GB2228828A - Inertia sensor - Google Patents

Abstract

An inertia sensor comprises two individual sensors 13 each of which has a poor response to accelerations in a given direction or directions. The sensors 13 are arranged so that a direction of poor sensitivity of one sensor is different from that of the other. When the assembly is subjected to acceleration in a direction to which one sensor has poor sensitivity, the other sensor will respond with greater sensitivity and its output can then be used as an output of the assembly. Each sensor 13 is held in a rest position by a magnet 14 and bridges two contacts 11, 12 when a sufficient acceleration is applied. <IMAGE>

Description

INERTIA SENSOR This Invention relates to an inertia sensor.

One form of inertia sensor is disclosed in WO 84io3585. It has an inertia boay locatea in a chamber. The cnamber provides a rest position or the boay to whicn it is biassea by gravity or other means ano from which it can move under the influence of an imposed acceleration. The chamber is also proviaed with contacts which can be bridged in either the rest position or in positions spaced from the rest position to make or wreak an electrical contact.The sensor or i(J 84/03585 has a chamber with an inverted conical base with a vertical axis, forming the rest position for the spherical inertia Dody at the bottom of the inverlea cone. The inertia bocy is of magnetic material ano is biased to its rest position ny a magnet located beiow the apex of the cone. An upper electrode is provided above the cone at the top of the chamber. the two electrodes being bridged by a conductive surface of the inertia body when it rises up the cone of the chamber.This type of sensor could be modified to be normally closed, in which case the contacts to be bridged by the body in its rest position are arranged around the ring contact of the body in its rest position with the lower electrode. The sensor is sensitive to accelerations above a given threshoid outside the cone of no response which is the cone subtended at the centre of the body by the ring contact of the body with the conical base, the body moving up the side of the cone. It is not sensitive to accelerations within the cone of no response since it is simply pressed by such accelerations more firmly into its rest position.

The present invention is intended to extend the sensitivity of a sensor which has a poor response to accelerations in a given direction or directions. It provides an inertia sensor assembly comprising two such sensors arranged in different orientations such that a direction of poor sensitivity of one sensor is different from those of the other. Unless a sensor has poor sensitivity in opposed directions, a convenient arrangement is to have the two sensors in opposed orientation.

Some components may be shared between sensors making up the assembly. For a normally open switch, the contacts of the two sensors are arranged in parallel; when it is normally closed, they would be arranged in series. More than two such sensors can be included in the assembly, if required.

Examples of the invention will now be described with reference to the accompanying drawings in which: Figure l is a diagram of a first embodiment in one orientation, Figure 2 is a diagram of the same embodiment in another orientation, Figure 3 is a diagram of a second embodiment, and Figure 4 is a central section through a sensor similar to that of Figures 1 and 2.

In each of the embodiments the basic sensor comprises a conical first electrode 11, a plane second electrode 12 spaced from the first electrode and arranged transversely to the axis of the cone, a conductive ball 13 of magnetic material such as steei and a magnet 14 arranged below the apex of the cone.

The ball 13 is biassed into its rest position at the apex of the cone by the magnet 14. When a sufficient acceleration outside the cone of no response is applied to the ball, it breaks free from its rest position and moves to one edge of the conical electrode where it bridges the two electrodes ii and 12, making the electrical switch of the sensor.

Each embodiment comprises two such sensors arranged in opposition that is the cone of no response of one sensor is directed opposite to the cone of the other sensor. Thus above a riven threshold, it one sensor does not respond ~ to the ecceleranlon applied, the other one will respond. By arranging normally open switch sensors in parallel or normally closes switch sensors in series, the combined sensor will have improvea response to accelerations in any direction.

in Figures l ana 2 the sensors have a single magnet 14 biassing botch balls 13A and 13B to their rest postition. The conical electrodes are joined to 8 first terminal 21 and the plane electrodes are joined to a second terminal 22. so that the switches of the two sensors are arranges in parallel.

In Figure 1 the applied acceleration indicates by the arrow is at right angles to the line 23 joining the two sensors and gravity acts along that line. Both sensors will in due course respond to the acceleration as it increases but the lower seror responds first since the combined effect of gravity and the applied acceleration has a greater component opposing the puil of the central magnet. The lower ball 13B is shown deflected from its rest position and bridging the electrodes 11 and 12.

In Figure 2 the applied acceleration lies along the line 23 joining the sensors and gravity acts at rignt angles to that line. Sensor A does not respond at all to the applied acceleration since it is within its cone of non-response, but ball 13B is pulled away from the magnet 14 as the applied acceleration increases and gravity pulls the ball down to the lower rim of the sensor where it bridges the two electrodes 11 and 12.

In Figure 3 the sensors are arranged with their plane electrodes 12 immediately adjacent. This has the advantage that although separate plane electrodes are illustrated, one plane electrode can be used for both sensors, but it has the oisaavantage that separate magnets 124 are required for the two sensors.

The sensors.illustrated have the advantage that they will respond to an accelerations irrespective of their orientation and so it is not necessary to specify closely how they are to be mounted and they will operate even if an acceleration is encountered in an unexpected direction. The economies of scale in sharing a magnet 14 or a plane electrode 12 is another advantage.

Figure 4 shows a prototype of the sensor of Figures 1 and 2.

A central plastics body 31 has a central passage 32, within the centre of which is mounted the magnet 14. Shims 33 separate the magnet 14 from the bases of the conical electrodes 11 and the diameter of the passage varies to locate the magnet and the shims centrally. The conical electrodes extend on one side of the body to form terminals 34.

nsulating columns or a single insulating ring 35 separate(sj each conical electrode 11 from its associated plane electrode 12, which is also extended at one side to form the corresponding terminal 36. The whole assembly is secured together by pins 37 extending through the whole height of the assembly at each of the four corners. The pins should be insulating or at least insulated from either of the sets of electrodes.

Claims (4)

CLAIMS:

1. An inertia sensor comprising two sensors, each of which has a poor response to accelerations in a given direction or directions, the said two sensors being arranged in different orientations such that a direction of pocr sensitivity of one sensor is different from those of the other

2. A sensor assembly as claimed in Claim 1 wherein said two sensors are arranged with opposed orientation.

3. A sensor assembly as claimed in Claim 1 or Claim 2 wherein some components are shared between said sensors making up the assembly.

4. A sensor assembly substantially as hereinbefore described with reference to the accompanying drawings.