Vacuum suction end-effector development for robotic harvesters of fresh market apples

Abstract

Timely harvesting of fresh apples faces challenges due to labour shortage, and the modern approach of robotic harvesting has the potential to address this issue. The prevailing process of apple harvest robotics could not meet the demands of practical applications, mainly due to the lack of a suitable manipulator, because the existing ones are associated with low picking rates, fruit damage, and high costs. A prototype apple harvesting manipulator was developed, which includes a vacuum three-revolute-degrees-of-freedom end-effector, a three-prismatic-degrees-of-freedom Cartesian system, an RGB-D camera, and system integration. The vision positioning system and controller were designed to realise precise positioning and detachment of the manipulator. The major contribution of the current study is the three-revolute-degrees-of-freedom vacuum suction end-effector, whose performance evaluation was conducted in a commercial apple orchard. Experimental results showed that a 33ϕ mm diameter suction cup achieved superior performance over a 43ϕ mm cup. The method of rotation followed by pull proved to be more effective than only pulling for apple detachment. The results indicated that the apple’s equatorial region was the optimal area for suction. Furthermore, the vacuum pressure should be at least −65 kPa to guarantee successful detachment. Experimental results showed that 83.1% of harvested apples had stems intact. For the developed manipulator, a 33ϕ mm diameter suction cup, a rotate-and-pull separation method, and −65 kPa were recommended for practical applications. With the integrated new manipulator, the developed apple harvest robot has been demonstrated to have the potential to realise robotic apple harvesting.