GB2165928A - Mine simulator - Google Patents

Abstract

A pressure mine simulator comprises a body 10 with a base plate 11, and a top plate 12. The body and the top plate bear respective contact rings 24 and 23, and are separated by a ring 25 of crushable material. The body includes an explosive element, a battery, and a printed circuit board 21 bearing a firing circuit. Withdrawal of an arming key 30 connects the battery to the firing circuit, and pressure on the top plate 12 then crushes part of the ring 25, closes the contact 23-24, and fires the device. The firing is initiated by a very short (microseconds) closure of the contacts 23-24, and is not affected by physical damage to the top plate or the outer parts of the body immediately following such actuation. The device can therefore be of light construction yet respond correctly to heavy impact from mine clearance machinery. <IMAGE>

Description

SPECIFICATION Explosive mines The present invention relates to mines, and more particularly to mine simulators.

A pressure mine is an explosive device normally placed on or a little beneath the surface of the soil. There is a need for a mine simulator, which is a mine-like device which is intended for use in training, e.g. in the use of mine-clearing apparatus. Such a mine simulator can consist essentially of a normal mine, with a reduced charge in it so that it cannot do serious harm. However, although a mine simulator needs to match some of the characteristics of a real mine closely, there are other characteristics which need not match closely, and where in fact it is desirable for it to differ from a real mine.

The present invention is primarily concerned with such mine simulators.

Accordingly the present invention provides a mine simulator comprising a substantially circular body and top plate, the body including a battery, an explosive element, and a firing circuit, and the body and top plate being held apart by a ring of crushable material and having matching conductive annuluses forming a pair of contacts which complete the firing circuit. This mine simulator is of relatively light and simple construction. The firing circuit preferably includes a trigger circuit which is responsive to a very short pulse from a sensing mechanism to produce a detonating pulse of sufficient length and strength to fire a detonator. The device will therefore respond correctly to a firing force, e.g. the force of being struck by a flail of mine-clearing device, even though the device may suffer significant structural damage from the firing force.The sensing mechanism need only withstand the firing force for long enough to trigger the trigger circuit, i.e. for a matter of microseconds.

Once the trigger circuit has been triggered, physical damage to the sensing mechanism will not matter; the device need only be sufficiently robust to retain its structural integrity to the extent necessary for the trigger circuit to fire the detonator and the detonator to fire the main explosive charge.

An embodiment of the invention will now be described, by way of example, with reference to the drawings, in which: Figure 1 is a vertical section through the device; Figure 2 is a view of the device from underneath, with the base plate removed, and showing the section line I-I of Figure 1; Figure 3 shows the circuit of the device; and Figure 4 is a partial section along the line IV-IV.

Refering to Figure 1, the device has three major elements, a body 10, a base plate 11, and a top plate 12, which are preferably formed of reinforced plastics material. As seen in Figure 2, the body 10 is generally in the form of an inverted dish with steep sides and a wide rim turned back at its edge, and its main cavity is divided into three portions 13, 14, and 15. Cavity 13 contains the explosive charge 20, which has a detonator (not shown) inserted into it. Cavity 14 contains the bulk of the circuitry, mounted on a printed circuit board 21. Cavity 15 contains a battery of cells (not shown) which energize the circuitry. Access to the cavities is from beneath; the cavities are closed by means of the base plate 11.The base plate 11 may include a smaller removable plate (not shown) allowing access to the battery cavity 15 so that the cells can be inserted just before the device is to be used.

The top plate 12, as seen in Figure 1, is generally in the form of a flat disc, with two circular flanges 26 and 26'. A conductive an nulus 23 is attached to the plate 12 immediately inside the flange 26', and a second conductive annulus 24 is attached to the outer part of the top surface of the body 10. An annulus 25 of compressive membrane, such as foamed polyurethane, is mounted between the top plate 12 and the body 10 inwards of the annuluses 23 and 24. Connections are made to the two annuluses 23 and 24 by means of wires passing through a hole 27 in the top of the body 10 in the cavity 14, as shown.

Figure 3 shows the circuit of the device.

The battery 22 is normally isolated from the rest of the circuit by means of a safety switch SW1A, SW1B, described later. When this switch is closed, the two annuluses 23 and 24 form the sensing mechanism. A downwards force on the top plate 12 of the device sufficient to crush the membrane 25 will cause the two annuluses 23 and 24 to touch, thereby providing a positive voltage through a resistor R1 to the trigger of an SCR SCR1, firing it. (A resistor R2 normally ensures that SCR1 is off.) This positive voltage need only last for about 2 s to trigger the SCR. Once the SCR is triggered, a large current flows through the detonator DT, firing it and thereby the main charge 20. This firing will therefore occur even if the top plate 12 is cracked or broken by the firing force, resulting in only momentary contact between the two annuluses 23 and 24.

Figure 1 shows the arming key 30 in position in the device. This key comprises a tongue which enters the cavity 14 and a head which projects from the device. The printed circuit board 21 carries bent spring pieces 31 which form the moving contacts of the switch SW1A and SW1B. The key 30 is of insulating material, and when in position, holds these spring pieces 31 away from each other, keeping the switch open. The key 30 has shoul ders which abut against the body 10, the key 30 passing through a hole in that body. At its inner end, the key 30 has an enlarged head cooperating with inward-pointing angles of the springs 31 fit, so helping to locate and retain the key.

To arm the device, the key 30 is removed, so closing the switch SW1A and SWIB. The device will then explode in response to a sufficient pressure on the top plate 12. The firing pressure is preferably set, by means of a suitable choice of the compressive membrane 25, to a value greater than that which can be achieved manually.

The battery cavity portion 15 has fins formed in the body 10 to provide three zones 22-1, 22-2, and 22-3 to accommodate respective cells forming the battery. The zone 22-3 is shown in more detail in the part sectional view of Figure 4. For normal temperature ranges, only two cells are required for the battery. Accordingly zone 22-3 has a projecting contact 43 at one end, mounted on a fin 41, and has an extended contact 42 at the other end, mounted on a fin 40. These two contacts 42 and 43 normally touch with each other, as shown, so that a circuit from the battery is completed when there are only two cells inserted, in zones 22-1 and 22-2. But for extremely low temperatures, a third cell is needed.This third cell is inserted in zone 223, and its insertion automatically forces the free end of contact 42 flat and the free end of contact 43 against the fin 41, so breaking the contact between them and becoming inserted in series with the other two cells.

Most of the wiring of the device is in fact formed by means of flexible conductive strips, since connections to these can be made by means of press-stud connectors, so avoiding the need for soldering in proximity to the explosive 20.

It is intended that the device should normally be stored without the battery, with the battery being fitted shortly before use. Obviously the user would also make sure that the key 30 was in place, removing the key only when putting the device in position on the ground. The device is designed with a considerable gap between the two contact annuluses 23 and 24 and a high force requirement to crush the annulus 25, so it is very unlikely that false triggering could occur. As a further safety feature, however, distinctively coloured discs 28 (e.g. in fluorescent colour) can be fitted around the outer body 10 as shown, bridging the gap between the body and top plate. The user will then be able to check at a glance that the discs 28 are not damaged.

Coloured discs in a damaged condition indicate actuation of the annular switch which failed to bring about firing of the device. This constitutes a misfire situation and must be dealt with accordingly.

Claims (7)

1. A mine simulator comprising a substantially circular body and top plate, the body including a battery, an explosive element, and a firing circuit, and the body and top plate being held apart by a ring of crushable material and having matching conductive annuluses forming a pair of contacts which complete the firing circuit.

2. A mine simulator according to claim 1 wherein the body and top plate have corresponding outer flanges separated by a gap, and safety discs are attached to the matching flanges around the mine and bridging the gap.

3. A mine simulator according to either previous claim including an arming key which projects from the side of the mine and, when withdrawn from the mine, connects the battery to the firing circuit.

4. A mine simulator according to any previous claim including means for accommodating a variable number of electrical cells.

5. A mine simulator according to any previous claim wherein the body has a removable base plate.

6. A mine simulator according to any previous claim wherein the firing circuit includes a trigger circuit.

7. A mine simulator substantially as herein described and illustrated.