A Twining Robot for High-Trellis String Tying in Hops Production

Abstract

String twining is an essential and labor-intensive task in high-trellis hops production, and there is a high demand in the industry to have the operation mechanized. This article reports on a conceptual study of the development of a twining robot, consisting of six rotating actuators and three linear actuators, that mimics human hands tying a knot on an overhead cable. In this clove hitch knot-tying process, the robot uses a series of 15 coordinated string delivery and capturing actions to tie one knot. A proof-of-concept research platform was built to assess the effectiveness and robustness of this robotic knot-tying operation in a laboratory environment. Results showed that the conceptual robot, supported by the developed planning and control algorithm, could autonomously and correctly tie a clove hitch knot on a cable. A reliability test of the knotting robot was conducted with 121 continuous knotting cycles. The test machine achieved a tying success rate of 89%. Most of the failures were attributed to the interference of moving elements caused by imprecise fabrication of those parts. This result shows that the invented twining robot can successfully tie clove hitch knots satisfactorily for high-trellis hops production.