Development of potato seed-metering state monitoring system based on space capacitance sensors

Abstract: A spoon-type potato seed-metering has been widely used for easy preparation and seeding feasibility, due to its simple structure and low price, especially for small and medium-sized planters. But the relatively low reliability of seed-metering has led to the huge loss and significant reduction of yield, where the common miss-seeding rate can be about 5%-7%.Thetraditionalphotoelectric monitoring system cannot fully meet the high performance of anti-dust and anti-vibration. In this study, a new approach was proposed to construct a space capacitance sensor for the evaluation of seed-metering states and mass acquisition of seed potatoes. Specifically, the capacitance variation was obtained in the process of working seed spoon, when passing through the space surrounding the capacitor plates. A theoretical derivation was carried out first to evaluate the feasibility of the potato seed-metering state, according to the maximum net capacitance fluctuation (MNCF) signal. Furthermore, a Maxwell model was performed on the spatial capacitance sensor to determine the range of capacitance using the parameters and morphology of key components in a typical potato seeder. There was a direct influence of all parameters on the size of space capacitor plates to be constructed, including the shape of seed spoon, spoon chain, and the diameter of cutting seed tuber. Since the larger capacitance plates allowed for the higher base capacitance, there was no obvious fluctuation in the maximum net capacitance, when the seed tuber passed through the surrounding space. As such, the sensor sensitivity was reduced significantly. However, the misjudgment inevitably occurred, due to the insufficient sampling data, where the sampling frequency of the system was not enough, if the capacitor plate was too small, while the potato seed on the spoon moved quickly, particularly when the system working at a higher speed. Taking MAX038 as the core, the capacitance of the space capacitance sensor was indirectly obtained by c/f conversion-frequency measurement, and then the MNCF related parameters were calculated, according to Nyquist sampling. A special bench test of seed potato movement was also conducted under the constant temperature and humidity environment, thereby acquiring the regression models of temperature and humidity on the measured parameters. More importantly, the measurement data under different conditions was freely converted to a standard state. The specific parameters of the standard state were the temperature of 15℃ and humidity of 50% RH. In terms of different-sized seed potatoes with the same breed, there was a significant linear relationship between the MNCF and the weight. It was found that the system atic measurement error of spatial capacitance was less than 1%, and the error of seed potato mass acquisition was not more than 3%. The miss-seeding was determined accurately within the test range. Nevertheless, 2.33% of 1-seed normal-seeding was misjudged as the multi-seeding, and 2.78% of the 2-seeds multi-seeding was misidentified as normal-seeding, for the irregularity of test seeds. Misjudgment mainly occurred in an extreme case, particularly whether the single seed potato was too large, or the double seed potato was too small. Overall, the accuracy of the system was still higher than before. Correspondingly, the system performance under actual conditions can be widely expected to perform well on a complete judgment of normal-, miss- and multi-seeding at one time in the scheme. The finding can also provide a new reference for highly reliable monitoring of the potato seed-metering under severe dust and violent vibration environments.