Inspired by the structure of human arms, a modular cable-driven human-like robotic arm (CHRA) is developed for safe human–robot interaction. Due to the unilateral driving properties of the cables, the CHRA is redundantly actuated and its stiffness can be adjusted by regulating the cable tensions. Since the trajectory of the 3-DOF joint module (3DJM) of the CHRA is a curve on Lie group SO(3), an enhanced stiffness model of the 3DJM is established by the covariant derivative of the load to the displacement on SO(3). In this paper, we focus on analyzing the how cable tension distribution problem oriented the enhanced stiffness of the 3DJM of the CHRA for stiffness adjustment. Due to the complexity of the enhanced stiffness model, it is difficult to solve the cable tensions from the desired stiffness analytically. The problem of stiffness-oriented cable tension distribution (SCTD) is formulated as a nonlinear optimization model. The optimization model is simplified using the symmetry of the enhanced stiffness model, the rank of the Jacobian matrix and the equilibrium equation of the 3DJM. Since the objective function is too complicated to compute the gradient, a method based on the genetic algorithm is proposed for solving this optimization problem, which only utilizes the objective function values. A comprehensive simulation is carried out to validate the effectiveness of the proposed method.

Collaborative robots are used in scenarios requiring interaction with humans. In order to improve the safety and adaptability of collaborative robots during human–robot interaction, this paper proposes a modular wire-actuated robotic arm with symmetric variable-stiffness units. The variable-stiffness unit is employed to extend the stiffness-adjustment range of the robotic arm. The variable-stiffness unit is designed based on flexure, featuring a compact and simple structure. The stiffness–force relationship of the variable-stiffness unit can be fitted by a quadratic function with an R-squared value of 0.99981, indicating weak nonlinearity. Based on the kinematics and stiffness analysis of the symmetric joint module of the robotic arm, the orientation of the joint module can be adjusted by regulating the length of the wires and the stiffness of the joint module can be adjusted by regulating the tension of the wires. Because of the actuation redundancy, the orientation and stiffness of the joint module can be adjusted synchronously. Furthermore, a direct method is proposed for the stiffness-oriented wire-tension-distribution problem of the 1-DOF joint module. A simulation is carried out to verify the proposed method. The simulation result shows that the deviation between the calculated stiffness and the desired stiffness was less than 0.005%.

In this paper, a modular wire-actuated robotic arm was designed to improve the safety and adaptability of service robots during human-robot interaction. To raise the stiffness adjustment range of the robotic arm, a symmetric variable-stiffness unit was designed based on flexure, which had compact and simple structure, and lowly nonlinear stiffness-force relationship. In this paper, we focused on the research of the symmetric 1-DOF joint module. Based on the kinematics and stiffness analysis, the pose of the joint module could be adjusted by controlling the length of the wires, and the stiffness of the joint module could be adjusted by controlling the tension of the wires. Because of the actuation redundancy, the pose and stiffness of the joint module could be controlled synchronously. Furthermore, a directly method was proposed for the stiffness-oriented wire tension distribution problem of the 1-DOF joint module. A simulation was carried out to verify the proposed method.

With the rapid advancement of facility agriculture, traditional methods of zucchini seedling cultivation face increasing challenges in meeting modern demands for quality and resource efficiency. To address this, a series of experiments were conducted to optimize cultivation conditions aimed at enhancing seedling quality and water use efficiency (WUE). Using the ‘Technology No.1’ zucchini variety as a model, the study evaluated five substrate formulations, four tray specifications, and five concentrations of an alginate composite agent (ACA) under controlled irrigation based on evapotranspiration data. Key physiological parameters, including plant height, stem diameter, dry matter accumulation, root vitality, and WUE, were measured. The results revealed that a substrate mixture of peat, perlite, and vermiculite (0.7:0.2:0.1) significantly improved plant height (+17.0%), stem diameter (+41.9%), dry matter accumulation (+53.2%), and WUE (+40.6%) compared to the peat-only control. The 50-cell tray configuration provided the most effective balance between root development and spatial efficiency, enhancing root vitality by 8.3%. Among ACA treatments, 150 mg L^-1 yielded the highest WUE (44.3%) and biomass production, with significantly better performance than both lower and higher concentrations. These findings suggest that the integration of an optimized substrate, tray design, and ACA concentration (peat- perlite - vermiculite substrate + 50-cell tray + 150 mg L^-1 ACA) can synergistically improve zucchini seedling quality and water efficiency. This study offers a valuable theoretical foundation for the advancement of intensive and efficient seedling cultivation technologies in facility-based zucchini production.