Hold the batteries! Benet Labs engineers awarded "round counter" patent
September 21, 2010
- A team of engineers from Benet Labs received a patent in May for a battery-less round counter
- The round counter is powered by piezo ceramic technology
- The project was one of eight ARDEC technologies to win a 2009 Army Research & Development Achievement Award
With each round fired from a mortar or a gun tube, the weapon inches closer to its demise.
When each round is fired, damage accumulates in the tube. Reach a certain threshold and the tube may fail. "It could be catastrophic," said Mark Johnson, electronics engineer with the Benet Laboratories, Armament Technologies Division at the Watervliet Arsenal in N.Y.
To avoid gun-tube failures that could harm U.S. warfighters, the Army performs fatigue tests before fielding the guns and mortars. The goal is to determine the service life of a weapon so it can be retired from service before it can endanger troops. This is often accomplished by counting rounds fired from the gun tube.
As a result, U.S. service members have used paper cards since the 1950s to keep track of how many rounds are fired from gun tubes, according to Andrew Littlefield, a mechanical engineer who works at the same division of the U.S. Army Armaments Research and Development Center. The problem: "They sometimes lose the cards," he said.
When that happens, experts must carefully examine the tube for clues like visible erosion to estimate its remaining life. "We've had to send guys to Iraq to determine how much life is left in them because they didn't have the record cards, and we didn't know how much life was left in the tube," said Littlefield.
In the summer of 2005, Johnson joined Littlefield, an engineer with a doctorate in piezo-ceramics and who had been experimenting with his specialty as a means to control gun barrels.
"Piezos" as Littlefield refers to them, are materials that change shape when electricity is applied to them. Conversely, when pressure is applied to piezos, they discharge electricity.
It's the same physical property whereupon a piezo crystal needle applied to a spinning vinyl record generates a small current, which is amplified and enjoyed as music - should you recall from history class how the relatively recent "ancients" listened to their tunes before iPods and DVD players.
The two engineers sketched out a rough idea: attach a piezo to a barrel and capture enough of a charge from the weapon-firing to power an electronic counter. "We had a rough idea how much energy would be available from the piezo and a rough idea how much energy would be required by the electronics. We thought there was a good chance it would work, and it was worth pursuing," said Johnson.
It was an idea worthy of a patent: U.S. Patent Number 7,716,863 B1, to be exact, which was awarded in the name of the two engineers May 18, 2010.
Having obtained support for their in-house proposal and a provisional patent in February of 2006, Johnson began working with physicist Mark Doxbeck when Littlefield got assigned to another project.
"We wouldn't be as close to where we are now without Mark Doxbeck," said Johnson. The team developed models of the piezo, electronics, and hardware before designing the counter. They collected firing data at Aberdeen Proving Ground, Md. (APG), and used this information to develop a prototype.
At APG, tens of thousands of shots were simulated before the prototype was optimized. The tests of the prototype were a complete success, according to Johnson.
The support they received from the U.S. Army Project Manager for Mortars allowed the effort to continue, said Deborah Bleau, Branch Chief of Advanced Technologies at Benet.
Although the piezo generates only about 0.0003 percent of the energy that a 100 watt light bulb uses in one second, that is enough to store the round count in what is known as "non-volatile memory."
Data stored in this type of memory is retained for up to 40 years without power, according to Johnson. Everything is housed in a small enclosure mounted on the trigger clamp of the mortar, where it is out of the way and barely visible.
Having solved the technological challenges of obtaining enough power from the piezo during discharge to activate the counter, the remaining significant challenge for the Benet Labs team is to continue to improve the ability of the device's electronics to survive the high-heat environment of a mortar tube.
"Without temperature, we could use pretty much off-the-shelf stuff, said Littlefield. "It's getting it to survive in a relevant environment that's the hurdle."
The Benet Labs team plans to continue to improve the device for the 60 mm mortar, but it has also been contacted to develop a similar system for other guns, according to Johnson.
Team members are working with U.S. Special Operations Command to develop a device for the Multi-role Antiarmour Antipersonnel Weapon System shoulder-fired weapon. The U.S. Army Project Manager Heavy Brigade Combat Team has expressed interest in a device for the new XM360E1.
"The basic design will be the same, but the parameters will be different for each gun system," said Johnson. "We are using the modeling and simulation tools that were developed for the 60 mm mortar to greatly accelerate the process."
Johnson and Doxbeck were also named Aug. 24 as <a href="http://www.army.mil/-news/2010/09/01/44576-picatinny-benet-labs-engineers-recognized-by-the-army-for-scientific-advances/index.html" target="_blank">recipients of the 2009 Army Research and Development Achievement Award</a> in a memorandum by the Deputy Assistant Secretary of the Army (Research and Technology), Marilyn Miller Freeman for the work on the energy harvesting round counter.