It post can be called a continuation of the theme “Determination of the angles of the manipulator with the help of its mathematical model. Inverse problem”.
Consider the use of manipulators as multi-axis CNC machines.
Three-link manipulator with 5 degrees of freedom. In these examples one of the restrictions on the movement of the manipulator links is that the position of the last link coincides with the normal to the surface along the entire trajectory of the working point movement.
That is, we, as it were, mathematically transform a system with many degrees of freedom to an analog of a lever mechanism with one degree of freedom, so that we can do the necessary work in a convenient to us way.
It seems that this approach is fully applicable directly to multi-axis CNC machines.
(In the texts of the programs, the normalization is carried out with respect to the coordinates of the last point, in order that the lengths of the integration interval coincide with the path length.)