New inertial measurement units (IMU) at the AUVSI 2013 show were smaller and more sensitive than ever. IMUs are critical to in robotic navigation especially for drones (see Alternative UAV Navigation Systems). They are also important in the consumer market as MEMS technology makes IMUs practical for lower cost, mobile applications (see UAV Nav Systems Moves Into Consumer Markets). The increased use of sensor integration is a natural fit for IMUs (see The Essentials Of Hybrid Location Technologies).
The show included a number of IMU vendors with new products. These included Epson, Sensonor and Sparton.
Epson had a range of new IMUs (Fig. 1) with 6 degress of freedom (DOF) including 3-axis gyros and 3-axis accelerometers. The tiny V340 (12-mm by 10-mm by 4-mm) uses only 18 mA and sports an SPI/serial interface. It handles operating temperatures from -40° to +85° C . The gyro dynamic ranges is ± 450°/s and the accelerometer range is ± 6g. It has a sample rate of 180 Hz and a 7 degree/hour gyro bias instability.
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The V340 has a small connector on the bottom and a cover can be used to hold down the unit in rugged applications. The G350 and G550 are designed for rugged environments. The gyro dynamic ranges is ± 300°/s and the accelerometer range is ± 3g. The G352 has performance characteristics similar to the V340. The G362 has a 3 degree/hour gyro bias instability that approaches the performance of more expensive Fiber Optic Gyro (FOG) and Ring Laser Gyro (RLG) IMUs. The more rugged devices have a sample rate of 2 kHz.
Sensonor's STIM300 IMU (Fig. 2) has 9 DOF. The mix includes 3-axis gyros, 3-axis accelerometers and 3-axis inclinometers. It is an ITAR-free alternative to FOG and RLG units and it is insensitive to magnetic fields. The gyro bias instability is 0.5 degrees/hour and the gyro dynamic ranges is ± 400°/s. The accelerometer range is ± 10g. The inclinometers provide accurate leveling. The unit has a high speed RS-422 interface.
The Sparton Navigation and Exploration group introduced their IMU-10 MEMS-based sensing unit. Its user-programmable NorthTek interpreter interface provides a range of customization options via a SPI/serial interface that runs at speeds up to 1 Mbaud. The 10 DOF unit includes a 3-axis gyro, 3-axis accelerometer, a 3-axis magnetic sensor and a barometer). The gyro dynamic ranges is ± 450°/s. The accelerometer range is selectable (± 5g and ± 18g ). The magnetic range is ± 1.2 Gauss (± 900 mGauss). The rugged enclosure is IP67 rated (Fig. 3).
It has a sample rate of 2 kHz on all sensors. It supports sculling and coning compensation. It even supports high speed data logging capability to an off-board micro-SD card. It handles input voltages from 3 to 4.4 VDC and operating temperatures from -40° to +85° C .
The variety and range of IMUs is significant because they can be incorporated into almost any application from rugged UAVs to handheld devices. The MEMS devices are starting to compete with FOG and RLG in terms of performance and easily beat them in cost, size and reliability. The challenge these days is to determine what set of sensors is required and whether a single unit will provide the environmental status required for an application.
