Basic study for drive mechanism with synthetic fiber rope (Terminal fixation method using a grooved pulley and a figure-eight knot)

A synthetic fiber rope, which is lightweight and has a high tensile strength and flexibility, is receiving much attention as a replacement for a stainless steel wire rope. To exploit the maximum tensile strength of the rope, it is essential to develop a terminal fixation method with the sufficient fixing force. However, practical difficulty exists in the case of the synthetic fiber ropes because the synthetic fiber ropes have very small frictional coefficients compared with a stainless wire rope. This paper proposes a new terminal fixation method using a grooved pulley, a loop with figure-eight knot, and a pin. The grooved pulley is introduced to increase the friction between the synthetic fiber rope and the pulley by wedge effect, and the rope is wound around the grooved pulley. The end of the rope is hanged at a pin by a loop with a figure-eight knot. We experimentally derived the appropriate groove shape, and demonstrated that our method permits the maximum fixation force over 90 % of the rope breaking force. An example of implementation for a prototype model of a coupled-tendon multi-joints manipulator is also described.