A knot-tying end-effector for robotic hop twining

Twining is an essential but labour intensive task in high trellis hop production. Thus, there is a high demand within hop production to mechanise the operation. To mechanise the process a multi-actuator mechanical end-effector was proposed in this investigation. The prototype of the end-effector allows automated knot-tying by mimicking human hands making a clove hitch knot using a sequence of coordinated string delivery and capturing actions. A pneumatic actuating system, consisting of five pneumatic cylinders, accomplished twelve actions to tie a knot. The core in the development of this end-effector prototype development was the coordinated action planning and the control algorithms. A research prototype end-effector was built to validate the functionality, practicability and robustness of the proposed concept and control algorithms. Laboratory scale tests showed that the developed prototype could reliably tie the knot and that successful rates reached 100% and 98% with knot cycle times of 5.9 s and 4.8 s, respectively. The results indicated that the developed knot-tying end-effector could successfully tie clove hitch knots for twining in a laboratory environment.