Knot tying with single piece fixtures

Knot tying poses a challenge to robotic and human manipulation due to the need to regrasp a flexible string. Without sensing, it becomes nearly impossible to guess where the string is. However, by using a fixture, the string can be continually grasped during the entire tying process. We have developed fixtures for a simple overhand knot and a square knot, and have started developing a fixture for the two half hitches knot. We can tie knots in different types of wire and fishing line using these fixtures. In addition, we used a Cobra i600 SCARA arm to autonomously tie multiple overhand knots in sequence without sensing, using solder as the string-like material.