Research on the Fruit Movement Mechanism of Apple In-field Sorting Equipment

The apple in-field sorting system can reduce post-production costs and enhance the competitiveness of China’s apple industry. Our laboratory has developed computerized imaging-based apple in-field sorting equipment consisting of a variable-pitch screw conveyor, a computerized imaging system, and a sorting actuator. To achieve efficient sorting of apples, the screw conveyor needs to simultaneously convey, separate, and uniformly rotate spherical-like fruits, ensuring that the imaging system quickly detects the full surface information of the apples. In this study, three sizes of apples, each coated with six different colors, were conveyed while the conveyor bar operated at 2 and 3 r/s. The variable-pitch conveyor was evaluated by developing a color-based surface segmentation algorithm for moving apples, calculating the average cumulative percentage, and investigating the number of rotational revolutions, the rotational motion pattern, and the horizontal motion distance of the apples on the variable-pitch conveyor rod at the two conveyor speeds. This clarified the relationship between apple size, conveyor speed, and horizontal motion distance. The results showed that the imaging system could image the surface of each apple more than 2–3 times, achieving an efficiency that allows processing and grading the surface information of 12 apples simultaneously within 1.0 s. As the pitch increases, the distance traveled by an apple during one complete rotation gradually increases. The larger pitch ensures that the full surface information of the apples is obtained, making the horizontal movement of the apples more uniform and smooth after separation. This leads to a more efficient and reliable acquisition of image information, providing a theoretical basis for realizing efficient in-field sorting of apples.