A Coupler entity defines an algebraic relationship between the degrees of freedom of
two or three joints.
This constraint element may be used to model idealized spur gears, rack and pinion gears,
and differentials as simple constraints that relate the displacements in a set of joints.
Couplers can be used to specify relationships between translational, rotational, and
cylindrical joints only.
The topological information required to define an Coupler Joint is shown in the figure
below: Figure 1.
