direction of tilt, whilst still maintaining contact with the electrode and the base wall 13.

The sensitivity of the switch to tilting may be controlled by appropriate selection of the conical angle of the base wall 13. The smaller the conical angle, the more the switch must be tilted in order to open the circuit. Conversely, the greater the conical angle, the smaller is the required tilt to open the circuit.

Two (or even more) similar balls could be disposed in the cavity, to increase the electrical contact reliability. There will then be two parallel conducting paths between the electrode and cavity base wall, but the switch will still operate in essentially the same manner as has been described above.

Claims

1. An electrical tilt switch comprising: a switch body defining a cavity having a generally dish-shaped base wall and a side wall, at least the surface of the base wall being electrically conducting; an electrode projecting substantially centrally within the cavity defined by the body but insulated therefrom; and a ball having a conducting outer surface and disposed within said cavity so as normally to interconnect the electrode to the conducting surface of the base wall of the cavity, but which ball may roll away from said electrode upon tilting of the body beyond some pre-determined angle.

2. A tilt switch as claimed in Claim 1, wherein the cavity is of a substantially circular cross-sectional shape.

3. A tilt switch as claimed in Claim 1 or Claim 2, wherein the cavity is defined by a substantially cylindrical side wall upstanding from a base wall the central region of which is axially displaced from the edge region, in the direction away from the side wall.

4. A tilt switch as claimed in Claim 3, wherein the base wall is of a generally conical form, when viewed from within the cavity.

5. A tilt switch as claimed in Claim 3, wherein the base wall is of a generally concave form, when viewed from within the cavity.

6. A tilt switch as claimed in any of the preceding Claims, wherein a cap is provided for the cavity, and the electrode projects downwardly into the cavity from the cap.

7. A tilt switch as claimed in any of the preceding Claims, wherein the body comprises a unitary structure formed from or coated with a corrosion-resistant metal.

8. A tilt switch as claimed in any of the preceding Claims, wherein said ball comprises a metallic ball of a corrosion-resistant metal.

9. A tilt switch as claimed in any of the preceding Claims, wherein there is located within the cavity at least two similar balls.

10. A tilt switch as claimed in Claim 1 and substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.