Nonlinear phenomena in mechanical robots and multibody mechanical systems

The modeling and control of complex multibody systems, such as robots, is a challenging problem in the field of mechanical engineering. Nonlinear phenomena, namely friction, backlash, vibration, and impacts, cause additional dynamic loads, as well as faulty operation of machines and devices. Despite the investigation carried out so far, those phenomena are not fully understood, not only due to their randomness but also due to the diversity of reasons underlying the dynamic effects.

The special collection focuses on modeling and control of nonlinear dynamical phenomena in robotic systems and other complex multibody mechanisms. The selected manuscripts address advanced issues, and specific topics illustrate the broad impact of several emerging techniques in this area.

In the paper “Efficient hybrid method for forward kinematics analysis of parallel robots based on signal decomposition and reconstruction,” Qiming Wang, Jian Su, Zhichao Lv, Lan Zhang, Huiying Lin, and Guan Xu propose a new hybrid strategy for solving the forward kinematics problem of parallel robots. First, an initial guess for the end-effector’s position and orientation is determined based on signal decomposition and reconstruction. Then, using the estimation, a fifth-order numerical technique computes the exact problem solution. The method is shown to reduce up to 49.8% the required number of iterations when compared with the Newton–Raphson method. ¹

The paper “Inverse rigid-body dynamic analysis for a 3UPS-PRU parallel robot,” by Yongjie Zhao, Ziqiang Zhang, and Gang Cheng, studies the inverse kinematics and dynamics of a rigid-body 3UPS-PRU parallel robot. The robot position, velocity, acceleration, jerk, driving torque, driving power, energy consumption, and singularities are considered when deriving the analytical models, and their dynamical effects are analyzed. ²

In “On the utility of leg distal compliance for buffering landing impact of legged robots,” Jie Chen, Yubin Liu, Gangfeng Liu, and Jie Zhao investigate the effect of leg distal compliance for buffering landing impact of legged robots. They propose a simple spring-mass model that includes damping, pre-load, and realistic limitations on the spring compression. Experimental results are consistent with the numerical data, confirming that the spring-mass model can be useful in the design of distal compliance in legged robots. ³

Finally, the article “Study on multidisciplinary design optimization of a 2-degree-of-freedom robot based on sensitivity analysis and structural analysis,” by Jing Zhang, Jinzeng Liu, Chengjie Wang, Yang Song, and Bailin Li, presents a design multidisciplinary optimization procedure for a 2-degree-of-freedom robot. The approach involves kinematics, dynamics, mechanical structure, and control. The coupling relationship between the four topics is studied based on variable sensitivity analysis. The structural analysis results demonstrate the effectiveness of the method. ⁴

The selected papers allow readers to have a representative idea of ongoing research in this field and motivate further work toward the development of new techniques for advanced mechanical systems.