Design and experiment of detection mechanism for potato blackheart based on machine vision

Abstract: Potato blackheart is a kind of disease that happens in the inner of potato tuber. The potato with blackheart is difficult to be distinguished from the surface with the naked eye, which affects the quality of potato processed products seriously. In order to detect the potato with blackheart on the production line, a detection mechanism for potato blackheart was designed based on the light transmission properties of potato tuber internal organization in this study. The detection mechanism was composed of the supporting groove, the light source unit, the cooling fin, and the base. Firstly, the characteristics of size and morphology of potato tuber were analyzed based on the statistics rule. The potato tuber studied in this paper was round or elliptic fitted from the side direction, and the fitting diameter range was 40.0-100.0 mm. Then the light source wavelength was chosen as 705 nm according to the result of the research about potato black heart's high spectral transmission detection. Two area light sources were used in the detection mechanism, constituting multipoint transmission structure. The mechanism was designed against the fitted circle of potato tuber sample in the first place. Two common tangent lines for any size of potato tubers were defined, and the locations of 2 tangent points on each fitting circle were set as the light source locations. The value of the included angle formed by the radius passing the tangent point and the vertical centerline was a determinant to the light source location. A proper included angle could lead to uniform illumination and less light leaking to the potato sample, and improve the consistency of imaging in the camera. The angle value was chosen as 45° by the analysis in this study. After that, the structure of the supporting groove was obtained. The height range between the center of the fitted circle of potato tuber and the bottom of the supporting groove was 20.0-62.43 mm. It could be accepted as a certain range to ensure the consistency of imaging. At the same time, the energy of the area light source installed on the supporting groove was completely absorbed by the potato tuber for its horizontal projection was exactly in the range of potato tuber horizontal radius. When the mechanism was used in the detection of fitted ellipse of potato tuber, the light source position, the included angle and the size of the supporting groove all met the detection demands by the analysis. In order to test the performance of the detection mechanism, a batch of fresh potato samples were chosen and sealed in zip-lock bags, then stored in an incubator at the temperature of 37°. Twenty-nine black heart samples were obtained after 24 d.79 potato tuber samples, including 50 normal samples and 29 black heart samples were chosen to collect the transmission images. The transmission images of 50 normal potato samples under single-point transmission mode were collected at the same time. Then the samples were sealed in zip-lock bags and stored in an incubator at the temperature of 37°. They were taken out and the light transmission images were collected by the detection mechanism after 24 d. Twenty-nine blackheart samples were obtained through the verification. After the background elimination processing with MATLAB, the potato tuber target image and the high grayscale value area after binarization and masking were extracted. The value of their average grayscale value relative ratio was acquired to distinguish the uniformity of the light transmission and potato black heart. The discriminant accuracy of the normal and black heart samples were 98% and 96.6%, respectively. Results showed that, the mechanism introduced in the paper could be used to detect potato black heart. A reference is provided by the design of the detection mechanism in this study.