A string twining robot for high trellis hop production

• A full function multi-actuator prototype robot for high trellis hop twining was investigated.
• The prototype integrated three end-effectors, each of whose performance was evaluated separately.
• Function and reliability tests were conducted and their results reported.

The hop plant is usually trained to grow on strings in commercial production. String twining is a labor intensive task in high trellis hop fields, and there is a high demand from industry to have the operation mechanized. In this study, an innovative string twining robot, comprising end-effectors for knot tying, string feeding, and trellis wire capturing was designed to perform this task autonomously. A laboratory-scale, proof of concept prototype, was fabricated to validate the performance and effectiveness of this robotic device and associated control algorithms. Functionality assessment tests verified that the string feeding end-effector could feed 6 m length of string with acceptable variation. The trellis wire capturing end-effector could functionally achieve the required procedure for continuous twining. The comprehensive twining test proved that the integrated twining robot took approximately 11.2 s to coordinate all three end-effectors to complete one string twining cycle with a moving forward speed of the mobile platform at 0.19 m s−1. At this speed, the developed prototype robot achieved 97% of successful rate. The laboratory test results indicated that the developed prototype robot has the potential to be implemented for high trellis hop twining task.