The arm moves freely while the pen is positioned in areas required to build up the 3D model using extruded plastic. But when it attempts to move outside the area pre-defined by the source model, motors in the robot’s arm provide force feedback and physically limit where you can move it. Imagine the feeling of using a ruler to limit where you can scribble with a marker on a piece of paper. Whenever the marker hits the ruler, it abruptly stops.
At the same time, the robot arm can be used to gently guide the pen where it needs to be, if the user has forgotten to print an important detail. Or through vibrations and force feedback, it could modify the texture of the plastic being extruded. If you’ve ever tried to decorate a cake with a frosting bag while kids were banging on the table, you get the idea.
The Guided Hand system still has its limits. Since the majority of the 3D printing is still being left to human hands, the results will never be comparable to the precision of a dedicated 3D printer that takes hours to create even tiny objects. But for artists looking to dabble in the new medium, think of it like a virtual form of tracing, allowing them to add their own creative flourishes, while still producing a recognizable piece.