1. First three joint axes
are parallel.
3.Axes 1 and 2 are parallel,
axes 3 and 4 intersect.
5.Axes 2 and 3 are parallel,
3 and 4 intersect.
2.Axes 1 and 2 are parallel,
3 and 4 are parallel.
4.Axes 2, 3, and 4 are parallel.
6.Axes 1 and 2 intersect
2 and 3 are parallel.
Figure 5.1. Special 4-DOF structures.
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