The mechanism consists of 4 links (triangular panels) and 5 joints. Blue and orange panels are connected together by a spherical joint. Four remaining joints are revolute.
When the door is completely open or closed (death positions), force applied to the pink or green panels can not move the door. So do the gravity, thus the door is kept rather stable at open or closed positions. No problem for forces applied to the blue or orange panels.
Center of the sperical joint traces half of an ellise (green curve) so the door occupies less space than ordinary doors in moving.
Disadvantages:
- At closed position the panels lay outside the wall thickness.
- Not suitable for partly opening.
It looks like an art work more than an useful door.
The door is named after its designer, Klemens Torggler, an Austrian artist.
Mechanisms of square, pentagon and hexagon panels have been animated but they do not show practice applications.