A robotic knot-tying platform for high-trellis hop twining

The hop plant is usually trained to grow on strings in commercial production. String twining is a labor intense task in high trellis hop fields, and there is a high demand in the industry to have the operation mechanized. In this study, an innovative twining platform, consisting of a robotic knot-tying end-effector and a trellis wire holding system, was developed to perform this knot-tying process automatically in high-trellis hop fields. Kinematic analysis was carried out to illustrate the trajectory of the knot-tying process. A robotic twining platform, using a pneumatic actuating system, was built to validate the performance and effectiveness of the proposed concept and control algorithm. Two series of laboratory tests were conducted, one tested knot-tying only, and the other a test of the entire process. Knot-tying tests indicated that the developed robot knot-tying end-effector could achieve the required knot, and the successful rate was 100% under the cycle periods of 5.9 s. The entire process tests indicated that approximately 15 s was required to complete one entire cycle before reaching the next wire. This result showed that the invented robotic twining platform can successfully tie clove hitch knots satisfactorily for high trellis hops production.