Chengguang Zhang

The motion stability control of biped robots in unstructured environments is a prominent research hotspot in the field of robot control. The biped robot model features variable topology, strong nonlinearity, and multi-degree-of-freedom coupling, allowing for strong environmental interaction. The unstructured road environment imposes more significant requirements on the robot’s gait stability, joint coordination, and adaptability to its environment. In this study, a stability analysis of the motion of robots in unstructured environments was carried out using a disturbance balance control strategy and an application based on Zero Moment Point (ZMP)-Center of Pressure (CoP) testing for feedback control. The approach included a control strategy based on compensating for ankle joint trajectory and was tested using the Webots simulation platform and a real experimental platform. Multi-scene experiments involving NAO robots on stairs and in unstructured sandy environments were conducted to compare and analyze the gait stability and environmental adaptability of NAO robots in unstructured environments.

Laser-based powder bed fusion of metals (PBF-LB/M) is one of the most promising additive manufacturing technologies to fabricate complex-structured metal parts. However, its corresponding applications have been limited by technical bottlenecks and increasingly strict industrial requirements. Process optimization, a scientific issue, urgently needs to be solved. In this paper, a three-phase transient model based on the level-set method is established to examine the heat transfer and melt pool behavior in PBF-LB/M. Surface tension, the Marangoni effect, and recoil pressure are implemented in the model, and evaporation-induced mass and thermal loss are fully considered in the computing element. The results show that the surface roughness and density of metal parts induced by heat transfer and melt pool behavior are closely related to process parameters such as laser power, layer thickness, scanning speed, etc. When the volumetric energy density is low, the insufficient fusion of metal particles leads to pore defects. When the line energy density is high, the melt track is smooth with low porosity, resulting in the high density of the products. Additionally, the partial melting of powder particles at the beginning and end of the melting track usually contributes to pore formation. These findings provide valuable insights for improving the quality and reliability of metal additive manufacturing.