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Space manipulator is a key mechanism for on‑orbit inspection outside capsule and assisted astronaut extravehicular activities. In order to ensure the safety and efficiency of the whole process of manipulator operation, the motion process of on‑orbit operation needs to be planned in advance on the ground to generate motion control commands, and then the motion control commands are verified by digital simulation and deduction. Because of such problems, this paper mainly designs the ground simulation verification framework from the motion space limitation, motion speed limitation and joint torque limitation, proposes a simulation verification strategy based on kinematics and dynamics modeling and analysis of the relationship between motion space and collision, and gives the calculation methods of joint motion, joint torque and contact safety distance, as well as the criteria of over limit detection and risk judgment. Finally, through joint position overrun detection, velocity overrun detection, torque overrun detection, contact detection and safety distance calculation, the control command of space manipulator is effectively verified by ground simulation experiment. [ABSTRACT FROM AUTHOR]

Contact detection and computation efficiency has always been the key problem of three-dimensional discontinuous deformation analysis(3D-PEDDA), which is one of the most powerful numerical methods. Contact detection suffers from low efficiency, contact indeterminacy, and the incapability to deal with concave blocks. The efficiency of the entire DDA program is also one of the most crucial bottlenecks. This paper introduced the multi-cover method and the last entrance plane method to deal with lacking of efficiency and indeterminacy of contact detection, as well as the local convex decomposition method for concave polyhedron. In addition, in order to improve the computational efficiency, 3D explicit DDA was adapted to unify data reading and writing mode, and parallelized by adding precompile instructions. In order to expand to high-performance cloud computing and supercomputers, the new 3D-PEDDA programs were all developed on Linux system, and preliminary experiments were carried out on a simple cloud virtual machine. Numerical examples verified the efficiency and accuracy of the newly developed parallel 3D-PEDDA, and it is promising that it can be easily extended to high-performance virtual machines or supercomputers to realize the analysis of large-scale projects. [ABSTRACT FROM AUTHOR]

Aiming at the cutting condition monitoring in ultra-precision machining, the test method of contact detection and identification using acoustic emission technology was studied. Firstly, a lead zirconium titanate piezoceramic sensor with a resonance frequency of 1 MHz was installed close to the cutting point. Then, the acoustic emission analysis unit amplification and 100 kHz high pass filter were used to process the background noise, and the contact limit between cutting edge and workpiece was studied to achieve accurate detection of cutting-edge position. Fiually, to identify the cutting state, the change of acoustic emission signal caused by the change of cutting state was also monitored. The results show that:(1) In contact detection test, when the cutting speed is 60 m/min, the contact between the cutting edge and the workpiece can be detected at a cutting depth of 10 nm;(2) In the cutting state identification test, the acoustic emission signal waveform can identify the minor changes occurring during surface machining, and the average value of acoustic emission is highly positively correlated with the cutting speed, and the total energy of acoustic emission is proportional to the length of the contact arc. These results confirm the feasibility of acoustic emission technology for cutting condition monitoring. [ABSTRACT FROM AUTHOR]

The reliability of the results must be ensured when using the finite element method to calculate the contact stress distribution on the hole boundary of the composite mechanical connection structure. The basic principles and characteristics of two contact detection technologies, including small sliding contact detection and finite sliding contact detection, and three contact constraints, including Lagrange multiplier method, direct constraint method and penalty function method are studied in detail. In order to validate the accuracy and applicability of different contact algorithms, the commercial finite element analysis software Nastran, Marc and Abaqus are utilized as stress analysis platform, and the numerical simulation results are carried out to compare with the test result of bolted joints composite laminate. The results indicate that the finite sliding contact detection technology and penalty function method are more suitable for the finite element analysis of composite mechanical joints.

In order to improve the efficiency of sheet metal forming by meshless method, realize the contact detection and speed up the detection, the matrix method is proposed to handle with the contact detection and a sparse matrix was constructed to memorize the information including numbers of nodes and distances between the nodes and other neighbor nodes such that the nodes in the influence domain of the slave node can be detected quickly. Only those nodes in the influence domain of one slave node were used to construct the matrix smaller than the matrix built up based on all nodes in problem domain, therefore computational efforts for computation of determination of smaller matrix are reduced drastically to improve the efficiency of detection and the precision of treatment of complex contact detection. Numerical example shows that the use of matrix method in contact detection is suitable. [ABSTRACT FROM AUTHOR]