Accuracy and reliability are two key performances of inertial navigation system (INS). Rotation modulation (RM) can attenuate the bias of inertial sensors and make it possible for INS to achieve higher navigation accuracy with lower-class sensors. Therefore, the conflict between the accuracy and cost of INS can be eased. Traditional system redundancy and recently researched sensor redundancy are two primary means to improve the reliability of INS. However, how to make the best use of the redundant information from redundant sensors hasn't been studied adequately, especially in rotational INS. This paper proposed a novel triple rotary unit strapdown inertial navigation system (TRUSINS), which combines RM and sensor redundancy design to enhance the accuracy and reliability of rotational INS. Each rotary unit independently rotates to modulate the errors of two gyros and two accelerometers. Three units can provide double sets of measurements along all three axes of body frame to constitute a couple of INSs which make TRUSINS redundant. Experiments and simulations based on a prototype which is made up of six fiber-optic gyros with drift stability of 0.05° h −1 show that TRUSINS can achieve positioning accuracy of about 0.256 n mile h −1 , which is ten times better than that of a normal non-rotational INS with the same level inertial sensors. The theoretical analysis and the experimental results show that due to the advantage of the innovative structure, the designed fault detection and isolation (FDI) strategy can tolerate six sensor faults at most, and is proved to be effective and practical. Therefore, TRUSINS is particularly suitable and highly beneficial for the applications where high accuracy and high reliability is required.

Rotary optical encoder is an important component in rotational inertial navigation system. It is used to form a closed loop motor control system and calculate the system attitude. The system performance will be affected by the encoders’ error. Besides the installation errors, the working temperature variants will also lead to encoders’ error. Therefore, the paper proposes a method to calibrate and compensate temperature resulted errors for rotary optical encoders. Firstly, an independent testing mechanism with position limitation and rotatable platform is designed and produced to verify the temperature influences on encoders. Then, the temperature error of rotary optical encoder used in rotational inertial navigation system is calculated by the gyroscope whose sensitive axis is parallel to the same motor axis. The method is verified by a self-researched single axis rotational inertial navigation system. According to the experimental results, the attitude accuracy is increased more than 36.7% compared with traditional method.

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