summary
This paper analyzes the motion control processes of the handling robot, cutting device, and clamping device. Finally, considering the characteristics of vegetable grafting operations, a PLC-based automatic control system for cucumber grafting is developed. This includes the hardware and software design of the controller, as well as the design of self-diagnosis and self-processing programs for faults. It not only enables step-by-step control in manual operation mode, facilitating prototype debugging, program modification, and fault diagnosis, but also achieves automatic control of the grafting process to maximize its work efficiency. The machine has strong anti-interference capabilities, high reliability, and significantly improves grafting efficiency, making it highly valuable for widespread application.
Keywords: Grafting automated programmable logic controller (PLC) device
Foreword
With the rapid growth of my country's population and the rapid improvement of people's living standards, the demand for vegetables is increasing, and the requirements for vegetable quality are also becoming higher. Cucumber, as a popular vegetable in my country, has a large consumption volume, leading to rapid development in cucumber production and a considerable planting area. However, this has also brought problems such as continuous cropping and pests and diseases. Grafting is one of the most effective methods to solve these problems. However, manual grafting has low productivity and significant variations in grafting quality, making it difficult to meet the requirements of vegetable grafting seedling production. Therefore, research on grafting machines has important theoretical significance and practical value for promoting the mechanization of vegetable grafting.
Vegetable grafting technology is widely used in some agriculturally developed countries, but only a few countries, such as Japan, South Korea, and China, have conducted research on automated grafting technology for vegetable seedlings. Japan was the first country to conduct automated grafting of vegetable seedlings. Since my country began research on automated vegetable grafting in 1993, it has achieved significant progress in several areas, and some prototypes have already been put into production.
1. System Structure Design
The grafting machine is designed using a modular approach, dividing the entire system into several modules. It is an automatic cucumber grafting device, mainly comprising a rootstock and scion feeding mechanism, a rootstock and scion transport robot, a rootstock and scion cutting mechanism, and a clamping mechanism. This achieves functions such as feeding, cutting, and clamping the rootstock and scion seedlings. The seedling cutting mechanism employs a supported sliding cutting technique, which not only reduces cutting resistance but also ensures good stability in the cut position and shape, facilitating subsequent operations. Tests have shown that this cutting method significantly reduces damage to the rootstock and scion compared to the cutting method used in the 2JSZ-600 vegetable grafting machine. The robot gripper has a "V"-shaped alignment groove, and the gripper fingers are fitted with cushioning pads to prevent damage to the seedlings and absorb stem misalignment. Compared to other grafting machines, this machine has advantages such as simple structure, accurate operation, and high grafting efficiency.
2. Grafting machine components
The grafting method, including the bonding method, has significant advantages over other grafting methods in terms of ease of grafting, survival rate, and grafting speed, making it suitable for machine grafting. Therefore, this study uses the bonding method to achieve automated grafting of cucumber seedlings.
The grafting machine mainly consists of the grafting machine body, controller and sensing system, and its structural framework is shown in Figure 1.
Figure 1. Structure diagram of the automatic grafting machine system
1. Timber conveyor motor; 2. Flange; 3. Timber conveyor belt; 4. Timber direct-acting cylinder; 5. Timber clamping gripper and sensor; 6. Feeding direct-acting cylinder; 7. Cylinder fixing bracket; 8. Seedling clamp; 9. Seedling clamp; 10. Seedling clamp feed rail; 11. Seedling clamp damping block; 12. Rootstock conveyor belt; 13. Bearing seat; 14. Rootstock seedling tray; 15. Rootstock clamping gripper; 16. Direct-acting cylinder fixing seat; 17. Cylinder fixing bracket; 18. Rootstock conveyor motor; 19. Sensor; 20. Rotary cutter; 21. Cutting blade direct-acting cylinder; 22. Rotary cylinder; 23. Cylinder fixing bracket.
The grafting machine mainly consists of four parts: two seedling trays and a seedling transport system that drives the trays; a robotic arm for grasping and delivering seedlings to designated positions; a cutting device for cutting the rootstock and scion; a clamping mechanism for securing the cut rootstock and scion together; and a seedling conveyor belt for discharging the grafted seedlings. The seedling platform has two workstations, each equipped with a gripper for grasping and transporting the rootstock and scion. The gripper's grasping and extension are controlled by a direct-acting cylinder. According to the requirements of grafting operations, both the rootstock and scion need to be cut obliquely (monocotyledonous). Therefore, the cutting mechanisms for the rootstock and scion are similar, mainly composed of a cutting blade, a swing motor shaft, a spring, a cutting mechanism support, and a cutting support mechanism. The automatic clamping mechanism of the grafting machine mainly consists of a pushing cylinder, a pushing rod, and a slider.
3. The working process of the grafting machine
When the operator places the rootstock and scion seedlings onto their respective seedling platforms, the piezoelectric sensor is triggered, sending a signal to control the robotic arm's gripper to immediately grasp the seedling, awaiting the cutting blade's cut. To ensure operational safety, the cutting blade first extends to the cutting position under the action of a direct-acting cylinder. Then, a rotary motor (oscillating motor) drives the cutting device to rotate, achieving single-support cutting of the rootstock and scion seedlings. This ensures a stable cut surface and reduces impact and damage to the seedlings. The cutting mechanism then returns to its original position, awaiting the next cut. The process begins with the cutting process. At this point, the robotic arm holding the cutting seedling extends to the clamping position under the action of a direct-acting cylinder and engages at the center of the cutting blade's rotation. The feeding mechanism, under the action of the direct-acting cylinder, pushes out a clamp, opening it and feeding it towards the grafted seedling. When it reaches the clamping position, the seedling clamp closes under the action of a spring, thus clamping the rootstock and scion. Finally, by controlling the gripper cylinder, the robotic arm releases the rootstock and scion seedlings, allowing the grafted seedling to fall onto the seedling transport conveyor belt, thus transporting the seedling outwards and completing the grafting operation.
4. Design of rootstock and scion cutting device
(1) Structural design of cutting device
When grafting using the grafting method, it is required to cut the scion and rootstock separately with a blade. The rootstock needs to be cut at an angle with its monocotyledonous leaves, and the scion also needs to be cut at an angle. Therefore, the cutting mechanisms for the rootstock and scion are similar, mainly consisting of a direct-acting cylinder, a rotary cylinder (oscillating motor), a cutting blade, a cutting support mechanism, and a cylinder fixing mechanism. The cutting device is shown in Figure 2.
Figure 2. Structure diagram of the cutting device
1. Cutting tool 2. Cutting tool holder 3. Direct-acting cylinder 4. Rotary cylinder 5. Cylinder fixing mechanism
This study uses a rotary cylinder, i.e., a swing motor, to drive a gantry-shaped cutting bracket. Cutting blades are installed on both sides of the bracket to cut the rootstock and scion respectively. A schematic diagram of the rotary cutting is shown in Figure 3. This mechanism only requires one rotary cutting component to simultaneously cut the rootstock and scion, reducing the number of working and control components and making the entire grafting machine structure more compact.
Figure 3 Schematic diagram of rotary cutting
The swing motor uses the MB-type vane swing motor manufactured by Tianjin Tejing Park Pneumatic & Hydraulic Machinery Co., Ltd.
The output torque of the vane-type oscillating motor is a key performance parameter, representing the motor's output capacity. The magnitude of its torque is:
in:
M—Torque (Nm); D—Cylinder body diameter (m); d—Output shaft diameter (m); b—Blade output length (m); n—Number of blades; p—Working pressure (MPa)
(2) Design of the robotic arm
Based on the requirements of the grafting process for the robot's movements, the robot mainly consists of sensors, cylinder grippers, and direct-acting cylinders.
The direct-acting cylinder, employing a single-piston rod and double-piston design, features high reversing accuracy, torque resistance, strong load capacity, smooth operation, and simple assembly. It is widely used in pneumatic systems for gripping, feeding, assembly, and machining, and can serve as the drive unit for the body and arm of pneumatic robots. The allowable load and load characteristics of the direct-acting cylinder are shown in Figure 5. The allowable load F can be determined from the load characteristic diagram based on the stroke and cylinder diameter. In practical applications, it is required that…
Figure 4 Allowable load and load characteristics of direct-acting cylinder
Experiments show that the designed handling robot operates smoothly, has a strong overload capacity, and performs well.
5. Power Module Design
The power module design for the automatic cucumber grafting machine system requires supplying two voltages: 220V, 50Hz AC for the seedling motor and 24VDC for the electromagnetic reversing valve and programmable controller. The power module circuit is shown in Figure 6.
Figure 5 Power module circuit diagram
6. Hardware Design of PLC Control System
The hardware of the grafting machine control system mainly consists of a PLC and external devices. The main function of the PLC in the system is to coordinate the operation of each subsystem according to the grafting requirements. Therefore, it must not only perform various logic controls, but also monitor the system. Figure 7 is a schematic diagram of the automatic grafting machine control system.
Figure 6 Schematic diagram of the automatic grafting machine control system
7. Grafting machine control panel diagram
The control panel layout, based on the functional requirements of the grafting machine controller, is shown in Figure 8. During grafting machine operation, the operator interacts with the controller in real time through the control panel, which is equipped with buttons and indicator lights. The panel's indicators and controls are laid out in a modular, partitioned design. In the upper left corner, indicators 1 and 2 are fault and normal operation indicator lights; in the middle section, indicators 3 and 4 are the operating mode switch, with three positions: left for automatic mode, middle for stop, and right for manual mode; indicators 5 and 6 are the anvil gripper switches—upward gripping and downward releasing; indicators 7 and 8 are the anvil forward movement switches—upward movement forward and downward movement backward; indicators 9 and 10 are the cutting tool switches—upward movement forward and downward movement backward; indicators 11 and 12 are the start and stop buttons; indicator 13 is the manual rotary cutting button; indicator 14 is the manual clamping button; indicators 15 and 16 are the stubble gripper switches—upward gripping and downward releasing; and indicators 17 and 18 are the stubble forward movement switches—upward movement forward and downward movement backward.
Figure 7. Control panel diagram of the grafting machine
in conclusion
A PLC-based automatic control system for cucumber grafting was developed. It not only enables step-by-step control in manual operation mode, facilitating prototype debugging and program modification, but also achieves automatic control of the grafting process to maximize its working efficiency. Compared with current domestic single-chip microcomputer control systems, it has better debuggability and operational reliability. Grafting experiments on the designed cucumber grafting machine showed a high grafting success rate.
[Author Biography] Dong Jianmin (1979-), male, Han nationality, from Zibo, Shandong Province, postgraduate, assistant lecturer in the Measurement and Control Teaching and Research Section of the Electrical Engineering Department of Shandong Industrial Vocational College, mainly engaged in research and teaching of automatic control and communication technology.
Mailing Address: Department of Electrical Engineering, Shandong Industrial Vocational College, No. 69 Zhangbei Road, High-tech Development Zone, Zibo City, Shandong Province, 256414, China; Tel: +86 13280669298; E-mail: [email protected]
