In this paper, ReaxFF molecular dynamics simulations were used to look at how load and the number of nitrogen molecules affect how friction behavior in hydrogen-free diamond-like carbon (DLC). The presence of nitrogen molecules will inhibit the formation of C–C covalent bonds between the contact surfaces of the upper and lower DLC, thereby effectively suppressing the increase in friction during the initial friction phase. After the initial friction stage, the mechanical mixing of the contact surfaces brought on by the diffusion of nitrogen molecules results in considerable shear stress, which has significant impacts on the friction force. In addition, due to the existence of nitrogen molecules, the effect of graphitization of hydrogen-free DLC on friction is almost negligible.

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It is a challenging task for an aerial manipulator to complete dual-arm cooperative manipulation in an outdoor environment. In this study, a new dual-arm aerial manipulator system with flexible operation is developed. The dual-arm manipulator system is designed for the application of aerial manipulation, and it has the characteristics of low weight, low inertia, and a humanoid arm structure. The arm structure is composed of customized aluminum parts, each manipulator contains four degrees of freedom, similar to the arrangement of human joints, including shoulder yaw, shoulder pitch, elbow pitch, and wrist roll. Next, the workspace of the dual-arm manipulator is simulated and analyzed, and the relevant kinematic and dynamic models are deduced. Finally, through the lift load, accuracy and repeatability, cooperative bimanual manipulation tests on the test bench, and multiple groups of outdoor flight tests, the relevant performance analysis and verification of the dual-arm aerial manipulator system are carried out. The test results evaluate the feasibility of the designed dual-arm aerial manipulator system for outdoor cooperative manipulation.

Functional adaptability makes a product not only multifunctional but also compact in structure and flexible in application. An adaptable-function mechanical product generally demonstrates various degrees of similarity in its behavioral processes for different adaptable functions. Evaluation of this similarity is an important aspect of research for the design of such products, especially for redesigning existing products towards functional adaptability. Until present there lacks research on the design and development of this specific kind of products, including the work on the similarity evaluation of their behavioral processes. To address this problem, this paper investigates the functional and structural characteristics of adaptable-function products first. Based on this, by applying the function-behavior-structure design rationale, a redesign framework of mechanical product for functional adaptability was proposed, and the similarity characteristic of behavioral process was investigated, both on that of the behavior structure and that of behavior characteristics. Furthermore, the paper applied a fuzzy mathematics method for the evaluation of behavioral process similarity, for which a fuzzy comprehensive evaluation model was constructed and the corresponding evaluation method was proposed. Finally, a mini-combined machine tool with adaptable-functions was taken as an example to analyze the behavioral processes and to illustrate the proposed similarity evaluation procedure. The results demonstrated the feasibility and effectiveness of the proposed methodologies.

Considering accurate model information of robotic manipulators is hard to obtain in real applications, this article proposes a model-free trajectory tracking control scheme for the robotic system with input saturation, where a pre-defined tracking precision within prescribed time under any initial conditions is ensured. Firstly, to avoid a sharp corner when control input exceeds constraint, a new smooth function is used to approximate the saturated control torque and then a new robotic system model is built. Based on the rebuilt system, a time-delay estimation (TDE) method is used to estimate the lumped uncertainty containing unknown dynamics and external disturbance. Furthermore, a model-free adaptive controller is developed to ensure the tracking error converge to a preset small residual within given time, where adaptive law and auxiliary system are used to cope with the TED estimation error and control input saturation, respectively. With the developed practical prescribed-time function, there is no constraint on the initial value of the tracking error, thus global stability is guaranteed. Finally, a planar two-link robotic manipulator is simulated to show the effectiveness of the developed control scheme.

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