Abstract: Given the high environmental requirements, low reliability, high operator skill requirements, and limited applicability of traditional PC or microcontroller control systems in automatic grafting machine control, a PLC-based grafting machine control system is designed. This includes the hardware and software design of the controller, as well as the design of self-diagnosis and self-handling fault programs. This system overcomes the shortcomings of microcontroller control systems, enabling step-by-step control in manual mode and continuous operation in automatic mode, thus improving work efficiency and grafting reliability.
Keywords: Automatic grafting machine; Control system; PLC
Chinese Library Classification Number: TP273 Document Identification Code: B
Design of control system of automatic grafting machine
Mu Ai-xia Peng Li-ying
(Shandong Vocational College of Industry Shandong Zibo 256414)
Abstract: As a traditional PC or SCM system had the features of a strict working condition, a skill manipulator, and poor reliability, designed of a PLC control system of automatic grafting machine. including controller's hardware design, software design as well as breakdown from diagnosis and from processing and so on, not can only realize under the manual work pattern the stepping control, moreover may realize grafts the process the automatic control, enhanced greatly grafted the efficiency and the reliability.
Keywords: automatic grafting machine; control system; PLC
For the control of automatic grafting machines, most of the systems used at home and abroad are PC or microcontroller systems [1] . Given that PC and microcontroller systems have disadvantages such as high requirements for the working environment, weak anti-interference ability, low working reliability, high technical requirements for operators, and poor promotion [2] , the author developed a grafting machine control system with PLC as the controller. By controlling the seedling feeding device, cutting device, clamping device and other working parts through program control, the disadvantages of the microcontroller control system are overcome, continuous operation is realized, and the working efficiency and grafting reliability are improved.
1. Overall structural design of the grafting machine
The grafting machine mainly consists of the grafting machine body, controller and sensing system, and its structural framework is shown in Figure 1.
1.1 Composition of the grafting machine
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.
1.2 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 seedlings, awaiting the cutting blade to make the cut. To ensure operational safety, the cutting blade...
First, under the action of the direct-acting cylinder, it extends to the cutting position, and then the rotary motor (swing motor) drives the cutting device to rotate, so as to realize the single support cutting of the rootstock and scion seedling, so as to ensure a stable cut surface and reduce the impact and damage to the seedling; then the cutting mechanism returns to the position and waits for the next cutting; at this time, the mechanical arm holding the cutting seedling extends to the clamping position under the action of the direct-acting cylinder and engages at the center of the cutting blade rotation; under the action of the direct-acting cylinder, the clamping mechanism pushes out a clamp and sends it to the already joined seedling in an open state. When it reaches the clamping position, the seedling clamp closes under the action of the spring, realizing the clamping of the rootstock and scion. Finally, by controlling the gripper cylinder, the mechanical arm releases the rootstock and scion seedling, so that the grafted seedling falls onto the seedling transport conveyor belt, realizing the outward transport of the seedling and completing the seedling grafting operation [3].
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 mounting bracket 8. Seedling clamp cylinder 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 mounting base 17. Cylinder mounting bracket 18. Rootstock conveyor motor 19. Sensor 20. Rotary cutter 21. Cutting blade direct-acting cylinder 22. Rotary cylinder 23. Cylinder mounting bracket
2. Hardware Design of Grafting Machine 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 2 is a schematic diagram of the automatic grafting machine control system.
2.1 PLC Address and Function Terminals
The PLC has external signal input terminals and output terminals. The signal input terminals are connected to control elements such as switches; the signal output terminals are connected to actuators such as motors, cylinders, and robotic arms. The main address and function correspondences in the control system are shown in Table 1.
2.2 Grafting Machine Input/Output Wiring Diagram
The input/output wiring diagram of the grafting machine is shown in Figure 3.
SA1 is the operating mode switch with three positions: left for automatic mode, middle for stop, and right for manual mode. SB1 is the start button, SB2 is the stop button, SB3 is the manual cutting button, SB4 is the manual clamping button, SA2 is the anvil gripper switch, SA3 is the scion gripper switch, SA4 is the anvil straight-line switch, SA5 is the scion straight-line switch, SA6 is the cutting tool advance/retreat switch, SA7 is the cutting tool advance/retreat limit switch, LK is the limit switch, LP2 and LP3 are fault display and operation indicator lights, QA is the air switch, L1 is the live wire, N is the neutral wire, and QG is the solenoid directional valve, which controls the movement of the robot arm, cylinders, etc.
Figure 3. Wiring diagram of grafting machine input/output
Fig. 3 wiring diagram of input and output system of grafting machine
3. Software Design of Grafting Machine Control System
The control part of the grafting machine mainly includes the control of cylinders, robotic arms, cutting and clamping devices, etc. [6]. Its control system flow is shown in Figure 4.
Figure 4. Flowchart of the grafting machine control system
Fig4 flow chart of control system of grafting machine
To facilitate debugging, this system is designed with two working modes: manual mode and automatic mode [7]. During the debugging phase, manual mode is used, which can realize the control of a single step and a single action, making it easy to modify the program; the workflow in automatic mode is as follows:
Process description: When ready, press the "start" button. If the work indicator light is on, it means that the machine can start working normally. At this time, the working mode of the grafting machine can be selected by the working mode switch. The sensor detects the position of the rootstock and scion seedling. If they are in place, the rootstock and scion seedling are connected, the robot grabs the seedling, and prepares for cutting. The direct-acting cylinder of the cutting mechanism moves straight, and the limit position is determined by the limit switch. If it is in place, the swing motor controls the rootstock and scion seedling to rotate and cut. The cutting blade is reset, and the seedling grabbing robot pushes the seedling to the clamping position by the direct-acting cylinder to complete the clamping and bonding of the rootstock and scion seedling. Finally, the robot finger cylinder controls the robot to release the seedling, and the seedling is sent out by the conveyor belt. The robot is reset [8].
This design utilizes the Omron CPM2AE-60CDR-A programmable controller, a 60-point main unit with 36 inputs and 24 relay outputs. The key modules for the automatic grafting machine's operation are the seedling feeding mechanism, the cutting mechanism, and the clamping mechanism. During the design process, these three modules were designed and debugged separately, achieving the expected results.
4. Fault Detection and Diagnosis
The reliability of programmable logic controllers is very high. They have a complete self-diagnostic function. If a programmable logic controller fails, the faulty part and component can be easily found with the help of the self-diagnostic program. After replacement, it can be restored to normal operation. The failure rate of external input and output components of programmable logic controllers, such as limit switches, solenoid valves, contactors, etc., is much higher than that of programmable logic controllers themselves. When these components fail, programmable logic controllers generally cannot detect it and will not automatically stop. This may cause the fault to expand until the high-voltage protection device is activated and the machine stops. Sometimes, it may even cause equipment and personal accidents [9]. After the machine stops, it takes a lot of time to find the fault. In order to find the fault in time, to make the programmable logic controller automatically stop and alarm before an accident occurs, and to facilitate the finding of faults and improve maintenance efficiency, an automatic protection program is designed to realize the self-diagnosis and self-processing of faults.
The time required for each step of the equipment's operation is generally constant, and even if it varies, it won't be significant. Therefore, these times can be used as a reference. When the programmable logic controller (PLC) sends an output signal and the corresponding external actuator begins to operate, a timer is started. The timer's set value is approximately 20% longer than the normal duration of the operation. If the operation time exceeds the corresponding timer's set time, and the PLC has not yet received the operation completion signal, the normally open contact of the timer, which is delayed, sends a fault signal. This signal stops the normal loop program, activates the alarm and fault display, allowing operators and maintenance personnel to quickly identify the type of fault and take timely measures to troubleshoot it.
5. Conclusions and Outlook
Compared with other grafting machines, this device has the advantages of simple structure, accurate operation, high grafting efficiency, and strong anti-interference ability.
A PLC-based automatic grafting control system was developed. It not only enables step-by-step control in manual operation mode but also achieves automatic control of the grafting process and self-diagnosis of faults. Compared with current domestic single-chip microcomputer control systems, it improves work efficiency and grafting reliability. Prototype test results show that this device can graft at a speed of 1200 grafts/hour, more than double the efficiency of the 500 grafts/hour grafting speed of single-chip microcomputer-controlled grafting machines.
To adapt to rootstocks and scions of different shapes and ages, grafting robots can be designed with flexible arms that can change their working posture according to the shape of the seedling stem, ensuring a high success rate for grafting different seedlings.
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