Design and test of the seeding amount control system for the rape mechanical metering device

Abstract: A rapeseed centrifugal metering device has been widely used in field, due to its compact structure, high efficiency, low cost, and low seed crushing rate. The centrifugal force and seed gravity can also be utilized to realize the simultaneous seeding of multiple rows through the seed outlets of the upper edge of the outer cone canister. However, the seeding amount relies mainly on the forward speed of the planter, the filling quality of the inner cone canister, the size of seed particles, and seeding plant space. In this study, a seeding amount control system was designed to improve the performance of the rapeseed centrifugal metering devices. The system consisted of a microcomputer, a seeding detection, a speed measuring, a seed metering drive, and a human interaction module. Specifically, the microcomputer used a singlechip with the type of STM32F103C8T6 as a processor to coordinate the orderly operation of each functional unit. The seeding detection module was developed to real-time monitor the seeding amount of the seed metering device using a photoelectric sensor with the type of PG-602 and a signal amplifier with the type of PG-610. The speed measuring module was to monitor the sowing speed using a hall sensor with a magnetic steel disk. More importantly, the seed metering drive module was composed of a stepper motor with a model of 57HSE and a supporting driver with the type of HB808C. As such, the rapeseed centrifugal metering device was driven to rotate for the centrifugal force of seeding. Furthermore, a seeding control strategy was formulated to realize the uniform seed metering of sowing quantity. A seeding control model was selected to dynamically change the centrifugal speed of the centrifugal metering device via the seed metering drive module, in terms of the error between the actual and the theoretical seed metering amount. The actual seed metering number of the seed metering device was achieved within the seeding qualified range. A Bench test was carried out to determine the optimal seeding control model and operation parameters of the system. The results showed that the seeding control model was a linear model. The accuracy of the system for the seed amount detection was over 96.17%, and the optimal feedback time was 4 s. A performance test was also conducted to verify the response of the seeding amount control system to the changes in planter forward speed, the inner cone canister filling quality, the seed particle size, and the seeding plant space. The test results show that the qualified rate of seed metering regulation of the system was 92.11%, when the forward speed of the planter changes in a sinusoidal curve, indicating a better performance than that without a seeding amount control system. When the seed filling mass of the inner cone canister changed from 60 to 480 g, the seed metering errors of the control system were 9.55%, 6.91%, 6.53%, 3.89%, 4.73%, 4.2%, 2.33% and 4.98%, respectively, which were 47.68, 33.12, 3.05, 3.42, 6.06, 9.33, 11.42 and 8.55 percentage points lower than before. The metering errors of the control system for the large, medium, and small seeds were 4.70%, 3.98%, and 7.74% respectively, which were 10.79, 9.80, and 18.63 percentage points lower than before. The metering errors of the control system were 5.26%, 2.24%, and 6.53%, respectively, when the values of sowing plant spacing were 70, 100, and 130 mm, respectively. A field seeding experiment was performed on the improved system and the optimal feedback time. The results showed that the seeding error of the system was less than 10.00%, the average seeding error was 5.77%, and the qualified rate of seeding amount control was 90.68%, indicating a better seeding performance, and a much more uniform seedling emergence than before. Consequently, the new control system of seeding amount can be expected to effectively reduce the changes impact of planter forward speed, inner cone canister seed filling mass, seed particle size, and seeding plant space on the operating performance of rapeseed centrifugal metering device for the better function of uniform seeding.