There are two kinds of dynamic substructure methods in common use: fixed interface substructure method and free interface substructure method. The main advantages of the fixed interface substructure are its simplicity and high accuracy. The method of fixed interface dynamic substructure can be used to model the structure. According to the assembly form of the structure, the substructures such as boom and boom cylinder, stick and stick cylinder, bucket and bucket cylinder, connecting rod and rocker can be selected. Because the hinge point is the coupling interface and the hinge point does not transfer bending moment, the translational displacement can be selected as the coupling degree of freedom. Compared with free interface substructure, the main disadvantage of fixed interface substructure is that the higher the degree of freedom of interface coupling, the higher the cost of analysis. However, the number of coupling points of excavator is relatively small, and each hinge point can only take translational displacement as coupling degree of freedom, so the total coupling degree of freedom is relatively low, which can avoid this disadvantage.
When the attitude angle is changed, the internal points of each substructure will not produce corresponding rigid body displacement due to the change of attitude angle, so the substructure does not need secondary analysis, but the angle between the global coordinate system and the local coordinate system of the substructure will change due to the change of attitude angle. When assembling the stiffness matrix and mass matrix of the whole, it is necessary to reanalyze the whole model and consider the time-varying characteristics of the excavator structure. Because the whole model is built after reducing the degree of freedom, the cost of reanalysis is very small.
