The accuracy of gravity disturbance horizontal components is an obstacle in strapdown airborne vector gravimetry at present. In the strapdown inertial navigation system (SINS) field, the rotation modulation technique has been put into practice to improve the accuracy of navigation for decades, which could suppress the divergence of SINS errors. Since there is a close connection between SINS and strapdown vector gravimetry, we were inspired to research on introducing rotation modulation into strapdown airborne vector gravimetry in this study. In this paper, the second section introduced the connections and differences between SINS and vector gravimetry. Then, the third section analyzed three main obstacles in improving the horizontal components accuracy of strapdown airborne vector gravimetry. To solve these problems, the fourth section proposed the mechanism of rotation modulation vector gravimetry from system level which is inspired by rotation modulation inertial navigation system (RMINS). On the basis of the mechanism, the fifth section designed a yaw continous rotation modulation scheme for vector gravimetry. Simulation and real-world static experiment demonstrated that the designed scheme has better performance in horizontal components than the classical strapdown gravimetry. Moreover, the experiment with drift showed that rotation modulation could also suppress the effects of the accelerometer long-term drift on gravimetry results. In conclusion, the paper introduced the rotation modulation into strapdown airborne vector gravimetry for the first time. It will probably provide a reference for developing the next generation strapdown airborne vector gravimeter.

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Purpose The purpose of this paper is to use the redundancy of a new hybrid automatic fastening system (HAFS) for aircraft assembly in the best way. Design/methodology/approach First, the kinematic model of HAFS is divided into three sub-models, which are the upper/lower tool and parallel robot. With the geometric coordination relationship, a comprehensive kinematic model of the HAFS is built by mathematically assembling the sub-models based on the DH method. Then, a novel master-slave decoupling strategy for inverse kinematics solution is proposed. With the combination of the minimum energy consumption and the comfortable configuration, a multi-objective redundancy resolution method is developed to optimize the fastening configuration of the HAFS, which keep the HAFS away from the joint-limits and collision avoiding in the aircraft panel assembly process. Findings An efficient multi-objective posture optimization algorithm to use the redundancy in the best way is obtained. Simulation and an experiment are used to demonstrate the correctness of the proposed method. Moreover, the position and orientation errors of the drilling holes are within 0.222 mm and 0.356°, which are accurate enough for the automatic fastening in aircraft manufacturing. Practical implications This method has been used in the HAFS control system, and the practical results show the aircraft components can be fastened automatically through this method with high efficiency and high quality. Originality/value This paper proposes a comprehensive kinematic model and a novel decoupling strategy for inverse kinematic solution of the HAFS, which provides a reference to utilize the redundancy in the best way for a hybrid machine with redundant function.

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