• Linkage isomers : links have various nodes available to connect to other links' nodes.

• Depending on the particular connections of available links, the assembly will have different motion properties.

• The number of isomers possible from a given collection of links is far from obvious. • In fact the problem of mathematically predicting the number of isomers of all link

combinations has been a long-unsolved problem. • Table 2-3 shows the number of valid isomers found for one-DOF mechanisms with

revolute pairs, up to 12 links.

F2.15 a

F2.15 b

F2.15 c

F2.16

there are three possible configurations, as shown above. The parallelogram linkage may switch (uncontrollably!) to the anti-parallelogram linkage if care is not taken to prevent this.