PLC-based material automatic control system

1. Introduction The continuous batching automatic control system has a wide range of applications in cement, coal, metallurgy, chemical industry, feed, food and other industries. It has the characteristics of comprehensive functions, strong flexibility and high cost performance, and is welcomed by continuous batching system integrators and users. The system integrates modern logistics technology, warehousing technology, and automation technology. It is an important link in CIMS and has been widely used abroad. This technology is also gradually being applied to many industries in China.
After joining the WTO, China's commodity distribution and distribution service market will gradually expand its open areas and scope. And logistics is a key issue for the development of enterprises. Logistics will affect the overall survival and development of enterprises. In 2000, logistics costs accounted for 16.7% of the gross domestic product (GDP) of the domestic economy, compared with less than 10% in the United States. In particular, there is a huge gap between the level of logistics equipment of enterprises and developed countries, mainly manifested in low transportation efficiency and amazing waste in the logistics process. We know that the gap is potential and room for development. Therefore, improving the level of logistics equipment has become a top priority. Automatic batching truck is an important part of transportation and distribution in the logistics system. It is a system that can automatically store and retrieve materials.
2. Material automatic control system process production control The logistics automatic control system is mainly to control the conveying system to complete its material conveying task. There are elevators and conveyor lines at the entrance and exit of materials. In this way, within the scope of the warehouse, production workshop and packaging workshop, a closed circulation conveyor system that can reach each production location smoothly and at the same time is formed. All relevant materials and finished products used in the production process must be finally transported and loaded in a barcoded container. Under the action of the production order issued by the production management system, the materials enter the conveyor system from the designated entrance. The logistics automatic control system is shown in Figure 1.
Overall control requirements: As shown in the figure, the system consists of hopper, conveyor belt and detection system. The batching device can automatically identify the truck in place and automatically batch the truck. When the truck is full, the batching system automatically stops batching. When the material in the hopper is insufficient, the batching is stopped and the material is automatically fed.
The process control requirements are as follows:
(1) Initial state
After the system starts, the red light L2 is off and the green light L1 is on, indicating that the car is allowed to load. The hopper discharge port D2 is closed. If the level sensor S1 is set to OFF (the material in the hopper is not full), the feed valve opens the feed (D4 is on). When S1 is set to ON (the material in the hopper is full), the feeding is stopped (D4 is off). Motors M1, M2, M3 and M4 are all OFF.
(2) Loading control During the loading process, when the car drives into the loading position, the limit switch SQ1 is set to ON, the red signal light L2 is on, and the green light L1 is off; at the same time, the motor M4 is started. M3, start M2 after 2S, then start M1 after 2S, and then open the discharge valve (D2 light) after 2S, the material is discharged through the hopper.
When the car is full, the limit switch SQ2 is ON, the hopper is closed, M1 stops after 2S, M2 stops after M1 stops for 2S, M3 stops after M2 stops for 2S, and M4 stops after M3 stops for 2S. At the same time, the red light L2 is off and the green light L1 is on, indicating that the car can drive away.
(3) Shutdown control Turn off the SD switch, and the whole system of automatic batching and loading will stop running.

3. System hardware design
1. System schematic

2. I / O configuration and wiring In order to improve the reliability of the automatic control system and the working efficiency of the equipment, the system selects the FX1N-40MR PLC of MITSUBISHI as the controller. The I / O configuration is designed according to the requirements of automatic batching and loading control And wiring as shown in Figure 3.

The motors M1 ï½ž M4 are controlled by contactors KM1 ï½ž KM4; in order to facilitate operator monitoring, signal lights can also be used to show the running status of the motor.

4. System software design
1. Main program flow chart

2. The structure of the PLC control program of the system is programmed with basic logic instructions. In the automatic batching and loading control system, the feeding valve is controlled by the material level sensor S1. S1 has no monitoring signal, indicating that the material is not full. The monitoring signal indicates that the material is full and the feeding is stopped. The start of the batching system can be realized by the limit switch SQ1 under the platform scale. When the car enters the loading position, under its own weight, SQ1 is turned on and the batching system is started; when the car is loaded to the tonnage, the limit switch SQ2 is turned off to stop the batching.
Use ladder diagram language to compile PLC control program. The control program embodies the logistics control method and structure in a clear linear modular method. Can be divided into the following parts:
â‘ . Motion equipment / conveying path control All belt conveyors, roller conveyors and elevators are operated in the required mode to ensure that the cargo boxes can run smoothly and continuously on the conveyor line. According to the path identification code of the container, the conveyor line and other conveyor line exchange devices are controlled to realize the path selection during the transportation of the container.
â‘¡. Data processing of automatic identification system Communicate the barcode laser scanner and the real-time database of PLC to complete the automatic identification of the containers on the conveyor line.
â‘¢. Communication interface / real-time database management system of the production management system of the host computer Mainly handles the exchange of information with the host computer, including the communication protocol, message format, communication encoding and decoding, error diagnosis, etc. Use the data block to establish a record storage area to store the information of the cargo box. The function block is used to realize the operation of the database, which provides a control basis for the path identification of the conveying system.
â‘£. MCGS configuration monitoring data processing
In conjunction with MCGS monitoring and data processing, there are mainly alarm processing, data processing of equipment operating status, etc.
â‘¤. Material shortage for warehouse replacement When the material of the warehouse number has been allocated during the batching process, the system automatically prompts a material shortage alarm. Press the [Short Material Replacement] button, a dialog box pops up, enter the warehouse number to be replaced, confirm, and then press the [Clear Fault] button to complete the warehouse replacement and enter the automatic batching state. Note: After changing positions, the order of ingredients must be changed. Set the shortage warehouse to 0 and the newly replaced warehouse number to be consistent with the original order, which is convenient for report statistics.
It can be known from the analysis that this system is a control process that operates in a certain order. It can make each work step act in strict order. If it is programmed with step instructions, the program is easier to understand and easy to read.
5. Conclusion After the automatic control system of the material has been debugged and operated, its automatic distribution of production materials can meet the production needs of various products, and it can meet the high-level and efficient operation of the equipment and production of related logistics companies. In modern industrial control, the system is like a tireless porter, continuously carrying out material transportation in strict accordance with program instructions. The investment of this system has completely abandoned the manual operation of the enterprise, and the method of ingredients has entered scientific data production. Individuals have also been freed from the harsh labor environment such as dust and noise. Not only that, the stable and high-quality ingredients have brought the improvement of product quality. After the system is put into operation, the main technical indicators such as product density and false specific gravity have been greatly improved. Therefore, the logistics automatic control system is indeed in the field of manufacturing and processing, especially on the site of large-scale, high-efficiency, continuous production logistics companies. A technology worth promoting. The entire system is now in use, and it has important reference value for the development and design of logistics integrated systems such as the computer integrated manufacturing process of enterprises and institutions in the network information era and the network sales field.

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