AIS debuts miniature guidance

David Donald

Wednesday, 9 September, 2009

Atlantic Inertial Systems is launching its latest miniature silicon inertial measurement unit here at DSEi on stand 2233. MinIM packs a six-degrees-offreedom IMU into a unit that measures only 28mm in diameter and 28mm in height. The ‘one-inch’ IMU offers a new level of miniaturisation, allowing customers to widen the applications of precision guidance.

AIS is a supplier of inertial guidance systems and sensors. It has supplied more than five million traditional spinning wheel gyros for a wide range of applications, from tanks to intercontinental ballistic missiles, while more than 15,000 solid-state microelectronic machined systems (MEMS) are in use on various platforms, including the Raytheon Rolling Airframe Missile, Seawolf, APKWS, NLAW and Excalibur. It also produces the TERPROM system, which has been installed in more than 5,000 aircraft.

Building on the success of its MEMS products, AIS is launching MinIM. Weapons and systems designers are looking for ever smaller subsystems, and MinIM gives them the opportunity to provide inertial guidance in much smaller vehicles and projectiles than was previously possible. MinIM is also relatively cheap, and has lower power demands than larger systems. It represents a major step along the road to what many see as the weapon designer’s ‘holy grail’: the guided bullet. Not only do precision-guided weapons greatly reduce the chances of collateral damage, they are also more cost-effective, because fewer rounds are required to achieve the desired effect.

A ‘one-inch’ IMU also has numerous applications outside the weapons world. It weighs less than 50g, and with its low power demands it is ideal for integration into small hand-held UAVs. It has also been mooted as part of a personal navigation system for individual soldiers, and AIS holds a patent in this arena. The integration of a tiny IMU frees such a system from complete dependence on GPS.

The ‘A’ version of MinIM is currently undergoing trials. ‘B’ versions are expected to enter testing before the end of the year, with MinIM ready for production in 2010.

Driven by the demands of the initial customer, MinIM will initially be produced in a low-cost version with lower-spec accelerometers. A higher-spec version has been developed for other applications.

The initial MinIM project concerns an upgrade for standard 155mm artillery ammunition. Rather than throw away unwanted war-stock, the rounds can be updated to become precision-guided weapons at low cost. This is achieved by the replacement of the nose fuze assembly with a new unit housing MinIM inertial guidance, GPS and an actuation system. Only MinIM is tiny enough to fit into the small conical nose section.

Development work of MinIM continues, with an important stage being the integration of GPS to form a combined unit. AIS is also examining ways of increasing the performance. One of the disadvantages of very small IMUs is that they experience greater drift rates than larger systems. However, many of MinIM’s applications are for short-duration systems, where long-term drift is of little concern.

MEMS for Excalibur
AIS’s current main MEMS product is the gun-hard SiIMU02. Roughly three inches in diameter and weighing about 300g, it is used in the A-Darter air-to-air missile, APKWS, Roketsan guided missile and Excalibur. The latter is a Raytheon-led guided artillery round, which has undergone nine trial firings to date. Thanks in part to the SiIMU02, all tests have been successful and the system is ready for deployment.

Last month, AIS began high-rate production of the SiIMU02 for the Excalibur programme, which is running at 200 units a month. The 1,000th unit was produced during the first high-rate batch. The system has been shortlisted for the 2009 British Engineering Excellence Awards in the new products (electrical) category.

An AIS technician checks a MinIM inertial measurement unit. Inside the tiny package are three angular rate sensors and three linear accelerometers