Abstract:
Most of the motor drivers and monitoring sensors used in domestic electric drive precision maize planter are directly connected to the main controller. It’s difficult to expand the number of sowing rows and cannot meet the requirements of variable sowing operation for independent control of each single sowing unit. In order to reduce the coupling of the control system and alleviate the calculation pressure of the main controller, a hardware structure of row-unit controller based on STM32F103 was built, including motor drive circuit and seed quality detection circuit. The P-N 3-phase full-bridge BLDC (brushless direct current) motor drive circuit was based on FAN3278, which could regulate the rotate speed and prevent overload. The seed quality detection circuit was based on photoelectric sensor, which could realize photoelectric isolation and shaping of the sensor signal. The results of signal integrity test indicated that ripple voltage reduced 46.5%, signal transmission of each module was stable and working logic was reasonable. Moreover, a software architecture of the row-unit controller was constructed, the core algorithm included BLDC motor driving program and seed quality detection program was designed. A PID closed-loop control algorithm was used for BLDC motor driver to overcome the shortcomings of open-loop control. The final tuned PID parameter values:Proportional constant was 0.000 04,integration constant was 0.000 3,differential constant was 0.000 01. The results of no-load starting test on BLDC motor indicated that: within a set speed range of 300 -1 800 r/min, the max rise time was 0.4 s and the maximum overshoot was 1.56% on the speed response curve, the start performance met the requirement and speed of motor was improved. The data exchanged between the row-unit driver and the main controller via the CAN bus. The overall test results of the row-unit driver confirmed that it could realize the function of the seed metering driving, the seeding quality detection, and CAN communication with the main controller. The performance test results of seed metering device driving showed that the qualified index was more than 95.7% , the multiple index was less than 4.3%, and the miss index was less than 1.4% when forward speed was 3-9 km/h, which was higher than the national standard GB/T 6973-2005 requirement. The comparison test between the designed single unit driver and seed meter detector for performance evaluation revealed that the detection results were basically coincident. The maximum difference of precision index was only 0.1 percentage points when the speed was 3 km/h. The difference of the qualified index between the seed meter detector and the single unit driver was no more than 2 percentage points, the multiple index was no more than 1.1 percentage points, and the miss index was no more than 0.9 percentage points under different speed gradients. To sum up, the performance of the developed row-unit driver is applicable, and it can be applied in variable rate seeding.