Design and evaluation of a robotic apple harvester using optimized picking patterns

A robotic apple harvester consisting of a mobile platform, a manipulator, an end-effector, a stereo camera, and a host computer was constructed and evaluated using two picking motions. The field tests showed all apple picking with success rates of 80.17% and 82.93% when using anthropomorphic and “horizontal pull with bending” motions, respectively. The main reasons for picking failure were depth misalignment, detachment failure, and blocked grasp. The “horizontal pull with bending” and anthropomorphic motions took 1.14 s and 3.13 s, respectively. The full picking cycle process using “horizontal pull with bending” motion was 12.53 ± 0.53 s, 4.64 s less than the average picking time when using anthropomorphic picking motion (17.17 ± 0.36 s). The picking process using anthropomorphic motion experienced a lower dynamic payload, meaning less effort would be required by the manipulator joints; however, fruit slipping decreased the overall success rate. The “horizontal pull with bending” picking motion had a superior picking cycle time and success rate. Notably, there were no stem-pulled or bruised apples during picking process using either motion. Based on this study, both picking motions have the potential to be applied in harvesting robots.