Ocean wave parameters, including wave height, direction and period, are necessary to improve forecasts of ocean wave conditions. Their accurate observation contributes to safety of both offshore operations and military operations. However, conventional wave observation methods that combine the three-axis accelerometer-based wave sensor with the gyroscope may show problems such as inner arm error, transverse sensitivity effect, and gyroscope drift. The first two are due to non-coincidence of centroids inside the accelerometer. Such problems will reduce reliability of data. To solve the problems, a new type of parallel six-dimensional accelerometer is developed to reduce principle errors and improve stability of wave buoys. The solution features a single mass and 12-chain redundancy. When compared with the performance of highprecision sensors in the wave pool, the wave buoy based on six-dimensional accelerometer is proved to be more accurate in wave height measurement than 3.75 % × measurement value, with wave direction accuracy of ± 1 • , and the wave period measurement accuracy of ± 0.1s.
An investigation into the fault diagnosis of a six-axis accelerometer is of great significance because of the high reliability requirement in areas such as aerospace. The working principle and decoupling algorithm of a six-axis accelerometer are introduced. The six-axis accelerometer and the gyroscope form the measurement system and provide the basis for fault diagnosis and restoration by deriving force and deformation compatibility equations. Descartes three-dimensional coordinate system of fault diagnosis is put forward, which carries out the function of real-time diagnosis of the measurement system. In view of a specific fault case, restoration was performed by replacing fault data of a branch chain with correct data. A relevant experiment was carried out and the results confirm the effectiveness of the restoration.
For the development of a parallel mechanism (PM), it is necessary to establish a dynamic model which can accurately meet the requirements of real-time control. Compared with the general dynamic analysis model based on the inverse kinematics, the dynamic analysis model based on the forward kinematics has the advantage of low-complexity. In this paper, a new type of 3-DOF PM with analytical forward displacement analysis is proposed. Different from the general dynamic analysis based on the inverse kinematics, the displacement, velocity and acceleration equations of the PM are established and solved by forward kinematics. The inverse dynamic equation of the PM is constructed and solved by analyzing the forces on each link and based on Newton-Euler method. Then the theoretical results of an example are compared with the simulation results, which shows that the simulation results are basically consistent with the theoretical results. And the maximum error of the driving force of each pair is 1.32%, 5.8% and 5.2%, respectively, which verifies the correctness of the dynamic model. The PM has a potential application prospect in the grasping, spraying and picking of workpieces. The research results of this paper provide a theoretical basis for the design, manufacture and application of the PM.
The fastener installation in the wing-box faces with narrow space, and it has to be done manually at present. Since manual labor has size constraints, the efficiency is low, and there may be assembly quality instability, it urgently needs automation. Automatic fastening assembly using a robot undoubtedly is an appropriate solution. The existing industrial robots, snake robots, humanoid robots can not meet the fastening assembly requirements in the wing-box. We develop a new anthropomorphic robot with multiple links to perform the inner fastening. A prismatic pair is employed to fit the arm links entering into the wing-box. A shaft with 360 degrees rotation liked human shoulder is introduced to meet the circumferential positioning around the process hole. Arm links are used for robotic end effector reaching the local fastening site. Based on the limitation of assembly position in the wing-box, the link lengths are considered and determined. By using the geometric relation with the link lengths, the joint angle variables are presented. Then, S shape arm link is designed for the compact requirement and the dimensions are determined based on the cross-section of human arm. Finally, stable frame structure is set up through the rear door frame and the bridge beam, and the whole robot is integrated.
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