The Design and Development of the Precision Planter Sowing Depth Control System

Transcription

1 Sensors & Transducers 2014 by IFSA Publishing, S. L. The Design and Development of the Precision Planter Sowing Depth Control System 1 Liping WEN, 2 Xiongfei FAN, 1 Zhao LIU, 1 Yong ZHANG 1 College of Mechanical and Electrical Engineering, Inner Mongolia Agricultural University, Huhhot, , China 2 College of Electronic and Information Engineering, Inner Mongolia University, Huhhot, , China Tel.: zynmg@imau.edu.cn Received: 21 October 2013 /Accepted: 9 January 2014 /Published: 31 January 2014 Abstract: In view the accuracy requirements of sowing depth control for precision planter, we carried out the design and development of control system. This paper main includes the working principle of the control system, the hardware and software design of electro-hydraulic proportional control system. It also respectively explains the software programming of PLC, the software programming of touch screen. Practical application shows that this system has advantages of stable operation, high reliability, convenient operation and maintenance, with high promotion and use value. Copyright 2014 IFSA Publishing, S. L. Keywords: Precision panter, Sowing depth, Electro-hydraulic proportional control, PLC, Touch screen. 1. Introduction Sowing depth is one of the strict indicators of precision seeder in its operation and it has very big effect on the output. In order to ensure the quality of crop planting, more and more people pay attention to the precise control of sowing depth [1]. The hydraulic proportional system as an important part of control system, because of its simple control, high control precision and fast response, which is widely used in various industries [2]. As the PLC with a reliable, flexible, and easy to use, it is widely used in automatic control systems [3]. This system uses PLC as its control core, combining with the electrohydraulic proportional system, which realizes the accurate control of sowing depth. And we chose touch screen as human-computer interaction interface to control the related parameter setting and signal concentrated display, it greatly improves the operability of the control system [4]. 2. The Working Principle of the Control System The control system uses Siemens S7-200 PLC as its main controller, applying ultrasonic sensors to gather position signal on the surface of ups and downs. When the opener homework drives the ultrasonic sensors move together, the real-time position signal which is detected by the ultrasonic sensors is converted into voltage (current) signal. At the same time, the collected data put into the PLC controller to carry on the corresponding processing, and output the results to the analog output module and then drive solenoid valve for the corresponding Article number P_

2 actions and control the oil cylinder up or down. It will control the depth of the opener adjusting device in real time, ensure that quickly and accurately adjust the depth of the planting operation and effectively control the precise sowing depth. Through the integration of embedded touch screen, people can set relevant parameters in real-time. And touch screen through its communication port to realize the communication with PLC and centralized display the real-time collected information [5]. The schematic diagram of the working principle of the control system is shown in Fig. 1. can get the distance value between the object and the sensor. Ultrasonic sensor measure the distance principle is shown in Fig. 3. The ultrasonic sensor is shown in Fig. 4, its parameters are shown in Table 1. Fig. 3. Ultrasonic sensor measure the distance principle. Fig. 1. The schematic diagram of the working principle of the control system. 3. The Electro-hydraulic Proportional Control System The design diagram of seeding depth control system is shown in Fig. 2. Fig. 4. The ultrasonic sensor. Table 1. The ultrasonic sensor parameters. Product Name NU200F30TR-2MVA Center Frequency 200 khz Maximum Measuring Distance 2000 mm Blind Area 200 mm Target Board mm Supply Voltage 24 VDC Output Type 0-5 V Angle( ) 7 Material Metal Operating Temperature -40 C ~ +70 C Fig. 2. The design diagram of seeding depth control system Ultrasonic Sensors Ultrasonic sensors are used to measure the distance to the object. First, the ultrasonic sensor emits high frequency sound waves, usually khz, when sound waves encounter an object, it will be bounced back and received. By calculating the time of sound waves from the transmitter to the return, the time multiplies the propagation speed of sound waves in the media (344 m/s, in air), then we 3.2. Electro-Hydraulic Proportional System Proportional Flow Control Valve The valve can be used as priority flow regulator with pressure compensation, adjusting the bypass flow. When the bypass circuit is off, it also can be used as restrictive, two-pass, pressure compensated flow regulator. The proportional flow control valve will regulate the flow of the oil port, the flow is not subject to the system working pressure. With the solenoid current increases, the output flow will increase. The characteristic curve of proportional flow control valve is shown in Fig

3 Fig. 5. The characteristic curve of proportional flow control valve. cylinder rod is connected with the depth adjusting device, the cylinder rod moving up and down is controlled by hydraulic servo valve. When the pump started, the hydraulic oil inflows proportional flow valve via port (1), the opening degree of proportional flow valve is controlled by the controller input current, so as to control the flow of the oil port (2). When the solenoid valve 1, 2, 3, 4 are no electricity, the oil circuit is closed. When the solenoid valve 1 and 4 simultaneously energized, hydraulic oil will drive cylinder piston moving upward through the solenoid valve 1. Similarly, when the solenoid valve 2 and 3 simultaneously energized, hydraulic oil will drive cylinder piston moving downward through the solenoid valve Proportional Valve Controller The controller is controlled by closed loop current with superimposed dither. The current provides proportional control signal to proportional valve s solenoid. The input signal of controller is from 0~10 VDC. The controller has four input, two output, POW+ is connected to the positive electrode of 24 V DC power, POW- is connected to the negative electrode of 24 V DC power, V-IN is connected to the positive electrode of 0~10 V analog output signal, GAND is connected to the negative electrode of 0~10 V analog output signal, SOL+ and SOL- p are connected to the positive and negative electrode of the proportional flow control valve s solenoids. The proportional valve controller is shown in Fig. 6. Fig. 7. The hydraulic control system working principle. The picture of hydraulic system is shown in Fig. 8. Fig. 6. The proportional valve controller Electro-Hydraulic Proportional System Working Principle The hydraulic control system working principle is shown in Fig. 7. Hydraulic pump is the power source of the system, hydraulic cylinder is the actuator. Cylinder tube of the hydraulic cylinder is fixed, the Fig. 8. The picture of hydraulic system. 55

4 4. The Control System Software Design 4.1. S7-200 PLC Program Design The PLC programming software is STEP7- MicroWIN V4.0. It can use statement list (STL) or ladder diagram programming (LAD) in its running environment. The compiled program downloaded to the PLC by special PPI/USB communication cable after compiled, or let the PLC program upload to the first place machine PLC I/O Address Assignment This precision seeder includes 4 seeding channels, seeding cell components are designed for single, so that can separately control the sowing depth according to different size of surface relief. It is easier to set and adjust the control precision of planting operation actuator. PLC I/O address assignment is shown in Table 2. Table 2. PLC I/O address assignment. Port Corresponding Parts Address The start button of oil pump motor I0.0 The stop button of oil pump motor I0.1 The scram button of system I0.2 The fault of oil pump motor I0.3 The Operation of oil pump motor Q1.0 The decline solenoid valve of channel 1 Q0.0 The rising solenoid valve of channel 1 Q0.1 The distance measuring sensor of channel 1 AIW4 The channel 1 output of Proportional valve AQW The Program Compilation of PLC The PLC program includes the main program, subprogram 1 and 2. The main program mainly implements procedure calls, Subprogram 1 realizes analog sampling subroutine, PID arithmetic and distributes storage cell for analog sampling and PID arithmetic and then initialization. And it includes analog input or output module and the ratio between the amount of numerical conversion, etc. Subprogram 2 is mainly used in the motor control of the control system, such as the host and the oil pump motor start or stop, and according to the comparison results of the set value and measured value control the hydraulic cylinder upward or downward. The main codes of control program are as follows: 1) Channel 1 actual sowing depth with the set value difference calculation. LD M0.5 MOVR VD952, VD936 -R VD100, VD936 2) Actual difference compares with the set error limits. LDR< VD936, 0.0 *R -1.0, VD936 AENO AR>= VD936, VD920 LDR>= VD936, 0.0 AR>= VD936, VD920 OLD = M3.0 3) Cylinder down control program (similar to the cylinder up). LD M0.5 A M3.0 AR< VD100 LDN M0.5 A M0.6 OLD A Q1.0 AN Q0.1 = Q The Software Design of Touch Screen The program of touch screen is designed by special MCGS7.6 embedded version of the configuration software. It includes two parts: the configuration and running environment. Firstly, we can design the window operations, such as interface in the configuration environment. And after the completion of the design, it can simulate the configuration screen in the running environment and downloaded the compiled program to the memory of touch screen through the Ethernet front-end ports. MCGS provides complete solutions and development platform for users to solve the practical engineering problems. And it can realize functions of the data acquisition, real-time and historical data processing, alarm and security mechanism, process control, animation display, trend curve, report output and enterprise of monitoring network, etc. [6]. The MCGS configuration software includes five parts: the main control window, equipment window, user window, real-time database and operation strategy, and every part configures operation separately, completes different jobs and has different characteristics. Each part of its specific function is shown in Fig. 9. Fig. 9. Each part of its specific function. 56

5 The Visual Design of Touch Screen The touch screen software user interface design involves creating images and information, then they are connected with the PLC program. Including the following three steps: 1) Animating the display screen: Graphic design animation is divided into static and dynamic properties settings. The first part is similar to "paint", Users use the basic graphic elements and animation component library of MCGS configuration software, combined into a variety of complex picture in the user window. Graphic animation properties are set in another section, Graphic animation property is set in the other part, and connecting variable of the realtime database. It is used as a drive source of animated graphics [7]. 2) Configuring data variables: Screen elements and PLC I/O points and the storage unit are connected by the variable. So that the parameters of the PLC control system or instructions can be input via the touch screen, PLC current process values and alarm signal is output to the touch screen. This operation requires the establishment of a new variable in the real-time database, then the variable is connected with the PLC channel address in the device window. Part of the data configuration variables (seeding channel 1) is shown in Table 3. Fig. 10. The communication of system. TPC7062k touch screen and PLC via RS485 serial port to achieve communication. The specific parameters are set in the device window. The system PLC station address is 2, serial port number is 1, the communication baud rate is 9600 bps, data validation method is even parity Building the User Screen According to the test requirements, I established sowing depth monitoring system screen, including parameter setting and the curve display window etc. Through operating these windows, we can complete parameter settings, switching system running status, generate real-time curve and the historical curve etc. The main screen is shown in Fig. 11. Table 3. Data variable table. Variable name Channel name start I000.0 stop I000.1 Emergency Stop I000.2 Fault I000.3 Valve 1 open Q000.0 Valve open Q000.1 Pump run Q001.0 Manual / automatic switching M000.5 Set_value VDF100 P_set VDF118 Ts_set VDF122 Ti_set VDF126 Proportional valve opening show VDF134 Proportional valve opening set VDF138 Setting error limit VDF920 Actual sowing depth VDF952 Communication status SM000.0 Fig. 11. The main screen. 3) Setting communications parameters establish communication between the PLC and touch screen. The communication of system is shown in Fig. 10. PC and touch screen are connected via RJ45 interface, communication protocol uses Modbus TCP/IP protocol. Touch screen and PLC are connected via RS485 interface, communication protocol uses PPI protocol. 5. Conclusion The system is based on PLC to realize controlling electro-hydraulic proportional valve, its advantages include fast response, simple hardware circuit design, high accuracy. Also, using the PLC comes with PID control algorithm, the program is highly integrated, run fast and easy to implement rapid control, it is 57

6 better to meet the control requirements of electrohydraulic proportional system. In the sowing depth control system, using PLC and touch screen can not only reduce the number of electrical components on the operating table, omitting complex electrical wiring, but also it enables the operation of the entire control system more humane [8], the operating performance of the control system is greatly improved. Meanwhile, because of the system has a high value of promotion and use, it can also be applied to control and transformation of other sectors. Acknowledgements This research obtained the help from National Natural Science Foundation of China ( ), Dr. Start-up Fund of Inner Mongolia Agricultural University (Approval No. BJ08-11). We would like to express our sincere gratefulness to them. References [1]. X. Wang, H. Y. Zhang, J. Zhao, Research of electrohydraulic profiling institutions of soybean seeder, Journal of Agricultural Mechanization Research, Vol. 32, Issue 1, 2010, pp [2]. L. X. Li, X. Y. Mao, D. Y. Bian, Design the electrohydraulic proportional flow control system based on PLC, Journal of Machine Tool & Hydraulics, Vol. 41, Issue 4, 2013, pp [3]. S. Z. Wang, J. Y. Han, Research on PLC control system of precision drill, Journal of Modern Agriculture, Vol. 4, Issue 333, 2007, pp [4]. J. Dai, G. S. Hao, Y. Q. Zhou, The applications of touch screen and PLC in papermaking machinery control system, Journal of Electrical and Mechanical Engineering, Vol. 19, Issue 2, 2002, pp [5]. L. P. Wen, Y. Zhang, X. F. Fan, C. H. Zhang, The research of precision planter sowing depth control system based on PLC, Journal of Agricultural Mechanization Research, Vol. 36, Issue 2, 2014, pp [6]. H. Lan, The design of hydraulic test bed based on MCGS, Journal of Shanxi Coal Management Institute, Vol. 25, Issue 3, 2012, pp [7]. W. Zhou, P. Yang, D. Xu, The design of PC control system based on MCGS, Journal of Manufacturing Automation, Vol. 30, Issue 12, 2008, pp [8]. P. Lv, Application of control system composed of PLC and touch screen, Journal of Process Automation Instrumentation, Vol. 31, Issue 8, 2010, pp Copyright, International Frequency Sensor Association (IFSA) Publishing, S. L. All rights reserved. ( 58