Miniaturized FOG Inertial Measurement Unit

 Fiber optic gyroscope is a new type of angular velocity sensor based on Sagnac effect. Compared with mechanical gyroscope, fiber optic gyroscope has the advantages of all-solid structure, strong impact resistance and short start-up time. Compared with laser gyro, it uses passive fiber ring as the sensitive medium and has no blocking effect.

Since Vali and Shorthill demonstrated the feasibility of measuring angular velocity in the laboratory with the Sagnac interferometer in 1976, more than four decades of technological progress have been made. At home and abroad, including Honeywell, NorthropGrumman, Liton, Beijing University of Aeronautics and Astronautics, the 33rd Aerospace Science and Industry Group, the 502nd Aerospace Science and Technology Group, Ericco and other units have developed mature fiber optic gyro products, measuring accuracy covers high, medium and low precision applications. And has begun mass production, in many fields have replaced the traditional mechanical gyroscope.

 

Inertial measurement unit (IMU) is the core component of inertial navigation system (INS). With the development of fiber optic gyroscope technology, the FOG Inertial Measurement Unit as the angular velocity sensitive component has been maturely applied in aviation, aerospace, weapons and other fields, greatly improving the performance of inertial navigation system. However, in some special fields such as deep space exploration and manned spaceflight, the inertial navigation system has higher requirements for the volume, power consumption and reliability of FOG Inertial Measurement Unit due to the constraints of space environment and spacecraft loads. In order to meet the application requirements of miniaturized and low-power FOG Inertial Measurement Unit for inertial navigation systems in aerospace market, a design and implementation method of miniaturized FOG Inertial Measurement Unit is proposed. The results show that the weight of IMU components is 2.342 Kg, and the power consumption is 10.6 W at normal temperature, which can meet the requirements of IMU in inertial navigation system.

 

1. IMU design scheme
The framework of the miniaturized FOG Inertial Measurement Unit is proposed, which consists of two parts: IMU module and IMU circuit. The IMU assembly consists of four fiber optic gyroscopes and four quartz flexible accelerometers. The fiber optic gyroscopes/accelerometers receive the secondary power supply provided by the IMU line and output telemetry and pulse signals. The IMU component adopts the 4S structure scheme, and any three-axis fiber optic gyro/accelerometer can complete the angular velocity/acceleration measurement function, with 1 degree redundancy. The IMU circuit consists of a primary interface circuit, a backup interface circuit, and a power management circuit. The primary and backup interface circuits have the same functions and are used in cold backup. The interface circuit receives the primary power supply provided by the inertial navigation system, provides the secondary power supply to the fiber optic gyro/accelerometer, collects the output signal of the fiber optic gyro/accelerometer, and communicates with the inertial navigation system. The power management circuit works with the main and backup interface circuits to complete the independent power-on and power-off control of four fiber optic gyros and four accelerometers.
Interface circuit, power management circuit, accelerometer, fiber optic gyro are the important components of IMU, and their volume and power consumption directly affect the product status of IMU. After more than 40 years of technological progress, the technology of miniaturized fiber optic gyroscope has been relatively mature.

 

2. Design results
Through the interface circuit based on SIP device LSMEU01 and the miniaturized power management circuit based on magnetic hold relay, the volume of IMU circuit is reduced by about 1/2 and the weight is reduced to 0.778 Kg. The single-meter power consumption of the accelerometer is reduced to 0.9W by using the temperature compensation method based on the combined parameters. By using this measure, we can effectively reduce the volume and power consumption of IMU. The results show that the weight of IMU components is 2.342 Kg and the power consumption is 10.6W at normal temperature, which can meet the needs of the use of minisized IMU in inertial navigation system.

 

3. Summary
Ericco's ER-FIMU-50 is the smallest FOG Inertial Measurement Unit, which is widely used in AHRS, guidance and control systems, onboard attitude measurement inertial/satellite integrated navigation system, drilling system mobile mapping system, and satellite communication in motion. If you would like to obtain more technical data, please feel free to contact us.