To undestand how this joint
works, first imagine you have two concentric cylinders. Then cut
these cylinders obliquely at the same angle as see in the following
graphic.
Now attach a motor to rotate
both cylinders at the same time. The cylinders rotate with the same
angular velocity but with opposite directions. This can be done
with a sime planetary gear train design. Then do exactly the same
thing for the secont upper half of the joint. you connect the two
joints using two x-bearings to connect each cylinder with its counter
part.
The following simulations are
of the joint doing in-plane bending and orienting:
However, there is a problem
with desgin: when the two cut cylinders alligne in a such a way
that their axes of rotation are concident, then the joint loses
rigidity and becomes loose. A possible solution is either to add
a brake or to aviod getting into this configuration
