Newswise — In the field of mechanical engineering, redundant parallel robots have broad application prospects in industrial production, but their internal force antagonism (IFA) problem has become a key factor restricting their popularization. IFA refers to the phenomenon where, in the position control of parallel robots, position variables converge and stabilize, but internal forces within joints antagonize each other and keep increasing. This phenomenon can easily lead to mechanism damage or even safety accidents, making redundant parallel robots more difficult to control than fully actuated ones. To clarify the essence of IFA and compare the performance differences between redundant cable-driven parallel robots (RCDPRs) and redundant rigid parallel robots (RRPRs) in this aspect, a research team conducted a study entitled “Comparison of internal force antagonism between redundant cable-driven parallel robots and redundant rigid parallel robots”.
In this study, the team first analyzed the causes and influencing factors of IFA. It is pointed out that IFA is unique to redundant parallel robots, and its occurrence is related to robot redundancy, configuration and pose, and linkage type. On this basis, two evaluation indices for IFA were proposed: Index 1 (η₁), which is the maximum value of the Euclidean norm of joint forces, and Index 2 (η₂), which is the unit circle integral of Index 1 in the neighborhood of coordinate [0, G]. A specific iterative calculation algorithm based on gradient ascent was developed for Index 1. In addition, three graphical analysis methods were proposed: joint force solution space graph, external force space graph, and position space graph, which can visually display the IFA performance of robots under different conditions.
Through case studies on three configurations (three-linkage planar robot, seven-linkage spatial robot, and eight-linkage spatial robot), the research found that RRPRs produce IFA in nearly all areas of the workspace, while RCDPRs produce IFA in only some areas of the workspace, and the IFA in RCDPRs is milder. This is mainly because cables can only generate tension but not thrust, and their stiffness is much lower than that of rigid linkages. These characteristics make RCDPRs more fault-tolerant and easier to control, thus more conducive to industrial application and popularization.
The research results provide a new analysis framework for the IFA problem of redundant parallel robots, which is of great significance for the configuration optimization design, control, and human-robot interaction of parallel robots. In the field of industrial robots, this achievement can help improve the reliability and safety of redundant parallel robots, promote their wider application, and drive the development of related industries.
The paper “Comparison of internal force antagonism between redundant cable-driven parallel robots and redundant rigid parallel robots” authored by Yuheng WANG, Xiaoqiang TANG. Full text of the paper:
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