Term for a type of 5-axis-spindles used in CNC machining centers.
Robot heads have a C-axis as well as another tilting axis, from which the working spindle is suspended unilaterally. Initially, there were only versions with perpendicular rotational axes. In the mid-1990s, a special type was introduced, named prism head, where the tilting axis lies obliquely in space.
The term was borrowed from robotics, where this kind of constructions of this kind was first used.
For the design with the perpendicularly arranged rotating planes, one occasionally finds the term "unilaterally suspended forkshaped head", because their basic design corresponds to the rotational axes of a fork head. However, because of the unilateral mounting, they lack an important basic feature.
Commonly, one can find the - actually wrong - term cardan head for prism or robot heads since there is no standardized linguistic rule.
Due to their unilateral mounting, robot heads have a better dynamics and a larger working range, while, at the same time, using less space than fork heads.
The stiffness is somewhat lower, there is less freedom for vibrations and the use of heavy engines is limited.
Therefore, some manufacturers offer machines with robot heads as well as machines with cardan heads, depending on the purpose.