MARKING DEVICE

A Minefield Marking Device

Project Driver:

Current manual land mine detection techniques require that deminers slowly scan the ground to detect buried the presence of buried metals that may turn out to be mines. When they detect a positive signal they are expected to visually identify the location, turn around and place the metal detector on the ground, turn back, place a physical marker on the suspected mine, turn around, pick up the metal detector and scan the spot again to verify the location. If they have made a mistake, they repeat the process and correct the position of the marker. The process is iterative, slow and tedious. It also introduces significant risks for mistakes as it depends on the deminers memory.

Our objective was to construct a simple, cheap, lightweight device that can be mounted on the coil of a metal detector to allow a deminer to mark the ground without taking there eyesight off the suspect location. The development of such an aid would greatly improve the productivity and reduce the chances of error.

Three methods were investigated;

Powder Marker Concept

Development:

Early on it was decided that a system that used a powder as the marking agent would be best. This is because flour, talcum powder and other suitable powders are cheap and readily available.

Many designs were tried before a successful one was found. The main problem was due to the way the powders would build up and clog the delivery system or clump together and create a clear area around the exit hole (fig 1.). The earlier report Minefield Marking Devices Development covers these rejected designs.

The Design:

The eventual design (fig 2.) involved a fluidising bed of air to stir up the powder and pass it through the delivery tube easily. The burst of air is supplied from a simple puffer bulb with a non-return valve. The aeration of the powder stops clumps and holes forming in the powder and allows it to flow easily.

The cloth spreads the air over a large area so that it actually aerates the powder. Without the cloth, the air injected into the container tends to blast gaps through the powder and doesnít have a fluidising effect.

The position of the exit hole for the powder effects the amount of powder ejected, how long the powder reservoir lasts and the propensity for it to clog. The size of the hole has a similar effect on the performance. Experimentation determined that the exit hole works well with a 2.5mm diameter. This hole is placed approximately a centimetre above the cap. This varies depending on the size of the bottle used.

Two mounting variations can be applied to the device. The first method mounts it on the detector head of the metal detector (fig. 3), the second variation mounts the device on the metal detector handle (fig. 4) and carries powder to the detector head through a tube. In both variations bottle must be mounted close to a vertical position to give the best performance.

Part of the requirements was that the marker be cheap and simple. To this end everything in the marker is cheap and easily available. The plastic bottles are common oil sample bottles or similar. A hole is cut in the top and a rubber bung used to seal it, this is where the bottle is filled from. The cloth is any fabric with a weave fine enough to stop the powder falling back through. It is pushed partially into the neck of the bottle to form a bubble of cloth and held in place with the screw-on cap.

The cap has a hole drilled into it to form a friction fit with the plastic tubing that carries the air to the reservoir. PVC tubing with an internal diameter of 1.7 mm was used. Tubing with a similar internal diameter can be attached to the exit hole to carry the powder away. A length of 80cm with an internal diameter of 1.7mm was tested and this worked very effectively.

The rubber bulb must be fitted with a non-return valve. A battery hydrometer bulb works well when it is fitted with a simple non-return valve using a flap of thin rubber such as a car tyre inner tube (fig. 5).

The design was found to work well with flour, talcum powder and cement powder. Lime powder doesnít work as it clogs too much.

Cost estimates:

These are not available at the present time, but the final cost is expected to be below A$5 per unit for materials

Prototype:

Prototype powder marker fitted to metal detector, mark on cut grass is quite visible. (full size picture)

Powder marker in use (left); Powder mark on long grass is still visible, but vulnerable to wind movements (right)

Further Work:

Some parties have indicated that they are more interested in a system that uses a liquid marking medium. So other devices that use paint or a paste of a powder and water will be looked at.

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