Structural Graphs of the Theory of Mechanisms

On the example of planar mechanisms with rotational pairs, a comparison is made of two types of graphs that describe their structure. Graphs G of the first type, corresponding to hinged-lever mechanisms, consist of vertices corresponding to the hinges of the mechanism, and of edges corresponding to its levers. The vertices of graphs 
 of the second type correspond to links of the mechanism, and the edges correspond to kinematic pairs. It turns out that in the absence of combined hinges, the graphs G and @  are equivalent for describing the structure of mechanisms. In the presence of combined hinges, the graph graph @ and the graph 
 obtained by its modification in the theory of mechanisms, in contrast to the graph G, do not provide complete information about the structure of the mechanism.