On The Experiment Of Chaotic Mo-Tion For Underactuated Five-Bar Mechanism

An underactuated mechanism refers to a mechanism in which the number of actuation is less than its degrees of freedom. Some researches theoretically found that an underactuated mechanism often demonstrates chaotic motion with some in-put velocities of motion. However, these conclusions have not been verified by any experiments yet. Therefore, to experimentally study the motion of underactuated mechanisms will be valuable in both theory and practical application.Since the chaotic motion is sensitive to initial value, and, there definitely exist many disturbing factors in the experiment, it is consequently particular and neces-sary to study how to carry out the experiments for the chaotic motion of underactu-ated mechanisms. Until now, unfortunately, there have been very rare reports con-cerning with the study of experiment regarding the chaotic motion of underactuated mechanism.Under this situation, this paper focus on the experiment of underactuated five-bar mechanism, and discusses systematically the issues including the estab-lishment of experiment system, the elimination of disturbing factors as well as col-lection and processing of experiment data.The main works of this paper are as followed:The platform for dynamics analysis and design of planar linkage along with its hardware and software are introduced briefly. Regarding the chaotic motion of un-deractuated mechanism, the experiment system is properly established with the platform, TwinCAT system is configured and the PLC is programmed. At the same time, the process of operating on the platform is also designed.Also, disturbing factors, which might affect the results of the experiment, are analyzed, and methods to deal with them are proposed respectively. The study of this paper is limited to that the input angular velocity is less than50r/min, in order to keep the influences from vibration of the platform and deformations of the links small as possible; in addition, the impacts of clearances in kinematic pairs are ex-perimentally excluded; also, the combination of median filter with Gauss filter is proposed in this paper to reduce noises contained in the data from experiment.With the application of both the experiment system and the method proposed in this paper, the motions of the planar underactuated five-bar mechanism with the input angular velocity less than50r/min are studied. It is shown that if the input angular velocity is less than9.15r/min, the motion of the mechanism will be peri-odic; while if the input angular velocity is higher than15.44r/min, the motion of the mechanism will be certainly chaotic; and if the input angular velocity is between9.15r/min and15.44r/min, the motion of the mechanism alternates periodic and chaotic, and they are at the edge of chaos.Finally, simulations of underactuated five-bar mechanism are conducted with SimMechanics. The comparisons of the results from experiment and from simula-tion are made. It is shown that the conclusions regarding the evolution of the motion states of the mechanism are coincidence. This fact indicates that the experiment system established and the methods proposed in this paper are effective and valid. In addition, the study conducted in this paper might lay the foundations for both establishment of simulation model for underactuated five-bar mechanism and ex-tensive researches in future as well.