Terminal Mobility Of Polycyclic Coupled Mechanisms

Polycyclic coupled mechanism is a new kind of complicated mechanism whichhas been used in bio-robot, aviation, refuge and other areas. However, it is deficient intheoretical study. The most basic understanding for a new mechanism is to realize itsmobility. Nevertheless, there is a little theory about the hybrid mechanism mobility inkinematics. Due to the complexity and particularity of a polycyclic coupledmechanism, the mobility cannot be obtained by traditional methods. Therefore,exploring the mobility of polycyclic coupled mechanisms is a new research, which isthe basic of type design and kinematic analysis of polycyclic coupled mechanisms aswell.For solving the mobility issue mentioned above, the paper starts from the mosttwo important aspects including coupling property and constraint analysis, and putsforward a motion shunting measure, a decoupling measure as well as an equivalentmeasure, as thus a new method suitable for analyzing of the terminal mobility of apolycyclic coupled mechanism is formed. Analysis of some sample applications isalso performed to verify the effectiveness and adaptability of the new method. Themain contents are as follows:Study on coupling property is carried out. Three basic coupled models areinitially presented. Based on their kinematic characteristics, a motion shuntingmeasure and its tagging principle are proposed, which is extended to polycycliccoupled mechanisms. At the same time, a structure decoupling measure for coupledmechanisms is put forward, which can divide a polycyclic coupled mechanism intoseveral chains with independent motions among each other.Based on screw theory, motion and constraint of each independent chain areanalyzed. Using above-mentioned tagging measure, the motion and constraint of thefirst-level nod-link are analyzed. Using the equivalent method by a generalizedkinematic chains and iteration replacement in the next nod-link, the independentkinematic chain is ultimately replaced by a single chain. Then polycyclic coupledmechanism can be regarded as a common parallel mechanism.Analyze the continuous terminal mobility of the equivalent parallel mechanism.Calculate the motion screw and constraint screw of the equivalent mechanism, anduse the linear dependency to determine over-constraint. Then the mobility of theequivalent parallel mechanism is calculated by the Modified Grübler-Kutzbachcriterion. The number and property of mobility can be also determined by resolve thereciprocal screws of the output’s constraint screw system. At last, the continuous terminal mobility is identified according checking the continuous limitedconfigurations.The proposed method is applied to three typical kinds of polycyclic coupledmechanisms, including a hybrid mechanism with independent limbs and local coupledstructures, an asymmetric coupled mechanism as well as a symmetric coupledmechanism. Through modeling and simulation by the solidworks software orcomparison with other methods, the effectiveness and adaptability of the new mobilitymethod are identified.The proposed method is the development and innovation for existingmethodology based on screw theory, and it plays a positive role in promoting furtherdevelopments and applications of polycyclic coupled mechanisms.