**1. Introduction**

Maize is the largest food crop in China and occupies an extremely important position in the whole agricultural planting system. In the new era, with the rapid development of China's economy, the actual demand for corn has increased greatly [1,2]. Changes in corn supply and demand have a great influence on maintaining national food security and stabilizing the grain market and supply [3]. In recent years, with the major management mode of agricultural production gradually developing to a large-scale and intensive direction, to effectively ensure the cultivated area and grain production task and the completion of sowing operations in high-yield periods, higher quality requirements have been proposed for maize precision sowing technology [4–6]. Facing the higher cost-savings and efficiency requirements of farmers and the more urgent demand for agricultural time, the deficiencies of ground wheel drive are increasingly prominent [7,8]: (1) Low operation efficiency. At present, the operation of precision planters in China is still at a low-speed level of 6~8 km/h. (2) Unstable sowing quality. Under high-speed operation, it is easy to bump and slip, resulting in a series of problems, such as missed sowing, reseeding, and poor uniformity of plant spacing. (3) It is hard to monitor the sowing process [9]. Traditional machines and tools operate in a closed environment, requiring auxiliary personnel to follow the machine and observe, which is not only labor-intensive and costly but also easily causes personal injury, and the observation results make it difficult to eliminate the influence

**Citation:** Chen, J.; Zhang, H.; Pan, F.; Du, M.; Ji, C. Control System of a Motor-Driven Precision No-Tillage Maize Planter Based on the CANopen Protocol. *Agriculture* **2022**, *12*, 932. https://doi.org/10.3390/ agriculture12070932

Academic Editors: Jin Yuan, Wei Ji and Qingchun Feng

Received: 30 May 2022 Accepted: 24 June 2022 Published: 28 June 2022

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**Copyright:** © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

of human subjective factors. Sensor-based electronic metering systems can minimize the lacunae of mechanical metering systems. The application of electronic seed metering and control systems in planters is required for better seed uniformity in the field [10].

Sound and sustainable agriculture without electronics is inconceivable today, as electronic systems are used to reduce farm inputs, protect the environment, secure farm income, and produce high-quality products [11]. In the last few decades, a number of active seeding control and detection systems have been proposed to solve the above-mentioned problems. Yuan et al. [6] used prescription operation maps and GPS information, combined with speed, to drive a servo motor seed space and achieved precision planting that could be steplessly adjusted from 10 to 20 cm. Yang et al. [12] designed a mechatronic driving system. Compared to the mechanical driving system, the advantage of the mechatronic driving system is noticeable, especially when the forward speed is more than 11 km/h. Anil et al. [13,14] developed an electromechanical drive system (EMDS) for seed metering units of a classic single-seed planter to attain uniform seed spacing. EMDS realizes the recommended optimal seeding rate; the possibility for fast and simple setting, synchronization, and real-time control; the ability to work at higher speeds; single movement; and the control of each metering unit. The dynamic relationship model between the speed of the tractor and the speed of the metering plate is established to ensure the accurate matching of the tractor time and the seed entry to better realize seed spacing consistency. Ding et al. [15] proposed a control system of a motor-driven precision maize planter based on GPS speed measurements. At the same plant spacing and operating speed, the variation coefficient of the GPS velocity measurement method is smaller than that of the encoder velocity measurement method. At a high speed of 12 km/h, the average qualified GPS index is 14.32% higher than that of the encoder. This shows that the GPS velocity measurement method is more suitable for high-speed operation. Li et al. [16] resolved the problem that GPS receivers cannot meet the requirement of precision seeding at low speed based on a Kalman filter.

Variable-rate seeding (VRS) technology can adjust the seed input according to regional soil differences, ensure the most suitable plant density, make full use of nutrients and moisture in the soil, and exert the maximum yield potential in specific soil regions, thus significantly increasing yield and reducing cost. He et al. [17,18] developed a low-cost VRS control system based on a controller area network (CAN) bus and developed a compensation algorithm for seeding lag (CASL) that could decrease the seeding lag distance immensely. The developed VRS control system was capable of flexibly expanding planter rows and independently controlling each row's seeding rate. Ding et al. [19] developed a variable rate planter row-unit driver for maize. The overall test results of the row-unit driver confirmed that it could realize the functions of seed metering, seeding quality detection, and CAN communication with the main controller.

To improve the seeding uniformity of a maize planter, He et al. [20] designed a GPSbased turn compensation algorithm to offset the seeding rates of planter units. Field experiments indicated that a four-row planter equipped with the developed turn compensation control system had seeding accuracies (above 97%) and seeding coefficients of variation (below 1.52%) values better than those of a noncompensation planter under equivalent working conditions. To find the problem of seeding blockage and missing seeding in time, Meng et al. [21] developed a monitoring system to solve the phenomenon of maize precision seeding machines in operation and to improve the economy and efficiency of seeding. Xie et al. [22] conducted a study testing the accuracy of the sensor to monitor the seeding parameters of a precision metering device under different seeding speeds and seeding spacings. Improving the accuracy of the sensor's monitoring of the seed passing frequency is of great help in improving the seeding monitoring accuracy under the conditions of high seeding speed and small seeding spacing. Xie et al. [7] developed a precision seeding parameter monitoring system based on laser sensors Field tests showed that the average monitoring error of the seeding quantity was less than 1%, and the average

monitoring error of the seeding qualified rate was less than 1.5%. The monitoring system could trigger an alarm in time when the seeder had a missing seed fault.

In summary, most field experiments involving the seeder use four-row or six-row mechanical seeders. For the eighteen-row air suction seeder, in this study, an electrically driven precision sowing control system based on the CANopen protocol was designed, and a circuit board integrating the motor drive and sowing quality detection was developed. A seeding parameter dictionary with the CANopen protocol was constructed. A separable trapezoidal integral proportional integral derivative (PID) control algorithm was used to match the tractor speed and motor speed. In this paper, the performance of the control system was evaluated by laboratory bench and field tests.

#### **2. Materials and Methods**

#### *2.1. System Components*

The proposed maize precision planter system consisted of a monitoring subsystem and a mechanical device system. As shown in Figure 1, the required hardware components included a 12 V DC power supply, an on-board computer with a CAN bus (eMT3070B, Weintek Technology Co., Ltd., New Taipei, China), an in-house-designed integrated controller based on STM32F103VET6, an infrared monitoring sensor (Shandong Zhucheng Dilico Automotive Electronics Co., Ltd., Weifang, China), an inertial and satellite navigation module (WTGPS-200 WitMotion Shenzhen Co., Ltd., Shenzhen, China), brushed DC motors, and in-house-designed motor speed measurement modules. The mechanical part included a reducer, a planter plate, and a seed tube. The motor was used as an intermediary to integrate the control system and mechanical part.

**Figure 1.** Planter monitoring system.

In detail, the on-board computer communicated with the controller via a CAN bus and was used for setting the seed spacing, current threshold, and width; monitoring the various working states of the system (such as the motor current and rotational speed); and controlling the start and stop of a single motor. To reduce field wiring, in this paper, the controller was integrated with the motor drive and CAN communication, which was mounted on each planter unit, to expand flexibly based on the planter row number and to adjust the motor speed to achieve the desired seeding rate. In this study, speed acquisition was performed through inertial and satellite navigation modules with a velocity accuracy of 0.05 m/s, and bidirectional credit guaranteed communication with the controller through RS232. A brush DC motor was utilized to drive the seed meter at a desired speed, and a hall speed measurement module for the brushless DC motor was developed, nested on the shaft side of the motor, and a pulse was generated by an interaction with the magnetic

ring on the motor shaft. Additionally, a photoelectric sensor with a large field of view, high sensitivity, and strong dust resistance was installed on the seed tube to monitor the state of falling seeds. A circuit schematic diagram of the system with STM32F103VET6 as the main controller is shown in Figure 2.

**Figure 2.** Schematic diagram of the system circuit.
