In traditional laser-induced breakdown spectroscopy (LIBS) applications, the line intensity and analysis capability are susceptible to plasma shielding. To investigate the shielding effects on the characteristics of Cu plasma in air, a ~120-picosecond laser with a wavelength of 1064 nm was employed to produce plasma. The plasma temperature and electron density were calculated under the condition of local thermal equilibrium (LTE) and optically thin, while the relationships between the line intensity, plasma temperature and electron density were analyzed. Moreover, the LTE condition was validated by the McWhirter relation, plasma relaxation time and diffusion length, and the optically thin condition was observed through the variation in line intensity. The results indicated that when the focal point was below the target surface, the plasma shielding was the weakest, and the highest line intensity could be obtained. In addition, there was a positive correlation between the increased plasma temperature and the degree of shielding effect. When the focal point was above the target surface, the high-irradiance pulse directly broke down the free air and produced a shock wave. Under the high pressure of the over-heated shock wave, the line intensity, plasma temperature and electron density increased again. This study provides an important insight into the experiments and applications of picosecond LIBS.

To address the issue of low trajectory tracking accuracy in six-degree-of-freedom robotic arms, this study proposes a trajectory tracking control strategy that integrates a Radial Basis Function Neural Network (RBFNN) with non-singular fast terminal sliding mode (NFTSM) control. (1) The Lagrangian method is utilized to develop the dynamic model of the robotic arm. At the same time, a non-singular fast terminal sliding surface is designed to accelerate trajectory convergence and resolve the singularity problem commonly associated with traditional sliding mode control by integrating nonlinear and fast terminal terms. (2) The RBF neural network is employed to globally approximate and compensate for uncertainties in the model and variations in the parameters of the robotic arm. (3) To confirm the overall stability of the control system with the proposed NFTSM control strategy, the Lyapunov stability theory is applied to formulate a Lyapunov function. (4) The six-degree-of-freedom robotic manipulator is simulated in the MATLAB/Simulink environment to assess the effectiveness of the proposed control method. In addition, experimental validation is carried out on a real robotic manipulator to verify the effectiveness of the proposed method. The simulation and experimental results show that, compared with NFTSM and RBFNN-SMC, the proposed control strategy significantly enhances the trajectory tracking accuracy of the six-degree-of-freedom robotic manipulator, thereby offering an effective and practical solution for its trajectory tracking control.

With the rapid development of modern industry, robotic manipulators are required to achieve increasingly high trajectory-tracking accuracy and robustness in practical applications. To enhance tracking performance under complex operating conditions, this paper proposes an Adaptive Model Predictive Control with Sliding-Mode Robust Compensation (AMPC–SMC) scheme that integrates an adaptive mechanism with sliding-mode control theory. First, a dynamic model of the manipulator is established, and parameter linearization is employed to transform the nonlinear dynamics into a linearly parameterized form with unknown parameters. Second, an adaptive law is derived based on Lyapunov stability theory to update the model parameters online, thereby mitigating the adverse effects of parametric perturbations and external disturbances on tracking accuracy. Building on this, a receding-horizon optimization strategy is introduced by formulating a quadratic cost function that penalizes both tracking errors and control effort, and the optimal control input is obtained by solving the resulting optimization problem. Meanwhile, a sliding-mode term is incorporated as a robust compensator to eliminate residual tracking errors. Finally, the desired trajectory is generated via point-to-point path planning in Cartesian space, and the proposed method is validated on a real six-degree-of-freedom robotic manipulator. Comparative experiments against conventional model predictive control (MPC) and traditional sliding-mode control (SMC) demonstrate that the proposed AMPC-SMC controller achieves remarkably superior tracking performance compared with the conventional MPC and SMC controllers. In terms of tracking accuracy, the mean absolute errors (MAE) of Joint 2, Joint 4 and Joint 5 under AMPC-SMC are reduced by $91.7\%$, $92.1\%$ and $86.1\%$ respectively relative to MPC, and decreased by $76.1\%$, $77.3\%$ and $85.1\%$ compared with the standalone SMC controller.

In axial piston pumps under variable loading, the system-level excitation and local tribological responses of the slipper pair can become temporally and spatially decoupled. The scientific contribution of this paper is a phase-consistent chain that achieves three things: it resolves the central-pocket pressure boundary with a dual-orifice and dual-control-volume model instead of directly imposing piston chamber pressure, propagates this boundary through posture-dependent clearance to three-dimensional flow–thermal and single-slipper structural responses within the same local cycle, and screens candidate high-risk regions from the spatial proximity and phase relationship of multi-field cycle envelopes rather than from a single peak. The results show that the central pocket pressure exhibits peak attenuation, peak-time difference, and pressure-rate weakening relative to the piston chamber pressure. The steady peak attenuation ratio is $2.83$–$3.33\%$, while pressure-rate weakening under variable loading is $6.29$–$7.14\%$; the high-to-low unloading case gives the largest attenuation of $4.81\%$. Increasing steady load reduces the tilt amplitude and raises the minimum film thickness from about $13.024$ to $13.452\mathsf{\mu }\mathrm{m}$, but the maximum temperature rise increases from $34.12$ to $65.01\mathrm{K}$. A $10\%$ cycle-envelope projection shows no common overlap among the film-thinning, oil-film temperature-rise, and structural-stress core high-response regions with pairwise overlap ratios of 0–$3.27\%$. This traceable chain supports comparative lubrication-safety screening; the identified zones remain numerical candidates rather than experimentally confirmed wear or failure regions.