.ModelicaAdditions.MultiBody.CutJoints.Prismatic2Dloop

Information

A prismatic joint is a joint with 1 translational degree of freedom.
An instance of this class is used as cut joint to break a kinematic
loop of a multibody system. Note, that a Prismatic2Dloop joint can
only be used in a planar (2D) loop and NOT in a general 3D loop.
The reason is that in a 2D loop, e.g. the constraint force
orthogonal to the plane of the loop is not unique if only rigid
bodies are within the loop. For a unique solution, additional
assumptions have to be made, e.g., that this force is zero.
These additional assumptions are stated in class  Prismatic2Dloop .
Use class  PrismaticCut3D , if a revolute joint has to be used as
cut joint in a 3D loop.

Parameters:
  n  : Axis of translation with respect to the inertial frame in the
       home position.  n  must not necessarily be a unit vector.
  npz: Vector perpendicular to the planar loop (e.g., if the loop
       contains a revolute joint,  npz  has the same direction
       as the axis of rotation of the revolute joint).

Based on  n  and  npz , vector  npy  is constructed which
is perpendicular to both of the two vectors.
The 2 constraint equations on position level state, that the
distance between the origins of frame_a and frame_b, projected
onto  npy , as well as the projection of the three essential
elements of the relative direction cosine matrix onto  npz ,
are zero.
As constraint force fc the force in the direction of  npy , and
as constraint torque tc the torque in the direction of  npz  are
used, respectively. Due to the assumed planar (2D) loop, the force
in direction of  npz  and the torques in direction of  npy  and of
 npz  are assumed to be zero.