North Finding System using Multi-Position Method with a 2-Axis Rotray Table for a Mortar

Abstract

North-finding techniques involve detecting and calculating the azimuth angle, thus determining north using various kinds of sensors. North identification can be accomplished through the use of a digital magnetic compass. However, the accuracy of a magnetic sensor is easily degraded by spatial and temporal distortions due to ferrous material or electromagnetic interference. Moreover, GPS-based north-finding systems (NFSs) can accurately determine the azimuth by two separated GPS antennas. This still has a practical limitation in jamming or indoor environments, however. Therefore, an inertial NFS has been developed to replace the classic equipment used in estimating the fire direction of hand-carried projectile weapons such as with mortars. To improve the precision of seeking north with a middle grade gyro, multi-position method is implemented. Using only a single fiber optic gyroscope and two MEMS accelerometers on a rotary platform, the north orientation is accurately found by observing the horizontal component of the earth's rotation vector. With a minimum number of inertial sensors on a manual rotary platform, the NFS can be compact, light-weight, low-cost, and robust enough for easily portable mortar. Using additional auxiliary information which can be obtained by magnetic sensors, the time for locating north can be dramatically reduced. The test results compared with the navigation grade inertial navigation system show that a single digit mrad heading accuracy can be achieved. The operability of NFS mounted beside a mortar was tested in the field, in which the reference positions were acquired by DGPS (Differential GPS). To insure the durability in gun-fire shock, the drop-tower test was performed based on the shock profile measured in real mortar fire.

Removal of the rate table: MEMS gyrocompass with virtual maytagging

“…GPS-based NFSs are another common orientation technology. With separated GPS antennas, the azimuth information of body can be easily obtained, but they fail in GPS-denied environments (e.g., indoor, jamming, underwater domain) because the satellite signals cannot be received 4 , 5 . The traditional method of using reference celestial bodies (e.g., the sun, Polaris) for orientation continues to this day.…”

Research on Fast Self-alignment Method of SINS under Vehicle Jitter and Leveling Disturbance

“…Usually, in the traditional initial alignment method, the accuracy of the pitch angle/roll angle estimation needs to reach 0.01 degrees, so that the precise positioning filter can work within its linear range [13]. Moreover, the coarse alignment stage requires longer time (usually 30-120s) to suppress the interference of line motion and angular motion, and the coarse alignment result does not have a direct impact on the final alignment accuracy.…”

Performance Enhancement of Consumer-Grade MEMS Sensors through Geometrical Redundancy

“…Consumer-grade MEMS gyros can be affected by a bias instability in the order of 50 degrees per hour or more [ 9 ], while advanced sensors can reach tactical grade levels with a bias instability in the order of 10 −1 degrees per hour [ 10 ]. Tactical grade is defined as the condition when the gyro can measure the Earth rate, i.e., 15 degrees per hour; this term allows for performing autonomous initialization of heading by gyrocompassing [ 11 ]. The bias instability of gyros is the most important error term that defines the overall performance of an Inertial Measurement Unit.…”