MARKING DEVICES

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;

1. Powder marker
2. Plastic disc marker (developed separately in Pakistan and not discussed here)
3. Liquid Marker

Designs:

Flour was decided on as the first marking medium, being cheap, readily available and it marks the ground well. Alternative mediums of talcum powder, quicklime and graphite/flour mixes were tried with varied success.

The designs below are listed from the most successful to the least successful.

1. 
   

   The most successful design that used a bottle to deliver a powder involved increasing the air pressure inside the bottle to push a fine powder out a small hole (or holes) in the base (fig. 1). A tube can deliver air from a squeeze bulb on the metal detector´s handle to push out the powder, or the bottle can be physically squeezed.

   The powder tends to stop coming out after five or six bursts. This is due to the powder not settling after the burst and leaving clear areas above the holes. Shaking or tapping the bottle settles the powder and fixes the problem - though this could be difficult because the powder container has to be mounted on the coil of the metal detector.

   
   
2. 
   

   The first design that was trialled is a reservoir of flour sitting above a pipe running perpendicularly to the opening (fig. 2). The principle is that when air is blown through the pipe it will push the flour out to mark the ground. The difference in pressure created by the Venturi effect should ensure that the flour falls into the tube ready for the next blast of air.

   In practise the flour clogs in the opening of the bottle and the device won´t work consistently. Combinations of flour and graphite were trialled, though these met with little success. Talcum powder did not clog as often and proved reasonably successful for the device.

   
   

3. The third design involved a piston that collects flour then drops it when it is pushed through the opening (fig. 3). The fine powders: quicklime, flour and talcum powder; did not fall onto the piston when it was pulled back into the bottle. Sand grains were too large and jammed the piston when it was pulled up. A larger gap was placed between the neck of the bottle and the piston to stop the sand jamming the piston. This gap allowed the sand to continuously fall through.

   
   

4. The design in figure 4 shows a cylinder with an angle cut out. As the cylinder rotates the powder is collected in the hole, then dropped out when the cylinder has turned, 180 degrees. This idea wasn´t trialled because it was assumed that since the powder clogs the neck of the bottle in normal circumstances, having the cylinder there would only make the problem worse.

   
   
   

5. A method using a salt shaker type delivery for the powder and another that uses a slurry of powder and water are being explored.

   
   

6. A paint delivery system has also been trialled (fig. 5). An ordinary manual spray bottle was found to work the best. The spray bottle is attached to a plastic tube leading to the metal detector coil. The system was successful, however the high cost of the paint in developing countries counts against any paint-based systems.

   
   

7. Commercial compressed gas propelled spray paint was tested. The spray can was attached to a tube stretching to the metal detector head. With a commercial can of spray paint, the paint only arrives at the end of the tube a second after the trigger is released. This makes it a little inconvenient for marking a path, however it still would be useful for marking suspected mines. Again the cost of the paint is a major limiting factor.

Notes:

From the tests it was found that fine powders produced the highest visibility because they could coat the surfaces of odd shapes. Heavier materials such as sand fall through vegetation (especially grass), whereas the fine powders will coat the leaves. This creates a more visible marker.

The powders in order from the most successful to the least successful are:

The Current Prototype

Copyright reserved © 1998 UWA Demining Project
AUTHOR: Brian McLean

| Demining Home Page | James Trevelyan's Home Page | UWA Home page |

For more information on any of these send us E-mail at demining@mech.uwa.edu.au
All graphics by Demining Research Team. Aug 1998.
Webmaster: Edin Tabak