I. Introduction
Continuous batching and conveying automatic control systems are widely used in industries such as cement, coal, metallurgy, chemicals, feed, and food. They are characterized by comprehensive functions, high flexibility, and cost-effectiveness, making them popular with continuous batching system integrators and users. This system integrates modern logistics technology, warehousing technology, and automation technology, and is a crucial component of CIMS (Continuous Intake Management System). It has been widely adopted abroad, and this technology is gradually being applied to many industries in my country.
After joining the WTO, my country's commodity distribution and delivery service market will gradually expand its open areas and scope. Logistics is a key issue for enterprise development, impacting its overall survival and growth. In 2000, logistics costs accounted for 16.7% of China's GDP, while in the United States it was less than 10%. In particular, there is a significant gap between the logistics equipment levels of enterprises and those in developed countries, mainly manifested in low transportation efficiency and astonishing waste in the logistics process. We know that this gap represents potential and room for development; therefore, improving the level of logistics equipment has become an urgent task. Automated material handling vehicles are an important component of the transportation and distribution system in logistics; they are systems that automatically store and retrieve materials.
II. Automatic Material Control System for Process Production Control
The automated logistics control system primarily controls the conveying system to complete its material transport tasks. Elevators and conveyor lines are installed at the material inlet and outlet. This creates a closed-loop conveyor system within the warehouse, production workshop, and packaging workshop, ensuring smooth access to all production locations. All materials and finished products used in the production process must ultimately be loaded into barcode-labeled containers and transported to trucks. Under the influence of production instructions issued by the production management system, materials enter the conveying system from the designated inlet. The automated logistics control system is shown in Figure 1.
Overall control requirements: As shown in the figure, the system consists of a hopper, a conveyor belt, and a detection system. The batching device can automatically identify the arrival status of the trucks and automatically batch the materials onto them. When a truck is full, the batching system automatically stops batching. When the material in the hopper is insufficient, batching stops and automatic feeding begins.
The process control requirements are as follows:
(1) Initial state
After the system starts, red light L2 goes out and green light L1 lights up, indicating that the truck is allowed to enter for loading. The hopper outlet D2 is closed. If the level sensor S1 is OFF (the hopper is not full), the feed valve opens to feed material (D4 lights up). When S1 is ON (the hopper is full), feeding stops (D4 goes out). Motors M1, M2, M3, and M4 are all OFF.
(2) Loading control
During loading, when the truck enters the loading position, limit switch SQ1 is turned ON, red indicator light L2 illuminates, and green indicator light L1 turns off. Simultaneously, motor M4 starts. After 2 seconds, motor M3 starts, followed by motor M2 after another 2 seconds, and finally motor M1 after another 2 seconds. The discharge valve (D2 illuminates) opens after another 2 seconds, and material is discharged through the hopper. When the truck is full, limit switch SQ2 turns ON, the hopper closes, and motor M1 stops after 2 seconds. Motor M2 stops 2 seconds after M1 stops, motor M3 stops 2 seconds after M2 stops, and motor M4 stops 2 seconds after M3 stops. Simultaneously, red indicator light L2 turns off, and green indicator light L1 illuminates, indicating that the truck can drive away.
(3) Shutdown control
Turning off the SD start switch will terminate the entire automatic batching and loading system.
III. System Hardware Design
1. System Schematic Diagram
2. I/O Configuration and Wiring
To improve the reliability of the automatic control system and the working efficiency of the equipment, the MITSUBISHI FX1N-40MR PLC was selected as the controller. The I/O configuration and wiring are shown in Figure 3 according to the requirements of automatic batching and loading control.
Motors M1 to M4 are controlled by contactors KM1 to KM4; to facilitate monitoring by operators, indicator lights can also be used to display the operating status of the motors.
IV. System Software Design
1. Main program flowchart
2. Structure of the system's PLC control program
In the automatic batching and loading control system programmed with basic logic instructions, the feed valve is controlled by the material level sensor S1. If S1 has no signal, it indicates the material is not full, and feeding resumes after 5 seconds. If S1 has a signal, it indicates the material is full, and feeding stops. The batching system can be started via the limit switch SQ1 under the platform scale. When the truck enters the loading position, its own weight activates SQ1, starting the batching system. When the truck reaches the required tonnage, the limit switch SQ2 deactivates, stopping batching.
The PLC control program is developed using ladder logic. This program clearly demonstrates the logistics control method and structure through a linear, modular approach. It can be divided into the following parts:
①. Control of moving equipment/conveying path
All belt conveyors, roller conveyors, and elevators operate according to the required modes to ensure smooth and continuous movement of cargo boxes on the conveyor lines. Based on the cargo box's path identification code, the system controls the exchange devices between the conveyor lines and other conveyor lines to achieve path selection during cargo box transport.
②. Data processing of the automatic identification system
By communicating with the barcode laser scanner and the PLC's real-time database, the automatic identification of cargo boxes on the conveyor line can be achieved.
③. Communication interface of the host computer production management system / real-time database management system
It primarily handles information exchange with the host computer, including communication protocols, message formats, communication encoding and decoding, and error diagnosis. Data blocks are used to establish a record storage area to store cargo container information. Function blocks are used to implement database operations, providing control basis for path identification in the conveyor system.
④. Data processing for MCGS configuration monitoring
In conjunction with MCGS monitoring, the data processing mainly includes alarm processing and equipment operating status data processing.
⑤. Material shortage and warehouse relocation
When the material in a given bin is exhausted during the batching process, the system will automatically issue a material shortage alarm. Press the [Change Bin When Material Shortage] button, a dialog box will pop up. Enter the bin number to be changed, confirm, and then press the [Clear Fault] button to complete the bin change and enter automatic batching mode. Note: After changing bins, the batching order must be changed. Set the shortage bin to 0, and set the newly changed bin number to match the original order for easy report statistics.
Analysis shows that this system is a control process that operates in a certain sequence. Using step instructions ensures that each step is performed strictly in sequence. If step instructions are used for programming, the program will be easier to understand and read.
V. Conclusion
After debugging and operation, this automatic material control system demonstrates its ability to automatically deliver production materials, meeting the production needs of various products and ensuring high-level, high-efficiency operation of related logistics companies' equipment and production processes. In modern industrial control, this system acts like a tireless transporter, continuously conveying materials strictly according to programmed instructions. The implementation of this system has enabled enterprises to completely abandon manual operations, adopting a scientific and data-driven production method for material preparation, and freeing individuals from harsh working environments such as dust and noise. Furthermore, stable, high-quality material preparation has led to improved product quality. Since the system's implementation, key technical indicators such as product density and specific gravity have significantly improved. Therefore, the automatic logistics control system is indeed a technology worthy of promotion in the manufacturing and processing fields, especially in large-scale, high-efficiency, and continuous production logistics company sites. The entire system is now in use and has significant reference value for the development and design of automated logistics systems in enterprise computer-integrated manufacturing processes and online sales in the network information age.
References
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