Development of the End-Effector of a Picking Robot for Greenhouse-Grown Tomatoes

The objective of this study was to develop a grip-type end-effector for use in a picking robot designed to harvest greenhouse-grown tomatoes. The end-effector was designed with four fingers that have foam sponge pads inside to reduce damaging the fruit when bending and gripping. By controlling solenoid activation, the fingers are bent to reduce the opening of the tip, securing the fruit inside the end-effector. The center of the end-effector is a fruit suction device, which assists the fixation of fruit to the inside of end-effector, enhancing the holding performance. Test results show that the best suction performance is achieved using vacuum suction nozzles 15.0 mm in diameter and a suction force of 8.1 N/cm². The average suction attachment success rate is 95.3% and the average picking time is 74.6 s for each fruit. When picking the suction-attached fruit, the end-effector makes vertical inching movements over 60 mm for two cycles, achieving an optimal fruit picking success rate. Various twisting angles are examined in this study, and the picking force required is analyzed. The results show that before picking tomatoes, the end-effector should be rotated clockwise for 60° followed by a counterclockwise turn of 120° until the fruit is 60° counterclockwise to the starting alignment, repeated three times in relation to the fruit. The initial laboratory tests show promising results. Future integration with robotic tomato-harvesting systems for actual field tests of tomato picking should increase the feasibility of developing automatic robotic picking systems.